FIG. 5.

Representative tracings of the conduction of the vasomotor responses induced by focal electrical stimulation of cremasteric arterioles. The microcirculation of the cremaster muscle was prepared as described previously (54, 57). An Ag/AgCl reference electrode immersed in the superfusate was positioned symmetrically around the cremaster, and the arteriole was stimulated with a depolarizing train of pulses (30 Hz, 2 ms, 30 V) for 10 s by using a beveled micropipette (inner diameter, 3–4 μm) filled with 1 M NaCl. The stimulating pipette was inserted under the cremasteric mesothelium and positioned directly above the arteriole at a distance selected to evoke a local constriction of ~50% (54, 57). In separate stimuli, the changes in diameter were observed at the stimulation site (local), and at locations 500, 2,000, and 4,000 μm upstream. Variations in diameter were expressed as percentage of the maximal constriction or dilation possible (% maximum). Maximal diameter was estimated during superfusion of 1 mM adenosine. Focal electrical stimulation of the arteriole evoked a vasoconstriction that was restricted to a short vessel segment (~70–100 μm) at the stimulation site and, in addition, activated a rapid conducted vasodilation that spread along the length of the entire vessel without decay. Horizontal bars indicate the stimulation period.