Preliminary observations on ascidian and echinoderm neurons and neural explants in vitro

As part of a study on echinoderm and ascidian neural regeneration, attempts were made to develop a system for the maintenance of their neurons in vitro. It was found that neurons and neural tissue explants from the starfish, Asterias rubens, and the brittlestar, Ophiura ophiura, and explants from the brain of the ascidian, Ciona intestinalis, could be cultured for up to 6 weeks in a modified L15-based medium. Some cells extended axonal projections and produced growth cones under certain conditions. Attempts were made to stimulate neuron survival and outgrowth of echinoderm cultures with conditioned media containing growth factors or tissue extracts and with various substrates including extracellular matrix extracts from native tissue. Ascidian brain explants from both normal and regenerating animals were cultured in the standard conditions established for echinoderm tissue, with outgrowth being observed in 25% of explants. In these cultures labelling with bromodeoxyuridine suggested that regeneration continues in vitro, although results using substance P immunocytochemistry indicate neuronal differentiation may be impeded. These preliminary studies suggest it is possible to maintain adult echinoderm and ascidian neurons in vitro.