How should patient exclusions be monitored in randomized controlled trials?: Jane Sicurella, Holly Bradley, Michael Gent, and Robin Roberts McMaster University, Hamilton, Ontario, Canada(p26)

Abstract

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. We removed (unilaterally) and reimplanted, with normal orientation (n = 23) or after 180° rotation (n = 23), that part of the pallium where the barrelfield is to develop. These operations were made at birth (P0), at P1 or at P3. Our aim was to know 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. Of group (i) 16 animals survived of which 14 killed between P26 and P29 could be analyzed. We operated 11 at P0 and 4 of these had a normal barrelfield, two a rotated one (by about 30°) with some barrels in odd positions, one a wildly disorganized one 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. The results indicate that 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) we cannot rule out the ingrowth of thalamic afferents into the implant. 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.