Hong Won Suh

Inhibition of stress-induced plasma corticosterone levels by ginsenosides in mice: involvement of nitric oxide

GINSENG total saponins (GTS) injected intracere-broventricularly (i.c.v.) at doses of 0.1–1 μg inhibited the i.c.v. injection stress-induced plasma corticosterone levels in mice. The inhibitory action of GTS was blocked by co-administered NG-nitro-L-arginine methyl ester (L-NAME; 1.5 μg, i.c.v.), an inhibitor of nitric oxide synthase (NOS). Of the ginsenosides Rb1, Rb2, Rc, Rd, Re, Rf, Rg1, 20(S)-Rg3 and 20(R)-Rg3 injected i.c.v. at doses of 0.01–1 μg, 20(S)-Rg3 and Rc significantly inhibited the i.c.v. injection stress-induced plasma corticosterone levels. The inhibitory actions of 20(S)-Rg3 and Rc were blocked by co-administered L-NAME (1.5 μg, i.c.v.). These results suggest that GTS, 20(S)-Rg3 and Rc may inhibit the i.c.v. injection stress-induced hypothalamo-pituitary-adrenal response by inducing NO production in the brain.

Postischemic hypothermia induced by eugenol protects hippocampal neurons from global ischemia in gerbils

We studied whether eugenol provides neuroprotection against delayed neuronal death in the hippocampal CA1 region following a 5 min occlusion of the common carotid arteries bilaterally under either free-regulating temperature (TF) or maintained temperature (TM, 37 degrees C) conditions in gerbils. Right after occlusion of the carotid arteries, we injected eugenol intraperitoneally at concentrations of either 50, 100, or 200 mg/kg. There was significant preservation of neuronal cells in the CA1 region in the eugenol-treated groups 7 days after the ischemic insult in the TF condition, with respective survival values of 26, 43, and 68%. In the TM condition, however, significant neuroprotection was only seen with eugenol concentrations of 100 and 200 mg/kg (32% and 52%, respectively). When the rectal temperature was maintained at 38 degrees C for 30 min after occlusion of the carotid arteries, no reduction in CA1 damage was observed with any dose of eugenol. These results suggest that eugenol may provide neuroprotection against ischemic damage by its hypothermic action.

Analgesic effect of highly reversible ω-conotoxin FVIA on N type Ca2+ channels

BackgroundN-type Ca2+ channels (Cav2.2) play an important role in the transmission of pain signals to the central nervous system. ω-Conotoxin (CTx)-MVIIA, also called ziconotide (Prialt®), effectively alleviates pain, without causing addiction, by blocking the pores of these channels. Unfortunately, CTx-MVIIA has a narrow therapeutic window and produces serious side effects due to the poor reversibility of its binding to the channel. It would thus be desirable to identify new analgesic blockers with binding characteristics that lead to fewer adverse side effects.ResultsHere we identify a new CTx, FVIA, from the Korean Conus Fulmen and describe its effects on pain responses and blood pressure. The inhibitory effect of CTx-FVIA on N-type Ca2+ channel currents was dose-dependent and similar to that of CTx-MVIIA. However, the two conopeptides exhibited markedly different degrees of reversibility after block. CTx-FVIA effectively and dose-dependently reduced nociceptive behavior in the formalin test and in neuropathic pain models, and reduced mechanical and thermal allodynia in the tail nerve injury rat model. CTx-FVIA (10 ng) also showed significant analgesic effects on writhing in mouse neurotransmitter- and cytokine-induced pain models, though it had no effect on acute thermal pain and interferon-γ induced pain. Interestingly, although both CTx-FVIA and CTx-MVIIA depressed arterial blood pressure immediately after administration, pressure recovered faster and to a greater degree after CTx-FVIA administration.ConclusionsThe analgesic potency of CTx-FVIA and its greater reversibility could represent advantages over CTx-MVIIA for the treatment of refractory pain and contribute to the design of an analgesic with high potency and low side effects.

