title: Ultrastructural evidence for prominent postsynaptic localization of alpha2C-adrenergic receptors in catecholaminergic dendrites in the rat nucleus locus coeruleus.
abstract: Alpha-2-adrenergic receptor (alpha2-AR) agonists potently inhibit the activity of noradrenergic neurons of the locus coeruleus (LC), an effect that may be mediated by the A- and/ or C-subtypes of alpha2-AR (alpha2A- and alpha2C-AR). To gain insight into the functional significance of these alpha2-AR subtypes in the LC, we have examined their ultrastructural localization by using subtype-specific antibodies. We recently demonstrated that alpha2A-ARs are localized prominently in axon terminals and catecholaminergic dendrites in the LC. In the present study, we sought to identify the subcellular substrates underlying alpha2C-AR actions in the LC by analyzing the ultrastructural distribution of alpha2C-AR immunoreactivity (alpha2C-AR-IR) in sections that were dually labeled for the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH). Alpha-2C-AR-IR was predominantly localized in dendrites, most of which also contained immunolabeling for TH. Within such dendrites, alpha2C-AR-IR was associated with the plasma membrane and occasionally Golgi cisternae and tubulovesicles. The vast majority of dendrites containing alpha2C-AR-IR received asymmetric (excitatory) contacts from unlabeled axon terminals that often contained dense core vesicles. Alpha-2C-AR-IR was observed in some unmyelinated axons and astrocytic processes that were apposed to TH-immunoreactive dendrites but was rarely associated with axon terminals. These results provide the first ultrastructural evidence that alpha2C-ARs (1) are localized postsynaptically in catecholaminergic neurons of the LC and (2) may be strategically situated to modulate the activation of LC neurons by excitatory inputs.
authors.affiliation: Neuroscience Graduate Program, University of Virginia, Charlottesville 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: D000818:Animals; D001253:Astrocytes / Q000737:chemistry; D001369:Axons / Q000737:chemistry; D002395:Catecholamines / Q000032:analysis*; D003712:Dendrites / Q000737:chemistry* / Q000648:ultrastructure; D007150:Immunohistochemistry; D008125:Locus Coeruleus / Q000737:chemistry* / Q000648:ultrastructure; D008297:Male; D016253:Microscopy, Immunoelectron; D009186:Myelin Sheath / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018341:Receptors, Adrenergic, alpha-2 / Q000032:analysis*; D013569:Synapses / Q000737:chemistry*; D014446:Tyrosine 3-Monooxygenase / Q000032:analysis
chemical_list: D002395:Catecholamines; D018341:Receptors, Adrenergic, alpha-2; D014446:Tyrosine 3-Monooxygenase