Catecholamine-serotonin interaction effects on activity in rats neonatally treated with 6-hydroxydopamine

The effect of increased central serotonergic levels on motor activity was investigated in rats neonatally treated with 6-hydroxydopamine (6-OHDA) in the lateral ventricles. Regional brain assays of monoamine levels in 90-day-old rats showed depletion of catecholamines, but not of serotonin, in the forebrain accompanied by a large elevation of norepinephrine, and minor elevation of serotonin, in the hindbrain. Measures of behavioral activity in adulthood were taken after treatment with saline, pargyline, L-tryptophan, or pargyline given 30 min before L-tryptophan. The combined treatment of pargyline plus L-tryptophan produced hyperactivity in controls and this effect was blocked in the 6-OHDA-treated animals. These findings indicate that the serotonergic system is capable of influencing motor activity, but that this influence is blocked in animals permanently depleted of catecholamines in their terminal field regions.