The Journal of Neuroscience, November 15, 1998, 18(22):9365-9375
Heterotopic Neurogenesis in a Rat with Cortical Heterotopia
Kevin S.
Lee,
Jennifer L.
Collins,
Matthew J.
Anzivino,
Eric A.
Frankel, and
Frank
Schottler
Departments of Neuroscience and Neurological Surgery, University of
Virginia, Charlottesville, Virginia 22908
Early cellular development was studied in the neocortex of the
tish rat. This neurological mutant is seizure-prone and displays cortical heterotopia similar to those observed in certain epileptic patients. The present study demonstrates that a single cortical preplate is formed in a typical superficial position of the developing tish neocortex. In contrast, two cortical plates are formed: one in a
normotopic position and a second in a heterotopic position in the
intermediate zone. As the normotopic cortical plate is formed, it
characteristically separates the subplate cells from the superficial
Cajal-Retzius cells. In contrast, the heterotopic cortical plate is not
intercalated between the preplate cells because of its deeper position
in the developing cortex. Cellular proliferation occurs in two zones of
the developing tish cortex. One proliferative zone is located in a
typical position in the ventricular/subventricular zone. A second
proliferative zone is located in a heterotopic position in the
superficial intermediate zone, i.e., between the two cortical plates.
This misplaced proliferative zone may contribute cells to both the
normotopic and heterotopic cortical plates. Taken together, these
findings indicate that misplaced cortical plate cells, but not preplate
cells, comprise the heterotopia of the tish cortex. Heterotopic
neurogenesis is an early developmental event that is initiated before
the migration of most cortical plate cells. It is concluded that
misplaced cellular proliferation, in addition to disturbed neuronal
migration, can play a key role in the formation of large cortical heterotopia.
Key words:
heterotopia; neurogenesis; cortical development; epilepsy; preplate; tish rat
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