BEHAVIORAL BIOLOGY22,
190-202 (1978)
Effects of Frontal Cortical Lesions and Transverse Cortical Bisection on Spreading Depression-Induced Feeding I BERT SIEGFRIED AND JOSEPH P. HUSTON
Institute of Pharmacology, University of Ziirich, Institute of Psychology, University of Diisseldorf, Universitiitsstrasse l, Diisseldorf, West Germany, and Ziirich, Switzerland Experiment I showed that unilateral lesions of the frontal neocortex did not prevent ipsilateral cortical spreading depression (CSD)-inducedfeeding in rats. In experiments II and III one neocortical hemisphere was bisected by either a wide groove or a knife-cut transsection. This allowed us to restrict CSD to either the frontal or posterior halves of the neocortex. DC slow-potential changes were recorded to determine the effectiveness of the bisection in isolating the spreading depression. Feeding was elicited by posterior as well as anterior CSD. Placing reactions contralateral to the bisected hemisphere were absent. Taken together, the results suggest that the neocortex is equipotential with regard to the elicitation of feeding by cortical spreading depression. Feeding can be elicited by single waves of spreading depression (SD) triggered in the neocortex (Huston and Bureg, 1970; Huston and BroZek, 1971) as well as the hippocampus (Siegfried and Huston, 1977; Siegfried et al., 1977). Although it is possible that both hippocampus and neocortex are significantly involved in the control of feeding behavior, it could also be that SD-induced feeding is the result of massive neurochemical changes that a c c o m p a n y or follow SD irrespective of where in the brain SD occurs. H o w e v e r , unilateral amygdalectomy (Huston et al., 1976) as well as unilateral injection of 6 - O H D A into the substantia nigra (unpublished data) lead to (ipsi-) lateralized decrements in cortical SD-induced feeding, suggesting that specific mediating pathways and neurotransmitters can be identified. Furthermore, earlier onset of feeding after anterior compared to posterior cortical SD suggested that the frontal neocortex might play a special role in cortical SD-induced feeding (Huston et al., 1974; Siegfried et al., 1977). The frontal cortex has frequently been implicated in the control of c o n s u m a t o r y behavior (Brandes, 1972; Hus1 Supported by the Swiss National Science Foundation Grant No. 3.6610.75. Thanks to Miss L. Jakobartl for her help. Reprints may be obtained from J. Huston. 190 0091-6773/78/0222-0190502.00/0 Copyright© 1978by AcademicPress, Inc. All rights of reproductmn in any form reserved.
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ton and Bureg, 1973; Kolb and Nonneman, 1975; Lyons and Freedman, 1976; Richter and Hawkes, 1939). Hence, we considered it worthwhile to (a) assess the effects of frontal cortex lesions on cortical SD-induced feeding, and (b) to bisect the neocortex by aspiration and transsection in order to investigate the effects of SD isolated to the posterior and anterior halves of the neocortex. EXPERIMENT I. FRONTAL NEOCORTICAL LESIONS The intent of the first study was to determine whether unilateral aspiration of parts of the frontal cortex would have an influence on feeding induced by spreading depression triggered in the posterior cortex by application of KC1 solution.
Methods Animals. Seventeen male albino Sprague-Dawley rats of the SIV 50 strain (Tierspital Zdrich) with a preoperative weight of 280-320 g were used. All animals were housed individually under a 12 hr light/12 hr dark schedule with free access to food (Nafag, Nr. 890) and water. They were always tested during the light period. Surgery. Surgery was performed under pentobarbital anesthesia (60 mg/kg). After thinning the skull with a dental burr, a 2-3 mm diameter hole was opened unilaterally (left hemisphere) 2 mm in front of the bregma. The dura was then cut, and with the aid of a magnifying glass cortical tissue (either dorsomedial and/or dorsolateral and/or ventrolateral prefrontal cortical tissue) was removed by aspiration using a drawn glass pipette with a tip diameter of 0.5 ram. When all bleeding had ceased, the lesion was covered with coagulative cotton (Coagulen). One 22 gauge (0.71 mm o.d., 0.41 mm i.d., 16 mm long) stainless steel cannula, equipped with a stainless steel plug, was implanted into the occipital cortex of each hemisphere using the following coordinates referenced to bregma and the surface of the skull: 4.0 mm posterior; 2.5 mm lateral; 1.0 mm ventral. The cannulae were fixed and the opened skull (protected by cotton) was covered with dental acrylic. Spreading depression. Cortical spreading depression was induced by injecting 0.2 to 0.8 txl of a 25% (w/v) KCI solution. Since the effective dosage for eliciting SD increases slightly with number of testing trials, the volume of KC1 was increased by 0.2 txl per trial for a given injection site. This procedure, based on earlier electrophysiological work, guaranteed reliable elicitation of at least one wave of CSD per trial. Testing procedure, Testing was begun 3 to 5 days after the operation when the rats had regained their preoperative weight level. During the recovery period all animals were handled daily. Each rat was tested once daily over 9 days in its transparent plastic home cage (26 x 43 x 15 cm high), which was put into an observation box (66 x 118 x 68 cm high). The injection site was alternated from day to day, whereby nine animals
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were first injected into the lesioned hemisphere and eight animals into the intact hemisphere. On Day five the animals received one sham trial, during which they were handled similarly as during the KCI trials. A KC1 or sham trial consisted of a 20 min observation period during which onset latency and duration of eating, as well as incidence of drinking and circling behavior, were recorded. The criterion for a positive eating trial was a noninterrupted eating sequence of >/30 sec. A positive circling trial was registered when at least two turns in the same direction occurred within a period of 40 sec. Histology. At the completion of the study the brains were perfused with 38% (v/v) formalin solution. With a freezing microtome, sections were cut at 50 /zm through the regions of the ablated area. The sections were mounted and examined. Statistics. Statistical treatment for all experiments was performed with Wilcoxon tests (two-tailed).
