Successive position reversals in rats with septal and-or fronto-polar lesions

Emotionality and ability to reverse a position habit were examined in rats with septal lesions and/or frontal pole ablations. Ablation of the frontal poles alone or superimposed on septal lesion facilitated the first two out of eight position reversals. Septal lesions strongly impaired all eight reversals and lead to “septal rage” which was enhanced when frontal poles were additionally ablated.     

Visual cues in successive position reversals: retention deficits following septal lesions

Rats learned a Y-maze position habit and eight successive reversals in one of three experimental conditions, each distinguished by different visual cues on the goal box doors. Following a retention test septal lesions were produced and the animals retested. Reversal performance was best when the correct choice was associated consistently with a single visual cue. When two distinct visual cues were correlated with the correct choice in an alternating sequence, preoperative reversal performance did not differ from the condition with no overt visual cue, except for an increased amount of vicarious approaches. Septal lesions did not affect reversal performance when visual cues consistently signalled the correct choice, but produced significant decrements in the other two conditions. In the condition which lacked distinct visual cues, septal animals made more errors and vicarious approaches than in the condition which had visual cues associated with the correct choice in an alternating sequence. These results suggest that septal lesions impair ability to use spatial/positional cues. The extent to which this deficit is expressed depends on the relevance of the visual cues provided.     

Stimulus perseveration of rats with septal lesions

Rats with lesions of the medial and lateral septal nuclei were tested in four spontaneous alternation situations. The rats with septal lesions showed perseveration of intra-maze stimuli rather than spatial or extra-maze cues. The stimulus perseveration persisted in spite of the removal of the olfactory stimuli from the maze floor between trials. Changing a feature of the choice point between trials did not affect the perseverative behavior. When one of the two goal arms were blocked on Trial 1, the behavior of the rats with septal lesions approached chance level. The results are consistent with a hyper-reactivity interpretation of the effect of septal lesions.     

Variability and discrimination reversal learning in the open field following septal lesions in rats.

Response variability on a 10 position horizontal response task and a position-habit discrimination followed by 2 reversals was examined in groups of rats with septal damage and operated control rats in the open field. As revealed by the number of positions with responses and the one position with the most responses, the rats with septal damage were reliably less variable in responding than the controls. In addition, the rats with septal damage made a reliably greater number of responses during extinction of the response. In the second experiment, groups of animals were tested for discrimination learning in a 2 part experiment using both a free-ranging and restricted open field. In both parts of the experiment, the rats with septal lesions learned the discrimination and both reversals faster than the controls. Animals tested in the restricted field learned the discrimination slightly faster than those tested in the free-ranging field. The superior discrimination learning for the rats with septal lesions was discussed as a lesion-induced increase in the incentive value of positive reward, producing shorter observed response latencies, resulting in a shorter delay of reinforcement.     

Medial septal lesions and the frustration effect

Rats with medial septal lesions and sham operates were run in a straight runway. After running stabilized, food was omitted on selected trials and the running speed on the following trial was observed for a frustration effect (FE). The septals exhibited a significantly greater increase in speed on this trial than controls. This enhanced FE in septals is at variance with predictions from frustration theory considering the greater resistance to extinction in septals and suggests a dissociation between the immediate and conditionable effects of frustration in such animals.     

Factors affecting performance on a shock escape task in rats with septal lesions

Rats with septal lesions were compared to an operated control group on a shock escape task. It was found that little difference existed between the groups initially but the control group decreased the latency of responding over days, while the septal animals exhibited little change. As a result, the control group was significantly superior to septals in the later stages of testing. An analysis of incidental behavior indicated that the amount of time spent holding the bar paralleled performance on the escape task. The inferior performance of the septal group appeared to be secondary to a failure to remain at the bar during the intertrial interval. It is suggested that this behavior is consonant with a response disinhibition hypothesis of septal lesions, and that incidental behavior may be an important factor in other types of behavioral experiments.     

Open-field social behavior of rats following lateral or medial septal lesions

Long-Evans hooded rats were selected at random and assigned to one of six groups. Animals in each group were rated on an emotionality scale and observed in pairs on 10 successive preoperative days and 14 successive postoperative days in an open field. Total number of contacts, length of contact time, and number of aggressive or submissive behaviors which occurred in a 15 min observation period were recorded daily. Following surgery animals with lateral septal lesions displayed hyperemotionality which decreased after handling. The emotionality of the animals with medial septal or cingulate cortex lesions did not change postoperatively. Medial septal lesions resulted in a postoperative increase in contact time, a decrease in number of discrete contacts, and a higher frequency of submissive behaviors. Lateral septal lesions had little effect upon contact time or number of contacts but increased aggressive encounters slightly. Cingulate cortex lesions did not affect open-field social behavior. Changes observed in social behavior were related to changes in both an animal's tendency to emit behaviors and its tendency to react to behavior emitted by its partner.     

