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A short-term effect of amygdaloid lesions on food intake in the rat
EXPERIMENTAL
NEUROLOGY
27, 520-526
A Short-Term
Effect
on T.
(1970)
Food J.
CROW
of
Amygdaloid
Intake AND
in the I.
M.
Lesions Rat
WIIITAKER
Departmerzt of PhJlsiology, University of Aberdeen, Scotland Received February 18,197O Relatively small bilateral lesions in the amygdala resulted in a significant decrement in food intake in rats by comparison with similar lesions in the septal region or olfactory bulbs, or with a sham operation. This decrement was reflected in a relative decrease in body weight during the first 5 postoperative days, after which the rate of weight gain appeared to be normal. It is suggested that amygdaloid lesions may induce specific effects on food intake, and possibly other aspects of behavior which are related to the immediate sequelae of the lesion but not necessarily to interruption of amygdaloid circuitry. Water intake was significantly, and approximately equally, depressed in both the groups with septal and amygdaloid lesions. but to a lesser extent in the group with olfactory bulb lesions. Introduction
The literature on the effects of amygaloid ablation on food intake shows conflicting results. It has been reported that amygdaloid lesions have no effect on food intake (2,3) or may produce hyperphagia (1,9.10,13,14,17) or hypophagia (4,7,19). There have been few systematic investigations of this question and rarely have the reported effects of amygdaloid lesions been compared to those of lesions in other cerebral sites. The purpose of the present study was to clarify this situation by investigation, over the immediate postoperative period (18 days), of the effects on daily food and water intakes of circumscribed amygdaloid lesions. The changes induced by amygdaloid lesions were compared with those resulting from lesions of septal nuclei and olfactory bulbs. In this way it was hoped to contrast the effects of amygdaloid lesions with those of lesions to an area with similarly extensive hypothalamic connections (septum) and of lesions to an important source of sensory input (olfactory bulbs)‘. Methods
A’ubjects and Operatizle Procedure. Thirty-six male hooded Lister rats of mean age G months were used. They were divided into four groups of nine so that each group had approximately the same mean weight (430 g). 520
AMYGDALA
521
The groups were as follow : sham operation (SC) ; amygdaloid lesion (Sa) ; olfactory bulb lesion (So) ; and septal lesion (Ss). Anesthesia was induced by intraperitoneal injection of Nembutal (60 mg/kg body wt). Lesions were made bilaterally and each was made by passing a current of 0.5-2.0 ma for lo-40 set through a varnished steel electrode (anode) to give a total charge of 20 mcoul, the circuit being completed by an anal cathode. Electrode placement was accomplished stereotaxically through burr holes in the skull using the atlas of Fifkova and Marsala (S), the co-ordinates being: amygdala, AP 2.0, L 3.5, V 7.5 ; septum, AP 1.0, L 0.5, V 4.5. Lesions to the olfactory bulb were made, under direct vision, to the center of the bulb using the same procedure and current parameters. In the sham-operated animals burr holes were drilled in the skulls and the scalp was sutured without inserting electrodes into the brain. Two animals in each of groups Sa and Ss did not survive the operation and a further animal in group Ss died on the seventh postoperative day. Tl,‘ei@s. The weight of each animal was noted on the day of cperation and on postoperative days 3-11 and 16-1s. Weighings were carried out at the same time each day. Food and Water Intakes. Animals were housed in individual cages. Daily food and water intakes were measured on postoperative days 3-10 and 16-17. The animals were fed on a thick paste made by mixing equal quantities by weight of ground rat meal (Thompson cubes) and water ; 70 g of this paste were packed into a petri dish which, after weighing, was placed in the cage. Twenty-four hours later the dish was reweighed and the food intake for this period obtained by subtraction of the final from the initial weight. Inspection of the cages revealed minimal loss of food due to spillage. Water intake was measured by assessing the residue of water in each water bottle after 24 hr. Location of Lesions. On the eighteenth postoperative day the animals were killed by perfusion, under Nembutal anesthesia, of a 10% form01 saline solution through the left ventricle. Brains were removed and after fixing, dehydrating, and clearing, were mounted in paraffirr! wax. Sections 25 p thick were cut and every eighth section was mounted on a slide and stained with 1~x01 fast blue and cresyl violet (Kliiver’s techn.;que) . Slides were examined microscopically for site and size of lesions. Results
Weights. The mean daily weights for each group are shown in Fig. 1. At the time of operation there was no significant difference between any groups. During the whole of the postoperative period the weight of group
522
CROW
AND
WHITAKER
-sham -.mygdala --olfae.ry -s.pt.l
PO*.-op
da**
FIG. 1. Mean body weight of each group of rats with lesions compared with the sham-operated control group over an 19-day postoperative period.
