Role of nitric oxide in systemic effect of theophylline on mouse body temperature

Synergistic effect between quinpirole and L-NAME as well as sulpiride and L-arginine on the modulation of anxiety and memory processes in the 6-OHDA mouse model of Parkinson's disease: An isobologram analysis

We evaluated interactions between dopamine D2 receptor and nitric oxide (NO) actions on the regulation of anxiety and memory in the 6-hydroxydopamine (6-OHDA) mouse model of Parkinson's disease (PD). A unilateral guide cannula was stereotaxically implanted over the right striatum. Elevated plus-maze test (EPM) test-retest protocol was employed to evaluate anxiety and memory in mice. The results revealed that injection of L-NAME (9 mg/kg) induced anxiolytic and amnesic effects, while L-arginine (9 mg/kg) produced anxiogenic and memory-improvement effects in the 6-OHDA mouse model of PD. Administration of sulpiride (20 mg/kg) induced anxiogenic and memory-improvement effects, whereas quinpirole (20 mg/kg) caused anxiolytic and amnesic effects in PD mice. Co-injection of sulpiride (5, 10, and 20 mg/kg) plus L-NAME (3 mg/kg) induced anxiolytic and amnesic effects. Co-injection of sulpiride (20 mg/kg) plus L-arginine (3 mg/kg) induced anxiogenic and memory-improvement effects. Co-administrations of quinpirole (20 mg/kg) and L-NAME (3 mg/kg) induced anxiolytic effect, but co-administration of quinpirole (20 mg/kg) plus L-arginine (3 mg/kg) caused anxiogenic and memory-improvement effects. The isobologram analysis revealed that there is a synergistic effect between sulpiride and L-arginine as well as quinpirole and L-NAME upon induction of anxiogenic and anxiolytic effects, respectively in PD mice. Our results suggested: (1) NO and dopamine D2 receptor mechanisms affect anxiety and memory in PD mice; (2) L-NAME reversed anxiogenic and memory-improvement effect induced by sulpiride; (3) Anxiolytic and amnesic effects induced by quinpirole reversed by L-arginine; (4) There is a synergistic effect between dopamine D2 receptor and NO systems on the modulation of anxiety and memory.

Possible role of free radicals in theophylline-induced seizures in mice

Theophylline is a methylxanthine bronchodilator with a narrow therapeutic index and is prone to induce seizures, the mechanisms for which are not clearly defined. Free radicals have considerable neurotoxic potential and the present study evaluated the possible involvement of these bioactive moieties in aminophylline-induced seizures in mice. Aminophylline (50-250 mg/kg) induced convulsions and mortality in mice in a dose-dependent manner. The anti-oxidants, melatonin (25-100 mg/kg) and N-actylcysteine (100 and 200 mg/kg) attenuated aminophylline seizures and mortality. Similar antagonism of aminophylline seizures was also observed after pretreatments with nitric oxide (NO) synthase inhibitors, L-NAME (3 and 10 mg/kg) and 7-nitroindazole (10 and 30 mg/kg). Further, combined treatment with otherwise sub-effective doses of melatonin and L-NAME or 7-nitroindazole produced marked protective effects against these seizures. Aminophylline-induced seizures enhanced malondialdehyde (MDA) concentrations and NO metabolite (NOx) levels in the brain homogenates of mice, and these were attenuated by melatonin and L-NAME pretreatments. The results are suggestive of the possible involvement of free radicals (reactive oxygen and reactive nitrogen species) in the convulsiogenic effects of aminophylline.