A powerful GABA(B) receptor-mediated inhibition of GABAergic neurons in the arcuate nucleus

We combined histofluorescence with in situ hybridization to identify GABAergic neurons in the arcuate nucleus (ARC) following electrophysiological recordings, using GAD₆₅ as a marker. Intracellular recordings were made in hypothalamic slices prepared from ovariectomized guinea pigs. Over 90% of ARC neurons tested with the GABA(B) receptor agonist baclofen responded with a membrane hyperpolarization or an outward current. The hyperpolarization was dose-dependent, and the GABA(B) receptor antagonist CGP 35,348 produced a rightward shift in the agonist dose-response curve. Agonist potency was lower, and the efficacy greater, in GAD-positive neurons. The use of this novel technique for identifying GABAergic neurons thus reveals differences in the pharmacodynamics of GABA(B) receptor activation GABAergic and non- GABAergic ARC neurons.