Characteristics of action potentials recorded from cat spinal ganglion neurons in vivo.

Action potentials were recorded intracellularly from L4-S1 dorsal root ganglion (DRG) neurons of anesthetized cats. Based on the shape of their waveforms the action potentials were classified as either typical (n = 49) or atypical (n = 8). The atypical potentials were characterized by a slowly rising, well-defined early depolarization of small amplitude and long duration. This kind of prepotential randomly triggered spike potentials with varying latencies. The average rise time, duration, and area of atypical potentials were significantly different than those of typical ones. In some DRG neurons, the afterhyperpolarization was preceded by a delayed repolarization, or was followed by postspikes and long-lasting afteroscillations. In others, small depolarizations could be recorded during subthreshold stimulation. These depolarizations arose slightly later than the spike potential, and were all or none, with relatively stable onset latency and size. These results are explained by postulating the presence of chemical synapses and/or electrotonic coupling in the DRG.