Thyroid parafollicular cells. An accessible model for the study of serotonergic neurons.

Serotonergic neurons play key roles in modulating a wide variety of behavioral and homeostatic processes. However, there is a paucity of good model systems to study these neurons at a molecular level. In this review we will present evidence that cell lines derived from an unexpected source, thyroid parafollicular cells (PF) (also called C cells), fit the criteria for use as models for the study of serotonergic neurons. A strength of PF cell lines over other cell lines is that the parental PF cells have serotonergic properties and a neuronal potential that is consistent with their neural crest origin. Furthermore, PF cells and PF cell lines are capable of expressing the fundamental properties of serotonergic neurons, including: (1) serotonin (5-HT) biosynthesis by tryptophan hydroxylase (TPH), (2) vesicular 5-HT storage and regulated release, (3) expression of a 5-HT autoreceptor, and (4) expression of the 5-HT transporter. In this review, we will focus primarily on the serotonergic and neuronal properties of the rat CA77 PF cell line and the parental rat PF cells. The applicability of CA77 cells for molecular analyses will be described. First, their use for studies on the glucocorticoid regulation of the TPH gene will be discussed. Second, control of the calcitonin/calcitonin gene-related peptide (CT/CGRP) gene will be discussed, with particular emphasis on the application of serotonergic drugs in treating migraine headaches. These examples highlight the versatility of thyroid PF cell lines as a system for studying the control of both serotonin biosynthesis and physiological actions.