Soh Katsuyama

Intraplantar injection of bergamot essential oil induces peripheral antinociception mediated by opioid mechanism.

This study investigated the effect of bergamot essential oil (BEO) containing linalool and linalyl acetate as major volatile components in the capsaicin test. The intraplantar injection of capsaicin (1.6 μg) produced a short-lived licking/biting response toward the injected paw. The nociceptive behavioral response evoked by capsaicin was inhibited dose-dependently by intraplantar injection of BEO. Both linalool and linalyl acetate, injected into the hindpaw, showed a significant reduction of nociceptive response, which was much more potent than BEO. Intraperitoneal (i.p.) and intraplantar pretreatment with naloxone hydrochloride, an opioid receptor antagonist, significantly reversed BEO- and linalool-induced antinociception. Pretreatment with naloxone methiodide, a peripherally acting μ-opioid receptor preferring antagonist, resulted in a significant antagonizing effect on antinociception induced by BEO and linalool. Antinociception induced by i.p. or intrathecal morphine was enhanced by the combined injection of BEO or linalool. The enhanced effect of combination of BEO or linalool with morphine was antagonized by pretreatment with naloxone hydrochloride. Our results provide evidence for the involvement of peripheral opioids, in the antinociception induced by BEO and linalool. Combined administration of BEO or linalool acting at the peripheral site, and morphine may be a promising approach in the treatment of clinical pain.

Chapter 18 Intraplantar Injection Of Bergamot Essential Oil Into The Mouse Hindpaw: Effects On Capsaicin‐Induced Nociceptive Behaviors

Despite the increasing use of aromatherapy oils, there have not been many studies exploring the biological activities of bergamot (Citrus bergamia, Risso) essential oil (BEO). Recently, we have investigated the effects of BEO injected into the plantar surface of the hindpaw in the capsaicin test in mice. The intraplantar injection of capsaicin produced an intense and short-lived licking/biting response toward the injected hindpaw. The capsaicin-induced nociceptive response was reduced significantly by intraplantar injection of BEO. The essential oils of Clary Sage (Salvia sclarea), Thyme ct. linalool (linalool chemotype of Thymus vulgaris), Lavender Reydovan (Lavandula hybrida reydovan), and True Lavender (Lavandula angustifolia), had similar antinociceptive effects on the capsaicin-induced nociceptive response, while Orange Sweet (Citrus sinensis) essential oil was without effect. In contrast to a small number of pharmacological studies of BEO, there is ample evidence regarding isolated components of BEO which are also found in other essential oils. The most abundant compounds found in the volatile fraction are the monoterpene hydrocarbons, such as limonene, gamma-terpinene, beta-pinene, and oxygenated derivatives, linalool and linalyl acetate. Of these monoterpenes, the pharmacological activities of linalool have been examined. Following intraperitoneal (i.p.) administration in mice, linalool produces antinociceptive and antihyperalgesic effects in different animal models in addition to anti-inflammatory properties. Linalool also possesses anticonvulsant activity in experimental models of epilepsy. We address the importance of linalool or linalyl acetate in BEO-or the other essential oil-induced antinociception.

Peripherally injected linalool and bergamot essential oil attenuate mechanical allodynia via inhibiting spinal ERK phosphorylation.

Bergamot essential oil (BEO) is one of the most common essential oil containing linalool and linalyl acetate as major volatile components. This study investigated the effect of intraplantar (i.pl.) bergamot essential oil (BEO) or linalool on neuropathic hypersensitivity induced by partial sciatic nerve ligation (PSNL) in mice. The i.pl. injection of BEO or linalool into the ipsilateral hindpaw to PSNL reduced PSNL-induced mechanical allodynia in a dose-dependent manner. Peripheral (i.pl.) injection of BEO or linalool into the contralateral hindpaw did not yield anti-allodynic effects, suggesting a local anti-mechanical allodynic effect of BEO or linalool in PSNL mice. Anti-mechanical hypersensitivity of morphine was enhanced by the combined injection of BEO or linalool at an ineffective dose when injected alone. We also examined the possible involvement of spinal extracellular signal-regulated protein kinase (ERK) in BEO or linalool-induced anti-mechanical allodynia. In western blotting analysis, i.pl. injection of BEO or linalool resulted in a significant blockade of spinal ERK activation induced by PSNL. These results suggest that i.pl. injection of BEO or linalool may reduce PSNL-induced mechanical allodynia followed by decreasing spinal ERK activation.

