The large number of metabotropic glutamate receptor subtypes suggests diverse roles in brain function, although specific distribution patterns can give clues to subtype-specific functions [Hayashi Y. et al. (1993) Nature 366, 687-690; Nakajima Y. et al. (1993) J. biol. Chem. 268, 11868-11873; Nomura A. et al. (1994) Cell 77, 361-369; Ohishi H. et al. (1993), 1009-1018]. The metabotropic glutamate receptor mGluR7 is sensitive to the agonist L-2-amino-4-phosphonobutyric acid, a presynaptic inhibitor of neurotransmitter release. We examined the anatomic distribution of mGluR7 messenger RNA expression by in situ hybridization in the developing and adult rat central nervous systems. Our results demonstrate that mGluR7 messenger RNA is among the most widely distributed of metabotropic glutamate receptors in both the developing and adult rat nervous system and that mGluR7 messenger RNA is expressed in most neuronal groups known to respond to L-2-amino-4-phosphonobutyric acid, including mitral cells of the olfactory bulb, granule cells of the dentate gyrus and neurons of the entorhinal cortex and dorsal root ganglion. mGluR7 exhibits preferential expression in sensory afferent pathways and is highly represented in the periventricular zone of the hypothalamus, the latter implying a modulatory role for mGluR7 in neuroendocrine pathways. Most strikingly, the majority of neurons at all levels of olfactory circuitry are among the areas of highest mGluR7 messenger RNA content. The anatomic distribution of mGluyR7 messenger RNA suggests that mGluR7 activation may participate in the processing of hippocampal, sensory and olfactory information.