Anti-analgesic Effect Research Articles

Receptor Activator of NF-kB Ligand Induced Osteoclastogenesis in Cervical Spondylosis - Role of Balamula Ghritam (A Powerful Antioxidant Drug) as Uttarabhaktika Sneha

The discs which are located in between the vertebras to act as shock absorbers during jolts to prevent spine injuries get either dislocated, bulged out or get thinned on continuous pressure being exerted upon them either by travel or a posture that is unsuitable to their alignment. In cases of discs getting thinned out and the height of these discs get reduced due to various causes produce undue pressure over the cervical spine resulting in oxidative stress and production of free radicals in the body causing deterioration of bone tissue and bone mass leading to regulation of RANKL/OPG ratio levels causing degeneration of bone. It is possible to resurrect the dehydrated discs with rehydration using Balamula (Sida cordifolia root) with the help of its properties and actions that it can positively act upon the area by refilling the gaps of erosions and assure a recovery with the proper administration of it in the form of ghee which has been processed with it and its intake being after food. Material & Methods: Various Ayurvedic classical textbooks and published journal articles were reviewed and analysed. Results: Evidences from various studies show that the phytochemicals obtain from Balamula (Sida cordifolia root) and Go- Ghritam (cow’s ghee) acts as antioxidant, reduces the activity of osteoclast and bone resorption by inhibiting RANKL receptor pathway. It also has anti-inflammatory, anti-arthritic, anti-analgesic effect that found to be effective in reducing the symptoms of cervical spondylosis.

Effect of Balamula Ghrita Uttarabhaktika Sneha and Mashasaindhava Taila Pichu in the Management of Cervical Spondylosis - A Single Arm Prospective Open Randomized Clinical Study

In Ayurveda prevalence of Vayu mahabhuta is considered as prime factor that causes deterioration of qualities of Kapha in Greeva stana hence prescription of drugs having Vatanuloma and qualities of Prithvi and Jala mahabhuta would be very effective. In the present study humble attempt is made to evaluate the effect of Balamula Ghritam internally and combined with Mashasaindhava Tailam as external pack in arresting further degeneration. Materials and methods: 40 patients fulfilling the inclusion criteria after signing the informed consent form were selected from SJSACH [IEC N0-IEC/SJSACH/ 05/2021, CTRI N0 - CTRI/2021/07/034968]. It is a single arm prospective open randomized clinical study. Patients were administered with 10ml of Balamula Ghritam morning and night after food and Mashasaindhava Tailam as pichu (external pack) over the cervical area for 21 days with two follow ups after the completion of the trial. Result: Subjective parameters were assessed using Friedman test and Wilcoxon signed rank test and objective parameters were assessed using paired sample t test. All the parameters had highly significant results with significant p value at the end of the treatment. Conclusion: The combined effect of Balamula Ghritam and Mashasaindhava Tailam was very effective in the management of cervical spondylosis. The critical analysis of the contents of Balamula Ghritam and Mashasaindhava Tailam acts as antioxidant, removes free radicals ROS, reduces the activity of osteoclast and bone resorption by inhibiting RANKL receptor pathway. It also has anti- inflammatory, anti-arthritic, anti-analgesic effect that found to be effective in reducing the symptoms of cervical spondylosis.

Preventive effects of naldemedine, peripherally acting μ-opioid receptor antagonist, on morphine-induced nausea and vomiting in ferrets

