Journal of Neuroscience, Vol 9, 1414-1423, Copyright © 1989 by Society for Neuroscience
Impulse blockade by intraocular tetrodotoxin during optic regeneration in goldfish: HRP-EM evidence that the formation of normal numbers of optic synapses and the elimination of exuberant optic fibers is activity independent
WP Hayes and RL Meyer
Developmental Biology Center, University of California, Irvine 92717.
Optic fibers and synapses labeled with HRP were counted in the primary
optic innervation layer of tectum after continuously blocking visual
impulse activity with TTX during regeneration. Normal numbers of optic and
nonoptic fibers and synapses were found at both 30 and 60 d, and key
ultrastructural features of optic afferents such as fiber fasciculation,
myelination, terminal clustering, synaptogenesis onto different classes of
postsynaptic targets and general morphology were not notably affected by
impulse blockade. These findings indicate that during regeneration the
normal proliferation and elimination of optic fibers and the formation of
normal numbers of optic synapses are not regulated by activity and are
consistent with a pattern formation role for impulse activity rather than a
trophic one.