The effect of antiparkinsonian drugs on oxidative stress induced pathological [3H]dopamine efflux after in vitro rotenone exposure in rat striatal slices.

An in vitro model of mitochondrial dysfunction with subsequent oxidative stress was elaborated and utilized to study the effect of drugs, currently used for the treatment of Parkinson's disease, on pathological H(2)O(2)-evoked [(3)H]dopamine efflux and the formation of toxic dopamine metabolites in rat striatal slices. 60 min rotenone (0.1-10 muM) pretreatment decreased dopamine content and [(3)H]dopamine uptake, as well as ATP level and energy charge of the slices. In addition, a robust potentiation of H(2)O(2)-evoked [(3)H]dopamine efflux and the formation of dopamine quinone in the effluent was detected. l-DOPA (200 muM) markedly elevated resting but not 100 muM H(2)O(2)-evoked and electrically-induced [(3)H]dopamine efflux. Furthermore, l-DOPA promoted the formation of dopamine quinone. Ropinirole (100 nM) did not affect resting and H(2)O(2)-evoked [(3)H]dopamine efflux and inhibited the electrically evoked release only in untreated slices. l-deprenyl, at concentration of 0.01 muM potentiated, whilst between 1 and 50 muM diminished H(2)O(2)-evoked [(3)H]dopamine efflux. Rasagiline (0.01-50 muM) slightly inhibited H(2)O(2)-evoked [(3)H]dopamine efflux, and it was able to prevent the generation of dopamine quinone. Neither of the drugs was able to suppress both the pathological H(2)O(2)-evoked [(3)H]dopamine efflux and the formation of dopamine quinone with simultaneous augmentation of electrically evoked [(3)H]dopamine release what should be a future concept of antiparkinsonian drug-design.

Modulation of dopaminergic neurotransmission in rat striatum upon in vitro and in vivo diclofenac treatment.

Diclofenac (DCF) is a widely used non-steroidal anti-inflammatory drug, which also act as a mitochondrial toxin. As it is known that selective mitochondrial complex I inhibition combined with mild oxidative stress causes striatal dopaminergic dysfunction, we tested whether DCF also compromise dopaminergic function in the striatum. [3H]Dopamine ([3H]DA) release was measured from rat striatal slices after in vitro (2 h, 10-25 micromol/L) or in vivo (3 mg/kg i.v. for 28 days) DCF treatment. In vitro treatment significantly decreased [3H]DA uptake and dopamine (DA) content of the slices. H2O2 (0.1 mmol/L)-evoked DA release was enhanced. Intracellular reactive oxygen species production was not significantly changed in the presence of DCF. After in vivo DCF treatment no apparent decrease in striatal DA content was observed and the uptake of [3H]DA into slices was increased. The intensity of tyrosine hydroxylase immunoreactivity in the striatum was highly variable, and both decrease and increase were observed in individual rats. The H2O2-evoked [3H]DA release was significantly decreased and the effluent contained a significant amount of [3H]octopamine, [3H]tyramine, and [3H]beta-phenylethylamine. The ATP content and adenylate energy charge were decreased. In conclusion, whereas in vitro DCF pre-treatment resembles the effect of the mitochondrial toxin rotenone, in vivo it rather counteracts than aggravates dopaminergic dysfunction.

Chromatographic analysis of dopamine metabolism in a Parkinsonian model.

The present study examined the metabolism of released dopamine from rat striatum upon chronic rotenone exposure. The sample separation was carried out by two-dimensional, reversed-phase and ion pair reversed-phase chromatography using on-line solid phase extraction enrichment. Reduced dopamine content and decreased extracellular level of [(3)H] and endogenous dopamine evoked by electrical stimulation indicated the injury of dopaminergic pathway. Sensitivity of dopaminergic neurons were increased to oxidative stress with enhanced release of dopamine and formation of oxidized metabolite dopamine quinone (DAQ). Utilizing multidimensional detection, EC at -100 mV reduction potential, the method has been applied for identification of DAQ and aminochrome (DAC).

Glutamate stimulation of acetylcholine release from myenteric plexus is mediated by endogenous nitric oxide.

Glutamate was found to be an excitatory neurotransmitter in the enteric nervous system. Although several lines of evidence indicate a role of glutamate in the regulation of gut motility and secretion the physiological significance of glutamatergic transmission is not clear yet. We studied the effect of glutamate on [3H]acetylcholine release and nicotinamide adenine dinucleotide phosphate-diaphorase staining in longitudinal muscle strips with attached myenteric plexus of guinea pig ileum. L-glutamate (100 microM) significantly enhanced both the evoked [3H]acetylcholine release and the optical density of nicotinamide adenine dinucleotide phosphate-diaphorase positive neurones, i.e. the intensity of staining. The non-competitive N-methyl-D-aspartate receptor antagonist MK-801 (3 microM) abolished the stimulatory effect of L-glutamate on acetylcholine efflux. Similarly, the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine (100 microM) significantly reduced the effect of L-glutamate on [3H]acetylcholine release and nicotinamide adenine dinucleotide phosphate-diaphorase staining. Our data suggest that endogenous nitric oxide seems to mediate the stimulatory effect of glutamate on acetylcholine release from guinea pig myenteric neurons.

Increased sensitivity of striatal dopamine release to H2O2 upon chronic rotenone treatment.

It is believed that both mitochondrial dysfunction and oxidative stress play important roles in the pathogenesis of Parkinson's disease (PD). We studied the effect of chronic systemic exposure to the mitochondrial inhibitor rotenone on the uptake, content, and release of striatal neurotransmitters upon neuronal activity and oxidative stress, the latter simulated by H(2)O(2) perfusion. The dopamine content in the rat striatum is decreased simultaneously with the progressive loss of tyrosine hydroxylase (TH) immunoreactivity in response to chronic intravenous rotenone infusion. However, surviving dopaminergic neurons take up and release only a slightly lower amount of dopamine (DA) in response to electrical stimulation. Striatal dopaminergic neurons showed increased susceptibility to oxidative stress by H(2)O(2), responding with enhanced release of DA and with formation of an unidentified metabolite, which is most likely the toxic dopamine quinone (DAQ). In contrast, the uptake of [(3)H]choline and the electrically induced release of acetylcholine increased, in coincidence with a decline in its D(2) receptor-mediated dopaminergic control. Thus, oxidative stress-induced dysregulation of DA release/uptake based on a mitochondrial deficit might underlie the selective vulnerability of dopaminergic transmission in PD, causing a self-amplifying production of reactive oxygen species, and thereby contributing to the progressive degeneration of dopaminergic neurons.