Elzbieta Fonberg

Effects of small dorsomedial amygdala lesions on food intake and acquisition of instrumental alimentary reactions in dogs

Abstract Bilateral small stereotaxic lesions limited to dorsomedial part of the amygdaloid complex were made in 10 dogs. It resulted in aphagia with subsequent longlasting hypophagia, adipsia, vomiting and impairment of the acquisition of instrumental alimentary reactions. Also, other changes in behavior were observed such as apathy, lack of motivation, loss of interest in the surroundings and friendly relations with humans, negativism and catatonic-like bizarre postures.

Heart rate mechanisms in instrumental conditioning reinforced by petting in dogs

The aim of this experiment was to determine heart rate (HR) responses during conditioned stimuli (CS) and the petting reward (US) delivered by the experimenter to the dogs after performance of the instrumental conditioned response (CR). It was found that in five dogs for which petting served as a positive reinforcement the delivery of petting was accompanied by cardiac deceleration followed by sudden acceleration at the moment of petting withdrawal. Presentation of CS evoked heart rate deceleration until performance of the first CR. At the start of performance of CRs, heart rate accelerated. It was suggested that heart-rate deceleration is an important component of cardiac response to petting reward and, that probably, it is associated with the hedonic aspect of the reinforcement.

Characteristics of the heart rate in relation to the palatability of food in dogs

Cardiac activity during rewarding unconditioned alimentary responses was analyzed in six dogs. It was shown that the initial part of the eating produces a cardiac acceleration, after which heart rate decelerates and tends to return towards baseline. The pattern of the heart rate is dependent upon the reinforcing value of consumed food. The acceleration of heart rate on the beginning of consumption was greater when the most preferred food was offered and further cardiac deceleration was also more profound. These results indicate that activation of the autonomic system during consumption depends upon the hedonic value of food reinforcement.

Predatory versus alimentary behavior after amygdala lesions in cats

Abstract In cats the effort of small amygdala lesions on mouse-killing behavior and food intake was studied. After ventromedial amygdala lesions predatory behavior was abolished for several weeks whereas food intake was only slightly diminished. Lesions of dorsolateral amygdala did not impair the effective predatory behavior, but produced a decrease of food intake. It is supposed that within the amygdala in cats there exist separate regions connected with food getting, i.e., predatory behavior (ventromedial part of amygdala) and food intake from the bowl (dorsolateral part of amydala). Motivational basis of the predatory behavior and its relations with aggressive and alimentary mechanisms are discussed.

Improvement produced by lateral amygdala lesions on the instrumental alimentary performance impaired by dorsomedial amygdala lesions in dogs

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.

Predatory behavior after hypothalamic lesions in cats

Abstract Electrolytic lesions of the hypothalamus were performed in cats tested preoperatively as good mouse killers. It was found that mouse killing behavior was not impaired after hypothalamic damage, whereas mouse consumption was abolished for several weeks. Food intake was transiently diminished in most cats, but after a few days it reached or surpassed the preoperative level. It was concluded that ventro-postero-lateral hypothalamic lesions impair specific motivation for eating the prey.

Food-motivated behavior in rats with cortico-basomedial amygdala damage.

Twelve rats with amygdala damage (CBM) and 20 sham-operated controls were tested in several food-related situations. The CBM rats showed a longer latency to eat than controls in a novel environment due to more pronounced exploration. In the competition for food, CBM rats lost 85% of encounters with controls. Immediately after the contest, when allowed to eat singly, CBM rats displayed a higher persistence of alimentary responses to an emptied cup than did controls, presumably because they experienced more losses in the food competition. Both groups were equally able to overcome obstacles on the way to food, which suggests similar alimentary motivation. The only direct indication of a lowered responsiveness to hunger in CBM rats was 24-hr-fasting-induced hypophagia. The results of this study indicate the involvement of the cortico-basomedial amygdaloid region in the control of relations between alimentary and other motivations. The contribution of eventual changes of food motivation in the postoperative alteration of this balance is discussed.

The suppressing effect of chlorpromazine treatment on alimentary-social differentiation in amygdala dogs.

Experiments were performed on dogs with bilateral electrolytic damage of dorso-medial amygdala. Before the operation dogs were trained in alimentary-social reward differentiation. It consisted in conditioning of instrumental responses of either right or left foreleg to two different tones respectively.Chlorpromazine was injected intramuscularly in 1,5 mg/kg dose during four consecutive days, beginning at third to fifth week after the operation. Amygdala damage produced significant deterioration of the instrumental performance both reinforced by food and by social-sensory rewards. Chlorpromazine produced further dramatic decrease of performance of both responses.It was concluded that chlorpromazine exerts a suppressing effect on motivated behavior reinforced by positive rewards in amygdala dogs. As the effect of chlorpromazine and medial amygdalar damage are summated it may be suggested that the deficit of medial amygdala neurons impairs similar neurochemical mechanisms, (probably dopaminergic and α-adrenergic transmission) as does chlorpromazine.

Is Predatory Behavior a Model of Complex Forms of Human Aggression

The explosion of violence and crime in the contemporary world stimulates scientists to investigate intensively social, psychological, as well as biological aspects of multiple forms of human aggressive behavior and their complex mechanisms.

Heart rate changes during consumption of preferred and non-preferred food under amphetamine treatment

Heart rate was recorded in five dogs while they ate three kinds of foods varying in preference. Heart rate increased during the initial phase of eating, to the greatest extent with the most preferred food. dl-Amphetamine sulfate (0.2 mg/kg) injected intramuscularly produced a general decrease of heart rate. Nevertheless, the heart rate increase during first period of eating was as great as before treatment. Furthermore, the difference in heart rate increase between the most and least palatable foods was still present, and in some dogs even enhanced. It was concluded that amphetamine at this dose in dogs does not attenuate the hedonic properties of food, but may even intensify them. Therefore, the food intake-reducing effect of amphetamine cannot be due to its suppression of hedonic value of food but is the result of its action on other mechanisms such as hunger drive or control of movement.