title: Alpha(2A)-adrenergic receptors are present in mu-opioid receptor containing neurons in rat medial nucleus tractus solitarius.
abstract: Agonists of the alpha-2A-adrenergic- (alpha(2A)-AR) and the mu-opioid-receptor (muOR) jointly affect autonomic functions that are also disregulated in animals undergoing withdrawal from chronic administration of the muOR agonist morphine. Cardiovascular and gastrointestinal reflexes are mediated, in part, by the medial nucleus of the solitary tract (mNTS) at caudal (cNTS) and intermediate (iNTS) subregions. Together, this evidence suggests that alpha(2A)-AR and muOR may be colocalized within many of the same neuronal profiles in both the intermediate and caudal mNTS. In order to examine whether alpha(2A)-AR and muOR are present within common somata, dendrites, or axon terminals in the mNTS, we used electron microscopic immunocytochemistry for the detection of antisera against each receptor at intermediate and caudal levels of this brain region. Most of the dually labeled profiles were somata and dendrites. Of all dual-labeled profiles in the iNTS 49% were somata and were 47% dendrites, whereas in the cNTS 61% were somata and 32% were dendrites. Within dual-labeled profiles, the intracellular distribution of alpha(2A)-AR and muOR differed. MuOR was more frequently associated with the plasmalemma, whereas alpha(2A)-AR was often affiliated with vesicular organelles. Few axon terminals, and even fewer glia, contained both markers. We also frequently observed single-labeled alpha(2A)-AR glia that apposed exclusively muOR-containing dendrites or axon terminals. These findings indicate that somata and dendrites contain functional sites for convergent muOR and alpha(2A)-AR activation. In addition, each receptor is positioned for involvement in intercellular signaling between apposed neurons and glia. Activation of alpha(2A)-AR on muOR-containing somata or dendrites, or on glia apposed to muOR-containing neurons, may help to account for the efficacy of alpha(2A)-AR agonists in relieving some of the autonomic symptoms of opiate withdrawal.
authors.affiliation: Department of Neurology and Neuroscience, Division of Neurobiology, Weill Medical College of Cornell University, 410 E. 69th Street, New York, NY 10021, USA. mjg2003@mail.med.cornell.edu
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Glass
authors.forename: Virginia M
authors.initials: VM
authors.lastname: Pickel
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D001341:Autonomic Nervous System / Q000378:metabolism* / Q000648:ultrastructure; D002320:Cardiovascular Physiological Phenomena; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D003600:Cytosol / Q000378:metabolism / Q000648:ultrastructure; D003712:Dendrites / Q000378:metabolism / Q000648:ultrastructure; D005769:Gastrointestinal Motility / Q000502:physiology; D007150:Immunohistochemistry; D008297:Male; D008854:Microscopy, Electron; D009294:Narcotics / Q000494:pharmacology; D009457:Neuroglia / Q000378:metabolism / Q000648:ultrastructure; D009474:Neurons / Q000378:metabolism* / Q000648:ultrastructure; D009293:Opioid-Related Disorders / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D017729:Presynaptic Terminals / Q000378:metabolism / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism* / Q000648:ultrastructure; D017450:Receptors, Opioid, mu / Q000378:metabolism* / Q000648:ultrastructure; D017552:Solitary Nucleus / Q000378:metabolism* / Q000648:ultrastructure; D013375:Substance Withdrawal Syndrome / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D017833:Visceral Afferents / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: C547770:Adra2a protein, rat; D000316:Adrenergic alpha-Agonists; D009294:Narcotics; D018341:Receptors, Adrenergic, alpha-2; D017450:Receptors, Opioid, mu