Developmental Changes in Infant Rat Motor Learning after Mid-Thoracic Spinal Transection

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Prior work in this lab has demonstrated developmental trends in motor learning, both in the rat fetus and neonate. This learning alters the pattern of hindlimb coordination in response to an interlimb yoke, which links the two limbs together. After training, both older fetuses and young neonates not only acquire conjugate movements (simultaneous movements with parallel trajectories), but retain these movements for a substantial amount of time after the yoke has been removed. This motor learning also can be demonstrated in fetuses with mid-thoracic spinal transections, suggesting that spinal circuitry alone is sufficient for these adaptive changes in interlimb coordination. In contrast, postnatal day 10 (P10) rat pups do not show this type of learning. It is possible that this interlimb motor learning depends on spinal plasticity, which is diminished by descending inhibitory circuitry by P10. In this study, infant rats were prepared with either a mid-thoracic spinal transection or sham treatment on the day of birth (P0). Subsequently, on either P1 or P10, these two groups were tested in a 65-min session (5-min baseline, 30-min training period with an interlimb yoke, and 30-min testing period after the yoke is cut). Sham treated pups on P10 did not exhibit motor learning. However, transected pups on P10 showed substantial increases in conjugate limb movements. Shams and transected pups also differed on P10 in the spontaneous activity they exhibited (e.g. high amplitude movements and myoclonic twitching), suggesting that the type and amount of movements exhibited may play a role in this type of spinally mediated motor learning.


Abstract of poster presented at the 32nd Annual Meeting of the Society for Neuroscience, Orlando, FL, November 3-7, 2002.