V. Šušić

The activity of erythrocyte and brain Na+/K+ and Mg2+-ATPases in rats subjected to acute homocysteine and homocysteine thiolactone administration

Hyperhomocysteinemia is associated with various pathologies including cardiovascular disease, stroke, and cognitive dysfunctions. Systemic administration of homocysteine can trigger seizures in animals, and patients with homocystinuria suffer from epileptic seizures. Available data suggest that homocysteine can be harmful to human cells because of its metabolic conversion to homocysteine thiolactone, a reactive thioester. A number of reports have demonstrated a reduction of Na+/K+-ATPase activity in cerebral ischemia, epilepsy and neurodegeneration possibly associated with excitotoxic mechanisms. The aim of this study was to examine the in vivo effects of d,l-homocysteine and d,l-homocysteine thiolactone on Na+/K+- and Mg2+-ATPase activities in erythrocyte (RBC), brain cortex, hippocampus, and brain stem of adult male rats. Our results demonstrate a moderate inhibition of rat hippocampal Na+/K+-ATPase activity by d,l-homocysteine, which however expressed no effect on the activity of this enzyme in the cortex and brain stem. In contrast,d,l-homocysteine thiolactone strongly inhibited Na+/K+-ATPase activity in cortex, hippocampus and brain stem of rats. RBC Na+/K+-ATPase and Mg2+-ATPase activities were not affected by d,l-homocysteine, while d,l-homocysteine thiolactone inhibited only Na+/K+-ATPase activity. This study results show that homocysteine thiolactone significantly inhibits Na+/K+-ATPase activity in the cortex, hippocampus, and brain stem, which may contribute at least in part to the understanding of excitotoxic and convulsive properties of this substance.

The role of nitric oxide in convulsions induced by lindane in rats.

Lindane is an organochloride pesticide and scabicide. It evokes convulsions mainly trough the blockage of GABA(A) receptors. Nitric oxide (NO), gaseous neurotransmitter, has contradictor role in epileptogenesis due to opposite effects of L-arginine, precursor of NO syntheses (NOS), and L-NAME (NOS inhibitor) observed in different epilepsy models. The aim of the current study was to determine the effects of NO on the behavioral and EEG characteristics of lindane-induced epilepsy in male Wistar albino rats. The administration of L-arginine (600, 800 and 1000 mg/kg, i.p.) in dose-dependent manner significantly increased convulsion incidence and severity and shortened latency time to first convulsion elicited by lower lindane dose (4 mg/kg, i.p.). On the contrary, pretreatment with L-NAME (500, 700 and 900 mg/kg, i.p.) decreased convulsion incidence and severity and prolonged latency time to convulsion following injection with a convulsive dose of lindane (8 mg/kg, i.p.). EEG analyses showed increase of number and duration of ictal periods in EEG of rats receiving l-arginine prior to lindane and decrease of this number in rats pretreated with L-NAME. These results support the conclusion that NO plays a role of endogenous convulsant in rat model of lindane seizures.

Exercise Decreases Susceptibility to Homocysteine Seizures: the Role of Oxidative Stress

The aim of the study was to examine the effects of chronic exercise training on seizures induced by homocysteine thiolactone (HCT) in adult rats. Rats were assigned to: sedentary control; exercise control; sedentary+HCT; exercise+HCT group. Animals in the exercise groups ran 30 min daily on a treadmill for 30 consecutive days (belt speed 20 m/min), while sedentary rats spent the same time on the treadmill (speed 0 m/min). On the 31st day, the HCT groups received HCT (8.0 mmol/kg), while the control groups received vehicle. Afterwards, convulsive behavior and EEG activity were registered. Lipid peroxidation, superoxide dismutase (SOD) and catalase (CAT) activity were ascertained in the rat hippocampus. No signs of seizures were registered in sedentary and exercise control rats. Seizure latency was increased, while number of seizure episodes and spike-and-wave discharges (SWD) in EEG were decreased in the exercise+HCT compared to the sedentary+HCT group. Seizure incidence, the severity thereof and duration of SWDs were not significantly different between these groups. Exercise partly prevented increase of lipid peroxidation and decrease of the SOD and CAT activity after HCT administration. These results indicate beneficial effects of exercise in model of HCT-induced seizures in rats, what could be, at least in part, a consequence of improved antioxidant enzymes activity.

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.

ANTICONVULSANT, BUT NOT ANTIEPILEPTIC, ACTION OF VALPROATE ON AUDIOGENIC SEIZURES IN METAPHIT–TREATED RATS

1. The blocking effects of valproate (2‐propylpentanoic acid), a standard anti‐epileptic drug, on metaphit (1‐[1‐(3‐isothiocyanatophenyl)‐cyclohexyl]‐piperidine)‐induced audiogenic seizures as a model of generalized, reflex audiogenic epilepsy in adult Wistar male rats were studied. 2 Rats were stimulated using an electric bell (100 ± 3 dB, 5–8 kHz, 60 s) 60 min after i.p. metaphit (10 mg/kg) injection and afterwards at hourly intervals. For power spectra and electroencephalograph (EEG) recordings, three gold‐plated screws were implanted into the skull. Different doses of valproate (50, 75 and 100 mg/kg) were injected i.p. into rats with fully developed metaphit seizures after the eighth audiogenic testing. 3 In metaphit‐treated animals, the EEG appeared as polyspikes, spike–wave complexes and sleep‐like patterns, whereas the power spectra were increased compared with the corresponding controls. 4 Valproate reduced the incidence and intensity of convulsions and prolonged the duration of the latency period in a dose‐dependent manner 4 h after administration. 5 The ED50 of valproate in the first hour after injection was 63.19 mg/kg (95% confidence interval 51.37–77.71 mg/kg). 6 None of the doses of valproate applied eliminated the EEG signs of metaphit‐provoked epileptiform activity. 7 Taken together, these results suggest that all doses of valproate examined acted to suppresse behavioural but not epileptic EEG spiking activity in metaphit‐induced seizures.

