SPONTANEOUS AND SOUND-EVOKED DISCHARGE CHARACTERISTICS OF COMPLEX-SPIKING NEURONS IN THE DORSAL COCHLEAR NUCLEUS OF THE UNANESTHETIZED DECEREBRATE CAT

1. We examined the spontaneous and sound-evoked discharge characterist ics of 20 complex-spiking units recorded in the dorsal cochlear nucleu s (DCN) of 15 unanesthetized, decerebrate cats. 2. The extracellularly recorded complex spikes consisted of bursts of two to five action pot entials whose size gradually decreased during the burst. Complex spike s were observed both in the spontaneous and sound-evoked activity of t he units in our sample. 3. The spontaneous rates (SRs) of DCN complex- spiking units ranged from 0 to 30 spikes/s. Spontaneous activity consi sted of complex and simple (i.e., the common single neuronal action po tential) spikes. Comparison of the SR distributions of the DCN complex -spiking units with that of a total sample of 194 DCN units (from 9 ca ts) suggests that the complex-spiking units tended to be in the lower half of the DCN SR distribution. 4. Sound-evoked discharges could cons ist of both complex and simple spikes. On the basis of their sound-dri ven responses, we divided the DCN complex-spiking units into two group s. The majority (15 of 20, 75%) were weakly driven by pure tones and i nhibited by broadband noise. They tended to have broad response areas. Their response latencies to pure tone and noise stimuli were relative ly long (10-20 ms). The recording depths of these units tended to be s uperficial (i.e., 10 of 15 units were located within 400 mu m of the d orsal surface of the DCN). A minority (5 of 20, 25%) of the complex-sp iking units were strongly driven by pure tone and broadband noise stim uli. These units had more clearly defined excitatory regions of respon se areas than the weakly driven units. Their response latencies to pur e tone and noise stimuli were short (< 10 ms). The recording depths of these units tended to be deeper (i.e., 4 of 5 units were located at 4 00-700 mu m) than those of the weakly driven units. 5. Intracellular r ecording and labeling studies of in vitro DCN slice preparations have correlated complex spikes with the superficially located cartwheel cel ls. Given the complex spikes of the units, many of which were located superficially, we suggest that our sample, particularly the weakly dri ven group of neurons, corresponds to the cartwheel cells. 6. Cartwheel cells are putative inhibitory interneurons whose axons primarily cont act on the main projection neurons of DCN, the fusiform cells. The pre sent finding of sound-evoked discharges by the superficially located c omplex-spiking units suggests that cartwheel cells should play a role in modifying the sound-evoked responses of the fusiform cells.