MODULATION OF BEHAVIORAL-INHIBITION IN APPETITIVE EXTINCTION FOLLOWING MANIPULATION OF ADRENAL-STEROIDS IN RATS - IMPLICATIONS FOR INVOLVEMENT OF THE HIPPOCAMPUS

Two experiments were conducted in this study, utilizing 57 male Sprague-Dawley rats. Exp I investigated the functional behavioral significance of the hormone-brain interaction in the extinction of an appetitive runway response in normal Ss and in those with lesions of the hippocampus. During extinction, half of the Ss in each group were given daily sc injections of corticosterone. While the classical retardation effect of hippocampal lesions on appetitive extinction was replicated, hormone treatment was without effect in normal or hippocampally damaged Ss. The absence of a hormone effect in normals was primarily attributed to a saturated limited-binding system operating in the normal S. Exp II tested this notion, repeating the 1st experiment, with adrenalectomized (ADX), ADX + corticosterone replacement, and normal groups of Ss. Adrenalectomy produced a striking facilitation of extinction, which was speculated to be the result of hyperactive inhibitory neural organ free from an inhibitory endocrine feedback. This was supported when corticosterone treatment normalized the progress of extinction in ADX Ss. (40 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved). © 1979 American Psychological Association.