Results Figure 1 shows that in most animals the frontal neocortical lesions included dorsomedial and dorsolateral, as well as ventrolateral prefrontal tissue. In seven animals (numbers 11, 12, 14, 15, 17, 19, and 22) the ventral lesions reached the rhinal sulcus; in three animals (numbers 12, 17, and 22) the lesions also included parts of the pyriform cortex. Occasionally the lesions involved fibers of the corpus callosum and anterior or lateral portions of the caudoputamen. The olfactory system was intact in all animals. Of the 17 animals tested, eight animals (numbers 8, 12, 15, 19, 21, 22, 23, and 24) showed a higher incidence of spreading depression-induced eating in the lesioned hemisphere (68% versus 34%), whereas six animals (numbers 9, 11, 13, 14, 16, and 18) showed a higher incidence in the nonlesioned hemisphere (54% versus 21%). In three aminals (numbers 7, 17, and 20) the incidence of eating was equal (42%) for both lesioned and intact hemispheres. The data show that neither the site nor the size of the lesion influenced the incidence of CSD-induced feeding. The incidence of eating upon KC1 injection into the lesioned or intact cortical hemisphere is depicted in Fig. 2 A. The difference between the lesioned (47%) and the intact (43%) hemispheres was not significant. However, the incidence of eating was significantly higher during experimental trials on days four (53%) and six (65%) compared to sham trials on Day five (23%) (P < 0.05). No significant differences were obtained between lesioned and nonlesioned sides in the mean onset and duration times. However, most of the onsets for the lesioned side (43.7%) occurred within the 5-10-min interval, and for the nonlesioned side (34.5%) between 0-5 min after injection. The onset latencies of eating induced from the lesioned and intact hemispheres ranged from 1.7 to 17.7 min, whereby in 72% of the cases eating started between 1.7 and 10 rain, with an overall mean of 8.0
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7
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FIG. 1. Reconstructions of unilateral cortical lesions, shown from above and from the side for each animal tested.
min. Duration of eating ranged from 0.5 to 9.2 min (mean: 2.6 rain; 3 rain corresponds to about 1 g food consumed), whereby in 51% of cases eating lasted more than 2 rain. The range of durations and onset times of eating were similar during sham and KC1 trials. Drinking (/> 10 sec) occurred in 13% of all trials, and 47% of all animals tested. Turning behavior contralateral to the injection side was observed in 21% of all KC1 injection trials (in 24% of injections into intact, and in 18% of injections into lesioned side). No circling was recorded during sham trials.
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A
70
B
60 v- 5 0 z ,,= n~ uJ
40
30
20 10
lesioned intact hemisphere
anterior posterior to the slit
intact hemisphere
FIc. 2. (A) Mean incidence of eating induced by cortical spreading depression in the lesioned and intact cortical hemispheres of 17 rats (four trials/rat). White horizontal bars indicate incidence of eating during sham trials (one trial/rat). (B) Mean incidence of eating induced by cortical spreading depression in the isolated anterior (four trials/rat) and posterior (four trials/rat) cortices of the left hemisphere in 14 rats and in the posterior cortex of the intact right hemisphere in eight of these 14 rats (four trials/rat). (One sham trial was given per KC1 trial).
EXPERIMENT II. TRANSVERSE NEOCORTICAL BISECTION BY ASPIRATION Experiment I showed that unilateral lesions of the frontal neocortex did not diminish cortical SD-induced feeding. Another approach to the question of anatomical specificity within the neocortex with respect to the SD-induced feeding is to delimit the wave of SD to a restricted area of the cortex. Hence, in the present study the neocortex was bisected with a transverse slit in order to test for possible differences in elicited feeding between isolated anterior versus posterior neocortical spreading depression.
Methods Animals. Twenty-eight rats with a preoperative weight of 290-310 g were used. Rat strain and housing conditions were the same as in Experiment I. Surgery. A scalp incision was made along the midline of the head and subcutaneous tissue was deflected. The left temporal muscle was slightly detached from the bone in order to allow lateral opening of the skull. With
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a circular dental saw a transverse l-ram wide groove was cut into the skull (left hemisphere) at a level 0.5 to 1.0 mm posterior to the bregma. The length of the groove was 9.5-11.5 mm laterally from the midline. The exposed dura was cut and removed. Neocortical tissue as well as tissue from the pyriform cortex (and seldom from the entorhinal cortex) was aspirated, leaving a 1.2- to-4.0-mm wide transverse slit that bisected the neocortex (see also Fig. 3). Thus, the left hemisphere of the neocortex was divided into two isolated parts, separated from each other by an artificial slit. This preparation allowed u s to restrict CSD to either the frontal or occipital cortex. When all bleeding had ceased the damaged area was filled with coagulative cotton. Slow potential measurement. Prior to implantation of the KC1 injection eannulae, the preparation was tested to determine whether SD induced in the cortex anterior and posterior to the slit would remain localized in the respective portion of the cortex. For this purpose 0.1 to 0.3/xl of a 25% KCI solution was applied to the isolated anterior (+ 4.0 mm from bregma), or posterior (-5.5 mm) cortex of the anesthetized animals (through 0.51.0-ram diameter holes drilled through the skull at the given coordinates). Slow potential changes were picked up through skull openings by wick calomel electrodes positioned on the left cortical hemisphere anterior (+ 2.5 to 3.5 mm) and posterior ( - 2.5 to -4.0 ram) to the slit; an electrode placed on the right temporal muscle served as a reference electrode. In six of the above rats KC1 was injected into the right neocortical hemisphere and slow potential changes were recorded from this intact hemisphere with the electrode positions similar to that of the lesioned hemisphere (see
FIG. 3. Reconstruction of the unilateral cortical suction-bisection in 14 rats. The range of the width of the cut is given by the two most lateral solid lines. The smallest and largest slits are represented by the black and dashed area, respectively. The vertical solid line above shows the mean width of the cortical cut.
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"
~
3-5. 4-5
2-5-KCI-A
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FIG. 4. Cortical DC-recordings upon KC1 injection into the bisected and intact cortical hemispheres in one anesthetized rat. Slow potentials were measured between 1 and 5 (isolated frontal cortex) and 2 and 5 (isolated occipital cortex), as well as between 3 and 5 (frontal cortex of the intact hemisphere) and 4 and 5 (occipital cortex of the intact hemisphere). The common reference electrode (5) was placed on the right temporal muscle. KC1 was applied into the isolated frontal (A) and occipital (B) cortices of the bisected hemisphere, as well as into the frontal (C1) and occipital (CO cortices of the intact hemisphere, DC record: upward deflection indicates negativity of the active electrode.
