LIGHT AND ELECTRON-MICROSCOPIC DEMONSTRATION OF MGLUR5 METABOTROPIC GLUTAMATE-RECEPTOR IMMUNOREACTIVE NEURONAL ELEMENTS IN THE RAT CEREBELLAR CORTEX

The cellular and subcellular localization of the mGluR5 metabotropic g lutamate receptor subtype was studied in the rat cerebellar cortex, by using the preembedding immunoperoxidase and immunogold techniques. Li ght microscopic observations revealed an abundant, intense labeling of neurons in the granular layer as well as in the molecular layer. Luga ro and Golgi cells exhibited an intense mGluR5 immunoreactivity, while only a fraction of the neurons in the molecular layer were found to b e mGluR5 immunopositive. In addition to a dense plexus of immunoreacti ve dendrites in the molecular layer of the cerebellar cortex, the mGlu R5 immunopositive Golgi cell dendrites resembling axons at the light m icroscopic level were also labeled in the granular layer. At the ultra structural level, mGluR5 immunoreactivity was present in neuronal elem ents postsynaptic to axon terminals of different morphology. By using a pre-embedding immuno-gold method, it was found that mGluR5 immunorea ctivity is accumulated at the plasma membranes extrasynaptically as we ll as at the periphery of the postsynaptic specializations, mainly of the parallel fiber synaptic contacts. These findings provide morpholog ical evidence that mGluR5 is expressed by a population of neurons in t he cerebellar cortex and can synaptically be activated via the paralle l fiber system. (C) 1997 Wiley-Liss, Inc.