AimsNaldemedine is a peripherally acting μ-opioid receptor antagonists (PAMORAs) indicated for the treatment of opioid-induced constipation (OIC). We investigated the preventive effect of naldemedine on morphine-induced nausea and vomiting in ferrets and conducted a pharmacokinetic/pharmacodynamic (PK/PD) analysis. Main methodsThe antiemetic effect of naldemedine was evaluated as the frequency and time of retching (rhythmic abdominal contractile motion) and vomiting (throwing up vomit or similar reactions) caused by morphine in ferrets. After a single oral administration of naldemedine to ferrets, the plasma concentrations of naldemedine and morphine were measured by liquid chromatography–tandem mass spectrometry. Key findingsNaldemedine showed a potent and dose-dependent anti-emetic effects against morphine-induced emetic responses, for up to 6 h. The dose of naldemedine that produced half the maximal effect (ED50) value for anti-emetic effect of naldemedine in the morphine-treated ferrets was 0.033 mg/kg. The PK/PD analysis revealed that the antiemetic effect was related to the plasma naldemedine concentration, with a half maximal effective concentration that produces half the maximal effect (EC50) of 3.51 ng/mL. The plasma concentration producing an antiemetic effect was almost 200-fold lower than that inducing an anti-analgesic effect in rats. SignificanceNaldemedine showed potent inhibition of morphine-induced vomiting for up to 6 h after dosing. These data suggest that naldemedine possesses antiemetic properties and could be effective against opioid-induced nausea and vomiting (OINV).

Blockade of the orexin receptors in the CA1 region of hippocampus decreased the lateral hypothalamic-induced antinociceptive responses in the model of orofacial formalin test in the rats

The role of hippocampus and lateral hypothalamus (LH) in modulation of formalin-induced nociception has been established. The present study aims to examine the role of orexin receptors in the Cornu Ammonis 1 (CA1) region of hippocampus in modulation of the LH-induced antinociception in the orofacial formalin test. Male Wistar rats were unilaterally implanted with two cannulae into the LH and CA1. Intra-LH microinjection of carbachol was done 5min after intra-CA1 administration of SB-334867 (OX1R antagonist) or TCS OX2 29 (OX2R antagonist). After 5min, 50μl of 1% formalin was subcutaneously injected into the upper lip for inducing the nociceptive behaviors. Solely intra-LH administration of carbachol reduced early and late phases of formalin-induced orofacial nociception in a dose-dependent manner. The antinociception evoked by intra-LH injection of carbachol (0.5μl of 250nM carbachol) was antagonized by intra-CA1 administration of 0.5μl of 3, 10 and 30nM solutions of SB-334867 or TCS OX2 29 during the early and late phases of orofacial formalin test. This effect was more remarkable during the late phase in comparison to the early phase. In addition, anti-analgesic effect of SB-334867 was more than TCS OX2 29 during the early and late phases. The results suggest the interpretation that a neural pathway from the LH to the CA1 probably contributes to the modulation of formalin-induced orofacial nociception through recruitment of both CA1 orexin receptors. Clinical studies are recommended to study the probable effectiveness of orexinergic system in modulation of the orofacial nociceptive responses.

Role of orexin-2 receptors in the nucleus accumbens in antinociception induced by carbachol stimulation of the lateral hypothalamus in formalin test.

Orexins, which are mainly produced by orexin-expressing neurons in the lateral hypothalamus (LH), play an important role in pain modulation. Previously, it has been established that the nucleus accumbens (NAc) is involved in the modulation of formalin-induced nociceptive responses, a model of tonic pain. In this study, the role of intra-accumbal orexin-2 receptors (OX2rs) in the mediation of formalin-induced pain was investigated. A volume of 0.5 μl of 10, 20, and 40 nmol/l solutions of TCS OX2 29, an OX2r antagonist, were unilaterally microinjected into the NAc 5 min before an intra-LH carbachol microinjection (0.5 μl of 250 nmol/l solution). After 5 min, animals received a subcutaneous injection of formalin 2.5% (50 μl) into the hind paw. Pain-related behaviors were assessed at 5 min intervals during a 60-min test period. The findings showed that TCS OX2 29 administration dose dependently blocked carbachol-induced antinociception during both phases of formalin-induced pain. The antianalgesic effect of TCS OX2 29 was greater during the late phase compared with the early phase. These observations suggest that the NAc, as a part of a descending pain-modulatory circuitry, partially mediates LH-induced analgesia in the formalin test through recruitment of OX2rs. This makes the orexinergic system a good potential therapeutic target in the control of persistent inflammatory pain.

