Figure 4.

Flexor–extensor asymmetry. A1, A2, Flexor and extensor deletions during NMDA/5-HT-induced fictive locomotion in the isolated rat spinal cord. Smoothed and rectified traces of motoneuron activity recorded from the left (lL2, lL5) and right (rL2, rL5) lumbar ventral roots. L2 recordings show predominantly flexor motoneuron activity, while L5 recordings show predominantly extensor activity. The bars above each set of traces show the expected timing of the bursts if the rhythm were unperturbed during the deletion. A1 shows an example of a non-resetting flexor deletion recorded from the lL2 root (indicated by the pink bar) accompanied by tonic activity in the ipsilateral extensor (lL5) root, but with no obvious effects on flexor or extensor activity on the opposite side of the cord. A2 shows non-resetting extensor deletions (marked by blue bars) and a flexor deletion (marked by pink bar). During extensor deletions in lL5, the ipsilateral flexor activity (lL2) and contralateral activities were not perturbed, while the flexor deletion in rL2 was accompanied by tonic activity in the rL5 ventral root. Reproduced from Zhong et al. (2012), their Figure 1Aa,Ba, with permission. B, Changes in flexor and extensor phase durations during NMDA/5-HT-induced fictive locomotion in the isolated mouse spinal cord as a function of locomotor frequency. Red filled squares and blue filled circles show average flexor and extensor phase durations, respectively. Reproduced from Shevtsova et al. (2015), their Figure 9C, with permission.