on these levels were investigated. Mice were pre-treated with (PhSe)

In this work was investigated the effect of pre-treatment with (PhSe)(2) and (PhTe)(2) on chemical seizure and 4-aminopyridine-induced lethality in mice. Additionally, lipid peroxidation levels of whole brain after treatment with 4-aminopyridine and effect of pre-treatment with (PhSe)(2) and (PhTe)(2) on these levels were investigated. Mice were pre-treated with (PhSe)(2) or (PhTe)(2) (50, 100, or 150 micromol/kg) 30 min before 4-aminopyridine (12 mg/kg) administration. The treatment with 4-aminopyridine caused a significant incidence of seizures (clonic, tonic) and death. Pre-treatment with (PhSe)(2) and (PhTe)(2) significantly increased the latency for clonic and tonic seizures, and prevented 4-aminopyridine-induced death. Significantly, the pre-treatment with (PhSe)(2) or (PhTe)(2) increased the latency for clonic seizures in a dose-dependent manner. Additionally, a significant increase was observed in the brain lipid peroxidation level after treatment with 4-aminopyridine, which was significantly inhibited by pre-treatment with 150 micromol/kg (PhSe)(2) or (PhTe)(2). These results demonstrate that (PhSe)(2) and (PhTe)(2) counteract the harmful effects of 4-aminopyridine. It is possible that this effect results from modulation of the redox state of N-methyl-d-aspartate receptors and/or of Ca(2+) channel activity with subsequent alteration in neurotransmitter release. Importantly, this study provides evidence for anticonvulsant and antioxidant properties of (PhSe)(2) and (PhTe)(2), which indicates a neuroprotective activity of these compounds.


INTRODUCTION
Epilepsy is a collection of diverse disorders that together affect approximately 1-2% of the world population (Hauser & Hesdorffer, 1990;Mcnamara, 1999).Although epilepsy can manifest itself in a number of different ways, each type shares the common feature of increased neuronal excitability, culminating in seizures (Lothman et al., 1991;Mcnamara, 1994;1999).Typically, a seizure episode refers to a transient behaviour change due to abnormal, disordered, and at high-frequency firing of neuron populations in the central nervous system (CNS) (Lothman et al., 1991).
It is well established that excitatory and inhibitory neurotransmission in the CNS is mediated mainly by glutamate and GABA, respectively.Any dysfunction of these neurotransmitter systems, through a decrease in GABAergic and/or an increase in glutamatergic neurotransmission, can be involved in seizure development (Bradford, 1995;Meldrum, 1995).In addition, the amplification of neuronal unbalance that leads to the convulsive episodes, as well its subsidence, involves an interaction of GABAergic 2009 V. B. Brito and others inhibitory and glutamatergic excitatory mechanisms (Meldrum, 1995).
Evidence suggests that oxidative stress, due to an increase in reactive oxygen species (ROS) production, is an important factor involved in seizureinduced neuronal damage (Liang et al., 2007;Santos et al., 2008;Xin et al., 2008).This involvement is supported partially by observations that the oxidation of cellular macromolecules is increased by excitotoxins which produce seizures (Liang et al., 2000;Kaneko et al., 2002).Moreover, overactivation of excitatory amino-acid receptors can trigger the ROS formation, resulting in excitotoxic process (Arriba et al., 2006;Mueller-Burke et al., 2008) and in neuronal damage (Montiel et al., 2005).Importantly, it has been demonstrated that the cell death resultant from excitotoxic processes can be prevented by antioxidants (Cho & Lee, 2004;Liang et al., 2007;Santos et al., 2008).In fact, brain tissue is a vulnerable target of oxidative processes due to its composition and metabolic conditions, such as high oxygen consumption, high blood flow, and high concentration of neurotransmitters and polyunsaturated fatty acids (Clemens & Penetta, 1995) which can be oxidized.
