Abstract
The main source of excitation to the ventral cochlear nucleus (VCN) is from glutamatergic auditory nerve afferents, but the VCN is also innervated by two groups of cholinergic efferents from the ventral nucleus of the trapezoid body. One arises from collaterals of medial olivocochlear efferents, and the other arises from neurons that project solely to the VCN. This study examines the action of cholinergic inputs on stellate cells in the VCN. T stellate cells, which form one of the ascending auditory pathways to the inferior colliculus, and D stellate cells, which inhibit T stellate cells, are distinguished electrophysiologically. Whole-cell recordings from stellate cells in slices of the VCN of mice demonstrate that most T stellate cells are excited by cholinergic agonists through three types of receptors, whereas all D stellate cells tested were insensitive to cholinergic agonists. Nicotinic excitation in T stellate cells has two components. The faster component was blocked by alpha-bungarotoxin and methyllycaconitine, suggesting that receptors contained alpha7 subunits; the slower component was insensitive to both. Muscarinic receptors excite T stellate cells by blocking a voltage-insensitive, "leak" potassium conductance. Our results suggest that cholinergic efferent innervation enhances excitation by sounds of T stellate cells, opposing the inhibitory action of cholinergic innervation in the cochlea that is conveyed indirectly through the glutamatergic afferents. The inhibitory action of D stellate cells on their targets is probably not affected by cholinergic inputs. Excitation of T stellate cells by cholinergic efferents would be expected to enhance the encoding of spectral peaks in noise.