Rubiscolin-6, a delta opioid peptide derived from spinach Rubisco, has anxiolytic effect via activating sigma1 and dopamine D1 receptors

Rubiscolin-6 (Tyr-Pro-Leu-Asp-Leu-Phe) is a delta opioid peptide derived from the large subunit of spinach d-ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). We previously reported that rubiscolin-6 had an analgesic effect and stimulated memory consolidation. Here we show that intraperitoneally (i.p.) or orally administered rubiscolin-6 has an anxiolytic effect at a dose of 10 mg/kg or 100 mg/kg, respectively, in the elevated plus-maze test in mice. The anxiolytic effects of rubscolin-6 after i.p. (10 mg/kg) and oral (100 mg/kg) administration were blocked by a delta opioid receptor antagonist, naltrindole (1 mg/kg, s.c.), suggesting that the anxiolytic activity of rubiscolin-6 is mediated by delta opioid receptor. The anxiolytic effect of rubiscolin-6 (10 mg/kg, i.p.) was also blocked by a dopamine D(1) antagonist, SCH23390 (30 microg/kg, i.p.), but not by a dopamine D(2) antagonist, raclopride (15 microg/kg, i.p.). The anxiolytic effect of rubiscolin-6 (10 mg/kg, i.p.) was blocked by sigma(1) receptor antagonist, BMY14802 (0.5 mg/kg, i.p.) or BD1047 (10 mg/kg, i.p.). Taken together, the anxiolytic effect of rubiscolin-6 is mediated by sigma(1) and dopamine D(1) receptors downstream of delta opioid receptor.     

Glutamate antagonists attenuate the action of NC-1900, a vasopressin fragment analog, on passive avoidance task performance in mice

To examine the relationship between glutamate receptors and the action of NC-1900 on a step-through passive avoidance (PA) task in mice, MK-801, an NMDA receptor blocker, and (S)-4-carboxyphenylglycine (4CPG), a group I metabotropic receptor antagonist, were administered intraventricularly (i.c.v.) singly or as co-injections. The i.c.v. injection of MK-801 (0.8 microg) or 4CPG (2 microg) decreased the latency on the PA task. NC-1900 (1 ng/kg, subcutaneously (s.c.)) alone prolonged the latency on the retention trial in the PA task. MK-801 (0.2 and 0.8 microg) or 4CPG (0.5 and 2 microg) significantly inhibited the action of NC-1900, while the s.c. injection of NC-1900 did not affect latency in mice that received i.c.v. co-injection of MK-801 and 4CPG at any of the doses tested. These results suggest that glutamate receptors participate in the action of NC-1900 on learning and memory in PA task performance.     

Taxifolin ameliorates cerebral ischemia-reperfusion injury in rats through its anti-oxidative effect and modulation of NF-kappa B activation

Summary Infarction in adult rat brain was induced by middle cerebral arterial occlusion (MCAO) followed by reperfusion to examine whether taxifolin could reduce cerebral ischemic reperfusion (CI/R) injury. Taxifolin administration (0.1 and 1.0 μg/kg, i.v.) 60 min after MCAO ameliorated infarction (by 42%±7% and 62%±6%, respectively), which was accompanied by a dramatic reduction in malondialdehyde and nitrotyrosine adduct formation, two markers for oxidative tissue damage. Overproduction of reactive oxygen species (ROS) and nitric oxide (NO) via oxidative enzymes (e.g., COX-2 and iNOS) was responsible for this oxidative damage. Taxifolin inhibited leukocyte infiltration, and COX-2 and iNOS expressions in CI/R-injured brain. Taxifolin also prevented Mac-1 and ICAM-1 expression, two key counter-receptors involved in firm adhesion/transmigration of leukocytes to the endothelium, which partially accounted for the limited leukocyte infiltration. ROS, generated by leukocytes and microglial cells, activated nuclear factor-kappa B (NF-κB) that in turn signaled up-regulation of inflammatory proteins. NF-κB activity in CI/R was enhanced 2.5-fold over that of sham group and was inhibited by taxifolin. Production of both ROS and NO by leukocytes and microglial cells was significantly antagonized by taxifolin. These data suggest that amelioration of CI/R injury by taxifolin may be attributed to its anti-oxidative effect, which in turn modulates NF-κB activation that mediates CI/R injury. Yea-Hwey Wang, Wen-Yen Wang, Chia-Che Chang, and Kuo-Tong Liou contributed equally to this work.     

