[Effects of drugs on re-excitability of synapses of isolated frog ganglia].

Effects of different pharmacons on the non-excitable period (NEP) and on the relative excitable period (REP) was studied in the sympathetic ganglionic synapses of the frog (Rana esculenta). Using paired stimulation we demonstrated that hexamethonium, magnesium, pempidine, tetraethylammonium (TEA) and d-tubocurarine chlorides significantly prolonged both NEP and REP at ganglion blocking threshold concentrations. Their maximum effect occurred within 30-60 min after the start of the exposition. Hemicholine and neostigmine prolonged only NEP but not REP while lidocaine influenced neither period applying continuous repeated stimulation at low frequencies (0.1-12.5 Hz). TEA showed no effect, however, at higher frequencies (14.3-20.0 Hz) it exerted a frequency-dependent depressant effect on the amplitude of the compound action potential.