Protective effects of glucose-6-phosphate dehydrogenase on neurotoxicity of aluminium applied into the CA1 sector of rat hippocampus.

BACKGROUND & OBJECTIVES: Aluminum (Al) toxicity is closely linked to the pathogenesis of Alzheimer's disease (AD). This experimental study was aimed to investigate the active avoidance behaviour of rats after intrahippocampal injection of Al, and biochemical and immunohistochemical changes in three bilateral brain structures namely, forebrain cortex (FBCx), hippocampus and basal forebrain (BF). METHODS: Seven days after intra-hippocampal (CA1 sector) injection of AlCl3 into adult male Wistar rats they were subjected to two-way active avoidance (AA) tests over five consecutive days. Control rats were treated with 0.9% w/v saline. The animals were decapitated on the day 12 post-injection. The activities of acetylcholinesterase (AChE) and glucose-6-phosphate dehydrogenase (G6PDH) were measured in the FBCx, hippocampus and BF. Immunohistochemical staining was performed for transferrin receptors, amyloid ß and tau protein. RESULTS: The activities of both AChE and G6PDH were found to be decreased bilaterally in the FBCx, hippocampus and basal forebrain compared to those of control rats. The number of correct AA responses was reduced by AlCl3 treatment. G6PDH administered prior to AlCl 3 resulted in a reversal of the effects of AlCl3 on both biochemical and behavioural parameters. Strong immunohistochemical staining of transferrin receptors was found bilaterally in the FBCx and the hippocampus in all three study groups. In addition, very strong amyloid ß staining was detected bilaterally in all structures in AlCl3-treated rats but was moderate in G6PDH/AlCl3-treated rats. Strong tau staining was noted bilaterally in AlCl3-treated rats. In contrast, tau staining was only moderate in G6PDH/AlCl3-treated rats. INTERPRETATION & CONCLUSIONS: Our findings indicated that the G6PDH alleviated the signs of behavioural and biochemical effects of AlCl3-treatment suggesting its involvement in the pathogenesis of Al neurotoxicity and its potential therapeutic benefit. The present model could serve as a useful tool in AD investigations.

Influence of the green tea leaf extract on neurotoxicity of aluminium chloride in rats.

Aluminium may have an important role in the aetiology/pathogenesis/precipitation of Alzheimer's disease. Because green tea (Camellia sinensis L.) reportedly has health-promoting effects in the central nervous system, we evaluated the effects of green tea leaf extract (GTLE) on aluminium chloride (AlCl3 ) neurotoxicity in rats. All solutions were injected into the cornu ammonis region 1 hippocampal region. We measured the performance of active avoidance (AA) tasks, various enzyme activities and total glutathione content (TGC) in the forebrain cortex (FbC), striatum, basal forebrain (BFb), hippocampus, brain stem and cerebellum. AlCl3 markedly reduced AA performance and activities of cytochrome c oxidase (COX) and acetylcholinesterase (AChE) in all regions. It decreased TGC in the FbC, striatum, BFb, hippocampus, brain stem and cerebellum, and increased superoxide dismutase activity in the FbC, cerebellum and BFb. GTLE pretreatment completely reversed the damaging effects of AlCl3 on AA and superoxide dismutase activity, markedly corrected COX and AChE activities, and moderately improved TGC. GTLE alone increased COX and AChE activities in almost all regions. GTLE reduces AlCl3 neurotoxicity probably via antioxidative effects and improves mitochondrial and cholinergic synaptic functions through the actions of (-)-epigallocatechin gallate and (-)-epicatechin, compounds most abundantly found in GTLE. Our results suggest that green tea might be beneficial in Alzheimer's disease.

The effect of inhibition of nitric oxide synthase on aluminium-induced toxicity in the rat brain.

The goal of the present study was to examine the effectiveness of a non-specific nitric oxide synthase (NOS) inhibitor N-nitro-L-arginine methyl ester (L-NAME) to modulate the toxicity of aluminium chloride (AlCl3). Rats were killed at 3 h and at 30 days after treatments and the striatum was removed. Nitrite, superoxide, superoxide dismutase activity, malondialdehyde and reduced glutathione were determined. AlCl3 exposure promoted oxidative stress in the striatum. The biochemical changes observed in neuronal tissues show that aluminium acts as pro-oxidant, while the NOS inhibitor exerts antioxidant action in AlCl3-treated rats. We conclude that L-NAME can efficiently protect neuronal tissue from AlCl3-induced toxicity.

