Presynaptic electrical coupling in Aplysia: effects on postsynaptic chemical transmission.

The large cholinergic interneuron L10 in the abdominal ganglion of Aplysia mediates both chemical and electrical synaptic transmission. The amplitudes of postsynaptic potentials produced by different branches of L10 are differentially affected when the electrically coupled neuron L20 is depolarized or hyperpolarized. Polarizations applied to L20 are transmitted to L10 branches by the "presynaptic"electrical synapse. Depolarization increases the amplitude of the postsynaptic potential, while hyperpolarization has the opposite effect. The differential effects occur because current supplied through the electrical synapse undergoes more electrotonic decrement for the distant branches than for branches closer to the electrical synapse. These findings indicate that the presynaptic electrically coupled neuron may have an integrative role in the modulation of chemical synaptic efficacy mediated by L10.