also Fig. 4). DC potential changes were registered by two DC coupled differential amplifiers (Tektronix, type 26A2 and AM 502) and a fivechannel polygraph (Sefram, type RP5). If the preparation was satisfactory, i.e., if no transmission of CSD from occipital to frontal cortices, and vice versa, was noticed, the animal was implanted with two 22 gauge stainless steel cannulae into the left hemisphere: one into the anterior (+ 4.0 to 4.5 mm, 2.5 mm lateral, 1.0 mm ventral), and one into the posterior ( - 5.5 to 6.0 mm, 2.5 mm, 1.0 mm) cortex. In eight rats an additional cannula was implanted into the posterior part of the right intact cortical hemisphere using the same coordinates as above. If the preparation was not adequate, i.e., if SD was not restricted to the anterior and posterior cortices, the lesion was extended, and again confirmed by measuring slow potential changes upon KC1 injections. Testing procedure. Of the 28 rats operated 14 died within 1 to 3 days postoperatively. Testing of the remaining 14 animals started at a time (3 to 7 days after the operation) when the preoperative weight level was reached. Each animal was tested twice daily in its home cage (which was put in the observation box) always at the same time of the day, receiving either a cortical KC1 injection or a sham trial. A trial consisted of a 20 min observation period. The sequence of trials per day (KC1, sham) was changed daily. During the first 4 days half of the animals were only tested on the frontal and half on the occipital isolated neocortex; during the
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following 4 days cortical spreading depression and sham trials were administered on the yet not tested cortical part of those animals, i.e., each animal had eight KCI and eight sham trials on the left hemisphere, starting either with trials on the anterior or posterior cortex. Next, eight of these animals received four KCI and sham trials on the right intact cortical hemisphere. After the termination of the experiments, the animals were anesthetized, the acrylic cement and cannulae were removed and the skull was cleaned. In order to retest the effectiveness of the preparation, slow potential changes from the left hemisphere were again recorded after KC1 injection. Subsequently, the animals' brains were perfused, sliced, mounted, and histologically examined. Results The extent of the aspiration lesioned cortical area is represented in Fig. 3. The minimal width (black area) of the transcortical cut was 1.2 mm, the maximal width (dashed area) was 4.0 mm, whereby in 71% of all cases the slit was between 1.2 and 2.4 mm wide. Over all animals the width of the slit extended over a region from 1.4 mm anterior to 3.0 posterior to the bregma, with a mean width of 2.2 __+0.2 (SE) mm. All slits crossed the fissura rhinalis, however only 43% were complete, i.e., included also ventral parts of the pyriform and entorhinal cortex. Nevertheless, CSD remained isolated in the anterior and posterior neocortical tissue in all of the animals. Subcortical tissue (callosal fibres or parts of amygdaloid nuclei or the ventral hippocampus) was damaged only rarely. Figure 4 shows slow potential changes recorded in one anesthetized rat after dividing the left cortical hemisphere by a suction lesion. Simultaneous DC recording anterior and posterior to the slit upon either KC1 injection into the frontal (A) or occipital (B) part verified the effectiveness of the transsection. For comparison, Fig. 4 also shows slow potential changes upon KC1 application to the right intact hemisphere, whereby the injection as well as the recording sites corresponded to those in the lesioned hemisphere. It should be noted that no differences were observed between the pre- and posttest slow potential change records. As can be seen from Fig. 2B, the elicited eating was very similar across the various cortical injection sites. The incidence of SD-induced eating from the isolated frontal (50%) and occipital (48%) cortices did not differ significantly from that obtained in the intact right neocortical hemisphere (69%). Eating occurred significantly more often upon KC1 application to all three injection sites compared to the sham trials (P < 0.01). There were no significant differences in the mean durations and onset times between the three injection sites; however, most onsets of feeding after injection into the posterior half of the bisected hemisphere (45%) occurred in the
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5-10 min interval, whereas upon anterior (46.4%) and contralateral posterior (50%) injection most onsets occurred within the 0-5 min interval. Eating commenced between 2 and 19 min after KC1 application with 79% of the onsets occurring between 2 and 10 rain (calculated over all three injection sites). The overall mean onset time was 7.1 rain. Duration of eating ranged from 0.5 to 9.7 min (overall mean duration: 3.2 min), whereby in 59.7% of the cases the duration exceeded 2 min. During all sham trials eating commenced between 2.2 and 16 min with 78.3% of the onsets occurring between 2.2 and 10 rain. The overall mean onset time was 7.3 rain. Duration of eating ranged from 0.6 to 6.0 rain (overall mean duration 2.7 rain), whereby in 52% of the cases the duration exceeded 2 rain. There was a general tendency, however not at a significant level, of shorter onset latencies and longer eating durations from the frontal compared to the occipital KC1 injections on the left hemisphere; i.e., of the 14 animals used, seven animals started earlier and eight ate longer, three began later and ate for a shorter time. Turning contralateral to the injection side was never seen upon frontal and rarely upon occipital (3.6% of all trials in two animals) cortical injection of KC1 into the left lesioned hemisphere; it was observed more often upon cortical spreading depression in the intact right hemisphere (13.6% of all trials in three animals). (Drinking (> 10 sec) occurred in 7.6% of all KC1 trials in seven animals compared to 5.6% of all sham trials in three animals). EXPERIMENT Ill. NEOCORTICAL KNIFE-CUT BISECTION The preceding study showed that it was possible to isolate single waves of SD to the frontal and posterior cortices after bisecting the neocortex with a transverse groove. There was no difference in incidence of eating induced by posterior vs anterior cortical SD. The purpose of the present study was to try to simplify the bisection by transecting with a knife cut instead of the drastic aspiration groove used in Experiment II. In order to determine the degree of isolation of the SD to its cortical quadrant, the animals carried DC electrodes for chronic recording of slow potential changes. Methods Animals and surgery. Six 270-320 g animals yielded a satisfactory preparation, which was the same as in Experiment II, except in two points. Firstly, the unilateral cortical bisection was performed by a knifecut transsection, instead of by a suction lesion. The knife consisted of a stainless steel needle (0.5 mm diameter) which was bent at an angle of 45 °. The cutting part was 2 mm long. Secondly, in addition to the injection cannulae these animals were also equipped with three calomel DC recording electrodes for chronical use (a description of such electrodes is pro-
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vided by Shibata et al., (1977)). The DC electrodes were positioned according to the following coordinates referenced to bregma: anterior cortex: + 2.5 to + 3.0 ram/2.5 mm lateral/1.0 mm deep; posterior cortex: - 2.5 to - 3.0 ram/2.5 mm/1.0 mm; common reference electrode in the fight intact neocortex: - 6.0 ram/2.5 ram/1.0 ram. Testing procedure. The experiments were carried out in a black observation box (29 x 44 x 40 cm high) equipped with a drinking tube situated 12 cm high. During testing the home cage (containing food cubes liberally scattered over the floor) was placed into the observation box. This assembly was surrounded by an electrically shielded room (60 × 60 x 75 cm high). Each animal was tested once per day always at the same time. After at least 10 min adaptation to the test situation either 0.2- to 0.7-~1 25% KCI solution was injected into the posterior part of the left neocortical hemisphere, or a sham trial was carried out. Each animal received a total of four KCI and four sham trials. This experiment was exclusively concerned with the question of whether isolated posterior CSD waves can induce feeding. Hence, frontal KC1 injections served only for testing the frontal DC electrode, to ensure that feeding induced by posterior elicited CSD was not due to an eventually transmitted CSD to the frontal cortex. Thus, only those trials with posterior CSD waves in which the frontal DC electrode worked were analyzed.
