P63: Hydrogen sulfide inhibits opioid withdrawal-induced pain sensitization in rats by down-regulation of CGRP expression in the spine

Abstract

Hyperalgesia often occurs in opioid-induced withdrawal syndrome. In the present study, we found that three hourly injections of DAMGO (a μ -opioid receptor agonist) followed by naloxone administration at the fourth hour significantly decreased rat paw nociceptive threshold, indicating the induction of withdrawal hyperalgesia. Application of NaHS (a hydrogen sulfide donor) together with each injection of DAMGO attenuated naloxone-precipitated withdrawal hyperalgesia. RT-PCR analysis showed that NaHS significantly reversed the up-regulated spinal calcitonin gene related peptide (CGRP) expression in naloxone-treated animals. NaHS also inhibited naloxone-induced cAMP rebound and cAMP response element-binding protein (CREB) phosphorylation in rat spinal cord. In SH-SY5Y neuronal cells, NaHS inhibited forskolin-stimulated cAMP production and adenylate cyclase (AC) activity. Moreover, NaHS pretreatment suppressed naloxone-stimulated activation of protein kinase C (PKC) α , Raf-1, and extracellular signal-regulated kinase (ERK) 1/2 in rat spinal cord. In addition, both repeated DAMGO treatment and naloxone-precipitated withdrawal decreased endogenous H2S level in rat spinal cord, suggesting that the endogenous hydrogen sulfide is important to prevent hyperalgesia. Our data suggest that H2S prevents the development of opioid withdrawal-induced hyperalgesia via suppression of synthesis of CGRP in spine through inhibition of AC/cAMP and PKC/Raf-1/ERK pathways.