Effect of muscle pain and intrathecal AP-5 on electromyographic patterns during treadmill walking in the rat

1. A physio-neuropharmacological model to assess in the rat the contribution of muscular nociceptive input to motor dysfunction and pharmacological aspects of spinal sensorimotor interaction, during treadmill walking, is presented. 2. Rats were trained to walk on a treadmill prior to chronic electromyographic electrode implantation and intrathecal catheterization. 3. Changes in electromyographic activities were recorded from the median gastrocnemius and tibialis anterior muscles of the right hindlimb, during rhythmic locomotor movements. 4. Intramuscular hypertonic saline 6% was injected into the right triceps surae muscles to produce an experimental muscle pain during treadmill walking. 5. Pain produced a decrease in both median gastrocnemius and tibialis anterior electromyographic activities during rhythmic locomotion. Mean gastrocnemius burst duration decreased while tibialis anterior burst duration increased. 6. AP-5, an NMDA receptor antagonist known to block the synaptic excitatory drive to central pattern generators, was injected intrathecally at the level of the lumbar spinal cord to validate this neuropharmacological model. 7. Intrathecal AP-5 induced a decrease of both median gastrocnemius and tibialis anterior muscle activities during treadmill walking. This pharmacological intervention aggravated behavioural and motor effects of muscle pain.