Serotonin stimulates phosphorylation of Aplysia synapsin and alters its subcellular distribution in sensory neurons.
Only a small fraction of neurotransmitter-containing synaptic vesicles (SVs), the readily releasable pool, is available for fast Ca(2+)-induced release at any synapse. Most SVs are sequestered at sites away from the plasma membrane and cannot be exocytosed directly. Recruitment of SVs to the releasable pool is thought to be an important component of short-term synaptic facilitation by serotonin (5-HT) at Aplysia sensorimotor synapses. Synapsins are associated with SVs and hypothesized to play a central role in the regulation of SV mobilization in nerve terminals. Aplysia synapsin was cloned to examine its role in synaptic plasticity at the well characterized sensorimotor neuron synapse of this animal. Acute 5-HT treatment of ganglia induced synapsin phosphorylation. Immunohistochemical analyses of cultured Aplysia neurons revealed that synapsin is distributed in distinct puncta in the neurites. These puncta are rapidly dispersed after treatment of the neurons with 5-HT. The dispersion of synapsin puncta by 5-HT was fully reversible after washout of the modulator. Both 5-HT-induced phosphorylation and dispersion of synapsin were mediated, at least in part, by cAMP-dependent protein kinase and mitogen-activated protein kinase. These experiments indicate that synapsin and its regulation by 5-HT may play an important role in the modulation of SV trafficking in short-term synaptic plasticity.
Angers
Annie
A
Department of Neurobiology and Anatomy, W. M. Keck Center for the Neurobiology of Learning and Memory, The University of Texas-Houston Medical School, Houston, Texas 77030, USA.
Fioravante
Diasinou
D
Chin
Jeannie
J
Cleary
Leonard J
LJ
Bean
Andrew J
AJ
Byrne
John H
JH
D000818:Animals; D000918:Antibody Specificity; D001048:Aplysia; D002478:Cells, Cultured; D003001:Cloning, Molecular; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials; D005724:Ganglia / Q000737:chemistry / Q000187:drug effects / Q000502:physiology; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D008969:Molecular Sequence Data; D009473:Neuronal Plasticity; D009475:Neurons, Afferent / Q000378:metabolism* / Q000502:physiology; D010766:Phosphorylation; D020033:Protein Isoforms / Q000235:genetics / Q000276:immunology; D021381:Protein Transport; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D016704:Synapsins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D013572:Synaptic Vesicles / Q000378:metabolism
D004791:Enzyme Inhibitors; D020033:Protein Isoforms; D012702:Serotonin Antagonists; D016704:Synapsins; D012701:Serotonin; D017868:Cyclic AMP-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases