The descending pathway between the central nucleus of the amygdala (CeA) and the dorsal vagal complex (DVC) is an important substrate for autonomic functions associated with emotion. Activity in this circuit is crucially modulated by catecholamines and agonists of the alpha‐2A‐adrenergic receptor (α2A‐AR), which relieve cardiovascular and gastrointestinal symptoms associated with experience of aversive stimuli. The subcellular distribution of α2A‐AR within the CeA, however, has not been characterized. It is also not known if any α2A‐AR‐expressing neurons in the CeA project to the dorsal vagal complex. In order to address these questions, we examined the immunocytochemical labeling of α2A‐AR in the CeA of rats receiving microinjection of the retrograde tracer fluorogold (FG) into the dorsal vagal complex at the level of the area postrema, an area involved in cardiorespiratory and gastrointestinal functions. Of all α2A‐AR‐labeled profiles in the CeA, the majority were either dendrites (42%) or somata (24%). α2A‐AR labeling was often present on the plasmalemma in dendrites and was mainly found in endosome‐like organelles in somata. Of all α2A‐AR immunoreactive somata, 62% also contained immunolabeling for FG and 23% of all dendrites also showed labeling for the retrograde tracer. The intracellular distribution of α2A‐AR did not differ in somata or dendrites with or without detectable FG. The remaining singly labeled α2A‐AR profiles consisted of axons (11%), axon terminals (12%), and glial processes (13%). In numerous instances, α2A‐AR‐labeled glia or axon terminals were apposed to DVC projecting neurons. Together, this evidence suggests that the principal site for α2A‐AR activation is at extrasynaptic sites on dendrites of CeA neurons, many of which project to the DVC and also show endosomal receptor labeling. In addition, these results indicate that activation of α2A‐AR in the CeA may influence the activity of DVC projecting neurons through indirect mechanisms, including changes in presynaptic transmitter release or glial function. These results suggest that α2A‐AR agonists in the CeA may modulate numerous processes including stress‐evoked autonomic reactions and feeding behavior. Synapse 46:258–268, 2002. © 2002 Wiley‐Liss, Inc.
Synapse – Wiley
Published: Dec 15, 2002
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