Selective antagonism of peptidoleukotriene responses does not reduce myocardial damage or neutrophil accumulation following coronary artery occlusion with reperfusion

This study was designed to assess the effect of a peptidoleukotriene receptor antagonist, SK&F 104353, for limiting myocardial damage and neutrophil accumulation in rats subjected to myocardial reperfusion injury (MI/R). In conscious rats, SK&F 10,4353 (25 mg/kg, i.v.) antagonized LTD4-induced vasopressor responses by 90% and 60% at 1 and 4 hr, respectively, indicating effective blockade of peptido-leukotriene responses. In another group of animals subjected to 30 min of coronary artery occlusion with reperfusion for 24 hr, myocardial injury and neutrophil infiltration were determined by measuring creatine phosphokinase (CPK) specific activity and myeloperoxidase (MPO) activity, respectively, in the left ventricular free wall (LVFW). Myocardial CPK levels were 8.1 +/- 0.2 U/mg protein in Sham-MI/R vehicle-treated animals, and were significantly decreased to 6.4 +/- 0.6 U/mg protein in MI/R-vehicle animals. Myocardial MPO values were 1.5 +/- 0.5 U/g LVFW in Sham-MI/R vehicle-treated animals, and significantly increased to 4.3 +/- 0.6 U/g LVFW in MI/R-vehicle animals. Administration of SK&F 10,4353 (25 mg/kg, i.v.) 1 min prior to coronary occlusion and 3.5 hr post reperfusion had no effect on the loss of myocardial CPK specific activity or the increase in MPO levels (p greater than 0.05, compared to the MI/R-vehicle group). Thus, at a dose that antagonized LTD4-induced vasopressor responses, SK&F 104353 did not attenuate either the extent of myocardial injury or inflammatory cell accumulation associated with myocardial ischemia/reperfusion. These results suggest that peptidoleukotrienes do not contribute to the progression of myocardial ischemic/reperfusion injury.     

Selective antagonism of peptidoleukotriene response does not reduce myocardial damage opr neutrophil accumulation following coronary artery occlusion with reperfusion

This study was designed to assess the effect of a peptidol eukotriene receptor antagonist. SK&F 104353, for limiting myocardial damage and neutrophil accumulation in rats subjected to myocardial reperfusion injury (MI/R). In conscious rats, SK&F 104353 (25 mg/kg, i.v.) antagonized LTD₄-induced vasopressor responses by 90% and 60% at 1 and 4 hr, respectively, indicating effective blockade of peptidol eukotriene responses. In another group of animals subjected to 30 min of coronary artery occlusion with reperfusion for 24 hr, myocardial injury and neutrophil infiltration were determined by measuring creatine phosphokinase (CPK) specific activity and myeloperoxidase (MPO) activity, respectively, in the left ventricular free wall (LVFW). Myocardial CPK levels were 8.1 ± 0.2 U/mg protein in Sham-MI/R vehicle-treated animals, and were significantly decreased to 6.4 ± 0.6 U/mg protein in MI/R-vehicle animals. Myocardial MPO values were 1.5 ± 0.5 U/g LVFW in Sham-MI/R vehicle-treated animals, and significantly increased to 4.3 ± 0.6 U/g LVFW in MI/R-vehicle animals. Administration of SK&F 105353 (25 mg/kg, i.v.) 1 min prior to coronary occlusion and 3.5 hr post reperfusion and no effect on the loss of myocardial CPK specific activity or the increase in MPO levels (p > 0.05, compared to the MI/R-vehicle group). Thus, at a dose that antagonized LTD₄-induced vasopressor responses, SK&F 104353 did not attenuate either the extent of myocardial injury or inflammatory cell accumulation associated with myocardial ischemia/ reperfusion. These results suggest that peptidoleukotrienes do not contribute to the progression of myocardial ischemic/reperfusion injury.     

