HORMONES
AND BEHAVIOR
6, 27-33 (1975)
Lordosis After Cerebellar Damage in Female Rats1 FRANK P. ZEMLAN and DONALD
W. PFAFF
University o.f Pennsylvania and The Rockefeller University
Massive destruction of the cerebellum is consistent with both performance of lordosis by estrous female rats and the continuation estrous cyclicity.
the of
In the systematic investigation of sensory and motor aspects of lordosis (Pfaff et al., 1972) it is necessary to consider the role of brain regions which exert control over motor responses. For instance, an intact cerebral cortex is apparently not necessary for the performance of lordosis in female rats (Beach, 1944). The cerebellum is generally held to play an important role in sensory-motor coordination and may mediate motivated behaviors (Chambers, 1947; Zanchetti and Zoccolini, 1954; Reis, Doba, and Nathan, 1973). Therefore, we investigated the ability of female rats to perform lordosis after cerebellar damage. Experiment I concentrated on observations of lordosis after operation, while Experiment II investigated both endocrine and behavioral changes.
EXPERIMENT I Methods Female rats of the Sprague-Dawley strain (body wt, 240-310 g) were obtained from Hormone Assay Labs, and maintained on a 12-hr light 12-hr dark reverse day-night cycle. Food and water were available ad lib. After adaptation to the laboratory conditions, Ss were ovariectomized under Nembutal anesthesia. After a 3-wk recovery period, Ss were tested for their I We thank Mark Pomerantz and Catherine Lewis for diligent technical assistance and Dr. W. W. Chambers and Dr. R. Norgren for both expert technical advice and helpful comments regarding the manuscript. This research was supported by NIH Grants NS 10464 (to W. W. Chambers), HDa45 2206 (to N. T. Adler), and HD-05751 (to D. W. Pfaff).
27 Copyright @ 1975 by Academic Press, Inc. All rights of reproduction in any form reserved.
28
ZEMLANANDPFAFF
ability to show the lordotic reflex to mating attempts by male rats or manual stimulation. Ss were administered, by subcutaneousinjections in oil, estradiol benzoate (10 &animal/day for 8 days) and progesterone(1.0 mg/animal) 4 hr before testing. All Ss respondedmaximally. After testing Ss were cerebellectomized (N=6) under Nembutal anesthesia.With the head held rigidly by a stereotoxic device, the occipital bone over the cerebellum was removed and as much cerebellar tissue as possible aspirated. The resulting cavity was filled with moist gelfoam and the skin sutured. In addition to the cerebellectomized Ss other animals (N=3) were anesthetizedand the occipital bone removed but the cerebellum was not aspirated. After a 5 to 7-wk recovery period, experimental and sham-operated animals were given two postoperative tests. For each test Ss were administered estradiol benzoate (EB) and progesterone as in the preoperative tests. Four hours after each progesterone administration Ss were tested for lordosis to manual stimulation (pressure on the flank and perineal regions) and mating with male rats. Lordosis to manual stimulation was rated as either absent, fair, good, or excellent on each of five stimulus applications. Elicitation of lordosis by male rats was tested by putting the experimental female into a testing chamber (24 X 12 in, and 15 in. high) containing a vigorous stud male that was previously adapted to the testing chamber.The male delivered 10 mounts and the presenceor absenceof lordosis was noted, converted to a lordosis-tomount ratio and expressed as a lordosis quotient (LQ = no. of lordoses X lOO/no. of mounts). In addition, motion pictures of some tests were made using Super 8 color film, shot at normal (18 frames/set) or acceleratedspeeds (54 frames/set). After behavioral testing, operated Ss were anesthetized, sacrificed by cardiac perfusion with formalin, and their brains removed. Frozen sections 50 pm thick were cut in the coronal plane and alternate sections stained with cresyl violet and Weil stains. A planimetric systemwas employed to assessthe amount of cerebellum removed. Serial sections were studied using a projector and the Craigie atlas (Zeman and Innes, 1963). With the planimetric measurements, a ratio was formed of removed to total expected cerebellar tissue. A final estimated percentageof tissue removed was arrived at by averagingover all serial sections.
