[Postsynaptic potentiation and desensitization at the myoneural synapse of the frog induced by rhythmic stimulation of a motor nerve].

The contribution of postsynaptic potentiation (PSP) and desensitization (DS) to the changes in the amplitude and time course of miniature end-plate currents (mepc) recorded after 10 Hz repetitive stimulation of the motor nerve during 5 or 60 s was studied in the experiments on "cut" nerve-muscle preparation with inhibited acetylcholinesterase. After the short (5 s) train the mepc amplitude did not differ from the initial one while the decay time constant (tau mepc) increased by 32% (indication of PSP). The decrease of mepc amplitude by 23% was observed after the end of the long (60 s) train, while tau mepc did not differ from the original one (indication of DS). Similar but more marked two-phase changes occurred in the time course of end-plate currents. These effects were not observed when acetylcholinesterase was active. The PSP and DS manifestations were reproduced with acetylcholine addition into the bath. It was possible to change the ratio of PSP and DS under the action of aprodifen.