Exogenous synapsin I promotes functional maturation of developing neuromuscular synapses.
We have investigated the possible role of synapsin I, a nerve terminal-specific protein, in the maturation of neuromuscular synapses in Xenopus cell cultures. Purified synapsin I was loaded into embryonic spinal neurons by injection of the protein into one of the early blastomeres of a Xenopus embryo. At synapses made by synapsin I-loaded neurons, spontaneous synaptic currents occurred with higher frequency and amplitude, and the amplitude exhibited an earlier appearance of a bell-shaped distribution. These characteristics are indicative of more mature quantal secretion. Impulse-evoked synaptic currents also showed a significant increase in amplitude. Using cell manipulation techniques, enhanced transmitter release from synapsin I-loaded neurons was shown to occur at the onset of synaptogenesis, suggesting a presynaptic developmental action of synapsin I prior to synaptic contact. Taken together, these results suggest that endogenous synapsin I may participate in the functional maturation of synapses.
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Laboratory of Molecular and Cellular Neuroscience, Rockefeller University, New York, New York 10021.
Greengard
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D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D004553:Electric Conductivity; D066298:In Vitro Techniques; D009469:Neuromuscular Junction / Q000254:growth & development*; D013569:Synapses / Q000502:physiology*; D016704:Synapsins / Q000378:metabolism*; D009435:Synaptic Transmission; D013997:Time Factors; D014982:Xenopus laevis / Q000196:embryology
D016704:Synapsins; D000109:Acetylcholine