Neuropeptide Y in the Thyroid Gland: Neuronal Localization and Enhancement of Stimulated Thyroid Hormone Secretion*

Abstract

Nerve fibers displaying neuropeptide Y (NPY) immunoreactivity occurred around blood vessels and follicles in the thyroid gland of several mammals, including man. Removal of the superior cervical ganglia or chemical sympathectomy (6-hydroxydopamine treatment) markedly reduced the number of NPY-containing nerve fibers in the thyroid and eliminated norepinephrine[NE]-containing fibers. NPY-immunoreactive nerve cell bodies were numerous in the superior cervical ganglia of mouse, rat and guinea pig. Not unexpectedly, therefore, immunocytochemistry involving sequential staining with antibodies against dopamine-.beta.-hydroxylase (an enzyme marker for adrenergic neurons) and NPY revealed that most of the NPY fibers were adrenergic. As tested in mice in vivo, NPY did not affect basal or NE-stimulated thyroid hormone secretion, but enhanced isoprenaline-, TSH- and vasoactive intestinal polypeptide-induced iodothyronine release. NPY may have a modulatory role in the control of thyroid hormone secretion.