Electron microscopic identification of adrenergic nerve endings on thyroid epithelial cells.

Electron microscopic observations were made of the microinnervation of the thyroids of normal mice and of mice given false adrenergic neurotransmitters, and the effects of the drugs on thyroidal norepinephrine uptake were measured. In addition to adrenergic nerve terminals on thyroid blood vessels, structures resembling nerve endings were seen in close apposition to the bases of thyroid epithelial cells. Because they take up false adrenergic neurotransmitters, and undergo degenerative change after administration of cytotoxic false neurotransmitters (6-hydroxydopamine and 5,7-dihydroxytryptamine), which also reduce thyroid norepinephrine uptake, they probably represent adrenergic nerve terminals on thyroid follicles. If so, they afford a morphological basis for the direct effects of catecholamines on thyroid function, which have been reported.