Post-tetanic potentiation

Post-tetanic potentiation (PTP) is the transient increase in neurotransmitter release that follows a brief, high-frequency train of action potentials that can occur within central synapses and Neuromuscular junctions (NMJ). This form of short-term synaptic plasticity increases neurotransmitter release, resulting in a significant increase in evoked postsynaptic response.The resulting increase in synaptic output may last for tens of seconds to several minutes.Research suggests that PTP results from residual Ca2+ accumulation in the presynaptic terminal, which increases quantal release probability and enhances the readily releasable pool of synaptic vesicles.

Source: Wikipedia — Post-tetanic potentiation (CC BY-SA 4.0)