In the last decades, a variety of organic forms of selenium and tellurium have been investigated due to their interesting biological properties.Notably, the redox properties of the selenium and tellurium atoms confer considerable antioxidant activity, suitable as a tool in free-radical biology and medicine (Andersson et al., 1993;Commandeur et al., 2001;Nogueira et al., 2004).In fact, these organochalcogens have been pointed out as possible antioxidant agents because they exhibit glutathione peroxidase-like activity and thus can decompose H 2 O 2 or a variety of lipid hydroperoxides to H 2 O or appropriate alcohols using GSH or synthetic reduced thiols as electron donors (Klotz & Sies, 2003;Klotz et al., 2003;Nogueira et al., 2004).In addition, the organochalcogens retard the lipid peroxidation induced by a variety of oxidants (Engman et al., 1992;1995;Rossato et al., 2002a).
In brief, the purpose of this study was to investigate the effects of pre-treatment with (PhSe) 2 or (PhTe) 2 compounds on 4-AP-induced chemical seizure and lethality in mice.Additionally, brain lipid peroxidation levels after treatment with 4-AP, as well as the effect of pre-treatment with (PhSe) 2 and (PhTe) 2 on these levels, were investigated.Importantly, this study can be of great value as it suggests novel neuroprotective compounds against convulsant drugs and side effects of clinically used drugs, such as 4-AP.

MATERIALS AND METHODS
Chemicals.4-Aminopyridine (4-AP), sodium dodecyl sulfate (SDS), thiobarbituric acid (TBA), and malondialdehyde (MDA) were obtained from Sigma (St. Louis, MO, USA).Tris(hydroxymethyl)aminomethane and sodium chloride were obtained from Merck (Rio de Janeiro, Brazil).All other chemicals were of analytical grade and were obtained from standard commercial suppliers.Effect of (PhSe) 2 and (PhTe) 2 on 4-aminopyridine-induced seizure and lethality in mice Diphenyl diselenide (PhSe) 2 and diphenyl ditelluride (PhTe) 2 were prepared in our laboratory according to literature methods (Paulmier, 1986;Petragnani, 1994).Analysis of 1 H NMR and 13 C NMR spectra showed that obtained (PhSe) 2 and (PhTe) 2 presented analytical and spectroscopic data in full agreement with their assigned structures.The chemical purity of compounds (99.9%) was determined by GC/HPLC.These compounds were dissolved in DMSO (dimethyl sulfoxide at concentration of 10%).
Animals.Male mice (Mus musculus, about 3 month-old, 30-35 g body mass) from our own breeding colony (Animal House-holding, Federal University of Santa Maria -UFSM, Brazil) were maintained in separate animal's rooms, at 12 h light/dark cycle (07:00-19:00 h lights on) and at a room temp. of 22 ± 2°C.All animals were fed with a conventional ration (Labina ® , Purina, Canoas, Brazil), and had free access to food and water.The animals were used according to the guidelines of the Committee on Care and Use of Experimental Animal Resources of the Federal University of Santa Maria (Brazil).
In vivo experiments 4-AP-induced seizures.The animals were pretreated with a single injection of (PhSe) 2 or (PhTe) 2 (50, 100, or 150 µmol/kg, 2.5 ml per kg of body mass, subcutaneously (s.c.), dissolved in DMSO) or DMSO alone (vehicle).At 30 min after administration of organochalcogens, animals were treated with a single injection of 4-AP (12 mg/kg, 2.5 ml per kg of body mass, intraperitoneally (i.p.), dissolved in water), or water only (vehicle) and were divided as follows In short, mice were placed in individual Plexiglas chambers (20 × 20 × 19 cm), pre-treated with (PhSe) 2 or (PhTe) 2 or vehicle and their behaviour was observed for 30 min for the appearance of seizures (clonic, tonic) or death.Thereafter the animals were treated with 4-AP and the behaviour was observed for additional 60 min for the appearance of seizures (clonic, tonic) or death.Appearance of seizures was quantified as previously described by Maggio et al. (1995), as follows, except that recorded seizures lasted at least 5 s: 0.5 = facial myoclonus and forepaw myoclonus; 1 = clonic seizures, lasting at least 15 s with forelimb clonus, rearing and occasionally falling; 2 = explosive clonic seizures with wild running; 3 = tonic forelimb extension; 4 = tonic hindlimb extension.The observed clonic seizures were characterized for the appearance of facial myoclonus, forepaw myoclonus and forelimb clonus lasting at least 5 s.Conversely, tonic seizures were characterized as explosive clonic seizures with wild running and tonic forelimb and hindlimb extension lasting also at least 5 s.Moreover, the latency for the onset of the convulsive episode (clonic or tonic) and the latency for death were recorded as indicators of pro-or anticonvulsive effect of compounds.
