Response suppression on DRL by rats with septal damage

The effectiveness of the differential reinforcement for low rates of responding (DRL) contingency in suppressing response rates of septal rats was investigated by using a Multi-DRL-yoked-VI (variable interval) schedule of reinforcement. The yoking procedure equated the interreinforcement times on the two schedules. Each schedule was in effect for half of each session, and the change in schedule was signaled by the presence or absence of a cue light. Schedule order and DRL delay requirement were varied. For both normal and septal rats, the response rates were higher in the VI component than the DRL component; this effect demonstrates that the responding of septals as well as normals is suppressed by the differential reinforcement of a particular class of IRTs. A sharp difference in the level of responding occurred at the point of transition from one component of the multiple schedule to the other, which provides evidence of a discrimination between the two schedules for both normals and septals. The conclusion is that the responding of septals is suppressed by the DRL contingency and not controlled solely by the density and distribution of reinforcement.     

Cholinergic blockade, septal lesions, and DRL performance in the rat.

Four experiments describing the effects of cholinergic blockade produced by systemic injection of either atropine sulfate or atropine methyl nitrate on the differential reinforcement of low rate (DRL) responding of rats are reported. It was shown that atropine sulfate injected either chronically or at high dosage suppressed DRL responding. Injected acutely, atropine sulfate produced disinhibitory effects. When atropine was injected either chronically or acutely into animals with septal lesions, there was suppression of responding. It was suggested that the specific behavioral outcome resulting from cholinergic blockade depends on the balance resulting from the competing peripheral and central effects of such blockade.     

Effects of prefeeding on performance with body weight held constant

Two experiments are reported in which rats received either no prefeeding, nutritive substance prefeeding, or nonnutritive substance prefeeding prior to running in a straight alley. The running-speed data supported body weight as an overall measure of hunger drive. Performance was a function of body weight but not stomach weight or associated stomach bulk.     

Role of pituitary-adrenocortical system in mediating avoidance behavior of rats with septal lesions.

Three experiments examined the hypothesis that the effects of septal lesions and systemic injections of scopolamine on avoidance acquisition could be attributed to the effects of either of these treatments on adrenocorticotropic hormone (ACTH) secretion. Septal lesions and scopolamine facilitated 2-way conditioned avoidance response acquisition, and the lesions retarded passive avoidance acquisition. However, neither the injections of dexamethasone, a synthetic glucocorticoid which inhibited ACTH secretion as did septal lesions, nor injections of ACTH which mimicked the facilitatory effects of scopolamine on basal ACTH secretion, affected avoidance in these paradigms. Thus, the main hypothesis was not supported. The finding that scopolamine did not affect passive avoidance indicates that a cholinergic system may not be involved in mediating the suppressive effects of punishment.     

Preoperative enrichment and behavioral recovery in rats with septal lesions

To assess the behavioral effects of preoperative differential housing male rats were placed in either enriched or isolated environments at weaning prior to receiving either sham operations or septal lesions when 57 days of age. Rats with septal lesions showed reduced habituation of ambulation and initially made fewer rears in an empty open field but made more object-contacts coupled with a lack of habituation in the object-filled field. Septal rats also showed severe impairments when tested in a 12-arm radial maze with 7 arms baited and 5 arms unbaited. Preoperative enrichment did not significantly affect these lesion-induced changes. Nevertheless, enrichment significantly lowered ambulation (but did not affect habituation) in the open field and increased the number of manipulatory relative to nonmanipulatory contacts. However, preoperatively enriched septal rats showed a deficit in spontaneous alternation (45%) in contrast to the high levels (83%) shown by intact enriched rats, whereas both intact and septal isolated rats showed similar levels of spontaneous alternation (68%). These results conflict with earlier reports that preoperative enrichment "protects" rats against the deficits produced by septal lesions.     

Effects of physostigmine and d-amphetamine on the behavior of rats with selective fimbria-fornix lesions and intrahippocampal fetal septal cell transplants

Female Long-Evans rats were given electrolytic lesions of either the medial fimbria bilaterally (Fi, n = 24), the dorsal fornix (Fo, n = 24), or both structures (FF, n = 24) at 31 days of age. Ten rats were given sham-operations. Ten days later, half the rats with lesions received bilateral intrahippocampal grafts of embryonic septal cell suspensions (FiT, FoT, FFT, respectively). As already reported in a separate publication (J.C. Dalrymple-Alford, C.R. Kelche, J.C. Cassel, G. Toniolo, V. Pallage, & B.E. Will, 1987, Experimental Brain Research, 210, 115-128), 7 months after transplant surgery, grafted rats were found to be more impaired in an eight-arm radial maze than nongrafted rats. The present report concerns a pharmacological study carried out in the same rats 11 months after grafting. We examined the effects of ip injections of physostigmine (0.01, 0.05, 0.10 mg/kg) and then of d-amphetamine (1.6 mg/kg), as compared with baseline control injections of saline. Just prior to the drug treatments, performances of grafted and nongrafted rats did not differ significantly, but impairments in grafted rats reappeared during subsequent no-injection and saline control trials. Physostigmine failed to affect significantly the performances in rats of any group. d-Amphetamine improved performances in grafted rats with medial fimbria lesions, impaired performances in grafted rats with dorsal fornix lesions, and did not change performances in grafted rats with both lesions, as compared with their respective nongrafted counterparts. Histological analysis revealed variable reinnervation of the host structure and substantial graft-induced lesions of the hippocampus.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.