Abstract:In this investigation, microdialysis has been used to study the effects of 1-methyl-4-phenylpyridinium (MPP ϩ ), an inhibitor of mitochondrial complex I and ␣-ketoglutarate dehydrogenase and the active metabolite of the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), on extracellular concentrations of glutathione (GSH) and cysteine (CySH) in the rat striatum and substantia nigra (SN). During perfusion of a neurotoxic concentration of MPP ϩ (2.5 mM) into the rat striatum or SN, extracellular concentrations of GSH and CySH remain at basal levels (both ϳ2 M). However, when the perfusion is discontinued, a massive but transient release of GSH occurs, peaking at 5,000% of basal levels in the striatum and 2,000% of basal levels in the SN. The release of GSH is followed by a slightly delayed and smaller elevation of extracellular concentrations of CySH that can be blocked by the ␥-glutamyl transpeptidase (␥-GT) inhibitor acivicin. Low-molecular-weight iron and extracellular hydroxyl radical (OH ⅐ ) have been implicated as participants in the mechanism underlying the dopaminergic neurotoxicity of MPTP/MPP ϩ . During perfusion of Fe 2ϩ (OH ⅐ ) into the rat striatum and SN, extracellular levels of GSH also remain at basal levels. When perfusions of Fe 2ϩ are discontinued, a massive transient release of GSH occurs followed by a delayed, small, but progressive elevation of extracellular CySH level that again can be blocked by acivicin. Previous investigators have noted that extracellular concentrations of the excitatory/excitotoxic amino acid glutamate increase dramatically when perfusions of neurotoxic concentrations of MPP ϩ are discontinued. This observation and the fact that MPTP/MPP ϩ causes the loss of nigrostriatal GSH without corresponding increases of glutathione disulfide (GSSG) and the results of the present investigation suggest that the release and ␥-GT/dipeptidase-mediated hydrolysis of GSH to glutamate, glycine, and CySH may be important factors involved with the degeneration of dopamine neurons. It is interesting that a very early event in the pathogenesis of Parkinson's disease is a massive loss of GSH in the SN pars compacta that is not accompanied by corresponding increases of GSSG levels. Based on the results of this and prior investigations, a new hypothesis is proposed that might contribute to an understanding of the mechanisms that underlie the degeneration of dopamine neurons evoked by MPTP/ MPP ϩ , other agents that impair neuronal energy metabolism, and Parkinson's disease. Key Words: Parkinson's disease-Glutathione-Rat striatum-Rat substantia nigra-1-Methyl-4-phenylpyridinium-1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine-Fe (II)-Hydroxyl radical-Mitochondrial respiration inhibitors-Dopamine neuron degeneration.

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Reactive oxygen species (ROS) and reactive nitrogen species (RNS), particularly peroxynitrite, have been implicated as key participants in the dopaminergic neurotoxicity of 1-methyl-4-phenylpyridinium (MPP(+)). However, on the basis of available information, it is not clear whether the MPP(+)-induced overproduction of ROS and RNS occurs in the intraneuronal and/or extracellular compartment. Early steps in the neurotoxic mechanism evoked by MPP(+) include a profound dopaminergic energy impairment, which mediates a massive release of dopamine (DA), glutathione (GSH), and cysteine (CySH). In the event that MPP(+) mediates extracellular generation of ROS (such as superoxide and/or hydroxyl radicals) and/or peroxynitrite, released DA, GSH, and CySH should be oxidized forming thioethers of DA and disulfides. Using microdialysis experiments in which MPP(+) was perfused into the striatum of awake rats, the present study was unable to detect the presence of such biomarkers of extracellular ROS and/or RNS generation. However, MPP(+) induced a transient, concentration-dependent rise of extracellular l-3,4-dihydroxyphenylalanine (l-DOPA), identified on the basis of dialysate analysis using several HPLC methods and its conversion to DA by purified l-DOPA decarboxylase (DDC). Methamphetamine (30 mg/kg, i.p.) similarly caused a significant but transient rise of l-DOPA in the rat striatum. Antioxidants such as salicylate and mannitol had no effect on the MPP(+)-mediated elevation of extracellular l-DOPA, suggesting that it is not formed by nonenzymatic hydroxylation of l-tyrosine by ROS or RNS. Rather, in vivo, but not in vitro, MPP(+) caused rapid inhibition of DDC, which appears to result in intraneuronal accumulation and subsequent release of l-DOPA. Because l-DOPA can mediate l-glutamate release, as well as be an excitotoxin, the possibility is raised that l-DOPA may play a role in the dopaminergic neurotoxicity of MPP(+).

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The study of gene expression levels under defined experimental conditions is an important approach to understand how a living cell works. High-throughput microarray technology is a very powerful tool for simultaneously studying thousands of genes in a single experiment. This revolutionary technology results in an extensive amount of data, which raises an important question: how to extract meaningful biological information from these data? In this chapter, we survey data mining techniques that have been used for clustering, classification and association rules for gene expression data analysis. In addition, we provide a comprehensive list of currently available commercial and academic data mining software together with their features. Lastly, we suggest future research directions.