The Journal of Neuroscience, October 15, 1999, 19(20):8721-8729
Department of Physiology, University of Wisconsin Medical School,
Madison, Wisconsin 53706
AMPA receptors mediate rapid glutamatergic synaptic transmission.
In the mammalian cochlear nuclei, neurons receive excitatory input from
either auditory nerve fibers, parallel fibers, or both fiber systems.
The functional correlates of differences in the source of input were
examined by recording AMPA receptor-mediated, miniature EPSCs
(mEPSCs) in whole-cell voltage-clamp mode from identified neurons.
Bushy, octopus, and T-stellate cells of the ventral cochlear nucleus
(VCN) and tuberculoventral cells of the dorsal cochlear nucleus (DCN)
receive most of their excitatory input from the auditory nerve;
fusiform cells receive excitatory inputs from both the auditory nerve
and parallel fibers; cartwheel cells receive excitatory input from
parallel fibers alone. mEPSCs from bushy, octopus, T-stellate, and
tuberculoventral cells had significantly faster decay time constants
(0.35-0.40 msec) than did those from fusiform and cartwheel cells
(1.32-1.79 msec). Some fusiform cells had two populations of mEPSCs
with distinct time courses. mEPSCs in cells with auditory nerve input
alone were inhibited by philanthotoxin, a blocker of calcium-permeable AMPA receptors, whereas mEPSCs in cells with parallel fiber input were
not. Thus AMPA receptors postsynaptic to the auditory nerve differ from
those postsynaptic to parallel fibers both in channel-gating kinetics
and in their permeability to calcium. These results confirm the
conclusion that synaptic AMPA receptors are specialized according to
the source of input (Hunter et al., 1993; Rubio and Wenthold, 1997;
Wang et al., 1998).
Key words: mEPSCs; cochlear nuclei; AMPA receptors; auditory nerve; parallel fibers; time course; auditory pathways; philanthotoxin; calcium permeability; GluR2 subunit; polyamine