The Role Of N-methyl-D-aspartate Receptors In Remifentanil Induced Acute Tolerance And Hyperalgesia

Opioid drugs are widely used in clinical, are commonly used analgesic drugs as the main drug of a preoperative medication, adjuvant drug and general anesthesia, as well as for postoperative analgesia and other pain treatmentwith good analgesic effect. The past 20 years, recent studies have provided that long-term use of Opioid drugs can induce hyperalgesia phenomenon (Opioid-induced hyperalgesia,OIH). OIH is that the application of opioids in treatment of pain, and has led to the patient more sensitive to pain, or increase their existing pain. At present, opioid mechanism of drug-induced hyperalgesia is not yet very clear.①The activation of central glutamyl peptide system, mainly throughed by N-methyl-D-aspartate (NMDA) receptor of the system steady-state of energy and enkephalin and opioid peptides, and while noxious stimuli is also very important.②Dynorphin, the spinal cord can cause the release of Dynorphin.③Opioid sensitive "excitement-type" cells in the head-end in the ventromedial medulla regulate descending facilitatory. Studies have shown that NMDA receptor activation play an important role in hyperalgesia.Remifentanil is a new type of ultra-short efficient synthetic opioid with rapid onset, effect a short time, eliminate rapidly, continuous infusion does not appearthe non-accumulation and metabolism is not dependent on liver and kidney function, which has a little impact on elimination by age, gender, body weight.So it has been widely used in a variety of patient general anesthesia, postoperative analgesia, and labor analgesia. It is known as an opioid for the 21 st century.With remifentanil widely used in clinical in recent years, many studies found that remifentanil has a pain-sensitized adverse reactions.If it is improperly used, it would increase the post-operative pain that is not conducive to patient's postoperative recovery. At present, the mechanism underlying opioid-associated hyperalgesia has yet to be elucidated. A significant body of literature suggests a pivotal role of a pain facilitatory system involving the NMDA-receptor in the development of opioid-associated hyperalgesia. Activation of the NMDA-receptor at the level of the spinal cord is critical for the expression of nerve injury related hyperalgesia. Analogous to nerve injury, the NMDA-receptor response can be facilitated via activation of theμ-opioid receptor co-localized on the same neuron. Activation may also occur via anμ-opioid mediated modulation of neuronal circuits within the spinal cord resulting in an increased synaptic availability of excitatory amino acids. Such odulatory effects were shown after several days of opioid exposure. Finally, the rostral ventral medulla and descending pain facilitatory pathways have been linked to the hyperalgesic response associated with repeated opioid administration.These investigators suggested a critical role for spinal dynorphin, which may trigger the release of amino acids and other excitatory neurotransmitters. NMDA-antagonist S-ketamine is not used for postoperative analgesia large-scale in Clinical, because it easily lead to sensory and cognitive abnormalities as well as the illusion.But recently, studies promoted that low-dose (<1 mg/kg) can avoid these shortcomings, small doses of ketamine alone has no effect on pain thresholds, but can inhibit or flip morphine tolerance, reducing the application of postoperative analgesic doses, can be prevented the occurrence of postoperative hyperalgesia.The impacts of Opioid withdrawal hyperalgesia have many factors, such as, experimental objects, delivery mode, duration, infusion method, etc. Previous studies mainly adopt for volunteers, or clinical operations, due to ethical issues,administration of the dose and the main speed limit, evaluation of pain indicators are subject to many restrictions; in animal experiments, experimental animals and dose are different, so It has always been disputed whether remifentanil lead to withdrawal hyperalgesia or not.This study adopt intravenous infusion of different doses of remifentanil, observe thresholds of tail flick test, and determine whether the effects related with different doses; Further to explore the intrathecal injection of small doses of ketamine can prevent and treat of remifentanil induced-hyperalgesia, and identify whether NMDA receptors play an important role in the remifentanil induced hyperalgesia. To provide a theoretical basis for prevention and treatment of remifentanil induced-hyperalgesia and to direct reasonable opioids using in Clinic.All data are reported as the mean±standard deviation (x±s). SPSS 13.0 were sused to analyze the data. Analysis of paired t test was used to evaluate pain threshold before and after catheterization. Analysis of one-way-anova was used to evaluate the body weight, baseline threshold of mechanical and heat stimulus.Post Hoc multiple comparisons among each time spot in different groups and different time spots in each group were analyzed by using LSD test. P values of <0.05were accepted as significant.Part I Effects of different doses of remifentanil intravenous continuous infusion on pain threshold in ratsObjective To determine effects of different doses of remifentanil intravenous continuous infusion on analgesia and observe the changes in threshold with dose relationship in rats.Methods Forty adult male Sprague-Dawley rats were divided randomly into 5 groups (n=8), The model of long-term