Effect of plantar subcutaneous administration of bergamot essential oil and linalool on formalin-induced nociceptive behavior in mice.

This study investigated the effect of bergamot essential oil (BEO) or linalool, a major volatile component of BEO, on the nociceptive response to formalin. Plantar subcutaneous injection of BEO or linalool into the ipsilateral hindpaw reduced both the first and late phases of the formalin-induced licking and biting responses in mice. Plantar subcutaneous injection of BEO or linalool into the contralateral hindpaw did not yield an antinociceptive effect, suggesting that the antinociceptive effect of BEO or linalool in the formalin test occurred peripherally. Intraperitoneal and plantar subcutaneous injection pretreatment with naloxone hydrochloride, an opioid receptor antagonist, significantly attenuated both BEO- and linalool-induced antinociception. Pretreatment with naloxone methiodide, a peripherally acting opioid receptor antagonists, also significantly antagonized the antinociceptive effects of BEO and linalool. Our results provide evidence for the involvement of peripheral opioids in antinociception induced by BEO and linalool. These results suggest that activation of peripheral opioid receptors may play an important role in reducing formalin-induced nociception.

Involvement of glial cells in the nociceptive behaviors induced by a high-dose of histamine administered intrathecally.

The involvement of spinal glial cells in the nociceptive behaviors induced by 1600 pmol of histamine was determined in mice. Histamine injected intrathecally (i.t.) produced nociceptive behaviors, consisting of scratching, biting and licking. The nociceptive behaviors induced by histamine were significantly suppressed by i.t. pretreatment with the glial cell inhibitor DL-fluorocitric acid or minocycline. In Western blot analysis using lumber spinal cords, i.t. treatment with histamine increased the phosphorylation of the NR1 subunit of N-methyl-D-aspartate (NMDA) receptors. The increased phosphorylation of the NR1 subunit of NMDA receptors by histamine was abolished by i.t. pretreatment with DL-fluorocitric acid or minocycline. We have previously reported that the nociceptive behaviors induced by 1600 pmol of histamine were significantly suppressed by the i.t. co-administration of (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cycloheptene-5,10-imine (MK-801), an ion channel blocker of NMDA receptors, or agmatine, an antagonist for the polyamine recognition site on the NR1 subunit of NMDA receptors. In the present study, the increased phosphorylation of the NR1 subunit of NMDA receptors by histamine was also abolished by i.t. co-administration of agmatine or MK-801. The present results suggest that histamine at 1600 pmol elicits nociceptive behaviors by stimulating the polyamine recognition site on the NR1 subunit of NMDA receptors on spinal glial cells.

Antinociceptive effects of spinally administered nociceptin/orphanin FQ and its N-terminal fragments on capsaicin-induced nociception

