Cyclohexanol analogues are positive modulators of GABA _A receptor currents and act as general anaesthetics in vivo

GABA _A receptors meet all the pharmacological criteria required to be considered important general anaesthetic targets. In the following study, the modulatory effects of various commercially available and novel cyclohexanols were investigated on recombinant human γ-aminobutyric acid (GABA _A, α ₁β ₂γ _2s) receptors expressed in Xenopus oocytes, and compared to the modulatory effects on GABA currents observed with exposures to the intravenous anaesthetic agent, propofol. Submaximal EC ₂₀ GABA currents were typically enhanced by co-applications of 3-300 μM cyclohexanols. For instance, at 30 μM 2,6-diisopropylcyclohexanol (a novel compound) GABA responses were increased ∼ 3-fold (although similar enhancements were achieved at 3 μM propofol). As regards rank order for modulation by the cyclohexanol analogues at 30 μM, the % enhancements for 2,6-dimethylcyclohexanol ∼ 2,6-diethylcyclohexanol ∼ 2,6-diisopropylcyclohexanol ∼ 2,6-di-sec-butylcyclohexanol ≫2,6-di-tert-butylcyclohexanol ∼ 4-tert-butylcyclohexanol > cyclohexanol ∼ cyclopentanol ∼ 2-methylcyclohexanol. We further tested the potencies of the cyclohexanol analogues as general anaesthetics using a tadpole in vivo assay. Both 2,6-diisopropylcyclohexanol and 2,6- dimethylcyclohexanol were effective as anaesthetics with EC ₅₀s of 14.0 μM and 13.1 μM respectively, while other cyclohexanols with bulkier side chains were less potent. In conclusion, our data indicate that cyclohexanols are both positive modulators of GABA _A receptors currents and anaesthetics. The positioning and size of the alkyl groups at the 2 and 6 positions on the cyclohexanol ring were critical determinants of activity.