Differential contribution of orexin receptors within the ventral tegmental area to modulation of persistent inflammatory pain.

Orexinergic neurons in the lateral hypothalamus (LH) play an important role in pain modulation. In addition, ventral tegmental area (VTA) is known as a part of descending pain modulatory circuitry. Little is known about the interaction between the LH and neural substrates involving in modulation of formalin-induced nociception. Accordingly, we aimed to examine the pain modulatory role of VTA orexin receptors in the formalin test. Seventy-eight male Wistar rats were unilaterally implanted with two cannulae above the LH and VTA. Intra-VTA administration of SB-334867 (orexin-1 receptor antagonist) or TCS OX2 29 (orexin-2 receptor antagonist) was performed 5min before intra-LH microinjection of carbachol (a cholinergic receptor agonist). The procedure was followed by subcutaneous injection of formalin after 5-min interval time. Carbachol attenuated formalin-induced biphasic pain responses and SB-334867 or TCS OX2 29 administration dose-dependently antagonized the LH-induced analgesia during both phases. Blockade of orexin-1 and -2 receptors had more profound effects on the reduction of antinociception during the late phase compared to the early phase. Also, contribution of orexin-1 receptors in mediation of LH-induced analgesia was greater than orexin-2 receptors during the late phase. Formalin test, a model of persistent inflammatory pain, mimics the conditions encountered in clinical situations. Pain modulatory role of orexinergic system in the formalin test through a neural pathway from the LH to the VTA provides the evidence that orexins can be useful therapeutic targets for chronic pain treatment. WHAT DOES THIS STUDY ADD?: There is a pathway from the lateral hypothalamus (LH) to the ventral tegmental area (VTA) which modulates biphasic formalin-induced pain. Blockade of VTA orexin receptors dose-dependently reduces LH-induced analgesia during both phases. Anti-analgesic effect of orexin receptor antagonists is more considerable during the late phase. Contribution of orexin-1 receptors to mediation of LH-induced analgesia is more than orexin-2 receptors during the late phase.

Prophylactic administration of ondansetron in prevention of intrathecal morphine-induced pruritus and post-operative nausea and vomiting in patients undergoing caesarean section.

BackgroundIntrathecal morphine is commonly used for post caesarean analgesia. However, their use is frequently associated with the incidence of troublesome side effects such as nausea, vomiting and pruritus. Various mechanisms have been postulated for the opioid-induced pruritus, with a variety of medications with different mechanisms of actions formulated for the prevention and treatment. But, the results are inconsistent and hence the prevention and treatment of opioid-induced pruritus still remains a challenge. Ondansetron which is antiemetic, non-sedative and has no antianalgesic effect is an antagonist to 5-HT3 receptor, the receptor with which opioids interacts and imparts its effects. Ondansetron, thus, would be an attractive treatment strategy for both opioid-induced pruritus and post-operative nausea and vomiting.MethodsAfter the approval from institutional review committee and written consent received from the patient, 50 healthy parturients of ASA I and II physical status undergoing caesarean section under spinal anaesthesia were enrolled for the study. They were randomly categorized into placebo group (2 ml normal saline) and treatment group (2 ml of 4 mg ondansetron), each group containing 25 patients. Pruritus and post-operative nausea and vomiting scores were recorded up to 24 hours after the administration of intrathecal morphine. Statistical analysis was performed using chi-square test.ResultsThe incidence, severity and necessity of treatment for pruritus in the treatment group was significantly reduced compared to the placebo group (16% vs 88%). Similarly, the risk of post-operative nausea and vomiting in the treatment group was less compared to the placebo group (8% vs 56%).ConclusionProphylactic administration of ondansetron to parturients receiving intrathecal morphine for post-operative analgesia provides a significant reduction of intrathecal morphine-induced pruritus and nausea and vomiting.Trial registrationCTRI/2015/01/005362 registered on 07/01/2015 in Clinical Trials Registry – India (ctri.nic.in).