All cerebellectomized Ss performed lordosis after operation, both to manual stimulation and to mounting by the male rat (Table 1). The quality of the responseto manual stimulation received the averagerating of Good. The averagelordosis quotient of 57, during tests with stud male rats, includes results from two rats that could not stand up at all and lay lopsided during mating tests. If the data from these two rats were not included, the average
29
LORDOSIS IN FEMALE RATS TABLE 1 Postoperative Tests of Lordotic Reflex After EB and Progesterone Priming Lordosis to male rat
Lordosis to manual stimulation % Rats responding
Rating
% Rats responding
LQ
95
Sham operated (N = 3)
100
GoodExcellent
100
Cerebellar damaged (N = 6)
100
Gooda
100
‘Includes results from two rats that could not stand up at all. See text.
postoperative LQ for cerebellectomizedS’sis 79. Sham-operatedanimals also exhibited lordosis to manual stimulation and to mounting by the male rat. Histological examination demonstrated extensive damageto the cerebellum in all operated animals. The averageamount of tissue totally removedwas 45%, and some of the remaining tissue was obviously disorganized. In some cases,most of the deep cerebellar nuclei were removed, indicating a massive impairment of cerebellar function. There did not appear to be any destruction of extracerebellarbrainstem tissue. EXPERIMENT II Methods
Female rats of the Sprague-Dawleystrain (body wt, 175220 g) were obtained from Charles River Inc. Ss were maintained on a 14-hr light IO-hr dark reverseday-night cycle. Food and water were available ad lib. Ss were assignedto one of two experimental groups: (1) examination of endocrine changesresulting from cerebellectomy (N=16) or, (2) postoperative changes of the lordotic reflex (N=7). Ss selected for examination of the endocrine system had vaginal smears taken daily to ascertain their normal cyclic pattern. Only females showing three consecutive 4-day cycles were selected. After meeting this criterion “endocrine females” were divided into three groups: cerebellectomized(.=6), sham operated (N=4), or anesthetized only (3~6). The head was firmly held in a stereotaxic instrument, the occipital bone removed and the exposed cerebellum aspirated.Care was taken
30
ZEMLANANDPFAFF
to leave the tela chorioidea and vestibular nuclei intact. The resulting cavity was covered with moist gelfoam and the skin sutured. The operation was performed under a combination of Equithesin and Halothane anesthesia. The sham group was subjected only to that part of the operation up to and including removal of the occipital bone. The third group was anesthetized but not operated upon. After the experimental treatment females continued to have daily vaginal smears taken to assess their postoperative endocrine condition. Animals examined for lordotic behavior were ovariectomized and adrenalectomized to remove all sources of endogenous estrogen and progesterone. Operated animals had 15% dextrose and 0.9% saline solutions freely available. An im injection of EB (10 E.cgin 0.10 cc of cottonseed oil) was given postoperatively to maintain estrogen-dependent tissue. After a recovery period of 2-3 wk vaginal smears were taken. Only Ss showing an absence of endogenous estrogen, as judged by a leukocytic smear, were subsequently used. The preparation of the animal for testing began with a single im injection of varying amounts of EB 46-48 hr before behavioral testing. Six hours before testing Ss were injected im with 0.4 mglanimal of progesterone dissolved in cottonseed oil. The EB dosage was varied, with the progesterone dosage (0.4 mg/animal) held constant. Initially, females were tested with 2 pg/kg of EB with progesterone administered about 40 hr later. If lordotic behavior was not induced, the dosage was increased by 1 pg/kg until responding occurred. The EB threshold was taken to be that dosage which permitted lordosis on at least two of 10 mounts. A twice-threshold dosage was then administered to verify the threshold determination and finally a just subthreshold dosage of EB was administered to determine whether the threshold had been lowered due to repeated hormone administration. The time interval between successive EB administrations was that time necessary for the cornification of the vaginal mucosa to revert to a leukocytic state, approximately 7-10 days. The experimental test for lordosis consisted of placing the experimental female with a vigorous male. The testing chamber was 24 in. wide, 18 in. deep, and 14 in. high, fitted with a Plexiglas front. Testing was initiated early in the dark portion of the day-night cycle. The male delivered 10 mounts and the presence or absence of lordosis was noted, converted to a lordosis-tomount ratio and expressed as a lordosis quotient (LQ). In addition to direct observation of the behavioral tests, 16-mm color motion pictures were made of some of the tests. After testing, animals were anesthetized, perfused, the brain embedded in parlodion, sliced at 45 pm, and stained with hematoxylin. Percentage of removed tissue was calculated by comparing the experimental slides with appropriate atlas plates (Pellegrino and Cushman, 1967; Sidman et al., 1971).
