A class of thyroid hormone metabolites has dramatic physiological effects on 
metabolism and heart rate by still-unknown mechanisms of action. A recent study 
has discovered that thyronamines can inhibit neuronal reuptake of 
neurotransmitters and prevent the intracellular transport of monoamines for 
release. This discovery presents a third signaling pathway for thyroid hormone, 
expands the role that thyroid plays in the central nervous system, and suggests 
mechanisms of action for the effects of thyronamine-derived neuromodulators.