Alternating rhythmic activity induced by dorsal root stimulation in the neonatal rat spinal cord in vitro

Electrical stimuli applied to a single dorsal root (DR) of the neonatal rat spinal cord in vitro were used to test the possibility that the central pattern generator responsible for locomotion could be activated by synaptic inputs. Brief pulse trains evoked oscillatory patterns recorded from pairs of lumbar ventral roots. These patterns alternated rhythmically between the left and right sides and between predominantly flexor and extensor motoneuronal pools on the same side, thus displaying properties similar to the fictive locomotor pattern elicited by bath-applied excitatory transmitter agonists like NMDA and serotonin. Usually pulse trains rather than single pulses were necessary to induce these patterns, the period of which was independent of stimulation frequency (1-10 Hz) and only moderately dependent on stimulus intensity. Patterns reached a steady rhythm during the stimulus train, lasted for 50 +/- 20 s with gradual period lengthening and finally ceased. Since DR stimuli activated the central pattern generator for locomotion in the rat isolated spinal cord, it is suggested that sensory inputs from the periphery can reach the spinal locomotor network and trigger its operation.