Tetramethylpyrazine induces heme oxygenase-1 expression and attenuates myocardial ischemia/reperfusion injury in rats

The accumulation of oxygen free radicals and activation of neutrophils are strongly implicated as pathophysiological mechanisms mediating myocardial ischemia/reperfusion injury. Heme oxygenase-1 (HO-1) has been reported to play a protective role in oxidative tissue injuries. In this study, the cardioprotective activity of tetramethylpyrazine (TMP), an active ingredient of Chinese medicinal herb Ligusticum wallichii Franchat, was evaluated in an open-chest anesthetized rat model of myocardial ischemia/reperfusion injury. Pretreatment with TMP (5 and 10 mg/kg, i.v.) before left coronary artery occlusion significantly suppressed the occurrence of ventricular fibrillation. After 45 min of ischemia and 1 h of reperfusion, TMP (5 and 10 mg/kg) caused a significant reduction in infarct size and induced HO-1 expression in ischemic myocardium. The HO inhibitor ZnPP (50 μg/rat) markedly reversed the anti-infarct action of TMP. Superoxide anion production in ischemic myocardium after 10 min reperfusion was inhibited by TMP. Furthermore, TMP (200 and 500 μM) significantly suppressed fMLP (800 nM)-activated human neutrophil migration and respiratory burst. In conclusion, TMP suppresses ischemia-induced ventricular arrhythmias and reduces the infarct size resulting from ischemia/reperfusion injury in vivo. This cardioprotective activity of TMP may be associated with its antioxidant activity via induction of HO-1 and with its capacity for neutrophil inhibition.     

A new sigma ligand, (+/-)-PPCC, antagonizes kappa opioid receptor-mediated antinociceptive effect

The compound (1R,2S/1S,2R)-2-[4-hydroxy-4-phenylpiperidin-1-yl)methyl]-1-(4-methylphenyl) cyclopropanecarboxylate [(+/-)-PPCC] is a ligand with high affinity for sigma (sigma) sites of which the selectivity towards several other receptor systems has been demonstrated. Given the existence of a relationship between the sigma system and the kappa opioid (KOP)-mediated analgesia, to characterize the pharmacological properties of (+/-)-PPCC we analyzed its influence on the analgesic effect of the systemic injected kappa agonist (-)-U-50,488H comparing the effects with those shown by (+)-pentazocine and BD1047. The results demonstrate that the systemic administration of (+/-)-PPCC (1 mg/kg s.c.) does not modify basal tail-flick latency. Pre-treatment with (+/-)-PPCC, at the same dose, significantly decreased the antinociceptive effect of (-)-U-50,488H, analogously to the sigma compounds used. This study confirms that (+/-)-PPCC plays the role of sigma agonist in this model and strengthens the hypothesis of the sigma receptor modulatory role on KOP-mediated analgesia.     

Polynitroxyl albumin plus tempol attenuates liver injury and inflammation after hepatic ischemia and reperfusion

PNA+Tempol, albumin containing conjugated (polynitroxyl albumin; PNA) and free (4-hydroxyl-2,2,6,6-tetramethyl-piperidinyl-1-oxyl; Tempol) nitroxide may protect against injury caused by reactive oxygen species. Therefore, the actions of PNA+Tempol on liver injury and inflammation induced by hepatic ischemia and reperfusion (I/R) were examined. Rats were subjected to 1 h ischemia followed by 24 h reperfusion in the absence (I/R) or presence of PNA+Tempol (25%; 15 mL/kg, i.v.) (I/R+PNA+Tempol) or human serum albumin (23%; 13.5 mL/kg, i.v.) (I/R+HSA). Test solutions were administered prior to and for 2 h during reperfusion. Sham-operated rats underwent surgery with neither ischemia nor infusion. I/R+PNA+Tempol rats had significantly less liver injury and inflammation than I/R rats. I/R+PNA+Tempol livers exhibited focal lesions whereas I/R livers exhibited global necrosis. Likewise, plasma ALT activity was significantly lower in I/R+PNA+Tempol rats. PNA+Tempol reduced I/R-induced neutrophil accumulation and intercellular adhesion molecule-1 (ICAM-1) expression. HSA did not alter I/R-induced liver injury or inflammation. Sham-operated rats exhibited normal liver morphology and no inflammation. Attenuation of I/R liver injury by PNA+Tempol may be mediated by its effect on inflammation, the major contributor to I/R injury. Reduction of inflammation by PNA+Tempol is most likely due to the antioxidative nature of the nitroxides.     

