V. B. Narkevich

The influence of anticonvulsant and antioxidant drugs on nitric oxide level and lipid peroxidation in the rat brain during penthylenetetrazole-induced epileptiform model seizures

Nitric oxide (NO) generation in the brain cortex of Wistar rats was measured by direct method of electron paramagnetic resonance (EPR) spectroscopy. Dramatic (fivefold) elevation of NO production was found during penthylenetetrazole (PTZ)-induced epileptiform seizures. The level of secondary products of lipid peroxidation (LPO; thiobarbituric acid reactive substances, TBARS) was also significantly increased in the cerebral cortex of rats with PTZ-evoked seizures. The effects of anticonvulsant drugs phenobarbital, lamotrigine, phenazepam, as well as antioxidant substances alpha-tocopherol and novel original Russian synthetic drug mexidol (2-ethyl-6-methyl-3-oxypiridine succinate), were investigated. All the substances studied significantly decreased seizure manifestations and partially prevented both enhancement of NO generation and increase in TBARS formation. Mexidol and phenobarbital were found to be the most effective in the preventing of PTZ-induced seizures among all the substances studied. The data obtained support our speculation that neuroprotective action of mexidol may correlate with its ability to inhibit not only excessive reactive oxygen species (ROS) formation but also NO generation. While the molecular mechanism underlying action of mexidol and phenobarbital still remains unclear, it is likely that the effect of these drugs on NO production is contributing to their neuroprotective action. It might be concluded that both the suppression of seizure-induced NO generation and LPO enhancement may be involved in the mechanism of action of antiepileptic drugs.

Nitric oxide content measured by ESR-spectroscopy in the rat brain is increased during pentylenetetrazole-induced seizures

Nitric oxide (NO) content in rat cerebral cortex was measured using Electron Spin Resonance (ESR) spectroscopy. A nearly fivefold elevation in NO content was found at the peak time of pentylenetetrazole (PTZ)-induced seizures. The administration of N-nitro-l-arginine (L-NNA), a competitive inhibitor of NO-synthase, at the dose of 250 mg/kg, completely prevented the NO increase induced by PTZ, although clonic convulsions in the animals have been observed. L-NNA (10 mg/kg) was shown to delay the onset of clonic seizures as well as to shorten the latency of the first convulsive twitch. The level of lipid peroxidation secondary products measured as the content of thiobarbituric acid reactive species (TBARS) was increased in the cerebral cortex of PTZ-treated rats. L-NNA (250 mg/kg) failed to prevent the increased TBARS level produced by PTZ. The results support the notion that NO may play a trigger role in the pathophysiology of convulsive seizures.

Strain differences in profiles of dopaminergic neurotransmission in the prefrontal cortex of the BALB/C vs. C57Bl/6 mice: consequences of stress and afobazole.

We found that in mice the basal activity of monoamine oxidase B (MAO-B) in the medial prefrontal cortex (mPFC) is lower in BALB/C than in C57Bl/6J mice, whereas activity of MAO-A is similar between strains. BALB/C mice, in comparison to C57Bl/6N mice, have higher basal content of dopamine in the mPFC, in both microdialysates and tissue content. Novelty stress (open field test) elicits a further increase in the microdialysate levels of dopamine in BALB/C, but not in C57Bl/6N mice; a subsequent accumulation of extracellular 3,4-dioxyphenylacetic acid (DOPAC) reaffirms the difference in catabolic capacity of monoaminergic systems between the strains. We demonstrated that in stress-susceptible BALB/C mice the novel anxiolytic afobazole, 5mg/kg, selectively mitigates trait anxiety; however it does not change the behavioral response in stress-resilient C57Bl/6N mice. Afobazole inhibits MAO-A in in vitro; it also lowers the microdialysate DOPAC levels in both strains (which testifies to its MAO-A inhibiting activity in vivo) and slightly suppresses dopamine release when elevated. Therefore, it is likely that the drug may mediate its anxiolytic activity via modulation of volume dopaminergic transmission at level of the mPFC.

The effects of irradiation by 12C carbon ions on monoamine exchange in several rat brain structures

Rats were irradiated with carbon ions (12C) in a Nuklotron accelerator. The irradiation dose was 1 Gy, the energy of the ions was 500 MeV/nuclon, and the linear energy transmission (LET) was 10.6 keV/micron. The animals were decapitated 1 day after irradiation. We isolated the prefrontal cortex, nucleus accumbens, hypothalamus, hippocampus, and striatum, where we determined the concentrations of monoamines and their metabolites. Strong changes were observed in three structures, viz., the prefrontal cortex, nucleus accumbens, and hippocampus. However, significant changes were found in the prefrontal cortex and weaker changes were seen in the nucleus accumbens, whereas changes were insignificant in the hippocampus. This reaction may be related to the fact that the animals were examined on the 2nd day after irradiation. It was shown that an increase in the interval between irradiation and examination of animals results in enhancement of the effects of radiation treatment. The experiments revealed the high sensitivity and reactivity of the prefrontal cortex, which we relate to the key role of this structure in vitally critical processes of behavior.

Effect of space flight factors simulated in ground-based experiments on the behavior, discriminant learning, and exchange of monoamines in different brain structures of rats

Experimental treatment (long-term fractionated γ-irradiation, antiorthostatic hypodynamia, and the combination of these factors) simulating the effect of space flight in ground-based experiments rapidly restored the motor and orienting-investigative activity of animals (rats) in “open-field” tests. The study of the dynamics of discriminant learning of rats of experimental groups did not show significant differences from the control animals. It was found that the minor effect of these factors on the cognitive performance of animals correlated with slight changes in the concentration of monoamines in the brain structures responsible for the cognitive, emotional, and motivational functions.

