Figure 2.

Excitatory effects from ventral root conditioning are sensitive to cholinergic and glutamatergic receptor antagonists. A, Addition of mecamylamine (mec) significantly decreased the recurrent excitatory effects of L5 ventral root conditioning on an L5 reflex (∗p < 0.05; n = 25). B, Essential role of AMPA/kainate receptors in the expression of VRERs. Drugs and applied concentrations are shown on the abscissa. Note that CNQX had a greater effect on the ventral-root-evoked but not the dorsal-root-evoked reflex. Peak amplitudes were measured from the first 100 ms after stimulus artifact in arbitrary units (A.U.) (∗p < 0.05; n ≥4). C, NMDA receptors contribute to the VRER. Similar results obtained in B except that the order of application of non-NMDA and NMDA receptor antagonists is reversed. Sample raw traces are shown within each treatment group. Ventral root reflexes were evoked by stimulation of L4 at 150 μA, 50 μs, with an interval of 30 s between episodes shown for a given drug application. Note that, whereas high doses of the NMDA receptor antagonist APV did not completely block the ventral-root-evoked reflex, CNQX completely and reversibly blocked the evoked response (∗p < 0.05; n ≥ 3). This experiment was conducted in the presence of bicuculline (5 μm) to facilitate expression of ventral-root-evoked reflexes (see Fig. 3A). Average background noise was subtracted from each of the signals in B and C.