Hypothalamic multiunit activity correlates of the adrenocortical response to stress.

The corticotropic response to stress was studied by means of multiple unit activity (MUA) recording from the adrenocorticotropic region of the hypothalamus, and plasma corticosterone (B) determination. MUA was permanently obtained and B was measured at 2, then 5 and 10 min intervals before and after neurogenic (electrical shocks) or systemic (ether inhalation) stress was applied. Experiments were made on steady unanesthetized, unrestrained thalamic pigeons. Post-stress alterations of MUA and B were closely in parallel, exhibiting a rapid and sustained increase in firing rate and shifting by 5-10 min, in corticosteronemia. Three successive and progressively decreasing peaks of MUA and B could be observed. Basal resting values were restored by approximately 90 min. Adrenocorticotropic responses to stress appear to be modulated through neural thalamic and/or rhombencephalic mechanisms.