Presynaptic activation of silent synapses and growth of new synapses contribute to intermediate and long-term facilitation in Aplysia.
The time course and functional significance of the structural changes associated with long-term facilitation of Aplysia sensory to motor neuron synaptic connections in culture were examined by time-lapse confocal imaging of individual sensory neuron varicosities labeled with three different fluorescent markers: the whole-cell marker Alexa-594 and two presynaptic marker proteins-synaptophysin-eGFP to monitor changes in synaptic vesicle distribution and synapto-PHluorin to monitor active transmitter release sites. Repeated pulses of serotonin induce two temporally, morphologically, and molecularly distinct presynaptic changes: (1) a rapid activation of silent presynaptic terminals by filling of preexisting empty varicosities with synaptic vesicles, which parallels intermediate-term facilitation, is completed within 3-6 hr and requires translation but not transcription and (2) a slower generation of new functional varicosities which occurs between 12-18 hr and requires transcription and translation. Enrichment of empty varicosities with synaptophysin accounts for 32% of the newly activated synapses at 24 hr, whereas newly formed varicosities account for 68%.
Kim
Joung-Hun
JH
Howard Hughes Medical Institute, Columbia University, New York, NY 10032, USA.
Udo
Hiroshi
H
Li
Hsiu-Ling
HL
Youn
Trisha Y
TY
Chen
Mary
M
Kandel
Eric R
ER
Bailey
Craig H
CH
D000818:Animals; D001048:Aplysia / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D017774:Long-Term Potentiation / Q000187:drug effects / Q000502:physiology*; D009475:Neurons, Afferent / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology*; D013569:Synapses / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D013572:Synaptic Vesicles / Q000187:drug effects / Q000378:metabolism / Q000502:physiology