Serotonin modulates neuromuscular transmission in frogs

The effect of 5-hydroxytryptamine (serotonin) on neuromuscular transmission in frog skeletal muscle was studied using voltage clamp technique. Serotonin produced no effect on end-plate currents during low frequency electrical stimulation of the motor nerve, but increased the amplitude depression of multiquantal currents during high-frequency stimulation similar to motor commands fired by motoneurons. It was shown that the inhibitory effect of serotonin on neuromuscular transmission is determined by slow potential-dependent block of open ionic channels in the postsynaptic membrane accumulating during rhythmic activation of the synapse.