ALPHA(2A)-ADRENERGIC RECEPTORS IN THE RAT NUCLEUS LOCUS-COERULEUS - SUBCELLULAR-LOCALIZATION IN CATECHOLAMINERGIC DENDRITES, ASTROCYTES, AND PRESYNAPTIC AXON TERMINALS
A. Lee et al., ALPHA(2A)-ADRENERGIC RECEPTORS IN THE RAT NUCLEUS LOCUS-COERULEUS - SUBCELLULAR-LOCALIZATION IN CATECHOLAMINERGIC DENDRITES, ASTROCYTES, AND PRESYNAPTIC AXON TERMINALS, Brain research, 795(1-2), 1998, pp. 157-169
To define the anatomic substrates subserving the inhibitory actions of
alpha(2)-adrenergic receptors (alpha(2)-ARs) in the locus coeruleus (
LC), we used dual-label immunoelectron microscopy with antibodies dire
cted against the A-subtype of alpha(2)-AR (alpha(2A)-AR) and the catec
holamine-synthesizing enzyme tyrosine hydroxylase (TH). Of the profile
s containing peroxidase labeling for alpha(2A)-AR (alpha(2A)-AR-IR) in
the LC (n = 735), most were dendrites (similar to 50%), glial process
es (similar to 30%), and axon terminals (similar to 15%). alpha(2A)-AR
-IR was also observed in unmyelinated axons and perikarya. Within dend
rites, alpha(2A)-AR-IR was associated with nonsynaptic regions of the
plasma membrane and subsurface cisternae. Approximately 60% of dendrit
es with alpha(2A)-AR-DR were dually labeled for TH. Fifty percent of t
he axon terminals contacting alpha(2A)-AR-immunoreactive dendrites for
med asymmetric (excitatory) synaptic contacts. Axon terminals with alp
ha(2A)-AR-IR were not dually labeled for TH and generally formed asymm
etric synapses with TH-immunoreactive dendrites that contained or lack
ed alpha(2A)-AR-IR. Astrocytic processes exhibiting alpha(2A)-AR-LR we
re closely apposed to TH-labeled dendrites, These results extend previ
ous ultrastructural observations of alpha(2)-ARs in the LC and suggest
that the inhibitory actions of norepinephrine and epinephrine in this
region may be mediated by postsynaptic alpha(2A)-ARs on catecholamine
rgic dendrites and presynaptic alpha(2A)-ARs on excitatory inputs to c
atecholaminergic dendrites. In addition, the localization of alpha(2A)
-AR-IR in astrocytic processes apposed to TH-immunoreactive dendrites
suggests a role for alpha(2A)-ARs in functional interactions between c
atecholaminergic dendrites and neighboring astrocytes. (C) 1998 Elsevi
er Science B.V. All rights reserved.