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.     

Disinhibition and external inhibition of response following septal lesions in rats

Septal-lesioned and sham-operate rats were tested for reactivity to extraneous stimuli (clicks or flashing lights) presented during periods of low or high responding generated by a 120-sec FI schedule of reinforcement. While septal-lesioned rats tended to show greater disinhibition and less external inhibition than sham-operates, the magnitude of the deficits was not considered sufficiently great to warrant the conclusion that the septal syndrome results from increased susceptibility to disinhibition.     

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.     

Changes of acetylcholinesterase activity in the brain following septal lesions in the rat

Acetylcholinesterase activity in different parts of the limbic system (hippocampus, hypothalamus and amygdala) was decreased following medial septal lesions. On the other hand, this activity in the thalamus, frontal cortex, bulbus olfactorius, nucleus ruber, substantia nigra and basal ganglia was unaffected.These results raise the possibility that there is a functional relationship of the medial septum and those parts of the limbic system that we have studied.     

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.     

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.     

Faster acquisition of an olfactory discrimination following septal lesions in male albino rats.

Normal rats and rats with septal lesions were maintained on a 23.5-hr water deprivation schedule and trained to bar press for water reinforcement, which was available during the presentation of one odor (SD) but not another (Sdelta). Vanilla and vinegar were the olfactants. Both groups showed evidence of discrimination within the first 2-hr of training and reached asymptotic discrimination ratios greater than 90 percent, but the rats with septal lesions reached successively higher levels of discrimination faster than the controls. The results suggest a septal inhibitory influence on the olfactory bulbs.     

Entrainment of activity to multiple feeding times in rats with suprachiasmatic lesions

Entrainment of wheel running to two or three food access times per day was investigated in rats with SCN lesions. When two feeding times (1.5 hr each) were presented 8 hr apart, all rats entrained to both. Anticipatory activity (AA) to the second feeding time was greatly diminished when the interval was reduced to 5 hr. An 8 hr phase delay of one feeding time resulted in delaying transients and a concomitant reduction of AA to the unshifted schedule. Seven rats were maintained on 3 feeding times (1 hr each) per day at 6-6-12 hr intervals, followed by 8-8-8 hr intervals. Six rats displayed some AA to two of three access times, but no rat anticipated all 3 access times simultaneously. AA occasionally shifted from one access time to another. In all conditions, entrainment was much less stable compared to single access times. Typically, the instabilities in AA were suggestive of transients, i.e., a temporary loss of entrainment. The results appear most consistent with a model consisting of 2 internally coupled pacemakers that are entrained by feeding.     

Effects of lateral and medial septal lesions on various activity and reactivity measures in rats

Roles of the lateral and medial septum in the regulation of activity, reactivity and open field behavior in rats were examined in the present study. Effects of lateral, medial and combined lateral and medial septal lesions were studied, respectively. Our results indicate that lateral septal lesions significantly decreased locomotor activity and tended to decrease rearing response. While it also markedly increased movement time in the activity monitor, stereotyped behavior and tactile startle amplitude. The most significant findings with medial septal lesions were decreased activity, especially in the center area of an open field and decreased exploratory behavior in rats. For most behavioral measures, effects of combined lateral and medial septal lesions were similar to that of medial septal lesions alone except that it augmented startle response with a different response pattern compared to that of lateral septal lesions alone. The locomotion patterns of these animals also revealed some qualitative difference in their behavior. These results are further discussed in the scope of anatomical, neurochemical and pharmacological differentiations of the septum complex.     

Recovery of anticipatory activity to restricted feeding in rats with ventromedial hypothalamic lesions

Entrainment of circadian activity rhythms to a fixed daily mealtime was measured in intact and ventromedial hypothalamic (VMH) lesioned rats housed in tilt-cages. Intact rats showed a clear increase in activity for 2–3 hr prior to the 2 hr daytime feeding period. Anticipatory activity in lesioned rats was attenuated or absent during restricted feeding 5–9 weeks after surgery, but was evident in all rats, even those bearing apparently total VMH damage, during a second restricted feeding schedule 14–21 weeks after surgery. These results show recovery of function and argue against a necessary role for the VMH in food entrained rhythms.     

