Effects Of Amygdaloid Lesions Research Articles

Effects of amygdaloid lesions, hippocampal lesions, and buspirone on black-white exploration and food carrying in rats

Unlesioned rats exploring a black-white two compartment box spent most of the time in the covered, black half of the box and only little time in the uncovered, white half (67 s/5 min). Large radio-frequency lesions of the amygdala or hippocampus did not alter this pattern of exploration, but rats with hippocampus lesions were more active than the other two groups of rats. Treatment with the 5-HT 1A receptor agonist buspirone (0.1 mg/kg, s.c.) increased the time that unlesioned rats spent in the uncovered compartment (103 s), an effect that was less pronounced in hippocampus-lesioned rats and completely abolished by amygdala lesions. In a food transport test, unlesioned rats that traveled from a home cage to an exposed food source consumed small and medium-sized pellets immediately at the food source. Larger pellets, however, were carried back to the home cage for consumption. Rats with amygdala lesions ate fewer pellets at the food source and tended to carry more pellets back to the home cage for consumption than unlesioned rats. Rats with hippocampus lesions carried fewer pellets back to the home cage and ate more pellets at the food source. Buspirone (0.5–1.5 mg/kg, s.c.) reduced the carrying of large food items to the home cage and increased consumption of these pellets at the food source in all groups of rats. These results suggest that neither the amygdala nor the hippocampus play an important role in controlling exploratory behavior in a black-white compartment box, but that the amygdala may have some role in mediating the effect of buspirone to increase exploration of the white/open compartment. Further, the amygdala and hippocampus have opposing influences on the transport of food items to a shelter, the amygdala suppressing food carrying, and the hippocampus enhancing it. Neither structure is essential for the effect of buspirone to reduce food carrying. The hypothesis that limbic structures mediate `fear/anxiety' responses is discussed critically.

Effects of amygdaloid lesions on gastric erosion formation during exposure to activity-stress

To examine the role of the amygdala in the production of gastric ulcers induced by activity-stress, electrolytic lesions were placed in the centromedial (CENT) and medial (MED) amygdaloid nuclei, as well as in the intra-amygdaloid division of the bed nucleus of the stria terminalis (BNST). As compared to sham-operated controls (CONT), gastric ulceration was attenuated in rats with CENT lesions and exacerbated in rats with lesions located in the BNST or MED. Wheel running did not differ significantly between control animals and lesioned rats, but did differ within lesioned groups. Rats with MED lesions ran more than rats with CENT or BNST lesions. Results support the view that the integrity of the centromedial amygdala is critical for the maintenance of the viscera and demonstrate that neurogenic factors contribute to the development of gastric erosions during exposure to activity-stress.

Lack of a temporal gradient of retrograde amnesia in rats with amygdala lesions assessed with the fear-potentiated startle paradigm.

It is well known that lesions of the hippocampal formation produce a temporally graded retrograde amnesia for certain types of memory. A similar pattern of results has been reported with amygdaloid lesions in avoidance learning (K.C. Liang et al., 1982). The present study examined the effects of posttraining amygdaloid lesions using a Pavlovian conditioning task, fear-potentiated startle, in which the amplitude of the acoustic startle reflex is increased when elicited in the presence of a cue (e.g., a light) previously paired with footshock. Electrolytic lesions of the amygdala given either 6 or 30 days after training blocked the expression of potentiated startle, indicating no temporal gradient of amnesia over these intervals in this paradigm. The effects of amygdaloid lesions on different measures of aversive learning are discussed.

Lesions of the medial amygdala produce severe impairment of copulatory behavior in sexually inexperienced male rats

The effects of amygdaloid lesions on masculine copulatory behavior were examined in male rats. Sexually inexperienced male rats were castrated and subjected to bilateral lesions in one of the following areas: the medial amygdala, the cortical amygdala, or the basolateral amygdala. Three weeks later, all rats received implantation of silastic capsules containing testosterone. Then, four observations of copulatory behavior were carried out every 5 days following the implantation of testosterone. Rats with medial amygdala lesions showed a severe deficit of copulatory behavior, whereas rats with basolateral amygdala lesions showed no change in the performance of copulation. As for rats with cortical amygdala lesions, although their copulatory behavior was impaired, the effect was confined to a deficit in intromission and ejaculation responses. These findings suggest that the medial amygdala plays a critical role in regulating masculine sexual behavior in the rat.

