Study On The Relationship Between The Intrathecal Morphine-Induced Pruritus And Mast Cells

IntroductionPruritus is one of the severe obstacles in the treatment of intraspinal opioid analgesia all over the world.In the previous study,it was found that the incidence of epidural morphine pruritus was 18.6%after cesarean section,but there was no obvious pruritus after intrathecal injection of morphine in MrgprB2-/-mice.Previous studies have also suggested that morphine can activate mast cells.Based on this study,we constructed a model of intraspinal morphine pruritus in mice with Naive mice and Kit W-sh/W-sh mice and studied the correlation between intraspinal morphine-induced pruritus and mast cells.This study also aim to find out whether it is possible for morphine to directly activate mast cells in central nervous system and mediate its degranulation to promote the release of substances.The purpose of this study is to provide a new therapeutic perspective for alleviating intraspinal morphine-induced pruritus.MethodTo establish intraspinal morphine-induced pruritus model in mice and explore the difference of pruritus and analgesia behavior of different mice after intraspinal morphine administration:C57BL/6 mice,MrgprB2-/-mice and Kit W-sh/W-sh mice were intrathecally injected with 0.5μg morphine.To explore the effect of intrathecal morphine on pruritus behavior in mast cell deficient mice:Kit W-sh/W-sh mice were randomly divided into normal saline group,0.25 μg morphine group,0.5 μg morphine group and 1.0 μg morphine group.To explore the role of histamine in intraspinal morphine pruritus:C57BL/6 mice and Kit W-sh/W-sh mice were injected with 0.5 μg morphine,0.5 μg morphine+10 μg histamine,1.0 μg morphine,1.0μg morphine+50μg histamine respectively.After intrathecal injection,the pruritus behavior of mice in each group was recorded within 30 minutes after intrathecal injection.Hot water tail flick method was used to measure the latency of tail flick before and 120 min after intrathecal injection,and the maximum analgesic effect percentage%MPE and area under curve AUC were calculated to compare the analgesic effect.ResultsIn this study,intraspinal morphine-induced pruritus models were successfully established in C57BL/6 mice,and intrathecal injection of morphine was performed in MrgprB2-/-mice and Kit W-sh/W-sh mice.The first part of the experiment confirmed that MrgprB2-/-mice and Kit W-sh/W-sh mice had less scratching behavior after intrathecal injection of 0.5 μg morphine,but the analgesic effect was similar.It is suggested that mast cells and mrgprB2 receptors may play a role in the intraspinal morphine-induced pruritus without affecting the analgesic effect.In the second part of the experiment,the analgesic effect of Kit W-sh/W-sh mice increased gradually with the increase of morphine dose,but no obvious itching was observed.This further suggests that mast cells are related to intraspinal morphine-induced pruritus,and may be related to histamine released by mast cells after degranulation.The third part of the experiment showed that low-dose histamine reduced the scratching behavior of C57BL/6 mice,but increased the scratching behavior of Kit W-sh/W-sh mice;the analgesic effect was weakened,but more obvious in C57BL/6 mice.High dose of histamine can increase the scratching behavior of C57BL/6 mice and Kit W-sh/W-sh mice,but the time is relatively late.This suggests that histamine may play a late role in pruritus,and the correlation between histamine and intraspinal morphine-induced pruritus needs further study.Conclusions(1)MrgprB2-/-mice and Kit W-sh/W-sh mice showed no obvious scratching behavior after intraspinal injection of 0.5 μg morphine;(2)There was no obvious scratching behavior in Kit W-sh/W-sh mice after intraspinal injection of different doses of morphine;(3)Low dose histamine decreased scratching behavior in C57BL/6 mice,but increased scratch behavior in Kit W-sh/W-sh mice;(4)High dose of histamine increased scratching behavior in C57BL/6 mice and Kit W-sh/W-sh mice,but the time was relatively late;(5)Both low and high dose histamine attenuated the analgesic effect of morphine,but it was more obvious in C57BL/6 mice.