Wang_1996_J.Physiol_491 ( Pt 1)_187

1. The role of actin microfilaments in synaptic transmission was tested by monitoring spontaneous and evoked transmitter release from developing neuromuscular synapses in Xenopus nerve-muscle cultures, using whole-cell recording of synaptic currents in the absence and presence of microfilament-disrupting agents cytochalasins B and D. 2. Treatment with cytochalasins resulted in disruption of microfilament networks in the growth cone and the presynaptic nerve terminal of spinal neurons in Xenopus nerve-muscle cultures, as revealed by rhodamine-phalloidin staining. 3. The same cytochalasin treatment did not significantly affect the spontaneous or evoked synaptic currents during low-frequency stimulation at 0.05 Hz in these Xenopus cultures. Synaptic depression induced by high-frequency (5 Hz) stimulation, however, was reduced by this treatment. Paired-pulse facilitation for short interpulse intervals was also increased by the treatment. 4. These results indicate that disruption of microfilaments alters short-term changes in transmitter release induced by repetitive activity, without affecting normal synaptic transmission at low frequency. 5. Our results support the notion that actin microfilaments impose a barrier for mobilization of synaptic vesicles from the reserve pool, but do not affect the exocytosis of immediately available synaptic vesicles at the active zone.