Results The knife-cut preparation yielded a cut of !.0-1.2 mm width and 1.82.5 mm depth. Eating induced by an isolated occipital CSD is shown in Fig. 5. The long-lasting negative slow-potential from the posterior cortex is typical. It was observed in 75% of all trials and was due to diffusion of KC1; i.e., to the close vicinity of recording electrode and injection cannula. In four trials in three animals a slow potential change was also recorded in the homolateral nontreated frontal part of the cortex with a delay of 8 min in one case and approximately 16 min in three cases. This was probably due to an incomplete invasion of multiple elicited CSD waves from the posterior cortex into only partially transsected nonneocortical structures (e.g., entorhinal cortex). During these trials no eating occurred. Eating induced by isolated posterior cortical SD began with a mean onset time of 6.8 rain and lasted for an average of 3.1 rain. Eating occurred significantly more often upon KC1 injection into the isolated posterior cortex (46%) compared to the sham trials (4%) (P < 0.05). Placing reactions (Brooks and Peck, 1940; Bureg et al., 1974) contralateral to the side of the slit were totally absent after the operation and during the experiment up to the time the animals were sacrificed 3 to 4 weeks later.
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1~3~
2-3 ~
~ KCI- B
1-3 2-3
KC, A
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FIG. 5. Cortical DC recordings during consummatory behavior induced by KCI injection into the isolated occipital cortical area at B. Slow potentials were measured between 1 and 3 (isolated frontal cortex) and 2 and 3 (isolated occipital cortex). The common reference electrode (3) was placed into the posterior right intact cortical hemisphere. To check the functioning of the DC electrode in the isolated frontal cortex KC1 was injected into this area at A. Feeding is indicated by the solid, drinking by the dotted line. The dashed line (record: 2-3) gives the DC baseline.
DISCUSSION The main result of Experiment I is that unilateral aspiration of frontal cortical tissue did not prevent feeding induced by ipsilateral neocortical spreading depression. The lack of apparent difference between the lesioned and intact hemispheres in incidence of induced feeding suggests that, contrary to speculation based on shorter onset latencies of anterior vs posterior CSD-induced feeding (Huston, et al., 1974; Siegfried and Huston, 1977), the frontal cortex may not be critically involved in this phenomenon. Experiments II and III support this conclusion by showing that it was possible to induce feeding with spreading depression restricted to the posterior quadrant of a bisected hemisphere. Although there was no difference in the incidence of isolated frontal vs posterior CSD-induced feeding, the feeding induced by frontal cortical injection of KC1 tended to last longer and begin sooner. Furthermore, the incidence of induced feeding from the bisected hemisphere was lower (though not statistically significant) than from the intact hemisphere (49% vs 69%). In summary, although some equivocal evidence suggests that the bisection lesion may have somewhat attenuated ipsilateral SD-feeding, and that frontal CSD may be a bit more effective than posterior CSD in eliciting feeding, the frontal cortex is not a critical focus. Hence, the neocortex seems to be more or less equipotential with
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respect to CSD-induced feeding. Transmission of the wave of CSD to the caudate nucleus occurs infrequently and also does not play a role in induced feeding (Jakobartl and Huston, 1977). On the other hand, unilateral amygdalectomy significantly attenuated ipsilateral CSD-induced feeding, although it failed to abolish it (Huston, et al., 1976). Similarly, unilateral injection of 6-OHDA into the substantia nigra attenuated CSDinduced feeding more from the ipsilateral than from contralateral hemisphere, suggesting a participation of telencephalic catecholamines in the CSD-induced feeding phenomenon. Bilateral nigral 6-OHDA lesions abolished CSD-induced feeding in rats that had recovered from aphagia, showing the importance of the nigrostriatal DA-system in the elicited feeding (unpublished data). Frontal pole lesions did not influence the incidence of CSD-induced contralateral turning. Contralateral turning induced from the bisected hemisphere, however, was reduced, whereas from the intact hemisphere in these animals the percentage of turning was comparable to that of earlier reports (Jakobartl and Huston, 1977; Siegfried and Huston, 1977). Therefore, we can conclude that CSD-invasion into the caudate nucleus was almost totally prevented by the unilateral cortical bisection. REFERENCES Brandes, J. (1972). Overeating in the rat induced by high doses of insulin. Ph.D. Dissertation, Univ. Pennsylvania. Brooks, M. C. and Peck, M. E. (1940). Effect of various cortical lesions on development of placing and hopping reactions in rats. J. Neurophysiol. 3, 66-73. Bureg, J., Bure~ov~, O., and K~ivhnek, J. (1974). "The Mechanism and Applications of Lefio's Spreading Depression of Electroencephalographic Activity," Prague: Academia. Huston, J. P., Avrith, D., Waser, P. G., and Siegfried, B. (1976). Effect of amygdaloid lesions on eating elicited by cortical spreading depression. Physiol. Behav. 16,201-205. Huston, J. P. and Bro~ek, G. (1971). Arousal of consummatory behavior in rabbits by single waves of cortical spreading depression. Physiol. Behav. 7, 595-600. Huston, J. P. and BureL J. (1973). Effects of cortical spreading depression on behaviors elicited by hypothalamic stimulation in rats. Physiol. Behav. 10, 775-780. Hnston, J. P. and Buret, J. (1970). Drinking and eating elicited by cortical spreading depression. Science 169, 702-704. Huston, J. P., Siegfried, B., Ornstein, K., Waser, P. G., and Borbrly, A. (1974). Eating elicited by spreading depression or electrical stimulation of the hippocampus and neocortex: A common cause. Brain Res. 78, 164-168. Jakobartl, L. and Huston, J. P. (1977). Circling and consumatory behavior induced by striatal and neocortical spreading depression. Physiol. Behav. 19, 673-677. Kolb, B. and Nonneman, A. J. (1975). Prefrontal cortex and the regulation of food intake in the rat. J. Comp. Physiol. Psychol. 88, 806-815. Lyons, H. I. and Freedman. N. L. (1976). Functional cortico- and amygdalohypothalamic interaction in drinking behavior. Physiol. Psychol. 4, 447-450. Richter, C. P. and Hawkes, C. D. (1939). Increased spontaneous activity and food intake produced in rats by removal of the frontal poles of the brain. J. Neurol. Psychiat. 2, 231-242.
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Shibata, M., Siegfried, B., and Huston, J. P. (1977). A miniature calomel electrode for recording DC potential changes accompanying spreading depression in the freely moving rat. Physiol. Behav. 18~ 1171-1174. Siegfried, B. and Huston, J. P. (1977). Properties of spreading depression-induced behaviors in rats. Physiol. Behav. 18, 841-851. Siegfried, B., Shibata, M., and Huston, J. P. (1977). Electrophysiological concomitants of eating induced from neocortex and hippocampus by electrical stimulation and injection of KC1 or norepinephrine. Brain Res. 121, 97-112.
