Effects of hypothalamic deafferentation on basal and stress-induced adrenocortical acitivity in the pigeon.

Partial and complete deafferentation of the hypothalamus of the pigeon was performed using a modified Halasz-Pupp microknife. After complete neural isolation the plasma corticosterone level stabilized at a point intermediate between the morning and evening levels found in intact pigeons. No diurnal rhythm was observed and the response to neurogenic stimulus (restraint) was suppressed. Ether stress, however, induced a rise in plasma corticosterone. Posterior deafferentation had no effect on the diurnal corticosterone rhythm but did block the rise normally found after restraint. Anterior deafferentation did not suppress the stress-induced response but provided the cuts were large enough they inhibited the diurnal corticosterone rhythm. It is suggested therefore that the neural afferents to the hypothalamus which are necessary for diurnal fluctuations in pituitary-adrenal function pass through a sector located anteriorly between 45 degrees and 60 degrees on either side of the mod-line while stress-induced adrenocortical activation is triggered through posterior connexions.