Effect of Hippocampal Stimulation on the Plasma Thyrotropin (THS) and Corticosterone Responses to Acute Cold Exposure in the Rat

Abstract

Seven days after the stereotaxic implantation of a bipolar electrode in the gyrus dentatus of the hippocampus of adult male rats, exposure to cold (20 min at −5 °C) increased both plasma TSH and corticosterone concentrations, whereas exposure in association with a minor environmental disturbance (presence of an observer) suppressed the TSH response to cold and enhanced the corticosterone response. Concurrent stimulation of the hippocampus with monophasic square waves of 1.3–1.5 V, 10 c.p.s., and 0.1 ms duration was found to restore the TSH response to cold and to inhibit the secretion of adrenocorticotropin (ACTH) (as reflected by the plasma corticosterone concentration). These findings suggest that the concurrent stimulation of ACTH release and inhibition of TSH secretion induced by nonspecific stress are possibly related to depressed hippocampal activity.