Despite intensive research on the neurobiological mechanisms of chronic pain, this therapeutic area remains one of the least satisfactorily covered by current drugs. Glutamate activates two major classes of receptors: ionotropic and metabotropic. Ionotropic receptors are classified into three major subclasses:a-amino-3- hydroxy-5-methyl-4- isoxazolepropionic acid (AMPA), kainate and N-methyl-D-aspartate (NMDA). NMDA receptor activation, at the level of the spinal cord and peripheral tissue has been shown to play an important role in the facilitation of nociption in several animal models. Although the efficacy of NMDA receptor antagonists in various experimental and clinical pain situations has been well documented, their use as analgesics is limited by serious side effects such as memory impairment, psychotomimetic effects, ataxia and motor incoordination. Two promising current approaches to obtain effective analgesia devoid of side effects are by subtype-selective NMDA receptor antagonism in central nervous system (CNS) or peripheral use of NMDA receptor antagonist that do not interfere with central glutamate processing. NR2B subunit of NMDA receptor was predominantly found in the superficial dorsal horn of spinal cord. Recent discoveries have revealed that the transfection of small interfering RNAs (siRNAs) into animal cells results in the potent, long-lasting post-transcriptional silencing of specific genes. Thus, two approaches of antagonizing NMDA receptor in CNS and peripheral nervous system (PNS) for pain relief using siRNAs or pharmacological agents are investigated in this study. The first approach involves intrathecal administration of NR2B-siRNA into subarachnoid space and transfection of siRNA into cell of spinal cord by transfection agent of polyethylenimine (PEI). Formalin test was used to induce inflammatory pain in the hind paw of rats. Behavior response to formalin test was observed and recorded on 3rd, 7th, 14th, and 21th day after injection of siRNA. The spinal cords were dissected immediately after formalin test and used for analysis of mRNA and protein. The results revealed that the use of siRNA targeting the NR2B subunit could abolish formalin induced pain behaviors and not impair motor coordination in rat model. The expression of NR2B mRNA and its associated protein as demonstrated by real time reverse transcription-polymerase chain reaction (RT-PCR) and western blotting were decreased. Significant reduction of NR2B immunoreactivity in dorsal horn of spinal cord were detected after 7 days treated by NR2B siRNA. The peak effect of gene knockdown occurred on day 3 for mRNA and day 7 for its protein, following intrathecal injection of 5 µg of siRNA targeting NR2B subunit. The inhibition of NR2B mRNA and protein lasted about 14 days and recovered on 21th days after injection of siRNA. The nociceptive response induced by formalin was decreased during the period of downregulation of NR2B protein. A novel intrathecal delivery of siRNA transfected with PEI into cell of dorsal horn reduced formalin-induced pain. The second approach involves subcutaneous injection of NMDA receptor antagonist and topical use of alpha2-adrenergic agonist for abolishing surgical pain. Additionally, we proved the upregulation of glutamate receptors in human inflamed skin. The study examined whether the peripheral ionotropic glutamate receptors (iGluRs) increased in inflamed human skin taken from patients having inflammatory pain over inflamed skin and surrounding area. Real time RT-PCR and western blot were used for quantitation of mRNA and protein of iGluR in normal and inflamed human skin. A significant increase in mRNA and protein for the subunits of NMDA, AMPA, and kainate receptor were detected in inflamed skin when compared to normal skin. The results demonstrate that mRNA and protein level of iGluRs are increasingly expressed during states of persistent inflammation, and that this increased activity may be involved in mediating clinical inflammatory pain in human skin. To examine the postoperative analgesic effect and adverse effect of local NMDA receptor antagonist (ketamine), ketamine (0.3%, 3 ml) or saline was subcutaneous infiltrated pre-incisionally in 26 patients equally assigned to two groups undergoing circumcision surgery. The saline-infiltrated subjects also received 9-mg intramuscular ketamine into the upper arm to control for any related systemic analgesic effects. The postoperative analgesic and adverse effects were followed for 24 hours. For ketamine infiltrated patients, the time interval until first analgesic demand was prolonged and the incidence of pain free (pain score = 0) during movement and erection was significant higher than saline infiltrated patients. No significant differences were noted in the incidence of adverse effects between the two groups. Pre-incisional subcutaneous infiltration of ketamine acting via a peripheral mechanism can suppression postoperative pain after circumcision surgery. Apraclonidine hydrochloride (AH) is a topical, relatively selective alpha2-adrenergic agonist that has limited access to the CNS and exhibits fewer systemic (adverse) effects such as dizziness and hypotension. Eighty patients scheduled for arthroscopic knee surgery received either intraarticular (IA) normal saline, 50 ug IA AH, 150 ug IA AH, or 150 ug IA clonidine subsequent to surgery. The IA application of 150 ug apraclonidine and 150 ug clonidine provide similar degree of postoperative analgesia and similar incidence of adverse effect. The promise is that both approaches attenuating nociception state devoid of CNS adverse effects provide novel approach for the management of chronic pain.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0130105-094652 |
| Date | 30 January 2005 |
| Creators | Tan, Ping-Heng |
| Contributors | Hung-Tu Huang, Lin-Cheng Yang, Kang Liu, Lee-Wei Chen, 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-0130105-094652 |
| Rights | withheld, Copyright information available at source archive |
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