Reorganization of rat vibrissa barrelfield as studied by cortical lesioning on different postnatal days.

A small lesion was placed in the rat somatosensory vibrissa cortex on postnatal days (PND) 0, 5, 10, 14 or 20. At the age of three months, the animals were sacrificed and tangential sections of the somatosensory cortex were reacted for detection of succinic dehydrogenase or cytochrome oxidase activity to see if the lesion had produced a defect in the barrelfield. In animals of the groups of PND 0, 5 and 10, the entire barrelfield formed normally, but avoided the lesioned cortex. In a few cases, however, the lesion was found between rows of barrels but never between arcs of barrels. This latter type of result was seen only in the PND-0 group. In animals of the groups of PND 14 and 20, the lesion typically resulted in a defect in the barrelfield. It is concluded that the vibrissa cortex attains its final topographic specificity between day 10 and 14 postnatally. In view of the date of barrelfield formation in normal animals (postnatal day 5), it is thought that the barrelfield is subject to plastic reorganization for some days after its formation; at least for the period between postnatal days 5 and 10.