Ki-Jung Han

Antinociceptive mechanisms of orally administered decursinol in the mouse

Antinociceptive profiles of decursinol were examined in ICR mice. Decursinol administered orally (from 5 to 200 mg/kg) showed an antinociceptive effect in a dose-dependent manner as measured by the tail-flick and hot-plate tests. In addition, decursinol attenuated dose-dependently the writhing numbers in the acetic acid-induced writhing test. Moreover, the cumulative response time of nociceptive behaviors induced by an intraplantar formalin injection was reduced by decursinol treatment during the both 1st and 2nd phases in a dose-dependent manner. Furthermore, the cumulative nociceptive response time for intrathecal (i.t.) injection of TNF-alpha (100 pg), IL-1 beta (100 pg), IFN-gamma (100 pg), substance P (0.7 microg) or glutamate (20 microg) was dose-dependently diminished by decursinol. Intraperitoneal (i.p.) pretreatment with yohimbine, methysergide, cyproheptadine, ranitidine, or 3,7-dimethyl-1-propargylxanthine (DMPX) attenuated inhibition of the tail-flick response induced by decursinol. However, naloxone, thioperamide, or 1,3-dipropyl-8-(2-amino-4-chloro-phenyl)-xanthine (PACPX) did not affect inhibition of the tail-flick response induced by decursinol. Our results suggests that decursinol shows an antinociceptive property in various pain models. Furthermore, antinociception of decursinol may be mediated by noradrenergic, serotonergic, adenosine A(2), histamine H(1) and H(2) receptors.

effect of ginsenoside Rd on nitric oxide system induced by lipopolysaccharide plus TNF-α in C6 rat glioma cells

Effects of ginsenosides on nitric oxide (NO) production induced by lipopolysaccharide plus TNF-a (LNT) were examined in C6 rat glioma cells. Among several ginsenosides, ginsenoside Rd showed a complete inhibition against LNT-induced NO production. Ginsenoside Rd attenu-ated LNT-induced increased phosphorylation of ERK. Among several immediate early gene products, only Jun B and Fra-1 protein levels were increased by LNT, and ginsenoside Rd attenuated Jun B and Fra-1 protein levels induced by LNT. Furthermore, LNT increased AP-1 DNA binding activities, which were partially inhibited by ginsenoside Rd. Our results suggest that ginsenoside Rd exerts an inhibitory action against NO production via blocking phosphory-lation of ERK, in turn, suppressing immediate early gene products such as Jun B and Fra-1 in C6 glioma cells.

Antinociceptive Profiles of Platycodin D in the Mouse

Platycodin D (PD), one of several triterpene saponins, was isolated from roots of Platycodon grandiflorum. We previously reported that intracerebroventricular (i.c.v.) administration of PD showed an antinociceptive effect as measured by the tail-flick assay. However, its exact role in the regulation of antinociception in the various types of pain models has not yet been characterized. Thus, we attempted to find antinociceptive profiles of PD in various pain models. PD administered intraperitoneally (i.p.), i.c.v. or intrathecally (i.t.) showed antinociceptive effects in dose-dependent manners as measured by the tail-flick, writhing and formalin tests. In the tail-flick test, PD at the low doses reached the peak after 15 minutes and returned to the control level after 60 minutes. However, higher doses of PD showed a strong antinociception at least for 1 hour. PD administered i.t. showed stronger antinociception than that induced by i.c.v. administration PD in both tail-flick and writhing tests. In the formalin test, PD administered i.p., i.c.v. or i.t. showed antinociceptive effects during both the first (direct nociceptive stimulation) and second (late inflammatory) phases. Pretreatment with naltrexone i.p., i.c.v. or i.t. did not affect PD-induced inhibition of the tail-flick response. Our results suggest that PD shows a strong antinociceptive effect on the tail-flick, writhing and formalin tests, acting on central nervous system. However, PD-induced antinociception may not be mediated by the opioid receptors.

Possible antinociceptive mechanisms of opioid receptor antagonists in the mouse formalin test.

