Abstract
The effects of hyperthyroidism or hypothyroidism, alone or in combination with the tricyclic antidepressant desmethylimipramine (DMI), on brain beta-adrenergic and serotonin (5HT
2) receptors were studied in adult male Sprague-Dawley rats. Intraperitoneal administration of T
3 or T
4 for 7 days increased the number of cortical beta-adrenergic and 5HT
2 receptors. These increases were significant at levels of 250 μg/kg or above for both hormones. Neither thyroidectomy nor “reverse” T
3 (rT
3) (500 μg/kg) produced an effect on either receptor type. The down-regulation of beta-adrenergic receptors produced by daily subcutaneous injections of 20 mg/kg of DMI for 7 days was partially offset by concurrent administration of T
4, whereas the down-regulation of 5HT
2 receptors produced by the drug was not affected by concurrent administration of either T
3 or T
4. Hypothyroidism (thyroidectomy) did not significantly affect the adaptation of these receptor populations to DMI.
As regards brain regions other than cortex, T
4 (250 μg/kg) produced the same changes in hippocampus as in cortex, while thyroidectomy decreased beta-adrenergic receptors only in the cerebellum. Thyroxine also elevated 5HT
2 receptors in the hippocampus; thyroidectomy caused a significant decrease in 5HT
2 receptors in the striatum.
