Neuronal nets and nerve cell interactions in vitro in insect systems

Summary The development of a synthetic medium that supports growth and differentiation of insect embryonic tissues afforded the possibility of studying the interactions between nerve and other cell types in long term cultures. The mechanical dissociation of embryonic nerve tissues results in survival of nerve cells but not of glial cells. The dissociated glial-free neurons produce a dense fibrillar network in the presence, but not in the absence, of foregut explants or other tissues from same donors. Nerve fiber bundles outgrowing from dissociated neurons enter foregut segments and establish synaptic connections with muscle cells. Foregut explants undergo differentiation and become contractile in long term cultures when innervated by dissociated nerve cells. The progressive deterioration of similar foregut tissues cultured alone contrasts with the excellent condition of innervated explants and suggests that this is due to trophic factors released by nerve fibers. The same in vitro systems provided the opportunity of studying the interaction between nerve fibers produced by the autonomic ingluvial ganglion, which adheres to the surface of the alimentary tract, and muscle cells. Multiple esophagus explants from cockroach embryos become interconnected by fibers emerging from ingluvial ganglia, when the explants are combined in vitro at short distance from each other. Muscle cells migrating from the esophagi line up on axons branching out in the medium, or form contractile ribbons which, in turn, establish connections with nerve fibers. The thigmotropism of muscle cells and strong affinity for nerve fibers reveal a new aspect of muscle cells-to-fibers interaction, amenable to further analysis in vitro. This work was supported in part by United States Public Health Service grant NS-03777 and grant GB-16330 X from the National Science Foundation