CNRS Laboratoire de Neurobiologie et Mouvements, 31 chemin Joseph Aiguier BP 71, 13402 Marseille cedex 20, France
bLaboratoire de Physiologie Animale, Université Sidi Mohamed Ben Abdellah, Faculté des Sciences et Techniques Saiss-Fes, km3 route d'Immouzzer BP2202 Fez, Morocco
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 GABA
B receptors. In conclusion, this study emphasizes the
role played by GABA at various levels in the control of the
locomotor network in mammals.