190-202 (1978)
Effects of Frontal Cortical Lesions and Transverse Cortical Bisection on Spreading Depression-Induced Feeding I BERT SIEGFRIED AND JOSEPH P. HUSTON
Institute of Pharmacology, University of Ziirich, Institute of Psychology, University of Diisseldorf, Universitiitsstrasse l, Diisseldorf, West Germany, and Ziirich, Switzerland Experiment I showed that unilateral lesions of the frontal neocortex did not prevent ipsilateral cortical spreading depression (CSD)-inducedfeeding in rats. In experiments II and III one neocortical hemisphere was bisected by either a wide groove or a knife-cut transsection. This allowed us to restrict CSD to either the frontal or posterior halves of the neocortex. DC slow-potential changes were recorded to determine the effectiveness of the bisection in isolating the spreading depression. Feeding was elicited by posterior as well as anterior CSD. Placing reactions contralateral to the bisected hemisphere were absent. Taken together, the results suggest that the neocortex is equipotential with regard to the elicitation of feeding by cortical spreading depression. Feeding can be elicited by single waves of spreading depression (SD) triggered in the neocortex (Huston and Bureg, 1970; Huston and BroZek, 1971) as well as the hippocampus (Siegfried and Huston, 1977; Siegfried et al., 1977). Although it is possible that both hippocampus and neocortex are significantly involved in the control of feeding behavior, it could also be that SD-induced feeding is the result of massive neurochemical changes that a c c o m p a n y or follow SD irrespective of where in the brain SD occurs. H o w e v e r , unilateral amygdalectomy (Huston et al., 1976) as well as unilateral injection of 6 - O H D A into the substantia nigra (unpublished data) lead to (ipsi-) lateralized decrements in cortical SD-induced feeding, suggesting that specific mediating pathways and neurotransmitters can be identified. Furthermore, earlier onset of feeding after anterior compared to posterior cortical SD suggested that the frontal neocortex might play a special role in cortical SD-induced feeding (Huston et al., 1974; Siegfried et al., 1977). The frontal cortex has frequently been implicated in the control of c o n s u m a t o r y behavior (Brandes, 1972; Hus1 Supported by the Swiss National Science Foundation Grant No. 3.6610.75. Thanks to Miss L. Jakobartl for her help. Reprints may be obtained from J. Huston. 190 0091-6773/78/0222-0190502.00/0 Copyright© 1978by AcademicPress, Inc. All rights of reproductmn in any form reserved.
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ton and Bureg, 1973; Kolb and Nonneman, 1975; Lyons and Freedman, 1976; Richter and Hawkes, 1939). Hence, we considered it worthwhile to (a) assess the effects of frontal cortex lesions on cortical SD-induced feeding, and (b) to bisect the neocortex by aspiration and transsection in order to investigate the effects of SD isolated to the posterior and anterior halves of the neocortex. EXPERIMENT I. FRONTAL NEOCORTICAL LESIONS The intent of the first study was to determine whether unilateral aspiration of parts of the frontal cortex would have an influence on feeding induced by spreading depression triggered in the posterior cortex by application of KC1 solution.
Methods Animals. Seventeen male albino Sprague-Dawley rats of the SIV 50 strain (Tierspital Zdrich) with a preoperative weight of 280-320 g were used. All animals were housed individually under a 12 hr light/12 hr dark schedule with free access to food (Nafag, Nr. 890) and water. They were always tested during the light period. Surgery. Surgery was performed under pentobarbital anesthesia (60 mg/kg). After thinning the skull with a dental burr, a 2-3 mm diameter hole was opened unilaterally (left hemisphere) 2 mm in front of the bregma. The dura was then cut, and with the aid of a magnifying glass cortical tissue (either dorsomedial and/or dorsolateral and/or ventrolateral prefrontal cortical tissue) was removed by aspiration using a drawn glass pipette with a tip diameter of 0.5 ram. When all bleeding had ceased, the lesion was covered with coagulative cotton (Coagulen). One 22 gauge (0.71 mm o.d., 0.41 mm i.d., 16 mm long) stainless steel cannula, equipped with a stainless steel plug, was implanted into the occipital cortex of each hemisphere using the following coordinates referenced to bregma and the surface of the skull: 4.0 mm posterior; 2.5 mm lateral; 1.0 mm ventral. The cannulae were fixed and the opened skull (protected by cotton) was covered with dental acrylic. Spreading depression. Cortical spreading depression was induced by injecting 0.2 to 0.8 txl of a 25% (w/v) KCI solution. Since the effective dosage for eliciting SD increases slightly with number of testing trials, the volume of KC1 was increased by 0.2 txl per trial for a given injection site. This procedure, based on earlier electrophysiological work, guaranteed reliable elicitation of at least one wave of CSD per trial. Testing procedure, Testing was begun 3 to 5 days after the operation when the rats had regained their preoperative weight level. During the recovery period all animals were handled daily. Each rat was tested once daily over 9 days in its transparent plastic home cage (26 x 43 x 15 cm high), which was put into an observation box (66 x 118 x 68 cm high). The injection site was alternated from day to day, whereby nine animals
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were first injected into the lesioned hemisphere and eight animals into the intact hemisphere. On Day five the animals received one sham trial, during which they were handled similarly as during the KCI trials. A KC1 or sham trial consisted of a 20 min observation period during which onset latency and duration of eating, as well as incidence of drinking and circling behavior, were recorded. The criterion for a positive eating trial was a noninterrupted eating sequence of >/30 sec. A positive circling trial was registered when at least two turns in the same direction occurred within a period of 40 sec. Histology. At the completion of the study the brains were perfused with 38% (v/v) formalin solution. With a freezing microtome, sections were cut at 50 /zm through the regions of the ablated area. The sections were mounted and examined. Statistics. Statistical treatment for all experiments was performed with Wilcoxon tests (two-tailed).
