Antinociception In Tail-flick Test Research Articles

Differential Tolerance to FTY720-Induced Antinociception in Acute Thermal and Nerve Injury Mouse Pain Models: Role of Sphingosine-1-Phosphate Receptor Adaptation.

The immunomodulatory prodrug 2-amino-2-(2-[4-octylphenyl]ethyl)-1,3-propanediol (FTY720), which acts as an agonist for sphingosine-1-phosphate (S1P) receptors (S1PR) when phosphorylated, is proposed as a novel pain therapeutic. In this study, we assessed FTY720-mediated antinociception in the radiant heat tail-flick test and in the chronic constriction injury (CCI) model of neuropathic pain in mice. FTY720 produced antinociception and antiallodynia, respectively, and these effects were dose-dependent and mimicked by the S1PR1-selective agonist CYM-5442. Repeated administration of FTY720 for 1 week produced tolerance to acute thermal antinociception, but not to antiallodynia in the CCI model. S1PR-stimulated [35S]GTPγS autoradiography revealed apparent desensitization of G protein activation by S1P or the S1PR1 agonist 5-[4-phenyl-5-(trifluoromethyl)-2-thienyl]-3-[3-(trifluoromethyl)phenyl]-1,2,4-oxadiazole (SEW-2871) throughout the brain. Similar results were seen in spinal cord membranes, whereby the Emax value of S1PR-stimulated [35S]GTPγS binding was greatly reduced in repeated FTY720-treated mice. These results suggest that S1PR1 is a primary target of FTY720 in alleviating both acute thermal nociception and chronic neuropathic nociception. Furthermore, the finding that tolerance develops to antinociception in the tail-flick test but not in chronic neuropathic pain suggests a differential mechanism of FTY720 action between these models. The observation that repeated FTY720 administration led to desensitized S1PR1 signaling throughout the central nervous system suggests the possibility that S1PR1 activation drives the acute thermal antinociceptive effects, whereas S1PR1 desensitization mediates the following: 1) tolerance to thermal antinociceptive actions of FTY720 and 2) the persistent antiallodynic effects of FTY720 in neuropathic pain by producing functional antagonism of pronociceptive S1PR1 signaling.

Antinociceptive effects of the endogenous cannabinoid peptide agonist VD-hemopressin(β) in mice

Cannabinoids (CBs) play important roles in pain modulation. Recently, VD-hemopressin(β) [VD-Hpβ], a 12-residue β-hemoglobin-derived peptide, was reported to activate both CB1 and CB2 receptors in vitro. To further characterize in vivo actions of VD-Hpβ, its antinociceptive activity and site(s) were evaluated in the mouse tail-flick test, and supraspinal antinociception of VD-Hpβ was further assessed in the writhing test. Our results demonstrated that supraspinal, intrathecal, subcutaneous and intraperitoneal administrations of VD-Hpβ produced analgesia in the tail-flick test. When given at the same levels, the CB1 antagonist AM251, rather than the CB2 antagonist AM630 diminished VD-Hpβ-induced antinociception. Furthermore, our results indicated that supraspinal, intrathecal or subcutaneous pretreatment with AM251 significantly inhibited VD-Hpβ-induced systemic antinociception. In the writhing test, supraspinal VD-Hpβ inhibited pain-related behaviors, which was partially prevented by AM251. Notably, supraspinal administration of VD-Hpβ failed to affect motor function at the antinociceptive doses. These findings suggest that VD-Hpβ induces CB1 receptor-mediated antinociception in tail-flick test in various routes of administration, and its systemic antinociception is mediated by both central and peripheral CB1 receptor. In addition, VD-Hpβ produces analgesic activity in the writhing test, which is at least partially mediated by CB1 receptor. Therefore, our present animal models show a CB1 agonistic character of VD-Hpβ, an endogenous cannabinoid peptide.

Involvement of orexin-1 receptors in the ventral tegmental area and the nucleus accumbens in antinociception induced by lateral hypothalamus stimulation in rats

