VISUALIZATION OF THE VESICULAR ACETYLCHOLINE TRANSPORTER IN CHOLINERGIC NERVE-TERMINALS AND ITS TARGETING TO A SPECIFIC POPULATION OF SMALLSYNAPTIC VESICLES

Immunohistochemical visualization of the rat vesicular acetylcholine t ransporter (VAChT) in cholinergic neurons and nerve terminals has been compared to that for choline acetyltransferase (ChAT), heretofore the most specific marker for cholinergic neurons, VAChT-positive cell bod ies were visualized in cerebral cortex, basal forebrain, medial habenu la, striatum, brain stem, and spinal cord by using a polyclonal anti-V AChT antiserum, VAChT-immunoreactive fibers and terminals were also vi sualized in these regions and in hippocampus, at neuromuscular junctio ns within skeletal muscle, and in sympathetic and parasympathetic auto nomic ganglia and target tissues, Cholinergic nerve terminals contain more VAChT than ChAT immunoreactivity after routine fixation, consiste nt with a concentration of VAChT within terminal neuronal arborization s in which secretory vesicles are clustered. These include VAChT-posit ive terminals of the median eminence of the hypothalamus, not observed with ChAT antiserum after routine fixation, Subcellular localization of VAChT in specific organelles in neuronal cells was examined by immu noelectron microscopy in a rat neuronal cell line (PC12-c4) expressing VAChT as well as the endocrine and neuronal forms of the vesicular mo noamine transporters (VMAT1 and VMAT2). VAChT is targeted to small syn aptic vesicles, while VMAT1 is found mainly but not exclusively on lar ge dense-core vesicles. VMAT2 is found on large dense-core vesicles bu t not on the small synaptic vesicles that contain VAChT in PC12-c4 cel ls, despite the presence of VMAT2 immunoreactivity in central and peri pheral nerve terminals known to contain monoamines in small synaptic v esicles, Thus, VAChT and VMATZ may be specific markers for ''cholinerg ic'' and ''adrenergic'' small synaptic vesicles, with the latter not e xpressed in nonstimulated neuronally differentiated PC12-c4 cells.