Submitted on August 28, 2007
Accepted on October 17, 2007
Synaptic inputs to granule cells of the dorsal cochlear nucleus
Veeramuthu Balakrishnan1 and Laurence O Trussell2*
1 Auditory Neuroscience, L-335A, Oregon Health Sciences University, Portland, Oregon, United States; OHRC/Vollum Institute, Oregon Health and Science University, Portland, Oregon, United States
2 Auditory Neuroscience, L-335A, Oregon Health Sciences University, Portland, Oregon, United States
* To whom correspondence should be addressed. E-mail: larry.trussell{at}yahoo.com.
The mammalian dorsal cochlear nucleus (DCN) integrates auditory nerve input with non-auditory signals via a cerebellar-like granule cell circuit. Although granule cells carry non-auditory information to the DCN, almost nothing is known about their physiology. Here we describe electrophysiological features of synaptic inputs to granule cells in the DCN by in vitro patch-clamp recordings from P12 to P22 rats. Granule cells ranged from 6 to 8 µm in cell body diameter and had high input resistance. Excitatory postsynaptic currents consisted of both AMPA receptor-mediated and N-methyl-D-aspartate (NMDA) receptor-mediated currents. Synaptically evoked EPSCs ranged from -25 pA to -140 pA with fast decay time constants. Synaptic stimulation evoked both short and long-latency synaptic responses which summated to spike threshold, indicating the presence of a polysynaptic excitatory pathway in the granule cell circuit. Synaptically evoked IPSCs in Cl-- loaded cells ranged from -30 to -1021 pA and were mediated by glycine and, to a lesser extent, GABAA receptors. Unlike cerebellar granule cells, DCN granule cells lacked tonic inhibition by GABA. The glycinergic synaptic conductance was mediated by heteromeric glycine receptors and was far stronger than the glutamatergic conductance, suggesting that glycinergic neurons may act to gate non-auditory signals in the DCN.
