The effects of enantiomers of the neurosteroid analogues, 3α-hydroxy- 5α-pregnan-20-one (DHP) and 3α-hydroxy-5α-androstane-17β-carbonitrile (ACN), and the benz[e]indene, BI-1, on synaptic currents were examined in microcultures of rat hippocampal neurons. Over the range of 0.1-10 μM, the (+)-enantiomers were more potent and effective than their (-)-enantiomeric counterparts in enhancing γ-aminobutyric acid (GABA)A receptor-mediated evoked synaptic currents. The (+)-enantiomers had small effects on peak currents, but slowed the decay of inhibitory synaptic currents, resulting in 2-3-fold increases in charge transfer during inhibitory synaptic events at 10 μM. Similar prolongations of spontaneous miniature inhibitory postsynaptic currents (IPSCs) and responses to brief GABA pulses to outside-out patches suggest that the prolongations of evoked synaptic currents result primarily from postsynaptic effects. In contrast, the (-)-enantiomers had little effect on evoked IPSCs at concentrations ≤1 μM, but enhanced inhibitory transmission at 10 μM. At concentrations ≤1 μM, neither the (+)- nor (-)- enantiomers altered glutamate-mediated excitatory synaptic currents. At 10 μM, (+)-DHP and (+)-ACN depressed excitatory responses in a bicuculline- sensitive fashion, suggesting that direct chloride channel gating by the steroids contributed to the depression. These data indicate that certain steroids and benz[e]indenes augment inhibitory synaptic transmission enantioselectively and provide strong support for the hypothesis that steroids act at specific sites on synaptic GABA(A) receptors rather than via alteration of membrane lipids.

Original languageEnglish
Pages (from-to)162-171
Number of pages10
Issue number2
StatePublished - Jun 1998


  • Autapses
  • Enantiomers
  • GABA
  • Hippocampus
  • IPSCs
  • Neurosteroids


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