Growth hormone releaser attenuates beta-amyloid (1 - 42)-induced memory impairment in mice.

Accumulating evidence indicates that growth hormone (GH) might be effective at preventing the development of Alzheimer's disease. However, exogenous GH treatment has exhibited side effects for clinical application; thus supplementation with amino acids to promote the release of GH could be a possible alternative treatment. In this study, mice that were fed with a diet of GH-releasing supplements had significantly attenuated memory impairments and hippocampal changes in the acetylcholinesterase activity and acetylcholine level induced by amyloid beta protein (Abeta) (1 - 42). Our results suggest that the use of GH-releasing supplement exerts beneficial effects on the memory impairment induced by Abeta (1 - 42).

Ginsenosides attenuate methamphetamine-induced behavioral side effects in mice via activation of adenosine A2A receptors: possible involvements of the striatal reduction in AP-1 DNA binding activity and proenkephalin gene expression.

Current evidence suggests that ginsenosides inhibit methamphetamine (MA)-induced changes in behavior, but the precise mechanisms that underlie this effect are yet to be determined. We examined the role of adenosine receptors in the ginsenoside-induced changes in hyperlocomotion and conditioned place preference (CPP) in mice that occurred in response to administration of MA (2 mg/kg, i.p. x 1 or 2 mg/kg, i.p. x 6). Changes in circling behavior paralleled changes in CPP in the presence of MA. Pre-treatment with ginsenosides (50 or 150 mg/kg, i.p.) attenuated the MA-induced circling behavior and CPP. This attenuation was reversed by the adenosine A2A receptor antagonist 1,3,7-trimethyl-8-(3-chrostyryl)xanthine (CSC; 0.5 and 1.0 mg/kg) in a dose-dependent manner, but neither the adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dimethylxanthine (CPT; 0.5 and 1.0 mg/kg) nor the A2B receptor antagonist alloxazine (ALX; 1.5 and 3.0 mg/kg) had any such effect. MA-induced increases in activator protein (AP)-1 DNA binding activity, Fos-related antigen immunoreactivity (FRA-IR), proenkephalin mRNA expression, and proenkephalin-like immunoreactivity were reduced consistently in the striatum of animals that were pretreated with ginsenosides. These reductions were largely prevented by CSC, but not by CPT or ALX. Our results suggest that the stimulation of A2A receptors by ginsenosides attenuates the changes in behavior and the increases in AP-1 DNA binding activity, FRA-IR, and proenkephalin gene expression in mouse striatum that are induced by MA.

The dextromethorphan analog dimemorfan attenuates kainate-induced seizures via sigma1 receptor activation: comparison with the effects of dextromethorphan.

In a previous study, we demonstrated that a dextromethorphan analog, dimemorfan, has neuroprotective effects. Dextromethorphan and dimemorfan are high-affinity ligands at sigma1 receptors. Dextromethorphan has moderate affinities for phencyclidine sites, while dimemorfan has very low affinities for such sites, suggesting that these sites are not essential for the anticonvulsant actions of dimemorfan. Kainate (KA) administration (10 mg kg(-1), i.p.) produced robust convulsions lasting 4-6 h in rats. Pre-treatment with dimemorfan (12 or 24 mg kg(-1)) reduced seizures in a dose-dependent manner. Dimemorfan pre-treatment also attenuated the KA-induced increases in c-fos/c-jun expression, activator protein (AP)-1 DNA-binding activity, and loss of cells in the CA1 and CA3 fields of the hippocampus. These effects of dimemorfan were comparable to those of dextromethorphan. The anticonvulsant action of dextromethorphan or dimemorfan was significantly counteracted by a selective sigma1 receptor antagonist BD 1047, suggesting that the anticonvulsant action of dextromethorphan or dimemorfan is, at least in part, related to sigma1 receptor-activated modulation of AP-1 transcription factors. We asked whether dimemorfan produces the behavioral side effects seen with dextromethorphan or dextrorphan (a phencyclidine-like metabolite of dextromethorphan). Conditioned place preference and circling behaviors were significantly increased in mice treated with phencyclidine, dextrorphan or dextromethorphan, while mice treated with dimemorfan showed no behavioral side effects. Our results suggest that dimemorfan is equipotent to dextromethorphan in preventing KA-induced seizures, while it may lack behavioral effects, such as psychotomimetic reactions.

Attenuation of cocaine-induced conditioned place preference by Polygala tenuifolia root extract.

