Glial cells play a significant role in the link between the endocrine and nervous systems. Among hormones, thyroid hormones (THs) are critical for the regulation of development and differentiation of neurons and glial cells, and hence for development and function of the central nervous system (CNS). THs are transported into the CNS, metabolized in astrocytes and affect various cell types in the CNS including astrocyte itself. Since 3,3’,5-triiodo-L-thyronine (T3) is apparently released from astrocytes in the CNS, it is a typical example of glia-endocrine system.
The prevalence of thyroid disorders increases with age. Both hypothyroidism and hyperthyroidism are reported to increase the risk of cognitive impairment or Alzheimer’s disease (AD). Therefore, understanding the neuroglial effects of THs may help to solve the problem why hypothyroidism or hyperthyroidism may cause mental disorders or become a risk factor for cognitive impairment. In this review, THs are focused among wide variety of hormones related to brain function, and recent advancement in glioendocrine system is described.