Ankica Jelenković

Effects of extremely low-frequency magnetic field in the brain of rats.

An extremely low-frequency magnetic field (50 Hz, 0.5 mT) was used to investigate its possible effect on the brain of adult male Wistar rats following a 7-day exposure. The control rats were sham-exposed. Superoxide dismutase activities and production of superoxide radicals, lipid peroxidation, and nitric oxide were examined in the frontal cortex, striatum, basal forebrain, hippocampus, brainstem, and cerebellum. Significantly increased superoxide radical contents were registered in all the structures examined. Production of nitric oxide, which can oppose superoxide radical activities, was significantly increased in some structures: the frontal cortex, basal forebrain, hippocampus, and brainstem. Augmentation of lipid peroxydation was also observed, with significance only in the basal forebrain and frontal cortex, in spite of the significantly increased superoxide dismutase activities and nitric oxide production in the basal forebrain, and increased production of nitric oxide in the frontal cortex. The results obtained indicate that a 7-day exposure to extremely low-frequency magnetic field can be harmful to the brain, especially to the basal forebrain and frontal cortex due to development of lipid peroxidation. Also, high production of superoxide anion in all regions may compromise nitric oxide signaling processes, due to nitric oxide consumption in the reaction with the superoxide radical.

Nitric oxide (NO) and convulsions induced by pentylenetetrazol.

Abstract: 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.

Beneficial Effects of Ceftriaxone Against Pentylenetetrazole-Evoked Convulsions

Although considered to be generally safe, a number of β-lactam antibiotics have been associated with epileptic seizures in humans. Furthermore, some β-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 β-lactam antibiotic, which are not uniform across the mouse population. Our results provide new insight into the effects of ceftriaxone, which need further investigation.

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 Alzheimers 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 Alzheimers disease. Copyright

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.

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.

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 (AlCl3) 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. AlCl3 injection resulted in increased nitrite concentrations, superoxide anion production, malondialdehyde concentrations and reduced glutathione contents in the forebrain cortex, suggesting that AlCl3 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 non-specific nitric oxide synthase (NOS) inhibitor, L-NAME, exerted anti-oxidant actions in AlCl3-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.

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

Abstract: 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.

The Effect of Extremely Low-Frequency Magnetic Field on Motor Activity of Rats in the Open Field

Abstract: 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.

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.