The electrophysiological and morphological characteristics of feline dorsal root ganglion cells.

The electrophysiological characteristics of physiologically typed L7 and S1 dorsal root ganglion (DRG) cells have been studied in the cat by intracellular recording. The injection of the fluorescent dye Lucifer Yellow has enabled us to study the morphology of these neurons. Our results show that over the entire range of primary sensory afferents there is a linear relationship between the peak rate of rise of somatic action potentials (dv/dt) and axonal conduction velocity. There is a prominent inflexion on the repolarizing phase of the somatic action potentials of group III and group IV afferents. This is not seen in the action potentials of group II or group I afferents. These results correlate with the observation that the total action potential duration (APD) is inversely related to conduction velocity. Primary afferent somata were observed to have an ellipsoidal shape with the long axis in the rostrocaudal dimension. It was observed that for all afferents studied the volume of a dorsal root ganglion cell was linearly related to its peripheral axonal conduction velocity. We were able to show further that group IV somata, some of whose axons supplied nociceptors, were among the smallest in the ganglion.