Ronald L. Meyer
Ph.D., California Institute of Technology, 1974
Development of nerve connections, nerve injury and regeneration
Email address: rlmeyer@uci.edu
During their development, neurons extend long axonal processes to synapse
on specific target neurons. This growth capacity is lost in the mature
central nervous system of mammals so that when an axon such as an optic
axon is severed, it can no longer regrow to restore functional
connections. We have found culture conditions, however, that allow adult
mouse optic axons to regenerate in vitro indicating that they
retain the inherent capacity to grow. Molecular comparison with embryonic
optic fibers reveal that adult fibers differ in intracellular axonal
proteins and cell surface receptors that regulate growth and mediate
interactions with the glial cells of the mature nervous system. A
specific axon-glia interactions may be the cause of regenerative failure
in adult mammals.
In contrast to mammals, optic fibers in adult goldfish will regrow until
connections are reestablished. Our pharmacological and
electrophysiological studies indicate that growth regulation involves
transmitter induced activity in the target cells. This target activity
may trigger growth stopping signals in the axons when connections are
reestablished. Using low level light imaging technology, we have been
able to observe fluorescently labeled axons regenerating in the living
fish to study the dynamics of this activity mediated growth regulation.
Selected Publications
Bates, C. and R.L. Meyer. 1993. The heavy neurofilament protein is
expressed in regenerating adult but not embryonic mammalian optic fibers
in vitro. Exp. Neurol. 119:249.
Meyer, R.L., J.A. Miotke and L.I. Benowitz. 1994. Injury induced
expression of GAP-43 in adult mouse retinal ganglion cells in vitro.
Neurosci. 63:591 .
Danks, A.M., P. Kim, Z. Wang and R.L. Meyer. 1994. Imaging of individual
normal and regenerating optic fibers in the brain of living adult
goldfish. J. Comp. Neurol. 345:253.