The doses of (PhSe) 2 and (PhTe) 2 were selected in accordance with previous work which showed typical animal behaviour with the administration of such doses (Meotti et al., 2003;Nogueira et al., 2003a).In addition, the convulsive dose of 4-AP was selected in accordance with Wong et al. (2002).
Ex vivo experiments.At the end of the observation period, animals of groups 1, 7, and 8 were sacrificed under mild ether anesthesia.All animals of group 2 died within 60 min after administration of 4-AP.Hence, brains of these animals were immediately removed without ether anesthesia and TBARS assay started immediately.Whole brains were quickly removed, placed on ice, and homogenized in ten volumes of cold 50 mM Tris/HCl (pH 7.5).The homogenate was immediately centrifuged at 4000 × g and 4°C for 10 min to yield a low-speed supernatant fraction that was used for Thiobarbituric Acid Reactive Species (TBARS) assay.For the analysis of lipid peroxidation levels only animals pre-treated with 150 μmol/kg (PhSe) 2 and (PhTe) 2 were selected, as this dose increased latency for seizures and death more than others.
Lipid peroxidation.TBARS levels were determined according to Ohkawa et al. (1979) with some modifications according to Rossato et al. (2002b).In short, reaction mixture contained 100 µL 8.1% SDS, 500 µL 1.267 M acetic acid/270 mM HCl (pH 3.5), and 500 µL 0.8% thiobarbituric acid (TBA).TBARS levels were quantified by addition of 200 µL of lowspeed supernatant fraction directly to the above reaction medium.Samples were incubated at 90°C for 60 min and then centrifuged at 1000 × g for 15 min.The amount of TBARS produced in the supernatant was measured at 532 nm, using MDA for standard curve.
Statistical analysis.Data for latency of onset of the first convulsive episode, clonic or tonic, between groups were analyzed by Kruskal-Wallis analysis of variance followed by the two-tailed Mann-Whitney U-test.The incidence of seizure and death was analyzed by Fischer's exact test.TBARS values between groups were analyzed by one-way analysis of variance (ANOVA, SPSS for Windows 8.0, SPSS 1998, Chicago, IL, USA) followed by Duncan's Multiple Range Test.Pearson's correlation coefficients were determined by linear regression analysis.Results are expressed as means ± S.E.M., and differences were considered significant when P < 0.05.

RESULTS
Table 1 shows that a single administration of 4-AP (12 mg/kg) caused clonic and tonic seizures in all mice, and all died after administration of this drug.In contrast, pre-treatment of animals with (PhSe) 2 at doses of 50, 100, or 150 µmol/kg caused a significant latency of clonic seizures and completely prevented the incidence of tonic seizures as well as death.In addition, pre-treatment of mice with (PhSe) 2 caused an increase in latency for clonic seizures in a dose-dependent manner (r = 0.880, P < 0.001).Importantly, when the animals were injected with (PhSe) 2 only, in all doses tested, seizures were not observed and the survival was 100%.Also, the pre-treatment with (PhSe) 2 , at all doses tested, reduced the number of animals that presented seizures (clonic and tonic) in relation to animals treated with 4-AP only.