Effects of amygdaloid lesions on morphine-induced hyperactivity in C57BL/6 mice

Effects of amygdaloid lesions on morphine-induced hyperactivity in C57BL/6 mice

Hippocampal and amygdaloid involvement in working memory for nonspatial stimuli.

Hippocampal lesions in rats lead to an impairment of performance in spatial delayed conditional discriminations. The effect of such lesions on nonspatial tasks is controversial. In monkeys, both the hippocampus and the amygdala are involved in nonspatial delayed conditional discriminations. The effect of amygdaloid lesions in rats on this type of task has not been studied. To clarify the role of hippocampus and amygdala in a cue-relevant/space-irrelevant delayed conditional discrimination, rats were trained on a delayed match-to-sample task with visual and tactile cues as discriminative stimuli. Rats were then given one of five lesions: control, complete fimbria-fornix, partial fimbria-fornix, complete amygdala, or partial amygdala. Amygdaloid lesions, partial or complete, did not impair choice accuracy. Fimbria-fornix lesions did impair choice accuracy, and the magnitude and duration of the impairment was a function of the size of the lesion. Partial fimbria-fornix lesions produced a slight impairment that disappeared with continued testing. Complete fimbria-fornix lesions produced chance performance throughout postoperative testing. These results indicate that the fimbria-fornix, but not the amygdala, is involved in nonspatial delayed match-to-sample.

Dopaminergic facilitation of recovery from amygdaloid lesions which affect hypothalamic defensive attack in cats

Influence of dopamine agonists, methamphetamine (MAT, 1 mg/kg, i.p.) and apomorphine (APO, 1 mg/kg, i.p.), on the effects of amygdaloid lesions on thresholds for the defensive attack behavior elicited by electrical stimulation of the ventromedial hypothalamic nucleus was studied in cats. The thresholds were measured in two situations, one with provocation by a human and the other without provocation. Electrolytic lesions of the basolateral part of the amygdala attenuated markedly facilitatory influences of the visual provocation on the thresholds, but subsequent administration of MAT or APO rapidly abolished the effects of the lesions. The effects of MAT lasted for at least 3.5 h while the effects of APO were of shorter duration. The results were discussed from the viewpoint of possible rapid compensation by the remaining intact tissue of the amygdala which was produced by excessive dopaminergic inputs to it.

Delayed reinforcement of switch-off behavior and amygdaloid lesions in cats

Effects of amygdaloid lesions on the switch-off behavior (SOB) and behavioral changes induced by a delayed reinforcement (DR) for SOB were investigated in 12 cats. The DR consisted of putting a delay time of 1.6 or 2.4 sec between a plate-pushing response and the actual termination of hypothalamic stimulation, and it produced a marked prolongation of response time for SOB (delay phenomenon). Bilateral electrolytic lesions of the amygdala had only limited effects on the SOB and the delay phenomenon; they tended to enhance the prolongation of response time induced by DR in 6 cats and it was accompanied by mild prolongation of response time of subsequent immediate reinforcement trials. These effects were interpreted to be due to apparent attenuation of emotion-producing potency of the hypothalamic stimulation, induced by reduction of facilitatory environmental influences on it.

Effect of amygdaloid lesions on ethanol intake in rats

The effect of electrolytic lesions of the amygdala on ethanol intake in ethanol naïve rats has been studied. Rats with basolateral nuclei and lateral nuclei lesions showed a reduced neophobic response to an ethanol solution. However, the ethanol intake was too small in normal and lesioned rats to augment aversion through conditioning. Oral intake of ethanol supplemented by intraperitoneal ethanol injection to reach 2 g/kg indeed enhanced the initial sensory aversion to ethanol. This induced aversion was attenuated after basolateral lesions. An initial aversion to a mixed ethanol-sucrose solution was abolished after basolateral lesions, while the lateral lesions induced an initial preference for this solution. The initial oral intake of ethanol-sucrose in normal rats was again too small to induce the conditioned taste aversion (C.T.A.). Despite the high oral intake of this solution, rats with basolateral lesions did not show a conditioned aversion while laterally lesioned rats exhibited a strong conditioned aversion to the ethanol-sucrose mixture. The results which confirm the suppression of the C.T.A. by basolateral amygdala lesions are discussed in relation to the role of toxicophobia in ethanol intake by rats.

