Figure 1.

Structures of types of GABA potentiating and GABA antagonistic neuroactive steroids used in this study. (a) 3α5αP and 3α5βP (allopregnanolone and pregnanolone) are GABA_A receptor potentiators despite their structural differences. (b) Sulphated pregnane and pregnene steroids are effective non-competitive GABA_A receptor antagonists. (c–h) Other structural modifications tolerated by potentiating steroids. (c) Alphaxalone is a synthetic anaesthetic steroid (Phillipps, 1975; Barker et al., 1987). (d) 3α5βTHDOC is a naturally occurring steroid (Majewska et al., 1986; Mellon et al., 2001). (e–h) Synthetic neuroactive steroids with substitutions at C₁₁ are shown as ZCM 32, ZCM 34 and ZCM 41 (5α-reduced series) and ZCM 27, ZCM 33 and ZCM 40 (5β-reduced series). C11-NBD 3α5αP has a fluorescent substituent at carbon 11.