Removal and Reimplantation of the Parietal Cortex of Mice During the First Nine Days of Life: Consequences for the Barrelfield

Vibrissal follicles on one side of the mouse whiskerpad are topologically connected to barrels in the contralateral somatosensory cortex. Barre's develop from postnatal day 3 to 6. Recently, I have observed that the barrelfields still develop in pieces of parietal cortex that were removed and reimplanted, in the same place and with the original orientation, on the day of birth, or on postnatal days 1 or 3. Now, two questions were asked: (i) Can the barrelfield form and/or remain in place after interrupting thalamocortical connections at different ages (from birth to postnatal day 9)? (ii) How does the cortex behave, in terms of cellular layers, after the interruption of thalamocortical connections? To answer these questions the parietal cortex was removed and reimplanted in the same place with the original orientation, in 79 mice from a C3H strain. Fifty-one mice survived and were processed for histology. Their brains were cut coronally to facilitate the identification of the limits of the reimplanted cortex and of its cellular layering. In 29 cases the reimplanted cortex could be identified, and in 17 cases barrel-like structures had developed. The "barrelfields" were obtained from coronal sections of each piece of reimplanted cortex, by means of a computer program which permitted reconstructing these pieces of cortex and rotating them in space. In this way, barrel-like structures and "barrelfields" could be visualized as if obtained from sections made tangential to the parietal cortex. "Barrelfields" were found in pieces of cortex reimplanted at different ages up to postnatal day 9. Cortical layers appeared to be more close to normal in cases operated after postnatal day 5.