Karunanithi Shanker, Marin Leo, Wong Kar, Atwood Harold L
Department of Physiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8.
J Neurosci. 2002 Dec 1;22(23):10267-76. doi: 10.1523/JNEUROSCI.22-23-10267.2002.
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 at Drosophila 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 and lap) 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 of Drosophila result in part from intrinsic differences in vesicle size.
化学突触处的量子大小和变化可以在突触前由从突触小泡释放的神经递质的量来决定，或者在突触后由可用于激活的受体数量来决定。我们在由支配同一肌肉细胞的两个不同运动神经元形成的果蝇谷氨酸能神经肌肉突触处研究了这些可能性。在这两个神经元的野生型突触处，我们发现量子大小的差异对应于平均突触小泡体积的差异。同样的发现也适用于两个突触小泡大小发生改变的突变体（dlg和lap）。野生型和突变型突触处的量子方差相似，并且可以由小泡体积的变化来解释。几种不同基因型的量子大小与小泡体积之间的线性关系表明，在所有情况下谷氨酸都被稳态调节到相同的小泡内浓度。因此，果蝇谷氨酸能神经元之间突触强度的功能差异部分源于小泡大小的内在差异。
