Ovarian hormones alter the behavioral response of the medial preoptic anterior hypothalamus to arginine-vasopressin

In Syrian hamsters (Mesocricetus auratus) arginine-vasopressin (AVP) within the medial preoptic-anterior hypothalamus (MPOA-AH) plays a critical role in the control of a hormone-dependent behavior caned flank marking. The present study investigated whether ovarian hormones influence 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 of the estrous cycle with the lowest levels of Bank marking observed on estrus. A second experiment demonstrated that administration of progesterone significantly reduced AVP-stimulated flank marking in estradiol-treated ovariectomized hamsters. These data support the hypothesis that the changing levels of estradiol and progesterone during the estrous cycle influence flank marking by altering the sensitivity or response of the MPOA-AH to AVP. Copyright (C) 1996 Elsevier Science Inc.