Role of endogenous opioid peptides in protection of ischemic preconditioning in rat small intestine

This study investigated the protective effects of ischemic preconditioning on intestinal ischemic injury and the role of endogenous opioid peptides (EOP) in these effects. Ischemia-reperfusion (I/R) induced by 30-min of ischemia and 60-min of reperfusion significantly increased the levels of malondialdehyde (MDA) and lactate dehydrogenase (LDH) and resulted in serious intestinal edema (wet weight/dry weight). The ischemic preconditioning (PC) elicited by three 8-min occlusion periods interspersed with 10-min reperfusion markedly attenuated intestinal injury caused by ischemia-reperfusion. Pretreatment with morphine (300 microg x kg(-1), i.v.) 10-min before ischemia and reperfusion mimicked the protection produced by PC. Naloxone (3 mg x kg(-1), i.v.) abolished the protection of morphine-induced preconditioning and ischemic preconditioning in rat intestine. However, there were no changes between naloxone alone and control groups. Treatment with naloxone before ischemia-reperfusion had no effect on animals compared with the I/R group. In addition, we also measured the content of endogenous opioid peptides (Leu-enkephalin) in the effluent which was collected before and during preconditioning. It was shown that the release of leu-enkephalin was markedly increased during preconditioning. These results suggested that EOP might play an important role in PC in rat small intestine.     

Octreotide: a new approach to the management of acute abdominal hypertension

Acutely increased intra-abdominal pressure (IAP) may lead to abdominal compartment syndrome (ACS), which ischaemia/reperfusion (I/R) injury plays an important role. The main goal of the management of ACS is to lower the intra-abdominal pressure despite reperfusion injury. Octreotide (OCT), a synthetic somatostatin analogue, lowers the splanchnic perfusion. The aim of this study was to investigate whether OCT improves the reperfusion injury after decompression of acute abdominal hypertension.Under anesthesia, a catheter was inserted intraperitoneally and using an aneroid manometer connected to the catheter, IAP was kept at 20 mmHg (ischemia group; I) for 1h. In the I/R group, pressure applied for an hour was decompressed and 1h reperfusion period was allowed. In another group of I/R, OCT was administered (50 microg/kg i.p.) immediately before the decompression of IAP. The results demonstrate that kidney and lung tissues of malondialdehyde (MDA; an end product of lipid peroxidation) levels and myeloperoxidase (MPO; index of tissue neutrophil infiltration) activity were elevated, while glutathione (GSH; a key to antioxidant) levels were reduced in I/R group (P<0.001). Moreover, OCT treatment applied in the I/R group reduced the elevations in blood urea nitrogen (BUN) and serum creatinine levels. Our results implicate that IAP causes oxidative organ damage and OCT, by reducing splanchnic perfusion and controlling the reperfusion of abdominal organs, could improve the reperfusion-induced oxidative damage. Therefore, its therapeutic role as a "reperfusion injury-limiting" agent must be further elucidated in IAP-induced abdominal organ injury.     

Capsaicin-, resiniferatoxin-, and olvanil-induced adrenaline secretions in rats via the vanilloid receptor.

The effects of capsaicin analogs on adrenaline secretion were investigated in rats. Capsaicin (20-100 microg/kg, i.v.) caused biphasic adrenaline secretion. Capsazepine (20 mg/kg, i.v.), a specific competitive antagonist of the vanilloid (capsaicin) receptor, strongly inhibited both phases of adrenaline secretion by capsaicin (50 microg/kg). Next, the effects of two capsaicin analogs on the adrenal catecholamine secretion were examined. Resiniferatoxin (20-200 ng/kg, i.v.), a naturally occurring phorbolester-like compound, provoked slow onset adrenaline secretion in a dose-dependent manner. Olvanil (2.46-246 microg/kg, i.v.), a synthesized non pungent capsaicin analog, also stimulated delayed catecholamine secretion dose-dependently. Capsazepine (20 mg/kg, i.v.) pretreatment prevented the resiniferatoxin (50 ng/kg)- and olvanil (24.6 microg/kg)-induced catecholamine secretion. These results suggest that some vanilloids (capsaicin, resiniferatoxin, olvanil) excite adrenaline secretion and such excitation is via the vanilloid receptor.     

