Growth rate analysis of neurites extended from triploid spinal cord explants.

Nerve fibers extending from spinal cord explants of triploid frog tadpoles were analyzed by time-lapse cinephotomicrography. The triploid neurites grew at a mean rate that seemed to reflect the increased chromosomal dosage and had maximal velocities that were several times greater than for diploid neurites. Concurrently, the time between alternating episodes of acceleration and deceleration in triploid neurite elongation phases was decreased. During a 24-h period, however, triploid neurites spent less time elongating with a net result of shorter travel distances than for diploid neurites. The data suggest that the genome is one level of nerve fiber growth control that can be manipulated by dosage alterations.