Prevention versus treatment of intrathecal morphine-induced pruritus with ondansetron

BackgroundIntrathecal morphine is used for post-cesarean analgesia, but pruritus is a common side effect. Ondansetron would be an attractive treatment because it prevents nausea, is non-sedative or has no anti-analgesic effect. We undertook a study to assess the efficacy of ondansetron for treatment or prophylaxis of intrathecal morphine-induced pruritus. MethodsHealthy paturients undergoing cesarean delivery with intrathecal morphine 250μg and fentanyl 25μg were randomized to receive: prophylaxis (ondansetron 8mg at cord clamping, normal saline 4mL for treatment of pruritus in the post-anaesthesia care unit); treatment (normal saline 4mL at cord clamping, ondansetron 8mg as required in the post-anesthesia care unit) or control (normal saline 4mL in both). Visual analogue scale scores for pruritus, nausea and pain were recorded preoperatively, on arrival to, at 30, 60, and 120min and on discharge from the post-anesthesia care unit. The primary outcome was the peak pruritus score. ANOVA with Bonferroni correction or Fisher’s exact test were used to analyze data; P<0.05 was considered significant. ResultsThe study was terminated early when interim analysis indicated no effect. Eighty-two of the intended 180 paturients completed the protocol (26 in control group, 32 in treatment group and 24 in prophylaxis). There were no differences in the rate or severity of pruritus at any assessment point, or the request for treatment. Pruritus was reduced after administration of treatment syringe. ConclusionProphylactic ondansetron did not reduce pruritus when compared with placebo. The use of ondansetron as a treatment did not decrease the severity of pruritus when compared with placebo.

PC-FACS

PC-FACS

Modulation of pancreatic amylase secretion by tryptophan metabolite

Enterostatin (APGPR) found in the gastrointestinal tract and brain is an anorectic pentapeptide. We found that APGPR inhibited morphine-induced analgesia after intracerebroventricular administration in mice at a dose of 10 nmol/mouse. The anti-analgesic effect of APGPR was inhibited by pretreatment with lorglumide and LY225910, antagonists for cholecystokinin 1 (CCK1) and cholecystokinin 2 (CCK2) receptors, respectively. The anti-analgesic effect of APGPR may be mediated by CCK release, since APGPR does not have affinity for CCK receptors.

Anti-Analgesic Effect of the Mu/Delta Opioid Receptor Heteromer Revealed by Ligand-Biased Antagonism

Delta (DOR) and mu opioid receptors (MOR) can complex as heteromers, conferring functional properties in agonist binding, signaling and trafficking that can differ markedly from their homomeric counterparts. Because of these differences, DOR/MOR heteromers may be a novel therapeutic target in the treatment of pain. However, there are currently no ligands selective for DOR/MOR heteromers, and, consequently, their role in nociception remains unknown. In this study, we used a pharmacological opioid cocktail that selectively activates and stabilizes the DOR/MOR heteromer at the cell surface by blocking its endocytosis to assess its role in antinociception. We found that mice treated chronically with this drug cocktail showed a significant right shift in the ED50 for opioid-mediated analgesia, while mice treated with a drug that promotes degradation of the heteromer did not. Furthermore, promoting degradation of the DOR/MOR heteromer after the right shift in the ED50 had occurred, or blocking signal transduction from the stabilized DOR/MOR heteromer, shifted the ED50 for analgesia back to the left. Taken together, these data suggest an anti-analgesic role for the DOR/MOR heteromer in pain. In conclusion, antagonists selective for DOR/MOR heteromer could provide an avenue for alleviating reduced analgesic response during chronic pain treatment.

