Various studies have demonstrated the unique regenerative properties of the olfactory nerve. In intact nerves, the neurons turn over constantly and following axonal injury near the mucosa the entire nerve cell degenerates and is replaced by a new neuron differentiating from a mucosal basal cell. In a study performed on the garfish olfactory nerve 3 populations of axons with a 7-fold difference in their elongation velocities were shown to invade successively the nerve. Following removal of the cell bodies a proximodistal degeneration of the isolated axons has been characterized.
The specific aims of the study are: 1) To compare the composition and the velocity of the transported cytoskeletal polypeptides in intact and growing nerves; 2) To study the role of the transported cytoskeletal proteins in determining the differences in the elongation velocities of phase I and III developing neurons. The rate of slow flow has been shown to be identical in all developing axons. However, Phase I axons are able to grow at their maximal possible velocity: The rate of slow flow. Phase III axons, on the contrary, are unable to reach the upper elongation velocities set by slow flow; 3) To analyze the rate and amount of individual slowly transported polypeptides in nerves isolated from their cell bodies and to determine the alterations of the cytoskeleton which might be responsible for the slow proximodistal degeneration. A three-fold increase in the rate of slow flow has been measured in axons severed from their cell bodies. Several hypotheses will be tested to explain these changes. From kinetic and morphological data, we have hypothesized that in the isolated stump, the slow degeneration is the result of a proximodistal depletion of cytoskeletal elements still moving along the distal segment but no longer released by the cell bodies. The collapse of the axon might be the result of several different mechanisms which will be investigated; 4) To determine the molecular properties of a regenerating myelinated axon (the garfish optic nerve). From the results it should be possible to compare the regenerative properties of a myelinated and an unmyelinated nerve without introducing phylogenetic factors inherent to the use of nerve preparations from different animals. Methods will include the one and two dimensional electrophoresis of polypeptides synthesized in the cell body and transported along the axon at slow rate in degenerating and regenerating neurons.
| Cancalon, P F (1988) Axonal transport in the garfish optic nerve: comparison with the olfactory system. J Neurochem 51:266-76 |
| Cancalon, P; Brady, S T; Lasek, R J (1988) Slow transport in a nerve with embryonic characteristics, the olfactory nerve. Brain Res 466:275-85 |
