Long-duration, frequency-dependent motor responses evoked by ventrolateral funiculus stimulation in the neonatal rat spinal cord.

Three variations of the in vitro neonatal rat spinal cord preparation were used to investigate motor responses to stimulation of the ventrolateral funiculus (VLF). In a partially hemisected spinal cord preparation, stimuli elicited frequency-dependent activity in lumbar ventral roots that outlasted the stimulus train by up to 30 s. In a spinal cord-hindlimb preparation, trains of VLF stimuli elicited slow, step-like flexor-extensor hindlimb movement that also persisted for up to 30 s beyond the stimulus. Finally, in a partially hemisected spinal cord preparation where 5-hydroxytryptamine/N-methyl-D-aspartate was used to induce locomotor-like rhythmic activity, short trains of VLF stimuli were capable of perturbing the locomotor rhythm, transiently altering its frequency. Application of pharmacological antagonists suggests that these responses may be the result of stimulation of a descending pathway that includes glutamatergic and catecholaminergic fibres comprising part of a descending locomotor command path.