OVARIAN HORMONES ALTER THE BEHAVIORAL-RESPONSE OF THE MEDIAL PREOPTIC-ANTERIOR HYPOTHALAMUS TO ARGININE-VASOPRESSIN

In Syrian hamsters (Mesocricetus auratus) arginine-vasopressin (AVP) w ithin the medial preoptic-anterior hypothalamus (MPOA-AH) plays a crit ical role in the control of a hormone-dependent behavior caned flank m arking. The present study investigated whether ovarian hormones influe nce flank marking by altering the response of the MPOA-AH to AVP. The amount of Bank marking stimulated by microinjection of AVP (9 mu M in 200 nl saline) into the MPOA-AH varied significantly over the 4 days o f the estrous cycle with the lowest levels of Bank marking observed on estrus. A second experiment demonstrated that administration of proge sterone significantly reduced AVP-stimulated flank marking in estradio l-treated ovariectomized hamsters. These data support the hypothesis t hat the changing levels of estradiol and progesterone during the estro us cycle influence flank marking by altering the sensitivity or respon se of the MPOA-AH to AVP. Copyright (C) 1996 Elsevier Science Inc.