Defensive behaviors in rats following septal and septal--amygdala lesions

Rats with anterior septal lesions showed a pattern of consistent enhancement of defensive behaviors normally elicited by threatening conspecifics, with no enhancement of attack or general reactivity. Further division of this group indicated that damage to sites anterior and ventral to the septal area, sites previously implicated in the "septal syndrome," produces maximal effect on these behaviors. When amygdala lesions are combined with septal damage this enhanced defensive responding is almost completely eliminated. These results were interpreted as indicating that the septal syndrome represents hyperdefensiveness to conspecific threat stimuli rather than aggression or increased general reactivity, and that amygdaloid mechanisms are also involved in the regulation of conspecific defensive behaviors.     

The role of hyperdipsia in aggression following septal lesions in rats

Lesions of the septum in animal subjects are known to produce an increase in aggressiveness and an increase in water intake. A series of experiments was carried out to examine the possibility that aggression was secondary to hyperdipsia. When rats with septal lesions were restricted to preoperative levels of water intake, aggression scores declined significantly. When animals without lesions were preloaded, with either water or saline, aggression increased. Neither decreased shock threshold nor increased cell hydration provided a full explanation for the results. It is suggested that the aversive nature of the stomach turgescence caused by increased water intake may be an additional mediating factor in septal aggression.     

The effect of training procedures on fixed-interval responding following septal lesions in rats

Two experiments were conducted to assess the effects of training procedures on fixed-interval (FI) performance of rats with septal lesions. In Experiment 1, rats with septal lesions that had extensive preoperative FI experience responded at higher rates than did control rats in early periods of the FI and at lower rates during the later period of the FI for the first 10 sessions after surgery. Their subsequent FI behavior became equivalent to that of control rats. In Experiment 2, septal rats that were trained on an FI schedule of reinforcement entirely after surgery by gradually increasing the FI requirements had FI performance equivalent to that of rats with control operations. The results suggest that septal lesions result in a transient disruption in the FI performance of rats with previous FI experience without affecting the acquisition of appropriate FI behavior.     

Persistent depression of rearing behavior in rats after extensive septal lesions.

Extensive septal lesions produced a persistent (76 days) reduction in rearing behavior which was not directly attributable to altered deprivation states, emotionality, activity levels, or competing behaviors and which occurred in familiar as well as various novel testing environments. Changes in visual, olfactory, or conspecific stimuli ameliorated or had no effect on the lesion effect. The results indicate that the septal area is importantly involved in normal rearing behavior and that lesion-induced alterations in responsiveness to some forms of stimulation may play a modulatory role in reduced rearing. It is also suggested that the septal area may constitute a portion of a neural system responsible for the initiation of this form of response.     

Suppressive and enhancing effects of footshock on food-reinforced operant responding following septal lesions in rats.

Effect of septal lesions on suppression of an intermittently food-reinforced lever press by contingent and noncontingent footshock was measured. Rats with septal damage maintained higher response rates than did intact animals under both contingent and noncontingent shock. Furthermore, the difference in suppression produced by the contingent and noncontingent conditions was approximately the same for the experimental and control groups. In a second experiment, performance was measured during counter-conditioning in which the correlation between contingent shock and positive reinforcement was varied. Rats with septal lesions responded at higher rates than did controls. When only reinforced responses were punished, this lesion-induced elevation represented an increase above baseline performance without punishment. This finding suggests that the effect of septal damage on appetitive instrumental performance cannot be due solely to a deficit in response inhibition.     

Effects of prefeeding on the DRL preformance of rats with septal lesions.

Two experiments reported the effects of prefeeding normal and septal rats prior to their daily sessions on a differential reinforcement of low rates (DRL-20) schedule. Prefeeding reduced responses and increased reinforcements in the case of septal animals, regardless of the level of body weight. In the case of normal animals, prefeeding led to a decrease in responding and an increase in the number of reinforcements obtained only when the animals were at 85% of ad-lib levels, prefeeding, although it decreased responding, also decreased the frequency of obtained reinforcements. These results implied an impairment in normal animals in the discrimination of response feedback by stimulation arising from stomach distention.