It has been reported that opioid receptor antagonist can induce antinociception in several nociceptive tests. In the intraplantar formalin pain model, however, opioid antagonist-induced antinociception, as well as its underlying mechanism, has not been well characterized. Therefore, in the mouse formalin test, we attempted to characterize the site of action and the possible opioid receptor subtypes. We found that naltrexone (a nonselective opioid antagonist) injected intraperitoneally (i.p., 1-20 mg/kg), intrathecally (i.t., 0.1-10 microg) and intracerebroventricularly (i.c.v., 0.1-10 microg) phase. Administration of beta-funaltrexamine (beta-FNA, 10-40 mg/kg i.p., 1.25-5 microg it or i.c.v.), naltrindole (1-10 mg/kg i.p., 1.25-5 microg it or i.c.v.) and nor-binaltorphimine (nor-BNI, 1-10 mg/kg i.p., 10-40 microg it or i.c.v.), which are selective mu-, delta- and kappa-opioid antagonists, respectively, also produced antinociception during the second phase. Additionally, we examined the involvement of the descending monoaminergic systems in the naltrexone-induced antinociception in the formalin test. Pretreatment with 5,7-dihydroxytryptamine (5,7-DHT, a serotonergic neurotoxin, 20 microg i.t.), but not N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4, a noradrenergic neurotoxin, 20 microg i.t.), reversed the naltrexone-induced antinociception during the second phase. Our results suggest that blockade of supraspinally or spinally located opioid receptors may play roles in the regulation of antinociception during the tonic painful stage. In addition, opioid receptors localized at the neuroterminal of the descending serotonergic, but not noradrenergic, inhibitory system in the spinal cord appear to be involved in opioid antagonist-induced antinociception during the second tonic phase of the formalin test.

Antinociceptive Effect of Nicotine in Various Pain Models in the Mouse

The antinociceptive effect of nicotine administered intracereboventricularly (i.c.v.) or intrathecally (i.t) in several pain models was examined in the present study. We found that i.t. treatment with nicotine (from 5 to 20 g) dose-dependently blocked pain behavior revealed during the second phase, but not during the first phase in the formalin test. In addition, i.c.v. treatment with nicotine (from 0.1 to 10 μg) dose-dependently attenuated pain behavior revealed during both the first and second phases. In addition to the formalin test, nicotine administered i.c.v. or i.t. attenuated acetic acid-induced writhing response. Furthermore, i.c.v. or i.t. administration of nicotine did not cause licking, scratching and biting responses induced by substance P, glutamate, TNF-α (100 pg), IL-1β (100 pg) and INF-γ (100 pg) injectied i.t. The antinociception induced by supraspinally-administered nicotine appears to be more effective than that resulting from spinally administered nicotine. Our results suggest that nicotine administration induces antinociception by acting on the central nervous system and has differing antinociceptive profiles according to the various pain models.

Cycloheximide inhibits neurotoxic responses induced by kainic acid in mice.

In the present study, we examined the effect of cycloheximide on various pharmacological responses induced by kainic acid (KA) administered intracerebroventricularly (i.c.v.) in mice. In a passive avoidance test, a 20-min cycloheximide (200mg/kg, i.p.) pretreatment prevented the memory impairment induced by KA. The morphological damage induced by KA (0.1microg) in the hippocampus was markedly concentrated in the CA3 pyramidal neurons and cycloheximide effectively prevented the KA-induced pyramidal cell death in CA3 hippocampal region. In immunohistochemical study, KA dramatically increased the phosphorylation of extracellular signal-regulated protein kinase (p-ERK), c-Jun N-terminal kinase 1 (p-JNK1), and calcium/calmodulin-dependent protein kinase II (p-CaMK II). Cycloheximide attenuated the increased p-ERK, p-JNK1, and p-CaMK II levels induced by KA. Furthermore, cycloheximide inhibited the increased c-Fos and c-Jun protein expression levels induced by KA in the hippocampus. The activation of microglia was detected in KA-induced CA3 cell death region by immunostaining with a monoclonal antibody against the OX-42. Cycloheximide inhibited KA-induced increase of OX-42 immunoreactivity. Our results suggest that the increased expression of the c-Fos, c-Jun, and phosphorylation of ERK, JNK1, and CaMK II proteins may play important roles in the memory impairment and the cell death in CA3 region of the hippocampus induced by i.c.v. KA administration in mice. Furthermore, the activated microglia may be related to phagocytosis of degenerated neuronal elements induced by KA.

