Volume 17, Number 17,
Issue of September 1, 1997
pp. 6798-6806
Copyright ©1997 Society for Neuroscience
Granule Cell Activation of Complex-Spiking Neurons in Dorsal
Cochlear Nucleus
Received March 19, 1997; revised June 5, 1997; accepted June 10, 1997.
Kevin A. Davis and
Eric D. Young
Department of Biomedical Engineering and Center for Hearing
Sciences, Johns Hopkins University, Baltimore, Maryland 21205
Dorsal cochlear nucleus (DCN) principal cells receive, in addition
to their well known auditory inputs, various nonauditory inputs via a
cerebellar-like granule cell circuit located in the superficial layers
of the DCN. Activation of this circuit (granule cell axons make
excitatory synapses on the principal cells but also contact inhibitory
interneurons that project to the principal cells) produces strong
inhibition of the principal cells. Here we investigate the role of
cartwheel cells, 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 the granule cells (i.e., by stimulation of their inputs
from the somatosensory 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-pulse 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 (inhibition-excitation-inhibition) response. As
expected, cartwheel cells are excited by granule cell activation; the
latencies and four-pulse amplitudes 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. Nevertheless, these results show that
cartwheel cells convey inhibitory polysensory information to DCN
principal cells.
Key words:
dorsal cochlear nucleus;
granule cells;
cartwheel cells;
complex spikes;
electrical stimulation;
somatosensory/auditory
interaction