31
LORDOSIS IN FEMALE RATS
RESULTS The effect of cerebellectomy on the endocrine condition was transitory. Preoperative 4-day cycles were interrupted by pseudopregnancywhether the animals were cerebellectomized (4/6, 12-day averagelength), sham-operated (3/4, 13-day average length), or only anesthetized (3/6, 1Qday average length). After pseudopregnancyall animals returned to a normal 4-day cycle. Animals not becoming pseudopregnant maintained 4-day cycles throughout the experiment. Behavioral tests in ovariectomized, adrenalectomizedfemaleswere conducted to assesschangesin the postoperative hormone threshold for lordosis. In all six Ss receiving cerebellectomy the individual pre- and postoperative hormone thresholds were the same(Table 2). Subject 112 could not stand up during the mating tests, which decreased the postoperative LQ score. In addition to the totally cerebellectomizedSs, one female was given a localized lesion of the paravermal cortex. As with the totally cerebellectomizedfemales the pre- and postoperative EB thresholds were the same(both 6 E.cg/kg). Histology revealed that the major portion of the cerebellum had been removed. Representative histology is presented in Fig. 1. In addition to the TABLE 2 Hormonal Threshold for Induction of Lordotic Behavior Before and After Cerebellectomy. Animals were Treated with the Indicated Amount of EB plus Progesterone (0.4 mg/Animal) Postoperative
Preoperative S No.
EB dosage
105
2 e/kg
LQ
EB dosage
LQ
0
2 I.rglkg
0
3 a/k
100
3 /.&kg
90
10 fig/k 11 pg/kg
0 IO
10 /.%/kg 11 ccdkg
0 50
1 rdkg
0 80
2 /.&is
2 /-dkg
0
2 /&g
3 /a/kg
100
3 /a/kg
ld
118
3 /-s/kg 4 4%
0 100
3 m/k 4 Icg/kg
0 70
119
2 e/k
108 111
2 ccdk 112
3 Ccg/k
0
100
“Could not stand during test. See text.
1 Icg/kg
2 idk 3 /.&kg
0 50 0
0
70
32
ZEMLAN AND PFAFF
Fig. 1. Drawings from representative histological sections from rat 119, whose behavioral results are shown in Table 2. Heavy line encloses area of cerebellum which was removed by aspiration. Levels of sections matched to plates in the atlas of Pellegrino and Cushman (1967). Abbreviations: CBLLM, cerebellum; BS, brainstem; CI, inferior colliculus.
destruction of most of the cerebellar cortical tissue, the deep cerebellar nuclei had been removed. On the average,70% of the cerebellum was removed.The remaining tissue was mostly anterolateral cerebellar cortex. The one animal bearing a lesion of the paravermal cortex was observedto have small bilateral lesions which sparedthe deep cerebellar neclei. DISCUSSION From these results we conclude that normal function of the cerebellum is not necessaryfor the performance of lordosis. If an absolutely complete (100%) removal of cerebellar tissue had been achieved,it would be possible to conclude that the cerebellum is not necessaryat all for lordosis. However, the possibility of additional blood loss or fatal damageto the brainstem prevented more extensive cerebellar extirpation. In tests with vigorous male rats it appeared that if the female could stand up she could show lordosis, even if she could not locomote normally. It is possible that with further detailed testing, some differences in lordosis latency, intensity, or duration would appear between control and cerebellectomized subjects. For instance, in several cerebellectomizedfemales the lordosis reflex appeared slightly delayed, even though it was of normal intensity and was exhibited on a high percentage of mounts. However, the reflex in our subjects was normal enough that males could achieve intro-
LORDOSIS IN FEMALE RATS
33
missionsin a substantial percentageof casesin which lordosis occurred. In line with the above observation, the performanceof lordosis after massivecerebellar damagedoes not necessarilyindicate that other experimental manipulations of cerebellar tissue would be without effect on the lordosis reflex. For example, lesioning of the fastigial nucleus of the cerebellum does not drastically alter food intake, but electrical stimulation induces feeding (Reis, Doba, and Nathan, 1973).
