EMBRYONIC XENOPUS NEURITES INTEGRATE AND RESPOND TO SIMULTANEOUS ELECTRICAL AND ADHESIVE GUIDANCE CUES

Nerve cells detect and respond to multiple extrinsic guidance cues dur ing development and regeneration using a motile growth cone. Navigatio nal decisions may be required of the growth cone when different guidan ce cues are encountered simultaneously. We have tested the relative po tencies of two opposing cues by presenting Xenopus spinal cord nerve c ells growing on a micropatterned laminin culture substratum with an or thogonal DC electric field. Substrata composed of repeating 25-mu m la minin tracks and spaces failed to influence the position of neuritogen esis from nerve cell soma. Once established, however, growth cone move ment was constrained by laminin tracks such that neurites of 65% of ce lls were aligned after 5 h in vitro. Two hours after the application o f a 100-140 mV/mm DC field the majority of cells remained aligned with the laminin tracks. Around 70% of Xenopus neurites normally orient ca thodally on homogenous laminin substrata; therefore the galvanotropic response was impeded by prior exposure to a patterned laminin substrat e. However, a proportion of aligned neurites did orient cathodally and evidence of a response to both directional cues was even found within the same cell. Video-enhanced contrast, differential interference con trast (VEC-DIC) microscopy was used to examine the detailed behavior o f growth cones on micropatterned laminin substrata, The present study has demonstrated that growth cones can detect and integrate at least t wo morphogenetic guidance cues simultaneously. The strength of the gal vanotropic response in Xenopus growth cones, however, was often insuff icient to override established adhesive guidance in this model system. (C) 1996 Academic Press, Inc.