Thyroid hormone control of serotonin in developing rat brain.

The influence of thyroid hormone on serotonin was studied in different regions of the rat brain. Surgical thyroidectomy of adult male rats led to significant increases in the level of serotonin in the hypothalamus but had no effect on this biogenic amine in the brain stem and basal ganglia. Experimental cretinism, induced by daily propylthiouracil treatment starting at birth, caused increased serotonin levels in all brain regions studied. In contrast. neonatal hyperthyroidism, produced by daily administration of L-triiodothyronine from birth, had no effect on the ontogenic patterns of serotonin. The turnover of serotonin, estimated by determining the rate of increase of the amine following administration of the monoamine oxidase inhibitor, pargyline, was decreased in the brains of 30-day-old cretinous rats when compared to their control littermates. The data suggest that thyroid hormone may exert an important regulatory influence on serotonin metabolism in the developing brain.