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ABSTRACT: L-DOPA and manganese both induce oxidative stress-mediated apoptosis in catecholaminergic PC12 cells. In this study, exposure of PC12 cells to 0.2 m M MnCl<sub>2</sub> or 10-20 μ M L-DOPA neither affected cell viability, determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, nor induced apoptosis, tested by flow cytometry, fluorescence microscopy, and the TUNEL technique. L-DOPA (50 μ M ) induced decreases in both cell viability and apoptosis. When 0.2 m M MnCl<sub>2</sub> was associated with 10, 20, or 50 μ M L-DOPA, a concentration-dependent decrease in cell viability was observed. Apoptotic cell death also occurred. In addition, manganese inhibited L-DOPA effects on dopamine (DA) metabolism (i.e., increases in DA and its acidic metabolite levels in both cell lysate and incubation medium). The antioxidant N -acetyl-L-cysteine significantly inhibited decreases in cell viability, apoptosis, and changes in DA metabolism induced by the manganese association with L-DOPA. An increase in autoxidation of L-DOPA and of newly formed DA is suggested as a mechanism of manganese action. These data show that agents that induce oxidative stress-mediated apoptosis in catecholaminergic cells may act synergistically.
Journal of Neurochemistry 10/1999; · 4.06 Impact Factor
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ABSTRACT: Abstract : L-DOPA and manganese both induce oxidative stress-mediated apoptosis in catecholaminergic PC12 cells. In this study, exposure of PC12 cells to 0.2 mM MnCl2 or 10-20 μM L-DOPA neither affected cell viability, determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, nor induced apoptosis, tested by flow cytometry, fluorescence microscopy, and the TUNEL technique. L-DOPA (50 μM) induced decreases in both cell viability and apoptosis. When 0.2 mM MnCl2 was associated with 10, 20, or 50 μM L-DOPA, a concentration-dependent decrease in cell viability was observed. Apoptotic cell death also occurred. In addition, manganese inhibited L-DOPA effects on dopamine (DA) metabolism (i.e., increases in DA and its acidic metabolite levels in both cell lysate and incubation medium). The antioxidant N-acetyl-L-cysteine significantly inhibited decreases in cell viability, apoptosis, and changes in DA metabolism induced by the manganese association with L-DOPA. An increase in autoxidation of L-DOPA and of newly formed DA is suggested as a mechanism of manganese action. These data show that agents that induce oxidative stress-mediated apoptosis in catecholaminergic cells may act synergistically.
Journal of Neurochemistry 08/1999; 73(3):1155 - 1163. · 4.06 Impact Factor
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ABSTRACT: Recent findings have shown that systemic morphine increases extracellular dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), ascorbic acid (AA) and uric acid concentrations in the striatum of freely moving rats. The morphine-induced increase in DA oxidative metabolism is highly correlated with that of xanthine. In the present study, we evaluated the effects of subcutaneous (s.c.) naloxone (1 mg/kg) on morphine-induced changes in DA, DOPAC, HVA, 5-hydroxyindoleacetic acid (5-HIAA), AA, uric acid and glutamate in the striatum of freely moving rats using microdialysis. Dialysates were assayed by high performance liquid chromatography with electrochemical detection or (glutamate) ultraviolet detection. Morphine (5–20 mg/kg) given s.c. increased DA, DOPAC+HVA, 5-HIAA, AA and uric acid and decreased glutamate dialysate concentrations over a 3 h period after morphine. Morphine (1 mM), given intrastriatally, did not affect all the above parameters, with the exception of an early short-lasting decrease in AA concentration. Naloxone antagonised all morphine-induced changes with the exception of AA increase and glutamate decrease in dialysate concentrations. Systemic or intrastrial (0.2–2 mM) naloxone increased AA and decreased glutamate dialysate concentrations. When given intranigrally, morphine (1 mM) increased DOPAC+HVA, AA and uric acid and decreased glutamate dialysate concentrations over a 2 h period after morphine; DA and 5-HIAA concentrations were unaffected. These results suggest that: (i) morphine increases striatal DA release and 5-hydroxytryptamine oxidative metabolism by a μ-opioid receptor-mediated mechanism mainly at extranigrostriatal sites; (ii) morphine increases DA and xanthine oxidative metabolism and affects glutamate and AA release by a μ-opioid receptor mediated mechanism acting also at nigral sites; and (iii) a μ-opioid receptor-mediated mechanism tonically controls at striatal sites extracellular AA and glutamate concentrations.