Sa was significantly lessthan that of group SC (p
significantly lower ; So vs Sc, p
than for the sham-operated ; Ss vs SC, p
group
Histology. Typical examples of lesions from groups Sa and Ss are shown in Fig. 3. The subnuclei of the amygdala most commonly involved were the basal and lateral divisions. The lesions did not extend as far forward
523
AMYGDALA
port
-op
days
FIG. 2. Mean daily food and water intakes per 100 g body wt. All groups show a significant postoperative depression in food intake up to 5 days after operation but
this
is greater
in the rats
with
amygdaloid
lesions
than
in the other
three
groups.
as the anterior nucleus and usually extended back as far as the rostra1 part of the cortical nucleus. Destruction of the septal regions usually bordered the lateral ventricle. Discussion
It is clear from the results obtained that, for 5 days postoperatively, amygdaloid lesions produced hypophagia which in turn produced a deficit of approximately 10% in body weight by comparison with other groups with lesions. After this period, despite a return to normal levels of food consumption, the body weights of the amygdaloid group remained significantly lower although increasing in parallel with those of the other groups. The difference had not diminished by the time of killing. Such results do
524
CROW
AND
K’IIITAKER
FIG. 3. Sites of lesions (shaded black) in two typical animals from each of the amygdaloid and septal groups. The amygdaloid lesions (upper two) invade the cortical, basal, and lateral nuclei. The septal lesions (lower two) border on the lateral ventricle.
not appear to have been reported previously. Scrutiny of the records published by some workers (e.g., ref. 2, Fig. 1 and 3) shows a definite postoperative depression of food intake after amygdaloid ablation but this is not remarked upon by the authors, possibly because it has been attributed to the general effects of operation. However, the results in our other animals with lesions (Fig. 1) show that this explanation is untenable. The effect appears to be specific to amygdaloid lesions. The only explicit report of an initial temporary decrease in food intake appears to be that of Fonberg (7) who found that amygdalectomized dogs showed aphagia which lasted for 8-10 days. The explanation offered by Fonberg, that the effect represents a genuine impairment of food-regu-
AMYGDALA
525
lating mechanisms which is subsequently compensated by hypothalamic controls, is clearly a possible, but rather complex, interpretation. In view of the time course of the effect we have observed, it seems more reasonable to suppose that it is in some way related to a process of degeneration or repair subsequent to the lesion process, and that it affects the connections of the amygdala specifically. It is well established that the ventromedial nucleus of the hypothalamus is critically involved in the regulation of food intake and it has recently been shown by Heimer and Nauta (12) that terminals of the stria terminalis are profusely distributed around this nucleus. A simple hypothesis, therefore, would be that the process of degeneration in this pathway at least temporarily disorganizes the hypothalamic control of food intake. An observation which may be relevant to our finding is that of Fonberg and Delgado (8) that a lo-set stimulation of the amygdala in cats inhibited food intake for several hours. This interesting phenomenon seems to deserve further investigation. Water intake was found to be significantly reduced in all lesioned groups. Grossman and Grossman (11) suggested that the amygdala has both facilitatory and inhibitory effects on water intake and that such effects are elicited by way of the hypothalamus has recently been demonstrated (17). Earlier work by Fisher and Coury (6), who demonstrated that cholinergic stimulation of many limbic structures produced drinking, suggests that rather widespread anatomical systems have some influence on drinking behavior. However, a nonspecific influence of cerebral lesions on water intake cannot be excluded by our data. There seems to be little doubt that the amygdala exerts an influence over food and water intakes, probably by an action on the hypothalamic centers responsible for these processes. The indiscriminate nature of food intake after amygdalectomy is well documented (15,16,18) and the possibility exists that the amygdala modulates the action of the diencephalic feeding centers, facilitating ingestion of edible substances and inhibiting that of nonedible substances. It is, therefore, perhaps not surprising that, when amygdaloid lesions are considered as a whole, the effects on food intake are inconsistent. Our results, however, demonstrate a further source of confusion in that it is clear that short-lasting changes in food intake can occur after amygdaloid lesions. These changes may not necessarily implicate the amygdala in the permanent neuronal circuitry involved in food intake control because within 6 days of the lesion normal levels of food intake had been established. The temporary changes in food intake are reflected, however, in longer-lasting diminutions of body weight which should be considered in any interpretations of the role of the amygdala in the control of total body mass.
