Journal of Neuroscience, Vol 12, 96-103, Copyright © 1992 by Society for Neuroscience
Electrical activity increases growth cone calcium but fails to inhibit neurite outgrowth from rat sympathetic neurons
TK Garyantes and WG Regehr
Division of Biology, Caltech, Pasadena, California 91125.
Previous studies have shown that the growth of axons from both mouse dorsal
root ganglion neurons and Helisoma neurons is arrested when the cells are
electrically stimulated (Cohan and Kater, 1986; Fields et al., 1990a).
Furthermore, in the case of Helisoma neurons, this arrest has been
attributed to a rise in the calcium concentration in the growth cones
(Cohan et al., 1987). To test the generality of these results, we examined
the response of cultured rat superior cervical ganglion (SCG) neurons to
electrical stimulation and changes in cytoplasmic calcium. Suprathreshold
electrical stimulation of SCG neurons at 10 Hz by extracellular patch
electrodes for periods of up to 1 hr had no measurable effect on their rate
of growth. In agreement with previous studies, electrical stimulation was
accompanied by a rise in the internal calcium concentration: when measured
by the fluorescence of fura-2, growth cone calcium levels rose from about
100 nM to greater than 500 nM and then settled to a plateau value of about
350 nM. Despite this increase, however, growth of SCG neurons' processes
continued. Our results show that electrical activity is not a universal
signal for neurons to stop growing and that a rise in internal calcium does
not always arrest the migration of growth cones.