Ernest D. Kemble

Taming in wild rats following medial amygdaloid lesions

Flight behavior, startle reactions, and defensiveness to nonpainful stimuli were examined before and after medial amygdaloid lesions in wild Rattus norvegicus and R. rattus. Lesions which included bilateral damage to the medial nucleus strongly reduced defensiveness but had no effect on flight behavior. In contrast, damage to nearby medial structures, which spared the medial nucleus, had no effect on defensiveness but reduced flight behavior. All lesions produced a transient decrease in activity but had no effect on startle reactions. The results suggest a differential organization of flight and defense behavior within the medial amygdala.

Runway performance of rats following amygdaloid lesions.

Abstract Amygdaloid lesions in rats produced an initial increase in response latencies during the acquisition of a runway response which disappeared with further training. This disruption may have resulted from a lesion-produced interference with normal attentional processes. The lesions also decreased responsivity to shifts in magnitude of reward and decreased response latencies during extinction trials. This finding appears to reflect response perseveration by the amygdaloid rats.

Effects of regional amygdaloid lesions on flight and defensive behaviors of wild black rats (Rattus rattus)

Flight and defensive behaviors of wild black rats (R. rattus) in response to nonpainful threatening stimuli were examined before and after regional amygdaloid lesions. Striking disruption of flight was found following damage to all major amygdaloid regions. In contrast, reduced defensiveness was most consistently associated with damage to cortical and, perhaps, central nuclei. The diffuse organization of flight behavior may result from extensive modality-specific cortical afferents to the amygdala and the varied provided by naturalistics threats. The more restricted representation of defensive attack may have resulted from diminished responsiveness to vibrissal stimulation mediated by medial and dorsomedial amygdaloid structures.

Effects of central amygdaloid nucleus lesions on ingestion, taste reactivity, exploration and taste aversion.

Abstract Central amygdaloid nucleus lesions in rats had no effect on recovery of preoperative body weight and food consumption levels. The brain damaged rats also recovered preoperative levels of water consumption as rapidly as control rats but then developed a mild but persistent hypodipsia. The experimental rats also drank less than control rats when food deprived and showed marginally reliable decreases in 0.1% quinine solution consumption and latency to consume a novel food. There was no detectable lesion effect on 0.1% saccharin solution consumption, exploration of a novel environment or formation of a learned taste aversion. It is suggested that the central amygdaloid nucleus has a role in mediating the relationship between food and water intake and in some taste mediated consummatory behavior.

Cyclic activity changes during extinction in rats: A potential model of depression*

Rats’ open-field activity immediately following extinction trials in a runway rose sharply from baseline, then dropped below baseline, and finally recovered. There was no discernible relationship between activity levels and runway performance during acquisition or extinction. The data confirm a theory that a sequence of invigoration, depression, and recovery of noninstrumental locomotor activity (an “incentive-disengagement cycle”) may regularly accompany incentive loss, including experimental extinction.

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

Abstract 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 septal-forebrain lesions on maternal aggression and maternal care

Septal-forebrain lesions significantly increased the defensive reactions of lactating Long-Evans rats (n = 13) relative to nonlesioned control females. The lesions greatly enhanced defensive behaviors on a number of standard tests (e.g., responsiveness to humans and anesthetized conspecifics) while abolishing aggression toward intruding male conspecifics. The lesions also produced a striking disruption in maternal behavior as evidenced by absence of nest building, reduced litter weights, failure to retrieve, lick, or nurse pups, and increased cannibalization. While these results cannot be interpreted as indicating that maternal aggression is equivalent to offense, they are congruent with such a view. Certainly they are not supportive of a view that maternal aggression is primarily defensive. The lesion-induced abolition of maternal attack may have resulted from an inhibition of offensive tendencies by heightened defensiveness and/or reduced pup stimulation. There was no evidence that the lesion-induced impairment in maternal behavior resulted from a failure to sequence the individual behavioral acts comprising maternal behavior. Rather, all features of maternal care seemed to be greatly attenuated.

Limbic lesions and the inhibition of startle reactions in the rat by conditions of preliminary stimulation

Abstract The startle reflex to intense acoustic stimuli and its inhibition by light and sound prepulses was examined before and after septal, amygdaloid or hippocampal lesions or control procedures. There was no effect of limbic damage on acoustic startle or its inhibition. Lesions which included damage to the optic tracts or lateral geniculate nucleus abolished the light prepulse produced inhibition of startle but left auditory prepulse produced inhibition unaffected.

Failure to form a learned taste aversion in rats with amygdaloid lesions

Rats sustaining bilateral amygdaloid lesions failed to develop aversion to 0.1% saccharin solution after it had been paired with a 0.12 M LiCl injection. These data confirm an important role for the amygdaloid complex in the formation of learned taste aversion and further substantiate the role of this structure in a wide variety of aversively motivated behaviors.

Effects of food deprivation on caffeine consumption in male and female rats

The effect of food deprivation on caffeine consumption was investigated in male and female rats utilizing two-bottle preference tests. During ad lib food and water access, proportional consumption of six increasingly concentrated caffeine solutions (0.01-0.125%) steadily declined as concentration increased with no sex differences. Across concentrations, females tended to ingest more mg/kg caffeine than males. Food deprivation increased both proportional and mg/kg caffeine consumption in both sexes. When returned to ad lib food, proportional, but not mg/kg, caffeine consumption returned to pre-deprivation levels. Consumption of a quinine solution (0.02%), comparable to the caffeine in two-bottle preference, declined somewhat during food deprivation. These results indicate that caffeine preference and mg/kg consumption are increased by food deprivation and that this effect does not result from increased preference for bitter tastes per se. Rather, the results suggest that increased caffeine intake during food deprivation is due to a specific interaction between reduced body weight and the drug. The results also suggest that the deprivation effect is somewhat weaker in females than males, perhaps due to sex differences in reactivity to caffeine.