Fig. 4.
Effect of 3β-hydroxypregnane steroids on other 5α-reduced and 5β-reduced steroid potentiators of GABAAresponses. A, Concentration dependence of 3α5αTHDOC potentiation in the absence (filled circles) and presence (open squares) of 10 μm3β5βTHDOC. GABA (2 μm) was coapplied with steroids, and the response to 2 μm GABA was used as the normalizing response (IN). B,C, Similar analyses using the 5β-reduced steroids 3α5βP and 3α5βTHDOC as potentiators. In allpanels, the solid line through the concentration–response values in the absence and presence of 3β5βTHDOC is the best fit of the Hill equation. Parameters of the fits and n values are given in Table 1.