526
CROW
AND
WHITAKER
References
1. 2. 3. 4. 5.
6. 7. 8.
9
10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
L. K. and M. E. DITRIKH. 1965. Effects of lesions of the limbic system on emotional reactions and conditioned reflexes in rats. Fed. Proc (Truns Suppl) 24 : 1003-1007. ANAND, B. K., and J. K. BROBECK. 1952. Food intake and spontaneous activity of rats with lesions in the amygdaloid nucleus. /. A~cu~opltysiol. 15: 421-431. ANAND, B. K., and S. Du.4. 1955. Stimulation of limbic system of brain in waking animals. Science 122 : 1139. BRUTKOWSKI, S., E. FONBERG, J. KREINER, and E. MEMPEL. 1962. Aphagia and adipsia in a dog with bilateral complete lesion of the amygdaloid complex. Acta Biol. Exp. Warsaw 22 : 43-50. FIFKOVA, J.. and J. MARSALA. 1967. Rat brain stereotaxic atlas, pp. 653-695. In “Electrophysiological Methods in Biological Research,” Appendix I. J. Bures, M. Petran. and J. Zachar teds.]. Academic Press, New York. FISI~FX, A. E., and J. N. COURY. 1962 Cholinergic tracing of a central neural circuit underlying the thirst drive Science 138 : 691-693. FONBERG. E. 1966. Aphagia, produced by destruction of the dorsomedial amygdala in dogs. Bull. Acad. Pol. Sci. Ser. Sci. Biol. 14 : 719-722. FONBERG, E., and J. M. R. DELGADO. 1966. Inhibitory effects of amygdala on food intake and conditioning. Fed. Proc. 20 : 1. FULLER, J., H. ROSVOLD, and K. PRIBRAM. 1957. The effect on affective and cognitive behaviour in the dog of lesions of the pyriform-amygdala-hippocampal complex. J. Camp. Phgsiol. Psychol. 50 : 89-96. GREEN, J. D., C. D. CLEMENTE, and J. E. DE GROOT. 1957. Rhinencephalic lesions and behaviour in cats. J. Camp. Neurol. 108 : 505-545. GROSSMAN, S. P., and L. GROSSMAN. 1963. Food and water intake following lesions or electrical stimulation of the amygdala Amer. J. Physiol. 205 : 761-765. HEIMER, L.. and W. J. H. NAUTA. 1969. Hypothalamic distribution of the stria terminalis in the rat. Brain Res. 13 : 286297. LEWINSKA, M. K. 1967. Ventromedial hypothalamus: Participation in control of food intake and functional connections with ventral amygdala. Acta Biol. Erp. Warsaw 27 : 297-302. MORGANE, P. J., and A. J. KOSMAN. 1957. Alterations in feline behaviour following bilateral amygdalectomy. Fed. Proc. 18 : 90. PRIBRAM, K. H., and M. BAGSHAW. 1953. Further analysis of temporal lobe syndrome utilising fronto-temporal ablations. J. Conrp. Neural. 88 : 347-375. SCHREINER, L., and A. KLING. 1953. Behavioural changes following rhinencephalic injury in cat. J. Neuropltysiol. 18 : 643-659. SINGER, G., and R. B. MONTGOMERY. 1969. Functional relationship of lateral hypothalamus and amygdala in control of drinking. Physiol. Behav. 4: 505-507. WOOD, C. D. 1958. Behavioural changes following discrete lesions of temporal lobe structure. Neurology 8 : 215-220. YAMADA, T., and M. A. GREER. 1960. The effect of bilateral ablation of the amygdala on endocrine function in the rat. Endocrmology 88 : 565-574. ALLIKMETS,
NEUROLOGY
27, 520-526
A Short-Term
Effect
on T.