Nitric oxide synthase inhibitors partially inhibit oxidative stress development in the rat brain during sepsis provoked by cecal ligation and puncture.

IOxidative stress development in different brain structures and the influence of nitric oxide (NO) overproduction during sepsis was investigated using male Wistar rats. Rats were subjected to cecal ligation and puncture (CLP) or were sham-operated. To evaluate the source of NO production, 30 min before the operation septic and control animals were treated with single intraperitoneal doses of NO synthase (NOS) inhibitors: L-NAME and aminoguanidine (AG) (10, 30 or 90 mg/kg) and 7-nitroindazole (7-NI) (30 mg/kg). The concentration of GSH in the cortex, brain stem, cerebellum, striatum and hippocampus significantly decreased post CLP at both early and late stage sepsis. Lipid peroxidation also occurred in the cortex and cerebellum in late stage sepsis. Pre-treatment with a non-selective NOS inhibitor (L-NAME) and with selective inducible and neuronal NOS inhibitors (AG and 7-NI) revealed benefit effects on the GSH concentrations. Unexpectedly, NOS inhibition resulted in diverse effects on TBARS concentrations, suggesting the importance of specific quantities of NO in specific brain structures during sepsis.

Effects of L-NAME, a non-specific nitric oxide synthase inhibitor, on AlCl3-induced toxicity in the rat forebrain cortex.

The present experiments were done to determine the effectiveness of a non-specific nitric oxide synthase inhibitor, N-nitro-L-arginine methyl ester (L-NAME), on oxidative stress parameters induced by aluminium chloride (AlCl(3)) intrahippocampal injections in Wistar rats. Animals were sacrificed 3 h and 30 d after treatments, heads were immediately frozen in liquid nitrogen and forebrain cortices were removed. Crude mitochondrial fraction preparations of forebrain cortices were used for the biochemical analyses: nitrite levels, superoxide production, malondialdehyde concentrations, superoxide dismutase (SOD) activities and reduced glutathione contents. AlCl(3) injection resulted in increased nitrite concentrations, superoxide anion production, malondialdehyde concentrations and reduced glutathione contents in the forebrain cortex, suggesting that AlCl(3) exposure promoted oxidative stress in this brain structure. The biochemical changes observed in neuronal tissues showed that aluminium acted as a pro-oxidant. However, the nonspecific nitric oxide synthase (NOS) inhibitor, L-NAME, exerted anti-oxidant actions in AlCl(3)-treated animals. These results revealed that NO-mediated neurotoxicity due to intrahippocampal AlCl3 injection spread temporally and spatially to the forebrain cortex, and suggested a potentially neuroprotective effect for L-NAME.

Beneficial effects of ceftriaxone against pentylenetetrazole-evoked convulsions.

Although considered to be generally safe, a number of beta-lactam antibiotics have been associated with epileptic seizures in humans. Furthermore, some beta-lactam antibiotics, including ceftriaxone, are used to evoke convulsions under experimental conditions. Recently it was demonstrated that ceftriaxone increased expression of the glutamate transporter (GLT1) and its biochemical and functional activity in the brain of rodents. GLT1 regulates extracellular concentrations of glutamate, an excitatory amino acid involved in the pathogenesis of seizures and epilepsy. Because of its rapid transfer of glutamate into neurons and adjacent glial cells, GLT1 diminishes glutamate toxicity. We investigated whether ceftriaxone (200 mg/kg body wt) administered intraperitoneally (ip) for 6 days could modify the convulsant effects of pentylenetetrazole (PTZ, 100 mg/kg ip) in inbred male BALBcAnNCR and C57 black (BL)/6 mice aged 4 and 12 weeks. Ceftriaxone pretreatment provided significant protective effects against PTZ-evoked generalized clonic convulsions (GCCs), generalized clonic-tonic convulsions (GCTCs), and convulsion-induced mortality during a period of 30 mins after PTZ administration. The incidence of GCCs, GCTCs, and death was statistically significantly lower for BALBcAnNCR mice of both ages, particularly younger mice. The latency time for each of the three parameters was significantly greater, with the exception of GCCs in adult mice. Protective effects of ceftriaxone were also noticed in adult C57BL/6 mice but not in prepubertal C57BL/6 mice. This is the first demonstration of anticonvulsant effects of ceftriaxone or any other beta-lactam antibiotic, which are not uniform across the mouse population. Our results provide new insight into the effects of ceftriaxone, which need further investigation.