Brain Research 07/1998; · 2.73 Impact Factor
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ABSTRACT: Recent ex vivo findings have shown that morphine increases dopamine (DA) and xanthine oxidative metabolism and ascorbic acid (AA) oxidation in the rat striatum. In the present study, we evaluated the effects of subcutaneous daily morphine (20 mg/kg) administration on DA, dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), AA and uric acid in the striatum of freely moving rats using microdialysis. Dialysates were assayed by high performance liquid chromatography with electrochemical detection. On the first day, morphine administration caused a significant increase in extracellular DA, DOPAC, HVA, AA and uric acid concentrations over a 3 h period after morphine. In all treated rats (n=7), individual concentrations of DOPAC+HVA were directly correlated with individual AA and uric acid concentrations. Last morphine administration on the 4th day increased DOPAC, HVA, AA and uric acid concentrations but failed to increase those of DA. Individual DOPAC+HVA concentrations were still directly correlated with individual AA and uric acid concentrations. These results suggest that systemic morphine increases both striatal DA release and DA and xanthine oxidative metabolism. Only the former effect undergoes tolerance. The increase in DA oxidative metabolism is highly correlated with that of xanthine. The subsequent enhancement in reactive oxygen species production may account for the increase in extracellular AA.
Brain Research 02/1997; · 2.73 Impact Factor
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ABSTRACT: Since ascorbic acid (AA) reportedly suppresses tolerance to and dependence on morphine in humans and rodents, levels of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 3-methoxytyramine (3-MT), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), AA, dehydroascorbic acid (DHAA), uric acid, xanthine, hypoxanthine, glutamate and γ-amino-butyric acid (GABA) were determined by high-pressure liquid chromatography (HPLC) in the striatum and in the limbic forebrain of the rat following morphine treatment (single or repeated) and withdrawal. Single morphine administration (20 mg/kg s.c.) increased DOPAC + HVA/DA, 5-HIAA/5-HT and DHAA/AA ratios, uric acid levels, and decreased xanthine, hypoxanthine, glutamate and GABA levels in both regions. 3-MT levels were decreased in the striatum and increased in the limbic forebrain. After 7 days of morphine treatment, striatal DOPAC + HVA/DA and DHAA/AA ratios and uric acid levels were still higher and striatal and limbic xanthine levels still lower than in controls, while all other parameters were in the range of control values in both regions. Morphine treatment also increased the glutamate/GABA ratio in the striatum. In all morphine-treated rats, individual striatal DOPAC + HVA/DA and DHAA/AA ratio values were directly correlated. After a 48 h withdrawal period, both striatal AA oxidation and glutamate/GABA ratio further increased; limbic 3-MT levels further decreased, while all other parameters did not differ from control values. We conclude that: (i) tolerance to morphine-induced increase in hypoxanthine, xanthine and AA oxidation develops in the limbic forebrain faster than in the striatum; (ii) the morphine-induced increase in striatal and limbic AA oxidation may be considered a consequence of increased formation of reactive oxygen species due to increased DA, hypoxanthine and xanthine oxidative metabolism; (iii) a striatal excitotoxic imbalance characterizes the withdrawal state and may be taken into account to explain the further increase in striatal AA oxidation.
Brain Research 07/1996; · 2.73 Impact Factor
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ABSTRACT: Rats whose frontoparietal cortex had been bilaterally ablated were allowed 21 days for recovery and then treated with apomorphine (APO), 1 mg/kg SC or scopolamine (SCOP), 0.6 mg/kg SC. Soon after a behavioral test, dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), ascorbic acid (AA), and dehydroascorbic acid (DHAA) levels were determined by HPLC/EC in striatal synaptosomes (left side) and whole striatum (right side). SCOP behavioural effects were attenuated by cortical ablation, while those of APO were affected to a lesser extent. In the striatum of unoperated and sham-operated rats DHAA contents and DHAA/AA ratio resulted increased after drugs administration. No change in AA oxidation was observed in the striatum of ablated rats. In the synaptosomes of unoperated and sham-operated rats both drugs led to a decrease in DHAA contents and DHAA/AA ratio. In unoperated and sham-operated rats APO and SCOP caused a decrease of the DOPAC/DA ratio in the whole striatum and striatal synaptosmes. In ablated rats APO caused a decrease of DOPAC/DA ratio in the whole striatum and synaptosomes, while SCOP effects on DA turnover resulted attenuated in the whole striatum and abolished in synaptosomes. We conclude that drug-induced AA oxidation is likely to occur in the extracellular space and requires intact corticostriatal glutamatergic pathways. The latter may play an enabling role in SCOP behavioral effects.
