Diversity in Glycine and NMDA Receptor Subunit Composition in the Rat Cochlear Nucleus and Superior Olivary Complex and Changes with Deafness

Abstract

Much of the processing of ascending auditory information in the auditory brain stem is mediated by synapses using an excitatory or an inhibitory amino acid as transmitters and acting at an amino acid receptor. When adjacent sections are immunostained for gamma aminobutyric acid (GABA), glycine or glutamate, over 90% of the terminals on ventral cochlear nucleus and lateral superior olivary complex principal cells are im- munoreactive for one or more of these amino acids (Altschuler et al, 1993, Juiz et al, 1996, Helfert et al, 1992). While other neurotransmitters such as acetylcholine (e.g. Godfrey et al, 1993) and neuropeptides (e.g. Adams et al, 1993) also have important roles in the auditory brain stem and may often be co-contained in terminals with an amino acid transmitter, certainly amino acid transmitters and receptors have a major role in acoustic signal processing. There is now increasing information that the properties of excitatory and inhibitory amino acid synapses can be influenced by the composition of their receptors. The excitatory amino acid, most likely to be glutamate and the inhibitory amino acids GABA and glycine all act at ionotropic receptors whose properties can vary as a function of their subunit composition. These ionotropic receptors are pentamers with five mem-brane spanning subunits clustered around an ion channel. Depending upon which subunits a neuron uses to compose the complete receptor there can be different binding properties, actions on the ion channel and recovery at the synapses.