Synaptic activity modulates presynaptic excitability

Synaptic activity modulates synaptic efficacy and is important in learning and development. Here we show that development of excitability in presynapt ic motor neurons required synaptic activation of postsynaptic muscle cells. Synaptic blockade broadened action potentials and decreased repetitive fir ing of presynaptic neurons. Consistent with these findings, synaptic blocka de also decreased potassium-current density in the presynaptic cell. Applic ation of neurotrophin-3, but not related neurotrophins, prevented these cha nges. Recordings from patches of somatic membrane indicated that modificati ons of presynaptic potassium and sodium currents occurred in a remote, nons ynaptic compartment, Thus, activity-dependent postsynaptic signals modulate d presynaptic excitability, potentially regulating transmission at all syna pses of the presynaptic cell.