Involvement of dynorphin in immobilization stress-induced antinociception in the mouse

The effect of antiserum against [Met(5)]-enkephalin, [Leu(5)]-enkephalin, beta-endorphin, or dynorphin A-(1-13) administered intracerebroventricularly (i.c.v.) or intrathecally (i. t.) on immobilization-induced antinociception was studied in ICR mice. Antinociception was assessed by the tail-flick assay. Immobilization of the mouse increased inhibition of the tail-flick response at least 1 h. The i.c.v. or i.t. injection with antiserum against dynorphin A-(1-13) at the dose of 200 microg significantly attenuated immobilization-induced inhibition of the tail-flick response. However, antiserum against [Met(5)]-enkephalin, [Leu(5)]-enkephalin, or beta-endorphin did not affect the immobilization stress-induced antinociception. Furthermore, i.c.v. or i.t. injection with nor-binaltorphimine (Nor-BNI; from 1 to 20 microg) effectively inhibited immobilization stress-induced inhibition of the tail-flick response in a dose-dependent manner. However, beta-FNA (from 0.5 to 2 microg) or naltrindole (from 1 to 20 microg) administered i.c.v. or i.t. did not affect immobilization stress-induced antinociception. Our results suggest that supraspinally and spinally located dynorphin appears to be involved in the production of immobilization stress-induced antinociception via stimulating kappa-opioid receptors.

Differential modulatory roles of cholera toxin and pertussis toxin in the regulation of pain responses induced by excitatory amino acids administered intrathecally in mice.

The present study was designed to characterize the possible roles of spinally located cholera toxin (CTX)- and pertussis toxin (PTX)-sensitive G-proteins in excitatory amino acids induced pain response. Intrathecal (i.t.) injection of glutamate (20 microg), N-methyl-D-aspartic acid (NMDA; 60 ng), alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA; 13 ng), and kainic acid (12 ng) showed pain response. Pretreatment with CTX (0.05 and 0.5 microg, i.t.) attenuated pain response induced by glutamate, NMDA, AMPA and kainic acid administered i.t. in a dose-dependent manner. On the other hand, i.t. pretreatment with PTX further increased the pain response induced by glutamate, NMDA, AMPA and kainic acid administered i.t., especially at the dose of 0.5 microg. Our results suggest that, at the spinal cord level, CTX- and PTX-sensitive G-proteins appear to play opposite roles in modulating the pain response induced by spinally administered. Furthermore, CTX- and PTX-sensitive G-proteins appear to modulate pain response induced by stimuli of both NMDA and non-NMDA glutamate receptors.

Effects of intrathecal or intracerebroventricular pretreatment with pertussis toxin on antinociception induced by β-endorphin or morphine administered intracerebroventricularly in mice

We have previously demonstrated that β-endorphin and morphine, when administered supraspinally, produce antinociception by activating different descending pain inhibitory systems in both rats and mice. However, the signal transduction mechanisms involved in the descending pain-inhibitory systems that are activated by β-endorphin and morphine administered intracerebroventricularly (i.c.v.) have not been characterized. Therefore, in the present study, the effects of intrathecal (i.t.) and i.c.v. pretreatments with pertussis toxin (PTX) on antinociception induced by β-endorphin or by morphine administered i.c.v. were studied in ICR mice. Antinociception was assessed by the tail-flick assay and by the hotplate assay. Intrathecal pretreatment with PTX (0.5 μg) for 6 days effectively reduced the inhibition of the tail-flick response induced by β-endorphin (1 μg) or by morphine (1 μg) administered i.c.v. However, i.t. pretreatment with PTX was not effective in reducing the inhibition of the hot-plate response induced by β-endorphin or by morphine administered i.c.v. Intracerebroventricular pretreatment with PTX (0.5 μg) for 6 days effectively reduced the inhibition of the tail-flick and hot-plate responses induced by morphine (1 μg), but not that induced by β-endorphin (1 μg), administered i.cv. Our results suggest that there are PTX-sensitive G proteins coupled to the spinal descending pain inhibitory systems that are activated by β-endorphin and morphine administered i.c.v. At a supraspinal level, i.cv. morphine- but not β-endorphin-induced antinociception is mediated by PTX-sensitive G proteins.

