Multiple receptors mediate the trophic effects of serotonin on ventroposterior thalamic neurons in vitro

Serotonin (5-HT) exerts prominent morphogenetic roles during development. For example, somatosensory cortical barrel formation is altered in mouse models characterized by excessive extracellular 5-HT, suggesting that 5-HT affects development of thalamic afferents and/or neocortical target regions. The present study assessed 5-HT effects in primary cultures of fetal ventroposterior thalamic (VPT) neurons. 5-HT produces concentration-dependent trophic effects, with impressive 59% and 106% peak increases in total neurite length and number of branching points, respectively, at a dose of 30 μM 5-HT. The exposure of VPT neurons to specific 5-HT receptor agonists 8-OH-DPAT (5-HT1A), CGS-12066A (5-HT1B), DOI (5-HT2A/2C), and m-CPBG (5-HT3), enhances primary neurite length and number of branching points with rank-order potency 5-HT1B > 5-HT2A/2C = 5-HT3 > 5-HT1A = vehicle. Trophic 5-HT effects on embryonic VPT neurons are thus much more prominent than previously reported, and can be mediated by multiple 5-HT receptor subtypes.