SPONTANEOUS ACTIVITY OF CAT SPINAL GANGLION NEURONS INVIVO

Recordings were made from L4-S1 spinal ganglion neurons of anesthetize d cats while their associated dorsal root and the sciatic nerve were l eft intact, locally anesthetized, or locally anesthetized and sectione d, In all three experimental conditions spontaneous discharges were re corded. These discharges occurred in the absence of any electrical sti mulation of the dorsal root or sciatic nerve, and were not due to peri pheral exploration of receptive fields or sustained firing in joint or muscle afferents. The spontaneous discharges were relatively rhythmic , and their firing frequency ranged from 5 to 100 impulses per s. Inte ractions between spontaneous and electrically evoked discharges were o bserved that depended on the impulse's frequency of firing. High frequ ency discharges always abolished low frequency impulses regardless of whether these latter were spontaneous or evoked. Extra spikes and post spike events that followed impulses evoked by stimulation of the dorsa l root or sciatic nerve were also recorded from some spinal ganglion n eurons. These results suggest that spontaneous discharges may originat e within the spinal ganglion itself, and that they can occur under nor mal circumstances.