Results Figure 1 shows that in most animals the frontal neocortical lesions included dorsomedial and dorsolateral, as well as ventrolateral prefrontal tissue. In seven animals (numbers 11, 12, 14, 15, 17, 19, and 22) the ventral lesions reached the rhinal sulcus; in three animals (numbers 12, 17, and 22) the lesions also included parts of the pyriform cortex. Occasionally the lesions involved fibers of the corpus callosum and anterior or lateral portions of the caudoputamen. The olfactory system was intact in all animals. Of the 17 animals tested, eight animals (numbers 8, 12, 15, 19, 21, 22, 23, and 24) showed a higher incidence of spreading depression-induced eating in the lesioned hemisphere (68% versus 34%), whereas six animals (numbers 9, 11, 13, 14, 16, and 18) showed a higher incidence in the nonlesioned hemisphere (54% versus 21%). In three aminals (numbers 7, 17, and 20) the incidence of eating was equal (42%) for both lesioned and intact hemispheres. The data show that neither the site nor the size of the lesion influenced the incidence of CSD-induced feeding. The incidence of eating upon KC1 injection into the lesioned or intact cortical hemisphere is depicted in Fig. 2 A. The difference between the lesioned (47%) and the intact (43%) hemispheres was not significant. However, the incidence of eating was significantly higher during experimental trials on days four (53%) and six (65%) compared to sham trials on Day five (23%) (P < 0.05). No significant differences were obtained between lesioned and nonlesioned sides in the mean onset and duration times. However, most of the onsets for the lesioned side (43.7%) occurred within the 5-10-min interval, and for the nonlesioned side (34.5%) between 0-5 min after injection. The onset latencies of eating induced from the lesioned and intact hemispheres ranged from 1.7 to 17.7 min, whereby in 72% of the cases eating started between 1.7 and 10 rain, with an overall mean of 8.0
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7
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FIG. 1. Reconstructions of unilateral cortical lesions, shown from above and from the side for each animal tested.
min. Duration of eating ranged from 0.5 to 9.2 min (mean: 2.6 rain; 3 rain corresponds to about 1 g food consumed), whereby in 51% of cases eating lasted more than 2 rain. The range of durations and onset times of eating were similar during sham and KC1 trials. Drinking (/> 10 sec) occurred in 13% of all trials, and 47% of all animals tested. Turning behavior contralateral to the injection side was observed in 21% of all KC1 injection trials (in 24% of injections into intact, and in 18% of injections into lesioned side). No circling was recorded during sham trials.
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A
70
B
60 v- 5 0 z ,,= n~ uJ
40
30
20 10
lesioned intact hemisphere
anterior posterior to the slit
intact hemisphere
FIc. 2. (A) Mean incidence of eating induced by cortical spreading depression in the lesioned and intact cortical hemispheres of 17 rats (four trials/rat). White horizontal bars indicate incidence of eating during sham trials (one trial/rat). (B) Mean incidence of eating induced by cortical spreading depression in the isolated anterior (four trials/rat) and posterior (four trials/rat) cortices of the left hemisphere in 14 rats and in the posterior cortex of the intact right hemisphere in eight of these 14 rats (four trials/rat). (One sham trial was given per KC1 trial).
EXPERIMENT II. TRANSVERSE NEOCORTICAL BISECTION BY ASPIRATION Experiment I showed that unilateral lesions of the frontal neocortex did not diminish cortical SD-induced feeding. Another approach to the question of anatomical specificity within the neocortex with respect to the SD-induced feeding is to delimit the wave of SD to a restricted area of the cortex. Hence, in the present study the neocortex was bisected with a transverse slit in order to test for possible differences in elicited feeding between isolated anterior versus posterior neocortical spreading depression.
Methods Animals. Twenty-eight rats with a preoperative weight of 290-310 g were used. Rat strain and housing conditions were the same as in Experiment I. Surgery. A scalp incision was made along the midline of the head and subcutaneous tissue was deflected. The left temporal muscle was slightly detached from the bone in order to allow lateral opening of the skull. With
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a circular dental saw a transverse l-ram wide groove was cut into the skull (left hemisphere) at a level 0.5 to 1.0 mm posterior to the bregma. The length of the groove was 9.5-11.5 mm laterally from the midline. The exposed dura was cut and removed. Neocortical tissue as well as tissue from the pyriform cortex (and seldom from the entorhinal cortex) was aspirated, leaving a 1.2- to-4.0-mm wide transverse slit that bisected the neocortex (see also Fig. 3). Thus, the left hemisphere of the neocortex was divided into two isolated parts, separated from each other by an artificial slit. This preparation allowed u s to restrict CSD to either the frontal or occipital cortex. When all bleeding had ceased the damaged area was filled with coagulative cotton. Slow potential measurement. Prior to implantation of the KC1 injection eannulae, the preparation was tested to determine whether SD induced in the cortex anterior and posterior to the slit would remain localized in the respective portion of the cortex. For this purpose 0.1 to 0.3/xl of a 25% KCI solution was applied to the isolated anterior (+ 4.0 mm from bregma), or posterior (-5.5 mm) cortex of the anesthetized animals (through 0.51.0-ram diameter holes drilled through the skull at the given coordinates). Slow potential changes were picked up through skull openings by wick calomel electrodes positioned on the left cortical hemisphere anterior (+ 2.5 to 3.5 mm) and posterior ( - 2.5 to -4.0 ram) to the slit; an electrode placed on the right temporal muscle served as a reference electrode. In six of the above rats KC1 was injected into the right neocortical hemisphere and slow potential changes were recorded from this intact hemisphere with the electrode positions similar to that of the lesioned hemisphere (see
FIG. 3. Reconstruction of the unilateral cortical suction-bisection in 14 rats. The range of the width of the cut is given by the two most lateral solid lines. The smallest and largest slits are represented by the black and dashed area, respectively. The vertical solid line above shows the mean width of the cortical cut.
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FIG. 4. Cortical DC-recordings upon KC1 injection into the bisected and intact cortical hemispheres in one anesthetized rat. Slow potentials were measured between 1 and 5 (isolated frontal cortex) and 2 and 5 (isolated occipital cortex), as well as between 3 and 5 (frontal cortex of the intact hemisphere) and 4 and 5 (occipital cortex of the intact hemisphere). The common reference electrode (5) was placed on the right temporal muscle. KC1 was applied into the isolated frontal (A) and occipital (B) cortices of the bisected hemisphere, as well as into the frontal (C1) and occipital (CO cortices of the intact hemisphere, DC record: upward deflection indicates negativity of the active electrode.
