A kinematic comparison of L-DOPA-induced air-stepping and swimming in developing rats

In Experiment 1, rats of 5, 10, 15, and 20 days of age were injected with L‐DOPA to elicit stepping and videotaped while suspended in air and in warm water. Inter‐ and intralimb coordination were similar for L‐DOPA‐induced air‐stepping and swimming at all ages. Other parameters of locomotion, such as step length and step rate, varied by substrat. In Experiment 2, pups of 5 to 20 days of age received an injection of L‐DOPA or the vehicle and were videotaped while freely swimming. L‐DOPA‐induced free swimming was more stereotyped and “automatonlike” than that of vehicle‐injected animals. Through 15 days of age, all pups swam using all four limbs, but L‐DOPA induced stricter synchrony of movement in diagonal limbs than was used by pups injected with the veicle. At postnatal Day 20, vehicle‐injected pups adopted the adult swimming pattern in which only the hindlimbs were used, whereas L‐DOPA‐injected pups continued to use the immature pattern, diagonal progression with all four limbs. These results suggest that L‐DOPA‐induced air‐stepping and swimming are manifestations of the same central and/or biomechanical effects of the substrate. Although the free swimming of L‐DOPA‐injected pups was kinematically similar to vehicle‐treated pups, L‐DOPA retarded transition to the adult swimming pattern. © 1997 John Wiley & Sons, Inc. Dev Psychobiol 30: 313–327, 1997