H-reflex up-conditioning after sciatic nerve transection and regeneration may increase VGLUT-1 terminals and GluR2/3 immunoreactivity in spinal motoneurons

Abstract

The H-reflex (HR) as an electrical analog of operant conditioning of the spinal stretch reflex, can affect motoneuron responses to primary afferent input. Recent data suggest that up-conditioning of the soleus (SOL) HR could enhance functional recovery after sciatic nerve transection. To explore the morphological correlates of this plasticity, the effect of HR up-conditioning on vesicular glutamate transporter-1 (VGLUT-1) on SOL motoneurons and glutamate receptor (GluR) 2/3 in spinal motoneurons was analyzed after sciatic nerve transection and repair. The right SOL and tibialis anterior (TA) of rats were implanted with electromyogram electrodes and the right posterior tibial (PT) nerve was inserted with stimulating cuffs. After control data collection, the right sciatic nerve was transected and repaired and then the rat was exposed for 120 days either to continue control data collection or to perform soleus HR up-conditioning. At the end of data collection, motoneurons that had reinnervated SOL were labeled retrogradely with fluorescent dye. VGLUT-1 and GluR2/3 were studied immunohistochemically. The final HR was significantly larger in transected/up-conditioned (TU) rats than that in transected/control (TC) rats. In TU rats, the number of VGLUT-1 terminals on soleus motoneuron was significantly more than that in TC rats. The intensity of GluR2/3 immunopositive neurons in TU rats was stronger significantly than that in TC rats. Combined with the larger HR in TU rats, these findings indicated that SOL HR up-conditioning strengthened primary afferent reinnervation of SOL motoneurons and promoted the glutamatergic input after sciatic nerve injury.