Vol. 289, Issue 1, 405-411, April 1999

Ethanol-Like Discriminative Stimulus Effects of Endogenous Neuroactive Steroids: Effect of Ethanol Training Dose and Dosing Procedure¹

Carrie A. Bowen² , Robert H. Purdy and Kathleen A. Grant

Department of Physiology and Pharmacology, Wake Forest University School of Medicine, Winston-Salem, North Carolina (C.A.B., K.A.G.); and Department of Neuropharmacology, Scripps Research Institute, La Jolla, California (R.H.P.)

A number of endogenous steroids exhibit rapid, nongenomic effects on the central nervous system and are called neuroactive steroids. The rapid mechanisms of action include modulation of -aminobutyric acid type A (GABA_A) and N-methyl-D-aspartate (NMDA) receptors, which are two receptors implicated in the behavioral effects of ethanol. It was hypothesized that neuroactive steroids that positively modulate GABA_A receptors or negatively modulate NMDA receptors, analogous to the actions of ethanol, would produce discriminative stimulus effects similar to ethanol. Two groups of male Long-Evans rats (n = 6-8/group) were trained to discriminate between 1.0 or 2.0 g/kg ethanol (i.g.) and water (i.g.). The neuroactive steroids allopregnanolone, pregnanolone, epipregnanolone, allotetrahydrodeoxycorticosterone, pregnanolone sulfate, epipregnanolone sulfate, dehydroepiandrosterone, dehydroepiandrosterone sulfate, pregnenolone, and pregnenolone sulfate (PS), all administered i.p., were tested for substitution with acute and cumulative dosing procedures (n = 4-8/steroid). The GABA_A-positive modulatory steroids allopregnanolone, pregnanolone, and allotetrahydrodeoxycorticosterone substituted for ethanol, as did the low-efficacy steroid 3,5-P. GABA_A-negative modulators, such as dehydroepiandrosterone sulfate and PS, and all of the NMDA modulators tested, including PS, pregnanolone sulfate, and epipregnanolone sulfate, did not substitute for ethanol. These results show that certain endogenously occurring neuroactive steroids produce discriminative stimulus effects similar to those of ethanol.