The unilateral 6-OHDA rat model of Parkinson's disease revisited: an electromyographic and behavioural analysis.

The characteristic locomotor disturbances of Parkinson's disease (PD) include shuffling gait, short steps and low walking velocity. In this study we investigated features of walking and turning in a rat model of PD caused by unilateral infusion of the neurotoxin 6-hydroxydopamine (6-OHDA). We assessed gait and electromyographic (EMG) patterns of the ankle flexor tibialis anterior and the knee extensor vastus lateralis of the hindlimb, and triceps brachii of the forelimb, during overground locomotion, spontaneous rotation (turning) and apomorphine-induced rotation. When compared with control rats, rats with unilateral dopamine depletion displayed a shuffling gait and short stride lengths. This locomotor pattern was accompanied by prolonged ankle flexor activity on the ipsilateral side, and prolonged activity of knee extensors on the contralateral side. The dopamine depletion also led to enhanced contraversive rotations after an apomorphine challenge. The EMG recordings during drug-induced rotation suggested that hindlimb stepping was a reflective response to an active drive produced by forelimbs. The EMG recordings of the contralateral side during rotation were marked by reduced ankle flexor activity and increased knee extensor activity. Furthermore, EMG recordings indicated that dopamine-agonists induce rotational bias by altering the coupling between ipsi- and contralateral hindlimbs, and between forelimbs. In straight walking, however, the gait of 6-OHDA lesion animals reflected normal, coupled hindlimb stepping as controlled by spinal pattern generators. The data suggest that the unilateral rat model of PD resembles key features of human parkinsonian gait, and that asymmetric descending input may underlie the observed changes in gait patterns.