Abstract

Vaginocervical stimulation (VCS) of the female rat during copulation is known to be the primary stimulus responsible for a decreased duration of the receptivity period called behavioral estrus. Central mechanisms by which VCS accelerates the onset of estrus termination in rats are not completely understood yet. Hence, the present study investigated the role of the ventromedial hypothalamus (VMH) in estrus termination using sexually experienced ovariectomized female rats. First, females were administered subcutaneous injections of estradiol benzoate and progesterone before being assigned to 4 different treatment groups. The first group received a microinfusion of a Na + channel blocker, tetrodotoxin (TTX), into the VMH an hour before receiving 50 manual VCSs, with a lubricated glass rod distributed over the course of 1h, while the second group received a microinfusion of TTX and sham VCSs. The remaining groups received a microinfusion of saline and their respective VCSs treatment. Each female was then tested for sexual behavior with sexually vigorous males in bilevel testing chambers 12, 16 and 20h after the beginning of the VCS treatment. Compared to females in the other groups, the infusion of TTX to the VMH delayed the decrease of lordosis responsiveness typical of estrus termination but no interaction between drug and stimulation treatments was established.