Electrical properties of rat dorsal root ganglion neurones with different peripheral nerve conduction velocities.

Abstract

The electrical characteristics of individual rat dorsal root ganglion neurons were studied and related to the peripheral axon conduction velocity and morphological cell type. Neurons were divided into 4 groups based on the conduction velocity of their peripheral axons (A.alpha., 30-55 m/s; A.beta., 14-30 m/s; A.delta., 2.2-8 m/s and C < 1.4 m/s). Electrophysiological parameters examined included membrane potential, action potential amplitude and duration, after-potential height and duration, input resistance and the occurrence of time-dependent rectification. The mean duration of the somatic action potentials was characteristic for each of the conduction velocity groupings. There was considerable overlap between groups. The fast-conducting (A.alpha.) and slowly conducting (A.alpha.) myelinated fibers had short-duration action potentials, within the ranges 0.49-1.35 and 0.5-1.7 ms at the base respectively. The A.beta. and C cells had somatic action potentials with durations in the ranges of 0.6-2.9 and 0.6-7.4 ms respectively. The longer action potential durations could be related to the presence of an inflexion on the repolarizing phase seen in a third of A.beta. neurons (called A.beta.1 neurons) and in all C neurons. The action potential overshoot was larger in C neurons and A.beta.1 neurons than in the other neuron groups. The mean duration of the after-hyperpolarization was several times greater in C neurons than in A neurons. A.delta. neurons displayed the shortest and greatest amplitude after-hyperpolarizations. Large, long-lasting after-hyperpolarizations were not limited to neurons displaying an inflexion. The electrophysiological properties of the soma membrane of A.delta. neurons closely resembled those of A.alpha. neurons, while in several respects those of C neurons resembled the A.beta.1 neuronal properties. The input resistance was much greater in C than in A cells, although there was no significant difference between specific membrane resistance values calculated for the different groups. A number of A cells exhibited time-dependent rectification.