Comparison of the regenerative capacity of the cerebral cortex in neonatal mice following traumatic or ischemic injury

We have previously shown that the murine medial frontal cortex (MFC) regenerates, anatomically and functionally, when it is removed by aspiration during the early postnatal period. The cells that repopulate the aspirated MFC arise from progenitor cells in the lateral ventricles that migrate into the lesion site rather than to their normal target, the olfactory bulbs. The possibility that the postnatal brain is capable of large-scale neuronal replacement has obvious implications for pathological conditions that result in large areas of cell death, however, this has not been directly addressed. In the present study we assessed whether the neonatal MFC was equally capable of regeneration when it is damaged using a clinically relevant model of injury - stroke. We also set out to identify the molecular factors that affect regeneration following brain injury. We adopted a model of stroke for use in the neonatal mouse that is relatively non-invasive and very reliable in producing an area of injury identical to that provided by the aspiration method. In this model, the photoreactive dye, rose bengal, was injected systemically (50 mg/kg; i.p) on postnatal day (PD) 7 and the MFC was irradiated through the intact skull with laser light (532 nm; 20 mW; 90 s). This reaction causes platelets to aggregate and a thrombus to form in the laser-exposed blood vessels. The regenerative capacity of the MFC in these animals was compared to that of animals experiencing aspiration lesions on PD7. All animals were administered BrdU (50 mg/kg once daily for 2 or 3 days post-lesion) and were allowed to survive from 2 to 8 days post-lesion, after which the brains were removed for anatomical evaluation. The number and phenotypes of cells occupying the aspiration and ischemic lesion area were compared using BrdU, and neuron- and glia-specific antibodies. A proteomics approach was used to investigate the molecular factores affecting regeneration, where we compared the proteins expressed in and around the lesion area from both modes of injury using two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). We found that, unlike aspiration lesions, regeneration of the MFC did not occur following damage induced by focal ischemia. Using 2D-PAGE we were able to resolve and compare the expression of over 1200 proteins in the lesion area; 174 that were unique to aspiration-injury, and 100 that were unique to ischemic injury. The characterization of these proteins will allow us to identify those factors that facilitate or prevent regeneration following injury induced in the neonatal brain.