Effects of Vitamin D3 on the NADPH Oxidase and Matrix Metalloproteinase 9 in an Animal Model of Global Cerebral Ischemia.

Decreased blood flow in the brain leads to a rapid increase in reactive oxygen species (ROS). NADPH oxidase (NOX) is an enzyme family that has the physiological function to produce ROS. NOX2 and NOX4 overexpression is associated with aggravated ischemic injury, while NOX2/4-deficient mice had reduced stroke size. Dysregulation of matrix metalloproteinases (MMPs) contributes to tissue damage. The active form of vitamin D3 expresses neuroprotective, immunomodulatory, and anti-inflammatory effects in the CNS. The present study examines the effects of the vitamin D3 pretreatment on the oxidative stress parameters and the expression of NOX subunits, MMP9, microglial marker Iba1, and vitamin D receptor (VDR), in the cortex and hippocampus of Mongolian gerbils subjected to ten minutes of global cerebral ischemia, followed by 24 hours of reperfusion. The ischemia/reperfusion procedure has induced oxidative stress, changes in the expression of NOX2 subunits and MMP9 in the brain, and increased MMP9 activity in the serum of experimental animals. Pretreatment with vitamin D3 was especially effective on NOX2 subunits, MMP9, and the level of malondialdehyde and superoxide anion. These results outline the significance of the NOX and MMP9 investigation in brain ischemia and the importance of adequate vitamin D supplementation in ameliorating the injury caused by I/R.

The effect of extremely low-frequency magnetic field on motor activity of rats in the open field.

Exposure to extremely low-frequency magnetic field (ELF-MF, 50 Hz, 0.5 mT) for seven days did not change spontaneous motor activity of rats in the open field compared to sham-exposed animals. Pre-exposure to ELF-MF decreased locomotor and stereotypic activity induced by amphetamine (1.5 mg/kg body weight) and accordingly increased the resting time compared to sham-exposed and amphetamine-treated rats. Vertical activity (rearing) of these two groups was similar. Our results indicate that ELF-MF has different effects on some parameters of amphetamine-induced motor activity, probably due to brain region-specific effects on catecholaminergic systems responsible for movement control.

The effects of exposure to extremely low-frequency magnetic field and amphetamine on the reduced glutathione in the brain.

Continuous exposure to extremely low-frequency magnetic field (ELF-MF, 50 Hz, 0.5 mT) alone and combined with D-amphetamine (1.5 mg/kg) affected the reduced glutathione content in brain regions of rats. Compared to sham-exposed rats, the glutathione content in the forebrain cortex of the ELF-MF-exposed rats decreased (P < 0.001), but this reverted after giving amphetamine upon ELF-MF exposure. In this group, the glutathione content was increased in the brain stem and cerebellum (P < 0.05 compared to the sham-exposed, ELM-MF-exposed, and amphetamine-treated groups). It is suggested that biogenic monoamines are involved in the reduced glutathione changes observed. The changes are not uniform in the brain regions examined.

Different effects of chronic exposure to ELF magnetic field on spontaneous and amphetamine-induced locomotor and stereotypic activities in rats.

The effects of chronic (7 days) exposure to an extremely low frequency magnetic field (ELF-MF, 50 Hz, 0.5 mT) on spontaneous and amphetamine-induced (1.5mg/kg, i.p.) locomotor and stereotypic activities in adult rats were examined by open field test for 2h on exposure days 1, 3, and 7. After 1 day of exposure to ELF-MF, the spontaneous locomotor activity was increased clearly at the first hour of observation and significantly at the second one as compared to the corresponding values in other series with ELF-MF and sham-exposed animals. After 7 days of exposure to ELF-MF, an amphetamine enhancing effect on the locomotor activity was significantly reduced at the second hour of observation as compared to that in 1-day- and sham-exposed rats treated with amphetamine. In contrast to the locomotor activity, the amphetamine-induced stereotypic behaviour in 7-day pre-exposed rats was significantly reduced at the first hour versus sham-exposed rats. While at the second hour of observation this effect was significant as compared to 1- and 3-day exposed animals (but not sham-exposed rats). Our results indicate that an extremely low frequency magnetic field is able to affect differently two types of behaviour, which are dependent on both the time course of exposure and the imbalance in the brain mediatory systems.

