The vesicular monoamine transporter 2 is present in small synaptic vesicles and preferentially localizes to large dense core vesicles in rat solitary tract nuclei.

Abstract

In central neurons, monoamine neurotransmitters are taken up and stored within two distinct classes of regulated secretory vesicles: small synaptic vesicles and large dense core vesicles (DCVs). Biochemical and pharmacological evidence has shown that this uptake is mediated by specific vesicular monoamine transporters (VMATs). Recent molecular cloning techniques have identified the vesicular monoamine transporter (VMAT2) that is expressed in brain. This transporter determines the sites of intracellular storage of monoamines and has been implicated in both the modulation of normal monoaminergic neurotransmission and the pathogenesis of related neuropsychiatric disease. We used an antiserum against VMAT2 to examine its ultrastructural distribution in rat solitary tract nuclei, a region that contains a dense and heterogeneous population of monoaminergic neurons. We find that both immunoperoxidase and immunogold labeling for VMAT2 localize to DCVs and small synaptic vesicles in axon terminals, the trans-Golgi network of neuronal perikarya, tubulovesicles of smooth endoplasmic reticulum, and potential sites of vesicular membrane recycling. In axon terminals, immunogold labeling for VMAT2 was preferentially associated with DCVs at sites distant from typical synaptic junctions. The results provide direct evidence that a single VMAT is expressed in two morphologically distinct types of regulated secretory vesicles in central monoaminergic neurons.The uptake of monoamines into the secretory vesicles of neurons and adrenal chromaffin cells is mediated by specific vesicular monoamine transporters (VMATs) (1). These monoamine transporters use the proton electrochemical gradient to drive monoamine uptake and are potently inhibited by reserpine and tetrabenazine (1). In the rat, two distinct but closely related proteins with these pharmacological characteristics have been identified: one that is detected in chromaffin cells (VMAT1 or CGAT) and one that is expressed in neurons and other cells (VMAT2 or SVAT) (2-4). Recent evidence has suggested that the VMATs may also play a role in neuroprotection since they have the capacity to sequester neurotoxins into vesicles or other acidic intracellular compartments (3, 5, 6). As a result, the VMATs have been implicated both in the modulation of normal monoaminergic neurotransmission and in the pathogenesis of neuropsychiatric disease (7).To determine the potential sites of intracellular storage of monoamines and sequestration of neurotoxins, we examined the in vivo distribution of the VMAT that is expressed in central neurons. We used an anti-peptide antiserum to characterize the ultrastructural localization of VMAT2 in the nuclei of the solitary tract (NTS), which contain a dense and heterogeneous population of monoaminergic neurons (8). We used two distinct immunocytochemical markers: the avidinbiotin immunoperoxidase complex, a highly sensitive technique that maximizes the detection of low-abundance, membrane-bound antigens (9); and immunogold-silver, a less sensitive but p...

A Biochemical and Functional Protein Complex Involving Dopamine Synthesis and Transport into Synaptic Vesicles

“…In neurons and neuroendocrine cells, monoamines are stored in large dense core vesicles (LDCVs) and small synaptic vesicles (SVs) (7)(8)(9)(10)(11) that undergo regulated exocytosis through a complex network of protein-protein interactions (12). Loading of monoamines into LDCVs and SVs of neurons and neuroendocrine cells is mediated by two vesicular monoamine transporter isoforms: VMAT 1 (13) and VMAT 2 (14).…”

“…VMAT 1 is mostly present in LDCVs of neuroendocrine cells, including chromaffin and PC12 cells, whereas VMAT 2 is primarily expressed by monoaminergic neurons of the central nervous system (15). In midbrain DA neurons, VMAT 2 is sorted to LDCVs and SVs in axon terminals and to LDCVs and tubulo-vesicular structures in the somatodendritic compartment (7)(8)(9)(10)(11)15).…”

The use of viral gene transfer in studies of brainstem noradrenergic and serotonergic neurons

“…The predominant population (more than 95%) had a mean quantal content of approximately 1.2 Â 10 5 NA molecules, which may originate from the 80 -120 nm diameter dense core vesicles that have been found in central monoaminergic neurons by EM studies (Bloom & Aghajanian 1968;Nirenberg et al 1995;Pickel et al 1996). As intravesicular NA loading of vesicles is a dynamic process that depends on CA uptake and metabolism, a broad concentration range would be expected within actively signalling tissue.…”

Pancreatic innervation in mouse development and β-cell regeneration

“…Additionally, there is a wealth of evidence suggesting that peripheral sympathetic neurons modulate visceral responses through the slow, nonsynaptic release of monoamines from DCVs in axon terminals (Nirenberg et al 1995;Vizi 1991;Beaudet and Descarries 1978). Monoamines can also be released from dendrites, occasionally by exocytosis from DCVs (Li et al 2005;Nirenberg et al 1995;Morris and Pow 1991;Geffen et al 1976). The ultrastructural studies that would further define the intracellular localization of VMAT2 in postganglionic sympathetic pancreatic neurons have yet to be done.…”

“…The presence of VMAT2 provides clues to the status of autonomic function in developmental and disease states of the pancreas Intracellular localization of VMAT2 to small synaptic vesicles (SSVs) and dense core vesicles (DCVs) has been reported in catecholaminergic neurons in the CNS (Nirenberg et al 1995(Nirenberg et al , 1996(Nirenberg et al , 1997a(Nirenberg et al , 1997b. Additionally, there is a wealth of evidence suggesting that peripheral sympathetic neurons modulate visceral responses through the slow, nonsynaptic release of monoamines from DCVs in axon terminals (Nirenberg et al 1995;Vizi 1991;Beaudet and Descarries 1978).…”