Non-linear summation at an identified synapse in Aplysia.

The degree of non-linear summation of postsynaptic potentials at the RC1-R15 synapse in Aplysia californica was determined. Two independent methods were used to reduce the size of the postsynaptic potential: voltage clamp of the postsynaptic potential and pharmacologic blockade of the postsynaptic receptors. Results from both methods demonstrate that non-linear summation is significant at this synapse. The non-linear correction formula of Stevens produces a reasonable compensation of measured EPSP amplitudes for the contribution of non-linear summation. The experiments also provide additional evidence that all of the variations in EPSP amplitude seen at this synapse are due to changes in the number of postsynaptic channels opened and not due to changes in the non-synaptic membrane properties of R15.