Antidepressant-like Effect of Kaempferol and Quercitirin, Isolated from Opuntia ficus-indica var. saboten.

Opuntia ficus-indica var. saboten. is widely cultivated in Jeju Island (South Korea) for use in manufacture of health foods. This study described antidepressant effect of two flavonoids (kaempferol and quercitrin) isolated from the Opuntia ficus-indica var. saboten. The expression of the hypothalamic POMC mRNA or plasma β-endorphin levels were increased by extract of Opuntia ficus-indica var. saboten or its flavoniods administered orally. In addition, antidepressant activity was studied using tail suspension test (TST), forced swimming test (FST) and rota-rod test in chronically restraint immobilization stress group in mice. After restraint stress (2 hrs/day for 14 days), animals were kept in cage for 14 days without any further stress, bet with drugs. Mice were fed with a diet supplemented for 14 days and during the behavioral test period with kaempferol or quercitrin (30 mg/kg/day). POMC mRNA or plasma β-endorphin level was increased by extract of Opuntia ficus-indica var. saboten and its flavoniods. In addition, immobility time in TST and FST was significantly reduced by kaempferol or quercitrin. In rota-rod test, the time of permanence was maintained to the semblance of control group in turning at 15 rpm. Our results suggest that two flavonoids (kaempferol and quercitrin) isolated from the Opuntia ficus-indica var. saboten. show a potent antidepressant effect.

Involvement of different subtypes of cholecystokinin receptors in opioid antinociception in the mouse

Various doses of sulfated cholecystokinin octapeptide (CCK-8s) injected intracerebroventricularly (ICV) alone did not show any antinociceptive effect. CCK-8s (0.01-1 ng) pretreated ICV for 10 min dose-dependently attenuated the inhibition of the tail flick response induced by ICV-administered morphine (2 micrograms). beta-endorphin (1 microgram), and U50,488H (trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl) cyclohexyl]benzeocetamide), 60 micrograms). However, ICV pretreatment with CCK-8s was not effective in reducing the inhibition of the tail flick response induced by [D-Pen(2)-D-Pen5]enkephalin (DPDPE; 10 micrograms) administered ICV. To determine what subtype(s) of CCK receptors are involved in antagonizing the antinociception induced by these opioids, effect of lorglumide sodium salt (a CCKA receptor antagonist) or PD135,158 N-methyl-D-glucamine salt (a CCKB receptor antagonist) on opioid-induced inhibition of the tail flick response was examined. Various doses of lorglumide sodium salt (lorglumide) or PD135,158 N-methyl-D-glucamine salt (PD135,158) injected ICV alone did not affect the basal tail flick response. The antagonistic effect of CCK-8s on morphine-, beta-endorphin-, and U50,488H-induced inhibition of the tail flick response was blocked in a dose-dependent manner by the co-ICV injection of PD135,158 (0.001-0.1 ng). The co-ICV injection of lorglumide (0.001-0.1 ng) dose-dependently blocked the antagonistic effect of CCK-8s on beta-endorphin- and U50,488H-induced, but not morphine-induced, inhibition of the tail flick response. Our results suggest that both CCKA and CCKB receptors are involved in antagonizing antinociception induced by beta-endorphin and U50,488H administered supraspinally. However, only CCKB (but not CCKA) receptors are involved in antagonizing antinociception induced by morphine administered supraspinally. CCK receptors are not involved in antagonizing the supraspinally administered DPDPE-induced antinociception.

