Ultrastructure of dissociated neurones from pupae of Spodoptera littoralis boisduval (Lepidoptera: Noctuidae) growing in culture

Growth properties of larval and adult locust neurons in primary cell culture

We developed a cell culture system for thoracic neurons of fifth instar or adult locusts (Locusta migratoria) in order to obtain maximum visualization of cellular morphology and direct access to the neurons for electrophysiological analysis. The dissociated neurons regenerated new neurites in a serum-free defined culture medium, in which they remained viable for up to 3 weeks. Viability of the cells was confirmed by intracellular recordings demonstrating active membrane properties and action potentials. While the morphology of the cultured neurons is distinct from their in vivo counterparts, they retained some cellular surface properties and markers related to transmitter metabolism. Two factors influencing cellular morphology in vitro were identified in Locusta: 1) the presence of a primary neurite stump, and 2) membrane contacts between cells. Dissociated neurons of the locust species Schistocerca gregaria grown in a hemolymph-enriched medium showed a marked reduction in branching patterns and a tenfold increase in neurite length compared to neurons growing in a medium without hemolymph. This culture system could prove useful for identifying the action of hemolymph-derived growth factors.

Differentiation of glial cells and neurite outgrowth obtained from embryonic locust central nervous system explants

Up to the present it has not been possible to obtain viable glial cells from dissociated insect nervous system cultures. We report here that the use of explant culture of locust embryo central nervous system (CNS) has been successful in allowing the proliferation of glial cells derived from glial precursors located at the periphery of the embryonic CNS. In such cultures, maintained for 3 months under specific conditions, 4 cell types at intermediate stages of differentiation can be distinguished around the explants after 2 weeks in vitro. They have been identified by scanning and transmission electron microscopy. The first type (stage 1) consists of flat epithelioid cells with an abundant and lucent cytoplasm containing little granular endoplasmic reticulum. These earliest cells subsequently develop flat ameboid prolongations forming an intermediate cell type (stage 2) which then differentiates into protuberant bipolar cells (stage 3) in which appear well-organized cisterns of granular endoplasmic reticulum. The last stage of differentiation (stage 4) is composed of multipolar cells with an electron-dense cytoplasm and well-defined processes characterized by the presence of ribosomes and granular endoplasmic reticulum. These (stage 4) differentiated cells resemble mature glial cells. In the same in vitro system, neurites, growing from neurons originating in the explants, form a network lying upon the glial cells and in close relationship with them. Neurites present growth cones and lack ribosomes and granular endoplasmic reticulum. We conclude that this model is a potentially useful system for use in in vitro studies of insect glia and neurite-glia interactions.