Physiology and Behavior, Vol. 14, pp. 711--717. Brain Research Publications Inc., 1975. Printed in the U.S.A.
Improvement Produced by Lateral Amygdala Lesions on the Instrumental Alimentary Performance Impaired by Dorsomedial Amygdala Lesions in Dogs ELZBIETA FONBERG
Limbic Laboratory, Department o f Neurophysiology, Nencki Institute o f Experimental Biology Warsaw, Poland
(Received 25 June 1974)
FONBERG, E. Improvement produced by lateral amygdala lesions on the instrumental alimentary, performance impaired by dorsomedial amygdala lesions in dogs. PHYSIOL. BEHAV. 14(6) 711-717, 1975. - The dorsomedial and subsequent lateral amygdala lesions were performed on 6 dogs. Lesions of the dorsomedial part produced transient aphagia, decrease of body weight and either abolishment or impairment of instrumental performance. Subsequent lesions of the lateral amygdala produced restoration or improvement and stabilization of the instrumental performance. It is supposed that the prevailing inhibitory influences from the lateral amygdala are the main cause of the impairment of instrumental performance after dorso-medial amygdalar lesions. The removal of this source of inhibition enabled restoration of instrumental performance and other alimentary positive functions. Amygdala
Instrumental performance
Brain lesions
IN our previous papers it was shown that bilateral electrolytic lesions of the dorsomedial part of the amygdaloid complex resulted in aphagia, followed by long lasting hypophagia, depression, decrease of body weight and other symptoms called by us the dorsomedial amygdalar syndrome [1,3]. The instrumental responses were severely impaired, and it concerned both the initial training [2] and postoperative retention [ 1 ]. The anatomical verification of all lesions showed that, although in many cases the damage involved also surrounding structures, a small lesion of medial and central nuclei was sufficient to produce aphagia [2,8]. On the other hand, lesions localized in the basolateral part of the amygdala produced hyperphagia and increase of body weight [4]. This last damage did not produce impairment of the instrumental responses to positive stimuli, but the responses appeared during intertrial intervals, and sometimes also to the negative (nonreinforced) stimuli [7]. Anatomical verification indicated that the ventral lateral
part of the amygdala was the most crucial to produce the hyperphagia [4]. These results were the basis for the hypothesis that, with respect to alimentary functions, the amygdaloid complex is divided into two systems with opposite action, the dorsomedial part being facilitatory and the lateral inhibitory [3, 6, 7]. This point of view was later accepted by other authors (e.g. [9] ). Our recent experiments showed [6] that electrocoagulation of the lateral part of the amygdala, performed a few weeks after the damage of the dorsomedial part, produced restoration of food intake and general arousal, which had been decreased by the effect of the first operation. The possibility of restoration of the alimentary functions, impaired by the dorsomedial amygdala lesion, by the subsequent damage of the lateral part, furnishes some further evidence for the antagonistic role of these two amygdaloid areas. On the other hand, it indicates that the effect of dorsomedial lesions was not produced by the damage of
t Preliminary results were reported at the meeting of the Pol. Soc. Physiol. Ass. Olsztyn 1972, and at the Ciba Foundation Symposium, London, 1972. ~This investigation was supported by Project 09.4.1 of the Polish Academy of Sciences and by Foreign Research Agreement 05.275.2 of the U.S. Department of Health, Education and Welfare under PL 480. aThanks are due to Dr. I. Lukaszewska for reading the manuscript and for valuable suggestions; for Mrs. A. Kurzaj, Mrs. U. Miaczynska, and Mrs. M. Raurowicz for their technical assistance; and Mrs. D. Borkowska for reconstruction of lesions. 711
712
FONBERG
neurons indispensible for alimentary functions, but rather by the changed balance between the activity of the lateral and dorsomedial parts, i.e., the excess of inhibitory influences from the lateral amygdala. These results may also explain why several authors obtained controversive results if their lesions were localized in opposite systems of the amygdala, and no effect because the lesions involved both medial and lateral areas. All these problems were discussed widely in a recent review paper [7]. The most interesting fact was the possibility of restoring the normal alimentary behavior of the dog by the lateral amygdaloid lesion. It seemed probable, however, that such a lesion is efficient only in respect to basic alimentary functions, which are mostly controlled by the hypothalamus, whereas instrumental alimentary responses trained to conditioned stimuli might be impaired irreversibly by dorsomedial lesions, as the amygdala is involved with the motivational control of external stimuli. We know from our previous work that impairment or even total abolishment of instrumental performance lasted in many cases for 3 - 5 months after the dorsomedial lesion, although the food intake was in some of those cases restored after a few weeks. These facts suggest that the lateral amygdalar damage might be insufficient to restore the instrumental performance. The present experiment was undertaken to study this problem. METHOD
