The effects of hypothyroidism on 5-HT1A and 5-HT2A receptors and the serotonin transporter protein in the rat brain.

The effects of hypothyroidism on 5-HTIA and 5-HT2A receptors and the serotonin transporter protein were studied in thyroidectomized male Wistar rats in two experimental groups: 1) animals kept on an iodine-free diet hypothyroid rats) and 2) animals kept on thyroxine (15 microg/kg) for 21 days (giving normal thyroid hormone levels. euthyroid animals). Sham-operated rats served as controls. Binding of [3H]8-OH-DPAT with 5-HTIA receptors and [3H]citalopram with the transporter protein in the hippocampus and midbrain showed no changes in hypothyroid rats as compared with controls. Conversely. there were significant decreases in [3H]ketanserin binding to 5-HT2A receptors in the frontal cortex in hypothyroid rats as compared with controls; this decrease was reversed by thyroxine treatment. Thus, losses of cortical 5-HT2A receptors appears to be the main consequence of hypothyroidism at the level of the serotonin system of the brain.