Nociceptive Behavior In Mice Research Articles

Supraspinal nocistatin and its amide derivative antagonize the hyperalgesic effects of nociceptin in mice

Nocistatin (NST) and nociceptin (NCP)/orphanin FQ are new neuropeptides derived from the same precursor molecule, and which are involved in pain transmission. Nocistatin has been shown to antagonize several effects of nociceptin by acting on a different receptor. We examined the effects of supraspinal nocistatin and nocistatin amide, and their interaction with nociceptin on nociceptive behavior in mice, using hotplate response times. We found that both nocistatin and nocistatin amide did not change the response time compared to control mice, whereas increasing doses of nociceptin caused progressive shortening of response times. Nocistatin and nocistatin amide were both able to antagonize the hyperalgesic effect of nociceptin. The effect of nocistatin amide was longer lasting and more potent, suggesting that the C-terminal free carboxyl group of nocistatin is not necessary for its biological activity, and that the amide derivative may be more biologically stable.

The Mechanosensitivity of Mouse Colon Afferent Fibers and Their Sensitization by Inflammatory Mediators Require Transient Receptor Potential Vanilloid 1 and Acid-Sensing Ion Channel 3

Mechanical hypersensitivity of the colon underlies in part the chronic abdominal pain experienced by patients with irritable bowel syndrome, yet the molecules that confer mechanosensitivity to colon sensory neurons and their contribution to visceral pain are unknown. We tested the hypothesis that transient receptor potential vanilloid 1 (TRPV1) and acid-sensing ion channel 3 (ASIC3) are peripheral mechanosensors in colon afferent neuronal fibers that mediate visceral nociceptive behavior in mice. Visceral nociception, modeled by the visceromotor response to colorectal distension, and colon afferent fiber mechanosensitivity were assessed in control (C57BL/6) mice and two congenic knock-out mouse strains with deletions of either TRPV1 or ASIC3. Phasic colon distension (15-60 mmHg) produced graded behavioral responses in all three mouse strains. However, both TRPV1 and ASIC3 knock-out mice were significantly less sensitive to distension, with an average response magnitude only 58 and 50% of controls, respectively. The behavioral deficits observed in both strains of knock-out mice were associated with a significant and selective reduction in afferent fiber sensitivity to circumferential stretch of the colon, an effect that was mimicked in control preparations by pretreatment with capsazepine, a TRPV1 antagonist, but not amiloride, a nonselective ASIC antagonist (both 500 microM). In addition, whereas stretch-evoked afferent fiber responses were enhanced by chemical inflammatory mediators in control mice, this effect was differentially impaired in both knock-out mouse strains. These results demonstrate a peripheral mechanosensory role for TRPV1 and ASIC3 in the mouse colon that contributes to nociceptive behavior and possibly peripheral sensitization during tissue insult.

Differential inhibitory effects of μ-opioids on substance P- and capsaicin-induced nociceptive behavior in mice

The antinociceptive mechanisms of the selective μ-opioid receptor agonists [ d-Ala 2,NMePhe 4,Gly(ol) 5]enkephalin (DAMGO), H-Tyr- d-Arg-Phe-β-Ala-OH (TAPA) or H-Tyr- d-Arg-Phe-β-Ala-NH 2 (TAPA-NH 2) against substance P (SP)- or capsaicin-elicited nociceptive behaviors was investigated in mice. DAMGO, TAPA or TAPA-NH 2 given intrathecally inhibited the nociceptive behaviors elicited by intrathecally administered SP or capsaicin, and these antinociceptive effects were completely eliminated by intrathecal co-administration with d-Phe-Cys-Tyr- d-Trp-Orn-Thr-Pen-Thr-NH 2 (CTOP), a selective μ-opioid receptor antagonist. Pretreatment subcutaneously with naloxonazine, a selective μ 1-opioid receptor antagonist, partially attenuated the antinociceptive effect of TAPA-NH 2, but not DAMGO and TAPA, against SP. However, the antinociception induced by TAPA, but not DAMGO and TAPA-NH 2, against capsaicin was significantly inhibited by naloxonazine. On the other hand, co-administration intrathecally with Tyr- d-Pro-Trp-Gly-NH 2 ( d-Pro 2-Tyr-W-MIF-1), a selective μ 2-opioid receptor antagonist, significantly attenuated the antinociceptive effects of DAMGO, but not TAPA and TAPA-NH 2, against capsaicin, while the antinociceptions induced by three opioid peptides against SP were significantly inhibited by d-Pro 2-Tyr-W-MIF-1. These results suggest that differential inhibitory mechanisms on pre- and postsynaptic sites in the spinal cord contribute to the antinociceptive effects of the three μ-opioid peptides.

