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 ovariecto mized (OVX) estradiol-17beta-benzoate (EB) treated female guinea pigs activates lordotic responding and that (2) inhibition of alpha-adrener gic neurotransmission in the MBH inhibits lordotic responding in EB an d progesterone (EB + P) treated females (Neuroendocrinology, in press) . In this study, we investigated the relative influence of selective d rugs 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 agoni st UK-14,304 increased the number of seconds EB + P treated females he ld lordosis at test periods starting 15 min after infusion until test periods 1.5 h after infusion into the MPOA (maximum effect at test per iod 30 min after infusion, 265% vehicle (VEH); P < 0.005). UK-14,304 a lso 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 se lective 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 regio ns of the MPOA and the MBH facilitates lordotic responding in the guin ea pig.