RT Journal Article SR Electronic T1 Quantal Size and Variation Determined by Vesicle Size in Normal and Mutant Drosophila Glutamatergic Synapses JF The Journal of Neuroscience JO J. Neurosci. FD Society for Neuroscience SP 10267 OP 10276 DO 10.1523/JNEUROSCI.22-23-10267.2002 VO 22 IS 23 A1 Shanker Karunanithi A1 Leo Marin A1 Kar Wong A1 Harold L. Atwood YR 2002 UL http://www.jneurosci.org/content/22/23/10267.abstract AB Quantal size and variation at chemical synapses could be determined presynaptically by the amount of neurotransmitter released from synaptic vesicles or postsynaptically by the number of receptors available for activation. We investigated these possibilities atDrosophila glutamatergic neuromuscular synapses formed by two separate motor neurons innervating the same muscle cell. At wild-type synapses of the two neurons we found a difference in quantal size corresponding to a difference in mean synaptic vesicle volume. The same finding applied to two mutants (dlg andlap) in which synaptic vesicle size was altered. Quantal variances at wild-type and mutant synapses were similar and could be accounted for by variation in vesicular volume. The linear relationship between quantal size and vesicular volume for several different genotypes indicates that glutamate is regulated homeostatically to the same intravesicular concentration in all cases. Thus functional differences in synaptic strength among glutamatergic neurons ofDrosophila result in part from intrinsic differences in vesicle size.