vascular access to mouse was established.The rats in remifentanil A, B,C,D group were injected with remifentanil0.3μg·kg-1·min-1, 0.6μg·kg-1·min-1,1μg·kg-1·min-1,1.5μg·kg-1·min-1 through jugular vein.The rats in saline group were injected with0.1μg·kg-1·min-1 saline through jugular vein. All rats were continuous exposed to remifentanil for 4 h. The response to mechanical noxious stimulation and thermal noxious stimulation was determined before and 1/2 h,1 h,2 h,3 h,4 h after the beginning of remifentanil infusion and 1/2 h,1 h,2 h,24 h and 48 h after the finishing of remifentanil infusion (treatment groups) or saline (control group).Results1. Descriptive statisticsQuantitative analysis:40 experimental rats can successfully were placed catheters into the jugular vein, and accomplish infusion demands without obvious discomfortable, no catheter swapped out from the vein, no catheter was blocked and no infection, no autophagic death, fully integrated into the statistical results.2. Basic informationThere is no significant difference among body weight, baseline threshold of mechanical and heat stimulus.3. There is no significant difference in baseline threshold of mechanical and heat stimulus after jugular vein catheterization in rats.4. There are significant differences in mechanical pain threshold in the process of continuous infusion among in the two groups, time points and different doses of the same time of rats a difference (F=4.936 P=0.000;F=151.244 P=0.000;F=18.361 P=0.000). R4 group was higher than N in T3,R1, R2 and R3 groups were significantly different (P=0.002), R3 group was higher than N, R1, R2 group, and R1 were significantly different (P=0.003), R4 group was higher than R1, R2, R3 Group, there is significant difference (P=0.028), there was a significantly difference in T7 point between R1 and R2 (P=0.049), with the infusion time,the curve of threshold decreased after stopping, and the lowest was in the T8 piont,there were significantly differences between R1,R2,R3,R4 group and N group.there was a significant difference in T9 and T10 point between R4 and R1,R2, After the threshold gradually returned to preoperative levels at T11.Groups comparison, the threshold value reached the maximumT3 in each group, T8 point to a minimum.The constant-rate remifentanil infusion for 4 h demonstrated the threshold of motor response to pressure reached themaximum level at 1/2 h and began to decline by1 h -2 h, The phenomenon of hyperalgesia was founded at 1/2 h-2 h of finishing remifentanil infusion.The experiments with the constant-rate remifentanil infusion demonstrated that remifentanil induced tolerance and delayed hyperalgesia.ConclusionThe constant-rate remifentanil infusion for 4 h demonstrated that the threshold of motor response to pressure reached themaximum level at 1/2 h,0.3μg·kg-1·min-1 and 0.6μg·kg-1·min-1 groups don't appear acute tolerance, but 1μg·kg-1·min-1 and 1.5μg·kg-1·min-1 groups began to decline after 1 h, high doses remifentanil infusion appear acute tolerance easier than low doses.The phenomenon of hyperalgesia was alse founded at 1/2 h-2 h of finishing remifentanil infusion. The higher dose infused, the longer hyperalgesia lastedPart II Effect of intrathecal ketamine on acute tolerance and hyperalgesia of induced remifentanil and espression of NMDA receptor in the spinal cord on rats.Objective To evaluated effect of intrathecal ketamine on acute tolerance and hyperalgesia of induced remifentanil, and observe changes in the expression of NMDA receptors in the spinal cord using immunohistochemistry.Methods Twenty-four adult Sprague-Dawley male rats were randomly divided into three groups (n=8 each.). Two microspinal catheters were inserted into the jugular vein and lumbar subarachnoid space. Group C and Group R administrated saline (0.1μg·kg-1·min-1) or remifentanil (1μg·kg-1·min-1) for 4 h. Group RK administrated remifentanil 1μg·kg-1·min-1) after 1/2 h of intrathecal ketamine (10μg). Nociception sensitivity was evaluated at different time points using pressure and heat. 2 hours after the cessation of remifentanil, perfusion, taking L4-5 spinal segment and observing changes in the expression of NMDA receptors in the spinal cord using immunohistochemistry.Results1. Descriptive statisticsQuantitative analysis:24 experimental rats can successfully were placed catheters into the jugular vein, and accomplish infusion demands without obvious discomfortable, no catheter swapped out from the vein, no catheter was blocked and no infection, no autophagic death, fully integrated into the statistical results.2. Basic informationThere is no significant difference among body weight, baseline threshold of mechanical and heat stimulus (P>0.05).3. There is no significant difference in baseline threshold of mechanical and heat stimulus after jugular vein catheterization in rats (P>0.05).4. The threshold in group R was significantly higher at T2 to T6 and lower at T7 toT9 than group N. The threshold comparison of group KR and group N had significant different at T2 to T9 The comparison of the threshold group KR and group R had no significant different at T2 to T5, but had significant different at T7 to T9.5. Immunohistochemistry results showed that the expression of NMDA receptors increased expression in R group, while decreased expression in KR group and close to the level of group N.ConclusionIntravenous high dose remifentanil produces acute tolerance and withdrawal hyperalgesia, the effect can reverse or protected by prior intrathecal low ketamine.