The effects of dopaminergic receptor antagonists on dizocilpine-induced increase in extracellular acetylcholine (ACh) levels in the rat parietal cortex were examined in freely-moving rats, using an in vivo brain microdialysis method. Dizocilpine (0.5mg/kg) significantly increased extracellular ACh levels in the rat parietal cortex and hippocampus, but not in the striatum. Pretreatment with α-methyl-p-tyrosine methyl ester (αMpT) delayed the onset but prolonged the duration of the dizocilpine-induced increases in extracellular ACh levels. The dopamine D2 receptor antagonist, haloperidol, showed dual effects similarly to αMpT, while the dopamine D1 receptor antagonist, SCH23390, prolonged, but did not delay, the onset of the dizocilpine-induced increases in ACh levels. These results suggest that the dopaminergic system is involved in the dizocilpine-induced increase in the extracellular ACh level in the parietal cortex in two ways, through both dopamine D1 and D2 receptors.
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