Effects of alpha-2-adrenergic drugs in the medial preoptic area and medial basal hypothalamus on lordosis in the guinea pig.

We have recently demonstrated that (1) stimulation of alpha-adrenergic neurotransmission in the medial basal hypothalamus (MBH) of ovariectomized (OVX) estradiol-17 beta-benzoate (EB) treated female guinea pigs activates lordotic responding and that (2) inhibition of alpha-adrenergic neurotransmission in the MBH inhibits lordotic responding in EB and progesterone (EB + P) treated females (Neuroendocrinology, in press). In this study, we investigated the relative influence of selective drugs altering alpha-2-adrenergic neuronal transmission within the MBH and medial preoptic area (MPOA) on lordotic responding in EB + P primed females. In EB + P primed females the selective alpha-2-adrenergic agonist UK-14,304 increased the number of seconds EB + P treated females held lordosis at test periods starting 15 min after infusion until test periods 1.5 h after infusion into the MPOA (maximum effect at test period 30 min after infusion, 265% vehicle (VEH); P < 0.005). UK-14,304 also facilitated lordotic responding 15-30 min and 1.5 h after infusion into the MBH of EB + P primed females (maximum effect at test period 30 min after infusion, 223% VEH; P < 0.025). Furthermore, infusing the selective alpha-2-adrenergic antagonist yohimbine (YOH) into the MBH of EB + P primed females inhibited lordotic responding between 1.0 and 2.0 h after treatment (maximum 1.5 h, 42% VEH; P < 0.05). These results demonstrate that alpha-2-adrenergic neurotransmission within the regions of the MPOA and the MBH facilitates lordotic responding in the guinea pig.