Table 2 shows that pre-treatment with (PhTe) 2 , in all doses tested, significantly increased latency for seizures (clonic and tonic) and completely abolished death.In addition, 150 µmol/kg (PhTe) 2 completely prevented the appearance of clonic and tonic seizures.As with the (PhSe) 2 , pretreatment of animals with (PhTe) 2 caused an increase in latency for clonic seizures in a dose-dependent manner (r = 0.764, P < 0.001).When animals were injected with (PhTe) 2 only, in all doses tested, seizures were not observed and survival was 100%.Pre-treatment with (PhTe) 2 , at all doses tested, reduced the number of animals that presented sei-zures (clonic and tonic) in relation to animals treated with 4-AP only.
The involvement of oxidative stress in this model of 4-AP-induced seizure was investigated.For this purpose, brain lipid peroxidation levels of groups 1, 2, 7, and 8 were investigated.Figure 2 shows that the administration of 4-AP caused a significant increase, by approx.4.15 times, in TBARS level in relation to control group (from 37.55 ± 3.4 to 135.88 ± 8.23 nmol MDA/g tissue).This effect was significantly inhibited by pre-treatment with 150 µmol/kg of (PhSe) 2 or (PhTe) 2 , with a decrease of approx.2.08 and 2.05 times, respectively, in relation to animals treated with 4-AP only (from 135.88 ± 8.23 to 65.25 ± 12.57 nmol MDA/g tissue and to 66.29 ± 7.99 nmol MDA/g tissue, respectively).

DISCUSSION
Our data demonstrated that administration of (PhSe) 2 or (PhTe) 2 previously to the treatment of mice with 4-AP significantly increased the latency for seizures and prevented death.The animals pretreated with (PhSe) 2 or (PhTe) 2 showed an increase in the latency for clonic seizures in a dose-dependent manner.In addition, pre-treatment of mice with 150 µmol/kg (PhSe) 2 or (PhTe) 2 significantly inhibited the increase in 4-AP-induced TBARS levels.Importantly, this study demonstrated, for the first time, an antioxidant effect of (PhSe) 2 and (PhTe) 2 against 4-AP-induced oxidative damage in murine brain, in addition to a marked anticonvulsant effect.
The 4-AP action occurs through a K + -channel blockade at the presynaptic neuron level, mediated by its entry into the channel pore in the open, closed, or intermediate state (Thesleff, 1980;Rogawski & Barker, 1983).Thereby, efflux of intracellular K + is suppressed and calcium influx is enhanced, leading to an increase in neurotransmitter release and, therefore, to an increase in nervous signal (Molgó et al., 1985).Particularly, this is also the characteristic responsible for the therapeutic properties of 4-AP.In fact, in the last decades, 4-AP has been indicated for the treatment of diverse neuromuscular disorders, including myasthenia gravis, Lambert-Eaton syndrome, and botulism (Lundh et al., 1979;Sellin, 1981;McEvoy et al., 1989).More recently, clinical trials have demonstrated an efficient role of 4-AP in enhancement of the signal conduction after spinal cord trauma (Hayes et al., 1994;Halter et al., 2000;Jensen & Shi, 2003;McBride et al., 2006), as well as in demyelinizing diseases and multiple sclerosis (Davis et al., 1990).Nevertheless, the clinical use of 4-AP is still limited by its narrow therapeutic range and by the risk of seizures and toxicity to the CNS.
