Subcellular localization of alpha-2A-adrenergic receptors in the rat medial nucleus tractus solitarius: regional targeting and relationship with catecholamine neurons.
alpha-2A-adrenergic receptor (alpha2A-AR) agonists modulate diverse autonomic functions. These actions are believed to involve functionally specialized, second-order neurons in catecholamine-containing portions of the medial nucleus tractus solitarius (mNTS) at both intermediate (NTSi) and caudal (NTSc) levels. However, the cellular mechanisms subserving alpha2A-AR-mediated actions within the mNTS have yet to be established. Immunocytochemistry was employed to examine the subcellular distribution of alpha2A-AR in both the intermediate and caudal mNTS and its association with cells containing the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH). Quantitative regional comparison using immunogold showed that this receptor was distributed differentially to dendrites (NTSi, 46%; NTSc, 31%) and glia (NTSi, 29%; NTSc, 48%) at different levels of the NTS. Somata, axons, and terminals less frequently contained alpha2A-AR. The subcellular distribution of alpha2A-AR relative to catecholaminergic neurons also was similar within both subregions. Approximately 50% of alpha2A-AR-labeled somata also contained TH. In somatic profiles, alpha2A-AR labeling was often found in the cytosol and in association with endoplasmic reticulum and Golgi complexes, sites of receptor synthesis and trafficking. Approximately 20% of alpha2A-AR-immunoreactive dendrites also contained TH, where the receptor was often found on extrasynaptic portions of the plasma membrane near unlabeled terminals, some of which made symmetric contacts. However, TH-labeled terminals and dendrites usually were detected in the neuropil at a short distance (<10 microm) from alpha2A-AR-labeled neurons. alpha2A-AR-labeled glia frequently apposed unlabeled dendrites and terminals and were often located near TH-immunoreactive dendrites. These results indicate that, within the mNTS, alpha2A-AR is involved in a variety of autonomic processes, including postsynaptic modulation of mostly noncatecholaminergic dendrites, as well as influencing glia functions.
Department of Neurology and Neuroscience, Division of Neurobiology, Weill Medical College of Cornell University, New York, New York 10021, USA. mjg2003@mail.med.cornell.edu
M J
MJ
Glass
J
J
Huang
S A
SA
Aicher
T A
TA
Milner
V M
VM
Pickel
D000818:Animals; D002395:Catecholamines / Q000378:metabolism; D007150:Immunohistochemistry; D008297:Male; D009474:Neurons / Q000378:metabolism; D020033:Protein Isoforms / Q000378:metabolism; D051381:Rats / Q000378:metabolism*; D017207:Rats, Sprague-Dawley; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D017552:Solitary Nucleus / Q000166:cytology / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism*; D014018:Tissue Distribution; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
D002395:Catecholamines; D020033:Protein Isoforms; D011942:Receptors, Adrenergic, alpha; D014446:Tyrosine 3-Monooxygenase