1966 Volume 16 Issue 5 Pages 551-569
The neurohumoral interaction in the feedback control of ACTH secretion was studied by means of EEG observation before and after intravenous administration of adrenocorticotrophic hormone, SU-4885 which is an inhibitory substance for the adrenocortical hormone production by the adrenal cortex, and hydrocortisone acetate in rabbit. For further clarification of this problem, crystalline hydrocortisone acetate was implanted or a localized lesion was made in the brain and alterations in the stress response were observed.
The results were as follows:
A. The EEG activity showed the following alterations after injection of adrenocorticotrophic hormone.
1. In jection of adrenocorticotrophic hormones brought about a decrease in slower components of 2-13 cps in the dorsal hippocampus (alveus) and the median eminence-periventricular arcuate nucleus, and an increase in the amygdala (lateral basal portion), anterior hypothalamic area, mammillary body and the midbrain reticular formation. In some cases 40 cps spindle-like burst increased after injection. The medial preoptic area revealed a diphasic alteration by injection, first an increase and then a decrease in the slower components. Little change occurred in the activity of the posterior hypothalamic area.
2. With administration of SU-4885, there was an increase in the slower frequency components in the dorsal hippocampus, anterior hypothalamic area, median eminence-periventricular arcuate nucleus and the posterior hypothalamic area. In the amygdala these components first decreased but from 2-4 hours after injection then increased. In some cases the 40 cps waves showed a remarkable increase. In the midbrain reticular formation the slower components showed a diphasic change, first a decrease and then an increase.
3. With hydrocortisone acetate injection, there was an increase in the slower components of the dorsal hippocampus and the median eminence-periventricular arcuate nucleus, but these components markedly decreased in the amygdala, anterior hypothalamic area and the midbrain reticular formation.
B. After implantation of hydrocortisone acetate or localized electrolytic destruction in the median eminence-periventricular arcuate nucleus and the nucleus ventromedialis hypothalami, the stress response of the rabbit, as indicated by the decrease of blood lymphocytes or the increase of urinary Porter-Silber chromogen excretion, showed a depression. In cases of the septum pellucidum, posterior hypothalamic area, central grey and the midbrain reticular formation, no remarkable change occurred following these treatments in the stress response.
On a basis of these results it was suggested that the basal hypothalamus might be a focus for the negative feedback control for the maintenance of homeostasis of adrenocorticotrophic hormone and adrenocortical hormone, and that the hippocampus and the amygdala might participate in this mechanism by acting on the basal hypothalamus when their activities were influenced by the changes in adrenocorticotrophic or adrenocortical hormone level.