(+)-Morphine attenuates the (−)-morphine-produced tail-flick inhibition via the sigma-1 receptor in the mouse spinal cord

Aims We have previously demonstrated that pretreatment with (+)-morphine given intrathecally attenuates the intrathecal (−)-morphine-produced tail-flick inhibition. The phenomenon has been defined as antianalgesia against (−)-morphine-produced analgesia. Present experiments were then undertaken to determine if the antianalgesic effect induced by (+)-morphine given spinally is mediated by the stimulation of the sigma-1 receptor in the mouse spinal cord. Main methods Sigma-1 receptor ligands, N-[2-(3,4-Dichlorophenyl)ethyl]- N-methyl-2-(dimethylamino)ethylamine dihydrobromide (BD1047) and (+)-pentazocine were used to determine if (+)-morphine-induced antianalgesia is mediated by the stimulation of sigma-1 receptors in the mouse spinal cord. Tail-flick test was employed to measure the nociceptive response. All compounds were given intrathecally. Key findings Pretreatment with BD1047 (1–10 μg) or (+)-pentazocine (0.1–10 μg) dose-dependently reversed the attenuation of the (−)-morphine-produced tail-flick inhibition induced by (+)-morphine (10 pg). BD1047 and (+)-pentazocine injected alone did not affect (−)-morphine-produced tail-flick inhibition. Significance The finding indicates that (+)-morphine attenuates the (−)-morphine-produced tail-flick inhibition via the activation of the sigma-1 receptors in the mouse spinal cord. Sigma-1 receptors may play an important role in opioid analgesia in the mouse spinal cord.

L-type calcium channel blockers, morphine and pain: Newer insights

Earlier, we had reported that co-administration of opioids and L-type calcium channel blockers (L-CCBs) like diltiazem could prove useful in the treatment of cancer pain. Much of this report was based upon earlier published work involving animal models of pain exposed to brief periods of noxious radiant heat without any tissue injury. However, pain in clinical situations usually result from tissue injury. Thus, the aim of the current investigation was to study the analgesic effect of this combination of drugs in the rat formalin test which is associated with actual tissue injury. Wistar rats (n=60) received either L-CCB (nifedipine/nimodipine/verapamil/diltiazem i.p.) or morphine (s.c.) or both drugs. The formalin test was done 30 min after morphine or placebo injection. The naloxone reversal test was also done. Administration of L-CCBs alone, particularly diltiazem, increased pain in the formalin test. In contrast, co-administration of these L-CCBs with morphine led to decreased pain response, though statistically significant decrease was noted only with nimodipine + morphine. Naloxone reversed this analgesic effect, indicating that it was primarily an opioid-mediated effect. The results show that administration of L-CCBs alone may prove counterproductive in the therapeutic management of pain (anti-analgesic effect). However, co-administration of both drugs (morphine and nimodipine) in quick succession could lead to adequate pain relief.

Enterostatin (APGPR) suppresses the analgesic activity of morphine by a CCK-dependent mechanism

Enterostatin (APGPR) found in the gastrointestinal tract and brain is an anorectic pentapeptide. We found that APGPR inhibited morphine-induced analgesia after intracerebroventricular administration in mice at a dose of 10 nmol/mouse. The anti-analgesic effect of APGPR was inhibited by pretreatment with lorglumide and LY225910, antagonists for cholecystokinin 1 (CCK 1) and cholecystokinin 2 (CCK 2) receptors, respectively. The anti-analgesic effect of APGPR may be mediated by CCK release, since APGPR does not have affinity for CCK receptors.

A Subanalgesic Dose of Morphine Eliminates Nalbuphine Anti-Analgesia in Postoperative Pain

