The development and recovery of motor function in spinal cats. II. Pharmacological enhancement of recovery.

The effects of the gamma-aminobutyric acid (GABA) antagonist bicuculline (BCC) on hindlimb motor performance was examined in mature spinal cats with spinal cord transections made either on the day of birth or at approximately two weeks postpartum and in chronic adult cats with spinal transections made in adulthood. In those adult operates, whose pre-drug performance was poor compared to neonatal operates, treadmill locomotion and weight support were improved dramatically by BCC administration. In neonatal operates (examined as adults), BCC administration increased the force of extension to abnormal levels and this increase appeared to disrupt locomotion. Immunocytochemical localization of GABA's synthetic enzyme, glutamic acid decarboxylase (GAD) within the spinal cords of these animals revealed an abnormal distribution of GAD reaction product only in newborn operates. The behavioral results indicate that the full extent of recovery in adult operates is prevented by inhibitory influences and this may contribute to the comparatively superior performance of neonatal operates i.e., the infant lesion effect. The anatomical results suggest that one requirement for the normal development of some intrinsic spinal circuitry is transneuronal regulation mediated by the maturation of descending systems.