Postnatal transient expression of long-lasting descending inhibitory effect on spinal reflexes in the rat

In the spinal cord isolated from neonatal rats, stimulation of the ipsilateral lateral column at the thoracic level strongly inhibited monosynaptic segmental reflex in the lumbar cord for about 60 s. The descending inhibition was not associated with any changes in the membrane potential or conductance in lumbar motoneurons when the excitatory postsynaptic potentials in response to stimulation of the dorsal root were depressed. The descending inhibition was diminished with age and could not be detected at 5 months of age. It is suggested that certain inhibitory pathways in the descending spinal tract are rearranged during postnatal development of rats.