also Fig. 4). DC potential changes were registered by two DC coupled differential amplifiers (Tektronix, type 26A2 and AM 502) and a fivechannel polygraph (Sefram, type RP5). If the preparation was satisfactory, i.e., if no transmission of CSD from occipital to frontal cortices, and vice versa, was noticed, the animal was implanted with two 22 gauge stainless steel cannulae into the left hemisphere: one into the anterior (+ 4.0 to 4.5 mm, 2.5 mm lateral, 1.0 mm ventral), and one into the posterior ( - 5.5 to 6.0 mm, 2.5 mm, 1.0 mm) cortex. In eight rats an additional cannula was implanted into the posterior part of the right intact cortical hemisphere using the same coordinates as above. If the preparation was not adequate, i.e., if SD was not restricted to the anterior and posterior cortices, the lesion was extended, and again confirmed by measuring slow potential changes upon KC1 injections. Testing procedure. Of the 28 rats operated 14 died within 1 to 3 days postoperatively. Testing of the remaining 14 animals started at a time (3 to 7 days after the operation) when the preoperative weight level was reached. Each animal was tested twice daily in its home cage (which was put in the observation box) always at the same time of the day, receiving either a cortical KC1 injection or a sham trial. A trial consisted of a 20 min observation period. The sequence of trials per day (KC1, sham) was changed daily. During the first 4 days half of the animals were only tested on the frontal and half on the occipital isolated neocortex; during the
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following 4 days cortical spreading depression and sham trials were administered on the yet not tested cortical part of those animals, i.e., each animal had eight KCI and eight sham trials on the left hemisphere, starting either with trials on the anterior or posterior cortex. Next, eight of these animals received four KCI and sham trials on the right intact cortical hemisphere. After the termination of the experiments, the animals were anesthetized, the acrylic cement and cannulae were removed and the skull was cleaned. In order to retest the effectiveness of the preparation, slow potential changes from the left hemisphere were again recorded after KC1 injection. Subsequently, the animals' brains were perfused, sliced, mounted, and histologically examined. Results The extent of the aspiration lesioned cortical area is represented in Fig. 3. The minimal width (black area) of the transcortical cut was 1.2 mm, the maximal width (dashed area) was 4.0 mm, whereby in 71% of all cases the slit was between 1.2 and 2.4 mm wide. Over all animals the width of the slit extended over a region from 1.4 mm anterior to 3.0 posterior to the bregma, with a mean width of 2.2 __+0.2 (SE) mm. All slits crossed the fissura rhinalis, however only 43% were complete, i.e., included also ventral parts of the pyriform and entorhinal cortex. Nevertheless, CSD remained isolated in the anterior and posterior neocortical tissue in all of the animals. Subcortical tissue (callosal fibres or parts of amygdaloid nuclei or the ventral hippocampus) was damaged only rarely. Figure 4 shows slow potential changes recorded in one anesthetized rat after dividing the left cortical hemisphere by a suction lesion. Simultaneous DC recording anterior and posterior to the slit upon either KC1 injection into the frontal (A) or occipital (B) part verified the effectiveness of the transsection. For comparison, Fig. 4 also shows slow potential changes upon KC1 application to the right intact hemisphere, whereby the injection as well as the recording sites corresponded to those in the lesioned hemisphere. It should be noted that no differences were observed between the pre- and posttest slow potential change records. As can be seen from Fig. 2B, the elicited eating was very similar across the various cortical injection sites. The incidence of SD-induced eating from the isolated frontal (50%) and occipital (48%) cortices did not differ significantly from that obtained in the intact right neocortical hemisphere (69%). Eating occurred significantly more often upon KC1 application to all three injection sites compared to the sham trials (P < 0.01). There were no significant differences in the mean durations and onset times between the three injection sites; however, most onsets of feeding after injection into the posterior half of the bisected hemisphere (45%) occurred in the
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5-10 min interval, whereas upon anterior (46.4%) and contralateral posterior (50%) injection most onsets occurred within the 0-5 min interval. Eating commenced between 2 and 19 min after KC1 application with 79% of the onsets occurring between 2 and 10 rain (calculated over all three injection sites). The overall mean onset time was 7.1 rain. Duration of eating ranged from 0.5 to 9.7 min (overall mean duration: 3.2 min), whereby in 59.7% of the cases the duration exceeded 2 min. During all sham trials eating commenced between 2.2 and 16 min with 78.3% of the onsets occurring between 2.2 and 10 rain. The overall mean onset time was 7.3 rain. Duration of eating ranged from 0.6 to 6.0 rain (overall mean duration 2.7 rain), whereby in 52% of the cases the duration exceeded 2 rain. There was a general tendency, however not at a significant level, of shorter onset latencies and longer eating durations from the frontal compared to the occipital KC1 injections on the left hemisphere; i.e., of the 14 animals used, seven animals started earlier and eight ate longer, three began later and ate for a shorter time. Turning contralateral to the injection side was never seen upon frontal and rarely upon occipital (3.6% of all trials in two animals) cortical injection of KC1 into the left lesioned hemisphere; it was observed more often upon cortical spreading depression in the intact right hemisphere (13.6% of all trials in three animals). (Drinking (> 10 sec) occurred in 7.6% of all KC1 trials in seven animals compared to 5.6% of all sham trials in three animals). EXPERIMENT Ill. NEOCORTICAL KNIFE-CUT BISECTION The preceding study showed that it was possible to isolate single waves of SD to the frontal and posterior cortices after bisecting the neocortex with a transverse groove. There was no difference in incidence of eating induced by posterior vs anterior cortical SD. The purpose of the present study was to try to simplify the bisection by transecting with a knife cut instead of the drastic aspiration groove used in Experiment II. In order to determine the degree of isolation of the SD to its cortical quadrant, the animals carried DC electrodes for chronic recording of slow potential changes. Methods Animals and surgery. Six 270-320 g animals yielded a satisfactory preparation, which was the same as in Experiment II, except in two points. Firstly, the unilateral cortical bisection was performed by a knifecut transsection, instead of by a suction lesion. The knife consisted of a stainless steel needle (0.5 mm diameter) which was bent at an angle of 45 °. The cutting part was 2 mm long. Secondly, in addition to the injection cannulae these animals were also equipped with three calomel DC recording electrodes for chronical use (a description of such electrodes is pro-
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vided by Shibata et al., (1977)). The DC electrodes were positioned according to the following coordinates referenced to bregma: anterior cortex: + 2.5 to + 3.0 ram/2.5 mm lateral/1.0 mm deep; posterior cortex: - 2.5 to - 3.0 ram/2.5 mm/1.0 mm; common reference electrode in the fight intact neocortex: - 6.0 ram/2.5 ram/1.0 ram. Testing procedure. The experiments were carried out in a black observation box (29 x 44 x 40 cm high) equipped with a drinking tube situated 12 cm high. During testing the home cage (containing food cubes liberally scattered over the floor) was placed into the observation box. This assembly was surrounded by an electrically shielded room (60 × 60 x 75 cm high). Each animal was tested once per day always at the same time. After at least 10 min adaptation to the test situation either 0.2- to 0.7-~1 25% KCI solution was injected into the posterior part of the left neocortical hemisphere, or a sham trial was carried out. Each animal received a total of four KCI and four sham trials. This experiment was exclusively concerned with the question of whether isolated posterior CSD waves can induce feeding. Hence, frontal KC1 injections served only for testing the frontal DC electrode, to ensure that feeding induced by posterior elicited CSD was not due to an eventually transmitted CSD to the frontal cortex. Thus, only those trials with posterior CSD waves in which the frontal DC electrode worked were analyzed.