REFERENCES Beach, F. A. (1944). Effects of injury to the cerebral cortex upon sexual receptivity in the female rat. Psychosom. Med. 6, 40-55. Chambers, W. W. (1947). Electrical stimulation of the interior of the cerebellum. Amer. J. Anat. 80, 55-93. Pellegrino, L. J., and Cushman, A. J. (1967). A Stereotaxic Atlas of the Rat Brain. Appleton-CenturyCrofts, New York. Pfaff, D. W., Lewis, C., Diakow, C., and Keiner, M. (1972). Neurophysiological analysis of mating behavior responses as hormone-sensitive reflexes. In (E. Stellar and J. M. Sprague, (Eds.) ), Progress in Physiological Psychology, Vol. 5, Academic Press, pp. 253-297. New York. Reis, D. J., Doba, N., and Nathan, M. A. (1973). Predatory attack, grooming, and consummatory behaviors evoked by electrical stimulation of the cat cerebellar nuclei. Science 182, 845-847. Sidman, R. L., Angevine, J. B., and Pierce, E. T. (1971). Atlas of the Mouse Brain and Spinal Cord. Harvard University Press, Cambridge, Mass. Zanchetti, A., and Zoccolini, A. (1954). Autonomic hypothalamic outbursts elicited by cerebellar stimulation. J. Neurophysiol. 17, 475-483. Zeman, W., and Innes, J. R. M. (1963). Craigie’s Neuroanatomy of the Rat. Academic Press. New York.
AND BEHAVIOR
6, 27-33 (1975)
Lordosis After Cerebellar Damage in Female Rats1 FRANK P. ZEMLAN and DONALD
W. PFAFF
University o.f Pennsylvania and The Rockefeller University
Massive destruction of the cerebellum is consistent with both performance of lordosis by estrous female rats and the continuation estrous cyclicity.
the of
In the systematic investigation of sensory and motor aspects of lordosis (Pfaff et al., 1972) it is necessary to consider the role of brain regions which exert control over motor responses. For instance, an intact cerebral cortex is apparently not necessary for the performance of lordosis in female rats (Beach, 1944). The cerebellum is generally held to play an important role in sensory-motor coordination and may mediate motivated behaviors (Chambers, 1947; Zanchetti and Zoccolini, 1954; Reis, Doba, and Nathan, 1973). Therefore, we investigated the ability of female rats to perform lordosis after cerebellar damage. Experiment I concentrated on observations of lordosis after operation, while Experiment II investigated both endocrine and behavioral changes.
EXPERIMENT I Methods Female rats of the Sprague-Dawley strain (body wt, 240-310 g) were obtained from Hormone Assay Labs, and maintained on a 12-hr light 12-hr dark reverse day-night cycle. Food and water were available ad lib. After adaptation to the laboratory conditions, Ss were ovariectomized under Nembutal anesthesia. After a 3-wk recovery period, Ss were tested for their I We thank Mark Pomerantz and Catherine Lewis for diligent technical assistance and Dr. W. W. Chambers and Dr. R. Norgren for both expert technical advice and helpful comments regarding the manuscript. This research was supported by NIH Grants NS 10464 (to W. W. Chambers), HDa45 2206 (to N. T. Adler), and HD-05751 (to D. W. Pfaff).
