dl-Fenfluramine inhibits ethanol-induced ascorbic acid release in rat striatum studied by microdialysis

Effect of morphine on brain uracil release in mouse striatum detected by microdialysis

Effect of acute treatment of morphine is associated with neurotransmitter and neuromodulator changes in the brain. A possible relationship between pyrimidines and morphine has also been discussed. Uracil, a common and naturally occurring pyrimidine derivative which found in RNA, has been suggested to modulate many neurotransmitters or neuromodulators, especially in the mature central nervous system. The present study was performed to determine the effect of acutely intraperitoneal morphine treatment on the release of uracil in mouse striatum. The results showed that morphine significantly decreased the release of uracil at the dose of 10 and 20mg/kg in a dose dependent manner. Naloxone could reverse the morphine-induced reduction of uracil levels in mouse striatum, at the dose of 4 mg/kg, without affecting basal uracil release. The results suggest that the extracellular level of uracil in mouse striatum could be specifically regulated by the centrally acting drugs, such as morphine. However, the pharmacological implications of such regulation should be further evaluated.

Differential effects of clozapine on ethanol-induced ascorbic acid release in mouse and rat striatum

Previous studies have shown that acute systemic administration of ethanol-induced striatal ascorbic acid (AA) release in mice and rats. In the present study, in vivo brain microdialysis coupled with high performance liquid chromatography (HPLC) with electrochemical detection (ECD) was used to comparatively evaluate the effects of clozapine on ethanol-induced AA release in mouse and rat striatum. The results showed that clozapine, at the dose of 15 mg/kg i.p., had no effect on basal AA or ethanol-induced AA release in rat striatum. The potentiating effect of clozapine on ethanol-induced striatal AA release was still observed in rats, at the higher dose of 30 mg/kg. In contrast, clozapine significantly inhibited ethanol-induced AA release in mouse striatum, at the dose of 15 and 30 mg/kg, without affecting basal AA release. The present study suggested that clozapine differentially regulated ethanol-induced AA release in the mouse and rat striatum.

Effects of clozapine, olanzapine and haloperidol on ethanol-induced ascorbic acid release in mouse striatum

The effects of clozapine, olanzapine and haloperidol on ethanol-induced striatal ascorbic acid (AA) release in mice were compared by using microdialysis coupled to high performance liquid chromatography with electrochemical detection. Ethanol (4.0 g/kg i.p.) significantly stimulated striatal AA release by about 200% of baseline in mice. Clozapine and olanzapine, two atypical neuroleptic drugs, at the dose of 1.0 mg/kg s.c., had no effect on basal AA or ethanol-induced AA release. However, both drugs, at the dose of 10 mg/kg s.c., significantly inhibited ethanol-induced AA release. In contrast, haloperidol, a typical neuroleptic drug, at the doses of 0.1-2.0 mg/kg, had no effect on both basal and ethanol-induced AA release. The present study demonstrated that similar actions were exhibited by clozapine and olanzapine, but not by haloperidol, for the regulation of ethanol-induced AA release in the mouse striatum.

Ascorbic acid antagonizes the inhibitory effect of acute ethanol on nitrite levels in the striatum of freely moving mice

The effect of exogenous ascorbic acid (AA) on acute ethanol-induced decrease in extracellular nitrites contents in striatum of freely moving mice was investigated by using microdialysis coupled to high performance liquid chromatography with electrochemical detection. The results showed that exogenous AA had no effect on basal extracellular levels of nitrites, but significantly increased striatal extracellular contents of AA in a dose-depended manner. Co-administration of AA with ethanol significantly antagonized the ethanol-induced decrease in extracellular nitrites contents, but did not affect ethanol-induced release of AA. These data provided the first evidence of an antagonistic action of AA on ethanol-induced decrease in extracellular nitrites contents in striatum of freely moving mice.

Role of nitric oxide in ethanol-induced ascorbic acid release in striatum of freely moving mice

In the present study, in vivo brain microdialysis coupled with high performance liquid chromatography (HPLC) and electrochemical detection were used to evaluate the effects of either L-arginine (L-Arg), the substrate of nitric oxide synthase (NOS), Nomega-nitro-L-arginine methyl ester hydrochloride (L-NAME), a non-selective NOS inhibitor, or sodium nitroprusside (SNP), a donor of NO, on the ethanol-induced release of ascorbic acid (AA) in the striatum of freely moving mice. Drugs were administered intrastriatally via the microdialysis probe and ethanol (2-4 g/kg) was administered intraperitoneally. The results showed that L-arginine (1-10 mg/ml) had no effect on either the basal AA contents in striatal extracellular fluid or the ethanol-induced release of AA. L-NAME (10(-4) to 10(-3) mg/ml) and SNP (10(-4) to 10(-3) mg/ml) both reduced the basal AA concentrations in striatal extracellular fluid. L-NAME significantly inhibited ethanol-induced release of AA, while SNP only had a transient inhibitory effect on the ethanol-induced release of AA. SNP significantly increased dehydroascorbic acid (DHAA) contents and DHAA/AA ratio but had no effect on the total AA contents (AA and DHAA contents) in striatal extracellular fluid, while L-NAME had no effect on DHAA contents but decreased the total AA contents in striatal extracellular fluid. Only high concentration L-NAME induced a transient increase in DHAA/AA ratio. Our results suggest that nitric oxide (NO) might not directly be involved in the mechanism of ethanol-induced release of AA in mouse striatum.

