| Background: Neuropathic pain which originates from a lesion of the nervous syste is the common complication of central and peripheral nervous system diseases, such as direct nerve trauma, chronic epilepsia, diabetic neuropathy, herpes zoster, herniated nucleus pulposus, inflammation or infection.The patients with neuropathic pain usually feel unpleasant spontaneous sensations, allodynia, and hyperalgesia which are based on the neuronal hyper-excitability and increased calcium influx. It has been known that the large calcium–activated potassium channels (BKca) expressed in all typies of dorsal root ganglion neurons, and regulated the neuron excitability and electrophysiological characteristic in such a way that an increase in internal Ca2+ leaded to an efflux of K+ and a subsequent hyperpolarization of the membrane. In previous reports, some investigators considered that the AHP currents of BKca channels were decreased in axotomized (L5) neurons, but increased in adjacent (L4) DRG neurons in partial sciatic nerve ligation models. In vitro studies, activation of BKca channels also contributed to reducing depolarization and 4-aminopyridine-induced neuronal hyperexcitability in DRG neurons. These evidences suggested that inhibition of the exoscopic K+ currents via BKca channels could increase membrane excitability by enhancing the frequency and amplitude of depolarization, setting inter-spike interval, mediating spike-frequency adaptation and controlling neurotransmitter release.However, little is known about whether the expression and disposition of BKca channels were changed after periphery spinal nerve injury and the role of these channels in the molecule mechanism of neuropathic pain. In consideration of these, our study adopted improved chronic constriction injury of the sciatic nerve models which was simulating the clinical pathological proceeding of neuropathic pain to test the changes of BKca-αsubunit in dorsal root ganglion neurons.Objective: The aim of this study is to compare the principle and characteristic of pain proceeding as well as the level of oxidative stress after peripheral spinal nerve injuries between three neuropathic pain models and observe the the expression changes of mRNA and protein of BKca-αsubunit in dorsal root ganglion neurons in order to investigating the role it plays in the chronic neuropathic pain..Method: This study is composed two parts.(1) Establishment, evaluation and selection of NPP models. Sixty female SD rats (weighted from 180 to 230g ) were divided into four groups (group Sham, group CCI, group iCCI, group SNI, n = 15)randomly. The sciatic nerve of the right hind leg was exposed without any injury in group Sham, but operated according to the methods described following in group CCI, group iCCI and group SNI. Then appraisaling the degree of neuropathic pain by scores of 50 % paw withdrawal mechanical threshold and radiant heat stimulation before the surgery and 1, 3, 7, 10,14,17,21 days later. The activities of SOD and contents of MDA were measured respectively in the lumbosacral spinal cord 7, 14, 21 days later after surgery .(2) The expression of mRNA and protein of BKca-αsubunit in dorsal root ganglion neurons of iCCI models. One hundred and fifteen healthy male Sprague-Dawley rats were divided randomly into seven groups:normal control group, sham7,14,21d group, iCCI7,14,21d group(n=15). The sciatic nerve of the right hind leg was exposed without any injury in group Sham, but operated according to the methods of Bennett and Xie with slightly improvement in group iCCI. The homolat dorsal root ganglions of the L4~L6 segments of spinal cord were executed respectively at different time points and the expressed variation and redistribution of the BKca-αmRNA and protein were detected by RT-PCR,Western blotting and immunohistochemistry.Result(1) During experiments, any sign of mechanical or heat allodynia did not occur in group Sham (P >0.05). But the surgical procedure in group CCI and iCCI produced an apparent and stable hyperalgesia to noxious heat and mechanical stimulation since the 7th day after operation, and reached the lowest peak on the 14th day bothly (P<0.05). The degression of pain threshold was more responsive in group iCCI than group CCI after the 7th day of the surgery. The SNI group showed insensitive to heat stimulation but more sensitive to the mechanical stimulation than group CCI and iCCI.(2) There was a significant difference of the oxidative stress between the three NPP models (P<0.05).The activities of SOD dropped while the contents of MDA raised in all of the surgery groups but Group Sham. The aseptic inflammation induced by the nerve ligation and alienum had most powerful activation of oxidative stress in iCCI models (P<0.05).The change amplitude of SOD/MDA was iCCI >CCI > SNI..(3) There was no significant difference in BKca-αsubunit mRNA and protein expression between the Control and Sham groups (P >0.05). But the expression was hardly decreased in iCCI groups as well as a redistribution of BKca-αsubunits in DRG neurons. The reduction of BKca-αmRNA was consistent with the changes of PWMT and PWTL threshold in iCCI groups.Conclusion:(1) The principles of pain proceeding and levels of MDA, SOD were different between the three NPP models. Rats in iCCI group exhibited a more intensity hyperalgesia phenomena and allodynia than traditional CCI and SNI group. This suggested that different peripheral spinal nerve injuries might have different influences in the mechanism of neuropathic pain and oxidative metabolism, and the iCCI model should be a typical and stable neuropathic pain in research.(2) The down-regulation of the mRNA and protein expression of the BKca-αsubunit in the dorsal root ganglion neurons might play an important role in neurons excitability increase and spinal cord sensitiveness which was due to the emerging and developing of neuropathic pain.
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