Effect of morphine on striatal dopamine metabolism and ascorbic acid and uric acid release in freely moving rats
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: The effects of dl -fenfluramine, dl -5-hydroxytryptophan(5-HTP) and fluoxetine on ethanol-induced striatal ascorbic acid (AA) release in rat were studied by microdialysis coupled to high performance liquid chromatography with electrochemical detection. Ethanol (3.0 g/kg, i.p.) stimulated striatal AA release to more than 200% above the baseline. dl -Fenfluramine (20 mg/kg, i.p. or 40 mug/rat, i.c.v.), 10 min before ethanol administration, markedly inhibited ethanol-induced AA release. A similar result was also observed following dl -5-HTP (100 mg/kg, i.p.) administration. However, fluoxetine (10, 30 mg/kg, i.p.) showed no antagonistic effect on ethanol-induced AA release. The suppressing effect of dl -fenfluramine and dl -5-HTP on ethanolinduced AA release could be reversed by the 5-HT receptor antagonist cyproheptadine (10 mg/kg, s.c.). All these drugs had no effect on basal AA release. The results give a first evidence for the involvement of central serotonergic system, and suggest that differential activities may exist between dl -fenfluramine, dl -5-HTP and fluoxetine in regulating ethanol-induced AA release in rat striatum.Addiction Biology 07/1998; 3(3):295-308. · 5.93 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; · 2.83 Impact Factor
- Yakugaku zasshi journal of the Pharmaceutical Society of Japan 01/2006; 126(8):671-675. · 0.31 Impact Factor