RESUMO
Methylphenidate (MPH) is widely used as a "nootropic" agent and in the treatment of disorders of attention, and has been shown to modulate synaptic plasticity in vitro. Here we present in vivo evidence that this MPH-induced metaplasticity can last long after the end of treatment. MPH (0, 0.2, 1 and 5mg/kg) was administered daily to male rats from postnatal day 42 for 15 days. The animals were tested daily in a radial maze. Long-term potentiation (LTP), a marker of neural plasticity, was induced in vivo in the prefrontal cortex after 2-3h, 15-18 days or 5 months without treatment. The behavioral performance of the 1mg/kg group improved, while that of animals that had received 5mg/kg deteriorated. In the 1 and 5mg/kg groups LTP induced 2-3h after the last MPH treatment was twice as large as in the controls. Further, 15-18 days after the last MPH administration, in groups receiving 1 and 5mg/kg, LTP was about fourfold higher than in controls. However, 5 months later, LTP in the 1mg/kg group was similar to controls and in the 5mg/kg group LTP could not be induced at all. No significant changes of LTP were seen in the low-dose group of animals (0.2mg/kg). Thus, firstly, doses of MPH that improve learning coincide approximately with those that augment LTP. Secondly, MPH-induced increases in LTP can last for several weeks, but these may disappear over longer periods or deteriorate at high doses.
Assuntos
Potenciação de Longa Duração/efeitos dos fármacos , Aprendizagem em Labirinto/efeitos dos fármacos , Metilfenidato/farmacologia , Nootrópicos/farmacologia , Córtex Pré-Frontal/efeitos dos fármacos , Animais , Estimulantes do Sistema Nervoso Central/farmacologia , Relação Dose-Resposta a Droga , Potenciação de Longa Duração/fisiologia , Masculino , Aprendizagem em Labirinto/fisiologia , Microeletrodos , Córtex Pré-Frontal/crescimento & desenvolvimento , Córtex Pré-Frontal/fisiologia , Ratos Sprague-DawleyRESUMO
BACKGROUND: There are doubts wether generic medications have the same bioavailability and efficacy compared with the original drugs developed by pharmaceutical companies with research capabilities. AIM: To compare the pharmacokinetics and clinical (motor) responses of Sinemet and Grifoparkin (generic carbidopa/levodopa 250/25 mg) in patients with advanced Parkinson's disease. PATIENTS AND METHODS: Patients were randomly assigned to Sinemet (15 patients 62 +/- 12 years old; mean disease duration 11 +/- 7 years) or Grifoparkin (15 patients, 64 +/- 11 years old; mean disease duration 12 +/- 4 years) groups. Medication and food were withheld 12 h before the study. Fifteen blood samples were collected (starting 9 AM) immediately before (sample 1, t = 0 min) and after (samples 2-15, t = 20-360 min) oral administration of a single dose of Sinemet or Grifoparkin, and plasmatic L-DOPA was quantified using HPLC with electrochemical detection. Additionally, each patient was clinically evaluated every 20 minutes, using the tapping test and the unified Parkinson's disease scale Hoehn & Yarh. RESULTS: Tmax (time at which the maximal L-DOPA concentration was reached) were 69 +/- 12 min and 64 +/- 11 min for Sinemet and Grifoparkin respectively (NS). Cmax (maximal L-DOPA concentration reached) was 3161 +/- 345 ng/ml for Sinemet and 3274 +/- 520 ng/ml for Grifoparkin (NS). The t1/2 (half life time), CL (clearance) and volume of distribution (Vd) values calculated were 159 +/- 32 min, 51.7 +/- 5.1 1/h and 3.6 +/- 1.2 l/kg for Sinemet and 161 +/- 48 min, 58.7 +/- 8 l/h and 3.0 +/- 0.7 l/kg for Grifoparkin (NS). UPDRS-III value for the best on state and for the worst off state were 23 +/- 11 and 50 +/- 19 for Sinemet and 20 +/- 7 and 46 +/- 13 for Grifoparkin respectively (NS). CONCLUSION: The results obtained showed that both drugs are bioequivalent in patients with advanced Parkinson's disease.
Assuntos
Humanos , Masculino , Feminino , Pessoa de Meia-Idade , Antiparkinsonianos/farmacocinética , Carbidopa/farmacocinética , Doença de Parkinson/metabolismo , Levodopa/farmacocinética , Antiparkinsonianos/administração & dosagem , Carbidopa/administração & dosagem , Combinação de Medicamentos , Disponibilidade Biológica , Doença de Parkinson/tratamento farmacológico , Levodopa/administração & dosagem , Método Duplo-CegoRESUMO
Propionic and methylmalonic acidemic patients have severe neurologic symptoms whose etiopathogeny is still obscure. Since increase of lactic acid is detected in the urine of these patients, especially during metabolic decompensation when high concentrations of methylmalonate (MMA) and propionate (PA) are produced, it is possible that cellular respiration may be impaired in these individuals. Therefore, we investigated the effects of MMA and PA (1, 2.5 and 5mM), the principal metabolites which accumulate in these conditions, on the mitochondrial respiratory chain complex activities succinate: 2,6-dichloroindophenol (DCIP) oxireductase (complex II); succinate: cytochrome c oxireductase (complexII+CoQ+III); NADH: cytochrome c oxireductase (complex I+CoQ+complex III); and cytochrome c oxidase (COX) (complex IV) from cerebral cortex homogenates of young rats. The effect of MMA on ubiquinol: cytochrome c oxireductase (complex III) and NADH: ubiquinone oxireductase (complex I) activities was also tested. Control groups did not contain MMA and PA in the incubation medium. MMA significantly inhibited complex I+III (32-46%), complex I (61-72%), and complex II+III (15-26%), without affecting significantly the activities of complexes II, III and IV. However, by using 1mM succinate in the assay instead of the usual 16mM concentration, MMA was able to significantly inhibit complex II activity in the brain homogenates. In contrast, PA did not affect any of these mitochondrial enzyme activities. The effect of MMA and PA on succinate: phenazine oxireductase (soluble succinate dehydrogenase (SDH)) was also measured in mitochondrial preparations. The results showed significant inhibition of the soluble SDH activity by MMA (11-27%) in purified mitochondrial fractions. Thus, if the in vitro inhibition of the oxidative phosphorylation system is also expressed under in vivo conditions, a deficit of brain energy production might explain some of the neurological abnormalities found in patients with methylmalonic acidemia (MMAemia) and be responsible for the lactic acidemia/aciduria identified in some of them.