GABAergic control of spinal locomotor networks in the neonatal rat

We studied the GABAergic control of the spinal locomotor network using an isolated brain stem/spinal cord from newborn rats, in which locomotor-like activity was recorded. We demonstrate that endogenously released GABA controls the locomotor network, by decreasing or completely abolishing all locomotor-like activity. At first, we investigated the role played by GABA in the control of the locomotor period. By separately superfusing various compartments of the lumbar cord, we identified the targets of GABA. When bath-applied on the upper lumbar segments (L1/L2), GABA or its agonists (muscimol, baclofen) modulated the locomotor period, whereas it had no effects when bath-applied on the caudal lumbar cord (L3/L6). In the second step we studied how GABA may presynaptically control the locomotor drive arising from the locomotor network located in L1/L2. By use of the partitioned spinal cord, intracellular recordings from the caudal pool motoneurons (L4/L5) were performed, while initiating locomotor-like activity in L1/L2. We found that GABA or its agonists decreased the monosynaptic locomotor drive that the motoneurons received from the L1/L2 network, and we found a presynaptic effect exerted through the activation of GABAB receptors. In conclusion, this study emphasizes the role played by GABA at various levels in the control of the locomotor network in mammals.