Disruption of Spinal Noradrenergic Activation Delays Recovery of Acute Incision-Induced Hypersensitivity and Increases Spinal Glial Activation in the Rat

Results of clinical studies suggest that descending inhibitory controls from the brain stem are important for speeding recovery from pain after surgery. We examined the effects of destroying spinally projecting noradrenergic neurons via intrathecally administered antibody to dopamine beta-hydroxylase conjugated to saporin (D beta H-saporin) on recovery in an acute incisional pain model. Mechanical and thermal paw withdrawal thresholds and nonevoked spontaneous guarding scores were tested for several weeks postoperatively and analyzed using mixed effects growth curve modeling. D beta H-saporin treatment resulted in a significant prolongation in the duration of mechanical and to a lesser degree thermal hypersensitivity in the ipsilateral paw of incised rats but did not increase the duration of spontaneous guarding. D beta H-saporin treatment was also associated with increased microglial and astrocyte activation in the ipsilateral spinal cord 21 days after incision compared with immunoglobulin G-saporin treated controls. Chronic intrathecal administration of the alpha 2 adrenergic receptor antagonist atipamezole (50-200 mu g/d) produced similar effects. These data suggest that spinally projecting noradrenergic pathways and spinal alpha 2 adrenergic receptor activation are important for speeding recovery from hypersensitivity after surgical incision possibly by reducing spinal glial activation. Interventions that augment the noradrenergic system might be important to speed recovery from pain after surgery. (C) 2016 by the American Pain Society