CHRONIC NEUROSTEROID TREATMENT PRODUCES FUNCTIONAL HETEROLOGOUS UNCOUPLING AT THE GAMMA-AMINOBUTYRIC-ACID TYPE-A BENZODIAZEPINE RECEPTOR COMPLEX IN MAMMALIAN CORTICAL-NEURONS

We have investigated the effects of chronic treatment with the neurost eroid 5 alpha-pregnan-3 alpha-ol-20-one (5 alpha 3 alpha) On the gamma -aminobutyric acid (GABA)(A) receptor complex in cultured mammalian co rtical neurons. Chronic 5 alpha 3 alpha treatment (up to 2 mu M, 5 day s) did not produce any changes in the morphological appearance or the cell protein content of cortical neurons. The basal binding of [H-3]fl unitrazepam, [H-3]Ro15-1788, and [H-3]Ro15-4513 was not altered after the chronic treatment. Chronic 5 alpha 3 alpha treatment did not alter the K-d or B-max values of [H-3]flunitrazepam binding to intact corti cal neurons. However, chronic 5 alpha 3 alpha treatment produced uncou pling between GABA, barbiturate, and neurosteroid sites and the benzod iazepine site. The EC(50) values of these ligands were not significant ly altered; however, their E(max) values were decreased after chronic 5 alpha 3 alpha treatment. The 5 alpha 3 alpha-induced uncoupling was time and concentration dependent. The binding of [H-3]GABA and t-[S-35 ]butylbicyclophosphorothionate was also decreased after chronic 5 alph a 3 alpha treatment. Chronic 5 alpha 3 alpha treatment decreased the B -max of the low affinity GABA(A) receptor sites, without affecting the high affinity sites, and decreased the B-max of t-butylbicyclophospho rothionate binding sites. The EC(50) Value for GABA-induced Cl-36(-) i nflux was not altered, whereas the E(max) value was decreased after ch ronic 5 alpha 3 alpha treatment. Furthermore, the 5 alpha 3 alpha-indu ced uncoupling was reversed by concomitant exposure of the cortical ne urons to 5 alpha-pregnan-3 beta-ol-20-one or R5135, suggesting an invo lvement of the neurosteroid and GABA recognition sites in the observed uncoupling. Taken together, these results suggest that chronic 5 alph a 3 alpha treatment produces heterologous uncoupling at the GABA(A) re ceptor complex.