Table 1. Experimental set up.

Groups	Exposure
Juvenile mice
Group 1	Vehicle control (0.9% saline)
Group 2	ZnO NPs (5 mg per kg b. wt.)
Group 3	ZnO NPs (50 mg per kg b. wt.)
Adult mice
Group 4	Vehicle control (0.9% saline)
Group 5	ZnO NPs (5 mg per kg b. wt.)
Group 6	ZnO NPs (50 mg per kg b. wt.)
Aged mice
Group 7	Vehicle control (0.9% saline)
Group 8	ZnO NPs (5 mg per kg b. wt.)
Group 9	ZnO NPs (50 mg per kg b. wt.)