Spike afterpotentials in single, identified fast and slow motor neurons in the crab Pachygrapsus crassipes

Ethanol decreases the velocity of spike propagation along a fast motor axon

Intracellular recordings were made from the fast bender excitor motor axon in autotomized crab limbs bathed in normal saline, and in salines made with up to 240 mM of ethanol. The presence of ethanol reduced the amplitude, the rise time and the decay time of the evoked action potential, and decreased the velocity at which the spike was conducted down the axon. There was a linear relationship between each of these four parameters and the concentration of ethanol in the saline. The close relationship between spike rise time and conduction velocity suggests that ethanol slows the rate of membrane depolarization by the spike and thus decreases the velocity at which action potentials are propagated along the axon.

The effects of ethanol on intracellular potassium and the membrane potential of an identified crab motor axon

1. Observations were made on the fast bender excitor axon in autotomized crab walking limbs bathed in normal crab saline, and in salines made up with 0.2 M sucrose or 0.2 M ethanol. Microelectrode techniques were used to measure the resting membrane potential and the intracellular level of potassium. 2. Sucrose-saline had little effect on the membrane potential or the intracellular level of potassium. Ethanol-saline hyperpolarized the membrane potential by about 3 mV and increased the level of intracellular potassium. 3. The ethanol-induced changes in intracellular potassium levels and membrane potential took place with the same time course. Further, the changes in membrane potential could be accounted for by changes in the equilibrium potential for potassium, Ek as predicted by the Nernst equation.

Differential effects of alcohols on the spike threshold of an identified motor axon in a crab (Pachygrapsus crassipes)

Observations were made on the fast bender excitor (FBE) axon in autotomized crab limbs bathed in salines made up with different alcohols. It has been shown previously that the presence of ethanol at a certain level causes a single action potential to generate additional spikes in the peripheral axon branches. The present study examines the level of different alcohols required to induce peripheral spike generation. For primary alcohols, increasing the molecular weight decreased the level of alcohol required to produce peripheral spike generation. The threshold level of 2-butanol was greater than 1-butanol, but less than tertiary-butanol. These results are explained in terms of the partition coefficient, so that an alcohol with a higher partition coefficient enters the lipid bilayer more readily, thus a lower threshold level of that alcohol is required in the saline to generate additional spikes.