Antidepressant-like effect of 17beta-estradiol: involvement of dopaminergic, serotonergic, and (or) sigma-1 receptor systems

17beta-estradiol has been reported to possess antidepressant-like activity in animal models of depression, although the mechanism for its effect is not well understood. The present study is an effort in this direction to explore the mechanism of the antidepressant-like effect of 17beta-estradiol in a mouse model(s) of behavioral depression (despair behavior). Despair behavior, expressed as helplessness to escape from a situation (immobility period), as in a forced swim test in which the animals are forced to swim for a total of 6 min, was recorded. The antiimmobility effects (antidepressant-like) of 17beta-estradiol were compared with those of standard drugs like venlafaxine (16 mg/kg, i.p.). 17beta-estradiol produced a U-shaped effect in decreasing the immobility period. It had no effect on locomotor activity of the animal. The antidepressant-like effect was comparable to that of venlafaxine (16 mg/kg, i.p.). 17beta-estradiol also exhibited a similar profile of antidepressant action in the tail suspension test. When coadministered with other antidepressant drugs, 17beta-estradiol (5 microg/kg, i.p.) potentiated the antiimmobility effect of subeffective doses of fluoxetine (5 mg/kg, i.p.), venlafaxine (2 mg/kg, i.p.), or bupropion (10 mg/kg, i.p.), but not of desipramine (5 mg/kg, i.p.) or tranylcypromine (2 mg/kg, i.p.), in the forced swim test. The reduction in the immobility period elicited by 17beta-estradiol (20 microg/kg, i.p.) was reversed by haloperidol (0.5 mg/kg, i.p.; a D(2) dopamine receptor antagonist), SCH 23390 (0.5 mg/kg, i.p.; a D(1) dopamine receptor antagonist), and sulpiride (5 mg/kg, i.p.; a specific dopamine D(2) receptor antagonist). In mice pretreated with (+)-pentazocine (2.5 mg/kg, i.p.; a high-affinity sigma-1 receptor agonist), 17beta-estradiol (5 microg/kg, i.p.) produced a synergistic effect. In contrast, pretreatment with progesterone (10 mg/kg, s.c.; a sigma-1 receptor antagonist neurosteroid), rimcazole (5 mg/kg, i.p.; another sigma-1 receptor antagonist), or BD 1047 (1 mg/kg, i.p.; a novel sigma-1 receptor antagonist) reversed the antiimmobility effects of 17beta-estradiol (20 microg/kg, i.p.). Similarly, in mice pretreated with a subthreshold dose of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, a 5-HT1A serotonin receptor agonist), 17beta-estradiol (5 microg/kg, i.p.) produced an antidepressant-like effect. These findings demonstrate that 17beta-estradiol exerted an antidepressant-like effect preferentially through the modulation of dopaminergic and serotonergic receptors. This action may also involve the participation of sigma-1 receptors.     

Anti-inflammatory effect of exendin-4 postconditioning during myocardial ischemia and reperfusion

High mobility group box 1 protein (HMGB1) plays an important role in myocardial ischemia and reperfusion (I/R) injury. Preconditioning of exendin-4 (Ex), a glucagon-like peptide-1 receptor agonist, has been reported to attenuate myocardial I/R injury. The current study investigated whether Ex postconditioning also attenuated myocardial I/R injury and the potential mechanisms. Anesthetized male rats were subjected to ischemia for 30 min and treated with Ex (5 μg/kg, i.v.) 5 min before reperfusion, in the absence and/or presence of exendin (9–39) (an antagonist of glucagon-like peptide-1 receptor, 5 μg/kg, i.v.), followed by reperfusion for 4 h. Lactate dehydrogenase (LDH), creatine kinase (CK), tumor necrosis factor-α, interleukin-6, and infarct size were measured. HMGB1 expression was assessed by immunoblotting. Postconditioning with Ex significantly decreased infarct size and levels of LDH and CK after 4 h reperfusion (all p < 0.05). Ex also significantly inhibited the increase in malondialdehyde level and decreased the level of superoxide dismutase (both p < 0.05). In addition, the increase in HMGB1 expression induced by I/R was significantly attenuated by Ex postconditioning. Administration of exendin (9–39) abolished the protective effect of Ex postconditioning (all p < 0.05). The present study suggests that Ex postconditioning may attenuate myocardial I/R injury, which may in turn be associated with inhibiting inflammation.     