Mechanisms involved in the nociception produced by peripheral protein kinase c activation in mice

Protein kinase C (PKC) is able to phosphorylate several cellular components that serve as key regulatory components in signal transduction pathways of nociceptor excitation and sensitisation. Therefore, the present study attempted to assess some of the mechanisms involved in the overt nociception elicited by peripheral administration of the PKC activator, phorbol 12-myristate 13-acetate (PMA), in mice. The intraplantar (i.pl.) injection of PMA (16–1600 pmol/paw), but not its inactive analogue α-PMA, produced a long-lasting overt nociception (up to 45 min), as well as the activation of PKCα and PKCε isoforms in treated paws. Indeed, the local administration of the PKC inhibitor GF109203X completely blocked PMA-induced nociception. The blockade of NK 1, CGRP, NMDA, β 1-adrenergic, B 2 or TRPV1 receptors with selective antagonists partially decreased PMA-induced nociception. Similarly, COX-1, COX-2, MEK or p38 MAP kinase inhibitors reduced the nociceptive effect produced by PMA. Notably, the nociceptive effect promoted by PMA was diminished in animals treated with an antagonist of IL-1β receptor or with antibodies against TNFα, NGF or BDNF, but not against GDNF. Finally, mast cells as well as capsaicin-sensitive and sympathetic fibres, but not neutrophil influx, mediated the nociceptive effect produced by PMA. Collectively, the results of the present study have shown that PMA injection into the mouse paw results in PKC activation as well as a relatively delayed, but long-lasting, overt nociceptive behaviour in mice. Moreover, these results demonstrate that PKC activation exerts a critical role in modulating the excitability of sensory neurons.

Antinociceptive mechanism of l-DOPA

The mechanism of l-DOPA for antinociception was investigated. Nociceptive behaviors in mice after an intrathecal (i.t.) administration of substance P were evaluated. l-DOPA (i.t.) dose-dependently attenuated the substance P-induced nociceptive behaviors. Co-administration of benserazide (i.t.), a DOPA decarboxylase inhibitor, abolished the antinociceptive effect of l-DOPA. The l-DOPA-induced antinociception was antagonized by sulpiride, a D2 blocker, but not by SCH 23390, a D1 blocker. These results suggest that l-DOPA relieves pain after conversion to dopamine, with the dopamine sedating pain transmission by way of the dopamine D2 receptor.

Noxious Cold Ion Channel TRPA1 Is Activated by Pungent Compounds and Bradykinin

Six members of the mammalian transient receptor potential (TRP) ion channels respond to varied temperature thresholds. The natural compounds capsaicin and menthol activate noxious heat-sensitive TRPV1 and cold-sensitive TRPM8, respectively. The burning and cooling perception of capsaicin and menthol demonstrate that these ion channels mediate thermosensation. We show that, in addition to noxious cold, pungent natural compounds present in cinnamon oil, wintergreen oil, clove oil, mustard oil, and ginger all activate TRPA1 (ANKTM1). Bradykinin, an inflammatory peptide acting through its G protein-coupled receptor, also activates TRPA1. We further show that phospholipase C is an important signaling component for TRPA1 activation. Cinnamaldehyde, the most specific TRPA1 activator, excites a subset of sensory neurons highly enriched in cold-sensitive neurons and elicits nociceptive behavior in mice. Collectively, these data demonstrate that TRPA1 activation elicits a painful sensation and provide a potential molecular model for why noxious cold can paradoxically be perceived as burning pain.

Unaltered pain-related behavior in mice lacking NMDA receptor GluRε1 subunit

Noxious afferent input following tissue damage and inflammation triggers a state of neuronal hyperexcitability—a phenomenon of central sensitization—which manifests behaviorally as allodynia and hyperalgesia. At the molecular level, maintenance of central sensitization is largely dependent on the N-methyl- d-aspartate receptor (NMDAR) activation. NMDARs are composed of GluRζ1 (NR1) and one of four GluRε (NR2) subunits, which determine the functional properties of native NMDARs. Although there is accumulating evidence to implicate GluRε2-containing NMDARs in pain mechanisms, the functional significance of GluRε1-containing NMDARs in this setting has not been examined in detail. Here, we used hind paw injection of formalin, complete Freund's adjuvant and a nerve injury model to investigate the effects of GluRε1 subunit gene deletion on pain-related behavior in mice. In all of the models tested, GluRε1-deficient mice exhibited responses similar to wild-type controls. These results suggest that GluRε1 disruption does not result in altered nociceptive behavior in mice. Although the contribution of other nociceptive pathways cannot be ruled out, we speculate that the preserved function of GluRε2-containing NMDARs could explain unaltered nociceptive behavior in mutant mice.