Differential effects of acute administration of haloperidol and clozapine on ethanol-induced ascorbic acid release in rat striatum

Antipsychotic drugs were initially considered to act predominantly through their antagonism at dopamine D(2)-like receptors. However, reports have demonstrated that the typical neuroleptic drug haloperidol and the atypical neuroleptic drug clozapine showed differential actions in clinical, behavioral and biochemical studies. Since ascorbic acid has a potential usefulness in psychological therapeutics, the present study investigates the actions of these two drugs on ethanol-induced ascorbic acid release in the striatum in order to help explain the different mechanisms of these drugs. The results showed that clozapine, at the doses of 15 and 30 mg/kg, i.p., had no effect on basal ascorbic acid release. However, a synergistic tendency at a dose of 15 mg/kg and a significant synergism at a dose of 30 mg/kg were observed on ascorbic acid release when clozapine was used with ethanol. In contrast, haloperidol, at the doses of 0.5, 1.0 and 2.0 mg/kg, i.p., administered alone did not affect the basal release of striatal ascorbic acid, and when used together with ethanol had neither a potentiating nor an antagonizing effect on ethanol-induced ascorbic acid release. Chlorpromazine, a nonselective dopamine receptor antagonist, at the dose of 5 mg/kg, i.p., affected neither the basal nor the ethanol-induced ascorbic acid release. Ritanserin, a 5-HT(2) receptor antagonist, at the dose of 1 mg/kg, s.c., significantly antagonized ethanol-induced ascorbic acid release. These results demonstrate that clozapine dose-dependently potentiates the stimulatory effect of ethanol on striatal ascorbic acid release and this effect of clozapine may not be related to its dopamine D(2) receptor antagonism.

Potentiation of ethanol-induced loss of the righting reflex by ascorbic acid in mice: interaction with dopamine antagonists

The present investigation was carried out to determine the effect of ascorbic acid on ethanol-induced loss of the righting reflex (LORR) and the interactions between ascorbic acid and dopamine receptor antagonists in affecting this action of ethanol in mice. To test the effect of each drug on ethanol-induced LORR, ascorbic acid (31.25, 62.5, 125, 250, 500, 1000 mg/kg intraperitoneally [IP]) and dopamine receptor antagonists (haloperidol 0.5, 1.0 mg/kg; L-sulpiride 20, 40, 80 mg/kg; clozapine 0.625, 1.25, 2.5 mg/kg; SCH 23390 0.5, 1.0, 2.0 mg/kg subcutaneously [SC]) were administered, respectively, 30 min before ethanol (4.0 g/kg IP) administration. Ascorbic acid, at the dose of 1000 mg/kg, significantly potentiated ethanol-induced LORR in mice. Dopamine D(2) antagonists haloperidol (0.5, 1.0 mg/kg SC), and L-sulpiride (80 mg/kg SC) also significantly prolonged the duration of LORR induced by ethanol. Clozapine and SCH 23390, at the doses used, did not affect ethanol-induced LORR. In the interaction study, the synergistic effect of ascorbic acid (1000 mg/kg IP) on ethanol-induced LORR was significantly enhanced by dopamine D(2) antagonists haloperidol, L-sulpiride, and clozapine, and the highest dose of dopamine D(1) antagonist SCH 23390. These results suggest that ascorbic acid may potentiate ethanol-induced LORR partially via a mechanism mainly linked to blockade of dopamine D(2) receptors.

Involvement of the corticostriatal glutamatergic pathway in ethanol-induced ascorbic acid release in rat striatum

The mechanism of ethanol-induced ascorbic acid (AA) release in striatum is not well understood. In the present work, the possible involvement of NMDA receptors in the corticostriatal pathway was studied by microdialysis coupled to high performance liquid chromatography with electrochemical detection. Ethanol (3.0 g/kg i.p.) stimulated significant striatal AA release to more than 200% above the baseline. This effect of ethanol could be partially antagonized by amantadine, a non-selective NMDA receptor antagonist and dopamine releaser, at a dose of 200 mg/kg i.p. and significantly antagonized by MK-801, a non-competitive NMDA receptor antagonist, at the doses of 0.5 and 1.0 mg/kg i.p. Furthermore, deafferentation of the glutamatergic projection from cortex to striatum by undercutting the prefrontal cortex completely eliminated ethanol-induced AA release in rat striatum. The basal level of AA in striatum could only be reduced by high doses of MK-801, but not by low doses of MK-801, amantadine or decortication. The results further confirm that NMDA receptors are involved in ethanol-induced AA release and provide the first evidence for the necessity of the activation of corticostriatal glutamatergic pathway in ethanol-induced AA release in rat striatum.