The pharmacologic treatment of painful neuropathy continues to pose problems and challenges in clinical practice. This is largely due to a limited understanding of the underlying etiologies of such neuropathic pain and insufficient knowledge of the optimal effective doses that would cause only minimal systemic side effects. The use of molecular methods, such as gene deletion from knockout mice and the development of cellular mini-pumps for the delivery of biologic antinociceptive molecules have led to a better understanding of the underlying mechanisms involved in the induction of intractable neuropathic pain. It is now known that the initiation of an excitatory cascade after injury or disease leads to the induction of various second messenger systems, and the loss or down-regulation of the endogenous inhibitory spinal system and central sensitization, both of which cause such pain. Currently, there are novel approaches that use genetic therapy in the management of neuropathic pain. Two such approaches which have been determined to be safe are proposed to be investigated in this study using animal models of pain. The first approach involves cell-mediated delivery of antinociceptive molecules to the cerebrospinal fluid using cultivated spinal progenitor cells transplanted into the subarachnoid space. Chronic constriction injury (CCI) of the sciatic nerve was used to induce chronic neuropathic pain in the hind paw of rats. 1x106 spinal progenitor cells (SPCs) were implanted intrathecally on the third day after the CCI surgery. The behavioral response to thermal hyperalgesia was observed and recorded during the 14 days post surgery. Various techniques were utilized to trace the progenitor cells, confirm the differentiation, and identify the neurotransmitters involved. Glutamic acid decarboxylase (GAD) immunoreactivity was revealed for 65% of the cultivated SPCs in our study. We also determined that transplanted cells could survive more than four weeks post intrathecal implantation. Significant reductions were demonstrated for responses to thermal stimuli for the CCI rats that had received intrathecal SPC transplantation. A novel intrathecal delivery with SPCs reduced CCI-induced neuropathic pain. The second approach involves the use of a newly developed intrathecal electroporation probe in the delivery of antinociceptive peptides to reduce expression of endogenous nociceptive molecules in the spinal cord. To investigate the feasibility of delivering exogenous genes into spinal cord using direct in vivo electrotransfection, pE-GFP C1 vector was used to achieve the goal. Gene transfer to the spinal cord was accomplished via direct intrathecal injection of, followed by 5 electric pulses for 50 ms at 200 V delivered intrathecally. The spinal cords were retrieved and analyzed with fluorescence microscopy, reverse transcription polymerase chain reaction (RT-PCR), and western blotting. At day 1, 3 or 7 following electroporation a clear green fluorescence protein (GFP) expression in spinal cord tissue was detected. The most prominent transfection occurred in the meningeal cells and superficial layer of the spinal cord. Successful transfection was also confirmed with RT-PCR and western blotting. The expression of GFP protein was peaked between 3-7 days after electroporation and significantly decreased at 14 days. No behavioral or spinal neurodegenerative changes were detected at any time point. This study demonstrates that direct in vivo electrotransfection represents an effective and simple method for spinal gene delivery. Furthermore, the optimal pulse characteristics (voltage, pulse duration, number of shocks) were investigated for in vivo electroporation for gene transfer into the spinal cord. The expression of pre-opiomelanocortin (POMC) gene from electroporated plasmid DNA was then evaluated in this study using RT-PCR and western blot. We conclude that the optimal conditions for electroporation are a pulse voltage of 200 V, 75-ms duration, 925-ms interval, for five iterations. Also, electroporation treatment for neuropathic pain was attempted for CCI rats using plasmid DNA that expresses the POMC gene. Intrathecal administrations of the POMC plasmid elevated spinal beta-endorphin levels, as manifested in significantly elevated pain threshold for the CCI limbs. We also tested whether intrathecal electric stimulation would reduce the tolerance of chronic morphine usage and the severity of precipitated morphine withdrawal symptoms. Rats received intrathecal electrode catheter implantation and a continuous intrathecal infusion of morphine (2 nmol/hr) or saline for seven days. Intrathecal electric stimulations (0, 20V, 200V) were performed once daily during the same period. Daily tail flick and intrathecal morphine challenge tests were performed to assess the effect of intrathecal electric stimulation on antinociception and tolerance of morphine. Naloxone withdrawal (2mg/kg) was performed to assess morphine dependence, and changes in spinal neurotransmitters were monitored by microdialysis. The antinoceptive effect of intrathecal morphine was increased by 200V electric stimulation. The magnitude of tolerance was decreased in the rats receiving 2 nmol/hr infusion with daily intrathecal electric stimulation. The severity of naloxone-induced withdrawal symptom was lower in the rats receiving 200V stimulation. Intrathecal stimulation thus enhances analgesia and attenuates naloxone-induced withdrawal symptoms in rats receiving chronic intrathecal morphine infusion. Increases in spinal glycine release may be the underlying mechanisms. The promise is that, both approaches attenuate or reverse persistent nociceptive states; they could be exploited for use in the development of gene therapy for the management of pain.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0715102-091614 |
| Date | 15 July 2002 |
| Creators | Lin, Chung-Ren |
| Contributors | Lin-Cheng Yang, Ming-Hong Tai, Po-Wu Gean, Hung-Tu Huang, Jiin-Tsuey Cheng |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0715102-091614 |
| Rights | unrestricted, Copyright information available at source archive |
Page generated in 0.002 seconds