Distribution of mGluR1α and mGluR5 immunolabeling in primate prefrontal cortex

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Abstract
Metabotropic glutamate receptors (mGluRs) mediate important modulatory glutamatergic influences throughout the brain. However, the specific localization and functions of group I mGluR subtypes (mGluR1α and mGluR5) in cortical neurotransmission are not well known, particularly in primates. To address this issue, we used immunoelectron microscopy to compare the subcellular localizations of mGluR1α and mGluR5 in the prefrontal cortex of macaque monkeys. Both receptor subtypes were found in a variety of subcellular compartments, including spines, dendrites, preterminal axons, axon terminals, and glia; however, quantitative differences were found in the relative abundance of labeled elements for each receptor. The mGluR1α‐immunoreactive (‐IR) elements were overwhelmingly the spines and dendrites, with labeled terminals, axons, and glia seen more rarely. The mGluR5‐IR elements were also mostly spines and dendrites, but the proportion of labeled unmyelinated axons, terminals, and glia was higher than for mGluR1α‐IR elements. Double labeling with SMI‐32 and parvalbumin confirmed that both receptors were found in pyramidal cell and interneuron dendrites. The localization of mGluR1α to pyramidal cells in primate cortex contrasts with reports that mGluR1α is found almost exclusively in interneurons in rodent cortex. By using double labeling, we found no evidence for mGluR1α or mGluR5 in dopaminergic afferents to prefrontal cortex. The data presented here provide an anatomical substrate for a differential role of mGluR1α and mGluR5 in post‐and presynaptic actions of glutamate in primate prefrontal cortex. They further suggest differences in the cortical distribution of group I mGluRs between primates and rodents. J. Comp. Neurol. 467:521–535, 2003.

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