The agonist-antagonist kappa-opioid nalbuphine administered for postoperative pain produces greater analgesia in females than in males. In fact, males administered nalbuphine (5 mg) experience pain greater than those receiving placebo, suggesting the existence of an anti-analgesic effect. These sexually dimorphic effects on postoperative pain can be eliminated by coadministration of a fixed ratio of the prototypical opioid receptor antagonist naloxone with nalbuphine, implying a role for opioid receptors in the anti-analgesic as well as analgesic effects of nalbuphine. In the present study, we further evaluated the role of opioid receptors in the sex-specific effects on pain produced by nalbuphine by coadministering a dose of morphine low enough that it does not produce analgesia. After extraction of bony impacted third molar teeth, nalbuphine (5 mg) was administered alone or in combination with either of 2 low doses of morphine (2 mg or 4 mg). Both doses of morphine reversed nalbuphine-induced anti-analgesia in males, but only the lower dose (2 mg) reached statistical significance. Neither dose affected nalbuphine-induced analgesia in females, and when administered alone in either males or females, morphine (2 mg) had no analgesic effect. Though not observed in females, the effect of morphine in males argues that, like naloxone, low-dose morphine may act as an anti-analgesia opioid receptor antagonist. Previously, we reported that the nalbuphine produces both analgesic and anti-analgesic effects and that the opioid antagonist naloxone can enhance nalbuphine analgesia by selectively antagonizing the anti-analgesic effect. Here we show that morphine, given in a subanalgesic dose, reverses nalbuphine-induced anti-analgesia in males, perhaps by a similar mechanism.

Stereoselective action of (+)-morphine over (−)-morphine in attenuating the (−)-morphine-produced antinociception via the naloxone-sensitive sigma receptor in the mouse

We have previously demonstrated that (+)-morphine and (-)-morphine given spinally stereoselectively attenuate the spinally-administered (-)-morphine-produced tail-flick inhibition in the mouse. The phenomenon has been defined as antianalgesia. Present studies were then undertaken to determine if the systemic administration of (+)-morphine and (-)-morphine also stereoselectively attenuates the systemic (-)-morphine-produced tail-flick inhibition and the effects of (+)-morphine and (-)-morphine are mediated by the naloxone-sensitive sigma receptor activation in male CD-1 mice. Pretreatment with (+)-morphine at a dose of 0.01-10 ng/kg given subcutaneously dose-dependently attenuated the tail-flick inhibition produced by subcutaneously-administered (-)-morphine (5 mg/kg). Pretreatment with (-)-morphine (0.01-1.0 mg/kg) given subcutaneously also attenuates the (-)-morphine-produced tail-flick inhibition. The ED50 values for (+)-morphine and (-)-morphine for inhibiting the (-)-morphine-produced tail-flick inhibition were estimated to be 30.6 pg/kg and 97.5 microg/kg, respectively. The attenuation of the (-)-morphine-produced tail-flick inhibition induced by (+)-morphine or (-)-morphine pretreatment was reversed by the pretreatment with (+)-naloxone or by the sigma receptor antagonist BD1047 (N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine dihydrobromide) given subcutaneously. Pretreatment with (+)-pentazocine, a selective sigma receptor agonist, (1-10 mg/kg) given subcutaneously also attenuates (-)-morphine-produced tail-flick inhibition, which was restored by (+)-naloxone (4 mg/kg) or BD1047 (10 mg/kg) pretreated subcutaneously. It is concluded that (+)-morphine exhibits extremely high stereoselective action over (-)-morphine given systemically in attenuating the systemic (-)-morphine-produced antinociception and the antianalgesic effect of (+)-morphine and (-)-morphine is mediated by activation of the naloxone-sensitive sigma receptor.

Neuroleptics Antagonize Nalbuphine Antianalgesia

To evaluate the role of σ receptors in the sexually dimorphic antianalgesic effect of agonist-antagonist κ opioids, 2 neuroleptics, haloperidol, a σ receptor antagonist, and chlorpromazine, which has minimal effect at σ receptors, were administered with the agonist-antagonist κ opioid nalbuphine in patients with postoperative pain. Before surgical extraction of bony impacted mandibular third molar teeth, patients received haloperidol (1 mg), chlorpromazine (10 mg), or placebo by oral administration. After surgery, the pain intensity did not differ significantly between the 3 treatment groups, suggesting lack of analgesic effect produced by either haloperidol or chlorpromazine. All patients were then administered nalbuphine (5 mg, intravenous). As previously reported, the group that did not receive a preoperative neuroleptic exhibited sexually dimorphic analgesia, with women experiencing greater analgesia than men. Antianalgesia was also observed, with men experiencing late onset increased pain compared with baseline, starting approximately 1 hour after nalbuphine administration. Both neuroleptics blocked nalbuphine antianalgesia, resulting in enhanced analgesia and elimination of the sex differences. Because chlorpromazine and haloperidol enhanced nalbuphine analgesia and eliminated sexual dimorphism, the receptor at which neuroleptics act to antagonize the “antianalgesia” might be a common site of action to both drugs. Perspective This study demonstrates that neuroleptics can block the antianalgesic effect of agonist-antagonist κ opioids. These findings could help inform the development of novel analgesics.

