Less induced 1-methyl-4-phenylpyridinium ion neurotoxicity on striatal slices from guinea-pigs fed with a vitamin C-deficient diet

Semichronic Inhibition of Glutathione Reductase Promotes Oxidative Damage to Proteins and Induces both Transcription and Translation of Tyrosine Hydroxylase in the Nigrostriatal System

We have evaluated the effect of N,N-bis (2-chloroethyl)-N-nitrosourea (BCNU), an inhibitor of glutathione reductase (GR), on the oxidative status along with the integrity of the nigrostriatal dopaminergic system of the rat. The oxidative status was studied by the quantification of carbonyl groups coupled to protein homogenates. Moreover, the specific oxidations in glial fibrillary acidic protein (GFAP) and neurofilament-200 (NF-200) were also measured. The results show that oxidative damage in proteins in the nigrostriatal system is confined to the striatum. Specific carbonyl groups coupled to native NF-200 and GFAP were also increased. These changes were accompanied by reactive astrocytosis in striatum but not in substantia nigra. In substantia nigra, decreased levels of dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were observed following BCNU treatment. In contrast, DA levels were increased in the striatum along with an overall decrease in the ratios of DA metabolites to DA. We also studied the mRNA levels for tyrosine hydroxylase (TH) and the dopamine transporter (DAT) by in situ hybridization. TH mRNA but not DAT mRNA was significantly induced in substantia nigra following BCNU treatment, which was consistent with significant elevations in TH enzyme amount and activity and unchanged DA uptake in striatum. All these results support the DA free radical hypothesis and the key role of the striatal glutathione system in protecting the striatal system against oxidative stress.

Pharmacological, morphological and behavioral analysis of motor impairment in experimentally vitamin C deficient guinea pigs

The scurvy shows an inflammatory disease and gingival bleeding. Nevertheless, in an animal model for guinea pigs, described by Den Hartog Jager in 1985, scurvy was associated with a motor neuron disease with demyelinization of the pyramidal tract, provoking neurogenic atrophy of muscles. Aiming at searching the protective role of vitamin C in nervous system, a pharmacological, morphological and behavioral study was conducted. Three experimental groups were used: A100, animals receiving 100 mg/ vitamin C/ day; A5.0, animals receiving 5.0 mg/vitamin C/ day; and A0, animals without vitamin C. We analyzed the weight gain, muscular diameter and behavioral tests. In all tests examined, we found significant differences between the supplemented groups in comparison with scorbutic group (p<0.05). Thereafter, the animals were killed for histopathology of gastrocnemius muscle, spinal cord and tooth tissues. In addition, a morphometric study of periodontal thickness and alpha-motor neuron cell body diameter were done. The vitamin C-diet free regimen seemed to induce a disruption in spinal cord morphology, involving the lower motor neuron, as confirmed by a significant reduction in neuron perycaria diameter and muscular atrophy, complicated by increased nutritional deficit.

Low selenium diet induces tyrosine hydroxylase enzyme in nigrostriatal system of the rat

We have studied the effect of a selenium-deficient diet on the nigrostriatal dopaminergic system for 15 and 30 days. The neurochemical analysis demonstrated significant elevations in nigral DA levels after 15 and 30 days of selenium deficiency. The most significant change in striatum was an elevation in dopamine (DA) in 30-day-deficient animals. As a further step, we measured the levels of activity and mRNA expression of tyrosine hydroxylase (TH) and dopamine transporter (DAT). There were significant elevations in all of these parameters in the nigrostriatal system following selenium deficiency at the two time-points studied except for the striatal DA uptake at day 30, which dropped to control levels. Altogether, our results suggest that the decrease in antioxidant capacity due to a selenium deficiency promotes an increase in DA synthesis and turnover, which are clearly associated to the induction of TH. This effect may trigger a positive feed-forward mechanism that could increase the oxidative stress considering the capacity of DA to generate free radicals.

Inhibitors of mitochondrial respiration, iron (II), and hydroxyl radical evoke release and extracellular hydrolysis of glutathione in rat striatum and substantia nigra: potential implications to Parkinson's disease

In this investigation, microdialysis has been used to study the effects of 1-methyl-4-phenylpyridinium (MPP+), an inhibitor of mitochondrial complex I and alpha-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+ (2.5 mM) into the rat striatum or SN, extracellular concentrations of GSH and CySH remain at basal levels (both approximately 2 microM). 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 gamma-glutamyl transpeptidase (gamma-GT) inhibitor acivicin. Low-molecular-weight iron and extracellular hydroxyl radical (OH*) have been implicated as participants in the mechanism underlying the dopaminergic neurotoxicity of MPTP/MPP+. During perfusion of Fe2+ (OH*) into the rat striatum and SN, extracellular levels of GSH also remain at basal levels. When perfusions of Fe2+ 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+ are discontinued. This observation and the fact that MPTP/MPP+ 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 gamma-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+, other agents that impair neuronal energy metabolism, and Parkinson's disease.

Lack of involvement of glutamate-induced excitotoxicity in MPP+ toxicity in striatal dopaminergic terminals: possible involvement of ascorbate

1. The present study concerns the possible relationship between glutamate excitotoxicity and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/1-methyl-4-phenylpyridinium (MPTP/MPP+) neurotoxicity on striatal dopaminergic terminals. 2. MPP+ neurotoxicity has been studied by means of two MPP+ perfusions separated by 24 h. After the second MPP+ 1 mM perfusion, dopamine extracellular output, measured by microdialysis, was considered to be an index of the dopaminergic neurone damage produced by the first MPP+ 1 mM perfusion. 3. High concentration (10 mM) of glutamate uptake inhibitor L-trans-pyrrolidine-2,4-dicarboxylic acid (PDC) stimulated basal release of dopamine and protected against the neurotoxic effect of MPP+. 4. PDC 10 mM perfusion produced an increase in the extracellular output of glutamate and aspartate, and a decrease in that of ascorbate. 5. The protective effect against MPP+ toxicity observed with PDC 10 mM was completely abolished when this glutamate uptake inhibitor was co-perfused with ascorbate 0.5 mM. 6. These results suggest that glutamate-induced neurotoxicity is not involved in MPP+ toxicity. The protective effect found with the glutamate uptake inhibitor could be due to a decrease in extracellular ascorbate levels.