The Journal of Neuroscience, November 15, 1999, 19(22):9865-9877
Development of a Glia-Rich Axon-Sorting Zone in the Olfactory
Pathway of the Moth Manduca sexta
Wolfgang
Rössler,
Lynne A.
Oland,
Mark R.
Higgins,
John G.
Hildebrand, and
Leslie P.
Tolbert
ARL Division of Neurobiology, University of Arizona, Tucson,
Arizona 85721-0077
Olfactory receptor cells (ORCs) of a particular odor tuning are
dispersed in the olfactory epithelium, but their axons converge on
distinct glomeruli in primary olfactory centers. As a consequence, axon
associations must change to bring axons of ORCs with the same odor
specificity together. Studies in Manduca sexta have indicated that just before they enter the antennal lobe (AL), ORC axons
undergo extreme reorganization, finally entering the AL in fascicles
destined for subsets of glomeruli. This axon-sorting zone is heavily
populated by glial cells, and ORC axon growth cones often are in close
physical contact with the glia. In moths rendered glia deficient, ORC
axons fail to fasciculate in this region. Using propidium iodide to
label nuclei and 5-bromo-2'-deoxyuridine to monitor proliferation, we
found that the glia in the sorting zone arise from the AL, appearing
shortly after the first ORC axons arrive. Experimental removal of some
or all of the sensory innervation revealed that proliferation of
sorting-zone glia is triggered by ORC axons. A second set of glia
arises in the antenna and migrates along the antennal nerve toward the
brain, populating the nerve after the establishment of the sorting
zone. Development of this type of glial cell is independent of contact
of the ORC axons with their central targets. We conclude that the
sorting zone arises from CNS glia in response to ingrowth of ORC axons, and a critical number of glia must be present in the sorting zone for
axons to correctly establish new neighbor-neighbor associations.
Key words:
antennal lobe; sensory mapping; cell-cell interactions; olfactory glomeruli; glial cells; cell birth
Copyright © 1999 Society for Neuroscience 0270-6474/99/19229865-13$05.00/0
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