| Abstract: | Dorsal root ganglion neurons in culture proceed through a series of shape changes before growing nerve fibers. These shape changes involve: attachment to the substratum, extension of filopodia, and spreading of part of the cell to form broad lamellipodia. With the formation of lamellipodia, neurons adhere firmly to the substratum and retrogradely transport lectins (concanavalin A, wheat germ agglutinin) on their surfaces. In unspread neurons concanavalin A, but not wheat germ agglutinin, rapidly stimulates lamellipodium formation and neuron-substratum adhesion. Neurons treated with concanavalin A also have more, branched nerve fibers than untreated neurons, but otherwise appear similar. These effects of concanavalin A are concentration dependent, blocked by alpha-methyl-D-mannoside (100 mM), and are accompanied by receptor redistribution. Stimulation of lamellipodium extension by concanavalin A is inhibited by low temperature (4 degrees C), 2,4-dinitrophenol (0.2 mM), cytochalasin D (4 microM), or trifluoperazine (10 microM), but not by cycloheximide (360 microM) or colchicine (12.5 microM). Attachment of neurons to the culture substratum was affected little by these treatments. These results indicate differences in the neuron's metabolic requirements for simple attachment to the substratum and the early phases of nerve fiber growth. Moreover, they suggest a convenient system in which to study the cellular and biochemical events of rapid nerve fiber outgrowth in primary neuronal cultures. |
