Possible regeneration of rat medial frontal cortex following neonatal frontal lesions.

The experiments described here show that the cavity left by midline frontal cortex removals at 10 days of age (P10) fills in with neural tissue. Similar changes are not found at earlier and later ages. This neuronal filling is blocked by prior pretreatment by administration of Bromodeoxyuridine (BrdU) on embryonic day 13. Administration of BrdU following the P10 lesion does not interfere with regrowth. Subsequent immunohistochemical staining for BrdU demonstrates the regrown area to be composed of newly generated cells. which include pyramidal and nonpyramidal neurons. Injections of a retrograde tracer into the striatum or posterior parietal cortex shows that the new neurons have connections similar to those of undamaged brains. The regrowth of this tissue is correlated with recovery of function in a test of forelimb use. Thus, the mammalian brain, during some privileged postnatal stages of growth. is capable of extensive reorganization that includes regeneration of lost neurons. These results are discussed in relation to the proximity of the lesion to the stem cells in the lateral ventricle and their postnatal migrational activities.