Cortical and Striatal in Vivo Uptake and Metabolism of Plasma Choline in the Rat: Effects of Haloperidol and Apomorphine

Following intravenous injection of a tracer dose of radioactive choline (3H–Ch), blood 3H–Ch was incorporated into parietal cortex at 1.2% per min. while the corresponding rate in the striatum was 6.4. It is suggested that this linear relationship in the time–interval 10 sec. to 20 min. following 3H–Ch injection demonstrates the in vivo existence of active uptake mechanisms of plasma Ch into brain. Furthermore, 36 % per min. of cortical 3H–Ch was converted to Ch metabolites other than acetylcholine (ACh) while the striatal percentage was only 6. This is probably due to the distribution of 3H–Ch into an “ACh–available” Ch pool within the cholinergic neurones which show the highest density in the striatum. Based on the present results and data in the literature a hypothetical scheme for the fate of brain Ch is discussed. The above mentioned parameters were also examined in cataleptic rats following haloperidol treatment (2 mg/kg intraperitoneally) as well as in rats slightly hyperactive following combined treatment with haloperidol (2 mg/kg intraperitoneally) and apomorphine (10 mg/kg intravenously). The results can be interpreted in the light of a dopaminergic inhibition on intrastriatal cholinergic neurones.