Decreased substance P and NK1 receptor immunoreactivity and function in the spinal cord dorsal horn of morphine-treated neonatal rats

Probucol Ameliorates Complete Freund's Adjuvant-Induced Hyperalgesia by Targeting Peripheral and Spinal Cord Inflammation

The effect of the lipid-lowering agent probucol in inflammatory hyperalgesia and leukocyte recruitment was evaluated in a model of subacute inflammation by Complete Freund's adjuvant (CFA). As CFA induces long-lasting nociception characterized by peripheral and spinal cord inflammation, the anti-inflammatory activity of probucol was assessed at both foci. Probucol at 0.3-3 mg/kg was administrated per oral daily starting 24 h after CFA intraplantar injection. Mechanical and thermal hyperalgesia induced by CFA were determined using an electronic anesthesiometer and hot plate apparatus, respectively. Post-treatment with probucol at 3 mg/kg inhibited CFA-induced hyperalgesia over the course of 7 days as well as paw edema. Overt pain-like behaviors, which were determined by the number of flinches and time spent licking paw immediately following CFA injection, were also reduced by probucol at 3 mg/kg administered as a pre-treatment. To investigate the mechanisms underlying the analgesic effect of probucol, neutrophil recruitment to paw was assessed by myeloperoxidase activity, cytokine production, Cox-2 expression, and NF-κB activation in both paw and spinal cord by ELISA. Iba-1, GFAP, and substance P protein expression and nuclear localization of phosphorylated NF-κB were evaluated in the spinal cord by immunofluorescence. Probucol at 3 mg/kg attenuated neutrophil recruitment, cytokine levels, and NF-κB activation as well microglia and astrocyte activation, and substance P staining in the spinal cord. Taken together, the results suggest that probucol exerts its analgesic and anti-inflammatory activity in an experimental model of persistent inflammation by targeting the NF-κB pathway in peripheral and spinal cord foci.

4218T/C polymorphism associations with post-cesarean patient-controlled epidural fentanyl consumption and pain perception

BACKGROUND

The utilization of intrathecal opioids is an efficacious component of post-cesarean section pain management. Given that growing evidence indicates that calcitonin gene-related peptide (CGRP) plays a key role in the development of peripheral sensitization and is associated with enhanced pain, we hypothesized that CGRP 4218T/C polymorphism is associated with the variability in fentanyl consumption for post-cesarean analgesia.

METHODS

We recruited 548 patients who presented for elective cesarean delivery, and used polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method to analyze CGRP 4218T/C polymorphism. We examined the association of CGRP 4218T/C polymorphism and post-operative fentanyl consumption for analgesia as well as adverse reactions to fentanyl in those patients who received cesarean section surgeries.

RESULTS

We found that the CGRP 4218T/C polymorphism has a significant effect on pain perception, analgesic requirement, and nausea and vomiting for the first 24 h after cesarean delivery in patients who received PCEA fentanyl. Individuals with the C/C genotype had more pain, required more PCEA fentanyl, and experienced a lower incidence of nausea and vomiting.

CONCLUSION

These results indicated that patients with C/C genotype may have reduced sensitivity to fentanyl analgesia and/or increased pain perception, and were more willing to use PCEA fentanyl to manage their pain.

Neurokinin 1 and opioid receptors: relationships and interactions in nervous system

Opioid receptors and neurokinin 1 receptor (NK1R) are found highly expressed in the central nervous system. The co-localization of these two kinds of receptors suggests that they might interact with each other in both the transmission and modulation of the pain signal. In this review, we explore the relationships between opioid receptors and NK1R. Substance P (SP) plays a modulatory role in the pain transmission by activating the NK1R. Opioid receptor activation can inhibit SP release. NK1R is found participating in the mechanisms of the side effects of the opioids, including opioid analgesic tolerance, hyperalgesia, anxiety behaviors of morphine reward and opioids related respiratory depression. A series of compounds such as NK1R antagonists and ligands works on both mu/delta opioid receptor (MOR/DOR) and NK1R were synthesized as novel analgesics that enhance the clinical pain management efficacy and reduce the dosage and side effects. The current status of these novel ligands and the limitations are discussed in this review. Although the working mechanisms of these ligands remained unclear, they could be used as research tool for developing novel analgesic drugs in the future.

CGRP 4218T/C polymorphism correlated with postoperative analgesic effect of fentanyl

PURPOSE

Our study aimed at evaluating the association between α-calcitonin gene-related peptide (CGRP) 4218T/C polymorphism and the patient-controlled analgesic (PCA) effect of fentanyl on Chinese Han population.

