Adrenocortical Responses following Limbic Stimulation in Rats with Hypothalamic Deafferentations

Abstract

In view of the involvement of limbic structures in adrenocortical regulation, their afferent projections to the mediobasal hypothalamus were investigated. Electrical stimulation via chronically implanted electrodes in the dorsal hippocampus, the medial septal nuclei, the basolateral amygdala or the mesencephalic reticular formation all elicited a significant increment in plasma corticosterone levels in adult male rats under pentobarbital anesthesia. Complete or anterior hypothalamic deafferentation blocked these adrenocortical responses completely, and posterior hypothalamic deafferentation attenuated them to a marked extent. In animals with bilateral medial forebrain bundle lesions, hippocampal stimulation had no effect upon plasma corticosterone levels. These studies demonstrate that extrahypothalamic effects upon adrenocortical secretion are neurally mediated, and that the integrity of neural pathways impinging upon the mediobasal hypothalamus from both the rostral and the caudal directions is essential to these effects.

Differential Plasma Corticosterone Responses to Electrical Stimulation of the Medial and Lateral Septal Nuclei

“…In the present study in creased plasma corticosterone levels resulted from stimu lation o f the dorsal (LSD) and ventral (LSV) divisions o f the lateral, but not medial, septal nuclei. The explanation for the differences between the findings reported herein and the observations o f Feldman et al [12] is not known: diffe rences in experimental protocol preclude direct compari son o f observations. We have observed, however, increased plasma corticosterone levels subsequent to stimulation o f the V D B D ( fig.…”

“…In contrast to the above observations, Feldman et al [12] observed increased plasma corticosterone levels subseq uent to electrical stimulation o f the medial septum o f pen tobarbital anesthetized male rats. In the present study in creased plasma corticosterone levels resulted from stimu lation o f the dorsal (LSD) and ventral (LSV) divisions o f the lateral, but not medial, septal nuclei.…”

“…Addi tionally, a sizeable literature exists regarding a septal influence on pituitary-adrenal dynamics. Elevated non stress levels o f plasma corticosterone [19, 27], adrenal hy pertrophy [17] and enhanced adrenal responsiveness to stress stimuli [9, 18, 21] have been reported to follow septal ablation, and stimulation o f the septal nuclei purportedly inhibits adrenal activity in the rat [12]. Recently a series of studies was undertaken in this laboratory to reevaluate the role o f several limbic forebrain areas which have been im plicated in one or more aspects of A C T H control mecha nisms.…”

Effects of Single or Repeated Immobilization on Release of Norepinephrine and Its Metabolites in the Central Nucleus of the Amygdala in Conscious Rats

“…Anterior hypothalamic deafferentation, which interrupts the direct ventral pathway from the lower brain stem to the hypothalamus, or lesions of the ascending noradren ergic bundle can prevent increases in the HPA axis activ ity following amygdala stimulation [39,40]. These find ings suggest that lower brain stem catecholaminergic neurons may influence the HPA axis activity via ascend ing noradrenergic bundles to the ACE.…”

The Amygdala Regulates the Pituitary-Adrenocortical Response and Release of Hypothalamic Serotonin following Electrical Stimulation of the Dorsal Raphe Nucleus in the Rat

“…The activity of the HPA axis is also modulated by extrahypothalamic limbic structures, among which the amygdala plays a significant facilitatory role [3, 4, 5]. Thus, electrical stimulation of the amygdala in different animal species resulted in an increase in adrenocortical secretion [5, 6, 7]. Bilateral amygdalectomy blocked the adrenocortical responses to both somatosensory and olfactory stimuli [8].…”