DIFFERENTIAL EXPRESSION OF N-METHYL-D-ASPARTATE RECEPTOR IN THE COCHLEAR NUCLEUS OF THE MOUSE

Glutamate is used in the cochlear nucleus as a neurotransmitter by coc hlear nerve synapses and by local circuits of granule cell axons. In t he present study, immunocytochemistry and in situ hybridization were u sed to identify different types of neurons expressing N-methyl-D-aspar tate receptor subunit 1 (NMDAR1) in the mouse cochlear nucleus. N-Meth yl-D-aspartate receptor subunit 1 was expressed in most neuronal types , but granule cells in the dorsal cochlear nucleus had little, if any, expression, unlike their heavily labeled counterparts in the small ce ll shell and cerebellum. The findings do not support an analogy betwee n the dorsal cochlear nucleus and the cerebellar cortex. In the cochle ar nucleus the most heavily labeled structures were dendrites in the s mall cell shelf and superficial dorsal cochlear nucleus, including the fusiform cell apical dendrites, which are targets of granule cell axo ns. However, fusiform cell basal dendrites, which are the synaptic sit es of cochlear nerve fibers, did not express N-methyl-D-aspartate rece ptor subunit 1. Thus different parts of the fusiform cells can have di fferent subunits in their glutamate receptors. Also branches of the sa me cochlear nerve axons projecting to the octopus, stellate, and bushy cells of the ventral cochlear nucleus can use N-methyl-D-aspartate re ceptor, while their branches to fusiform cells cannot. Each cochlear n ucleus neuron type has a characteristic lever of N-methyl-D-aspartate receptor subunit 1 expression. Each type differs in its auditory respo nse properties, which may depend on synaptic activities requiring diff erent glutamate subunit patterns. Copyright (C) 1996 IBRO. Published b y Elsevier Science Ltd.