REMOVAL AND REIMPLANTATION OF THE PARIETAL CORTEX OF THE NEONATAL MOUSE - CONSEQUENCES FOR THE BARRELFIELD

The barrelfield, i.e., the cortical representation of the contralateral whiskerpad, develops in the mouse between postnatal days 4 and 6 (P4 and P6). The pattern of barrels in the barrelfield is dependent on that of the whiskers on the whiskerpad. The part of the pallium where the barrelfield is to develop was removed (unilaterally) and reimplanted, with normal orientation (n = 23) or after 180.degree. rotation (n = 23). These operations were made at birth (P0), at P1 or at P3. Whether a homeomorphic representation of the periphery would be established, by regeneration or by retarded growth of surviving thalamic fibers into the cortex, and if so, whether it could be modified in its orientation was studied. Of group (i) 16 animals survived of which 14, killed between P26 and P29, could be analyzed. At P0, 11 were operated and 4 of these had a normal barrelfield, 2 a rotated 1 (by .apprx. 30.degree.) with some barrels in odd positions, one a wildly disorganized 1 and 4 no barrels at all. Three mice operated at P3 presented a normal barrelfield. In group (ii)operated at PO, the 17 survivors, killed between P13 and P68, had no barrels. A homeomorphic representation of the periphery may be established in the somatosensory cortex after an early, complete and massive interruption not only of all its afferent and efferent fibers, but also of its vascularization. With respect to animals of group (ii), the ingrowth of thalamic afferents into the implant cannot be ruled out. The absence of barrels here may point to the existence of a certain degree of target-specificity of thalamic fibers which would fail to induce the formation of barrels when confronted with a wrong domain of parietal cortex.