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 (alpha|)-aminobutyric acid (GABA) receptor antagonists into either the medial preoptic area (mPOA) or the arcuate-ventromedial region (ARC-VMR) on LH secretion. Bicuculline methiodide (BMI, GABA(A) receptor antagonist), and either 2- hydroxysaclofen (SAC) or CGP 55845A (CGP, GABA(B) receptor antagonists) were used. In experiment 1, castrated rams received 4-h dialysis into either the mPOA (n = 5) or ARC-VMR (n = 4) of artificial cerebrospinal fluid (aCSF) followed by 4 h of either BMI (aCSF-BMI, 375 microM 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 microM), or aCSF-CGP (50 microM). In experiment 3, untreated or testosterone (T)-treated castrated rams (n = 6/group) received dialysis only in the ARC-VMR of aCSF-aCSF, aCSF-BMI (375 microM), or aCSF-CGP (500 microM). Jugular blood was collected at 10-min intervals. In experiment 1, BMI suppressed mean plasma LH (p < 0.05) and increased interpulse interval (IPI, p < 0.05) at both sites. In experiment 2, BMI significantly reduced mean LH and increased IPI (p < 0.01). In experiment 3, BMI reduced mean LH in both the presence (p < 0.05) and absence of T (p < 0.01) and increased IPI (p < 0.01) in the absence of T. SAC, CGP, 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 either castrated or T-treated castrated rams decreased LH release, whereas dialysis of GABA(B) antagonists at these sites was without detectable effect.