(1970)
Food J.
CROW
of
Amygdaloid
Intake AND
in the I.
M.
Lesions Rat
WIIITAKER
Departmerzt of PhJlsiology, University of Aberdeen, Scotland Received February 18,197O Relatively small bilateral lesions in the amygdala resulted in a significant decrement in food intake in rats by comparison with similar lesions in the septal region or olfactory bulbs, or with a sham operation. This decrement was reflected in a relative decrease in body weight during the first 5 postoperative days, after which the rate of weight gain appeared to be normal. It is suggested that amygdaloid lesions may induce specific effects on food intake, and possibly other aspects of behavior which are related to the immediate sequelae of the lesion but not necessarily to interruption of amygdaloid circuitry. Water intake was significantly, and approximately equally, depressed in both the groups with septal and amygdaloid lesions. but to a lesser extent in the group with olfactory bulb lesions. Introduction
The literature on the effects of amygaloid ablation on food intake shows conflicting results. It has been reported that amygdaloid lesions have no effect on food intake (2,3) or may produce hyperphagia (1,9.10,13,14,17) or hypophagia (4,7,19). There have been few systematic investigations of this question and rarely have the reported effects of amygdaloid lesions been compared to those of lesions in other cerebral sites. The purpose of the present study was to clarify this situation by investigation, over the immediate postoperative period (18 days), of the effects on daily food and water intakes of circumscribed amygdaloid lesions. The changes induced by amygdaloid lesions were compared with those resulting from lesions of septal nuclei and olfactory bulbs. In this way it was hoped to contrast the effects of amygdaloid lesions with those of lesions to an area with similarly extensive hypothalamic connections (septum) and of lesions to an important source of sensory input (olfactory bulbs)‘. Methods
A’ubjects and Operatizle Procedure. Thirty-six male hooded Lister rats of mean age G months were used. They were divided into four groups of nine so that each group had approximately the same mean weight (430 g). 520
AMYGDALA
521
The groups were as follow : sham operation (SC) ; amygdaloid lesion (Sa) ; olfactory bulb lesion (So) ; and septal lesion (Ss). Anesthesia was induced by intraperitoneal injection of Nembutal (60 mg/kg body wt). Lesions were made bilaterally and each was made by passing a current of 0.5-2.0 ma for lo-40 set through a varnished steel electrode (anode) to give a total charge of 20 mcoul, the circuit being completed by an anal cathode. Electrode placement was accomplished stereotaxically through burr holes in the skull using the atlas of Fifkova and Marsala (S), the co-ordinates being: amygdala, AP 2.0, L 3.5, V 7.5 ; septum, AP 1.0, L 0.5, V 4.5. Lesions to the olfactory bulb were made, under direct vision, to the center of the bulb using the same procedure and current parameters. In the sham-operated animals burr holes were drilled in the skulls and the scalp was sutured without inserting electrodes into the brain. Two animals in each of groups Sa and Ss did not survive the operation and a further animal in group Ss died on the seventh postoperative day. Tl,‘ei@s. The weight of each animal was noted on the day of cperation and on postoperative days 3-11 and 16-1s. Weighings were carried out at the same time each day. Food and Water Intakes. Animals were housed in individual cages. Daily food and water intakes were measured on postoperative days 3-10 and 16-17. The animals were fed on a thick paste made by mixing equal quantities by weight of ground rat meal (Thompson cubes) and water ; 70 g of this paste were packed into a petri dish which, after weighing, was placed in the cage. Twenty-four hours later the dish was reweighed and the food intake for this period obtained by subtraction of the final from the initial weight. Inspection of the cages revealed minimal loss of food due to spillage. Water intake was measured by assessing the residue of water in each water bottle after 24 hr. Location of Lesions. On the eighteenth postoperative day the animals were killed by perfusion, under Nembutal anesthesia, of a 10% form01 saline solution through the left ventricle. Brains were removed and after fixing, dehydrating, and clearing, were mounted in paraffirr! wax. Sections 25 p thick were cut and every eighth section was mounted on a slide and stained with 1~x01 fast blue and cresyl violet (Kliiver’s techn.;que) . Slides were examined microscopically for site and size of lesions. Results
Weights. The mean daily weights for each group are shown in Fig. 1. At the time of operation there was no significant difference between any groups. During the whole of the postoperative period the weight of group
522
CROW
AND
WHITAKER
-sham -.mygdala --olfae.ry -s.pt.l
PO*.-op
da**
FIG. 1. Mean body weight of each group of rats with lesions compared with the sham-operated control group over an 19-day postoperative period.
