ABSTRACT
Objective To investigate the roles of spinal extracellular signal-regulated protein kinases 5 (ERK5) on morphine withdrawal in rats.Methods Ninety-six male and adult SD rats weighting 230-250 g were randomly divided into saline-naloxone-DMSO group (group A),saline-naloxone-BIX02188 group (group B),morphine-naloxone-DMSO group (group C) and morphine-naloxone-BIX02188 group (group D).To set up morphine dependent model,rats were subcutaneously injected with morphine in the increasing dosage method.On day 6,4 h after the injection of morphine,rats were injected with naloxone (intraperitoneal) to precipitate morphine withdrawal syndrome.The scores of morphine withdrawal symptom and morphine withdrawal-induced allodynia were observed after intrathecal injection of ERK5 inhibitor BIX02188.Result There were not withdrawal symptoms and withdrawal-induced allodynia in group A and B after intraperitoneal injection of naloxone.Compared with group A,teeth chatting (7.5± 1.1),wet dog shacks (4.6± 0.7),jump (5.3± 0.7),abnormal position (8.9± 1.9),diarrhea (7.1 ± 1.6),salivation (2.8±0.6),weight loss (7.9±0.9),total withdrawal score (44.8±5.9),score of withdrawalinduced allodynia (14.6±2.4) of group C and teeth chatting (3.1±0.5),wet dog shacks (1.5±0.4),jump (2.2± 0.5),abnormal position (7.9± 1.6),diarrhea (1.8±0.5),salivation (2.8±0.9),weight loss (3.7±0.6),total withdrawal score (23.1± 1.3) and score of withdrawal-induced allodynia (3.5± 1.1) of group D were significantly increased (P＜0.05).Compared with group C,teeth chatting (3.1±0.5),wet dog shacks (1.5±0.4),jump (2.2±0.5),diarrhea (1.8±0.5),weigbt loss (3.7±0.6) and total withdirawal score (23.1±1.3),score of withdrawal-induced allodynia (3.5±1.1) of group D were significantly decreased (P＜0.05).But there was not significant change in abnoral position (7.9±1.6) and salivation (2.8±0.9).Conclusion Inhibition of the activation of spinal cord ERK5 can significantly alleviate withdrawal symptoms of morphine dependent rats by intrathecal injection BIX02188.