CHARACTERIZATION OF NEURONAL ZEBRA FINCH GABA(A) RECEPTORS - STEROID EFFECTS

Songbirds are widely studied to investigate the hormonal control of be havior. However, little is known about the effects of steroids on neur otransmission in these birds. We used electrophysiological and pharmac ological techniques to characterize gamma-aminobutyric acid (GABA) typ e A receptors (GABA(A)) of primary cultured telencephalic and hippocam pal neurons from developing zebra finches. Additionally, their modulat ion by 17 beta-estradiol(E-2), 5 alpha- and 5 beta-dihydrotestosterone (DHT), 5 alpha- and 5 beta-pregnan-3 alpha-ol-20-one, and corticoster one was examined. Whole-cell GABA-evoked currents were inhibited by pi crotoxin (10 mu mol l(-1)) and bicuculline methiodide (10 mu mol l(-1) ) and potentiated by pentobarbital (100 mu mol l(-1)) and propofol (3 mu mol l(-1)). Loreclezole (10 mu mol l(-1)) potentiated GABA-evoked c urrents, suggesting the presence of beta(2), beta(3) and/or beta(4) su bunits. Diazepam (1 mu mol l(-1)) potentiated currents, while Zn2+ (1 mu mol l(-1)) caused no inhibition, indicating the presence of gamma s ubunits. 5 alpha- and 5 beta-Pregnan-3 alpha-ol-20-one (100 nmol l(-1) ) potentiated currents, whereas E-2 (1 mu mol l(-1)), 5 alpha- and 5 b eta-DHT (1 mu mol l(-1)), and corticosterone (10 mu mol l(-1)) had no detectable effect. We conclude that zebra finch telencephalic and hipp ocampal GABA(A) receptors include alpha, beta, and gamma subunits and are similar to their mammalian counterparts in both their biophysical and pharmacological properties. Additionally, GABA-evoked currents are greatly potentiated by 5 alpha- and 5 beta-pregnan-3 alpha-ol-20-one but show little or no acute modulation by sex steroids or corticostero ne.