Plasticity of autonomic functions in rats with septal lesions

Comparison between the behavioural effects of septal and hippocampal lesions: a review

The literature on the behavioural effects of septal and hippocampal lesions is classified according to behavioural paradigm. The effects of the two kinds of lesion are summarized and compared to each other. A 'septo-hippocampal syndrome,' consisting of the effects common to both lesions, is delineated, and divergences between the effects of the two lesions are noted.

Forebrain norepinephrine and serotonin concentrations and cardiac conditioning in normal rabbits and rabbits with septal lesions

Septal lesioned or sham operated rabbits were subjected to two days of differential Pavlovian (classical) heart rate (HR) conditioning in which tones served as the conditioned stimuli and paraorbital electric shock served as the unconditioned stimulus. After completion of training, norepinephrine (NE) and serotonin (5-HT) concentrations were determined in the hippocampus and neocortex to determine if lesion-induced amine depletion was related to changes in HR conditioned response (CR). The magnitude of the bradycardiac CR was increased by septal lesions during the initial session but during the second session. several lesioned animals revealed accelerative HR changes resulting in an attenuated HR CR in the septal damaged group. The more accelerative HR responding in the septal lesioned animals was accompanied by increased EMG activity which appeared to be related to damage to more posteroventral areas of the septum. Septal lesions produced a depletion of forebrain NE of approximately 30%, but NE concentrations did not appear to be specifically related to lesion-induced changes in the HR CR. However, both NE and 5-HT concentrations were correlated with the magnitude of the HR CR in intact, but not in lesioned, animals.

Lateral hypothalamic lesions: effects on Pavlovian cardiac and eyeblink conditioning in the rabbit

Rabbits received either bilateral lesions of the far lateral hypothalamus (LH), or sham-operate lesions. After recovery from surgery the animals were exposed to Pavlovian conditioning in which eyeblink (EB), electromyographic (EMG), and heart rate (HR) conditioned responses (CRs) were recorded. Adaptation, acquisition and extinction training were studied. Subsequent to conditioning, free-field activity, paraorbital electric shock thresholds, and HR unconditioned responses (URs) were measured. At the end of behavioral testing forebrain norepinephrine (NE), dopamine (DA), an serotonin (5-HT) concentrations were assessed. Animals with LH lesions did not differ from controls on EB responding during either adaptation or acquisition. However, lesioned animals revealed more EB CRs during extinction than control animals. EMG CRs were minimal in both groups of animals. Lesioned animals showed smaller HR changes than control animals during all phases of training, although HR CRs tended to consist of bradycardia in all animals. No differences were observed in either shock thresholds or open field activity as a result of LH lesions. Cortical and hippocampal 5-HT and NE concentrations were significantly depleted in lesioned as compared to control animals. These findings were interpreted within the framework of the phasic control of attention by midbrain modulation of forebrain structures; however, the interruption of downward going fibers which mediate brain stem cardiac control cannot be ruled out.

The Septal Forebrain in Relation to REM Sleep, Hippocampal Theta and Sensory Regulation

Large lesions in the septal forebrain failed to influence the REM sleep of hooded rats under a number of different conditions. This was true whether the electrical activity of the cortex or the activity of the dorsal and ventral hippocampus were used as criteria to assess REM sleep. The amount of REM sleep of animals with and without lesions was the same under baseline and REM deprivations conditions, and also similar under conditions of different types of environmental noise. The most surprising finding was the persistence of hippocampal theta activity after septal co-agulation. As has been reported previously, REM deprivation causes an appreciable compensatory effect. The values of REM sleep obtained under baseline and deprivation conditions were comparable to that previously obtained in our laboratory.

Effect of avian basal forebrain lesions, including septum, on heart rate conditioning

The possible involvement of basal telencephalic structures in visually conditioned heart rate change (established by pairing light and foot-shock) was studied in 156 pigeons by evaluating conditioning performance following lesions of the septum or lobus parolfactorius. Extensive destruction of the septal complex had no effect on either the orienting response or the development of the conditioned response. Lesions of the lobus parolfactorius did not affect the orienting response or overall conditioned response levels, but it did slightly prolong the latency of the conditioned heart rate change. It is concluded that the septum, despite its being cardioactive, is not involved in conditioned heart rate change and that the lobus parolfactorius participates minimally. Thus, of the principal limbic structures of the avian telencephalon, only the amygdalar homologue appears critical in this defensive conditioning task [3].

Orienting and classical conditioning in the rabbit (Oryctolagus cuniculus): Effects of septal area lesions

Rabbits with either sham or septal lesions recieved differential classical conditioning training in which tones of different frequencies served as CSs and paraorbital shock served as the UCS. Eyeblink (EB), EMG, and heart rate (HR) CRs were concommitantly assessed. Free field activity was also studied in selected animals. Animals with septal lesions revealed an impaired EB discrimination which resulted from increased responding to the CS-. These animals showed HR CRs of greater magnitude than sham animals. The HR discrimination was, however, unimpaired by septal lesions. Differential EMG activity also occurred, but was unaffected by septal destruction. Septal lesions resulted in greater free-field activity associated with visual stimulation, but no differences were obtained between septal and sham animals in the dark. It is suggested that these results were due to an enhanced reactivity to environmental stimulation, possibly related to dysfunctions of the orienting reflex.