Propagation of voltage transients in arborized neurites of Retzius cells of the leech in culture.

Propagation of electrical signals is studied in Retzius cells of the leech in culture using voltage-sensitive fluorescent dyes at a spatial resolution of 8 x 8 microns 2 and 14 x 14 microns 2 and at a sampling interval of 0.12 ms. The neurons are stimulated by a microelectrode impaled in the soma. Action potentials of a half width of 2-3 ms are triggered close to the end of the primary neurite dissociated from the leech. They propagate back to the soma at invariant half width at a velocity of 50-230 microns/ms. They pervade extended aborized secondary neurites which are grown on extracellular matrix protein. Their width is enhanced up to a factor two. The velocity is around 100-150 microns/ms such that delays up to 3.5 ms are observed. Accordingly the neuritic trees are not isopotential. The features of propagation are found to be incompatible with passive spread.