An Electromyographic Study of the Hindlimb Locomotor Movements in the Acute Thalamic Rat

In this paper we have analysed the patterns of muscular activities that underlie hindlimb locomotor movements in the acute thalamic rat. Electromyographic activities of muscles representative of the functional muscle groups of the hindlimbs were recorded bipolarly during locomotion in acute thalamic rats. Locomotor movements occurred spontaneously, but could also be induced by electrical stimulation (0.1 ms pulses; 30 - 70 Hz; 75 - 300 microA) of the lateral hypothalamic area. The two hindlimbs displayed a wide variety of coordination patterns during both types of locomotion. However, alternated coordination of the hindlimbs occurred more frequently during induced than during spontaneous locomotion. Correspondingly, the duration of the spontaneous step cycles had a tendency to be shorter than that of the evoked step cycles, although they had a quite similar range. The patterns of muscular activities within one hindlimb were similar during spontaneous and induced locomotion. During each step cycle, (i) the hip and ankle flexors usually displayed a single burst in alternation with that displayed by the hip, knee and ankle extensors, (ii) a double bursting pattern was sometimes observed in flexors during fast locomotor movements, (iii) within flexors and extensors, muscles were recruited sequentially, and (iv) the activation of other muscles (semitendinosus, rectus femoris, extensor and flexor digitorum longus) consisted of single or double bursting patterns.