Journal of Neuroscience, Vol 13, 1292-1301, Copyright © 1993 by Society for Neuroscience
Role of substrate and calcium in neurite retraction of leech neurons following depolarization
MD Neely
Department of Pharmacology, Biocenter, University of Basel, Switzerland.
The aim of these experiments was to analyze how depolarization influences
neurite outgrowth in leech neurons and what role the substrate and Ca2+
play in this response. Neurons in culture were exposed to 60 mM
extracellular K+ for 30 min, which induced retraction of a subset of
neurites growing on extracellular matrix substrate (ECM), a response
comparable to that observed after electrical stimulation
(Grumbacher-Reinert and Nicholls, 1992). After normal medium had been
restored, the neurites continued to retract for about 1 hr to approximately
80% of the total starting neurite length. Retraction was reversible and
regrowth began after the cells had been in normal medium for about 3 hr.
Similar depolarization-induced neurite retraction was observed in both
Retzius and anterior pagoda cells. Retraction was inhibited by raised
extracellular Mg2+, suggesting a mechanism dependent on calcium. The effect
of high K+ on neurite outgrowth was also influenced by the substrate on
which the cells were plated. Cells plated on concanavalin A (ConA) did not
retract but continued to extend processes during exposure to high K+. To
understand the different behavior of cells grown on ECM and ConA, the
morphology of growth cones was analyzed by scanning electron microscopy.
The growth cones of cells grown on ECM and exposed to high K+ revealed
retraction of lamellipodial and filopodial structures. On ConA, however, no
differences were observed between growth cones of cells exposed to high K+
and those of control cells. These results demonstrate the importance of
substrate molecules in the responses of growth cones to depolarization and
therefore in the differentiation of neurons.