The Contraceptive Agent Provera Enhances GABAAReceptor-Mediated Inhibitory Neurotransmission in the Rat Hippocampus: Evidence for Endogenous Neurosteroids?

Open Access
Publisher Website
Google Scholar
Abstract
Neurosteroids typified by 5α-pregnan-3α-ol-20-one (5α3α) have emerged as the most potent endogenous positive modulators of the GABAAreceptor, the principal mediator of fast inhibitory transmission within the CNS. Neurosteroids can be synthesizedde novoin the brain in levels sufficient to modulate GABAAreceptor function and, thus, might play an important physiological-pathophysiological role. Indirect support for this proposal comes from the observation that neurosteroid action is region and neuron selective. However, the mechanism(s) that imparts specificity of action remains primarily elusive. Although neurosteroids are relatively promiscuous toward different GABAAreceptor isoforms, the contribution of local neurosteroid metabolism has been relatively unexplored. Here, we investigate the role of neurosteroid metabolism by using electrophysiological techniques to compare the actions of 5α3α and its metabolically stable synthetic analog ganaxolone on inhibitory neurotransmission in CA1 and dentate gyrus neurons. Furthermore, we evaluate the contribution of a key enzyme in neurosteroid metabolism [i.e., 3α-hydroxysteroidoxidoreductase (3α-HSOR)] to the inactivation of endogenous, or exogenously applied 5α3α. We show that low concentrations of ganaxolone, but not of 5α3α, enhance inhibitory transmission in dentate gyrus, whereas both steroids are similarly effective in CA1 neurons. Furthermore, inhibition of 3α-HSOR by the contraceptive agent Provera results in enhanced synaptic and extrasynaptic GABAAreceptor-mediated inhibition in the dentate gyrus but not in the CA1 region. Collectively, these findings advocate a crucial role for local steroid metabolism in shaping GABAAreceptor-mediated inhibition in a regionally dependent manner and suggest a novel action by the contraceptive agent on inhibitory centers in the CNS.

This publication has 37 references indexed in Scilit: