Calcium and chemotropic turning of nerve growth cones.

Cultured Xenopus spinal neurons exhibit chemotropic turning toward the source of neurotransmitters acetylcholine and glutamate. Here we review the experimental evidence that transmitter-induced turning of the growth cone is mediated by an influx of Ca2+, that a gradient of intracellular Ca2+ within the growth cone is responsible for the directional growth cone response, and that asymmetric filopodia formation precedes and is essential for the turning response.