Fluorescent false neurotransmitter reveals functionally silent dopamine vesicle clusters in the striatum

• DOI: 10.1038/nn.4252
• Publication Date: 2016-02-22T17:14:34Z
• Authors: Daniela B Pereira; Yvonne Schmitz; József Mészáros; Paolomi Merchant; Gang Hu; Shu Li; Adam Henke; José E Lizardi-Ortiz; Richard J Karpowicz; Travis J Morgenstern; Mark S Sonders; Ellen Kanter; Pamela C Rodriguez; Eugene V Mosharov; Dalibor Sames; David Sulzer
• Keywords: Male; Mice, Knockout; 0301 basic medicine; Neurotransmitter Agents; Mice, 129 Strain; Dopamine; Presynaptic Terminals; Mice, Transgenic; Article; Corpus Striatum; Exocytosis; 3. Good health; Mice, Inbred C57BL; Mice; 03 medical and health sciences; HEK293 Cells; Organ Culture Techniques; Animals; Humans; Female; Synaptic Vesicles; Cells, Cultured; Fluorescent Dyes

Neurotransmission at dopaminergic synapses has been studied with techniques that provide high temporal resolution, but cannot resolve individual synapses. To elucidate the spatial dynamics and heterogeneity of individual dopamine boutons, we developed fluorescent false neurotransmitter 200 (FFN200), a vesicular monoamine transporter 2 (VMAT2) substrate that selectively traces monoamine exocytosis in both neuronal cell culture and brain tissue. By monitoring electrically evoked Ca(2+) transients with GCaMP3 and FFN200 release simultaneously, we found that only a small fraction of dopamine boutons that exhibited Ca(2+) influx engaged in exocytosis, a result confirmed with activity-dependent loading of the endocytic probe FM1-43. Thus, only a low fraction of striatal dopamine axonal sites with uptake-competent VMAT2 vesicles are capable of transmitter release. This is consistent with the presence of functionally 'silent' dopamine vesicle clusters and represents, to the best of our knowledge, the first report suggestive of presynaptically silent neuromodulatory synapses.