Abstract
Dorsal cochlear nucleus (DCN) is known to process complex sounds. The principal cells are known to integrate inputs from auditory nerve fibers (ANFs) and parallel fibers. Axons of granule cells form parallel fibers and convey multimodal information. Granule cells cluster around ventral cochlear nucleus and DCN, and have mutual synapses between inhibitory interneurons; Golgi cells. Thus, Golgi cells may have some modulatory effects on parallel fiber activities; however, little is known. We studied the excitability of Golgi cells and interpreted the roles played by Golgi cells in the neuronal activity of DCN. By depolarizing current injection, Golgi cells fired repetitively and the firing frequency increased with current injection. At higher current intensity (300 pA-400 pA), steep firing adaptation was observed. By hyperpolarizing current injection, a depolarizing voltage sag emerged due to h-current activation. EPSCs evoked by ANFs stimulation were of multiple-peaks suggesting inputs through polysynaptic pathway. Because some cholinergic projections were expected, we tested cholinergic agonists: Carbachol induced a membrane hyperpolarization, accompanied with a decrease in the input resistance; muscarine evoked similar responses. These indicate the activation of muscarinic receptors, which hyperpolarized Golgi cells through the activation of GIRK. Therefore, cholinergic innervation may contribute in modulation of parallel fiber activity through inhibitory Golgi cells. [J Physiol Sci. 2006;56 Suppl:S161]