Nitric oxide (NO) and convulsions induced by pentylenetetrazol.

Data about the role of nitric oxide (NO) in epileptogenesis are contradictory. It is found to exert both proconvulsant and anticonvulsant effects. In an attempt to elucidate the role of NO in seizures, male Wistar rats were treated intraperitoneally by pentylenetetrazol (PTZ) (60, 80, and 100 mg/kg) and by a nitric oxide synthase antagonist, N-omega-nitro-L-arginine-methyl-ester (L-NAME) (10, 40, and 70 mg/kg), applied before PTZ. The time to onset and incidence of forelimb dystonia (FLD), generalized clonic convulsions (GCC), clonic-tonic convulsions (CTC), and mortality were recorded. The most successful convulsive response and mortality prevention were found in PTZ (80 mg/kg)-treated groups, where L-NAME (70 mg/kg) decreased the incidence by 29, 50, 67 (p = 0.052), and 50%, respectively, and significantly prolonged the time to onset, except that for mortality. Unexpectedly, L-NAME (40 mg/kg) increased incidence of GCC and mortality by 16%, similar to L-NAME (10 mg/kg) in PTZ (60 mg/kg)-treated groups, where GCC, CTC, and mortality increased by 14, 14, and 28%, respectively. Convulsive latency was prolonged in some PTZ (100 mg/kg) + L-NAME (40 and 70 mg/kg)-treated groups. In the experimental model and protocol used, it is concluded that (1) the effects of NO are L-NAME- and PTZ-dose dependent; (2) clonic-tonic convulsions are more strongly influenced by NO than limbic, probably because of PTZ limbic structure overstimulation; (3) L-NAME decreases the incidence of CTC and prolongs FLD, GCC, and CTC times to onset, indicating that NO acts as a proconvulsant; and (3) increased GCC, CTC, and mortality that suggests an anticonvulsant effect of NO needs further investigation.

Non-linearity in combined effects of ELF magnetic field and amphetamine on motor activity in rats.

The effects of short-term (15 min) pre-exposure of rats to extremely low-frequency magnetic field (ELF-MF, 50 Hz, 6 mT) on their motor (locomotor and stereotypic) activity induced by d-amphetamine sulphate (AMPH) at different doses (0.5, 1.5 and 4.5mg/kg, i.p.) were studied in the open field test. In saline-treated rats both parameters of motor activity were unaffected by ELF-MF irradiation. The rats pre-exposed to ELF-MF and injected with the lowest dose of AMPH showed the same locomotor activity as control animals, while their stereotypic behaviour was significantly elevated. ELF-MF in combination with AMPH at higher doses significantly enhanced motor activity when compared with values obtained in both control and combined experiments with the lowest dose of the drug. However, only combined locomotor effect at the middle dose of AMPH was significantly greater than those observed in corresponding experiments with AMPH alone. These results demonstrate that acute short-term exposure to ELF-MF is able to modify a motor activity in dependence on the extent of AMPH-induced neurotransmitter imbalance.

Cytochrome c oxidase activity and nitric oxide synthase in the rat brain following aluminium intracerebral application.

In the present study we investigated the cytochrome C oxidase (CO) activity and nitric oxide synthase (NOS) isoenzyme expression after intrahippocampal AlCl3 application in selective vulnerable brain structures. A single dose of AlCl3 was applied in the CA1 sector of rats hippocampus. For biochemical analysis, the animals were killed 10 min and three days after the treatment and forebrain cortex, basal forebrain and hippocampus were removed. Activity of CO was decreased bilaterally in the AlCl3-treated groups in all examined brain structures. We also applied immunohistochemical techniques to identify changes induced by AlCl3 injection after survival periods of 10 min and three days. Both the nNOS and eNOS stains were detected in the hippocampus of controls and AlCl3-treated animals, but iNOS labelling was present in the hippocampus only three days after AlCl3 application. An increased iNOS expression three days post AlCl3 administration could be involved in the mechanism of CO activity depletion.

Influence of NG-nitro-L-arginine methyl ester on clinical and biochemical effects of methylene blue in pentylenetetrazole-evoked convulsions.

