Effect of spinal cord lipocalin-2 on development of morphine tolerance in normal rats / 中国药理学通报

ABSTRACT

Aim To explore the effect of knockdown spinal cord LCN2 by RNAi on the development of mor-phine tolerance in normal rats.Methods After suc-cessful intrathecal implantation, fourty-eight male Sprague-Dawley rats weighing 1 80 -220 grams were randomly divided into 4 groups (n =1 2)group Icontrol group,group IImorphine tolerance group, group Ⅲmismatch siRNA group,group IVLCN2 siRNA group.The sixth day after intrathecal implanta-tion,rats were tested to ensure the position of cathe-ters,and it was recorded as d 0.On d 2 -8,rats were subcutaneously (s.c)injected of normal saline (NS) (group I)or morphine (group Ⅱ,Ⅲ,Ⅳ)1 0 μg· g -1 twice a day at 800 and 1 600.Before everyday s. c injection,rats were intrathecally injected of 1 0 μL DEPC solution (group Ⅰ,Ⅱ),1 0 μL DEPC solution containing 4 μg mismatch siRNA (group III)and 4 μg LCN2 siRNA solution (group IV).Paw withdrawal la-tencies to thermal stimuli (PWTL)were tested before morphine injection and 45 minutes after morphine in-jection on d 1 and d 9.The percentage of maximal pos-sible effect (% MPE)was calculated later.Animals were sacrificed on d 9 after the behavioral test and the lumbar enlargement segments of the spinal cord were removed for detecting the expression of phosphorylated-p38 mitogen-activated protein kinase (p-p38 MAPK) and LCN2 by Western blot and microglia marker Iba1 by immunofluorecence.Results On d 1 ,there was no significant difference in %MPE among four groups. On d 9,compared to group Ⅰ,%MPE was signifi-cantly reduced (P <0.05)while p-p38MAPK,LCN2 and Iba1 were markedly up-regulated in group Ⅱ andⅢ (P <0.05 ).On d 9,compared to group Ⅱ,%MPE was significantly increased while p-p38MAPK, LCN2 and Iba1 were markedly reduced in group IV (P<0.05).Conclusion Using LCN2 siRNA to knock-down spinal LCN2 relieves the development of mor-phine tolerance in normal rats possibly through inhibi-ting the activation of microglia and p38 MAPK in the spinal cord.