Sa was significantly lessthan that of group SC (p
significantly lower ; So vs Sc, p
than for the sham-operated ; Ss vs SC, p
group
Histology. Typical examples of lesions from groups Sa and Ss are shown in Fig. 3. The subnuclei of the amygdala most commonly involved were the basal and lateral divisions. The lesions did not extend as far forward
523
AMYGDALA
port
-op
days
FIG. 2. Mean daily food and water intakes per 100 g body wt. All groups show a significant postoperative depression in food intake up to 5 days after operation but
this
is greater
in the rats
with
amygdaloid
lesions
than
in the other
three
groups.
as the anterior nucleus and usually extended back as far as the rostra1 part of the cortical nucleus. Destruction of the septal regions usually bordered the lateral ventricle. Discussion
It is clear from the results obtained that, for 5 days postoperatively, amygdaloid lesions produced hypophagia which in turn produced a deficit of approximately 10% in body weight by comparison with other groups with lesions. After this period, despite a return to normal levels of food consumption, the body weights of the amygdaloid group remained significantly lower although increasing in parallel with those of the other groups. The difference had not diminished by the time of killing. Such results do
524
CROW
AND
K’IIITAKER
FIG. 3. Sites of lesions (shaded black) in two typical animals from each of the amygdaloid and septal groups. The amygdaloid lesions (upper two) invade the cortical, basal, and lateral nuclei. The septal lesions (lower two) border on the lateral ventricle.
not appear to have been reported previously. Scrutiny of the records published by some workers (e.g., ref. 2, Fig. 1 and 3) shows a definite postoperative depression of food intake after amygdaloid ablation but this is not remarked upon by the authors, possibly because it has been attributed to the general effects of operation. However, the results in our other animals with lesions (Fig. 1) show that this explanation is untenable. The effect appears to be specific to amygdaloid lesions. The only explicit report of an initial temporary decrease in food intake appears to be that of Fonberg (7) who found that amygdalectomized dogs showed aphagia which lasted for 8-10 days. The explanation offered by Fonberg, that the effect represents a genuine impairment of food-regu-
AMYGDALA
525
lating mechanisms which is subsequently compensated by hypothalamic controls, is clearly a possible, but rather complex, interpretation. In view of the time course of the effect we have observed, it seems more reasonable to suppose that it is in some way related to a process of degeneration or repair subsequent to the lesion process, and that it affects the connections of the amygdala specifically. It is well established that the ventromedial nucleus of the hypothalamus is critically involved in the regulation of food intake and it has recently been shown by Heimer and Nauta (12) that terminals of the stria terminalis are profusely distributed around this nucleus. A simple hypothesis, therefore, would be that the process of degeneration in this pathway at least temporarily disorganizes the hypothalamic control of food intake. An observation which may be relevant to our finding is that of Fonberg and Delgado (8) that a lo-set stimulation of the amygdala in cats inhibited food intake for several hours. This interesting phenomenon seems to deserve further investigation. Water intake was found to be significantly reduced in all lesioned groups. Grossman and Grossman (11) suggested that the amygdala has both facilitatory and inhibitory effects on water intake and that such effects are elicited by way of the hypothalamus has recently been demonstrated (17). Earlier work by Fisher and Coury (6), who demonstrated that cholinergic stimulation of many limbic structures produced drinking, suggests that rather widespread anatomical systems have some influence on drinking behavior. However, a nonspecific influence of cerebral lesions on water intake cannot be excluded by our data. There seems to be little doubt that the amygdala exerts an influence over food and water intakes, probably by an action on the hypothalamic centers responsible for these processes. The indiscriminate nature of food intake after amygdalectomy is well documented (15,16,18) and the possibility exists that the amygdala modulates the action of the diencephalic feeding centers, facilitating ingestion of edible substances and inhibiting that of nonedible substances. It is, therefore, perhaps not surprising that, when amygdaloid lesions are considered as a whole, the effects on food intake are inconsistent. Our results, however, demonstrate a further source of confusion in that it is clear that short-lasting changes in food intake can occur after amygdaloid lesions. These changes may not necessarily implicate the amygdala in the permanent neuronal circuitry involved in food intake control because within 6 days of the lesion normal levels of food intake had been established. The temporary changes in food intake are reflected, however, in longer-lasting diminutions of body weight which should be considered in any interpretations of the role of the amygdala in the control of total body mass.
