Closed head injury induces up-regulation of ErbB-4 receptor at the site ofinjury

ErbB-4 receptor tyrosine kinase and its ligand neu differentiation factor ( NDF/neuregulin) are widely expressed in the brain. The closed head injury m odel was used to investigate the possible role of ErbB-4 receptor in neurod egeneration. It is demonstrated that levels of ErbB-4 are dramatically incr eased at the site of injury. Activated microglia/macrophages constitute the major population of cells with the highest receptor levels at the site of injury. In addition ErbB-4 expression after injury is elevated also in neur ons but not in astrocytes. Confocal microscopy analysis suggests that the h igh level of ErbB-4 protein in activated microglia/macrophages is probably due to phagocytosis of neuronal cells. These findings show for the first ti me that ErbB-4 receptors play a role in brain responses to head trauma. Ove rexpression of ErbB-4 receptors may be important for directing activated mi croglia/macrophages to the lesion site.