Diversity and plasticity in amino acid receptor subunits in the rat auditory brain stem.

Glutamate, gamma aminobutyric acid (GABA) and glycine receptors have different properties depending on the specific subunit combination utilized. The subunit composition of amino acid receptors may help to shape the responses of neurons and can provide a diversity of response properties in different neuronal types and regions. This allows a synaptic fine tuning for an optimization of processing requirements and may also allow for changes in response to changes in input. This article reviews the diversity that has been found in the subunit composition of GABA, glycine, alpha amino-3-hydroxy-5-methyl-4 isoxazole propionic acid and N-Methyl, D-aspartate (NMDA) receptors in the mammalian auditory brain stem and provides new data on how the NMDAR1 glutamate receptor subunit changes as a consequence of deafness. In the latter study, quantitative in situ hybridization was used to assess NMDAR1 mRNA expression in six cell types of the rat cochlear nucleus. A unilateral cochlear ablation was performed and expression determined in the ipsilateral and contralateral cochlear nucleus 5 and 20 days later. Significantly decreased expression, compared to normal, was found 5 days following deafness, in ipsilateral spherical bushy cells, octopus cells and shell neurons, but not in fusiform cells, corn cells or granule cells. At 20 days the expression was not significantly different from normal in any of the six cell types.