Treadmill Locomotion in the Intact and Spinal Mouse

Abstract

Because the genetic characteristics of several inbred strains of mice are well identified, their use is becoming increasingly popular in spinal cord injury research. In this context, it appears particularly important to document adequately motor patterns, such as locomotion in normal mice, to establish some baseline values of locomotor characteristics. It also seems crucial to determine the extent to which mice can express a locomotor pattern after a complete spinal transection to establish a baseline on which one can evaluate the effects of treatments after spinal injury. Therefore, we have used conventional techniques to document the kinematics of treadmill locomotion in intact mice (n = 11) and in mice with a complete section of the spinal cord at T8 (n = 12). The results show that the kinematics and EMG of adult normal mice can be adequately monitored with such conventional equipment and that mice can re-express hindlimb locomotion within 14 d after spinalization, without any pharmacological treatments. The angular excursions of the hip, knee, and ankle are similar to those of the intact mice, although the joints are sometimes more flexed. After spinal cord transection, out-of-phase alternation between the homologous limbs recovered, whereas the timing between homolateral limbs was completely lost. This remarkable ability of mice to express hindlimb locomotion after a complete spinalization should be taken into account in the evaluation of various procedures aimed at promoting the functional recovery of locomotion after spinal lesions.

Semiquantitative assessment of hindlimb movement recovery without intervention in adult paraplegic mice

“…However, 'off-line' kinematic analysis methods may be useful for completely untrained observers or if higher levels of recovery are to be found due to treatments or training. 10 Altogether, this method offers fair advantages over other methods for 'drug-screening' studies where large number of protocols or treatments are to be tested and compared in complete spinal cord transected animals (eg, effects of various types of training and drug treatment on central pattern generator activation).…”

“…Movement amplitude was evaluated qualitatively, as for other assessment methods in open-field condition (eg, BBB, adapted motor score, Tarlov, etc), since detailed 2-D kinematic analyses would require movements to be performed on a treadmill. 10 Movement amplitude was characterized by assigning one of three values; 0 -if no movement was observed; 1 -if the amplitude of most movements was less than half the range of motion of normal steps; 2 -if the amplitude of most movements was at least more than half the range of motion of normal steps. 'Movement incidence' was defined as the total number of mice that displayed movements (NBA or BA) over all tested mice of the same group.…”

“…12,19 This is supported by recent results reporting that similar conditions (ie, tail pinching and treadmill) can also occasionally trigger rather complete step cycles in mice two weeks after spinal cord transection in some cases. 10 The cellular mechanisms responsible for the motor and locomotor-like recovery in complete spinal animals remain largely unknown. The progressive return of hindlimb movements over time could result from timedependent plastic changes in networks of the lumbosacral spinal cord that can generate walking in the absence of supraspinal input (ie, CPG 20 ).…”

“…These include mice with spinal cord contusion, displacement, crush, clip compression, ischemia, and transection. [4][5][6][7][8][9][10] However, it remains unclear from those studies if recovery attributed to descending fiber regeneration and reconnection across the lesion is not also partially due to spontaneous reorganization and plasticity at the sublesional level.…”

Training locomotor networks

“…There is one exception to this generalization. Leblond et al (2003) reported that adult spinal mice "can express hindlimb locomotion within 14 days of spinalization" and have "similar angular excursions of the hip, knee and ankle as intact mice". However, full weight-bearing on the hindlimbs was not observed in that the authors stated "the animal has to be supported and a lateral stability has to be provided by the experimenters".…”