Temporal and anatomical considerations involved in the effects of amygdaloid lesions on prolactin secretion in ovariectomized estrogenized rats

Plasma prolactin (PRL) levels were investigated in chronically catheterized control, sham-lesioned, and amygdala (AMYG)-lesioned rats under a variety of conditions. Ovariectomized (OVX) rats injected with 0.5 mg of polyestradiol phosphate (PEP) exhibited a circadian rhythm of PRL secretion characteristic of proestrus rats. Small bilateral lesions of the central AMYG area had no effect on this pattern of PRL secretion in animals bled over a 24-h period, 1 week following lesioning. A second group of rats bearing lesions or sham lesions of the corticomedial AMYG nuclei were studied at 1, 2 and 3 weeks following surgery and PEP treatment. PEP produced a significant afternoon surge of PRL in controls at weeks 1 and 2 but not week 3. Lesions of the corticomedial AMYG nuclei had no effect on basal PRL, but significantly blunted the afternoon surge occurring at weeks 1 and 2. The effect of a larger lesion encompassing a greater proportion of the corticomedial AMYG was examined in another group of rats at 6 weeks post-lesion and 2 weeks after PEP injection. This lesion significantly decreased PRL levels compared to controls at 5 of 6 time periods examined over a 24-h period. The effect of this lesion on PRL secretion in non-estrogenized OVX rats was also examined. There was no difference in the low, non-fluctuating 24-h PRL levels of control and lesioned rats bled at 3 or 4 weeks post-lesion.

Effects of amygdaloid lesions on reproductive function of grouped caged mice.

Amygdalotomized, sham-operated and intact wild-derived house mice of both sexes were group-caged (8-10) or singly caged for 3 weeks. The weights of ovaries (p is less than 0.05) and uteri (p is less than 0.01) were less in intact and sham-operated grouped females compared to singly caged intact and amygdalotomized females. The weight of the reproductive organs in amygdalotomized grouped female mice was not different from singly caged controls. Body weights among amygdalotomized grouped females were heavier (p is less than 0.05) than singly caged controls. Seminal vesicle weights of intact and sham-operated grouped males were less (p is less than 0.05) than that of singly caged controls and grouped amygdalotomized males. Plasma LH values from the various groups coincided with the morphological data. These results support the hypothesis that increased population density impairs reproductive function in mammals. Perhaps the effects of decreased pituitary-gonadal function associated with overcrowding are mediated via amygdalar nuclei.

Effects of amygdaloid lesions on the performance of rats in four passive avoidance tasks

The effects of amygdaloid lesions on shock punished step-down and rearing responses, quinine punished drinking, and ice water punished step-through responses were investigated in 4 experiments. Amygdaloid lesions impaired the suppression of step-down, rearing, and step-through responses but had no effect on the suppression of quinine consumption. Various interpretations of the response disinhibitory effects of amygdaloid damage are considered. It is concluded that no unitary explanation adequately explains this phenomenon. More extensive investigations of the conditions producing response disinhibition and their anatomical organization are suggested.

Effects of amygdaloid lesions on exploration by rats

Satiated rats with bilateral lesions of the amygdala exhibited more sniffing, rearing and walking (exploration) than control rats when both groups of animals were exposed to novel visual or olfactory stimuli. No differences were observed in amount of freezing or in responsiveness to food in these 2 groups of rats. In a second experiment, food deprived rats with similar lesions exhibited less exploration and more feeding in a novel environment than a group of control rats. The primary behavior patterns produced by the conditions of the 2 experiments were different: exploration was most prominent in Experiment 1 and feeding was most prominent in Experiment 2. In each case the amygdaloid lesions were associated with increases in these primary behavior patterns. The role of the amygdala in controlling behavior patterns associated with the general behavioral tone or tendency produced by experimental and environmental conditions is discussed.