Animals and Training Experiments were performed on 6 naive, male, mongrel dogs. Before the operation the dogs were trained to perform the instrumental reactions to the conditioned stimulus (CS). Initial training consisted of 2 - 4 days of accommodation to the experimental chamber and the noise of the moving feeder. When the dogs were accustomed to take food from the food bowls, the instrumental training started. The conditioned stimulus (tone of 1000 cycles) was introduced, which was followed by the passive movement of putting the right foreleg on the food tray. This was reinforced by morsels of food with meat and broth. Within a few experimental sessions, the dogs started to perform the response spontaneously (for details see Konorski and Miller method [10]). Experiments were performed every day, 6 days a week. Each experimental session consisted of 20 trials, occurring at random every 1 - 4 min. The preoperative criterion was at least 90 percent correct reactions during 10 successive experimental sessions. When the criterion was reached the dogs were subjected to the first operation.
Procedure Satiation test. Food intake was measured during 10-day periods before and after each operation. During this time the dogs were fed ad lib twice a day with standard food, i.e., cereal with meat and vegetables. During the satiation test the instrumental training was not performed, because feeding ad lib might change the level of alimentary motivation and influence the performance. Retention test and retraining. The first experimental session started on Day 1 1 - 1 3 postoperatively, depending on the general recovery of the individual dog. The dogs were subjected to 5 sessions of retention test, during which the conditioned stimulus was applied 20 times every ses-
sion, and was always reinforced by food, independently of the dog's reaction. If, during this time, the instrumental reaction did not appear, the postoperative training was performed in a way similar to initial training before the operation (i.e., by the method of passive movements). If the dog started to perform the instrumental response to CS during the first 5 days of the retention test, the procedure of passive movement training was not applied, even in such a case as when the dog performed the active movement only occasionally. Similarly, if the dog started to perform the active movement during the retraining, the procedure of passive movement was not continued. The second operation followed the first one after 5 - 9 weeks with the exception of the dog Flaming, which was lesioned after 3 1/2 months, and served as a control for the spontaneous recovery period. The different periods of time between two operations were designed to diminish the possibility of the coincidence of the moment of spontaneous recovery and the operation. Surgery. The operation was performed with nembutal anesthesia, under standard aseptic conditions. The first lesion was aimed at the dorsomedial part of the amygdala (DMA), and the second at the lateral (LA). In both cases, damage was made bilaterally, by electrocoagulation (DC anodal, 3 - 4 mA for 1 - 2 min), through stereotaxically directed electrodes insulated by enamel except for 0 . 5 - 1 . 0 mm at the tip. The stereotaxic coordinates were based on our previous anatomical verifications of efficient dorsomedial and lateral lesions with some help from the atlas of L i m e t a l . [11]. Histology. After the experiments were accomplished, the dogs were anesthetized, perfused by Formalin, their brains embedded in paraffin and cut in frontal sections of 20 u. They were then stained by Kliiver and Nissl's methods alternately, and subjected to anatomical verification. RESULTS
Dorso-medial Amygdala Lesion (DMA) General behavior and food intake. Complete aphagia was observed in all the dogs. It lasted from 5 to 16 days, and was followed by longlasting hypophagia. At the same time, adipsia or hypodipsia was also observed. The dogs were atonic, depressed, negativistic, and revealed all the symptoms described in previous papers as the dorsomedial amygdalar syndrome [2, 3, 6]. Instrumental reactions. Instrumental reactions were completely abolished in two dogs. In the remaining dogs, instrumental performance to CS reappeared within the first few postoperative experimental sessions of the retention test, but the dogs did not perform the instrumental movement to every CS, and the performance fluctuated from session to session; i.e., in one session it might be even close to 100 percent of performance, and in the next one it dropped to a very tow level, or even to nil. Comparison of the number of correct reactions during the 10-day period before and after the first operations showed a significant decrease for each particular dog and for the whole group (Mann-Whitney U-test, p
Improvement Produced by Lateral Amygdala Lesions on the Instrumental Alimentary Performance Impaired by Dorsomedial Amygdala Lesions in Dogs ELZBIETA FONBERG
Limbic Laboratory, Department o f Neurophysiology, Nencki Institute o f Experimental Biology Warsaw, Poland
(Received 25 June 1974)
FONBERG, E. Improvement produced by lateral amygdala lesions on the instrumental alimentary, performance impaired by dorsomedial amygdala lesions in dogs. PHYSIOL. BEHAV. 14(6) 711-717, 1975. - The dorsomedial and subsequent lateral amygdala lesions were performed on 6 dogs. Lesions of the dorsomedial part produced transient aphagia, decrease of body weight and either abolishment or impairment of instrumental performance. Subsequent lesions of the lateral amygdala produced restoration or improvement and stabilization of the instrumental performance. It is supposed that the prevailing inhibitory influences from the lateral amygdala are the main cause of the impairment of instrumental performance after dorso-medial amygdalar lesions. The removal of this source of inhibition enabled restoration of instrumental performance and other alimentary positive functions. Amygdala
