ASAY, M.J.*; BOYD, S.K.; University of Notre Dame; University of Notre Dame: Characterization of the GABAB receptor in Xenopus laevis

Gamma-aminobutyric acid (GABA) is a ubiquitous inhibitory neurotransmitter. The metabotropic GABA_B receptor acts via K⁺ and Ca²⁺ channels as well as adenylate cyclase to inhibit pre- and post-synaptic potentials. Although much information about the GABA_B receptor is available in mammals, little is known about the receptor in amphibians. We used the mammalian GABA analogue, [³H]CGP54626, to perform autoradiography and receptor binding assays in Xenopus laevis brains. Autoradiography showed widespread distribution of the receptor with high densities in specific regions of the olfactory bulb and forebrain. Receptor binding assays showed rapid association within 10 minutes. Dissociation experiments with baclofen showed little displacement of the radioligand after 20 minutes. An association experiment with both GABA and baclofen as competitors showed baclofen to be much less effective at displacing the labeled antagonist. The results suggest major features of GABA_B receptor binding are similar in amphibians and mammals but that ligand specificity may vary.