Cellular dynamics of macrophages and microglial cells in reaction to stab wounds in rat cerebral cortex

To examine the cellular dynamics of macrophages and microglial cells in response to cerebral injury, we studied the brain adjacent to cortical stab wounds in young adult rats. Brains were obtained 30 min after intravenous infusion of bromodeoxyuridine (BrdU) on one day (day 1) to 28 days (day 28) after wounding. Brain sections were double-labelled immunohistochemically for monocyte/macrophage antigen EDI and for BrdU. ED1-positive (ED1(+)) cells were classified morphologically into two groups, ED1(+)L and ED1(+)S cells, representing macrophages and microglial cells, respectively. ED1(+)L cells appeared on day 1 after wounding and rapidly increased in number to reach a maximum on day 3, but quickly disappeared by day 5. ED1(+)S cells also appeared on day 1, but the increase in number was slower, reaching a maximum only on day 7. ED1(+)L cells were all negative for BrdU, but some ED1(+)S cells were stained for BrdU, evidence of proliferation. The present investigation demonstrated different cellular dynamics for macrophages and microglial cells responding to a stab wound, and also indicated differing sources for the two cell type. It may be possible to prevent the accumulation of these cells which are harmful to the brain in reducing the damage suffered.