Am. Rajnicek et al., THE DIRECTION OF NEURITE GROWTH IN A WEAK DC ELECTRIC-FIELD DEPENDS ON THE SUBSTRATUM - CONTRIBUTIONS OF ADHESIVITY AND NET SURFACE-CHARGE, Developmental biology (Print), 203(2), 1998, pp. 412-423
We investigated the influence of the growth surface on the direction o
f Xenopus spinal neurite growth in the presence of a de electric field
of physiological magnitude. The direction of galvanotropism was deter
mined by the substratum; neurites grew toward the negative electrode (
cathode) on untreated Falcon tissue culture plastic or on laminin subs
trata, which are negatively charged, but neurites growing on polylysin
e, which is positively charged, turned toward the positive electrode (
anode). Growth was oriented randomly on all substrata without an elect
ric field. We tested the hypothesis that the charge of the growth surf
ace was responsible for reversed galvanotropism on polylysine by growi
ng neurons on tissue culture dishes with different net surface charges
. Although neurites grew cathodally on both Plastek substrata, the fre
quency of anodal turning was greater on dishes with a net positive cha
rge (Plastek C) than on those with a net negative charge (Plastek M).
The charge of the growth surface therefore influenced the frequency of
anodal galvanotropism but a reversal in surface charge was insufficie
nt to reverse galvanotropism completely, possibly because of differenc
es in the relative magnitude of the substratum charge densities. The i
nfluence of substratum adhesion on galvanotropism was considered by gr
owing neurites on a range of polylysine concentrations. Growth cone to
substratum adhesivity was measured using a blasting assay. Adhesivity
and the frequency of anodal turning were graded over the range of pol
ylysine concentrations (0 = 0.1 < 1 < 10 = 100 mu g/ml). The direction
of neurite growth in an electric field is therefore influenced by bot
h substratum charge and growth cone-to-substratum adhesivity. These da
ta are consistent with the idea that spatial or temporal variation in
the expression of adhesion molecules in embryos may interact with natu
rally occurring electric fields to enhance growth cone pathfinding. (C
) 1998 Academic Press.