Investigating how aromatic solvent exposure impacts acoustic reflexes

Some volatile aromatic solvents have similar or opposite effects to anesthetics in the central nervous system. Like for anesthetics, the mechanisms of action involved are currently the subject of debate. The purpose of this in vivo study was to determine whether direct binding or modifications of the membrane fluidity explain how solvents counterbalance anesthesia’s depression of the middle-ear reflex (MER). Part of this multidisciplinary study investigates the combined effects of exposure to a mixture of ketamine and xylazine, and inhaled solvents in rats. The respective effects of anesthetics and five different solvents on the MER amplitude are investigated. Additionally, the effect of solvent exposure (toluene) on membrane fluidity is evaluated by solid-state Nuclear Magnetic Resonance (NMR) analysis of 31P residual CSA. The Tm gel (L’) to liquid-crystalline phase (L) transition temperature is evaluated by 1H NMR measurements, to assess how solvent molecules modify overall membrane fluidity. Our findings show that the stereospecificity of the solvent molecule plays a pharmacological role in the modification of the MER amplitude. Solid-state NMR analysis also confirms that toluene used at relevant concentrations does not alter membrane fluidity. Therefore, we hypothesize that aromatic solvents act on neuroreceptor channels involved in the acoustic reflex circuit rather than on membrane fluidity.