526
CROW
AND
WHITAKER
References
1. 2. 3. 4. 5.
6. 7. 8.
9
10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
L. K. and M. E. DITRIKH. 1965. Effects of lesions of the limbic system on emotional reactions and conditioned reflexes in rats. Fed. Proc (Truns Suppl) 24 : 1003-1007. ANAND, B. K., and J. K. BROBECK. 1952. Food intake and spontaneous activity of rats with lesions in the amygdaloid nucleus. /. A~cu~opltysiol. 15: 421-431. ANAND, B. K., and S. Du.4. 1955. Stimulation of limbic system of brain in waking animals. Science 122 : 1139. BRUTKOWSKI, S., E. FONBERG, J. KREINER, and E. MEMPEL. 1962. Aphagia and adipsia in a dog with bilateral complete lesion of the amygdaloid complex. Acta Biol. Exp. Warsaw 22 : 43-50. FIFKOVA, J.. and J. MARSALA. 1967. Rat brain stereotaxic atlas, pp. 653-695. In “Electrophysiological Methods in Biological Research,” Appendix I. J. Bures, M. Petran. and J. Zachar teds.]. Academic Press, New York. FISI~FX, A. E., and J. N. COURY. 1962 Cholinergic tracing of a central neural circuit underlying the thirst drive Science 138 : 691-693. FONBERG. E. 1966. Aphagia, produced by destruction of the dorsomedial amygdala in dogs. Bull. Acad. Pol. Sci. Ser. Sci. Biol. 14 : 719-722. FONBERG, E., and J. M. R. DELGADO. 1966. Inhibitory effects of amygdala on food intake and conditioning. Fed. Proc. 20 : 1. FULLER, J., H. ROSVOLD, and K. PRIBRAM. 1957. The effect on affective and cognitive behaviour in the dog of lesions of the pyriform-amygdala-hippocampal complex. J. Camp. Phgsiol. Psychol. 50 : 89-96. GREEN, J. D., C. D. CLEMENTE, and J. E. DE GROOT. 1957. Rhinencephalic lesions and behaviour in cats. J. Camp. Neurol. 108 : 505-545. GROSSMAN, S. P., and L. GROSSMAN. 1963. Food and water intake following lesions or electrical stimulation of the amygdala Amer. J. Physiol. 205 : 761-765. HEIMER, L.. and W. J. H. NAUTA. 1969. Hypothalamic distribution of the stria terminalis in the rat. Brain Res. 13 : 286297. LEWINSKA, M. K. 1967. Ventromedial hypothalamus: Participation in control of food intake and functional connections with ventral amygdala. Acta Biol. Erp. Warsaw 27 : 297-302. MORGANE, P. J., and A. J. KOSMAN. 1957. Alterations in feline behaviour following bilateral amygdalectomy. Fed. Proc. 18 : 90. PRIBRAM, K. H., and M. BAGSHAW. 1953. Further analysis of temporal lobe syndrome utilising fronto-temporal ablations. J. Conrp. Neural. 88 : 347-375. SCHREINER, L., and A. KLING. 1953. Behavioural changes following rhinencephalic injury in cat. J. Neuropltysiol. 18 : 643-659. SINGER, G., and R. B. MONTGOMERY. 1969. Functional relationship of lateral hypothalamus and amygdala in control of drinking. Physiol. Behav. 4: 505-507. WOOD, C. D. 1958. Behavioural changes following discrete lesions of temporal lobe structure. Neurology 8 : 215-220. YAMADA, T., and M. A. GREER. 1960. The effect of bilateral ablation of the amygdala on endocrine function in the rat. Endocrmology 88 : 565-574. ALLIKMETS,