Emergence of posttetanic potentiation as a distinct phase in the differentiation of an identified synapse in Aplysia.

The developmental time course of posttetanic potentiation was studied at an identified chemical synapse. In stage 11 juveniles (3 weeks after metamorphosis), the synaptic connections made by cholinergic neuron L10 onto postsynaptic neurons L2 to L6 were present but showed no posttetanic potentiation. In stage 13 adults (12 weeks after metamorphosis), the same tetanus resulted in an increase of 300 percent in the synaptic potential. A similar pattern was observed at two other identified synapses in the abdominal ganglion. Thus, the initial steps in synapse formation do not include the expression of this plastic capability. Rather, at least 10 weeks is required between the onset of synaptic function and the final expression of mature synaptic properties.