DIFFERENTIAL EXPRESSION OF THE METABOTROPIC GLUTAMATE-RECEPTOR MGLUR1-ALPHA BY NEURONS AND AXONS IN THE COCHLEAR NUCLEUS - IN-SITU HYBRIDIZATION AND IMMUNOHISTOCHEMISTRY

mGluR1 alpha is a metabotropic glutamate receptor involved in synaptic modifiability. A differential expression in specific neuronal types c ould reflect their different connections and response properties in ce ntral auditory processing. Using in situ hybridization and immunohisto chemistry, we studied mGluR1 alpha receptor expression throughout the cochlear nucleus. Robust labeling occurred in the dorsal cochlear nucl eus and small cell shell, with less in the ventral cochlear nucleus. A mong the most intensely labeled were the granule cells of the small ce ll shell. In the dorsal cochlear nucleus, most cell types expressed me ssage and receptor protein, except granule cells. High levels of recep tor were expressed by corn cells and cartwheel cells. The terminal den drites and synaptic spines of cartwheel and fusiform cells contained r eceptor protein in the molecular layer, where they could synapse with parallel fibers. Fusiform dendrites also expressed mRNA for mGluR1 alp ha. The basal dendrites of fusiform cells contained receptor protein i n the region where they receive cochlear nerve synapses. Immunostainin g of terminal axons was prominent in the molecular layer and the small cell shell, where they were associated with synaptic nests, structure s thought to provide long-term changes in excitability. Differential e xpression levels may reflect different functional requirements of spec ific cell types, including inhibitory interneurons, like corn cells an d cartwheel cells, and excitatory interneurons, like granule cells in the small cell shell, which may participate in local circuits involved in modulatory or gating functions, such as stimulus enhancement or su ppression. In presynaptic axons, mGluR1 alpha may relate to the long-t erm signaling requirements of their modulatory functions. (C) 1998 Wil ey-Liss, Inc.