ABSTRACT
Objective To determine the change in PSD95 mRNA expression in spinal dorsal horn in a rat model of neuropathic pain. Methods Twelve female SD rats weighing 150-200 g were randomized into 2 groups (n = 6 each) : control group in which left sciatic nerve and its branches were exposed but not cut; SNI group in which the branches of the left sciatic nerve-tibial and common fibular nerves were ligated and cut. Pain threshold was measured by foot-lift response to mechanical stimulation of ipsilateral hindpaw with 12 g and 2 g produced by plantar touch stimulator (Ugo Basile Co. Italy) representing hyperalgesia and allodynia respectively, 3 days before, immediately after and on the 1st, 3rd, 5th, 7th, 9th and 11th day after operation. On the 11th day the animals were killed after measurement of pain threshold and L4-6 segment of the spinal cord was removed for determination of expression of NR2B and nNOS by immuno-histochemistry and expression of PSD95 mRNA by RT-PCR.Results Starting from the 5th day after operation all rats in SNI group developed a relative mechanical allodynia. The expression of NR2B and nNOS was mainly distributed in Ⅰ or Ⅱ laminae of dorsal horn. The expression of NR2B and nNOS was significantly higher in SNI group than in control group. The expression of PSD95 mRNA in SNI group was significantly decreased when compared to control group (P
ABSTRACT
Objective To determine if there is any difference in neuronal and glial(astrocytic and microglial)activation in the spinal cord in three rat models of neuropathic pain.Methods Twenty-four SD rats weighing 150-200 g were randomly divided into 4 groups(n=6 each):Ⅰ control group;Ⅱ chronic constrictive injury group(CCI);Ⅲ spinal nerve ligation group(SNL)and Ⅳ spared nerve injury(SNI).No operation was performed in control group.In CCI group left sciatic nerve was exposed and loosely ligated with catgut.In SNL group the L_5 spinal nerve was exposed and ligated with silk suture and cut.In SNI group tibial nerve and common fibular nerve were ligated and cut.Pain threshold was measured using plantar tactile stimulator(Ugo,Basile Co. Italy)every other day from 3 days before until 15 days after operation.50% paw withdrawal threshold was measured using up-and-down sequential mechanical stimulation of different intensity(0.45,0.70,1.20,2.00, 3.63,5.50,8.50,15.10 g)applied to the plantar surface of the injured paw.On the 15~(th) day after operation after pain threshold was measured the animals were anesthetized with intraperitoneal 10% chloral hydrate 400 mg? kg~(-1).The L_(5,6) segment of the spinal cord was isolated.Neuronal,astrocytic and microglial activation was determined by immuno-histochemistry with antibodies of c-Fos(a proto-oncogene protein),GFAP(an astrocyte marker)and OX-42(a microglial marker).Results The 50% paw withdrawal threshold reached the lowest level on the 7~(th) day after operation.The lowest level was maintained until the 15~(th) day after operation in group CCI,SNL and SNI.The 50 % paw withdrawal threshold was(14.1+1.5)g in control group,(2.5+0.5)g in CCI group, (1.5?0.6)g in group SNL and(0.8?0.4)g in group SNI.The number of c-Fos positive neurons in laminae Ⅳ-Ⅵ of dorsal horn was significantly greater in group CCI,SNL and SNI than in control group,but there was no significant difference among the 3 peripheral nerve injury groups.The activation of astrocytes and microglias in laminae Ⅰ-Ⅳ of dorsal horn was significantly increased in group CCI,SNL and SNI than in control group but there was no significant difference among the 3 peripheral nerve injury groups.Condusion There is no significant difference in activation of neurons and astrocytes and microglias in the ipsilateral dorsal horn among the 3 pain models.