σ receptor 1 is preferentially involved in modulation of N-methyl-D-aspartate receptor-mediated light-evoked excitatory postsynaptic currents in rat retinal ganglion cells

Using patch-clamp whole-cell recording, we investigated how activation of the sigma receptor 1 (σR1) modulates light-evoked excitatory postsynaptic currents (eEPSCs) of ganglion cells (GCs) in rat retinal slice preparations. Bath application of the σR1 agonist SKF10047 (SKF) suppressed N-methyl-D-aspartate (NMDA) receptor-mediated eEPSCs at different holding potentials in ON, OFF and ON-OFF GCs, and the effects were blocked when the preparations were pre-incubated with the σR1 antagonist BD1047. In contrast, SKF had no effects on α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated eEPSCs of these GCs. Furthermore, application of SKF did not affect AMPA receptor-mediated miniature EPSCs of GCs, suggesting that activation of σR1 did not change the release of glutamate from bipolar cells. These results suggest that σR1 may be involved in the regulation of output signaling of GCs by preferentially modulating NMDA receptor-mediated eEPSCs of these retinal neurons.     

Brain kinin B1 receptor is upregulated by the oxidative stress and its activation leads to stereotypic nociceptive behavior in insulin-resistant rats

Kinin B1 receptor (B1R) is virtually absent under physiological condition, yet it is highly expressed in models of diabetes mellitus. This study aims at determining: (1) whether B1R is induced in the brain of insulin-resistant rat through the oxidative stress; (2) the consequence of B1R activation on stereotypic nocifensive behavior; (3) the role of downstream putative mediators in B1R-induced behavioral activity. Sprague-Dawley rats were fed with 10% d-glucose in their drinking water or tap water (controls) for 4 or 12 weeks, combined either with a standard chow diet or a diet enriched with α-lipoic acid (1 g/kg feed) for 4 weeks. The distribution and density of brain B1R binding sites were assessed by autoradiography. Behavioral activity evoked by i.c.v. injection of the B1R agonist Sar-[D-Phe⁸]-des-Arg⁹-BK (10 μg) was measured before and after i.c.v. treatments with selective antagonists (10 μg) for kinin B1 (R-715, SSR240612), tachykinin NK1 (RP-67580) and glutamate NMDA (DL-AP5) receptors or with the inhibitor of NOS (L-NNA). Results showed significant increases of B1R binding sites in various brain areas of glucose-fed rats that could be prevented by the diet containing α-lipoic acid. The B1R agonist elicited head scratching, grooming, sniffing, rearing, digging, licking, face washing, wet dog shake, teeth chattering and biting in glucose-fed rats, which were absent after treatment with α-lipoic acid or antagonists/inhibitors. Data suggest that kinin B1R is upregulated by the oxidative stress in the brain of insulin-resistant rats and its activation causes stereotypic nocifensive behavior through the release of substance P, glutamate and NO.     

In vivo evaluation of (+)-MR200 as a new selective sigma ligand modulating MOP, DOP and KOP supraspinal analgesia

The compound (+)-MR200 [(+)-methyl (1R,2S)-2-{[4-(4-chlorophenyl)-4-hydroxypiperidin-1-yl]methyl}-1-phenylcyclopropanecarboxylate] is a sigma ligand with increased affinity and selectivity compared to the structurally related ligand haloperidol. From the results of a previous study on the modulation of a systemically injected KOP opioid agonist analgesia by (+)-MR200, we analysed the influence of this sigma ligand on the antinociceptive effect of centrally injected MOP, DOP, and KOP selective agonists using the tail-flick test in rats. The results obtained confirmed that systemic administration of (+)-MR200 (1mg/Kg s.c.) did not modify basal tail-flick latency. Pre-treatment with 1mg/Kg s.c. of (+)-MR200 provided a significant increase in the antinociceptive effect of DAMGO (100ng/rat i.c.v.) and DPDPE (20 microg/rat i.c.v.). Conversely to previous reports, pre-treatment with (+)-MR200 reversed, in these experimental conditions, U-50488H (100 microg/rat i.c.v.) analgesia. The mechanism involved in these effects was not clear, but provided additional data on a diverging modulator role of selective sigma-1 antagonists on KOP analgesia.     

