THYROID-HORMONES AND THE TREATMENT OF DEPRESSION - AN EXAMINATION OF BASIC HORMONAL ACTIONS IN THE MATURE MAMMALIAN BRAIN

Numerous clinical reports indicate that thyroid hormones can influence mood, and a change in thyroid status is an important correlate of dep ression. Moreover, thyroid hormones have been shown to be effective as adjuncts for traditional antidepressant medications in treatment-resi stant patients. In spite of a large clinical literature, little is kno wn about the mechanism by which thyroid hormones elevate mood. The lac k of mechanistic insight reflects, in large part, a longstanding bias that the mature mammalian central nervous system is not an important t arget site for thyroid hormones. Biochemical, physiological, and behav ioral evidence is reviewed that provides a clear picture of their impo rtance for neuronal function. This paper offers the hypothesis that th e thyroid hormones influence affective state via postreceptor mechanis ms that facilitate signal transduction pathways in the adult mammalian brain. This influence is generalizable to widely recognized targets o f antidepressant therapies such as noradrenergic and serotonergic neur otransmission. (C) 1997 Wiley-Liss, Inc.