A comparative study of aminophylline- and acepifylline-induced seizures and death in the chemoconvulsion model in rats

Differential neuromodulatory role of NO in anxiety and seizures: an experimental study

Nitric oxide is a simple, ubiquitous, diatomic molecule with complex neuromodulatory functions. Anxiety and seizures are closely similar neurobehavioral disorders and are regulated by limbic system. The present study evaluated the regulatory roles of NO in these pathophysiological states in experimental models. In test for anxiety, aminophylline induced anxiogenic responses were assessed by the elevated plus maze (EPM) test, and a low dose of the drug (50 mg/kg) reduced both open arm entries and open arm time in rats. Pretreatment with the NO mimetic, L-arginine (500 and 1000 mg/kg) and melatonin (50 mg/kg) attenuated aminophylline induced anxiogenesis whereas the NO synthase inhibitors, L-NAME and 7-NI (30 mg/kg) aggravated the anxiogeneic response. Such aminophylline induced neurobehavioral suppression in the EPM activity was accompanied by increases in MDA levels and reductions in GSH and NOx activity in brain homogenates - changes which were reversed by L-arginine and melatonin pretreatments. In tests for seizures, aminophylline induced seizures and mortality at higher dose levels of the drug (300 mg/kg). Interestingly, such seizures and mortality in rats were antagonized by L-NAME and 7-NI pretreatments. On the other hand, L-arginine tended to potentiate seizures after sub-convulsive dose (100 mg/kg) of this methylxanthine. Aminophylline induced seizures were accompanied by greater elevations in brain MDA levels, whereas, GSH levels were consistently lowered. Unlike that seen during anxiety, NOx levels were increased in brain homogenates of these rats. The changes in oxidative stress markers were neutralized by NO synthase inhibitors. Synergistic anticonvulsant effect on aminophylline seizures was seen when L-NAME was combined with melatonin. These pharmacological and biochemical data indicate that aminophylline induced anxiety and seizures are differentially modulated by NO.

Methylxanthines, seizures, and excitotoxicity

Clinical evidence, in particular the wide use of theophylline as a bronchodilator, suggests that methylxanthines can cause seizures in patients without known underlying epilepsy. Theophylline is also known to be an added risk factor for seizure exacerbation in patients with epilepsy. The proconvulsant activity of methylxanthines can best be explained by their antagonizing the brain's own anticonvulsant adenosine. Recent evidence suggests that adenosine dysfunction is a pathological hallmark of epilepsy contributing to seizure generation and seizure spread. Conversely, adenosine augmentation therapies are effective in seizure suppression and prevention, whereas adenosine receptor antagonists such as methylxanthines generally exacerbate seizures. The impact of the methylxanthines caffeine and theophylline on seizures and excitotoxicity depends on timing, dose, and acute versus chronic use. New findings suggest a role of free radicals in theophylline-induced seizures, and adenosine-independent mechanisms for seizure generation have been proposed.

Dose-finding study with nimodipine: a selective central nervous system calcium channel blocker on aminophylline induced seizure models in rats

Nimodipine, a dihydropyridine derivative central nervous system (CNS) selective calcium channel blocker was studied at four different dosage schedules in five different models of seizures in rats. At a dose of 5 mg/kg, i.p. with pretreatment time of 15 min, nimodipine significantly antagonized aminophylline (175 and 200 mg/kg, i.p.), electroshock (150 mA for 0.2 s), pentylenetetrazole (60 and 75 mg/kg, i.p.), aminophylline (100 mg/kg i.p.) + electroshock (66mA for 0.2 s), and aminophylline (100 mg/kg, i.p.) + pentylenetetrazole (40 mg/kg, i.p.) induced seizures in rats. No hemodynamic alteration was observed with this dose of nimodipine. However, 2 mg/kg, i.p. (pretreatment time of 15 min and 30 min) and 5 mg/kg, i.p. (pretreatment time of 30 min) doses of nimodipine failed to demonstrate any significant anticonvulsant effect. The study highlighted the critical role of calcium ion flux into the neurons for the genesis of seizure activity to aminophylline, electroshock, and pentylenetetrazole in rats. Furthermore, the critical dose requirement for nimodipine could be explained on the basis of its short half-life and shorter duration of protection against seizures. Therefore, nimodipine may be tried clinically as an anticonvulsant in patients who are on aminophylline because of bronchial asthma or chronic obstructive pulmonary disease, when such patients have concomitant epilepsy or other seizure prone neurological deficits or are scheduled to undergo electroshock therapy.