Adrenocrotical responses to systemic or neurogenic stress and to hypothalamic stimulation in chronically catheterized thalamic pigeons.

Thalamic and intact pigeons were equipped with a chronic arterial catheter and with a miniature electronic device for hypothalamic telestimulation. Chronic catheterization allowed for repetitive blood sampling in freely moving birds subjected to either systemic (ether inhalation) or neurogenic (electrical foot shocks) stress and to electrical stimulation of the hypothalamic corticotropic area. Corticosterone levels were determined by protein binding assay at 2-, then 5- and 10-min intervals, for 100 min. Basal and experimentally modified plasma corticosterone concentrations were not different in thalamic and intact pigeons. Corticosterone profile exhibited episodic increase including three peaks at 12, 35 and 60 min after stress application. Only the first peak of plasma corticosterone appeared after hypothalamic stimulation. It is suggested that extrahypothalamic neuronal networks are responsible for the long-lasting repetitive adrenocorticotropic response to stress, which are not involved in the single response to hypothalamic stimulation itself. Furthermore, such extrahypothalamic neuronal networks shoudl be located at the diencephalic or rhombencephalic level since hemispherectomized pigeons exhibited the same profile of stress-induced episodic hypercorticosteronemia as seen in intact birds.