BACKGROUND/AIM: Despite years of research in a number of experimental models the question whether nitric oxide (NO) and methylene blue (MB) have pro- or anticonvulsant effects remains to be fully resolved. Methods. In adult Wistar rats the influence of a nonselective inhibitor of nitric oxide synthase NG-nitro-L-arginine methyl ester (L-NAME, 10 microg) on clinical and biochemical effects of MB (10 microg) given before the intraperitoneally administered chemical convulsant pentylenetetrazole (PTZ, 80 mg/kg) was examined. MB and L-NAME were applied intracerebroventricularly. PTZ application was followed by a 4-minute observation time, after which rats were sacrificed and elements of oxido-reductive balance were measured in a crude mitochondrial fraction of forebrain cortex, hippocampus and striatum. RESULTS: Convulsive responses (forelimb dystonia--FLD, generalised clonic- and clonic-tonic convulsions--GCC and GCTC respectively) were observed in all rats received PTZ, together with significantly decreased lipid peroxidation in the forebrain cortex and striatum and increased superoxide dismutase activity in the hippocampus, in comparison to controls (saline treated). It was registered anticonvulsant effects of L-NAME pretreatment. However, these effects were insignificant. In the hippocampus of these animals there was decreased lipid peroxidation (p < 0.01, p < 0.05 vs saline-treated and PTZ-treated rats, respectively) and reverted PTZ-induced increase of superoxide dismutase activity. But MB individually pretreatment significantly decreased the incidence of CTCs and GCCs (FLD: p = 0.0513), prolonged the convulsive latent time for FLD, GCTCs and GCCs, in all the examined brain regions increased lipid peroxidation and decreased the level of superoxide anion. Administration of L-NAME 10 minutes before MB reverted all MB-evoked clinical and biochemical effects. CONCLUSION: Methylene blue applied individually before PTZ has strong anticonvulsant effects that were eliminated by L-NAME pretreatment. These effects and changed biochemical parameters in the brains of animals treated by L-NAME before MB in comparison to MB-treated group suggest involvement of NO in MB's effects in the animal model of PTZ-evoked convulsions.

N-nitro-L-arginine methyl ester influence on aluminium toxicity in the brain.

We investigated the influence of a non-specific nitric oxide synthase (NOS) inhibitor, N-nitro-L-arginine methyl ester (L-NAME), on brain nitrite concentration and acetylcholine esterase activity in AlCl3-treated Wistar rats. Animals were killed 10 min, three hours, three days and 30 days after the treatment and hippocampus and basal forebrain were removed. The biochemical changes observed in neuronal tissues show the involvement of NO in the AlCl3 toxicity and cholinergic neurotransmission, and that L-NAME may have potential neuroprotective effects. Active avoidance learning was significantly impaired after AlCl3 application, while pretreatment with L-NAME prevented the behavioural deficits caused by AlCl3. We also applied immunohistochemical techniques to identify changes induced by AlCl3, L-NAME+AlCl3, as well as L-NAME injections after survival periods of three days and 30 days. Immunoreactivity of astrocytes and phagocytic microglia based on glial fibrillary acidic protein (GFAP) and a useful marker for rat macrophages (ED1), respectively, revealed a greater inflammatory response in AlCl3-injected animals compared to controls.

Nitric oxide synthase inhibitors protect cholinergic neurons against AlCl3 excitotoxicity in the rat brain.

The present experiment was carried out to determine the effectiveness of nitric oxide synthase inhibitors: 7-nitroindazole and aminoguanidine in modulating the toxicity of aluminium chloride on acetylcholine esterase activity, as well as behavioural and morphological changes of Wistar rats. For biochemical analysis the animals were killed 10 min, 3 h, 3 days and 30 days after the treatment and forebrain cortex, striatum, basal forebrain and hippocampus were removed. The biochemical changes observed in neuronal tissues show that nitric oxide synthase inhibitors exert as protective action in aluminium chloride-treated animals. In the present study, active avoidance learning was significantly impaired after aluminium chloride injection, while pretreatment with nitric oxide synthase inhibitors prevented the behavioural deficits caused between 26th and 30th day after intrahippocampal application of neurotoxin. Our data suggest that aluminium may cause learning and memory deficits, while the treatment with specific nitric oxide synthase inhibitors may prevent learning and memory deficits caused by aluminium chloride. We have also applied immunohistochemical techniques to identify neuronal- and inducible-nitric oxide synthase expression 30 days after aluminium chloride and nitric oxide synthase inhibitors injections. Our data suggest that 7-nitroindazole and aminoguanidine can be effective in the protection of toxicity induced by aluminium chloride.