27 Copyright @ 1975 by Academic Press, Inc. All rights of reproduction in any form reserved.
28
ZEMLANANDPFAFF
ability to show the lordotic reflex to mating attempts by male rats or manual stimulation. Ss were administered, by subcutaneousinjections in oil, estradiol benzoate (10 &animal/day for 8 days) and progesterone(1.0 mg/animal) 4 hr before testing. All Ss respondedmaximally. After testing Ss were cerebellectomized (N=6) under Nembutal anesthesia.With the head held rigidly by a stereotoxic device, the occipital bone over the cerebellum was removed and as much cerebellar tissue as possible aspirated. The resulting cavity was filled with moist gelfoam and the skin sutured. In addition to the cerebellectomized Ss other animals (N=3) were anesthetizedand the occipital bone removed but the cerebellum was not aspirated. After a 5 to 7-wk recovery period, experimental and sham-operated animals were given two postoperative tests. For each test Ss were administered estradiol benzoate (EB) and progesterone as in the preoperative tests. Four hours after each progesterone administration Ss were tested for lordosis to manual stimulation (pressure on the flank and perineal regions) and mating with male rats. Lordosis to manual stimulation was rated as either absent, fair, good, or excellent on each of five stimulus applications. Elicitation of lordosis by male rats was tested by putting the experimental female into a testing chamber (24 X 12 in, and 15 in. high) containing a vigorous stud male that was previously adapted to the testing chamber.The male delivered 10 mounts and the presenceor absenceof lordosis was noted, converted to a lordosis-tomount ratio and expressed as a lordosis quotient (LQ = no. of lordoses X lOO/no. of mounts). In addition, motion pictures of some tests were made using Super 8 color film, shot at normal (18 frames/set) or acceleratedspeeds (54 frames/set). After behavioral testing, operated Ss were anesthetized, sacrificed by cardiac perfusion with formalin, and their brains removed. Frozen sections 50 pm thick were cut in the coronal plane and alternate sections stained with cresyl violet and Weil stains. A planimetric systemwas employed to assessthe amount of cerebellum removed. Serial sections were studied using a projector and the Craigie atlas (Zeman and Innes, 1963). With the planimetric measurements, a ratio was formed of removed to total expected cerebellar tissue. A final estimated percentageof tissue removed was arrived at by averagingover all serial sections.
All cerebellectomized Ss performed lordosis after operation, both to manual stimulation and to mounting by the male rat (Table 1). The quality of the responseto manual stimulation received the averagerating of Good. The averagelordosis quotient of 57, during tests with stud male rats, includes results from two rats that could not stand up at all and lay lopsided during mating tests. If the data from these two rats were not included, the average
29
LORDOSIS IN FEMALE RATS TABLE 1 Postoperative Tests of Lordotic Reflex After EB and Progesterone Priming Lordosis to male rat
Lordosis to manual stimulation % Rats responding
Rating
% Rats responding
LQ
95
Sham operated (N = 3)
100
GoodExcellent
100
Cerebellar damaged (N = 6)
100
Gooda
100
‘Includes results from two rats that could not stand up at all. See text.
postoperative LQ for cerebellectomizedS’sis 79. Sham-operatedanimals also exhibited lordosis to manual stimulation and to mounting by the male rat. Histological examination demonstrated extensive damageto the cerebellum in all operated animals. The averageamount of tissue totally removedwas 45%, and some of the remaining tissue was obviously disorganized. In some cases,most of the deep cerebellar nuclei were removed, indicating a massive impairment of cerebellar function. There did not appear to be any destruction of extracerebellarbrainstem tissue. EXPERIMENT II Methods
Female rats of the Sprague-Dawleystrain (body wt, 175220 g) were obtained from Charles River Inc. Ss were maintained on a 14-hr light IO-hr dark reverseday-night cycle. Food and water were available ad lib. Ss were assignedto one of two experimental groups: (1) examination of endocrine changesresulting from cerebellectomy (N=16) or, (2) postoperative changes of the lordotic reflex (N=7). Ss selected for examination of the endocrine system had vaginal smears taken daily to ascertain their normal cyclic pattern. Only females showing three consecutive 4-day cycles were selected. After meeting this criterion “endocrine females” were divided into three groups: cerebellectomized(.=6), sham operated (N=4), or anesthetized only (3~6). The head was firmly held in a stereotaxic instrument, the occipital bone removed and the exposed cerebellum aspirated.Care was taken