Effect of amygdaloid lesions on eating elicited by cortical spreading depression

To investigate the possible role of the amygdala in the phenomenon of eating induced by single waves of cortical spreading depression, 10 rats received bilateral and 5 rats unilateral electrolytic lesions in the amygdaloid complex. They were tested for spreading depression-induced eating by injection of 0.5–1.0 μl of 25% KCl into the neocortex. Bilateral lesions of the amygdala significantly attenuated, but did not completely abolish elicited eating. Unilateral lesions significantly decreased the incidence of elicited eating from the ipsilateral but not the contralateral hemisphere.

Effects of amygdaloid lesions in rats on food and water intake and body weight under varied ambient temperatures

Food and water intake and body weight were measured in amygdala-lesioned and control Ss under three (70°, 60°, and 80° F) ambient temperature conditions. Both experimental and control Ss responded similarly to these manipulations with no suggestion of lesion-induced deficiency. These data are consistent with other research, which suggests that damage to basolateral portions of the amygdala leaves daily food and water regulatory mechanisms intact.

Effects of amygdaloid lesions upon FR performance in rats

Large amygdaloid lesions in nondeprived rats produced a decrease of responding at medium fixed-ratio values (FR4, FR8). At both low (FR1, FR2) and high fixed-ratio values (FR32) performance of controls and amygdaloid animals was similar. Food deprivation equally enhanced responding of both groups. The results provide additional evidence for an amygdaloid role in the regulation of incentive-reward mechanisms.

Effect of amygdaloid lesions on dietary intake of disproportionate amounts of amino acids

Male rats with bilateral electrolytic lesions in the anterior, medial or posterior aspects of the ventral amygdala and groups of intact rats were fed, in turn, basal, imbalanced or deficient amino acid diets involving threonine or isoleucine as the limiting amino acid, and then a low protein (6% casein) followed by a high protein (75% casein) diet. No change in food intake was observed in animals fed the threonine basal diet postoperatively. When the threonine or isoleucine imbalanced diet was substituted for the respective basal diet, animals with lesions in certain areas of the medial amygdala showed little or no depression in food intake of the imbalanced diets, while all other rats with amygdala lesions reduced their food intake markedly, as did intact controls, when fed such diets. All animals, however, curtailed their food intake of the deficient or high protein diets. The lack of responsiveness of the animals with medial amygdaloid lesions to the imbalanced diets suggests that these areas may be involved in a system regulating food intake of animals fed diets containing imbalanced amino acid mixtures.

Effects of amygdaloid lesions on reversal learning in the deermouse

Electrolytic lesions were placed in the basolateral, cortical or medial amygdaloid nuclear groups in male deeermice using the stereotaxic atlas for this species. Sham-operated and intact control groups were also included in the study. After allowing the animals a two-week recuperative period, they were tested in a black sheet metal T-shaped water maze especially constructed for mice. Following habituation to the water maze, all animals were run through original learning and four reversal learning stages. Results indicate that a decrement of learning occurred in animals with lesions in the cortical or basolateral amygdaloid nuclear groups while those animals with lesions in the medial amygdaloid area did not exhibit any significant changes when compared to either the sham-operated or intact control groups.

The effects of amygdaloid lesions on a classically conditioned auditory discrimination in the rabbit (Oryctalagus cuniculus)

The performance of rabbits (Oryctolagus cuniculus) sustaining amygdaloid lesions was compared to that of control Ss during the acquisition of a classically conditioned auditory discrimination. Amygdala damaged Ss showed a reliable (p <.05) elevation in the percentage of nictitating membrane CRs to the CS+ and a marginally significant (p <.10) elevation in CRs to the CS—. The lesion effects are discussed in terms of response inhibitory mechanisms or changes in shock-produced arousal. Additional experiments are suggested.

Effects of amygdaloid lesions on hypothalamic-hypophysial luteinizing hormone activity.

Summary. Bilateral lesions were made by electrocoagulation in one of the following amygdaloid areas : basolateral, cortical or medial in adult male deermice. Animals were killed 20 days after the operation, and determinations were made of pituitary lh concentrations, hypothalamic lh-RF potencies and seminal vesicle fructose concentrations. Data indicate that lesions placed in either the basolateral or cortical amygdaloid areas, but not in the medial, result in significant increases in pituitary lh and plasma lh as interpreted by the significant increases in dry seminal vesicle weight and fructose concentrations. Hypothalamic lh-RF concentrations decline significantly in animals with medial lesions while increasing significantly in animals with basolateral or cortical amygdaloid lesions.