Formalin-induced Nociception In Rats Research Articles

Toluene exposure enhances acute and chronic formalin-induced nociception in rats: Participation of 5-HT3 receptors

The purpose of this study was to evaluate the effect of acute toluene exposure on formalin (0.5% and 1%)-induced acute and long-lasting nociceptive hypersensitivity in rats. In addition, we sought to investigate the role of peripheral 5-HT3 receptors in the pronociceptive effect of toluene. Toluene exposure (6000ppm) for 30min enhanced 0.5% or 1% formalin-induced acute nociception and long-lasting secondary allodynia and hyperalgesia. In contrast, exposition to toluene for 30min in rats previously injected (six days before) with 1% formalin did not affect long-lasting hypersensitivy. Local peripheral pre-treatment with alosetron (5-HT3 receptor antagonist, 10–100 nmol) reduced the pronociceptive effect of toluene in acute nociception and long-lasting secondary allodynia and hyperalgesia. Alosetron (100nmol) was also able to reduce the nociceptive effects of 1% formalin in absence of toluene. Moreover, local peripheral injection of m-CPBG (5-HT3 receptor agonist, 300 nmol) enhanced 0.5% formalin-induced acute and long-lasting nociception in air- and toluene-exposed rats. Alosetron (10nmol) blocked the pronociceptive effects of m-CPBG (300nmol) on 0.5% formalin-induced acute and long-lasting hypersensitivity in rats exposed to toluene. Alosetron (at 10nmol) did not modify formalin-induced nociceptive behaviors. Finally, local peripheral pre-treatment with methiothepin (non-selective 5-HT receptor antagonist, 1.5nmol), did not affect the pronociceptive effect of toluene on 1% formalin-induced acute and long-lasting hypersensitivity. Our data demonstrate that acute exposure to toluene has pronociceptive effects in formalin-induced acute nociception and long-lasting hypersensitivity. Our data suggest that this pronociceptive effect depend on activation of peripheral 5-HT3, but not methiothepin-sensitive 5-HT, receptors.

Synergistic Interaction Between Intrathecal Ginsenosides and Morphine on Formalin-Induced Nociception in Rats

We defined the nature of the pharmacological interaction between ginsenosides and morphine in a nociceptive state and clarified the role of the different types of opioid receptor in the effects of ginsenosides. An intrathecal catheter was placed in male Sprague-Dawley rats. Pain was induced by formalin injection into the hindpaw. Isobolographic analysis was used to evaluate drug interactions. Furthermore, a nonselective opioid receptor antagonist (naloxone), a μ opioid receptor antagonist (CTOP), a δ opioid receptor antagonist (naltrindole), and a κ opioid receptor antagonist (GNTI) were given intrathecally to verify the involvement of the opioid receptors in the antinociceptive effects of ginsenosides. Both ginsenosides and morphine produced antinociceptive effects in the formalin test. Isobolographic analysis revealed a synergistic interaction after intrathecal delivery of the ginsenosides-morphine mix. Intrathecal CTOP, naltrindole, and GNTI reversed the antinociceptive effects of ginsenosides. RT-PCR indicated that opioid receptors’ mRNA was detected in spinal cord of naïve rats and the injection of formalin had no effect on the expression of opioid receptors’ mRNA. Taken together, our results indicate synergistic antinociception following intrathecal coadministration of a ginsenosides/morphine mix in the formalin test, and that μ, δ, and κ opioid receptors are involved in the antinociceptive mechanism of ginsenosides. Perspective This article concerns the antinociceptive activity of ginsenosides, which increases antinociception by morphine. Thus, a spinal combination of ginsenosides and morphine may be useful in the management of acute pain as well as facilitated state pain.