Nociceptin/orphanin FQ (N/OFQ), the endogenous ligand for the N/OFQ peptide (NOP) receptors, has been shown to be metabolized into some fragments. We examined to determine whether intrathecal (i.t.) N/OFQ (1-13), (1-11) and (1-7) have antinociceptive activity in the pain-related behavior after intraplantar injection of capsaicin. The i.t. administration of N/OFQ (0.3-1.2 nmol) produced an appreciable and dose-dependent inhibition of capsaicin-induced paw-licking/biting response. The N-terminal fragments of N/OFQ, (1-13) and (1-11), were antinociceptive with a potency lower than N/OFQ. Calculated ID₅₀ values (nmol, i.t.) were 0.83 for N/OFQ, 2.5 for N/OFQ (1-13) and 4.75 for N/OFQ (1-11), respectively. The time-course effect revealed that the antinociceptive effects of these N-terminal fragments lasted longer than those of N/OFQ. Removal of amino acids down to N/OFQ (1-7) led to be less potent than N/OFQ and its fragments, (1-13) and (1-11). Antinociception induced by N/OFQ or N/OFQ (1-13) was reversed significantly by i.t. co-injection of [Nphe¹]N/OFQ (1-13)NH₂, a peptidergic antagonist for NOP receptors, whereas i.t. injection of the antagonist did not interfere with the action of N/OFQ (1-11) and (1-7). Pretreatment with the opioid receptor antagonist naloxone hydrochloride did not affect the antinociception induced by N/OFQ and its N-terminal fragments. These results suggest that N-terminal fragments of N/OFQ are active metabolites and may modulate the antinociceptive effect of N/OFQ in the spinal cord. The results also indicate that N/OFQ (1-13) still possess antinociceptive activity through NOP receptors.

The cannabinoid 1 receptor antagonist AM251 produces nocifensive behavior via activation of ERK signaling pathway

Intrathecal (i.t.) injection of AM251, a cannabinoid 1 (CB(1)) receptor antagonist, into the spinal lumbar space of mice elicited a behavioral response consisting of biting and licking with a few scratchings. In this study, we investigated to determine whether i.t. AM251 could influence the activity of extracellular signal-regulated kinase-1 and -2 (ERK1/2), a mitogen-activated protein kinase (MAPK) in neuronal nitric oxide synthase (nNOS) and inducible NOS (iNOS) activation. The CB(1) receptor agonist ACEA, neurokinin 1 (NK(1)) receptor antagonists and NMDA receptor antagonists, inhibited i.t. AM251-induced behavioral response in a dose-dependent manner. The CB(2) receptor agonist, JWH-133 gave no effect on response elicited by i.t. AM251. Both non-selective NOS inhibitors, L-NAME and 7-NI, and N(ω)-propyl-L-arginine, a selective inhibitor of nNOS resulted in a dose-dependent inhibition of i.t. AM251-induced behavioral response. The selective iNOS inhibitor, 1400W, in relatively large doses, inhibited in a non dose-dependent manner. The i.t. injection of AM251 produced a definite activation of ERK1/2 in the lumbar dorsal spinal cord. Behavioral experiments showed that U0126, a MAPK/ERK kinase (MEK) inhibitor, dose-dependently attenuated the behavioral response to i.t. AM251. Spinal activation of ERK1/2 following i.t. AM251 was reduced clearly by N(ω)-propyl-L-arginine and U0126, while 1400W gave a significant effect on only ERK1 activation. These findings suggest that the nNOS-ERK pathway in spinal cord neurones plays an important role in AM251-induced nocifensive behavior and its inhibition may provide significant anti-nociception.

Spinal ERK2 activation through δ2-opioid receptors contributes to nociceptive behavior induced by intrathecal injection of leucine-enkephalin.

Intrathecal (i.t.) injection of leucine-enkephalin (Leu-ENK), co-administered with peptidase inhibitors, phosphoramidon (an endopeptidase 24.11 inhibitor), and bestatin (a general aminopeptidase inhibitor), produced behaviors consisting of the biting and/or licking of the hindpaw and the tail along with hindlimb scratching directed toward the flank, which peaked at 10-15 min after an injection. This characteristic behavior was not observed in mice treated with i.t. Leu-ENK alone. We also investigated the effect of the extracellular signal-regulated kinase (ERK) in spinal processing of nociception induced by i.t. co-administration of Leu-ENK with phospharamidon and bestatin. Western blot analysis of phospho-ERK (pERK) showed a significant increase of pERK2 in the lumbar spinal cord in response to i.t. Leu-ENK co-injected with peptidase inhibitors. The MAP kinase-ERK inhibitor, U0126 dose-dependently attenuated the nociceptive behavior and spinal ERK activation to i.t. Leu-ENK co-injected with peptidase inhibitors. Furthermore, the nociceptive behavior and spinal ERK activation evoked by i.t. Leu-ENK in combination with peptidase inhibitors were inhibited by co-administration of the non-selective δ-opioid receptor antagonist, naltrindole, the selective δ2-opioid receptor antagonist, naltriben, the non-competitive N-methyl-D-aspartate (NMDA) antagonist, MK-801 or the non-selective nitric oxide synthase inhibitor, L-NAME, the selective nNOS inhibitor, N(ω)-propyl-L-arginine or the selective iNOS inhibitor, W1400, but not by the selective δ1-receptor antagonist, BNTX (7-benzylidenenaltrexone). These results suggest that spontaneous nociceptive behaviors produced by i.t. co-administration of Leu-ENK with peptidase inhibitors may be induced by an activation of the glutamate-NO-ERK pathway through the δ2-opioid receptor in the dorsal spinal cord.

