2.2.1. 8-Hydroxydeoxyguanosine (8OHdG a Marker of Oxidative DNA Damage) Immunoreactivity

In the vehicle-sham group, 8OHdG immunoreactivity was weakly shown in the intact pyramidal cells of CA1-3 (Figure 4(Aa,Ca)). In the vehicle-IR group, 8OHdG immunoreactivity in the CA1 and 2/3 pyramidal cells was significantly increased (331% and 310% of the vehicle-sham group, respectively) at one day after IR (Figure 4(Ab,B,Cb,D)). At two days after IR, 8OHdG immunoreactivity in the CA1-3 pyramidal cells was decreased; at this point in time, many of the CA1-3 pyramidal cells were lost (dead) (Figure 4(Ac,B,Cc,D)). At five days after IR, 8OHdG immunoreactivity in the CA1-3 pyramidal cells was more significantly decreased: at this time, an extensive loss of the CA1-3 pyramidal cells occurred (Figure 4(Ad,B,Cd,D)). In the ATX-sham group, 8OHdG immunoreactivity in the pyramidal cells of CA1-3 was not different from that shown in the vehicle-sham group (Figure 4(Ae,B,Ce,D)). In the ATX-IR group, 8OHdG immunoreactivity in the CA1 and CA2/3 pyramidal cells was increased (278% and 226% of the ATX-sham group, respectively) at one day after IR, but the immunoreactivity was significantly lower (82% and 72% of the vehicle-IR group, respectively) than that in the vehicle-IR group (Figure 4(Af,B,Cf,D)). Thereafter, 8OHdG immunoreactivity in the CA1-3 pyramidal cells was slightly and gradually decreased with time (Figure 4(Ag,Ah,B,Cg,Ch,D)). This finding means that damage of DNA in the pyramidal cells of CA1-3 was significant at one day after severe IR, and ATX could attenuate the DNA damage induced by severe IR.

**Figure 4.** (**A**,**C**) Representative photographs of 8OHdG immunohistochemistry in CA1 (**A**) and CA2/3 (**C**) of the vehicle-treated (left column) and ATX-treated (right column) groups in sham (**Aa**,**Ca**,**Ae**,**Ce**), and on day 1 (**Ab**,**Cb**,**Af**,**Cf**), day 2 (**Ac**,**Cc**,**Ag**,**Cg**), and day 5 (**Ad**,**Cd**,**Ah**,**Ch**) after IR. In the vehicle-IR group, 8OHdG immunoreactivity in CA1-3 pyramidal cells (black asterisks in (**Ab**,**Cb**)) is significantly increased at one day after IR. However, in the ATX-IR group, 8OHdG immunoreactivity in CA1-3 pyramidal cells (white asterisks in (**Af**,**Cf**)) at one day after IR is significantly low when compared with the vehicle-IR group. Note that, at five days after IR, 8OHdG immunoreactivity is very weak (arrows in (**Ad**,**Cd**)) in the vehicle-IR group due to death of pyramidal cells. Scale bar = 60 μm; (**B**,**D**) ROD of 8OHdG immunoreactivity in CA1 (**B**) and CA2/3 (**D**). The bars indicate the means ± SEM (*n* = 7, respectively; \* *p* < 0.05 vs. corresponding sham group, # *p* < 0.05 vs. vehicle-IR group).
