title: Presynaptic control of striatal dopamine neurotransmission in adult vesicular monoamine transporter 2 (VMAT2) mutant mice.
abstract: The vesicular monoamine transporter 2 (VMAT2) plays a pivotal role in regulating the size of vesicular and cytosolic dopamine (DA) storage pools within the CNS, and can thus influence extracellular DA neurotransmission. Transgenic mice have been generated with a dramatically reduced (by approximately 95%) expression of the VMAT2 gene which, unlike complete knockout lines, survive into adulthood. We compared the pre-synaptic regulation of both impulse-dependent (exocytotic) and carrier-mediated (via reversal of the DA transporter, DAT) DA release in the dorsolateral caudate putamen (CPu) of striatal slices derived from adult homozygous VMAT2 mutant and wild-type mice using fast cyclic voltammetry. Impulse-dependent DA release, evoked by a single electrical pulse, was lower in homozygous (116 nm) than wild-type mice (351 nm) indicating smaller vesicular DA stores, an observation supported by the evanescent effect of amfonelic acid (300 nm) in homozygous mice. Amphetamine (2 microm) increased extracellular DA via DAT reversal in both wild-type (by 459 nm) and VMAT2 mutant (by 168 nm, p < 0.01 vs. wild-type) mice. In both cases, the effect was blocked by the DAT inhibitor GBR12935 (1 microm). Simultaneously, amphetamine decreased impulse-dependent DA release, albeit less in homozygous (by 55%) than in wild-type (by 78%) mice. In wild-types, this decrement was largely reversed by GBR12935 but not by the D2/D3 autoreceptor antagonist (-)sulpiride (1 microm). Conversely, in homozygous VMAT2 mutant mice, it was attenuated by (-)sulpiride but not GBR12935. The D2/D3 receptor agonist quinpirole inhibited impulse-dependent DA release with a lower EC50 value in homozygous mice (12 nm) compared with wild-types (34 nm), indicating the compensatory presence of functionally supersensitive release-regulating autoreceptors. However, analysis of DA reuptake kinetics obtained in the absence and presence of DAT blockade (by cocaine and amfonelic acid) revealed only minor differences in DAT functionality. These results demonstrate that impaired vesicular DA storage constrains extracellular DA levels in the dorsolateral CPu whether induced by either impulse-dependent or carrier-mediated mechanisms and that the relative importance of the DAT and terminal autoreceptors as control mechanisms in the actions of amphetamine are reversed in VMAT2 mutant mice.
authors.affiliation: Department of Neuroscience, Barts and The London, Queen Mary's School of Medicine and Dentistry, Queen Mary, University of London, Mile End Road, London E1 4NS, UK. j.patel@qmul.ac.uk
authors.forename: Jyoti
authors.initials: J
authors.lastname: Patel
authors.forename: Katrin A
authors.initials: KA
authors.lastname: Mooslehner
authors.forename: Pok Man
authors.initials: PM
authors.lastname: Chan
authors.forename: Piers C
authors.initials: PC
authors.lastname: Emson
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Stamford
mesh_terms: D000661:Amphetamine / Q000494:pharmacology; D000818:Animals; D017660:Autoreceptors / Q000037:antagonists & inhibitors / Q000378:metabolism; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D003042:Cocaine / Q000494:pharmacology; D003342:Corpus Striatum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism* / Q000493:pharmacokinetics; D018492:Dopamine Antagonists / Q000494:pharmacology; D050483:Dopamine Plasma Membrane Transport Proteins; D004558:Electric Stimulation; D004563:Electrochemistry; D066298:In Vitro Techniques; D008562:Membrane Glycoproteins / Q000172:deficiency* / Q000235:genetics; D049990:Membrane Transport Modulators; D026901:Membrane Transport Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D051379:Mice; D008818:Mice, Neurologic Mutants; D009268:Nalidixic Acid / Q000031:analogs & derivatives; D009287:Naphthyridines / Q000494:pharmacology; D009419:Nerve Tissue Proteins; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D009479:Neuropeptides; D010879:Piperazines / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D050492:Vesicular Biogenic Amine Transport Proteins; D050493:Vesicular Monoamine Transport Proteins
chemical_list: D017660:Autoreceptors; D000697:Central Nervous System Stimulants; D018492:Dopamine Antagonists; D050483:Dopamine Plasma Membrane Transport Proteins; D008562:Membrane Glycoproteins; D049990:Membrane Transport Modulators; D026901:Membrane Transport Proteins; D009287:Naphthyridines; D009419:Nerve Tissue Proteins; D009479:Neuropeptides; D010879:Piperazines; C493453:Slc18a2 protein, mouse; C493215:Slc6a3 protein, mouse; D050492:Vesicular Biogenic Amine Transport Proteins; D050493:Vesicular Monoamine Transport Proteins; D009268:Nalidixic Acid; C044630:1-(2 (diphenylmethoxy)ethyl)-4-(3-phenylpropyl)piperazine; D000661:Amphetamine; D003042:Cocaine; C006486:amfonelic acid; D004298:Dopamine