[Responses of the neuromuscular synapses of chronically desympathized frog muscles to tetanic nerve stimulation].

7--14 days after unilateral section of the abdominal sympathetic trunk, the quantum content of the end plate potential (e.p.p.) in the m. sartorius of the frog decreased. The facilitation and fluctuations of the e.p.p. amplitude during train of stimuli (20, 50, 100/sec) became more obvious. Noradrenaline (5-10(-6) g/ml) increased the amplitude of a single e.p.p. and the facilitation during repetitive stimulation. The effect of noradrenaline in sympathectomized muscles was more obvious than in the control muscles. After the noradrenaline administration, the fourfold increase of calcium concentration did not change the amplitude of e.p.p.s or the time course of the facilitation. The mechanism of depolarization--secretion coupling in the nerve terminal seems to be impaired by the sympathectomy.