Computer-assisted analysis of particulate axoplasmic flow in organized CNS tissue cultures

Using organized nervous system tissue cultures of embryonic mouse spinal cord, time-lapse motion pictures of intra-axonal particle movements were made using Nomarski optics. The paths of 272 particles were followed and analyzed using digital computer methods. Particles had a bidirectional saltatory motility with net anterograde and retrograde velocities which were shown to be the same (about 1 micron per second). When anterograde moving and retrograde moving particles were analyzed separately for anterograde and retrograde saltations, the velocities of saltation in the direction of net movement were found to be 1.5 times greater than saltations against the direction of net movement. These differences were statistically significant. In addition, it was shown that there were regions within the axon where variations in particle motion were similar from particle to particle as they passed, and that more disturbed motion was found to occur near intra-axonal objects which were judged to be mitochondria. No decrease of particle velocity was noted in regions away from mitochondria nor was in increase in velocity noted near them. Computer-drawn particle plots illustrate the various facets of particle motion.