Figure 2.

Changes in GABA_A receptor subunit expression at P7 in V1 (Left) and S1 (Right) induced by a neonatal lesion of the LGN and of VB, respectively. Transverse sections from two representative cases were processed for immunoperoxidase staining, digitized with a high resolution camera, and color-coded according to the relative intensity of the immunoreactivity (from black and dark blue for background to blue, pink, red, orange, yellow, and white for maximal intensity). On the left, the boundaries of V1 (dotted lines) are clearly visible in the control hemisphere, owing to the increased (α1) or decreased (α2, α3, and α5) staining in the superficial layers relative to adjacent association areas. In the lesioned hemisphere, the increase in α2, α3, and α5 subunit expression in layers I–IV of V1 results in a uniform distribution across the hemisphere and therefore in the disappearance of areal boundaries. By contrast, the α1 subunit IR is reduced, but remains slightly more intense in layer III of V1 than in association areas. Notice the lack of change in the expression of GABA_A receptor subunits in cingulate cortex, hippocampus, and thalamus between the control and lesioned hemisphere. The lesion (five-point star) can be seen best with the α2 and α5 subunit IR, which label the LGN intensely at this age. On the right, the reciprocal regulation of the α1 and α5 subunit IR in S1 induced by a thalamic lesion involving VB is depicted. In the control hemisphere, barrels are clearly outlined by the intense α1 subunit IR in layers III–IV (each of the five patches visible between the dotted lines represents a barrel), whereas the α5 subunit is lacking in the corresponding locations. In the lesioned hemisphere, the α1 subunit staining is reduced and barrels cannot be seen any longer. Like in V1, the α5 subunit staining in the deprived S1 is increased to a level similar to adjacent areas, resulting in the disappearance of areal boundaries. (Scale bar = 1 mm.)