Role of glutamate receptors and an on-going protein synthesis in the regulation of phosphorylation of Ca2+/calmodulin-dependent protein kinase II in the CA3 hippocampal region in mice administered with kainic acid intracerebroventricularly

In an immunohistochemical study, kainic acid (KA, 0.1 microg) administered intracerebroventricularly (i.c.v.) dramatically increased the expression of Ca2+/calmodulin-dependent protein kinase II (CaMK II) and the phosphorylation of CaMK II (p-CaMK II) in the CA3 hippocampal region of mice. Pre-treatment with cycloheximide (a protein synthesis inhibitor; 200 mg/kg) intraperitoneally prevented the expression of CaMK II and phosphorylation of CaMK II induced by KA. In addition, pre-treatment with MK-801 ((5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine; an NMDA receptor blocker, 1 microg, i.c.v.) or CNQX (6-cyano-7-nitroquinoxaline-2,3-dione; a non-NMDA receptor blocker, 0.5 microg, i.c.v.) attenuated the p-CaMK II, but not CaMK II, expression induced by KA. Our results suggest that KA administered supraspinally induces CaMK II and the phosphorylation of CaMK II expression in the CA3 hippocampal region, for which an on-going protein synthesis is needed. Furthermore, both NMDA and non-NMDA receptors appear to be involved in supraspinally administered KA-induced phosphorylation of CaMK II.

Antinociceptive Effects of Methysergide in Various Pain Models

Several studies have demonstrated that the nonselective opioid receptor antagonist naloxone produces a paradoxical antinociception in the formalin test. The opioid system is related to the serotonergic system for producing antinociception at the spinal level. Here we also asked whether systemic (i.p.) and intrathecal (i.t.) administrations of a nonselective serotonergic antagonist, methysergide, might produce paradoxical antinocicpetion similar to naloxone in the mouse formalin test. A diluted formalin solution was injected into the mouse plantar region of the hind paw and the duration of licking responses was measured at periods of 0–5 min (1st phase) and 20–40 min (2nd phase) after formalin injection. Methysergide administered i.p. and i.t. showed an attenuated licking duration only in the 2nd phase. The effect observed in the 2nd phase was reversed in the 5,7-dihydroxytriptamine, but not N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine pretreated group of mice, suggesting that descending serotonergic, but not noradrenergic, systems are involved in the methysergide antinociception. To further investigate the mechanism by which methysergide inhibited the nociceptive behaviors induced by formalin, the antinociceptive effect of methysergide was also tested in substance P (i.t.) and excitatory amino acids (i.t.), such as glutamate, N-methyl-D-aspartic acid, α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid, and kainic acid, which are major components in the formalin-induced nociceptive transmission in the spinal cord pain models. The duration of nociceptive behaviors shown in these models was significantly shortened by i.p. and i.t. administration of methysergide. These results suggest that methysergide also produces a paradoxical antinociception in various pain models including the formalin test, similar to the results of naloxone.

Formalin pretreatment attenuates tail-flick inhibition induced by β-endorphin administered intracerebroventricularly or intrathecally in mice

We examined the effect of the subcutaneous (s.c.) pretreatment of formalin into both hind paws of mice on the antinociception induced by the intracerebroventricularly (i.c.v.) or intrathecally (i.t.) administration of β-endorphin using the tail-flick test. Pretreatment with formalin (5%) for 5 h had no affect on the i.c.v. administered β-endorphin-induced tail-flick response. However, pretreatment with formalin for 40 h attenuated the tail-flick inhibition induced by i.c.v. administered β-endorphin. This antinociceptive tolerance to i.c.v. β-endorphin continued up to 1 week, but to a lesser extent. Pretreatment with formalin for 5 and 40 h significantly reduced the i.t. β-endorphin-induced inhibition of the tail-flick response, which continued up to 1 week. The s.c. formalin treatment increased the hypothalamic proopiomelanocortin (POMC) mRNA level at 2 h, but this returned to the basal level after 40 h. Our results suggest that the increase in the POMC mRNA level in the hypothalamus appears to be involved in the supraspinal or spinal β-endorphin-induced antinociceptive tolerance in formalin-induced inflammatory pain.