Results The knife-cut preparation yielded a cut of !.0-1.2 mm width and 1.82.5 mm depth. Eating induced by an isolated occipital CSD is shown in Fig. 5. The long-lasting negative slow-potential from the posterior cortex is typical. It was observed in 75% of all trials and was due to diffusion of KC1; i.e., to the close vicinity of recording electrode and injection cannula. In four trials in three animals a slow potential change was also recorded in the homolateral nontreated frontal part of the cortex with a delay of 8 min in one case and approximately 16 min in three cases. This was probably due to an incomplete invasion of multiple elicited CSD waves from the posterior cortex into only partially transsected nonneocortical structures (e.g., entorhinal cortex). During these trials no eating occurred. Eating induced by isolated posterior cortical SD began with a mean onset time of 6.8 rain and lasted for an average of 3.1 rain. Eating occurred significantly more often upon KC1 injection into the isolated posterior cortex (46%) compared to the sham trials (4%) (P < 0.05). Placing reactions (Brooks and Peck, 1940; Bureg et al., 1974) contralateral to the side of the slit were totally absent after the operation and during the experiment up to the time the animals were sacrificed 3 to 4 weeks later.
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1~3~
2-3 ~
~ KCI- B
1-3 2-3
KC, A
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FIG. 5. Cortical DC recordings during consummatory behavior induced by KCI injection into the isolated occipital cortical area at B. Slow potentials were measured between 1 and 3 (isolated frontal cortex) and 2 and 3 (isolated occipital cortex). The common reference electrode (3) was placed into the posterior right intact cortical hemisphere. To check the functioning of the DC electrode in the isolated frontal cortex KC1 was injected into this area at A. Feeding is indicated by the solid, drinking by the dotted line. The dashed line (record: 2-3) gives the DC baseline.
DISCUSSION The main result of Experiment I is that unilateral aspiration of frontal cortical tissue did not prevent feeding induced by ipsilateral neocortical spreading depression. The lack of apparent difference between the lesioned and intact hemispheres in incidence of induced feeding suggests that, contrary to speculation based on shorter onset latencies of anterior vs posterior CSD-induced feeding (Huston, et al., 1974; Siegfried and Huston, 1977), the frontal cortex may not be critically involved in this phenomenon. Experiments II and III support this conclusion by showing that it was possible to induce feeding with spreading depression restricted to the posterior quadrant of a bisected hemisphere. Although there was no difference in the incidence of isolated frontal vs posterior CSD-induced feeding, the feeding induced by frontal cortical injection of KC1 tended to last longer and begin sooner. Furthermore, the incidence of induced feeding from the bisected hemisphere was lower (though not statistically significant) than from the intact hemisphere (49% vs 69%). In summary, although some equivocal evidence suggests that the bisection lesion may have somewhat attenuated ipsilateral SD-feeding, and that frontal CSD may be a bit more effective than posterior CSD in eliciting feeding, the frontal cortex is not a critical focus. Hence, the neocortex seems to be more or less equipotential with
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respect to CSD-induced feeding. Transmission of the wave of CSD to the caudate nucleus occurs infrequently and also does not play a role in induced feeding (Jakobartl and Huston, 1977). On the other hand, unilateral amygdalectomy significantly attenuated ipsilateral CSD-induced feeding, although it failed to abolish it (Huston, et al., 1976). Similarly, unilateral injection of 6-OHDA into the substantia nigra attenuated CSDinduced feeding more from the ipsilateral than from contralateral hemisphere, suggesting a participation of telencephalic catecholamines in the CSD-induced feeding phenomenon. Bilateral nigral 6-OHDA lesions abolished CSD-induced feeding in rats that had recovered from aphagia, showing the importance of the nigrostriatal DA-system in the elicited feeding (unpublished data). Frontal pole lesions did not influence the incidence of CSD-induced contralateral turning. Contralateral turning induced from the bisected hemisphere, however, was reduced, whereas from the intact hemisphere in these animals the percentage of turning was comparable to that of earlier reports (Jakobartl and Huston, 1977; Siegfried and Huston, 1977). Therefore, we can conclude that CSD-invasion into the caudate nucleus was almost totally prevented by the unilateral cortical bisection. REFERENCES Brandes, J. (1972). Overeating in the rat induced by high doses of insulin. Ph.D. Dissertation, Univ. Pennsylvania. Brooks, M. C. and Peck, M. E. (1940). Effect of various cortical lesions on development of placing and hopping reactions in rats. J. Neurophysiol. 3, 66-73. Bureg, J., Bure~ov~, O., and K~ivhnek, J. (1974). "The Mechanism and Applications of Lefio's Spreading Depression of Electroencephalographic Activity," Prague: Academia. Huston, J. P., Avrith, D., Waser, P. G., and Siegfried, B. (1976). Effect of amygdaloid lesions on eating elicited by cortical spreading depression. Physiol. Behav. 16,201-205. Huston, J. P. and Bro~ek, G. (1971). Arousal of consummatory behavior in rabbits by single waves of cortical spreading depression. Physiol. Behav. 7, 595-600. Huston, J. P. and BureL J. (1973). Effects of cortical spreading depression on behaviors elicited by hypothalamic stimulation in rats. Physiol. Behav. 10, 775-780. Hnston, J. P. and Buret, J. (1970). Drinking and eating elicited by cortical spreading depression. Science 169, 702-704. Huston, J. P., Siegfried, B., Ornstein, K., Waser, P. G., and Borbrly, A. (1974). Eating elicited by spreading depression or electrical stimulation of the hippocampus and neocortex: A common cause. Brain Res. 78, 164-168. Jakobartl, L. and Huston, J. P. (1977). Circling and consumatory behavior induced by striatal and neocortical spreading depression. Physiol. Behav. 19, 673-677. Kolb, B. and Nonneman, A. J. (1975). Prefrontal cortex and the regulation of food intake in the rat. J. Comp. Physiol. Psychol. 88, 806-815. Lyons, H. I. and Freedman. N. L. (1976). Functional cortico- and amygdalohypothalamic interaction in drinking behavior. Physiol. Psychol. 4, 447-450. Richter, C. P. and Hawkes, C. D. (1939). Increased spontaneous activity and food intake produced in rats by removal of the frontal poles of the brain. J. Neurol. Psychiat. 2, 231-242.
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Shibata, M., Siegfried, B., and Huston, J. P. (1977). A miniature calomel electrode for recording DC potential changes accompanying spreading depression in the freely moving rat. Physiol. Behav. 18~ 1171-1174. Siegfried, B. and Huston, J. P. (1977). Properties of spreading depression-induced behaviors in rats. Physiol. Behav. 18, 841-851. Siegfried, B., Shibata, M., and Huston, J. P. (1977). Electrophysiological concomitants of eating induced from neocortex and hippocampus by electrical stimulation and injection of KC1 or norepinephrine. Brain Res. 121, 97-112.