A recent investigation indicated that Polygala tenuifolia Willdenow extract (PTE) possesses a potential antipsychotic effect. In this study, we examined the effects of PTE on the cocaine-induced changes in locomotor activity, conditioned place preference (CPP), fos-related antigen-immunoreactivity (FRA-IR), and activator protein (AP)-1 DNA binding activity. Cocaine-induced behavioral effects (hyperlocomotion and CPP) occurred in parallel with increases in FRA-IR and AP-1 DNA binding activity in the nucleus accumbens. These responses induced by cocaine were consistently attenuated by concurrent treatment with PTE (25 mg or 50 mg/kg/day, i.p. x 7). The adenosine A2A receptor antagonist, 1,3,7-trimethyl-8-(3-chlorostyrl)xanthine (0.5 or 1.0 mg/kg, i.p.), reversed the PTE-mediated pharmacological action in a dose related manner; neither the adenosine A(1) receptor antagonist, 8-cyclopentyl-1,3-dimethylxanthine (0.5 or 1.0 mg/kg, i.p.) nor the A2B receptor antagonist, alloxazine (1.5 or 3.0 mg/kg, i.p.) significantly affected this pharmacological action. Our results suggest that PTE prevents cocaine-induced behavioral effects, at least in part, via the activation of the adenosine A2A receptor.

Beta-amyloid (1-42)-induced learning and memory deficits in mice: involvement of oxidative burdens in the hippocampus and cerebral cortex.

We have demonstrated that oxidative stress is involved, at least in part, in beta-amyloid protein (Abeta)-induced neurotoxicity in vivo [Eur. J. Neurosci. 1999;11:83-90; Neuroscience 2003;119:399-419]. However, mechanistic links between oxidative stress and memory loss in response to Abeta remain elusive. In the present study, we examined whether oxidative stress contributes to the memory deficits induced by intracerebroventricular injection of Abeta (1-42) in mice. Abeta (1-42)-induced memory impairments were observed, as measured by the water maze and passive avoidance tests, although these impairments were not found in Abeta (40-1)-treated mice. Treatment with antioxidant alpha-tocopherol significantly prevented memory impairment induced by Abeta (1-42). Increased activities of the cytosolic Cu,Zn-superoxide dismutase (Cu,Zn-SOD) and mitochondrial Mn-superoxide dismutase (Mn-SOD) were observed in the hippocampus and cerebral cortex of Abeta (1-42)-treated animals, as compared with Abeta (40-1)-treated mice. The induction of Cu,Zn-SOD was more pronounced than that of Mn-SOD after Abeta (1-42) insult. However, the concomitant induction of glutathione peroxidase (GPX) in response to significant increases in SOD activity was not seen in animals treated with Abeta (1-42). Furthermore, glutathione reductase (GRX) activity was only increased at 2h after Abeta (1-42) injection. Production of malondialdehyde (lipid peroxidation) and protein carbonyl (protein oxidation) remained elevated at 10 days post-Abeta (1-42), but the antioxidant alpha-tocopherol significantly prevented these oxidative stresses. Therefore, our results suggest that the oxidative stress contributes to the Abeta (1-42)-induced learning and memory deficits in mice.

Protection against kainate neurotoxicity by pyrrolidine dithiocarbamate.

The effect of pyrrolidine dithiocarbamate (PDTC) on kainate (KA)-induced neurotoxicity was examined in Sprague-Dawley rats. At 10 mg/kg, i.p., KA produced seizures accompanied by neuronal loss in the hippocampus and increased levels of malondialdehyde (MDA) and protein carbonyl. Pretreatment with PDTC (100 or 200 mg/kg, p.o., every 12 h x 5) blocked KA-induced neurotoxicities (seizures, increases in MDA and protein carbonyl and neuronal losses) in a dose-dependent manner. These effects were counteracted by the adenosine A(1) receptor antagonist 8-cyclopentyl-1,3-dimethylxanthine (25 or 50 micro g/kg, i.p.), but not by the A(2A) receptor antagonist 1,3,7-trimethyl-8-(3-chlorostyryl)xanthine (0.5 or 1 mg/kg, i.p.) or the A(2B) receptor antagonist alloxazine (1.5 or 3.0 mg/kg, i.p.). Our results suggest that the anticonvulsant and neuroprotective effects of PDTC are mediated, at least in part, via adenosine A(1) receptor stimulation.

PAP 9704, a Korean herbal medicine attenuates methamphetamine-induced hyperlocomotion via adenosine A2A receptor stimulation in mice.

