A new model of cortical plasticity using rat whisker barrel cortex

Each snout whisker of the rat is represented in the contralateral cortex by a group of cells which, because of the group shape, is called a barrel. The barrel cortex represents invariant somatotopy and function from animal to animal. This model has been used frequently in animals with whisker trimming or removal to study use-dependent cortical plasticity. We have developed a model more relevant to clinical brain injury. Imaging of the cortical intrinsic signal evoked by single movement was used to define the somatotopy of the barrel cortex. A single barrel was then destroyed by injection of 0.1 μl of kainic acid (KA). Repeated maps of the barrel cortex were then made using optical imaging techniques. The whisker projecting to the barrel, which had been destroyed, became represented in nearby cortex. Additionally, the surrounding barrels had increased size which, over a period of several months, returned towards control levels. The lesions were associated with increases in both GAP-43 and brain derived neurotrophic factor (BDNF). Further investigation of the role that GAP-43 might play in cortical organization was evaluated using GAP-43 knockout mice. These mice had dramatically disrupted cortical organization. Preliminary results indicate that injection of pluripotential neural precursor cells into the area of the destroyed barrel appeared to result in restoration of the somatotopic organization of the cortex. We conclude that the original changes in cortical organization are likely related to decrease in surround inhibition and that intracortical sprouting completes this process. The mechanisms of the effects seen with precursor injection remain uncertain but are under further investigation.