Instrumental performance
Brain lesions
IN our previous papers it was shown that bilateral electrolytic lesions of the dorsomedial part of the amygdaloid complex resulted in aphagia, followed by long lasting hypophagia, depression, decrease of body weight and other symptoms called by us the dorsomedial amygdalar syndrome [1,3]. The instrumental responses were severely impaired, and it concerned both the initial training [2] and postoperative retention [ 1 ]. The anatomical verification of all lesions showed that, although in many cases the damage involved also surrounding structures, a small lesion of medial and central nuclei was sufficient to produce aphagia [2,8]. On the other hand, lesions localized in the basolateral part of the amygdala produced hyperphagia and increase of body weight [4]. This last damage did not produce impairment of the instrumental responses to positive stimuli, but the responses appeared during intertrial intervals, and sometimes also to the negative (nonreinforced) stimuli [7]. Anatomical verification indicated that the ventral lateral
part of the amygdala was the most crucial to produce the hyperphagia [4]. These results were the basis for the hypothesis that, with respect to alimentary functions, the amygdaloid complex is divided into two systems with opposite action, the dorsomedial part being facilitatory and the lateral inhibitory [3, 6, 7]. This point of view was later accepted by other authors (e.g. [9] ). Our recent experiments showed [6] that electrocoagulation of the lateral part of the amygdala, performed a few weeks after the damage of the dorsomedial part, produced restoration of food intake and general arousal, which had been decreased by the effect of the first operation. The possibility of restoration of the alimentary functions, impaired by the dorsomedial amygdala lesion, by the subsequent damage of the lateral part, furnishes some further evidence for the antagonistic role of these two amygdaloid areas. On the other hand, it indicates that the effect of dorsomedial lesions was not produced by the damage of
t Preliminary results were reported at the meeting of the Pol. Soc. Physiol. Ass. Olsztyn 1972, and at the Ciba Foundation Symposium, London, 1972. ~This investigation was supported by Project 09.4.1 of the Polish Academy of Sciences and by Foreign Research Agreement 05.275.2 of the U.S. Department of Health, Education and Welfare under PL 480. aThanks are due to Dr. I. Lukaszewska for reading the manuscript and for valuable suggestions; for Mrs. A. Kurzaj, Mrs. U. Miaczynska, and Mrs. M. Raurowicz for their technical assistance; and Mrs. D. Borkowska for reconstruction of lesions. 711
712
FONBERG
neurons indispensible for alimentary functions, but rather by the changed balance between the activity of the lateral and dorsomedial parts, i.e., the excess of inhibitory influences from the lateral amygdala. These results may also explain why several authors obtained controversive results if their lesions were localized in opposite systems of the amygdala, and no effect because the lesions involved both medial and lateral areas. All these problems were discussed widely in a recent review paper [7]. The most interesting fact was the possibility of restoring the normal alimentary behavior of the dog by the lateral amygdaloid lesion. It seemed probable, however, that such a lesion is efficient only in respect to basic alimentary functions, which are mostly controlled by the hypothalamus, whereas instrumental alimentary responses trained to conditioned stimuli might be impaired irreversibly by dorsomedial lesions, as the amygdala is involved with the motivational control of external stimuli. We know from our previous work that impairment or even total abolishment of instrumental performance lasted in many cases for 3 - 5 months after the dorsomedial lesion, although the food intake was in some of those cases restored after a few weeks. These facts suggest that the lateral amygdalar damage might be insufficient to restore the instrumental performance. The present experiment was undertaken to study this problem. METHOD
Animals and Training Experiments were performed on 6 naive, male, mongrel dogs. Before the operation the dogs were trained to perform the instrumental reactions to the conditioned stimulus (CS). Initial training consisted of 2 - 4 days of accommodation to the experimental chamber and the noise of the moving feeder. When the dogs were accustomed to take food from the food bowls, the instrumental training started. The conditioned stimulus (tone of 1000 cycles) was introduced, which was followed by the passive movement of putting the right foreleg on the food tray. This was reinforced by morsels of food with meat and broth. Within a few experimental sessions, the dogs started to perform the response spontaneously (for details see Konorski and Miller method [10]). Experiments were performed every day, 6 days a week. Each experimental session consisted of 20 trials, occurring at random every 1 - 4 min. The preoperative criterion was at least 90 percent correct reactions during 10 successive experimental sessions. When the criterion was reached the dogs were subjected to the first operation.
