*3.3. E*ff*ects on AChE Activity*

AChE decreases acetylcholine level and alleviates disease symptoms associated with the progressive loss of cholinergic function in AD [36]. Our results demonstrate that zebrafish subjected to Sco treatment exhibited increased AChE activity in the brain (*p* < 0.0001) as compared to the control group (Figure 5A). REO treatment significantly reduced AChE activity (*p* < 0.0001) in a dose-dependent manner, as compared to the Sco-treated group (Figure 5A). Thus, REO revealed an anti-AChE profile [19], which parallels improving memory parameters in zebrafish, as observed in NTT and Y-maze tests.

#### *3.4. E*ff*ects on SOD, CAT, and GPX Specific Activities*

Administration of Sco decreased the SOD specific activity (*p*<0.01) (Figure 5B) in the zebrafish brain as compared to the control group, suggesting the augmentation in oxidative stress. REO significantly increase (*p* < 0.0001) (Figure 5B) the specific activity of SOD in the Sco-treated fish showing its promising antioxidant potential. CAT specific activity significantly decreased (*p* < 0.01) (Figure 5C) in Sco-exposed zebrafish as compared to the control group, whereas the administration of REO led to a significant increase (*p* < 0.0001) (Figure 5C) of CAT activity in the Sco-treated fish, supporting its antioxidant action. Moreover, GPX specific activity upon Sco administration leads to a significant decrease (*p* < 0.0001) (Figure 5D) as compared to the control group. REO treatment significantly restored this dramatic decrease in the Sco-treated fish showing prompt antioxidant potential. The results sugges<sup>t</sup> that REO exhibits neuroprotective effects against oxidative stress, which is correlated with previously antioxidant properties of REO. Selmi et al. [37] reported that REO administration has significantly protected against alloxan-induced hepatic and renal oxidative stress due to the presence of phenolic and flavonoids compounds. Takayama et al. [38] demonstrated the antioxidant activity of REO against gastric damage induced by absolute ethanol in the rat. El-Hadary et al. [39] demonstrated antioxidant properties of REO against carbon tetrachloride-induced hepatotoxicity in rats mediated by phenolic compounds. Our results in accordance with the literature, suggesting the ability of REO to control brain oxidative damages by restoring the antioxidant enzyme activities.