30
ZEMLANANDPFAFF
to leave the tela chorioidea and vestibular nuclei intact. The resulting cavity was covered with moist gelfoam and the skin sutured. The operation was performed under a combination of Equithesin and Halothane anesthesia. The sham group was subjected only to that part of the operation up to and including removal of the occipital bone. The third group was anesthetized but not operated upon. After the experimental treatment females continued to have daily vaginal smears taken to assess their postoperative endocrine condition. Animals examined for lordotic behavior were ovariectomized and adrenalectomized to remove all sources of endogenous estrogen and progesterone. Operated animals had 15% dextrose and 0.9% saline solutions freely available. An im injection of EB (10 E.cgin 0.10 cc of cottonseed oil) was given postoperatively to maintain estrogen-dependent tissue. After a recovery period of 2-3 wk vaginal smears were taken. Only Ss showing an absence of endogenous estrogen, as judged by a leukocytic smear, were subsequently used. The preparation of the animal for testing began with a single im injection of varying amounts of EB 46-48 hr before behavioral testing. Six hours before testing Ss were injected im with 0.4 mglanimal of progesterone dissolved in cottonseed oil. The EB dosage was varied, with the progesterone dosage (0.4 mg/animal) held constant. Initially, females were tested with 2 pg/kg of EB with progesterone administered about 40 hr later. If lordotic behavior was not induced, the dosage was increased by 1 pg/kg until responding occurred. The EB threshold was taken to be that dosage which permitted lordosis on at least two of 10 mounts. A twice-threshold dosage was then administered to verify the threshold determination and finally a just subthreshold dosage of EB was administered to determine whether the threshold had been lowered due to repeated hormone administration. The time interval between successive EB administrations was that time necessary for the cornification of the vaginal mucosa to revert to a leukocytic state, approximately 7-10 days. The experimental test for lordosis consisted of placing the experimental female with a vigorous male. The testing chamber was 24 in. wide, 18 in. deep, and 14 in. high, fitted with a Plexiglas front. Testing was initiated early in the dark portion of the day-night cycle. The male delivered 10 mounts and the presence or absence of lordosis was noted, converted to a lordosis-tomount ratio and expressed as a lordosis quotient (LQ). In addition to direct observation of the behavioral tests, 16-mm color motion pictures were made of some of the tests. After testing, animals were anesthetized, perfused, the brain embedded in parlodion, sliced at 45 pm, and stained with hematoxylin. Percentage of removed tissue was calculated by comparing the experimental slides with appropriate atlas plates (Pellegrino and Cushman, 1967; Sidman et al., 1971).
31
LORDOSIS IN FEMALE RATS
RESULTS The effect of cerebellectomy on the endocrine condition was transitory. Preoperative 4-day cycles were interrupted by pseudopregnancywhether the animals were cerebellectomized (4/6, 12-day averagelength), sham-operated (3/4, 13-day average length), or only anesthetized (3/6, 1Qday average length). After pseudopregnancyall animals returned to a normal 4-day cycle. Animals not becoming pseudopregnant maintained 4-day cycles throughout the experiment. Behavioral tests in ovariectomized, adrenalectomizedfemaleswere conducted to assesschangesin the postoperative hormone threshold for lordosis. In all six Ss receiving cerebellectomy the individual pre- and postoperative hormone thresholds were the same(Table 2). Subject 112 could not stand up during the mating tests, which decreased the postoperative LQ score. In addition to the totally cerebellectomizedSs, one female was given a localized lesion of the paravermal cortex. As with the totally cerebellectomizedfemales the pre- and postoperative EB thresholds were the same(both 6 E.cg/kg). Histology revealed that the major portion of the cerebellum had been removed. Representative histology is presented in Fig. 1. In addition to the TABLE 2 Hormonal Threshold for Induction of Lordotic Behavior Before and After Cerebellectomy. Animals were Treated with the Indicated Amount of EB plus Progesterone (0.4 mg/Animal) Postoperative
Preoperative S No.
