Experiments were carried out in the rabbit, with a view to elucidating ihe nervous control of the ACTH- and ACH-rclcasing mechanism, especially of the role played by the hippocampus and the amygdala. Electrical stimulation was applied to the hippocampus and amygdala for 1 h through a chronically implanted coaxial electrode, either under normal conditions or during the last hour of a 5-h period of immobilization stress. At 10 or 240 min after cessation of stimulation the animal was decapitated and the biosynthctic activity of the adrenal cortex was measured, as indicated by the blood corticostcrone level or the incorporation from acetate-l-C14 into corticosterone and 17-OHCS by adrenal homogenates. All results were compared with those obtained in intact and/or unstimulated controls. Stimulation in the cornusammonis of the hippocampus as well as in an extensive area of the amygdala effectively increased the biosynthctic activity of the adrenal cortex under normal conditions, while stimulation of the alveus or the fascia dentata of the hippocampus seemed relatively ineffective. The increased effect was observed at 10 min but not at 240 min after stimulation. Immobilization stress had a facilitatory effect on biosynthesis of the adrenal cortex, but hippocampal stimulation during the immobilization cancelled out this facilitation. Therefore, hippocampal stimulation was found to inhibit corticosteroid biosynthesis under stress conditions while facilitating corticosteroid biosynthesis under normal conditions. Lcsioning of the stria tcrminalis decreased the biosynthctic activity, but hippocampal stimulation more or less augmented it. Lcsioning of the dorsal fornix notably decreased the biosynthesis of corticosteroid, while neither hippocampal stimulation nor immobilization exerted any effect on this parameter. Lcsioning of the periventricular arcuate nucleus or pituitary gland also decreased biosynthctic activity. © 1968 S. Karger AG, Basel.
