Long-term synaptic facilitation in the absence of short-term facilitation in Aplysia neurons.
Serotonin (5-HT) induces both short-term and long-term facilitation of the identified synaptic connections between sensory and motor neurons of Aplysia. Three independent experimental approaches showed that long-term facilitation can normally be expressed in the absence of short-term facilitation: (i) The 5-HT antagonist cyproheptadine blocked the induction of short-term but not long-term facilitation; (ii) concentrations of 5-HT below threshold for the induction of short-term facilitation nonetheless induced long-term facilitation; and (iii) localized application of 5-HT to the sensory neuron cell body and proximal synapses induced long-term facilitation in distal synapses that were not exposed to 5-HT and had not expressed short-term facilitation. These results suggest that short-term and long-term synaptic facilitation are induced in parallel in the sensory neurons and that the short-term process, because it is induced and expressed at the synapse, can occur locally, but the long-term process, because of its dependence on a nuclear signal, is expressed throughout the neuron.
Emptage
N J
NJ
Department of Psychology, Yale University, New Haven, CT 06520.
Carew
T J
TJ
D000704:Analysis of Variance; D000818:Animals; D001048:Aplysia; D003533:Cyproheptadine / Q000494:pharmacology; D008959:Models, Neurological; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects
D003533:Cyproheptadine; D012701:Serotonin