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.

Sleep disruption increases seizure susceptibility: Behavioral and EEG evaluation of an experimental model of sleep apnea.

Sleep disruption accompanies sleep apnea as one of its major symptoms. Obstructive sleep apnea is particularly common in patients with refractory epilepsy, but causing factors underlying this are far from being resolved. Therefore, translational studies regarding this issue are important. Our aim was to investigate the effects of sleep disruption on seizure susceptibility of rats using experimental model of lindane-induced refractory seizures. Sleep disruption in male Wistar rats with implanted EEG electrodes was achieved by treadmill method (belt speed set on 0.02 m/s for working and 0.00 m/s for stop mode, respectively). Animals were assigned to experimental conditions lasting 6h: 1) sleep disruption (sleep interrupted, SI; 30s working and 90 s stop mode every 2 min; 180 cycles in total); 2) activity control (AC, 10 min working and 30 min stop mode, 9 cycles in total); 3) treadmill chamber control (TC, only stop mode). Afterwards, the animals were intraperitoneally treated with lindane (L, 4 mg/kg, SI+L, AC+L and TC+L groups) or dimethylsulfoxide (DMSO, SIc, ACc and TCc groups). Convulsive behavior was assessed by seizure incidence, latency time to first seizure, and its severity during 30 min after drug administration. Number and duration of ictal periods were determined in recorded EEGs. Incidence and severity of lindane-induced seizures were significantly increased, latency time significantly decreased in animals undergoing sleep disruption (SI+L group) compared with the animals from TC+L. Seizure latency was also significantly decreased in SI+L compared to AC+L groups. Number of ictal periods were increased and duration of it presented tendency to increase in SI+L comparing to AC+L. No convulsive signs were observed in TCc, ACc and SIc groups, as well as no ictal periods in EEG. These results indicate sleep disruption facilitates induction of epileptic activity in rodent model of lindane-epilepsy enabling translational research of this phenomenon.

Sulfur – Containing Amino Acids in Seizures: Current State of the Art

BACKGROUND Homocysteine and taurine are non-proteinogenic sulfur-containing amino acids with numerous important physiological roles. Homocysteine and taurine are considered to be neurotransmitters and neuromodulators, the first showing clear hyperexcitability role, while the second is known by its inhibitory and neuroprotective properties. OBJECTIVE In this article we addressed the role of homocysteine and its related metabolite homocysteine thiolactone in the development of seizures, focusing on its experimental models in vivo, potential mechanisms of proepileptogenic activity via interactions with glutamatergic neurotransmission, sodium pump activity, oxidative stress, cholinergic system and NO-mediated neuronal signaling, as well as the pharmacological and non-pharmacological approaches to modulate its proconvulsive activity. Additionally, herein we will focus on taurine neuroprotective effects linked with its anticonvulsive properties and mediated by taurine interactions with GABA-ergic and glutamatergic system and oxidative stress.

13. L-Arginine, endogenous NO donor, potentiates lindane-induced seizures in rats

ine-treated (C, n = 10); (2) D,L homocysteine-thiolactone 8 mM/kg, i.p. (H, n = 7); (3) Valproate i.p. in doses: 50 (V50, n = 8), 100 (V100, n = 8) and 150 mg/kg (V150, n = 8) and (4) Valproate (V50,100,150) 30 min prior to H (V50H, n = 10; V100H, n = 10; and V150H, n = 8). Seizure behaviour was assessed by incidence, latency, number and intensity of seizure episodes. Seizure severity was determined by a descriptive scale with grades 0–4. Results: There were no behavioural signs of seizure activity in groups C, V50, V100 and V150 groups. Seizure incidence was reduced in all VH groups, but not statistically significant. Pre-treatment with valproate increased the latency to the first seizure onset in V100H (p < 0.05) and V150H (p < 0.01) comparing to the H. Valproate decreased median number of seizure episodes dose-dependently but statistical significance was attained only in V150H (p < 0.05) comparing to the H. Severity of seizure episodes was reduced in V150H (p < 0.01) comparing to the H group. Conclusions: Our findings suggest that valproate has a dosedependent anticonvulsive effect on D,L homocysteine-thiolactone induced seizures in adult rats.

10. Lipid peroxidation as a possible mechanism of acute lindane neurotoxicity in rats

range. We used Student t-test for statistical analysis. Results: In ET patients we recordedM-potential amplitude values of NP (6.77 ± 1.31 mV), which were statistically significantly lower than in CG (8.83 ± 1.64 mV). Other electrophysiological parameters values were not statistically different (p > 0.05) in two groups. Conclusions: ET may have some influence on single ENG parameter values, but most of ENG parameters in patients with ET are in normal ranges. Reduction of NP M-potential amplitude value in patients with ET may be associated with change of motor units function during tremor, chronic fatigue of muscles and other factors.