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The Journal of Neuroscience, October 22, 2008, 28(43):10835-10843; doi:10.1523/JNEUROSCI.0924-08.2008

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Cellular/Molecular
Synapsin IIa Controls the Reserve Pool of Glutamatergic Synaptic Vesicles

Daniel Gitler,^1,2 * Qing Cheng,^1 * Paul Greengard,³ and George J. Augustine¹

¹Department of Neurobiology, Duke University Medical Center, Durham, North Carolina 27710, ²Department of Physiology, Ben Gurion University, Beer-Sheva 84105, Israel, and ³Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York, New York 10021

Correspondence should be addressed to George Augustine, Department of Neurobiology, Duke University Medical Center, Box 3209, Durham, NC 27710. Email: georgea{at}neuro.duke.edu

Synapsins regulate synaptic transmission by controlling the reserve pool of synaptic vesicles. Each of the three mammalian synapsin genes is subject to alternative splicing, yielding several isoforms whose roles are unknown. To investigate the function of these isoforms, we examined the synaptic effects of introducing each isoform into glutamatergic cultured hippocampal neurons from synapsin triple knock-out mice. Remarkably, we found that synapsin IIa was the only isoform that could rescue the synaptic depression phenotype of the triple knock-out mice; other isoforms examined, including the well-studied synapsin Ia isoform, had no significant effect on the kinetics of synaptic depression. The slowing of synaptic depression by synapsin IIa was quantitatively paralleled by an increase in the density of reserve pool synaptic vesicles, as measured either by fluorescent tagging of the vesicle protein synaptobrevin-2 or by staining with the styryl dye FM4–64 [N-(3-triethylammoniumpropyl)-4-(6-(4-diethylamino)phenyl)-hexatrienyl)pyridinium dibromide]. Our results provide further support for the hypothesis that synapsins define the kinetics of synaptic depression at glutamatergic synapses by controlling the size of the vesicular reserve pool and identify synapsin IIa as the isoform primarily responsible for this task.

Key words: neurotransmitter release; synaptic vesicle trafficking; synaptic plasticity; alternative splice variants; synaptic physiology; glutamatergic neurons

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Received March 1, 2008; revised Aug. 13, 2008; accepted Sept. 12, 2008.

Correspondence should be addressed to George Augustine, Department of Neurobiology, Duke University Medical Center, Box 3209, Durham, NC 27710. Email: georgea{at}neuro.duke.edu

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