5-Hydroxytryptamine-induced locomotor rhythm in the neonatal mouse spinal cord in vitro.

We examined the 5-hydroxytryptamine (5-HT)-induced locomotor rhythm in isolated spinal cord preparations taken from neonatal mice on postnatal day (P) 0-3. Motor activity was recorded from L2 and L5 ventral roots. Bath application of 5-HT (15-100 microM) evoked rhythmic bursts that alternated between the two sides, and the bursts in the L2 ventral root alternated with those in the ipsilateral L5 ventral root. After transection of the mid-lumbar cord, the locomotor rhythm in L2 persisted, while that in the L5 ventral root was abolished. This suggests that the upper lumbar region has a greater ability to generate a locomotor rhythm than the lower lumbar spinal cord. Kynurenate, a broad-spectrum glutamate receptor antagonist, blocked the 5-HT-induced locomotor rhythm indicating that ionotropic glutamate receptors are required for the rhythm to be generated.