Hypothalamic region and pathways responsible for adrenocortical response to surgical stress in rats

Surgical stress produced no increase in the plasma corticosterone level in rats with complete deafferentation of the medial basal hypothalamus (MBH). 30 min after surgical stress, the adrenocortical response depended on the integrity of a well-circumscribed region of the hypothalamus: the lateral-basal region of the retroachiasmatic area (RCAL) that lies not more than 0.5 mm caudally from the optic chiasma and is about 0.2 mm high. One week after transsection of this region, surgical stress produced no elevation of plasma corticosterone; the effect of the operation was independent of whether various combinations of other regions and pathways to the MBH were left intact. In contrast, high plasma corticosterone levels were found after surgical stress with all kinds of hypothalamic deafferentation when the basal region of the RCAL was not transected. The possible origin of neuronal fibres running through the RCAL is discussed.