Fig. 2.

Comparison of facilitatory actions of DOI at 2 stimulation intensities. A and B: top waveforms in first 3 rows are recordings of L5 ventral root activity at the indicated intensities whereas last row is a recording of the dorsal root to identify recruited afferent volleys. Examples represent 5 raw traces superimposed. A: at left, short- and long-latency reflexes are evoked after selective recruitment of Aβ fibers (at 50 μA, 50 μs). Although after DOI washout LLFR is observed at all stimulus intensities, the greatest relative facilitation occurs at the low stimulation strength. B: in this example, reflexes are absent at a low stimulus intensity in control and DOI conditions but both short- and long-latency reflexes become unmasked after DOI washout. Note that in A and B recruitment of C fibers (right) does not enhance LLFR. C: under control conditions, stimulation of the L5 dorsal root (500 μA, 500 μs, 1/30 s) does not evoke reflexes in the L2 ventral root (top row, right column). However, after application of DOI and its wash, L5 dorsal root stimulation now evokes heterosegmental reflexes in the L2 ventral root (bottom row, right column). Gray bars indicate timing for the monosynaptic reflex. Note that there was no evidence of a heterosegmentally evoked monosynaptic reflex. Examples represent 20 superimposed raw traces.