Rapid Changes in Cerebral Blood Flow and Initial Visual Experience in the Developing Chick
.4 sin& cyc of young chicks was sewed shut for various times. Rcgions contr;ilatcr;il to and priniarily or secondarily innervated by the sutured eye had a reduccd rate of ccrcbral blood flow in comparison to the corrcspondingipsilatcral rcpions. However, upon rcopcning the suturcd eye ;iltcr 2 days, these eon1r;rlateral rcgions (optic lobes and cerebral hcmisphcres) exhibited a rapid itzcrrase in cerebral blood flow to a level significantly above that in control ipsilateral areas. Thc duration o f this effect was considerably prolonged in chicks that were monocularly sutured immediately after hatcliing without prior exposure t o light. Chicks that had 1 week of normal vision bcforc nionocular suture did not sliow this overcompensatory effect. I f the period of nionocular suture was extended to 7 days before restoration of vision to the occludcd eye, the overcompensatory vascular effect was delayed. The maximal effect was apparent only upon the 1st exposure of an eye to major visual input. A possible relation exists between this rapid increase in regional blood flow and the period when visud imprinting could normally bc cxpectcd to be maximal.
Reduction of visual input in the chick can depress the velocity of cerebral blood flow througli several brain areas (Bondy, 1973; Bondy & Morelos, 1971 ). Evidence also indicates that such blood flow can be modified by the attention-arousing quality of sensory input rather than merely the intensity of afferent light' (Bondy, Leliinan, & Purdy, 1974). 'The advantage of the avian visual pathway in these studies is that each eye solely innervates the contralateral optic lobe (Cowan, Adamson, & Powell. 1961). This, in conjuction with the absence of major interficmispheric commissures, rcduces interactions between the 2 halves of the brain. Thus, brain regions that are directly or secondarily innel-vated by a single eye that has been subjected t o modified visual input can be compared t o the corresponding regions innervated by the other eye of the same chick. Thc degree of information transfer between the 2 halvcs or the avian brain appears to depend on the nature of the acquired learning. Powerful aversive stimuli appear l o he rapidly transfcrred (Bcnowitz, 1974; Cherkin, 1970) whereas positive stimuli inay be unilaterally confined for some time (Levine, 1952; Zeier, 1070). Imprinting, liowever, is rapidly transferred in ducklings (Moltz & Stettner. 1961).
-Received f o r publication 3 January 1975 Revined for publication 10 March 1975 Ucvcbpmcnful Psychobiology, 9 (1): 31-38 (1 9 76) @ 1976 by John Wilcy ti Sons, Inc.
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BONDY AND PURDY
We are reporting here that large and widespread changes in cerebral blciod flow can occur rapidly in response to restoration of light to a visually deprived eye. Blood flow in affected regions may be elevated considerably above normal values. Studies involving variation of the age of chicks and the duration of suture lead t o the possibility that an increase of the blood supply to the brain may be concommit t m t with imprinting.
Me di od s Fertile eggs of the White Leghorn strain of chick (GaZZus domesticus, obtained fiom Meyer Bros., Creely. Colo.) were incubated a t 38°C under forced-air ventilation and automatic rotation. Humidity was 6476, appropriate for an altitude of 1680 m . After hatching, chicks were housed together in heated brooders with free access to food and water, and were exposed to 12 hr of light daily. The lids of a single eye were sewed shut with surgical silk under light chloroform anesthesia. Sutures were removed as required with a pair of fine scissors and forceps. The previously sutured eyes were undamaged by this reopening procedure. Croups of 8-16 clucks were given an intracardiac injection of .1 ml water containing 3.12 pCi N-methyl [CI4] antipyrine (15.6 mCi/mmole; New England Nuclear Corp.. Boston, Mass.) in order to determine the velocity of blood flow. Antipyrine is rapidly diffusible through both aqueous and lipid media, and can be used to estimate the relative distribution of cardiac output to various brain regions (Bondy & Morelos. 1971; Sapirstein. 1958). After 10 sec, birds were decapitated and cerebral hemispheres and optic lobes removed and rapidly weighed. Cerebral hemispheres were dissolved in 2 nil and optic lobes in 1 ml tissue solubilizer (NCS, Amersham-Searle Corp.. Arlington Heights, Ill.) at 48°C. After cooling, 20 ml of a standard scintillation mixture was added to each sample. Radioactivity was assayed in a Picker Liquimat counter at an efficiency of 65-699).Deoxyglucose uptake by the brain was determined in a similar mlinner except that 11.5 pCi of gaseously labeled 2 - d e o x y - D - g l ~ c o s e - [ ~ H (7.2 ] Ci/mmole) was used and birds were decapitated 2 hr after intracardiac injection. Data were calculated as counts/min/mg tissue (wet weight). Results were expressed as the ratio of the specific radioactivity in brain regions contralateral to the experimental eye ( E ) relative to the corresponding value of the paired region contralateral to the unmanipulated control eye (C). Thus. each experiniental area was compared t o the c o n ~ r o l area of the same bird. Eight or more individual comparisons were used to calculate
E
each data point presented. The natural logarithm of this ratio, - was delermined for C’ each chick t o avoid skewing the data. By taking the antilogarithm of t h e final mean logarithmic ratio. i t . , the geometric mean, these values were expressed as fractional differences in blood flow of experimental (E) regions relative t o control (C) regions. The significance of these internally paired sets of data was calculated by the 2-tailed [-test: p < .05 was taken as significant. Four experimental series were done: ( I ) Birds were monocularly sutured a t hatching before being exposed to light. Blood flow was determined 1 and 48 hr later. In other chicks, sutures werc removed after 48 hr and blood flow studied a t several times after restoration of binocular vision (Fig. 1).
