Comparative study of GABA-mediated depolarizations of lumbar A delta and C primary afferent neurones of the rat.

The distribution of GABA receptors on various categories of primary afferents was studied by means of intracellular recordings from rat dorsal root ganglion neurones. Cells were identified on the basis of their conduction velocity and classified as A delta and C neurones. Transient applications of GABA led to a decrease of membrane resistance and a concomitant depolarization. Maximal GABA-induced responses were weaker in C than in A delta and A beta cells. Smaller conductance changes in C cells suggest a lower density of GABAA receptors, and the heterogeneity of the "membrane potential/response amplitude" relationship indicate that the ionic mechanisms underlying GABA-induced responses may not be uniform on all primary afferents; this is supported by the wide range of reversal potential values recorded under voltage-clamp conditions in A delta cells.