Antinociceptive effects of maprotiline in a rat model of peripheral neuropathic pain: possible involvement of opioid system

OBJECTIVES Neuropathic pain remains a clinical problem and is poorly relieved by conventional analgesics. This study was designed to determine whether maprotiline administration was effective in alleviating symptoms of neuropathic pain and whether the antinociceptive effect of maprotiline mediated through the opioid system. MATERIALS AND METHODS Neuropathic pain was induced by chronic constriction injury (CCI) of the sciatic nerve in rats, which resulted in thermal hyperalgesia, and mechanical and cold allodynia. Maprotiline (10, 20 and 40 mg/kg, IP) was administered on the 7(th) and 14(th) days after surgery. To study the role of the opioid system in the antinociceptive effects of maprotiline, maprotiline (20 mg/kg, IP) was administered in combination with naloxone (1 mg/kg, SC) on the 7(th) post-surgery day. Behavioral tests were done at 45 min after drug injections on the 7(th) and 14(th) days after surgery. RESULTS Systemic administration of maprotiline blocked heat hyperalgesia, cold allodynia and reduced mechanical allodynia. Also antihyperalgesic effect of maprotiline was reversed by pretreatment with naloxone. CONCLUSION Our results suggest that maprotiline can be considered a potential therapeutic for the treatment of neuropathic pain, and the opioid system may be involved in the antihyperalgesic effects of maprotiline.