Indeed, 4-AP is used experimentally for induction of seizures in several species (Schafer et al., 1973;Fragoso-Veloz et al., 1990;Spyker et al., 1980;Yamaguchi & Rogawski, 1992).Our results are in close agreement with literature data showing that all mice developed seizures after systemic administration of 12 mg/kg 4-AP.When this drug is perfused in the striatum or hippocampus it generates behavioural and electroencephalographic seizures associated with an increase in the extracellular concentration of glutamate (Morales-Villagrán & Tapia, 1996;Peña & Tapia 1999).In addition, evidence has shown that an enhancement in glutamatergic neurotransmission is involved in the excitotoxic mechanisms of the seizures (Fragoso-Veloz & Tapia, 1992;Morales-Villagrán et al., 1996), and seems to be an important factor involved in many neurological disorders (Choi, 1988;Aarts & Tymianski, 2003;Alexander & Godwin, 2006).Taking into account these facts and the anticonvulsant action of (PhSe) 2 and (PhTe) 2 found in this work, it is possible to presume that through its wide redox activity, these organochalcogens directly interact with glutamatergic receptors, particularly the NMDA receptor, modulating its redox state.Hence, through a decrease in the over-activity of NMDA receptors, these organochalcogens can reduce glutamatergic neurotransmission and incidence of seizures.Moreover, acting as mediators of excitotoxic processes in the CNS, they can reduce the seizure-induced oxidative stress in the brain, manifested by enhanced lipid peroxidation.In this context, recent work has demonstrated that the antinociceptive effect of (PhSe) 2 , in a model of pain, can occur via interaction with redox modulatory sites of glutamatergic receptors, more specifically via V. B. Brito and others interaction with the NMDA receptor (Savegnago et al., 2007).The last decades have witnessed an increasing interest in the biochemical and pharmacological effects of organoselenium and organotellurium compounds due to the finding that a variety of such compounds possess interesting biological activity.Amongst organoselenium compounds, (PhSe) 2 was emphasized due to its attractive biological properties, such as anti-inflammatory, antinociceptive, neuroprotective, chemopreventive, and antioxidant (Commandeur et al., 2001;Rossato et al., 2002a;Nogueira et al., 2003b;Posser et al., 2008).Many of these activities are related to the biological importance of selenium (Se) as a trace element.In fact, Se has been shown as a nutritionally essential trace element to mammals, including humans (Rayman, 2000).This essentiality is due to selenocystein, a component of selenoproteins like the antioxidant enzyme glutathione peroxidase (GPx), among other selenoproteins that have important enzymatic functions (Behne et al., 1988;Behne & Kyriakopoulos, 2001;Kyriakopoulos & Behne, 2002).The fact that brain retains Se even after long-term Se deprivation (Behne et al., 1988) indicates the importance of this trace element to normal brain function.Indeed, several health conditions as immune system deficiency (Spallholz et al., 1990), reproductive problems (Behne et al., 1996), viral infections (Beck et al., 2001), cancer (Ganther, 2001), cardiovascular diseases (Neve, 1996), and seizures (Weber et al., 1991) have been linked to Se deficiency.In this sense, a preclinical study demonstrated the importance of Se deficiency in vivo to substantial increase in susceptibility to kainate-induced seizures in rats (Savaskan et al., 2002).That study showed that Sedeficient rats were more susceptible to kainate-induced excitotoxicity, which resulted in a higher seizure rate when compared with controls on a Seadequate diet.In a model of Fe 2+ -induced epileptic discharges, application of Se normalized the electroencephalographic pattern and reduced the tissue damage assessed by histological methods (Rubin & Willmore, 1980;Willmore & Rubin, 1981).Oztas and coworkers (2001) showed that in pentylentetrazol-induced seizures the breakdown of the bloodbrain barrier is attenuated by dietary Se administration.Additionally, when selenoprotein P (SePP), the major selenoprotein in the plasma, is absent in mice (SePP-knockout mice) reduced growth and development of ataxia are observed (Schomburg et al., 2003).
In 1986, Brown and coworkers suggested a clinical link between seizures and Se deficiency from observations of patients on total parenteral nutrition that were at risk of developing seizures until Se was incorporated into dietary formulation.Later it was shown that intractable epileptic seizures in children with low blood Se concentrations had a substantial improvement in the clinical state and electroencephalography recordings, with reduction of seizures after oral Se supplementation (Ramaekers et al., 1994;Weber et al., 2001).Recent work has demonstrated that patients with intractable epilepsy showed Se depletion compared to healthy children, and suggested that lower serum Se and RBC GPx activity support the concept of a crucial role of Se and GPx activity in the pathogenesis of epilepsy (Ashrafi et al., 2007a;2007b).These data demonstrate that selenium levels, within the physiological range, attenuate excitatory damage and render it not only a preventive role but also as a putative therapeutic substance in primary neuronal damage.In our study, the administration of (PhSe) 2 prior to the treatment with 4-AP provided to mice a Se source that was essential for seizure prevention, attenuating the 4-AP-induced excitatory brain damage.Moreover, considering that overactivation of excitatory amino-acid receptors can trigger ROS formation, the inhibition by (PhSe) 2 of exceeding brain excitatory events can play the central role in the decrease of 4-AP-induced brain lipid peroxidation.
