Role of Spinal Cord α 2-Adrenoreceptors in Noradrenergic Inhibition of Nociceptive Transmission During Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a problem during cancer treatment and for cancer survivors but the central mechanisms underlying CIPN remain understudied. This study aims to determine if CIPN is associated with alterations of noradrenergic modulation of nociceptive transmission at the spinal cord. CIPN was induced in male Wistar rats by paclitaxel injections. One month after CIPN induction, the behavioral effects of the administration of reboxetine (noradrenaline reuptake inhibitor), clonidine (agonist of a2-adrenoreceptors; a2–AR) and atipamezole (antagonist of a2–AR) were evaluated using the von Frey and cold plate tests. Furthermore, we measured the expression of the noradrenaline biosynthetic enzyme dopamine-ß-hydroxylase (DBH) and of a2–AR in the spinal dorsal horn. Reboxetine and clonidine reversed the behavioral signs of CIPN whereas the opposite occurred with atipamezole. In the 3 pharmacological approaches, a higher effect was detected in mechanical allodynia, the pain modality which is under descending noradrenergic control. DBH expression was increased at the spinal dorsal horn of paclitaxel-injected animals. The enhanced noradrenergic inhibition during CIPN may represent an adaptation of the descending noradrenergic pain control system to the increased arrival of peripheral nociceptive input. A potentiation of the a2–AR mediated antinociception at the spinal cord may represent a therapeutic opportunity to face CIPN.This study was supported by a grant of Norte 2020/NORTE-01-0145-FEDER-000008. JC-P is recipient of a Ph.D. grant of NORTE-08-5369-FSE-000026. The sponsors had no role in study design, collection, analysis, interpretation of data, and writing of the manuscript for publication