Discrimination behavior of rats with septal lesions in a cue addition deletion paradigm.

The discrimination behavior of rats with septal lesions is affected by their altered reactivity to stimulus conditions surrounding the learning situation. Compared to control animals rats with septal lesions are differentially affected by experience with cues relevant to the task itself. In the present experiment we examined the effects of septal lesions on how the rat responds to, and subsequently utilizes, cue information which is made relevant after the animal had achieved criterion performance in a discrimination task. Relative to control animals, rats with septal lesions apparently failed to attend to the newly relevant cues provided, and clearly were deficient when later called upon to utilize such information. However, the degree of deficit was related to the difficulty exhibited in acquisition of original learning. Thus, the more difficult the original learning task, the less deficient were lesioned animals compared to their control counterparts in subsequent situations demanding the utilization of new information. These findings are consistent with our notion that septal lesions alter the relative weighting placed on specific information which the CNS must process. Changes in learning performance reflect altered sensory reactivity.     

Differential effects of septal lesions on attack and defensive-submissive reactions during intraspecies aggression in rats

The effects of septal lesions on attack, threat, defense and submission were studied in rats without prior fighting experience (Experiment 1) and in rats that were either dominant or subordinate in preoperative aggressive encounters (Experiment 2). A factor analysis showed that the various components of agonistic behavior could be grouped into three factors characterizing attack/submission (Factor 1), threat/defense (Factor 2), grooming and crouching (Factor 3). Septal lesions impaired attack, threat, grooming and crouching in experienced dominant or socially naive animals in encounters with unoperated opponents. But septal lesions in experienced subordinate animals failed to alter significantly submissive-defensive reactions. Surprisingly, the immobile-crouch reaction, predominantly displayed by a subordinate rat in the presence of a dominant rat, remained unchanged after septal lesions. These results suggest that septal lesions affect only specific components of the rat's attack and defense behavior. Several current theories on the behavioral functions of the septum, emphasizing response inhibition, fear reduction, and species-specific dispositions, can only partly accommodate these results.     

Prandial drinking following septal lesions in rats

Septal rats maintained on a 23 hr food deprivation schedule drink more water than operated controls during the daily 1 -hr access to food pellets. Examination of the eating and drinking pattern showed that the elevated septal water intake arose from the adoption of an abnormal prandial drinking pattern similar to that previously reported for recovered lateral hypothalamic rats. The septal rats interrupted their eating once every two pellets on average by short bouts of drinking. It is suggested that the occurrence of prandial drinking resulted from a deficit in the control of salivation following septal damage.     

Receptivity,rejection and reactivity in female rats following kainic acid and electrolytic septal lesions

Sprague-Dawley rats were ovariectomized and received bilateral sham, electrolytic or kainic acid lesions of the septum. Kainic acid lesions are purported to destroy cell bodies while not appreciably damaging fibers of passage or afferent terminals. Following priming with estradiol benzoate (EB), animals received three consecutive tests of lordosis and rejection behavior. Animals also received six tests of reactivity; one prior to each EB priming regimen and one following each lordosis and rejection test. Reactivity measures included resistance to capture and magnitude and quantity of startle responses. Electrolytic and kainic acid lesions were equivalent in facilitating lordosis. Although both lesions also increased rejection frequency, kainic acid effects were transient and markedly smaller by 60–80%. Reactivity data generally demonstrated significantly higher scores for kainic acid and electrolytic lesions groups and apparently time-dependent decreases in these scores. The results suggest that rejection behavior is not necessarily correlated with either lordosis or hyperreactivity.     

Disruption of maternal behavior in rats with lesions of the septal area

Rats given septal lesions prior to mating did not build nests or nurse their pups. During retrieving tests they carried pups about the cage repeatedly and dropped them in scattered locations. Virgin rats induced to be maternal by housing with foster pups showed similar, but less marked, behavioral deficits. Rats administered septal lesions after parturition became hyperresponsive, ceased all maternal behaviors, and cannibalized their pups. The results indicated that the aberrant maternal behaviors shown by rats with septal lesions did not result from alterations in hormonal status. It was concluded that the lesions disrupted the typical pattern or sequence of maternal activities and that the deficits were probably related to an enhancement of response perseveration.     

Effects of septal lesions on electrically elicited hypothalamic rage in cats

Effects of septal lesions on thresholds of hypothalamic rage produced by electrical stimulation of the VMH were studied. Hissing and directed attack were selected from the hypothalamic rage for the threshold measurement. Hissing thresholds were measured in two situations, i.e., with provocation by the experimenter and without provocation. Those of directed attack were measured only in the former situation. The two thresholds under provocation situation lowered definitely after septal lesions in more than half cats. The most effective part for the lesion was the lateral septal area at the level of the anterior commissure and just rostral level of it. The hissing threshold under non-provocation situation was affected little. These effects disappeared in 7 or 10 days after the lesions. These findings suggest that the excitatory influence on the VMH produced by provocation was enhanced by the lateral septal lesions.     