Partial involvement of NMDA receptors and glial cells in the nociceptive behaviors induced by intrathecally administered histamine

The involvement of spinal glial cells in the nociceptive behaviors induced by 800 pmol of histamine was determined in mice. Histamine at 800 pmol injected intrathecally (i.t.) produced nociceptive behaviors, consisting of scratching, biting and licking. The nociceptive behaviors induced by histamine were significantly suppressed by i.t. co-administration with tachykinin NK(1) receptor antagonist CP99,994 or competitive antagonist for N-methyl-d-aspartate (NMDA) receptor d-(-)-2-amino-5-phosphonovaleric acid (d-APV). The i.t. pretreatment with the glial cell inhibitor dl-fluorocitric acid or minocycline failed to affect the nociceptive behaviors induced by histamine. However, in mice pretreated i.t. with dl-fluorocitric acid or minocycline, the nociceptive behaviors induced by histamine were significantly suppressed by i.t. co-administration with CP99,994 but not d-APV. In Western blot analysis using lumbar spinal cords, i.t. treatment with 800 pmol of histamine increased the phosphorylation of the NR1 subunit of NMDA receptors. The increased phosphorylation of the NR1 subunit of NMDA receptors by histamine was abolished by i.t. pretreatment with dl-fluorocitric acid or minocycline. The present results suggest that histamine at 800 pmol elicits nociceptive behaviors through activation of the neuronal NK(1) receptor and the NR1 subunit-containing NMDA receptors on glial cells in the spinal cord.

Antinociceptive Effects of the Serotonin and Noradrenaline Reuptake Inhibitors Milnacipran and Duloxetine on Vincristine-Induced Neuropathic Pain Model in Mice

Vincristine is an anticancer drug used to treat a variety of cancer types, but it frequently causes peripheral neuropathy. Neuropathic pain is often associated with the appearance of abnormal sensory signs, such as allodynia. Milnacipran and duloxetine, serotonin/noradrenaline reuptake inhibitors, have shown efficacy against several chronic pain syndromes. In this study, we investigated the attenuation of vincristine-induced mechanical allodynia in mice by milnacipran and duloxetine. To induce peripheral neuropathy, vincristine was administered once per day (0.1 mg/kg, intraperitoneally (i.p.)) for 7 days. Mechanical allodynia was evaluated by measuring the withdrawal response to stimulation with a von Frey filament. In vincristine-treated mice, mechanical allodynia was observed on days 3–28 of vincristine administration. A single administration of milnacipran (40 mg/kg, i.p.) or duloxetine (20 mg/kg, i.p.) had no effect on vincristine-induced mechanical allodynia. However, repeated administration of milnacipran (20 or 40 mg/kg, once per day, i.p.) or duloxetine (5, 10, or 20 mg/kg, once per day, i.p.) for 7 days significantly reduced vincristine-induced mechanical allodynia. These results suggest that chronic vincristine administration induces mechanical allodynia, and that repeated milnacipran and duloxetine administration may be an effective approach for the treatment of neuropathic pain caused by vincristine treatment for cancer.