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. Author manuscript; available in PMC: 2014 Feb 1.
Published in final edited form as: Horm Behav. 2012 May 2;63(2):254–266. doi: 10.1016/j.yhbeh.2012.04.016

Fig. 3. Neurosteroid modulation of GABA-A receptors.

Fig. 3

AP and related neurosteroids binds and potentiate the GABA-A receptor function leading protective effects against seizures. GABA-A receptors are believed to be pentameric with five protein subunits that form the chloride ion channel pore. The AP and THDOC binding site is thought to be at the “neurosteroid binding site”, which is distinct from sites for GABA, benzodiazepines and barbiturates. Postsynaptic GABA-A receptors, which are pentameric chloride channels composed of 2α2βγ subunits, mediate the phasic portion of GABAergic inhibition, while extrasynaptic GABA-A receptors, pentamers composed of 2α2βδ subunits, primarily contribute to tonic inhibition in the hippocampus. Neurosteroids activate both synaptic and extrasynaptic receptors and enhance the phasic and tonic inhibition. Therefore, they may promote maximal protection against seizure susceptibility.