α‐ADRENORECEPTORS AND FACILITATION AT A SYMPATHETIC NEUROEFFECTOR JUNCTION

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Abstract
Excitatory junction potentials (EJP) were recorded from the mouse vas deferens following 5 stimuli at 1 Hz and a single stimulus at times from 100 ms to 9 s later. EJP facilitate and facilitation decayed over a biexponential time course, with time constants of 120 ms and 4.3 s. Clonidine (10-8-10-7 M) depressed EJP amplitude, and also accelerated both phases of the decay of facilitation. Yohimbine (10-7 M) and piperoxan (10-7-10-6 M) increased the amplitude of all but the 1st EJP in a train, and slowed both phases of the decay of facilitation. One way in which prejunctional modulation by .alpha.-adrenoreceptors may occur is by modifying the carry-over of facilitation from 1 stimulus to the next.