EFFECTS OF DIALYZING GAMMA-AMINOBUTYRIC-ACID RECEPTOR ANTAGONISTS INTO THE MEDIAL PREOPTIC AND ARCUATE VENTROMEDIAL REGION ON LUTEINIZING-HORMONE RELEASE IN MALE SHEEP

We investigated the effects of microdialyzing gamma-aminobutyric acid (GABA) receptor antagonists into either the medial preoptic area (mPOA ) or the arcuate-ventromedial region (ARC-VMR) on LH secretion. Bicucu lline methiodide (BMI, GABA(A) receptor antagonist), and either 2-hydr oxysaclofen (SAG) or CCP 55845A (CGP, GABA(B) receptor antagonists) we re used. In experiment 1, castrated rams received 4-h dialysis into ei ther the mPOA (n = 5) or ARC-VMR (n = 4) of artificial cerebrospinal f luid (aCSF) followed by 4 h of either BMI (aCSF-BMI, 375 mu M in mPOA, 1 mM in the ARC-VMR for 2-1/2 h), or aCSF-SAC (5 mM). In experiment 2 , castrated rams received dialysis only in the ARC-VMR (n = 5) of aCSF -aCSF, aCSF-BMI (375 mu M), or aCSF-CGP (50 mu M) In experiment 3, unt reated or testosterone (T)-treated castrated rams (n = 6/group) receiv ed dialysis only in the ARC-VMR of aCSF-aCSF, aCSF-BMI (375 mu M), or aCSF-CGP (500 mu M). Jugular blood was collected at 10-min intervals. In experiment 1, BMI suppressed mean plasma LH (p < 0.05) and increase d interpulse interval (IPI, p < 0.05) at both sites. In experiment 2, BMI significantly reduced mean LH and increased IPI (p < 0.01). In exp eriment 3, BMI reduced mean LH in both the presence (p < 0.05) and abs ence of T (p < 0.01) and increased IPI (p < 0.01) in the absence of T. SAG, CCP, and aCSF did not affect LH in any experiment. These results show that dialysis of BMI, into either the mPOA or the ARC-VMR of eit her castrated or T-treated castrated rams decreased LH release, wherea s dialysis of GABA(B) antagonists at these sites was without detectabl e effect.