Effects of citalopram, a synthetic serotonin uptake inhibitor, on indoleamine and catecholamine concentrations in the cerebrospinal fluid of freely moving rats.

We studied changes in the concentrations of 5-hydroxytryptamine (5-HT), other indoleamines, and catecholamines in the cerebrospinal fluid (CSF) of freely-moving rats that had been administered citalopram, +/-1-[3- (Dimethylamino)propyl)-1-(4-fluorophenyl)-1, 3-dihydro-5-isobenzo-furancarbonitrile hydrobromide), a selective inhibitor of 5-HT uptake. In a microdialysis experiment, the intracerebral extracellular free 5-HT increased significantly, peaking 60 to 90 min after citalopram (30 mg/kg p.o.) was administered. The 5-HT concentrations in CSF from the cisterna magna increased significantly, reaching a maximum 6 hours after a single dose of citalopram (30 mg/kg p.o.) was given. Six hours after this dose, the CSF 5-HT concentration in the cisterna magna was significantly increased, and the 5-hydroxyindoleacetic acid (5-HIAA) concentration was significantly decreased. There were non-significant changes in the other indoleamines (tryptophan, 5-hydroxytryptophan, and kynurenine) and in the catecholamines (dopamine, homovanillic acid, normetanephrine, and 3-methoxy-4-hydroxyphenethyleneglycol). The 5-HT/tryptophan ratio was correlated significantly with the kynurenine/tryptophan ratio before treatment with citalopram (r = 0.81, p = 0.051), indicative that there is coordination of the serotonin and kynurenine pathways in normal rats. In the animals posttreatment there was no such correlation, suggesting that the changes in 5-HT are independent of the kynurenine system at least within the 6 hours postreatment. These CSF results appear to reflect selective inhibition of 5-HT uptake in brain tissues by citalopram that is not associated with changes in catecholamines.