Nerve Regeneration in Vitro: Comparative Effects of Direct and Induced Current and NGF. Appendix.

Abstract : This investigation focused on the response of sensory neurons (DRG) obtained from young (8 day) and older (14 day) chick embryos and 15 day old rat fetuses to low levels of direct (DC) or induced (PEMF) current or NGF. Direct current (10 nA) was applied continuously for 3 days through tantalum electrodes immersed in the media; current was induced by exposing cultures to pulsed electromagnetic fields (PEMF) using a single pulse, 72 Hz, 12 hrs/day for 2 days with coils supplied by Electrobiology Inc. The data presented in the Appendix indicates the following: in 8 day cultures, the growth response obtained with NGF, PEMF or DC was significantly increased over controls at 3 days and this was maintained only with NGF or DC by 6 days. PEMF effects were correlated with current density only when the coils were oriented vertically. Significantly-increased protein content and incorporation of 3H-proline/ganglia paralleled the increased growth response obtained with DC. In older (14 day) DRG, neurite outgrowth was enhanced only with DC. The growth response in 15 day fetal DRG was not influenced by PEMF or DC; only NGF stimulated growth. Neurophysiological studies found the resting potential of the DRG neurons to range from 30-60 mV; they exhibited overshooting potentials upon intracellular stimulation. Equivocal results were found in membrane potential changes when DC was applied.