Synaptic facilitation in Aplysia explored by random presynaptic stimulation

The identified interneuron L10 in the abdominal ganglion of Aplysia was stimulated to fire action potentials in a random sequence while the early inhibitory potential of its follower cell L2 was recorded. Application of Wiener nonlinear analysis to these data yielded a predictive model of the facilitating postsynaptic potential. The model shows that facilitation changes both the time-course and the magnitude of the early synaptic potential. The facilitated response has a longer duration than the unfacilitated response. Its magnitude is exponentially decreasing with increasing interstimulus interval between test and conditioning stimuli. Facilitation is abolished at short interstimulus intervals. The hypothesis that the magnitude only of transmitter release is increased cannot explain these results. The observed facilitation may be due to characteristics of pre- and postsynaptic morphology.