The study also could be important to physicians who prescribe thyroid hormones -- known for their mood-altering capability -- to treat depression, said Bill Henley, associate professor of biological sciences at Ohio University and co-author of the study.
The research was published in the February issue of the American Journal of Physiology.
Scientists examining the brains of rats with underactive thyroid glands -- or hypothyroidism -- found differences in neuronal responses to serotonin, a neurotransmitter that is important for circulatory control. Rats in the study received central administration of a drug that mimics serotonin and normally causes an increase in blood pressure.
"In the normal rat, blood pressure rose markedly, but in hypothyroid rats, blood pressure responses were attenuated substantially," Henley said. "This study, coupled with previously reported findings, tells us that the serotonergic neurons in the hypothyroid brain are different, and that has very important physiological implications."
Learning about these implications could increase physicians' understanding of the impact thyroid disease, which affects about 200 million people in the world, has on various bodily functions, Henley said.
"It's been known for years that thyroid hormones have a profound impact on developing brains, but most people believe that they're not important in the mature central nervous systems," he said. "But our findings provide evidence of an important impact on the brains of mature rats."
Understanding how mature brains react to these hormones is important for psychiatrists who prescribe these drugs to treat depression.
"This could change the way physicians use thyroid hormones as an adjunct therapy in the treatment of depression," Henley said.
The next phase of Henley's study will be to determine if other neural functions are affected by thyroid hormones.
"It's probable that the impact we're seeing on the serotonergic neurons is not specific to those neurons," he said. "Hypothyroidism is likely to cause broad-based disturbances in a host of neural functions."