CALCITONIN-GENE-RELATED PEPTIDE PROMOTES DIFFERENTIATION, BUT NOT SURVIVAL, OF RAT MESENCEPHALIC DOPAMINERGIC-NEURONS IN-VITRO

The aim of this study was to investigate putative effects of calcitoni n gene-related peptide on developing dopaminergic neurons in the ventr al mesencephalon. To determine a time-point for a physiological role o f calcitonin gene-related peptide in the development of this system, w e first investigated calcitonin gene-related peptide messenger RNA exp ression in the ventral mesencephalon of Wistar rats at embryonic days (E) 11-19. Calcitonin gene-related peptide messenger RNA was not detec table at E11, i.e. prior to the appearance of dopaminergic neurons in this area. From E14 to E19, calcitonin gene-related peptide messenger RNA was expressed in increasing amounts. We therefore investigated the effects of calcitonin gene-related peptide on serum-free cell culture s established from the E14 midbrain floor. Addition of calcitonin gene -related peptide (200 ng/ml) every other day significantly increased n euronal differentiation, including longer tyrosine hydroxylase-positiv e neurites, enhanced immunoreactivity for growth-associated protein-43 and increased dopaminergic uptake per neuron. These effects were maxi mal after seven to eight days. Calcitonin gene-related peptide acted s ynergistically with fibroblast growth factor-2 on these parameters. In contrast to fibroblast growth factor-2, however, calcitonin gene-rela ted peptide did not promote survival of tyrosine hydroxylase-immunorea ctive neurons. Lack of calcitonin gene-related peptide expression in t he mesencephalon at Ell was paralleled by a lack of effect of calciton in gene-related peptide on early presumptive dopaminergic neurons in t erms of eliciting this phenotype. Our data suggest that calcitonin gen e-related peptide may act physiologically as a differentiation-promoti ng factor for phenotypically defined dopaminergic neurons during a tim e period when dopaminergic neurons assemble in the ventral mesencephal on and grow axons towards their targets. (C) 1998 IBRO. Published by E lsevier Science Ltd.