The metabotropic glutamate receptor subtype mGluR 2/3 is located at extrasynaptic loci in rat spinal dorsal horn synapses

The position of neurotransmitter receptors relative to active neurotransmit ter release sites may be a major factor influencing neuronal responses. The location of the metabotropic glutamate receptor subtype mGluR2/3 was inves tigated in synaptic structures in the rat superficial spinal dorsal horn la minae by using a pre-embedding immunogold technique. Immunostaining for mGl uR2/3 occurred in laminae I through III. Gold particles were encountered bo th in the cytosol and along the plasma membrane. Distinctive plasmalemmal i mmunodeposits were detected in vesicle-containing profiles, where they were located to membrane compartments distant from active release sites rather than in the close vicinity of synaptic specialisations. No distinct immunol abelling was observed in profiles meeting characteristics of primary affere nt terminals. The extrasynaptic occurrence of mGluR2/3 suggests a presynapt ic heteroreceptor role for these receptor subtypes in the spinal dorsal hor n. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.