5A). not induce any of these changes. There were also significant numbers of neurons in the recovering cortical tissue. In the recovery region, reactive astrocytes radially extended processes, which appeared to influence the shapes of neuronal nuclei. The proximal reactive astrocytes also formed a cell layer, which appeared to serve as a protective barrier, blocking the spread of IgG deposition and migration of microglia from the lesion core to surrounding tissue. The recovery was preceded by perilesional accumulation of leukocytes expressing vascular endothelial growth factor. These results suggest that under intact skull conditions, focal brain injury is followed by perilesional reactive astrocyte activities that foster cortical tissue protection and recovery. = 3 at each time point), ** P 0.01, * P 0.05 ANOVA and Dunnetts test for multiple comparisons with 0.5 days. Reactive astrocyte subtypes following photo injury The structures of reactive astrocytes following photo injury were characterized by GFAP immunostaining, focusing on three regions showing marked differences, i.e., the proximal region (PR), the Betaxolol hydrochloride distal region (DR), and the normal region (NR) on day 12 (Fig. 5A). As shown at higher magnification in Fig. 5B (left), the Betaxolol hydrochloride PR included a dense layer of GFAP-positive fibers radially extending from the LC, and these were morphologically identical to the GFAP fibers found in the remodeling perilesional region on day 28 (Fig. 3Cc). In addition, there were generally distinct GFAP-positive structures extending from the PR into the LC, as indicated by the arrow in the figure. Similar extensions of GFAP-positive structures can be seen in the micrograph in Fig. 3A (GFAP-positive structure Betaxolol hydrochloride in LC on day 10), and also in Figs. 7B (arrow) and 8B (arrow). These extensions presumably reflect invasion of the LC by PR reactive astrocytes and may be one of the mechanisms of Rabbit Polyclonal to TNF12 perilesional broadening. A similar migration of reactive astrocytes into the lesion site was demonstrated in a spinal cord injury model and proposed as an important mechanism for scar formation (Hsu stab wound injury have recently been shown to be capable of generating a neuronal phenotype when transferred to tissue culture conditions (Buffo em et al. /em , 2008). Therefore, it is possible that some of the NeuN-positive cells in the expanded PR volume were newly generated neurons, and that our BrdU labeling protocols were inadequate. Further studies are planned to investigate this interesting possibility. Previous reviews suggested the existence of two structurally different post-lesional reactive astrocyte subtypes in areas proximal and distal to wounds, as seen here (Ridet em et al. /em , 1997; Sofroniew, 2009). It was suggested that the proximal reactive astrocytes develop scar tissue, which consists of gliotic tissue at the interface between lesion and normal tissue, whereas our findings indicating both the proximal astrocytes and neurons in the tissue expanding into the injury void (Fig. 3) suggested a novel tissue regenerative function of this reactive astrocyte subtype prior to scar formation. Other studies have demonstrated a number of degenerative functions of reactive astrocytes following different types of insult (Merrill, 1992; Rosenberg em et al. /em , 2001; Seiffert em et al. /em , 2004). The outcomes of injury-related changes are obviously complex and dependent on the model used. The DR reactive astrocytes may support the survival of neurons in ways different from the above. For example, non-proliferative reactive astrocytes, similar to the DR reactive astrocytes, are neuroprotective due to increased glutamate uptake (Beurrier em et al. /em , 2010), as well as producing a greater nutrient supply to neurons (Escartin em et al. /em , 2007). Thus, this reactive astrocyte subtype would be beneficial for neuronal survival, especially under excitotoxic conditions, such as would exist in the DR after injury, due to spillover of glutamate and K+ from the LC. Indeed, similar non-proliferating reactive astrocytes have been shown to be widespread in excitotoxicity models, such as kainite lesions (Mitchell em et al. /em , 1993). Thus, one of the anticipated protective functions of the DR reactive astrocytes is to attenuate the excitotoxic environment for neuronal survival. The degenerative mechanism underlying photo injury remains to be determined; however, the experiment detailed in Supplemental Information 2 suggested that light exposure likely caused tissue damage by moderate heating. As the heat stress associated with raising the core body temperature to 40C C 43C causes serious brain damage in mice (Sminia et al., 1994), this moderate focal heating by light exposure is thought to be sufficient to create localized.