Journal of Neuroscience, Vol 8, 3584-3597, Copyright © 1988 by Society for Neuroscience
The pattern of dendritic sprouting and retraction induced by axotomy of lamprey central neurons
GF Hall and MJ Cohen
Department of Biology, Yale University, New Haven, Connecticut 06511.
We have investigated some of the factors controlling the distribution of
axonal and dendritic sprouting following axotomy of a subset of Muller
giant interneurons (anterior bulbar cells or ABCs) in the hindbrain of the
larval sea lamprey (Petromyzon marinus). Sprouts originated from different
sites in the cell depending on the distance of the axonal lesion from the
soma. When the axon was cut close to the soma (within 500 microns), the
dendritic tips sprouted profusely, whereas the proximal axon stump showed
few sprouts and frequently disappeared entirely. Axotomy further from the
soma (1000-1400 microns) resulted in less sprouting from the dendrites and
more from the axon stump, with the total amount of dendritic plus axonal
sprouting remaining constant. Axotomy at sites distant from the soma (1 cm
or more) did not result in dendritic sprouting. No sprouts were ever
observed emerging from the soma proper or from the axon stump except at the
lesion site. Neuritic sprouts from dendrites and axon were similar in their
gross morphology. Sprouts resembled axons rather than dendrites whatever
their sites of origin; they followed linear, rostrocaudally oriented paths
in the "basal plate" region of the hindbrain. Dendritic and axonal sprouts
grew both rostrally and caudally within the brain. Either "close" or
"distant" axotomy resulted in the retraction of the dendritic tree and of
both dendritic and axonal sprouts by several months postaxotomy. Reaxotomy
close to the soma 30 d after a distant axotomy accelerated the onset of
this evoked dendritic retraction. Reaxotomy close to the soma also induced
sprouting significantly sooner than did close axotomy alone. These results
suggest that axotomy close to the soma causes axonal regeneration to be
shunted into ectopic locations at the dendritic tips. The emerging sprouts
then follow guidance cues appropriate for regenerating ABC axons.