Procedure Satiation test. Food intake was measured during 10-day periods before and after each operation. During this time the dogs were fed ad lib twice a day with standard food, i.e., cereal with meat and vegetables. During the satiation test the instrumental training was not performed, because feeding ad lib might change the level of alimentary motivation and influence the performance. Retention test and retraining. The first experimental session started on Day 1 1 - 1 3 postoperatively, depending on the general recovery of the individual dog. The dogs were subjected to 5 sessions of retention test, during which the conditioned stimulus was applied 20 times every ses-
sion, and was always reinforced by food, independently of the dog's reaction. If, during this time, the instrumental reaction did not appear, the postoperative training was performed in a way similar to initial training before the operation (i.e., by the method of passive movements). If the dog started to perform the instrumental response to CS during the first 5 days of the retention test, the procedure of passive movement training was not applied, even in such a case as when the dog performed the active movement only occasionally. Similarly, if the dog started to perform the active movement during the retraining, the procedure of passive movement was not continued. The second operation followed the first one after 5 - 9 weeks with the exception of the dog Flaming, which was lesioned after 3 1/2 months, and served as a control for the spontaneous recovery period. The different periods of time between two operations were designed to diminish the possibility of the coincidence of the moment of spontaneous recovery and the operation. Surgery. The operation was performed with nembutal anesthesia, under standard aseptic conditions. The first lesion was aimed at the dorsomedial part of the amygdala (DMA), and the second at the lateral (LA). In both cases, damage was made bilaterally, by electrocoagulation (DC anodal, 3 - 4 mA for 1 - 2 min), through stereotaxically directed electrodes insulated by enamel except for 0 . 5 - 1 . 0 mm at the tip. The stereotaxic coordinates were based on our previous anatomical verifications of efficient dorsomedial and lateral lesions with some help from the atlas of L i m e t a l . [11]. Histology. After the experiments were accomplished, the dogs were anesthetized, perfused by Formalin, their brains embedded in paraffin and cut in frontal sections of 20 u. They were then stained by Kliiver and Nissl's methods alternately, and subjected to anatomical verification. RESULTS
Dorso-medial Amygdala Lesion (DMA) General behavior and food intake. Complete aphagia was observed in all the dogs. It lasted from 5 to 16 days, and was followed by longlasting hypophagia. At the same time, adipsia or hypodipsia was also observed. The dogs were atonic, depressed, negativistic, and revealed all the symptoms described in previous papers as the dorsomedial amygdalar syndrome [2, 3, 6]. Instrumental reactions. Instrumental reactions were completely abolished in two dogs. In the remaining dogs, instrumental performance to CS reappeared within the first few postoperative experimental sessions of the retention test, but the dogs did not perform the instrumental movement to every CS, and the performance fluctuated from session to session; i.e., in one session it might be even close to 100 percent of performance, and in the next one it dropped to a very tow level, or even to nil. Comparison of the number of correct reactions during the 10-day period before and after the first operations showed a significant decrease for each particular dog and for the whole group (Mann-Whitney U-test, p
