The compensatory role of the parvocellular division of the red nucleus in operantly conditioned rats

To assess the role of the parvocellular division of the red nucleus in motor control, rats were operantly conditioned to walk on a rotating bar and their red nuclei were lesioned with the fiber sparing agent, quinolinic acid. Since both parvocellular and magnocellular divisions of the red nucleus overlap in the rat, they both became involved in this lesion. To differentiate between them, two paradigms were used. (1) Prior to the lesion, the magnocellular division was dysfunctioned by transecting its spinal output, namely, the rubrospinal tract, in the dorso-lateral funiculus (DLF) of the spinal cord. After compensation for this transection had occurred in a few days, the red nucleus was lesioned with quinolinic acid. Rats again compensated rapidly, suggesting that the remaining red nuclear outflow systems, such as the rubro-olivary tract, play no detectable role in the control of on-going movements. (2) In the second paradigm, the red nucleus was lesioned without a preceding DLF transection. This lesion involved both the rubro-bulbar and rubro-spinal projections. Rats did not compensate, or did so very slowly. For compensation to occur, therefore, rubro-bulbar projections need to be intact. This suggests that such projections, that include the rubro-olivary tract, play a role in the compensation for DLF transections.