Pharmacology Biochemistry and Behavior 02/1995; · 2.53 Impact Factor
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ABSTRACT: Levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), ascorbic acid and dehydroascorbic acid (DHAA) were measured by HPLC in the striatum of rats whose fronto-parietal cortex had been unilaterally ablated after a single injection of apomorphine (1 mg/kg s.c.), scopolamine (0.6 mg/kg s.c.) or L-glutamate (500 mg/kg i.p.). Unilateral cortical ablation decreased striatal levels of glutamate in both striata ipsilateral (35%) and contralateral (17–25%) to the lesion. Apomorphine and scopolamine significantly increased (+94 and +122%, respectively) the DHAA/ ascorbic acid ratio in the striata ipsilateral to the lesion in unoperated and sham-operated rats (+72 and +34%, respectively), but both drugs failed to increase it in ablated rats. L-Glutamate significantly increased the DHAA/ ascorbic acid ratio in unoperated (+53%) and ablated rats (+37%). The increase in sham-operated rats (+34%) did not reach statistical significance. Apomorphine and scopolamine significantly decreased the DOPAC/DA ratio in the striata ipsilateral to the lesion of unoperated, sham-operated and ablated rats. The decrease in the DOPAC/DA ratio induced only minor changes in striatal DA and DOPAC levels. We conclude that the apomorphine- and scopolamine-induced increase in ascorbic acid oxidation in the striatum requires intact cortico-striatal glutamatergic pathways. Cortical ablation potentiates the apomorphine- and scopolamine-induced inhibition of striatal DA turnover.
European Journal of Pharmacology 09/1992; · 2.52 Impact Factor
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ABSTRACT: Levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), ascorbic acid (AA) and dehydroascorbic acid (DHAA) were determined by HPLC in the striatum of male Wistar rats after single or repeated injections of apomorphine (1 mg/kg/day s.c.) and/or haloperidol (1 mg/kg/day i.p.), and 24 h after the last drug administration. Apomorphine significantly reduced the DOPAC/DA ratio and increased the DHAA/AA ratio; these ratio changes were significantly correlated ( r = −0.9969, P < 0.0005). Haloperidol greatly increased the DOPAC/DA ratio; the DHAA/AA ratio was also slightly increased, but there was no significant correlation. When apomorphine was associated with haloperidol, the resulting DOPAC/DA ratio was significantly lower than after haloperidol alone; the DHAA/AA ratio was also significantly reduced in contrast to the effect of apomorphine alone. It is concluded that a non-selective DA receptor activation mediates, in a correlated way, both the inhibition of DA turnover and the increase of AA oxidation in the rat striatum.
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ABSTRACT: Dopamine (DA). 3,4-dihydroxyphenylacetic acid (DOPAC), ascorbic acid (AA) and dehydroascorbic acid (DHAA) levels were determined by HPLC in the striatal synaptosomal fraction and in the whole striatum of rats, whose fronto-parietal cortex had been bilaterally ablated, after a single injection of d-amphetamine (2.0 mg/kg i.p.). d-Amphetamine significantly increased the DHAA/AA ratio in unoperated and sham-operated rats, but failed to increase it in ablated rats, as compared to pertinent saline-treated groups. In the synaptosomal fraction, d-amphetamine significantly decreased the DHAA/AA ratio in unoperated, sham-operated and ablated rats. d-Amphetamine significantly decreased the DOPAC/DA ratio in the whole striatum and significantly increased it in the striatal synaptosomal fraction in all experimental groups. Cortical ablation greatly increased d-amphetamine-induced motor hyperactivity. We conclude that the d-amphetamine-induced increase in AA striatal oxidation requires integrity of the cortico-striatal glutamatergic pathways. Further, AA oxidation occurs in the extracellular space. The cortico-striatal glutamatergic pathways exert an inhibitory modulation on d-amphetamine behavioral effects.
