Extracellular concentrations of serotonin in the dorsal hippocampus after acute and chronic treatment with citalopram.

Citalopram, 1 and 10 mg/kg i.p., that in a previous study using identical treatment and dialysis conditions had little or no effect on dialysate serotonin (5-HT) in the frontal cortex, dose-dependently raised the extracellular concentrations of 5-HT in the dorsal hippocampus, by 70% and 205% respectively at the peak. In animals given 10 mg/kg citalopram twice daily for 14 days, intraperitoneal doses of 1 and 10 mg/kg or infusion of 10(-8) - 10(-6) M through the hippocampal probe raised dialysate 5-HT in the dorsal hippocampus similarly in animals treated chronically with citalopram or saline. A dose of 100 micrograms/kg 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), an agonist at 5-HT1A receptors, reduced hippocampal extracellular 5-HT concentrations to the same extent in rats repeatedly given saline or citalopram. Half this dose had no such effect in either group. The effect of citalopram and the sensitivity of autoreceptors controlling 5-HT release in the dorsal hippocampus were unaffected by a chronic treatment known to facilitate the drug's effect on dialysate 5-HT and to reduce the sensitivity of 5-HT1A receptors controlling 5-HT release in the frontal cortex. The effects of acute and chronic treatment with citalopram on dialysate 5-HT in the rat brain thus appear to differ in at least two brain regions: the frontal cortex and the dorsal hippocampus.