METHODS

98 patients were involved in the experiment, but only 92 patients completed the experiment. 0.1 mg/kg fentanyl was given to the patients through intravenous injection ten minutes before the ending of surgery. The patients achieved PCA by controlling the fentanyl infusion pump and a single dose was 1 mg. The CGRP 4218T/C polymorphism was genotyped with polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) method. The fentanyl consumption within the 72 hours after the surgery was recorded and the pain was assessed with numeric rating scale (NRS) method.

RESULTS

The patients were divided into three groups of wild homozygote (T/T), heterozygote (T/C), and mutant homozygote (C/C). At the 6th hour and the 12th hour after the surgery, the fentanyl consumption for PCA of the T/C group was significantly higher than the T/T group (P<0.05). Meanwhile, the fentanyl consumption of the C/C group was much higher than the T/T group (P<0.05) at the 12th hour and the 24th hour. Besides, the fentanyl consumption of the C/C group was more than the T/C group (P<0.05) at the 24th hour. The differences in NRS scores, Ramsey scores, and postoperative adverse reactions between each group at all time points were not statistically significant.

CONCLUSIONS

CGRP 4218T/C polymorphism may be associated with the postoperative fentanyl consumption for analgesia.

Changing mechanisms of opiate tolerance and withdrawal during early development: animal models of the human experience

Human infants may be exposed to opiates through placental transfer from an opiate-using mother or through the direct administration of such drugs to relieve pain (e.g., due to illness or neonatal surgery). Infants of many species show physical dependence and tolerance to opiates. The magnitude of tolerance and the nature of withdrawal differ from those of the adult. Moreover, the mechanisms that contribute to the chronic effects of opiates are not well understood in the infant but include biological processes that are both common to and distinct from those of the adult. We review the animal research literature on the effects of chronic and acute opiate exposure in infants and identify mechanisms of withdrawal and tolerance that are similar to and different from those understood in adults. These mechanisms include opioid pharmacology, underlying neural substrates, and the involvement of other neurotransmitter systems. It appears that brain circuitry and opioid receptor types are similar but that NMDA receptor function is immature in the infant. Intracellular signaling cascades may differ but data are complicated by differences between the effects of chronic versus acute morphine treatment. Given the limited treatment options for the dependent infant patient, further study of the biological functions that are altered by chronic opiate treatment is necessary to guide evidenced-based treatment modalities.

Endogenous opiates and behavior: 2008

This paper is the 31st consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2008 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Rapid, opioid-sensitive mechanisms involved in transient receptor potential vanilloid 1 sensitization

TRPV1 is a nociceptive, Ca2+-selective ion channel involved in the development of several painful conditions. Sensitization of TRPV1 responses by cAMP-dependent PKA crucially contributes to the development of inflammatory hyperalgesia. However, the pathways involved in potentiation of TRPV1 responses by cAMP-dependent PKA remain largely unknown. Using HEK cells stably expressing TRPV1 and the mu opioid receptor, we demonstrated that treatment with the adenylate cyclase activator forskolin significantly increased the multimeric TRPV1 species. Pretreatment with the mu opioid receptor agonist morphine reversed this increased TRPV1 multimerization. FRET analysis revealed that treatment with forskolin did not cause multimerization of pre-existing TRPV1 monomers on the plasma membrane and that intracellular pools of TRPV1 exist mostly as monomers in this model. This suggests that increased TRPV1 multimerization occurred from an intracellular store of inactive TRPV1 monomers. Treatment with forskolin also caused an increase in TRPV1 expression on the plasma membrane not resulting from increased TRPV1 expression, and this rapid TRPV1 translocation was inhibited by treatment with morphine. Thus, potentiation of TRPV1 responses by cAMP-dependent PKA involves plasma membrane insertion of functional TRPV1 multimers formed from an intracellular store of inactive TRPV1 monomers. This potentiation occurs rapidly and can be dynamically modulated by activation of the mu opioid receptor under conditions where cAMP levels are raised, such as with inflammation. Increased translocation and multimerization of TRPV1 channels provide a cellular mechanism for fine-tuning of nociceptive responses that allow for rapid modulation of TRPV1 responses independent of transcriptional changes.

Substance P: An Inflammatory Peptide

Substance P (SP) is involved in neurogenic inflammation and in the pathogenesis of several inflammatory diseases, demonstrating that there is a narrow interrelationship between the nervous system and immunity. Macrophage functions are altered in stress, therefore, since SP is a macrophage activator, its biological effect has been intimately linked to stress. In fact, SP enhances LPS-induced macrophage TNFα production from stressed animals and stimulates the production of IL-8 CXC chemokine response in a mast cell line in vitro. The stress-induced cytokines from macrophage also alter and contribute to inflammation. Understanding the pathophysiology of inflammation and the role of the chemical mediator SP may improve inflammation management.