Measuring Minimum Alveolar Concentration

Measuring Minimum Alveolar Concentration

Interleukin-1 antagonizes morphine analgesia and underlies morphine tolerance

Pain sensitivity reflects a balance between pain facilitatory and inhibitory systems. To characterize the relationships between these systems we examined the interactions between the analgesic effects of morphine and the anti-analgesic effects of the pro-inflammatory cytokine interleukin-1 (IL-1). We report that administration of a neutral dose of IL-1β abolished morphine analgesia in mice, whereas acute or chronic blockade of IL-1 signaling by various IL-1 blockers (IL-1 receptor antagonist (IL-1ra), α-melanocyte-stimulating hormone, or IL-1 tri-peptide antagonist) significantly prolonged and potentiated morphine analgesia. Morphine-induced analgesia was also extended in strains of mice genetically impaired in IL-1 signaling (mice with transgenic over-expression of IL-1 receptor antagonist, deletion of the IL-1 receptor type I, or deletion of the IL-1 receptor accessory protein). The finding that IL-1 produces a marked anti-analgesic effect, suggests that it may also be involved in the development of opiate tolerance. Indeed, genetic or pharmacological blockade of IL-1 signaling prevented the development of tolerance following repeated morphine administration. Moreover, acute administration of IL-1ra in wild type mice, either immediately following the cessation of acute morphine analgesia, or following the development of chronic morphine tolerance, re-instated the analgesia, suggesting that blockade of the IL-1 system unmasks the analgesic effect of morphine. These findings suggest that morphine produces an IL-1-mediated homeostatic response, which serves to limit the duration and extent of morphine analgesia and which underlies the development of tolerance.

Nociceptin/orphanin FQ prevents the antinociceptive action of paracetamol on the rat hot plate test

Nociceptin/orphanin FQ (N/OFQ) is involved in many behavioural patterns; in particular, it exerts a modulating effect on nociception. Like other proposed antiopiates, nociceptin/orphanin FQ has been shown to have analgesic, hyperalgesic as well as antianalgesic properties. Among the various effects proposed on nociceptive sensitivity at supraspinal level, the antagonistic activity toward morphine analgesia seems to be of interest. Therefore, we decided to investigate whether nociceptin/orphanin FQ and [Arg 14, Lys 15] nociceptin/orphanin FQ (R-K, a nociceptin analogue) can have the same effect on the analgesia produced by nonopioid analgesics. In this study, we examined the antianalgesic effect of nociceptin/orphanin FQ and its analogue R-K on paracetamol-induced analgesia and evaluated by means of the hot plate test in rats. Nociceptin/orphanin FQ was intracerebroventricularly administered, and, after 5 min, a dose of 400 mg/kg paracetamol was injected intraperitoneally, 30 min before the hot plate test. Nociceptin/orphanin FQ and R-K showed a dose-dependent antagonism on the antinociceptive effect of paracetamol, and the activity of both drugs was significantly reduced by the antagonist [Nphe 1] Arg 14, Lys 15–N/OFQ–NH 2 (UFP-101). These data indicate that nociceptin/orphanin FQ and R-K have an antianalgesic effect on the analgesia produced by a nonopioid analgesic drug, like paracetamol, that seems to develop within the brain.