Anxiety-related behavior in hyperhomocysteinemia induced by methionine nutritional overload in rats: role of the brain oxidative stress

The aim of this study was to examine the effects of a methionine-enriched diet on anxiety-related behavior in rats and to determine the role of the brain oxidative status in these alterations. Adult male Wistar rats were fed from the 30th to 60th postnatal day with standard or methionine-enriched diet (double content comparing with standard diet: 7.7 g/kg). Rats were tested in open field and light-dark tests and afterwards oxidative status in the different brain regions were determined. Hyperhomocysteinemia induced by methionine-enriched diet in this study decreased the number of rearings, as well as the time that these animals spent in the center of the open field, but increased index of thigmotaxy. Oxidative status was selectively altered in the examined regions. Lipid peroxidation was significantly increased in the cortex and nc. caudatus of rats developing hyperhomocysteinemia, but unaltered in the hippocampus and thalamus. Based on the results of this research, it could be concluded that hyperhomocysteinemia induced by methionine nutritional overload increased anxiety-related behavior in rats. These proanxiogenic effects could be, at least in part, a consequence of oxidative stress in the rat brain.

Homocysteine thiolactone-induced seizures in adult rats are aggravated by inhibition of inducible nitric oxide synthase

Homocysteine and its metabolites (homocysteine thiolactone (HT)) induce seizures via different but still not well-known mechanisms. The role of nitric oxide (NO) in epileptogenesis is highly contradictory and depends on, among other factors, the source of NO production. The aim of the present study was to examine the effects of aminoguanidine, selective inhibitor of inducible NO synthase (iNOS), on HT-induced seizures. Aminoguanidine (50, 75, and 100 mg/kg, intraperitoneally (i.p.)) was injected to rats 30 min prior to inducing HT (5.5 mmol/kg, i.p.). Seizure behavior was assessed by seizure incidence, latency time to first seizure onset, number of seizure episodes, and their severity during observational period of 90 min. Number and duration of spike and wave discharges (SWDs) were determined in electroencephalogram (EEG). Seizure latency time was significantly shortened, while seizure incidence, number, and duration of HT-induced SWD in EEG significantly increased in rats receiving aminoguanidine 100 mg/kg before subconvulsive dose of HT. Aminoguanidine in a dose-dependent manner also significantly increased the number of seizure episodes induced by HT and their severity. It could be concluded that iNOS inhibitor (aminoguanidine) markedly aggravates behavioral and EEG manifestations of HT-induced seizures in rats, showing functional involvement of iNOS in homocysteine convulsive mechanisms.

Paradoxical sleep deprivation potentiates epilepsy induced by homocysteine thiolactone in adult rats

There is an intriguing and still poorly understood relationship between sleep deprivation and epilepsy. It has recently been shown that paradoxical sleep deprivation decreases levels of homocysteine, an amino acid involved together with its thiolactone metabolite in epileptogenesis. The aim of the present study was to investigate the effects of paradoxical sleep deprivation on homocysteine thiolactone (H)-induced seizures in rats, a model of generalized seizures. Selective deprivation of paradoxical sleep in adult male Wistar rats was achieved by the platform method. Animals with implanted electrodes for electroencephalogram (EEG) registration were assigned to appropriate experimental conditions (dry cage for control, large platform for stress control and small platform for paradoxical sleep deprivation) and 72 h later were intraperitoneally treated with either H (5.5 mmol/kg) or saline (0.9% NaCl). This study showed that paradoxical sleep deprivation increased the incidence and number of H-induced seizure episodes, shortened latency time to seizures and led to significant rates of lethality after H administration, but without effect on the seizure severity. Paradoxical sleep deprivation increased the number and duration of spikes-and-wave discharges, while decreased latency to its appearance in EEG. Judging by the behavioral and EEG findings, it could be concluded that paradoxical sleep deprivation can provoke the expression of factors that can potentiate H-induced seizures in adult rats.

[Sleep and metabolic disorders]

In the 20th century, the prevalence of obesity has been increasing worldwide at an alarming rate and it is followed by an increase in the diseases for which obesity is major risk factor, like metabolic syndrome, diabetes type 2 and hypertension. These facts has been resulting in explosion of investigation devoted to explanation of pathogenetic mechanisms of this serious social and medical problems with the main idea to find adequate way of prevention as well as of treatment. Together with the observed epidemy of obesity and Type 2 diabetes, it was found parallel tendency for sleep curtailment, that was confirmed in numerous epidemiological studies, that coincide with its beginning and progress with this two epidemies. This facts lead to investigations with the idea to try to explaine possible mechanisms of the association between sleep curtailment, obesity, type 2 diabetes, metabolic syndrome and polycistic ovary syndrome. Having in mind that insulin resistance is one of the fundamental pathogenetic mechanism in these disorders, numerous studies were done with the aim to explain association between sleep curtailment and insulin resistance in obesity, Type 2 diabetes, metabolic syndrome and polycistic ovary syndrome. It was demonstrated that sleep curtailment may affect energy homeostasis of human organism with the effects on body weight increase through three different ways: appetite increase, prolongation of time for food intake and through decrease of energy expenditure. There are several postulated mechanism for the effect of sleep curtailment on development of insulin resistance as well as for predisposition for Type 2 diabetes. Among possible mechanism are included: increase of sympathetic neuronal acitvity, decreased cerebral utilisation of glucose, increase in evening cortisol values, growth hormone increase and disorder of neuroendocrine control of appetite which increases the risk for getting the body weight. Metabolic systems are of particular interest in the discussion of possible mechanisms to account for elevated inflammatory mediators during sleep deprivation, particularly because of the contributory role of insulin resistance in the development of impaired vascular function and increased inflammation.