Previous studies have demonstrated that chemical stimulation of the lateral hypothalamus (LH) with carbachol has an important role in the induction of antinociception in tail-flick test as a model of acute pain. In this study, we tried to evaluate the involvement of orexin-1 receptors in the ventral tegmental area (VTA) and the nucleus accumbens (NAc) on antinociceptive responses induced by LH stimulation in rats. One hundred twenty adult male albino Wistar rats weighing 200–250g were unilaterally implanted with two separate cannulae into the LH, and VTA or NAc. Antinociceptive effects for two doses of intra-LH carbachol (125 and 250nmol/0.5μl saline), as a cholinergic agonist, were evaluated in this study. In another set of experiments, animals received intra-VTA or -NAc infusions of SB334867 as a selective orexin-A receptor antagonist (0.3, 1, 3 and 10nmol/rat), just 5min before microinjection of an effective dose of carbachol into the LH. In the tail-flick test, antinociceptive responses of drugs were obtained by tail-flick analgesiometer and represented as maximal possible effects (%MPE) at 5, 15, 30, 45 and 60min after their administrations. The results showed that unilateral intra-LH administration of carbachol (125 and 250nmol/rat) induced antinociception in rats (P<0.01). There were no significant differences between the antinociceptive effects of these two doses. In the second part of our study, intra-VTA and intra-accumbal administrations of different doses of SB334867, 5min before microinjection of carbachol, could dose-dependently prevent the development of LH stimulation-induced antinociception in rats. However, this effect was less in the NAc. It is supposed that the orexinergic projections from the LH to the VTA and NAc are direct/indirectly involved in the antinociception induced by LH chemical stimulation, and orexin-1 receptors in the ventral tegmental area have a more substantial role in this phenomenon.

Activation of supraspinal NMDA receptors by both D-serine alone or in combination with morphine leads to the potentiation of antinociception in tail-flick test of rats

Although there is a variety of information concerning the effects of the N-methyl-D-aspartate (NMDA) receptor on opioid-induced antinociception at the spinal level, little is known about the effects at the supraspinal level. To clarify the role of the NMDA receptor on the morphine-induced antinociception at the supraspinal level, we investigated the effects of the intracerebroventricular (i.c.v.) administration of D-serine, a selective agonist for the glycine site of the NMDA receptors, alone or in combination with morphine using the tail-flick test. The i.c.v. administration of D-serine, but not L-serine, alone produced a dose-dependent antinociception in the tail-flick response. D-Serine also dose-dependently potentiated the antinociceptive effect induced by the i.c.v. administration of morphine and the simultaneous administration produced an additive effect. The potentiation of the antinociception produced by both D-serine alone or in combination with morphine was dose-dependently attenuated by the i.c.v. administration of L-701,324, a selective antagonist for the glycine site of the NMDA receptors. In addition, the potentiation of the D-serine-induced antinociception was antagonized by the i.c.v. administration of naloxone, a nonselective opioid receptor antagonist. These observations, together with the fact that D-serine is an endogenous and selective co-agonist for the glycine site of the NMDA receptors, strongly suggested that the activation of the supraspinal NMDA receptors by D-serine leads to the potentiation of the antinociception in the tail-flick test and that endogenous D-serine could modulate the μ-opioid receptor mediated antinociception via the glycine site of the NMDA receptors at the supraspinal level.

The roles of different subtypes of opioid receptors in mediating the nucleus submedius opioid-evoked antiallodynia in a neuropathic pain model of rats

Previous studies have indicated that thalamic nucleus submedius is involved in opioid-mediated antinociception in tail flick test and formalin test. The current study examined the effects of opioids microinjected into the thalamic nucleus submedius on the allodynia developed in neuropathic pain model rats, and determined the roles of different subtypes of opioid receptors in the thalamic nucleus submedius opioid-evoked antiallodynia. The allodynic behaviors induced by L5/L6 spinal nerve ligation were assessed by mechanical (von Frey filaments) and cold (4°C plate) stimuli. Morphine (1.0, 2.5, and 5.0μg) microinjected into the thalamic nucleus submedius contralateral to the nerve injury paw produced a dose-dependent inhibition of the mechanical and cold allodynia, and these effects were reversed by microinjection of the non-selective opioid receptor antagonist naloxone (1.0μg) into the same site. Microinjection of endomorphin-1 (5.0μg), a highly selective μ-opioid receptor agonist, and [d-Ala2, d-Leu5]-enkephalin (10μg), a δ-/μ-opioid receptor agonist, also inhibited the allodynic behaviors, and these effects were blocked by selective μ-opioid receptor antagonist β-funaltrexamine hydrochloride (3.75μg). However, the [d-Ala2, d-Leu5]-enkephalin-evoked antiallodynic effects were not influenced by the selective δ-opioid receptor antagonist naltrindole (5.0μg). Microinjection of the selective κ-receptor agonist spiradoline mesylate salt (100μg) into the thalamic nucleus submedius failed to alter the allodynia induced by spinal nerve ligation. These results suggest that the thalamic nucleus submedius is involved in opioid-evoked antiallodynia which is mediated by μ- but not δ- and κ-opioid receptor in the neuropathic pain model rats.