Figure 1.

Excitatory effects of ventral root stimulation on motoneuron excitability. A, B, Schematic diagram (A) and results of condition/test paradigm (B) at various ventral root conditioning stimulation intensities. Recordings were from the same ventral root (L5) used for conditioning stimulation. Stimulation duration was 50 μs (∗p < 0.05; n = 25). C, D, Schematic diagram (C) and results of condition/test paradigm (D) for assessing changes in strength of the L5 monosynaptic test reflex after L2 ventral root conditioning. Note that the conditioned monosynaptic reflex amplitude almost doubled with a conditioning stimulation intensity of 300 μA, 200 μs (experiment performed in 5 μm bicuculline) (∗p < 0.05; n = 25). E, F, Example showing that ventral root stimulation on its own is capable of producing recurrent excitatory actions that were strong enough to recruit motor activity (recorded as a ventral-root-evoked reflex). E shows the stimulation paradigm, and F displays 10 raw traces superimposed. L4 ventral-root-stimulation-evoked motoneuron (L4 VR) firing in the third (L3 VR) and fifth (L5 VR) ventral root. In this and other figures, downward arrow demarcates stimulation artifact, and upward arrow identifies approximate onset of the evoked response. G, Ten superimposed raw traces demonstrate the requirement for Ca²⁺ in the ACSF for both dorsal (DR)- and ventral (VR)-root-evoked reflexes within the same lumbar segment (stimulation of L5 dorsal root at 300 μA, 50 μs and ventral root at 300 μA, 200 μs, recording from L5 ventral root). In this and the following figures, all error bars show SEM. MN, Motoneuron.