VISUAL EXPERIENCE AND CEREBRAL BLOOD FLOW
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(2) Birds were monocularly sutured 18 hr after hatching, having been continuously exposed to light during those 18 hr. Blood flow was measured before or after removal of sutures, at times identical to those described for Series 1 above (Fig. 2). (3) Newly hatched chicks were monocularly sutured for a week, at which time blood flow was determined. In other groups of 7-day-old sutured chicks blood flow was studied at various times after suture removal (Fig. 3). (4) Chicks that had been exposed to ambient light for a week were then monocularly sutured for 2 days. Blood flow was measured in these chicks and also in separate groups of chicks 10 min and 1 hr after suture removal (Fig. 4).
Results Within 1 hr of suture, regions contralateral to the occluded eye had a rate of blood flow significantly below that of control regions associated with the nonmanipulated eye. This asymmetry was maintained for some time as long as 1 eye remained sewn shut (Figs. 1-4). Asymmetry was lost within 2 min of suture removal in 2-day-old birds which had been monocularly sutured before being exposed to light (Fig. 1). Ten minutes after removal, asymmetry returned, but in the opposite direction to the original. Thus, blood flow through experimeatal regions was now greater than that through control regions. This excess blood flow in previously deprived regions persisted for 1 hr, but asymmetry was restored after chicks had both eyes open for 5 hr. Time of suture removal (rnin) 0 2 1 0 60
+
-e
30C
T
0.2
+0.1 -
c
c
0
Suture Removed
9 m F a,
0-
I
E ._ L al
X Q
w
-0.1
-
I
-0.2 * / * 1
48
Duration of suture (hr)
Fig. 1. Cercbral blood flow of experimental regions relative to control regions after unilateral visual deprivation followed by restoration of binocukdr vision. Chicks were monocularly sutured at hatching for 48 hr. Blood flow was measured at various times before and after suture removal. Bars indicate S.E.M., * = p < .05, 0-0 = optic lobes, 0-0 = cerebral hemkpheres.
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BONDY AND PURDY
In the experiment described above, chicks whose sutures were removed remained in the presence of other chicks and food. The question arose as t o whether t!ie observed "overcompensator" effect could be due t o the response of brain regions assciciated with the recently opened eye and to potential impriiiting stimuli such as the prcsencc of o t l x r chicks. Alternatively, these regions could be activated b y novel learning related to grain-pecking. We have previous evidence that attention t o grain can modify regional blood flow in tlie chick (Bondy e t al., 1974). Sutures were removed from a group of 2-day-old chicks monocularly sutured a t hatching. Each chick was placed alone in a plain Iiigli-walled white bowl. Under such isolation conditions. chicks have a tendency to close their eyes. In order to ensure that both eyes were fully open, we kept the ihicks in howls a t 8°C [or the duration :If the experiment. After 1 11r% each set of chicks had a markedly enhanced rate o f blood flow in regions contralateral to the previously suturcd eye ( 0 . 8 3 .I% for optic lohes, 7.0 t 2.7% for cerebral hemispheres).Thereforc the effect could not be related to any specific visual stimulus. Furthermore, the effect persisted under the somewhat stressful circumstance of cold-rnain tenance. Another group of chicks were exposed to light for 18 lir after hatchiiig and then monocularly sutured for 2 clays. Upon removal of sutures from these birds. blood fltow in experimental regions rapidly swung from below to significa~tlyabove control vdues (Fig. 2). This preponderance of blood flow in experimental areas only persisted f o r a short time and disappeared in 1 hr. One group o f chicks was monocularly sutured immediately at hatching and maintained for 7 days. By this time. symmetry of blood flow in the halves of the brain had returned (Fig. 3). This may represent an adaptive response t o the grosdy dissimilar scnsory input to each eye. Suture removal caused a slower rise of blood flow in experimental regions which significantly exceeded control values only after 1 hr.
*
Time of suture removal (mln) 0 10 60
30 I
T
+0.2
+01 A .
c 0
3 2
0
W
E W
a x
w
-01
-0 2
Duration of suture (hr)
k'i?. 2 . Cerehral tllood flow of evperimental rcpions relative t o control region\ :ifter unil;ricral visual deprivation followed by restoration of binocular vision. l~i~litecn-hour-l,lcichick\ wc'rr nlonocularl~ sutured for 45 h r . Blood flow was incasurcd at various tiincr before ;in11 aftcr suturt' rcinoval. Bars indictlie S.I