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The Journal of Neuroscience, November 11, 2009, 29(45):14120-14126; doi:10.1523/JNEUROSCI.1726-09.2009

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Cellular/Molecular
Individual Calcium Syntillas Do Not Trigger Spontaneous Exocytosis from Nerve Terminals of the Neurohypophysis

James M. McNally, Valérie De Crescenzo, Kevin E. Fogarty, John V. Walsh, and José R. Lemos

Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01665

Correspondence should be addressed to Dr. José R. Lemos, University of Massachusetts Medical School, 55 Lake Avenue North S4-137, Worcester, MA 01655. Email: Jose.Lemos{at}umassmed.edu

Recently, highly localized Ca²⁺ release events, similar to Ca²⁺ sparks in muscle, have been observed in neuronal preparations. Specifically, in murine neurohypophysial terminals (NHT), these events, termed Ca²⁺ syntillas, emanate from a ryanodine-sensitive intracellular Ca²⁺ pool and increase in frequency with depolarization in the absence of Ca²⁺ influx. Despite such knowledge of the nature of these Ca²⁺ release events, their physiological role in this system has yet to be defined. Such localized Ca²⁺ release events, if they occur in the precise location of the final exocytotic event(s), may directly trigger exocytosis. However, directly addressing this hypothesis has not been possible, since no method capable of visualizing individual release events in these CNS terminals has been available. Here, we have adapted an amperometric method for studying vesicle fusion to this system which relies on loading the secretory granules with the false transmitter dopamine, thus allowing, for the first time, the recording of individual exocytotic events from peptidergic NHT. Simultaneous use of this technique along with high-speed Ca²⁺ imaging has enabled us to establish that spontaneous neuropeptide release and Ca²⁺ syntillas do not display any observable temporal or spatial correlation, confirming similar findings in chromaffin cells. Although these results indicate that syntillas do not play a direct role in eliciting spontaneous release, they do not rule out indirect modulatory effects of syntillas on secretion.

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Received March 10, 2009; revised Aug. 26, 2009; accepted Sept. 10, 2009.

Correspondence should be addressed to Dr. José R. Lemos, University of Massachusetts Medical School, 55 Lake Avenue North S4-137, Worcester, MA 01655. Email: Jose.Lemos{at}umassmed.edu

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