Effects of paeoniflorin on the formalin-induced nociceptive behaviour in mice

In this study, we attempted to identify the mechanisms of paeoniflorin on antinociceptive effects in mice. Paeoniflorin (48, 96, 240, 480 μg, i.c.v.) showed dose-related antinociception both on the early and late phases of formalin test in mice. Moreover, paeoniflorin (48 μg, i.c.v.) could potentiate the antinociception of morphrine (0.5, 1.0 mg/kg, s.c.) in the formalin test. However, the antinociceptive effects of paeoniflorin were not potentiated by l-arginine (600 mg/kg, i.p.) or antagonized by β-funaltrexamine (β-FNA) (10 μg, i.c.v.), ICI-174,864 (1 μg, i.c.v.) and ryanodine (10 ng, i.c.v.) on both the early and late phases of formalin test. l-NAME (75 mg/kg, i.p.) could reverse the effect of paeoniflorin on the late phase of formalin test. Naloxone (1 mg/kg, i.p.) and nor-binaltorphimine (nor-BNI) (1 μg, i.c.v.) could block the paeoniflorin-induced antinociception on the early phase of formalin test. These results suggested that the central antinociceptive effects of paeoniflorin on formalin test in mice were mediated by the activation of κ-opioid receptor and not related to the increase of intracellular calcium.

Influence of Olfactory Stimulation on Nociceptive Behavior in Mice

Jahangeer, A-C., D. Mellier and J. Caston. Influence of olfactory stimulation on nociceptive behavior in mice. Physiol Behav 62(2) 359–366, 1997.—The reactions elicited by nociceptive stimulations were studied in mice exposed to the presence of different odors: positive (attractive), negative (aversive), or neutral. In a first set of experiments, the animals were not habituated to the odors before the nociceptive stimuli were applied; in this case, the olfactory environment during experienced pain had essentially no effect on the nociceptive reactions, whatever the nature of the odors. In a second set of experiments, the animals were habituated to the same odor for 20 days. The control group consisted of mice habituated to and tested in the presence of the odor of the laboratory. In that case, compared to controls, the neutral odor had no influence on nociceptive reactions. By contrast, the positive odor decreased and the negative odor increased the reactions, especially when the intensity of the nociceptive stimulus was low. Moreover, it has been shown that the reactions elicited during a second nociceptive stimulation period depend on the perception of pain animals experience during the first stimulation, which depended, in turn, on the odor associated with it. Results are discussed in terms of opioid-mediated interactions between olfaction and pain.

3-Aryl-1,2-diacetamidopropane derivatives as novel and potent NK-1 receptor antagonists.

Early structure-activity studies on racemic tryptophan ester and amide NK-1 antagonists 5-7 led to the discovery that the potency of the series could be markedly increased by moving the carbonyl function in these molecules to an off-chain position as in the 3-aryl-1,2-diacetamidopropane 9. Further medicinal chemistry incorporating this change resulted in the discovery of a novel series of highly potent aryl amino acid derived NK-1 antagonists of the R stereoisomeric series (IC50's = 100 pM to > 5 microM). Compounds in this series were shown to be competitive antagonists using an in vitro NK-1 smooth muscle assay, and this data correlated well with observed human NK-1 binding affinities. Two of these agents, (R)-25 and (R)-32, blocked intrathecal NK-1 agonist-driven [Ac-[Arg6,Sar9,Met(O2)11]- substance P 6-11 (Ac-Sar9)] nociceptive behavior in mice. Both compounds potently blocked the neurogenic dural inflammation following trigeminal ganglion stimulation in the guinea pig after intravenous administration. Further, upon oral administration in this model, (R)-32 was observed to be very potent (ID50 = 91 ng/kg) and have a long duration of action (> 8 h at 1 micrograms/kg). Compound (R)-32, designated LY303870, is currently under clinical development as an NK-1 antagonist with a long duration of action.