MULTIPLICATIVE INTERACTION BETWEEN INTRATHECALLY AND INTRACEREBROVENTRICULARLY ADMINISTERED MORPHINE FOR ANTINOCICEPTION IN THE MOUSE : INVOLVEMENT OF SUPRASPINAL NMDA BUT NOT NON-NMDA RECEPTORS

Concurrent administration of morphine to both supraspinal and spinal sites produced a multiplicative (synergistic) interaction for antinociception. The purpose of this study was to determine if supraspinal glutaminergic receptors are involved in the multiplicative interaction for antinociception induced by morphine. The antinociception was assessed by the tail-flick test. Effect of MK-801 [(+/-)-5-methyl-10, 11-dihydro-5H-dibenzo (a,d)cyclohepten-5,10-imine maleate], a non-competitive N-methyl-D-aspartic acid (NMDA) receptor antagonist, or CNQX (6-Cyano-7-nitroquinoxaline-2,3-dione), a competitive non-NMDA receptor antagonist on inhibition of the tail-flick response induced by a combined i.t. and i.c.v. administration of morphine was studied. Either i.t. or i.c.v. administration of morphine alone at the dose of 0.2 microgram slightly increased inhibition of the tail-flick response. However, concurrent i.t. and i.c.v. injections of morphine at the dose of 0.2 microgram increased the inhibition of the tail-flick response in a synergistic manner. Various doses of MK-801 (0.01-1 microgram) or CNQX (0.05-0.5 microgram) pretreated i.c.v. alone did not show any antinociceptive effect. MK-801 pretreated i.c.v. for 10 min dose-dependently attenuated the inhibition of the tail-flick response induced by concurrent i.t. and i.c.v. injections of morphine. However, CNQX pretreated i.c.v. for 10 min did not affect the inhibition of the tail-flick response induced by concurrent i.t. and i.c.v. injections of morphine. Our results suggest that supraspinal NMDA but not non-NMDA receptors are involved in mediating the antinociception produced by morphine-induced multiplicative interaction between spinal and supraspinal sites.

Differential modulation by muscimol and baclofen on antinociception induced by morphine, β-endorphin, d-Pen2,5-enkephalin and U50,488H administered intracerebroventricularly in the mouse

The present study was designed to investigate the modulatory effects of stimulation of GABAA and GABAB receptors at supraspinal sites on antinociception induced by supraspinally administered μ-, ɛ-, δ-, and κ-opioid receptor agonists. The effects of the GABAA and GABAB receptor agonists, muscimol and baclofen respectively, on the antinociception induced by morphine (a μ-receptor agonist), β-endorphin (an ɛ-receptor agonist), D-Pen2,5-enkephalin (DPDPE, a δ-receptor agonist) and U50,488H ({trans-3,4-di-chloroN-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl] benzeocetamide}; a κ-receptor agonist) injected intracerebroventricularly (i.c.v.) were studied. The anti-nociception was assayed using the tail-flick and hot-plate tests. Muscimol at doses of 25–200 ng, administered i.c.v. alone did not affect the latencies of tail-flick and hot-plate thresholds, but attenuated dose-dependently the inhibition of the tail-flick and hot-plate responses induced by i.c.v. administered morphine (2 μg), β-endorphin (1 μg), DPDPE (10 μg), and U50,488H (60 μg). Baclofen (1.25–10 ng) administered i.c.v. alone did not affect the latencies of the tail-flick and hot-plate responses, but attenuated dose-dependently the inhibition of the tail-flick and hot-plate responses induced by β-endorphin and U50,488H, without affecting morphine-or DPDPE-induced responses. Our results indicate that activation of GABAA receptors at the supraspinal sites by i.c.v. injection of muscimol antagonizes antinociception induced by supraspinally administered μ-, ɛ-, δ-, and κ-opioid receptor agonists. On the other hand, activation of GABAB receptors at supraspinal sites by i.c.v. baclofen antagonizes antinociception induced by i.c.v. administered ɛ- and κ-opioid agonists, but not μ- or δ-opioid agonists.