The effects of n-alcohols on synaptic potentials in rat hippocampal slices: The evidence for cutoff point in the central nervous system preparations in vitro

It has been reported that the potencies of anesthetic n-alcohols (C(n) H(2n+1) OH) in vivo are enhanced with an increase in carbon length (C(n)), and that the anesthetic action disappears around C¹² (cutoff point). It is unclear, however, whether n-alcohols exhibit these effects directly on the central nervous system (CNS). The effects of a series of n-alcohols were examined on evoked excitatory post-synaptic potentials (EPSPs) of the rat hippocampal preparation in vitro. EPSPs in area CA1 were elicited with a bipolar nichrome electrode placed on Schaffer collateral fibers, and recorded using a glass-microelectrode. Shorter-chain alcohols (C₁-C₇) were directly dissolved in ACSF, whereas longer-chain alcohols (C₈-C₁₁) were dissolved in ethahol and diluted in ACSF. The results indicated that n-alcohols (C₂- C₁₀) reduced the EPSP slope in a concentration-dependent manner, and that the potency disappeared at C₁₁ (cutoff point). Although the ED₅₀ values for the effects of C₂-C₆ correlated well (r² = 0.98) with membrane/buffer partition coefficient, the dependence of the ED₅₀ leveled off in the region of C₈-C₁₀. The present study demonstrated the evidence for cutoff phenomenon in the CNS preparations in vitro.