title: Normal biogenesis and cycling of empty synaptic vesicles in dopamine neurons of vesicular monoamine transporter 2 knockout mice.
abstract: The neuronal isoform of vesicular monoamine transporter, VMAT2, is responsible for packaging dopamine and other monoamines into synaptic vesicles and thereby plays an essential role in dopamine neurotransmission. Dopamine neurons in mice lacking VMAT2 are unable to store or release dopamine from their synaptic vesicles. To determine how VMAT2-mediated filling influences synaptic vesicle morphology and function, we examined dopamine terminals from VMAT2 knockout mice. In contrast to the abnormalities reported in glutamatergic terminals of mice lacking VGLUT1, the corresponding vesicular transporter for glutamate, we found that the ultrastructure of dopamine terminals and synaptic vesicles in VMAT2 knockout mice were indistinguishable from wild type. Using the activity-dependent dyes FM1-43 and FM2-10, we also found that synaptic vesicles in dopamine neurons lacking VMAT2 undergo endocytosis and exocytosis with kinetics identical to those seen in wild-type neurons. Together, these results demonstrate that dopamine synaptic vesicle biogenesis and cycling are independent of vesicle filling with transmitter. By demonstrating that such empty synaptic vesicles can cycle at the nerve terminal, our study suggests that physiological changes in VMAT2 levels or trafficking at the synapse may regulate dopamine release by altering the ratio of fillable-to-empty synaptic vesicles, as both continue to cycle in response to neural activity.
authors.affiliation: Centre for Neuronal Survival and Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada.
authors.forename: Benjamin G
authors.initials: BG
authors.lastname: Croft
authors.forename: Gabriel D
authors.initials: GD
authors.lastname: Fortin
authors.forename: Amadou T
authors.initials: AT
authors.lastname: Corera
authors.forename: Robert H
authors.initials: RH
authors.lastname: Edwards
authors.forename: Alain
authors.initials: A
authors.lastname: Beaudet
authors.forename: Louis-Eric
authors.initials: LE
authors.lastname: Trudeau
authors.forename: Edward A
authors.initials: EA
authors.lastname: Fon
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D004396:Coloring Agents / Q000494:pharmacology; D004298:Dopamine / Q000378:metabolism*; D004705:Endocytosis; D018698:Glutamic Acid / Q000378:metabolism; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000235:genetics*; D026901:Membrane Transport Proteins / Q000235:genetics*; D008636:Mesencephalon / Q000378:metabolism / Q000648:ultrastructure; D051379:Mice; D018345:Mice, Knockout; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence; D009474:Neurons / Q000378:metabolism* / Q000648:ultrastructure; D020033:Protein Isoforms; D013569:Synapses / Q000378:metabolism; D013572:Synaptic Vesicles / Q000502:physiology*; D013997:Time Factors; D050492:Vesicular Biogenic Amine Transport Proteins; D050493:Vesicular Monoamine Transport Proteins
chemical_list: D004396:Coloring Agents; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D020033:Protein Isoforms; C493453:Slc18a2 protein, mouse; D050492:Vesicular Biogenic Amine Transport Proteins; D050493:Vesicular Monoamine Transport Proteins; D018698:Glutamic Acid; D004298:Dopamine