Nj. Emptage et Tj. Carew, LONG-TERM SYNAPTIC FACILITATION IN THE ABSENCE OF SHORT-TERM FACILITATION IN APLYSIA NEURONS, Science, 262(5131), 1993, pp. 253-256
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 lon
g-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) concentra
tions of 5-HT below threshold for the induction of short-term facilita
tion nonetheless induced long-term facilitation; and (iii) localized a
pplication of 5-HT to the sensory neuron cell body and proximal synaps
es induced long-term facilitation in distal synapses that were not exp
osed to 5-HT and had not expressed short-term facilitation. These resu
lts suggest that short-term and long-term synaptic facilitation are in
duced in parallel in the sensory neurons and that the short-term proce
ss, because it is induced and expressed at the synapse, can occur loca
lly, but the long-term process, because of its dependence on a nuclear
signal, is expressed throughout the neuron.