Combined Comparative and Chemical Proteomics on the Mechanisms of levo-Tetrahydropalmatine-Induced Antinociception in the Formalin Test

This study investigated the mechanisms involved in the antinociceptive action induced by levo-tetrahydropalmatine (l-THP) in the formalin test by combined comparative and chemical proteomics. Rats were pretreated with l-THP by the oral route (40 mg/kg) 1 h before formalin injection. The antinociceptive effect of l-THP was shown in the first and second phases of the formalin test. To address the mechanisms by which l-THP inhibits formalin-induced nociception in rats, the combined comparative and chemical proteomics were applied. A novel high-throughput comparative proteomic approach based on 2D-nano-LC-MS/MS was applied to simultaneously evaluate the deregulated proteins involved in the response of l-THP treatment in formalin-induced pain rats. Thousands of proteins were identified, among which 17 proteins survived the stringent filter criteria and were further included for functional discussion. Two proteins (Neurabin-1 and Calcium-dependent secretion activator 1) were randomly selected, and their expression levels were further confirmed by Western Blots. The results matched well with those of proteomics. In the present study, we also described the development and application of l-THP immobilized beads to bind the targets. Following incubation with cellular lysates, the proteome interacting with the fixed l-THP was identified. The results of comparative and chemical proteomics were quite complementary. Although the precise roles of these identified moleculars in l-THP-induced antinociception need further study, the combined results indicated that proteins associated with signal transduction, vesicular trafficking and neurotransmitter release, energy metabolism, and ion transport play important roles in l-THP-induced antinociception in the formalin test.

Interaction between intrathecal ginsenosides and morphine on formalin-induced nociception in rats

Interaction between intrathecal ginsenosides and morphine on formalin-induced nociception in rats

Effects of Mepyramine and Famotidine on the Physostigmine-Induced Antinociception in the Formalin Test in Rats

In this study, the effects of mepyramine (H1-receptor antagonist), famotidine (H2-receptor antagonist), physostigmine (a cholinesterase inhibitor) and atropine (muscarinic-receptor antagonist) have investigated on the formalin-induced nociception in rats. The effects of mepyramine and famotidine have also examined on nociceptive changes induced by physostigmine and atropine. Nociception was induced by intraplantar injection of formalin (50 microL, 1%) into the right hind paw and the time spent licking and biting of the injected paw, was taken as a measure of pain. Formalin induced a marked biphasic (first phase: 0-5 min and second phase: 15-45 min) pain response. The used drugs did not change the first phase of formalin-induced pain. Subcutaneous injection of physostigmine significantly (p<0.05) suppressed pain. Subcutaneous injection of atropine alone did not change the intensity of pain, but pretreatment with atropine significantly (p<0.05) prevented physostigmine-induced antinociception. Intraperitoneal injections of mepyramine and famotidine significantly (p<0.05) decreased pain response. Mepyramine did not significantly change, but famotidine significantly (p<0.05) prevented analgesic effect of physostigmine on pain. Atropine did not inhibit the antinociceptive effects of both mepyramine and famotidine on formalin-induced nociception. These results indicate that physostigmine through muscarinic cholinergic receptors suppresses the pain induced by formalin. Both H1 and H2 receptor antagonists produce antinociception. Histamine H2, but no H1 antagonists may be involved in physostigmine-induced antinociception.

Antinociceptive Effect of Intraperitoneally Administered 5,5-dimethyl-1-pyrroline N-oxide on Formalin Induced Nociception in Rats

Background: Reactive oxygen species (ROS) is known to be involved in chronic and persistent pain. By using the ROS scavenger 5,5-dimethyl-1-pyrroline N-oxide (DMPO), we studied the effects of ROS on formalin-induced nociception in rats. Methods: 5% formalin was injected in the left hind paw after intraperitoneal injection of saline or various doses of DMPO (10 mg/kg, 30 mg/kg, 100 mg/kg). Number of flinches was measured in a 5 minute interval for 1 hour. Results: Formalin injected into the left hind paw induced a biphasic nociceptive behaviour. Intraperitoneal injection of DMPO diminished nociceptive behaviors dose-dependently during phase 2 but not phase 1. Conclusions: ROS might be involved in central sensitization and DMPO, a ROS scavenger, posses antinociceptive property in rats subjected to formalin induced hyperalgesia. (Korean J Anesthesiol 2008; 54: S 35～9)

Additive Antinociception between Intrathecal Sildenafil and Morphine in the Rat Formalin Test

