Probabilistic secretion of quanta from successive sets of visualized varicosities along single sympathetic nerve terminals.

Quantal secretion was recorded from adjacent sets of varicosities along the length of single sympathetic nerve terminals that had been visualized with the fluorescent dye, 3,3-diethyloxardicarbocyanine iodide (DiOC2(5)). Recordings were made with both small diameter microelectrodes (4-6 microns) placed over 1-3 varicosities and large diameter microelectrodes (20-50 microns) placed over 3-7 varicosities. The proportion of trials in which secretion occurred from sets of varicosities declined in general for the adjacent sets of varicosities along the length of single sympathetic nerve terminals. The amplitude-frequency distributions of excitatory junctional currents (EJCs) were in general predicted by Poisson statistics and occasionally by binomial statistics. The mean quantal content of the EJC in general declined over threefold along the length of single sympathetic nerve terminals for adjacent sets of varicosities.