Hepatic ischemia/reperfusion in rats induces iNOS gene transcription by activation of NF-kappaB.

It has been known that many immediately early genes are expressed during ischemia/reperfusion (I/R) injury. Here, employing a model of hepatic I/R, we show that inducible nitric oxide synthase (iNOS) is induced via the activation of nuclear factor kappaB (NF-kappaB) after I/R in rat liver. When liver was subjected to ischemia followed by reperfusion, but not ischemia alone, an NF-kappaB complex composed of p50/p65 heterodimer and p50 homodimer was rapidly activated within 1 h and remained elevated for up to 3 h, and then tended to decline after 5 h of reperfusion. Also, the expression of iNOS mRNA was initiated after 1 h and continued to increase after 5 h of reperfusion during the time course studied. This upregulated iNOS mRNA expression coincides with increased iNOS enzyme activity and NF-kappaB binding activity after hepatic I/R. Administration of N-acetylcysteine (NAC, 20 mg/kg i.v. 10 min before reperfusion), an antioxidant, not only significantly inhibited the expression of iNOS mRNA but also blocked upregulated NF-kappaB binding activity after reperfused liver. These results suggest that NF-kappaB is activated by oxidative stress during hepatic I/R and may play a significant role in the induction of the iNOS gene.     

Metabolism to dextrorphan is not essential for dextromethorphan's anticonvulsant activity against kainate in mice

The effects of dextromethorphan (DM), and its major metabolite dextrorphan (DX) on kainic acid-induced seizures in mice were examined. Intracerebroventricular DM or DX (5 or 10 microg/0.5 microl) pretreatment significantly attenuated seizures induced by kainic acid (0.07 microg/0.07 microl) in a dose-related manner. DM or DX pretreatment significantly attenuated kainic acid-induced increases in AP-1 DNA-binding activity and fos-related antigen-immunoreactivity as well as neuronal loss in the hippocampus. DM appears to be a more potent neuroprotectant than DX. Since the high-affinity DM binding sites are recognized as being identical to the sigma-1 site, we examined the role of the sigma-1 receptor on the pharmacological action mediated by DM or DX. Pretreatment with the sigma-1 receptor antagonist BD1047 (2.5 or 5 mg/kg, i.p.) blocked the neuroprotection by DM in a dose-related manner. This effect of BD 1047 was more pronounced in the animals treated with DM than in those treated with DX. Combined, our results suggest that metabolism of DM to DX is not essential for DM to exert its effect. They also suggest that DM provides neuroprotection from kainic acid via sigma-1 receptor modulation.     

Dextromethorphan attenuates trimethyltin-induced neurotoxicity via sigma1 receptor activation in rats

We showed that dextromethorphan (DM) provides neuroprotective/anticonvulsant effects and that DM and its major metabolite, dextrorphan, have a high-affinity for sigma(1) receptors, but a low affinity for sigma(2) receptors. In addition, we found that DM has a higher affinity than DX for sigma(1) sites, whereas DX has a higher affinity than DM for PCP sites. We extend our earlier findings by showing that DM attenuated trimethyltin (TMT)-induced neurotoxicity (convulsions, hippocampal degeneration and spatial memory impairment) in rats. This attenuation was reversed by the sigma(1) receptor antagonist BD 1047, but not by the sigma(2) receptor antagonist ifenprodil. DM attenuates TMT-induced reduction in the sigma(1) receptor-like immunoreactivity of the rat hippocampus, this attenuation was blocked by the treatment with BD 1047, but not by ifenprodil. These results suggest that DM prevents TMT-induced neurotoxicity, at least in part, via sigma(1) receptor stimulation.