However, the toxicological and pharmacological effects of organochalcogens depend on many factors that include chemical form, quantity of the element consumed, specie and age of animal, physiological state, nutritional and dietary interactions, route and scheme of administration (Maciel et al., 2003;Meotti et al., 2003;Nogueira et al., 2003a;Tingui, 2003).Clarifying this point, it was previously demonstrated that rat pups (12-14 postnatal days) showed seizures after oral administration of 50, 150 or 500 mg/kg (PhSe) 2 (160.3 µmol/kg, 480.8 µmol/kg, or 1602.6 µmol/kg, respectively), conversely, rat pups did not present seizures when administered with 5 mg/kg (PhSe) 2 (16.03 µmol/kg) (Prigol et al., 2007).In addition, a possible involvement of oxidative stress in (PhSe) 2 -induced seizures in rat pups was suggested.Those results clearly differ from these demonstrated here, however, these discrepancies can be related to differences in experimental model, such as the animal species, route of administration, age of the animals, and doses employed.In our study, adult mice were administered subcutaneously with 50, 100, or 150 µmol/kg (PhSe) 2 (15.6, 31.2, or 46.8 mg/kg, respectively), doses lower than those used in the cited work.It was previously demonstrated that (PhSe) 2 administered by the subcutaneous route did not produce seizure or death in male adult mice (Nogueira et al., 2003a).Moreover, the cytochrome P450-dependent metabolism of drugs can vary widely between species and the metabolizing capacity of murine liver is superior to that of the rat, for a variety of drugs.Importantly, the developing brain is Effect of (PhSe) 2 and (PhTe) 2 on 4-aminopyridine-induced seizure and lethality in mice particularly susceptible to seizures (Stafstrom et al., 2006), which can occur at any age, are far more common in children than adults, predominating in the first year of life and decreasing with age throughout childhood and adolescence (Cowan, 2002).
Similarly to organoselenium, organotellurium compounds can be readily oxidized from the divalent to the tetravalent state.Consequently, this property makes tellurides attractive as scavengers of reactive oxidizing agents (such as hydrogen peroxide, hypochlorite, and peroxyl radicals) and as inhibitors of lipid peroxidation in chemical and biological systems (Andersson et al., 1993;1994).High antioxidant activity of organotellurium compounds has been described (Engman et al., 1994;1995).Another point regarding the interesting chemistry of these compounds was reported by Albeck and coworkers in 1998.Those authors showed that organotellurium (IV) compounds can selectively inhibit cysteine proteases in its active-site thiol-nucleophile.Through an interaction of a tellurium atom with the reactive cysteine residues of inflammatory and apoptotic caspases, organotellurium (IV) compounds can lead to caspase inhibition.Indeed, involvement of proinflammatory cytokines in neuronal network excitability was suggested by the evidence that convulsant drugs increase mRNA levels of interleukin IL-1β, IL-6, and tumor necrosis factor-α (TNF-α) in rat brain after seizure induction (Minami et al., 1991).Particularly, intracerebral application of IL-1β prolongs the duration of electrographic and behavioral seizures in rodents, and the intracerebral injection of an IL-1β antagonist has a potent anticonvulsant action (Vezzani et al., 1999;2000).Importantly, caspase-1 is mainly required for processing pro-IL-1β and pro-IL-18 to their active forms (Fantuzzi et al., 1999), acting as a proconvulsant and its inhibition as an anticonvulsive strategy.The inhibition of caspase-1 selectively reduces the brain availability of IL-1β (Ravizza et al., 2006) which can modulate the hyperexcitability process by enhancing glutamatergic neurotransmission (Ye & Sontheimer, 1996;Kamikawa et al., 1998;Viviani et al., 2003).