The behavior and neurotransmitter contents in brain structures of rats with Alzheimer’s disease modeled by administration of Aβ25–35

We studied behavioral and neurochemical alterations that were induced by modeling of Alzheimer’s disease (AD) using bilateral intracerebroventricular administration of Aβ25–35 at a dose of 7.5 nmol in each ventricle. After 5.5 weeks, cognitive and psychoemotional alterations in the Morris spatial learning and Porsolt’s forced-swim tests were observed in rats with strong symptoms that are typical of AD. Measurement of the contents of monoamines and their metabolites in rat-brain structures was performed using the HPLC with the ECD method 1 day after the end of the tests. In the dorsal striatum, we found a decrease in the contents of metabolites of dopamine (DA), including homovanillic acid (HVA), 3,4-dihydroxyphenylacetic acid (DOPAC), and 3-methyltyramine (3-MT), and a decrease in the indices of DA utilization, including DOPAC/DA and HVA/DA, whereas the DA content was stable in this structure. In the nucleus accumbens (NA, ventral striatum), we found a decreased level of the HVA/DA ratio, which reflects the lower turnover of extracellular DA. We also found a lower turnover of serotonin (5-HT), which was seen as a decrease in the 5-hydroxyindolacetic acid (5-HIAA)/5-HT ratio, whereas the 5-HT content was elevated. In the hypothalamus, we revealed a significant decrease in the DA level and the levels of its metabolites, including 3-MT and HVA, and 5-HT turnover. We found that Aβ25–35 influenced the indices of amino-acidergic neurotransmission, which was reflected by the higher glutamate content in the striatum. Our data show that cerebral neurotransmitter systems, such as the tuberoinfundibular, mesolimbic, and nigrostrial dopaminergic and the striatal serotonergic and glutamatergic systems, are involved in pathophysiological mechanisms of the development of cognitive and psychoemotional impairments that occur in AD, as modeled by administration of Aβ25–35.

Modulating role of NO in haloperidol-induced catalepsy.

Injection of haloperidol during catalepsy modeling decreased the content of NO in rat cerebral cortex. NO precursor L-arginine arrested catalepsy and prevented the decrease in NO content.

The dynamics of monoamine metabolism in rat brain structures in the late period after exposure to accelerated carbon ions

We studied the effect of carbon ions (12C) with an energy of 500 MeV/nucleon at a dose of 1 Gy on monoamine metabolism in the brains of rats of different ages. Neurochemical parameters that characterize the distribution of noradrenaline (NA), dopamine (DA), serotonin (5-HT), and its metabolites were evaluated during 2 months on days 30 and 90 after the exposure to radiation. We studied the prefrontal cortex, hypothalamus, hippocampus, and striatum. The results showed changes in the activities of the NA, DA, and 5-HT systems in rats of different age groups after exposure to radiation. The most prominent differences in the exposed and control animals were observed in the prefrontal cortex and hypothalamus, which indicates the important role of these brain regions in long-term effects of exposure to radiation on the central nervous system. A comparison of animals from different age groups showed a decrease in the intensity of the temporal changes in all analyzed structures except the striatum in the exposed rats. Based on these findings, we assumed that the activation of compensatory and repairing mechanisms occurs in the late post-radiation period. At relatively low linear energy transfer of particles (10.6 keV/µm), it may lead to the partial recovery of brain functions that were impaired by radiation. At higher values of the linear energy transfer, the compensatory and recovery processes are activated to a lesser degree and functional impairment increases with time.

The distribution of monoamines and their metabolites in the brain structures of rats at later periods after exposure to 12C ions

We investigated the levels of monoamines and their metabolites in certain brain structures of rats at 30 and 90 days after exposure to carbon ions (12C) with an energy of 500 MeV/nucleon. The linear energy transfer and radiation dose were 10.6 keV/µm and 1 Gy, respectively. The concentrations of substances were measured in five structures of the brain, including the prefrontal cortex, nucleus accumbens, hypothalamus, hippocampus, and striatum. On day 30 after the exposure, the most pronounced changes in the concentration of monoamines and their metabolites were observed in the nucleus accumbens; the smallest changes were found in the hippocampus and striatum. After 90 days, significant changes were still present in the nucleus accumbens. At the same time, these changes became less evident in other structures. A comparison of our results with the data of similar previous experiments (24 hours after exposure) showed that the most pronounced effect was observed soon after radiation exposure. The induced damage diminished at a later period. Based on the results of our study, we made the hypothesis that the change in the metabolism of monoamines may be compensated if the linear-energy transfer values were relatively low (10.6 keV/μm). At higher values of linear-energy transfer, compensatory and regenerative processes did not occur; the effect increased with time. An increased susceptibility of the nucleus accumbens was found at all the time points after the exposure, which may indicate an important role of this brain structure in the radiation-induced impairment of cognitive functions and emotional and motivational states.

The relationship between the anxiolytic action of selank and the level of serotonin in brain structures during the modeling of alcohol abstinence in rats

We studied the in vivo effects of the peptide anxiolytic selank (0.3 mg/kg) on the behavioral parameters of the syndrome of alcohol withdrawal and the neurochemical indices of the serotonergic system in the brain structures in ex vivo experiments in outbred rats with a preference for a 10% solution of ethanol. We found that a single administration of selank eliminates the anxious response in the elevated plus maze at 48 h after the withdrawal of ethanol and increases the time spent in the open arms and the number of entries into the open arms. Using HPLC, we showed that selank prevents an increase in the serotonin level in the frontal cortex, hypothalamus, and amygdala, which may be related to a decrease in the synthesis of serotonin. The data we obtained indicate that selank has anxiolytic activity under conditions of alcohol abstinence, which suggests that the sphere of its use in clinical practice may be widened.