Coordination of hamster lordosis and flank marking behavior: role of arginine vasopressin within the medial preoptic-anterior hypothalamus.

The role of arginine vasopressin (AVP) within the medial preoptic area-anterior hypothalamus (MPOA-AH) in the neural coordination of lordosis and flank marking was investigated. AVP, but not saline, microinjected into the MPOA-AH of ovariectomized hamsters not given hormone replacement therapy stimulated high levels of flank marking when tested with a sexually experienced male, or when tested alone. In contrast, AVP microinjected into the MPOA-AH of ovariectomized hamsters given estradiol benzoate (EB) and progesterone did not stimulate flank marking or inhibit lordosis during tests with a sexually experienced male. However these same females exhibited high levels of flank marking in response to AVP when tested alone. A second experiment demonstrated that progesterone was not required for inhibition of AVP-induced flank marking in ovariectomized females given EB replacement and tested with sexually experienced males. The present study provides no evidence that AVP acts within the MPOA-AH to inhibit hamster lordosis, but demonstrates that ovarian hormones and male social contact block the induction of flank marking by AVP microinjected into the MPOA-AH. These data suggest that one component in the neural coordination of lordosis and flank marking is inhibition of the response of the MPOA-AH to AVP.