Depletion of tryptophan hydroxylase by 5,6-dihydroxytryptamine in rat brain. Time course and regional differences

—Wistar rats were injected intraventricularly with 75 μg 5,6-dihydroxytryptamine. Tryptophan hydroxylase was assayed in seven regions of the brain as well as spinal cord at intervals following injection. Spinal cord was depleted to 1 per cent of control by 12 days. Tectum was depleted to 32 per cent of control by 9 days. The time course of depletion in most regions was biphasic, with an early reduction of activity 1 h after injection with continued reduction of activity 1-2 days following injection, and a recovery of activity at 4-6 days. The activity again drops at 9-12 days, and this reduction of activity persists to varying degrees to 60 days, with slight recovery at this time in certain regions.