Serotonin and nialamide differentially regulate survival and growth of cultured serotonin and catecholamine neurons

Abstract

In this morphometric analysis of immunoreactive serotonin (5-HT) and tyrosine hydroxylase (TH) neurons in culture, 5-HT and the MAO inhibitor nialamide influenced the survival, cell body size and neurite outgrowth of embryonic day 14 (E14) 5-HT neurons after treatment from 1–3 days in vitro (DIV), but did not significantly affect E14 or E15 TH neurons of either the noradrenergic or dopaminergic phenotype. These treatments had minimal effects on 5-HT neurons derived from E15 embryos. The stimulatory effects of 5-HT on survival and somal growth of E14 5-HT neurons was in contrast to its inhibitory effects on neurite outgrowth, suggesting trophic and inhibitory autoregulation of different cellular compartments of developing 5-HT neurons. The decreased sensitivity of E15 5-HT neurons to these treatments, despite similar viability and growth of these neurons in control cultures, suggests the existence of a critical period for this regulation during the initial period of serotonergic neurogenesis when these neurons are forming the bilateral B4–9 raphe complex. The lack of significant effects of 5-HT on TH neurons suggests differential sensitivities of 5-HT and TH neurons to developmental regulation by this neurotransmitter.