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.     

Neuroestrogenic control of feeding behavior and body weight in rats with kainic acid lesions of the lateral septal area

The role of the lateral septal area (LS) in the regulation of energy balance and the estrogenic control of feeding behavior in the female rat has been examined. Food intake (FI) and body weight (BWt) were measured daily following kainic acid (KA) LS lesions (KALS) to assess any regulatory changes in energy balance. In all animals KA lesions of the LS produced major cell loss in the LS; however the extent of damage was variable. Associated with KA lesions of the LS was the concurrent loss of CA3-CA4 cell groups in the hippocampus which was comparable for all the lesioned animals. The extent of septal damage was quantified morphometrically and correlated with changes in FI and BWt following estrogen treatment. The significant effects of the KALS lesions, relative to the control animals were: an increase in BWt which was statistically significant 22 days following brain surgery, an increase in daily FI which was significant by day 6 post surgery, an attenuation in the anorexic effects of estrogen on FI and BWt, and a significant decrease in the present days of vaginal estrus. Moreover, the anorexic effects of estrogen were significantly correlated with the extent of LS damage, but not the amount of hippocampal damage. The present study confirms that an increase in BWt is produced by KA lesions of the LS and further indicates that a sustained period of increased FI precedes the increase in BWt.(ABSTRACT TRUNCATED AT 250 WORDS)     

Aggression in low and high brainweight mice following septal lesions

Septal lesions or control operations were performed on adult male mice genetically selected for either high or low brainweight. Following recovery from surgery, pairs of animals with a similar genetic and surgical history were matched in tests of agonistic behavior. Irrespective of strain, pairs of mice with septal lesions fought less than pairs of control animals. However, submissive postures and social exploration showed a clear interaction between genotype and surgical history. The importance of interactions between variables such as genotype, experience, and brain damage is discussed.     

DRL training and performance following anterior,posterior, or complete septal lesions in infant and adult rats

Animals received septal lesions, caudate lesions, electrode punctures, or skin incisions at seven days of age while their litter mates were allowed to develop normally until 119 days of age before receiving septal lesions. When trained to bar press on DRL schedules of reinforcement all animals with septal lesions which included the posterior septum and columns of the fornix were very inefficient. Animals with electrode punctures, caudate lesions or anterior septal lesions performed as efficiently as control animals. Age at the time of lesion did not effect the severity of the behavioral deficit; however, minor recovery of function was displayed following the 119 day recovery period.     

Differential effects of infralimbic cortical lesions on temperature and locomotor activity responses to feeding in rats

The time of food availability induces important behavioral and metabolic adaptations. Animals subjected to feeding restricted to a few daytime hours show increased locomotor activity and body temperature in anticipation of mealtime. In addition, animals under ad libitum feeding show a marked postprandial raise in body temperature and in thermogenesis. The areas of the brain commanding these responses to food are partially known. We investigated in the rat the role of the infralimbic area, located in the medial prefrontal cortex, and considered a visceral-autonomic motor area, in the responses to ad libitum or restricted feeding schedule. We performed infralimbic cortex excitotoxic lesions using injections of ibotenic acid, and measured body temperature and locomotor activity by telemetry in rats under ad libitum and restricted feeding conditions. We found that bilateral infralimbic area lesions prevented both the anticipatory and the postprandial increases in core temperature, decreased mean temperature by nearly 0.3 degrees C during both light/dark phases, and increased daily temperature variability. In contrast, the lesion caused a rapid induction of the anticipatory locomotor activity. These results show that behavioral and metabolic responses to the time of food availability are commanded separately and that the infralimbic area is a key structure to adjust the body temperature to an upcoming meal.