The effect of PAP 9704, a traditional prescription in Korea consisting of Polygala tenuifolia, Acorus gramineus, and Poria cocos at a ratio of 1:1:1 (dry weight), on methamphetamine (MA)-induced hyperlocomotion was examined in mice. The increased locomotor activity induced by MA (1 mg/kg/d, i.p. x 7) was significantly attenuated by co-administration with PAP 9704 (100 or 200 mg/kg/d, p.o. x 7) in a dose dependent manner. Consistently, it was found that the hyperlocomotor activity occurred in parallel with the expression of striatal fos-related antigen immunoreactivity. The adenosine A(2A) receptor antagonist, 1,3,7-trimethyl-8-(3-chlorostyryl)xanthine (0.5 or 1.0 mg/kg, i.p.), significantly reversed the pharmacological action of PAP 9704 in a dose related manner, but the adenosine A(1) receptor antagonist 8-cyclopentyl-1,3-dimethylxanthine (0.5 or 1.0 mg/kg, i.p.) and the A(2B) receptor antagonist alloxazine (1.5 or 3.0 mg/kg, i.p.) did not significantly affect this pharmacological action. Our results suggest that PAP 9704 prevents MA-induced hyperlocomotion, at least in part, via the stimulation of the adenosine A(2A) receptor.

Dimemorfan prevents seizures induced by the L-type calcium channel activator BAY k-8644 in mice.

A dextromethorphan (3-methoxy-17-methylmorphinan) analog, dimemorfan (3-methyl-N-methylmorphinan) that is not metabolized to dextrorphan [3-hydroxy-17-methylmorphinan, which induces phencyclidine (PCP)-like behavioral effects], attenuates maximal electroshock seizures. However, the pharmacological mechanism of action of dimemorfan remains to be determined. In this study, we assessed the locomotor activity mediated by these morphinans. Circling behavior was pronounced in mice treated with PCP or dextrorphan, while animals treated with dextromethorphan exhibited moderate behaviors. Dimemorfan did not show any significant behavioral effects. We used BAY k-8644 (an L-type Ca2+ channel agonist in the dihydropyridine class) to explore the effects of dextromethorphan and dimemorfan on the convulsant activity regulated by calcium channels. Intracerebroventricular injection of BAY k-8644 (37.5 microg) significantly induced seizures in mice. As with dextromethorphan (6.25 or 12.5 mg/kg), dimemorfan (6.25 or 12.5 mg/kg) pretreatment significantly attenuated BAY k-8644-induced seizures in a dose-dependent manner. BAY k-8644-induced seizure activity paralleled increased expression of c-fos and c-jun, AP-1 DNA binding activity, and fos-related antigen immunoreactivity. Pretreatment with dextromethorphan or dimemorfan significantly attenuated the expression induced by BAY k-8644. Therefore, our results suggest that the anticonvulsant effects of dextromethorphan and dimemorfan are mediated, at least in part, via L-type calcium channel, and that dimemorfan is equipotent to dextromethorphan in preventing BAY k-8644-induced seizures, while it lacks behavioral side effects related to psychotomimetic reactions.

Antioxidant propolis attenuates kainate-induced neurotoxicity via adenosine A1 receptor modulation in the rat.

We examined the effects of the antioxidant propolis on seizures induced by kainic acid (KA). Sprague-Dawley rats received propolis (75 and 150 mg/kg, p.o.) five times at 12 h intervals. KA (10 mg/kg, i.p.) was injected 1 h after the last propolis treatment. Pretreatment with propolis significantly attenuated KA-induced seizures and KA-induced increases in hippocampal AP-1 DNA binding activity in a dose-dependent manner. KA induced increases in the levels of malondialdehyde and protein carbonyl, and a decrease in the ratio of GSH/GSSG. These oxidative stresses and neuronal degenerations were significantly attenuated by pretreatment with propolis. The neuroprotective effects of propolis appeared to be counteracted by adenosine receptor antagonists [A1 antagonist, 8-cyclopentyl-1,3-dimethylxanthine (25 or 50 microg/kg); A2A antagonist, 1,3,7-trimethyl-8-(3-chlorostyryl)xanthine (0.5 or 1 mg/kg); and A2B antagonist, alloxazine (1.5 or 3.0 mg/kg)]. However, this counteraction was most pronounced in the presence of the A1 antagonist. Our results suggest that the protective effect of propolis against KA-induced neurotoxic oxidative damage is, at least in part, via adenosine A1 receptor modulation.

New morphinan derivatives with negligible psychotropic effects attenuate convulsions induced by maximal electroshock in mice.

