Effects of deafferentation on the electrophysiology of ventral cochlear nucleus neurons

When cochlear pathology impairs the afferent innervation of the ventral coc hlear nucleus (VCN), electrical responses of the auditory brainstem are alt ered and changes in cell and synaptic morphology are observed. However, the impact of deafferentation on the electrical properties of cells in the VCN is unknown. We examined the electrical properties of single neurons in the anterior and posterior VCN following bilateral cochlear removal in young r ats. In control animals, two populations of cells were distinguished: those with a linear subthreshold current-voltage relationship and repetitive fir ing of action potentials with regular interspike intervals (type II, and th ose with rectifying subthreshold current-voltage relationships and phasic f iring of 1-3 action potentials (type II). Measures of action potential shap e further distinguished these two groups. Two weeks following cochlear remo val, both electrical response patterns were still seen. Type I cells showed a higher input resistance. Deafferented single-spiking type II cells were slightly more depolarized, had smaller action potentials, smaller afterhype rpolarizations and shorter membrane time constants, whereas multiple-spikin g type II cells were apparently unaffected. These changes in the electrical properties of VCN neurons following cochlear injury may adversely affect c entral processing of sounds presented acoustically or electrically by prost heses. (C) 2000 Elsevier Science B.V. All rights reserved.