Effects of glutamate and aspartate on tone-evoked and spontaneous activity in posterior ventral and dorsal cochlear nucleus

Abstract

As previously reported [Caspary and Havey, Neurosci. Absts. 5, 17 (1979)], iontophoretic application of the excitant amine acids, glutamate and aspartate, can affect thresholds and response patterns of cochlear nucleus (CN) neurons. This and recent data [Godfrey et al., J. Histochem. Cytochem. 25, 417 (1977); Wenthold, Brain Res. 143, 544 (1978); 162, 338 (1979)] support the hypothesis that glutamate and/or aspartate may be the neurotransmitter(s) at acoustic nerve endings. Control rate-intensity curves were obtained from neurons in the posterior ventral CN “on” and “chopper” responders) and dorsal CN (“pauser” and “build-up” responders). Rate-intensity curves shifted to the left with iontophoretic application of effective dose levels of glutamate and aspartate. Data plotted as percent increase (above control response) against intensity demonstrated that the largest changes occurred at near threshold intensities. “Chopper” neurons displayed increased non-tone-evoked activity at lower doses (2–150 hA) of excitant amino acids than “on,” “pauser,” and “build-up” neurons (100–250 nA). These data further demonstrate that glutamaro and aspartate can differentially affect CN neurons. [Supported by NIH and the Deafness Research Foundation.]