AMPA/kainate receptors in the ventromedial hypothalamus mediate the effects of glutamate on estrus termination in the rat.

Infusions of glutamate or its selective receptor agonists to the VMH of ovariectomized (OVX) female rats primed with estradiol benzoate (EB) and progesterone (P) inhibit both appetitive and consummatory aspects of sexual behavior whereas selective glutamate receptor antagonists facilitate these measures in females primed with EB alone. Because vaginocervical stimulation (VCS) activates glutamate neurons in the VMH, and induces a faster termination of estros behavior, the present study examined the effects of the AMPA/kainate receptor antagonist DNQX on the induction of estrus termination by manual VCS. Ovx, sexually-experienced rats were primed with EB and P and subsequently received either 1 or 50 distributed VCSs, over the course of an hour, 12 h before a test with sexually vigorous males. Half of the females in each stimulus group received bilateral infusions of 1 μl/side of either DNQX (19.8 mmol/μl) or saline aimed at the VMH immediately prior to VCS or sham stimulation. Saline-infused females given VCS had lower lordosis quotients compared to females given sham stimulation. In contrast, females infused with DNQX prior to VCS displayed more appetitive behaviors and higher lordosis quotients and magnitudes compared to females infused with saline. These data indicate that activation of AMPA/kainate receptors in the VMH by increased glutamate transmission induced by VCS mediates estrus termination.