Ca. Frye et al., BICUCULLINE INFUSED INTO THE HAMSTER VENTRAL TEGMENTUM INHIBITS, WHILE SODIUM VALPROATE FACILITATES, SEXUAL RECEPTIVITY, Pharmacology, biochemistry and behavior, 46(1), 1993, pp. 1-8
Progesterone's (P) actions on both the ventral medial nucleus of the h
ypothalamus (VMH) and the ventral tegmental area (VTA) are essential f
or sexual receptivity in female hamsters. Evidence suggests that proge
sterone's actions in the hamster VMH may be genomic while those in the
VTA may be mediated nongenomically, via GABA(A). Ovariectomized femal
e hamsters were bilaterally implanted with cannulae aimed toward the V
TA. One week after surgery, animals were SC injected with 10 mug estra
diol benzoate (EB) and 40 h later with 200 or 500 mug P. At hour 43.5,
50 ng bicuculline, a GABA(A) antagonist, was infused into each availa
ble cannula. Control animals received 0.5 mul sterile saline vehicle,
or no infusion. At hour 44, animals were tested for sexual receptivity
in an observation arena with a sexually experienced male. Histology r
evealed that only animals with bicuculline infused into the VTA had re
duced lordosis durations compared to controls. Other animals, primed w
ith EB and 200 mug progesterone, showed a facilitation of sexual recep
tivity after infusion into the VTA of 50 mug sodium valproate, a GABA(
A) transaminase inhibitor. These results suggest that GABA(A) plays a
necessary role in the mechanism of progesterone's actions on sexual re
ceptivity in hamster VTA.