Response suppression in normal and septal rats

After 11 days of lever press training on a variable interval 30 sec schedule, separate groups of septal and normal rats were exposed for 10 days to one of two response-suppression procedures; extinction or differential reinforcement of other behaviors. Both procedures were effective in suppressing responding, with the septal rats taking longer to reach the suppression asymptote than did the normals. All rats then received 5 days of non-contingent food presentation. Under these conditions responding recovered to a much greater degree in rats previously given extinction than in those given DRO. Further, septal rats given extinction showed more recovery than did normals given extinction.     

Effects of capture procedures on emotionality scores in rats with septal lesions

Septal-lesioned rats, when approached from below (Anterior-Ventral capture) rather than from above, displayed a remarkably reduced emotionality-score as measured by standard scales. Vocalization and biting were almost completely absent, resistance to capture and handling were considerably reduced; head jerk and vibrissae stiffening were only slightly affected. It is suggested that the septum might be involved in higher order processing of information and that the increased emotionality observed after septal lesioning results from a distorted evaluation of the threat value of sensory input.     

Effect of nicotine on drinking and diuresis in septal lesioned rats

Lesions of septal nuclei in rats enhance water intake and urine outflow. The effects of nicotine tartrate (2.5 mg/kg) on drinking and diuresis were investigated in normal, sham and septal lesioned rats. Nicotine administration resulted in a surprising hyperdipsia and polyuria in lesioned animals, the mean output rose from 38 +/- 1.3 ml (before treatment) to 101.6 +/- 6.1 (during treatment) and water intake increased from 74.2 +/- 1.8 ml to 129.8 +/- 6.4 ml.     

Cue elimination effects on discrimination behavior of rats with septal lesions

In the present series of experiments we tested rats which had received septal lesions or had undergone control surgery on problems involving brightness, spatial, or spatio-temporal discriminations. The studies were designed to examine: (a) the rate and mode of learning a task with relevant, redundant cue solutions; and (b) the effects of making previously potential solution cues irrelevant after the initial criterion was reached. Cue elimination differentially influenced behavior of the two groups depending upon which of the previously successful strategies remained successful. These results were interpreted as consistent with the hypothesis that septal lesions alter how an organism differentially weights specific contextual cues in the process of integrating and acting upon available information.     

Septal lesions in rats and the acquisition of free-operant successive discrimination

In Experiment 1 septal and control rats received both preoperative and postoperative baseline training on food reinforcement VI schedules in the presence of two successively presented stimuli before responding was extinguished in the presence of one of the stimuli (S-). The septals showed: (1) higher asymptotic response rates in the S- stimulus; (2) higher terminal baseline response rates; and, (3) larger magnitudes of behavioral contrast. When the baseline rates of septal and normal rats were equated, the persistent responding in the S- stimulus remained whilst the difference in contrast was eliminated. In Experiment 2 it was found that if animals could perform a response in the S- stimulus which switched the stimulus and the reinforcement contingencies to those associated with S+ stimulus, then septal rats showed a higher terminal level of discriminative performance in terms of this response than controls. It is concluded that septal persistence represents a failure of response inhibition rather than a deficit in the ability to register or associate information about the withdrawal of reward and that the septal change in the magnitude of contrast is related to the elevation of the baseline response rate rather than to the occurrence of response persistence.     

Activity changes during a conditioned aversive stimulus in rats with septal lesions.

The effect of a stimulus previously associated with shock on the spontaneous activity of rats with septal lesions and operated control rats was determined. All rats first received 50 signaled inescapable shock trials and then the signal was presented during a spontaneous activity task. Presentation of the signal during the activity task resulted in an exaggerated increase in activity in rats with septal lesions whereas control rats displayed only a slight increase in activity alternated with periods of no activity. The results are consistent with a reduced freezing hypothesis of septal lesions in aversive learning situations.     

Time-dependent fornix influence on increased light aversion induced by septal lesions

Rats were tested for aversion to light both preoperatively and following various combinations of septal and fornix lesions. Septal lesions alone induced a sustained increased aversion to light. Fornix lesions alone had little effect on the preoperative aversion level. Fornix lesions prior to, simultaneously with, or up to 12 hr following septal lesions were successful in preventing the increase in light aversion expected after the septal lesions. Fornix lesions 24 hr or later following the septal lesions had no effect on the increased light aversion. Results suggest that intact septohippocampal connections are necessary for the initial establishment of an increased light aversion following septal lesions, but not for the continued maintenance of an already present increased light aversion.