INVOLVEMENT OF PRESYNAPTIC AND POSTSYNAPTIC MECHANISMS IN POSTTETANICPOTENTIATION AT APLYSIA SYNAPSES

Posttetanic potentiation (PTP) is a common form of short-term synaptic plasticity that is generally thought to be entirely presynaptic. Cons istent with that idea, PTP of evoked excitatory postsynaptic potential s at Aplysia sensory/motor neuron synapses in cell culture was reduced by presynaptic injection of a slow calcium chelator and was accompani ed by an increase in the frequency but not the amplitude of spontaneou s excitatory postsynaptic potentials. However, PTP was also reduced by postsynaptic injection of a rapid calcium chelator or postsynaptic hy perpolarization. Thus, PTP at these synapses is likely to involve a po stsynaptic induction mechanism in addition to the known presynaptic me chanisms.