[Effects of different thyroid states on 5-HT1A receptor in adult rat brain]

The effects of dysthyroidism on central 5-HT1A receptor subtype in adult Wistar rats were investigated. Hyperthyroidism and hypothyroidism were respectively produced with the administration of T3 and propylthiouracil (PTU) via gavage for 2 weeks. Heart rate, oxygen consumption, anal temperature and plasma T3 concentration were increased in hyperthyroid rats and decreased in hypothyroid rats significantly. Radioligand binding assay showed that the specific binding of [3H] 8-hydroxy-2-(di-n-propylamino) tetralin ([3H] 8-OH-DPAT) at 0.6 nmol/L concentration was highest in hippocampus, next in cerebral cortex, and lowest in hypothalamus, brain stem and corpus striatum in euthyroid rats. Hyperthyroidism increased the binding significantly in hippocampus but decreased in cortex. No change was found in the other brain regions. Scatchard analyses revealed that the Bmax was increased in hippocampus and decreased in cortex, whereas the KD was not consistently affected in hyperthyroid rats in comparison with that in euthyroid rats. However, there were no significant changes mentioned above in all these brain regions of hypothyroid rats. Our results indicate that there seems to exist an imbalance of the serotonergic activity mediated via 5-HT1A receptor between hippocampus and cerebral cortex in hyperthyroids. This might be one of the mechanisms leading to psychoneural disorders in hyperthyroidism.