Interest in dextromethorphan (DM) has been renewed because of its anticonvulsant and neuroprotective properties. However, DM at supra-antitussive doses can produce psychotomimetic effects in humans. Recently, we demonstrated that DM exerts psychotropic effects in mice [Neurosci. Lett. 288 (2000) 76, Life Sci. 69 (2001) 615]. We synthesized a series of compounds with a modified morphinan ring system, with the intention of developing compounds that retain the anticonvulsant activity with weak psychotropic effects [Bioorg. Med. Chem. Lett. 11 (2001) 1651]. In order to extend our understanding of the pharmacological intervention of these morphinans, we assessed their behavioral effects, and then examined whether they exert protective effects on maximal electroshock convulsions (MES) in mice. Repeated treatment (20 or 40 mg/kg, i.p./day x 7) with DM or dextrorphan (a major metabolite of DM; DX) significantly enhanced locomotor activity in a dose-related manner. This locomotor stimulation was accentuated more in the animals treated with DX, and might be comparable to that of phencyclidine (PCP). By contrast, treatment with a metabolite of DM [3-methoxymorphinan (3MM) or 3-hydroxymorphinan (3HM)], 3-allyloxy-17-methylmorphinan (CPK-5), or 3-cyclopropylmethoxy-17-methylmorphinan (CPK-6) did not significantly alter locomotor activity or patterns. The behavioral effects mediated by these morphinans and PCP paralleled the effects of conditioned place preference. DM, DX, CPK-5, and CPK-6 had anticonvulsant effects against MES, while 3MM and 3HM did not show any anticonvulsant effects. We found that DM, DX, CPK-5 and CPK-6 were high-affinity ligands at sigma(1) receptors, while they all had low affinity at sigma(2) receptors. DX had relatively higher affinity for the PCP sites than DM. By contrast, CPK-5 and CPK-6 had very low affinities for PCP sites, suggesting that PCP sites are not requisites for their anticonvulsant actions. Our results suggest that the new morphinan analogs are promising anticonvulsants that are devoid of PCP-like behavioral side effects, and their anticonvulsant actions may be, in part, mediated via sigma(1) receptors.

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.

Kainate treatment alters TGF-beta3 gene expression in the rat hippocampus.

In order to evaluate the role of transforming growth factor (TGF)-beta3 in the neurodegenerative process, we examined the levels of mRNA and immunocytochemical distribution for TGF-beta3 in the rat hippocampus after systemic kainic acid (KA) administration. Hippocampal TGF-beta3 mRNA level was reduced 3 h after KA injection. However, the levels of TGF-beta3 mRNA were elevated 1 day post-KA and lasted for at least 30 days. A mild TGF-beta3 immunoreactivity (TGF-beta3-IR) in the Ammon's horn and a moderate TGF-beta3-IR in the dentate granule cells were observed in the normal hippocampus. The CA1 and CA3 neurons lost their TGF-beta3-IR, while TGF-beta3-positive glia-like cells proliferated mainly throughout the CA1 sector and had an intense immunoreactivity at 7, 15 and 30 days after KA. This immunocytochemical distribution of TGF-beta3-positive non-neuronal populations was similar to that of glial fibrillary acidic protein (GFAP)-positive cells. Double labeling immunocytochemical analysis demonstrated colocalization of TGF-beta3- and GFAP-immunoreactivity in the same cells. These findings suggest a compensatory mechanism of astrocytes for the synthesis of TGF-beta3 protein in response to KA-induced neurodegeneration. In addition, exogenous TGF-beta3 (5 or 10 ng/i.c.v.) significantly attenuated KA-induced seizures and neuronal damages in a dose-related manner. Therefore, our results suggest that TGF-beta3 plays an important role in protective mechanisms against KA-induced neurodegeneration.

Oxidative damage causes formation of lipofuscin-like substances in the hippocampus of the senescence-accelerated mouse after kainate treatment.

We have demonstrated that seizures induced by kainic acid (KA) are, at least in part, mediated via oxidative stress in rats [Life. Sci. 61 (1997) PL373; Brain Res. 853 (2000) 215; Brain Res. 874 (2000) 15; Neurosci. Lett. 281 (2000) 65]. In order to extend our findings, we employed the rodent aging model in this study. After KA treatments (once a day for 5 days; 20,20,20,20 and 40 mg/kg, i.p.), several parameters reflecting neurotoxic behaviors, oxidative stress [malondialdehyde (MDA) and protein carbonyl] and aging (lipofuscin-like substances) were compared between senile-prone (P8) and resistant (R1) strains of 9-month-old male senescence-accelerated mice (SAM). KA-induced neurotoxic signs as shown by mortality and seizure activity were more accentuated in the SAM-P8 than in the SAM-R1. Levels of MDA and carbonyl are consistently higher in the hippocampus of SAM-P8 than that of SAM-R1. Significant increases in the values of MDA and carbonyl were observed 4 h or 2 days after the final KA administration. This finding was more pronounced in the SAM-P8 than in the SAM-R1. Although a significant loss of hippocampal neurons was observed 7 days post-KA, at this time the MDA and carbonyl content had returned to near control levels. In contrast, fluorescent lipofuscin-like substances and lipofuscin granules were significantly increased 7 days after KA treatments. Therefore, our data suggests that mice in the senescence model are more susceptible to KA-induced seizures/oxidative damage, and that oxidative damage could be one of the casual factors in the accumulation of lipofuscin.