The possible characteristics of spinal interaction between sildenafil (phosphodiesterase 5 inhibitor) and morphine on formalin-induced nociception in rats was examined. Then the role of the opioid receptor in the effect of sildenafil was further investigated. Catheters were inserted into the intrathecal space of male Sprague-Dawley rats. For induction of pain, 50 µL of 5% formalin solution was applied to the hind-paw. Isobolographic analysis was used for the evaluation of drug interaction between sildenafil and morphine. Furthermore, naloxone was intrathecally given to verify the involvement of the opioid receptor in the antinociception of sildenafil. Both sildenafil and morphine produced an antinociceptive effect during phase 1 and phase 2 in the formalin test. The isobolographic analysis revealed an additive interaction after intrathecal delivery of the sildenafil-morphine mixture in both phases. Intrathecal naloxone reversed the antinociception of sildenafil in both phases. These results suggest that sildenafil, morphine, and the mixture of the two drugs are effective against acute pain and facilitated pain state at the spinal level. Thus, the spinal combination of sildenafil with morphine may be useful in the management of the same state. Furthermore, the opioid receptor is contributable to the antinocieptive mechanism of sildenafil at the spinal level.

Effects of morphine on formalin-induced nociception in rats

This study focused on the antinociceptive action of morphine in the formalin test in rats. Formalin-induced behaviour is characterised by two phases relevant to acute and tonic pain. Morphine (1–6 mg/kg) was administered systemically before or after the early phase, and its ability to affect the late phase was investigated. Inhibitory effects of morphine (3 mg/kg) injected immediately after the early phase were significantly stronger (32±9%) compared to the preemptive administration (84±29%, relative to saline-treated controls, 5% formaldehyde). It appears that some neural and/or behavioural changes during the early phase limit effects of morphine on the late phase. Furthermore, manipulation of stimulation intensity (2% vs. 5% formaldehyde) significantly affected the ability of morphine (3 mg/kg) to suppress early (55±7% and 76±10%, respectively) but not late phase of formalin-induced behaviours. These results agree with the previous demonstrations on the effects of acute nociceptive stimulation intensity on analgesic potency of opiate drugs. Thus, the present study revealed two factors that affect the potency of morphine in formalin test: administration regimen and formalin concentration.

The role of spinal muscarinic acetylcholine receptors in clonidine-induced anti-nociceptive effects in rats.

We have examined the effects of intrathecal (i.t.) injection of the muscarinic acetylcholine receptor antagonist atropine on the clonidine-induced nociceptive effect in formalin-induced nociception in rats. The injection of 5% formalin into the hind paw caused biphasic nociceptive responses, and i.t. injection of clonidine inhibited both phases of the nociceptive response in a dose-dependent manner. Pretreatment with atropine (i.t.) only partially inhibited the nociceptive effect of clonidine. These results suggest that the nociceptive effect of clonidine in the rat formalin model may be at least partly mediated by muscarinic acetylcholine receptors in the spinal cord.

Dual effects of spinally delivered 8-bromo-cyclic guanosine mono-phosphate (8-bromo-cGMP) in formalin-induced nociception in rats

The rat formalin assay was used to assess effects of the cyclic guanosine mono-phosphate (cGMP) analog, 8-bromo-cGMP on nociception and cGMP dependent protein kinase I (protein kinase G; PKG-I) expression in lumbar spinal cord. Intrathecal (i.t.) delivery of low doses of 8-bromo-cGMP (0.1–0.25 μmol) reduced nociceptive behavior and formalin-induced upregulation of PKG-I in the spinal cord. Medium doses (0.5–1 μmol i.t.) had no effect and high doses (2.5 μmol i.t.) caused hyperalgesia associated with a further increase of PKG-I expression and a PKG-I clip. To explain these dose-dependent contrary effects we assessed the potential involvement of various cGMP targets: protein kinase G, cyclic nucleotide gated cation channels (CNGs), phosphodiesterases (PDE2 and PDE3) and AMPA-receptors. The PKG inhibitor, Rp-8-bromo-cGMPS did not antagonize the antinociceptive effects of 8-bromo-cGMP but caused antinociception itself. Inhibitors of CNGs, PDE2 and PDE3 had no effect on formalin evoked nociceptive behavior. S-AMPA however, antagonized the antinociceptive effects of 8-bromo-cGMP. Since AMPA receptor currents were found to be reduced by 8-bromo-cGMP in vitro a direct or indirect reduction of AMPA receptor currents might possibly contribute to the antinociceptive effects of 8-bomo-cGMP. On the other hand, 8-bromo-cGMP evoked antinociception appears to be largely independent of PKG-I, CNGs, PDE2 and PDE3. The antinociceptive effects of the PKG inhibitor suggest that a strong PKG activation may be responsible for ‘high dose’ 8-bromo-cGMP evoked hyperalgesia.

