Development of piriform cortex interhemispheric connections via the anterior commissure: progressive and regressive strategies
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The anterior commissure (AC) is a phylogenetically conserved inter-hemispheric connection found among vertebrates with bilateral symmetry. The AC connects predominantly olfactory areas but many aspects of its development and structure are unknown. To fill this gap, we investigated the embryonic and postnatal development of the AC by tracing axons with DiI and the piggyback transposon multicolor system. With this strategy, we show that axon growth during establishment of the AC follows a strictly regulated timeline of events that include waiting periods (“regressive strategies”) as well as periods of active axon outgrowth (“progressive strategies”). We also provide evidence that these processes may be regulated in the midline via overexpression of chondroitin sulfate proteoglycans. Additionally, we demonstrate that the ipsi- and contralateral innervation of piriform cortex occurs simultaneously. Morphologically, we found that 20% of axons were myelinated by postnatal day (P) 22, in a process that occurred fundamentally around P14. By immunohistochemistry, we described the presence of glial cells and two new subtypes of neurons: one expressing a calretinin (CR)−/MAP2+ phenotype, distributed homogeneously inside the AC; and the other expressing a CR+/MAP2+ phenotype that lies beneath the bed nucleus of the stria terminalis. Our results are consistent with the notion that the AC follows a strictly regulated program during the embryonic and postnatal development similarly to other distal targeting axonal tracts.
KeywordsAnterior commissure Piriform cortex Axons growth Embryonic development Versican Myelination PiggyBac
We thank Christine Kaliszewski for technical assistance with EM, Jaime Grutzendler for the CNPase antibody, and the very helpful discussions with all members of the Greer Lab.
Supported in part by NIH NIDCD DC013791, DC015438, and DC012441 to CAG.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All animal procedures were approved by Yale University Animal Care and Use Committee.
This manuscript has been approved by all co-authors and agreed with the submission of the manuscript to Brain Structure and Function.
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