In line with this, a recent report described the protective effect of an organotellurium compound -organotelluroxetane RF-07 -against the onset of pilocarpine-induced status epilepticus (Persike et al., 2008).RF-07 is a tellurium (IV) compound that exerts its anticonvulsant effects associated with the inhibition of caspases.In that work the authors demonstrated that caspase-1, -8, and -3 are activated in the hippocampus of rats in the acute phase of pilocarpine-induced status epilepticus, and suggest that caspase-1 activation may exacerbate seizures in the pilocarpine model.Moreover, intraperitoneal injection of RF-07 prior to pilocarpine suppressed seizure occurrence, suggesting a promising therapeutic potential of organotellurium (IV) compounds, through caspase-1 inhibition, as anticonvulsant and neuroprotective agents (Persike et al., 2008).
Therefore, the findings of the last decades regarding tellurium chemistry corroborate the useful pharmacological effects of organotellurium compounds and their use as promising neuroprotective agents.In this study, as with (PhSe) 2 , pre-administration of (PhTe) 2 to animals caused a significant increase in the latency for 4-AP-induced seizures, prevented death, and gave a marked antioxidant effect on 4-AP-induced oxidative brain damage.The inhibition of caspases, specially caspase-1, or modulation of the redox state of excitatory amino-acid receptors are possible mechanisms involved in the anticonvulsant effects of (PhTe) 2 on 4-AP-induced seizures.
An increase in brain lipid peroxidation levels was observed after treatment with 4-AP, which was significantly inhibited by pre-treatment with (PhSe) 2 or (PhTe) 2 .Thus, these results confirm the antioxidant property of (PhSe) 2 and (PhTe) 2 compounds and show, at first hand, an antioxidant effect of these organochalcogens against 4-AP-induced oxidative damage in murine brain.These effects are in accordance with previous studies of our group, showing that (PhSe) 2 and (PhTe) 2 are effective antioxidants against the increase in TBARS production induced by different pro-oxidant agents in vitro and in vivo (Rossato et al., 2002a;Burger et al., 2004;2006;Meotti et al., 2004).Furthermore, our results point out to an important involvement of brain lipid peroxidation in seizure process, indicating that oxidative stress and the excitotoxic process are important factors involved in seizure-induced neuronal damage (Said et al., 2000;Mueller-Burke et al., 2008;Santos et al., 2008).
Besides the interaction with the redox modulatory sites of glutamatergic NMDA receptors, (PhSe) 2 and (PhTe) 2 may interfere with the activity of Ca 2+ channels activity in the brain.Thereby, through an inhibition of Ca 2+ influx at the presynaptic neuron level, these compounds can modify neurotransmitters' release and conduction of signals.In this way, these organochalcogens may also act as modulators of excitotoxicity in CNS.In fact, a previous study of our group showed that, under depolarizing conditions through 4-AP, organochalcogens inhibited 45 Ca 2+ influx into rat brain synaptosomes (Moretto et al., 2003).
In summary, our results provide evidence for anticonvulsant and antioxidant properties of (PhSe) 2 and (PhTe) 2 .These data support neuroprotective characteristics of organoselenium and organotellurium compounds in the model of 4-AP-induced neurotoxicity in mice.However, we cannot extrapolate our findings to human and further studies are nec-

Table 1 . Influence of pre-treatment with (PhSe) 2 on latency to seizures (clonic and tonic) and death.
After 30 min of pre-treatment with 50, 100, or 150 μmol/kg (PhSe) 2 or DMSO, mice were injected with 4-AP (12 mg/kg) or vehicle.After treatment with 4-AP the behaviour was observed for additional 60 min.