Dynamic aspects of amphibian neurite growth and the effects of an applied electric field.

The dynamics of growth of earliest spinal neurites from Xenopus laevis have been studied in vitro in the presence and absence of an applied d.c. electric field. Control and cathode-directed neurites grew at a rate of about 30 micron/h: growth of anodal-facing neurites was 8 times slower. Periods of arrested growth were common in cultured neurones; these lasted 2-3 times longer in an applied electric field. The likelihood and the severity of neurite reabsorption was greatest in neurites directed towards the anode. Many neurites turned to direct their growth towards the cathode. As this happened their rate of growth increased 2-3-fold. The electric field further shaped neurite morphology by increasing the number of filopodia at the growth cone and by increasing the number of cytoplasmic spines along a neurite shaft. The electric field induced an asymmetry in the distribution of these cytoplasmic projections; greater numbers being found on the cathodal-facing than on the anodal-facing side. Implications of these data for nerve growth in development and in regeneration are discussed.