title: Synaptic relationship of the neurons containing a metabotropic glutamate receptor, MGluR5, with nociceptive primary afferent and GABAergic terminals in rat spinal superficial laminae.
abstract: Recent pharmacological evidence showed that metabotropic glutamate receptors (mGluRs), particularly mGluRs1/5, had a potential role in spinal nociceptive processing. However, previous morphological studies on mGluRs have been limited mainly to their distribution in the spinal cord. In the present study, electron microscopic immunocytochemistry was employed to identify the synaptic relationship of the neurons containing mGluR5, with nociceptive primary afferent and gamma-aminobutyric acid-ergic (GABAergic) terminals in the superficial dorsal horn of the spinal cord. Nociceptive C- and A(delta)-primary afferent terminals selectively labeled with horseradish peroxidase conjugated to wheat-germ agglutinin were in asymmetric synaptic contacts with or in direct apposition to mGluR5 positive dendritic profiles. The double-labeling studies revealed that mGluR5 immunoreactive dendrites also received symmetric synaptic contacts from axon terminals labeled with immunogold particles indicating GABA. The present demonstration of mGluR5 neurons receiving inputs from both nociceptive primary afferents and GABAergic terminals of presumed interneurons further supports the involvement of mGluR5 in the transmission and modulation of nociceptive information in the spinal cord.
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Blalock 1415, Johns Hopkins University School of Medicine, 600 North Wolfe Street, Baltimore, MD 21287-4965, USA.
authors.forename: Y X
authors.initials: YX
authors.lastname: Tao
authors.forename: Y Q
authors.initials: YQ
authors.lastname: Li
authors.forename: Z Q
authors.initials: ZQ
authors.lastname: Zhao
authors.forename: R A
authors.initials: RA
authors.lastname: Johns
mesh_terms: D000818:Animals; D007150:Immunohistochemistry; D008297:Male; D008854:Microscopy, Electron; D009411:Nerve Endings / Q000502:physiology* / Q000648:ultrastructure; D009474:Neurons / Q000502:physiology* / Q000648:ultrastructure; D009619:Nociceptors / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000378:metabolism*; D013116:Spinal Cord / Q000502:physiology* / Q000648:ultrastructure; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure; D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: C578937:Grm5 protein, rat; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate; D005680:gamma-Aminobutyric Acid