ELECTRIC FIELD-DIRECTED GROWTH AND BRANCHING OF CULTURED FROG NERVES - EFFECTS OF AMINOGLYCOSIDES AND POLYCATIONS

The direction and rate of earliest nerve growth are critical determina nts of neuronal architecture, One extrinsic cue that influences these parameters is a small direct current electric field, although the unde rlying mechanisms are unclear, We have studied the orientation, rate o f growth, and branching behavior of embryonic Xenopus spinal neurites exposed to aminoglycoside antibiotics, to raised external cations, to applied direct current electric fields, and to combinations of these t reatments, Field-induced cathodal turning and cathodal branching of ne urites were blocked by the aminoglycosides, by raised extracellular ca lcium ([Ca2+](0)) and by raised extracellular magnesium ([Mg2+](0)). N eomycin together with high external Ca2+, by contrast, induced a rever sal in the polarity of turning and branching, with neurites reorientin g and branching more frequently anodally. Aminoglycosides decreased ne urite growth rates, and for neomycin this was partially reversed by hi gh external Ca2+. Raised [Ca2+](0) alone but not raised [Mg2+](0) alte red growth rates in a field-strength dependent manner. Modulation of m embrane surface charge may underlie altered galvanotropic orientation and branching. Such an effect is insufficient to explain the changes i n growth rates, which may result from additional perturbations to Ca2 influx and inositol phospholipid metabolism. (C) 1995 John Wiley and Sons, Inc.