L-dopa-induced air-stepping in preweanling rats. II. Kinematic analyses

Coordination of air-stepping elicited by subcutaneous injections of L-DOPA (25-100 mg/kg) was studied in rats from the day of birth through 20 days of age. Results revealed a nearly linear increase in the rate of stepping from about 1.5 steps/s at day 0 to about 4.5 steps/s at day 20, independent of the dose of L-DOPA. The ontogenetic increase in the rate of stepping was found to result from decreases in the duration of both retraction and protraction phases of the step cycle, but the decrease in the retraction phase was greater. There was an ontogenetic increase in the amplitude of movement at the wrist, knee and ankle joints, a slight decline in the amplitude of movement at the elbow and little change in amplitude at either the shoulder or hip. The relative timing of movements at joints within each limb also changed with age. Forelimb movements were led by the wrist throughout development, followed by the elbow and then the shoulder, which increasingly lagged behind the other two joints of the forelimb. Hindlimb movements were increasingly led by the knee, followed by the ankle and then the hip. Diagonal progression, in which the diagonal limbs moved in phase with each other and in antiphase with the contralateral limb of the same girdle, was seen at all ages. However, other gaits, which resembled galloping (air-galloping) and swimming (air-swimming), became more prevalent between 10 and 20 days of age.(ABSTRACT TRUNCATED AT 250 WORDS)