Expression des cotransporteurs cation-chlorure KCC2 et NKCC1 au cours du développement de la moelle épinière de l’opossum Monodelphis domestica
Inhibition is necessary to generate coordinated outputs between antagonistic muscles during locomotion. Inhibition is set by a lowering in neuronal chloride concentration during mammalian development. This lowering relies on the proper balance between two cation-chloride cotransporters, KCC2 and NKCC1. KCC2 extrudes Cl- out of the cell while NKCC1 pumps Cl- into the cell. The opossum Monodelphis domestica is born at a very rudimentary stage of development. Newborn opossums show rhythmic and alternate movements of the forelimbs as they crawl on the mother's belly to a nipple. The hindlimbs are immobile paddle-shaped buds and their development is mostly postnatal. Thus, this species is an ideal model to study motor development. In order to investigate the mechanisms involved in the appearance of inhibition during motor development, we described the developmental expression of KCC2 and NKCC1 on postnatal opossums using immunohistochemistry in the spinal cord enlargements. Motoneurons and primary sensory afferents were identified using retrograde labeling with TRDA. Immunolabeling for both KCC2 and NKCC1 is detected in the ventral spinal cord in the presumptive grey and white matter from birth on, suggesting that the development of inhibition begins before birth, enabling the alternate movements exhibited by the newborns. The developmental expression of KCC2 and NKCC1 follows ventrodorsal and mediolateral gradients, similar to those demonstrated in rodents (rats and mice). The mature pattern for both cotransporters is observed around the 5th week at a time when opossums demonstrate mature patterns of locomotion. Between birth and P5, dendrites expressing KCC2 in the dorsal horn superimpose on the primary afferents, suggesting a role for KCC2 in the establishment of sensorimotor circuits.
Inhibition Locomotion Cation chloride cotransporters Development Inhibition Locomotion Mammals Spinal cord