EB dosage
105
2 e/kg
LQ
EB dosage
LQ
0
2 I.rglkg
0
3 a/k
100
3 /.&kg
90
10 fig/k 11 pg/kg
0 IO
10 /.%/kg 11 ccdkg
0 50
1 rdkg
0 80
2 /.&is
2 /-dkg
0
2 /&g
3 /a/kg
100
3 /a/kg
ld
118
3 /-s/kg 4 4%
0 100
3 m/k 4 Icg/kg
0 70
119
2 e/k
108 111
2 ccdk 112
3 Ccg/k
0
100
“Could not stand during test. See text.
1 Icg/kg
2 idk 3 /.&kg
0 50 0
0
70
32
ZEMLAN AND PFAFF
Fig. 1. Drawings from representative histological sections from rat 119, whose behavioral results are shown in Table 2. Heavy line encloses area of cerebellum which was removed by aspiration. Levels of sections matched to plates in the atlas of Pellegrino and Cushman (1967). Abbreviations: CBLLM, cerebellum; BS, brainstem; CI, inferior colliculus.
destruction of most of the cerebellar cortical tissue, the deep cerebellar nuclei had been removed. On the average,70% of the cerebellum was removed.The remaining tissue was mostly anterolateral cerebellar cortex. The one animal bearing a lesion of the paravermal cortex was observedto have small bilateral lesions which sparedthe deep cerebellar neclei. DISCUSSION From these results we conclude that normal function of the cerebellum is not necessaryfor the performance of lordosis. If an absolutely complete (100%) removal of cerebellar tissue had been achieved,it would be possible to conclude that the cerebellum is not necessaryat all for lordosis. However, the possibility of additional blood loss or fatal damageto the brainstem prevented more extensive cerebellar extirpation. In tests with vigorous male rats it appeared that if the female could stand up she could show lordosis, even if she could not locomote normally. It is possible that with further detailed testing, some differences in lordosis latency, intensity, or duration would appear between control and cerebellectomized subjects. For instance, in several cerebellectomizedfemales the lordosis reflex appeared slightly delayed, even though it was of normal intensity and was exhibited on a high percentage of mounts. However, the reflex in our subjects was normal enough that males could achieve intro-
LORDOSIS IN FEMALE RATS
33
missionsin a substantial percentageof casesin which lordosis occurred. In line with the above observation, the performanceof lordosis after massivecerebellar damagedoes not necessarilyindicate that other experimental manipulations of cerebellar tissue would be without effect on the lordosis reflex. For example, lesioning of the fastigial nucleus of the cerebellum does not drastically alter food intake, but electrical stimulation induces feeding (Reis, Doba, and Nathan, 1973).
REFERENCES Beach, F. A. (1944). Effects of injury to the cerebral cortex upon sexual receptivity in the female rat. Psychosom. Med. 6, 40-55. Chambers, W. W. (1947). Electrical stimulation of the interior of the cerebellum. Amer. J. Anat. 80, 55-93. Pellegrino, L. J., and Cushman, A. J. (1967). A Stereotaxic Atlas of the Rat Brain. Appleton-CenturyCrofts, New York. Pfaff, D. W., Lewis, C., Diakow, C., and Keiner, M. (1972). Neurophysiological analysis of mating behavior responses as hormone-sensitive reflexes. In (E. Stellar and J. M. Sprague, (Eds.) ), Progress in Physiological Psychology, Vol. 5, Academic Press, pp. 253-297. New York. Reis, D. J., Doba, N., and Nathan, M. A. (1973). Predatory attack, grooming, and consummatory behaviors evoked by electrical stimulation of the cat cerebellar nuclei. Science 182, 845-847. Sidman, R. L., Angevine, J. B., and Pierce, E. T. (1971). Atlas of the Mouse Brain and Spinal Cord. Harvard University Press, Cambridge, Mass. Zanchetti, A., and Zoccolini, A. (1954). Autonomic hypothalamic outbursts elicited by cerebellar stimulation. J. Neurophysiol. 17, 475-483. Zeman, W., and Innes, J. R. M. (1963). Craigie’s Neuroanatomy of the Rat. Academic Press. New York.