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ABSTRACT: Recent ex vivo findings have shown that morphine increases dopamine (DA) and xanthine oxidative metabolism and ascorbic acid (AA) oxidation in the rat striatum. In the present study, we evaluated the effects of subcutaneous daily morphine (20 mg/kg) administration on DA, dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), AA and uric acid in the striatum of freely moving rats using microdialysis. Dialysates were assayed by high performance liquid chromatography with electrochemical detection. On the first day, morphine administration caused a significant increase in extracellular DA, DOPAC, HVA, AA and uric acid concentrations over a 3 h period after morphine. In all treated rats (n = 7), individual concentrations of DOPAC + HVA were directly correlated with individual AA and uric acid concentrations. Last morphine administration on the 4th day increased DOPAC, HVA, AA and uric acid concentrations but failed to increase those of DA. Individual DOPAC + HVA concentrations were still directly correlated with individual AA and uric acid concentrations. These results suggest that systemic morphine increases both striatal DA release and DA and xanthine oxidative metabolism. Only the former effect undergoes tolerance. The increase in DA oxidative metabolism is highly correlated with that of xanthine. The subsequent enhancement in reactive oxygen species production may account for the increase in extracellular AA.
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ABSTRACT: In 3- and 18-month-old male Wistar rats, levels of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), ascorbic acid (AA), dehydroascorbic acid (DHAA), noradrenaline (NA), uric acid, glutathione (GSH) and 1-methyl-4-phenylpyridinium ion (MPP<sup>+</sup>) were determined by HPLC in the striatum and/or in the brainstem 24 h after single injections of MPTP (12–35 mg/kg i.p.). Aged rats had lower baseline levels of AA and GSH, compared to young rats. In aged rats, MPTP 35 mg/kg induced a 70% death rate and a decrease in striatal DOPAC/DA ratio which was correlated to MPP<sup>+</sup> concentrations ( r = −0.840, P < 0.005); in addition, MPTP did not increase AA oxidation. In the brainstem, the MPTP-induced decrease in NA levels and increase in uric acid levels were significantly correlated to the MPP<sup>+</sup> concentrations ( r = −0.709, P < 0.05, and r = +0.888, P < 0.001, respectively). In conclusion, evidence is given of a mechanism of toxicity of MPTP involving oxidative stress produced by xanthine oxidase; in addition, in aged rats the neuronal antioxidant system (levels of AA and GSH) is considerably lower than in young rats and may play an enabling role in the MPTP age-related neurotoxic effects on striatum and brainstem.
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ABSTRACT: Levels of dopaminc (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), ascorbic acid (AA), dehydroascorbic acid (DHAA), and uric acid were determined in the rat striatum following single apomorphine (1 mg/kg), scopolamine (0.6 mg/kg), pilocarpine (4 mg/kg), or pilocarpine + scopolamine (4 and 0.6 mg/kg, respectively) injections. The decrease in DOPAC levels and in the DOPAC/DA ratio, induced by the pharmacological manipulation, was linearly correlated with the increase in DHAA levels (r = −0.9060, P < 0.05) and with the increase in the DHAA / AA ratio (r = −0.9004, P < 0.05), respectively. I dopaminergic activaction or cholinergic inhibition both increase striatal AA oxidation, which is correlated with a decrease in DA turnover.
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ABSTRACT: Levels of dopaminc (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), ascorbic acid (AA), dehydroascorbic acid (DHAA), and uric acid were determined in the rat striatum following single apomorphine (1 mg/kg), scopolamine (0.6 mg/kg), pilocarpine (4 mg/kg), or pilocarpine + scopolamine (4 and 0.6 mg/kg, respectively) injections. The decrease in DOPAC levels and in the DOPAC/DA ratio, induced by the pharmacological manipulation, was linearly correlated with the increase in DHAA levels (r = −0.9060, P < 0.05) and with the increase in the ratio (r = −0.9004, P < 0.05), respectively. I dopaminergic activaction or cholinergic inhibition both increase striatal AA oxidation, which is correlated with a decrease in DA turnover.
European Journal of Pharmacology.
