Ethanol and temperature modify motor axon firing patterns

At high temperature a single orthodromic action potential in the excitor (E) axon to the stretcher muscle of the crab Pachygrapsus crassipes provokes the generation of additional spikes in the peripheral E axon branches. This phenomenon exhibits a critical temperature threshold. Bathing preparations in crab salines made up with ethanol at levels as low as 0.5% (109 mM) reversibly decreased the temperature threshold for peripheral spike generation. Higher levels of ethanol resulted in the peripheral generation of E axon spikes at lower temperatures. These results, together with the observation that the temperature threshold is dependent upon the acclimation temperature, indicate that the peripheral generation of action potentials in the E axon is associated with an increase membrane lipid fluidity.