title: alpha2A-adrenergic receptors in the rat nucleus locus coeruleus: subcellular localization in catecholaminergic dendrites, astrocytes, and presynaptic axon terminals.
abstract: To define the anatomic substrates subserving the inhibitory actions of alpha2-adrenergic receptors (alpha2-ARs) in the locus coeruleus (LC), we used dual-label immunoelectron microscopy with antibodies directed against the A-subtype of alpha2-AR (alpha2A-AR) and the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH). Of the profiles containing peroxidase labeling for alpha2A-AR (alpha2A-AR-IR) in the LC (n=735), most were dendrites ( approximately 50%), glial processes ( approximately 30%), and axon terminals ( approximately 15%). alpha2A-AR-IR was also observed in unmyelinated axons and perikarya. Within dendrites, alpha2A-AR-IR was associated with nonsynaptic regions of the plasma membrane and subsurface cisternae. Approximately 60% of dendrites with alpha2A-AR-IR were dually labeled for TH. Fifty percent of the axon terminals contacting alpha2A-AR-immunoreactive dendrites formed asymmetric (excitatory) synaptic contacts. Axon terminals with alpha2A-AR-IR were not dually labeled for TH and generally formed asymmetric synapses with TH-immunoreactive dendrites that contained or lacked alpha2A-AR-IR. Astrocytic processes exhibiting alpha2A-AR-IR were closely apposed to TH-labeled dendrites. These results extend previous ultrastructural observations of alpha2A-ARs in the LC and suggest that the inhibitory actions of norepinephrine and epinephrine in this region may be mediated by postsynaptic alpha2A-ARs on catecholaminergic dendrites and presynaptic alpha2A-ARs on excitatory inputs to catecholaminergic dendrites. In addition, the localization of alpha2A-AR-IR in astrocytic processes apposed to TH-immunoreactive dendrites suggests a role for alpha2A-ARs in functional interactions between catecholaminergic dendrites and neighboring astrocytes.
authors.affiliation: Neuroscience Graduate Program, University of Virginia, Charlottesville, VA 22908, USA.
authors.forename: A
authors.initials: A
authors.lastname: Lee
authors.forename: D L
authors.initials: DL
authors.lastname: Rosin
authors.forename: E J
authors.initials: EJ
authors.lastname: Van Bockstaele
mesh_terms: D000316:Adrenergic alpha-Agonists; D000818:Animals; D001253:Astrocytes / Q000737:chemistry* / Q000648:ultrastructure; D002395:Catecholamines / Q000032:analysis / Q000502:physiology; D003000:Clonidine; D003712:Dendrites / Q000737:chemistry* / Q000201:enzymology / Q000648:ultrastructure; D008125:Locus Coeruleus / Q000737:chemistry* / Q000502:physiology; D008297:Male; D016253:Microscopy, Immunoelectron; D017729:Presynaptic Terminals / Q000737:chemistry* / Q000201:enzymology / Q000648:ultrastructure; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D018341:Receptors, Adrenergic, alpha-2 / Q000032:analysis / Q000502:physiology*; D014446:Tyrosine 3-Monooxygenase / Q000032:analysis
chemical_list: D000316:Adrenergic alpha-Agonists; D002395:Catecholamines; D018341:Receptors, Adrenergic, alpha-2; D014446:Tyrosine 3-Monooxygenase; D003000:Clonidine