Antagonist of nicotinic acetylcholine receptors (nAChR) enhances formalin-induced nociception in rats: tonic role of nAChRs in the control of pain following injury

Following tissue injury, spinal neurons increase in spontaneous activity and in responsiveness to peripheral stimulation. These changes in spinal neurons may underlie abnormal pain behavior. Nicotinic acetylcholine receptor (nAChR) agonists are analgesic when evaluated in animal models of pain, but it is not known if the nAChRs differentially modulate acute and tonic pain. To test this, mecamylamine, a non-subtype selective nAChR antagonist, was systemically injected into rats prior or after hind paw injection of formalin. Formalin injection results in biphasic pain-related behaviors, characterized by a first phase (i.e. acute pain) immediately following formalin injection, then by a second phase (i.e. tonic pain) 15–60 min after formalin injection. Either pre- or post-formalin treatment with mecamylamine decreased phase 1 behaviors and significantly increased phase 2 pain behaviors in a dose-dependent manner. These results suggest that nAChRs may exert opposing effects on acute versus tonic pain and, as such, may have implications for the potential development of nAChR ligands for the treatment of pain.

痛覚過敏における脊髄後角 N 型 Ca チャネルおよびプロテインキナーゼ C の役割

Hyperalgesia following peripheral nociception may be mediated by up-regulated synaptic transmission of spinal cord. N-type Ca channel, which is ω-Conotoxin (ω-CgTx) sensitive, and the protein kinase C (PKC) localized at presynaptic terminal are possibly concerned in pain modulation. However, role of these synaptic regulation exerted by concurrent amino acids release and pain response is not fully understood. The purpose of the present study was to investigate whether manipulation by inhibitors for PKC and N-type Ca channel modulate similar pain-related response in relation to CSF amino acids following formalin-induced nociception in rats. In addition, we compared characteristics with morphine well-known as a potent pre-and post synaptic inhibitor in modulating hyperalgesia. Three days after intrathecal implantation of PE-10 catheter along with loop - type microdialysis probe in male Sprague-Dawley rats, 50 μl of 5% formalin was subcutaneously injected into left hind paw. Thereafter, simultaneous determinations of microdialysis at 10 min. -intervals for glutamate by HPLC-ECD and observation of flinches were performed for 60 min after intrathecal administration of either drugs (saline for control, the N-type Ca channel blocker ω-CgTx, the PKC inhibitor staurosporine (STU), STU combined with the PKC activator PDBu, the opioid receptor agonist morphine). Biphasic increases of flinches after injection of formalin were observed ; phase 1 (max. 13 flinches/min. at 1 min.) and phase 2 (max. 22 flinches/min. at 30-45 min.). ω-CgTx attenuated flinches during both phase 1 and 2 periods. STU attenuated flinches during phase 2 period and this inhibition was reversed by combined use of PDBu. CSF glutamate in saline group was transiently increased by 149±12% during first 10 min but this increase of glutamate was supressed by ω-CgTx and STU. With morphine, both increased CSF glutamate release and biphase of finchings after formalin injection were completely supressed. The present results clearly demonstrated that ω-CgTx inhibits the both phases of flinchings as shown with morphine, associated with supressed glutamate release, suggesting Ntype Ca channel may regulate neurotransmitter release evoked by C fiber activation. In contrast, the significant inhibition of second phase of flinches (hyperalgesia) with supression of glutamate release by PKC inhibitor, staurosporine, was reversed by combined use of PKC activator, suggesting possible contribution in developing hyperalgesia through the mechanism that PKC evokes both pre synaptic neurotransmitter release and activation of NMDA receptor at post synaptic event.