GRANULE CELL ACTIVATION OF COMPLEX-SPIKING NEURONS IN DORSAL COCHLEARNUCLEUS

Dorsal cochlear nucleus (DCN) principal cells receive, in addition to their well known auditory inputs, various nonauditory inputs via a cer ebellar-like granule cell circuit located in the superficial layers of the DCN, Activation of this circuit (granule cell axons make excitato ry synapses on the principal cells but also contact inhibitory interne urons that project to the principal cells) produces strong inhibition of the principal cells. Here we investigate the role of cartwheel cell s, homologs of cerebellar Purkinje cells, in producing this inhibition , The responses of type IV units (one type of principal cells) and of cartwheel cells were recorded to ortho-and antidromic activation of th e granule cells (i.e., by stimulation of their inputs from the somatos ensory cuneate and spinal trigeminal nuclei and by direct stimulation of their parallel fiber axons), Cartwheel cells were identified on the basis of recording depth and complex action potential shape. A four-p ulse facilitation paradigm (four pulses at 50 msec intervals) was used ; this stimulus allows separation of the apparently simple inhibitory somatosensory response-of type IV units into a three-component (inhibi tion-excitation-inhibition) response. As expected, cartwheel cells are excited by granule cell activation; the latencies and four-pulse ampl itudes of these responses correspond to the properties of the second, long-latency inhibitory component of type IV responses. The source of the first, short-latency inhibitory response is still unknown. Neverth eless, these results show that cartwheel cells convey inhibitory polys ensory information to DCN principal cells.