Effects of nano and conventional Zinc Oxide on anxiety-like behavior in male rats

Objectives: Current drug therapies for psychological disorders, such as anxiety, are not as effective as expected, and it has been shown that zinc supplements, such as zinc oxide (ZnO), can influence anxiety. ZnO nanoparticles (ZnO NPs) are among the most used nanomaterials produced and applied in many products. Materials and Methods: This study investigated the effects of ZnO NPs in comparison with conventional ZnO (cZnO) on anxiety-like behaviors. Adult male Wistar rats were divided into groups: Control (receiving saline 0.9%), ZnO NPs (5, 10, 20 mg/kg), and cZnO (5, 10, 20 mg/kg). All drugs were dispersed in saline 0.9%, and 30 minutes after intraperitoneal (i.p.) injection of drugs, elevated plus maze apparatus was used to evaluate anxiety. Results: ZnO NPs (5 mg/kg) and cZnO (10 and 20 mg/kg) significantly increased the percentage of time spent in open arm (open arm time % OAT) compared with the control group (P < 0.05). This indicates the anxiolytic effect of such components; in addition, ZnO NPs (20 mg/kg) reduced locomotor activity (P < 0.05). Serum zinc concentration increased by both anxiolytic dose of components (from 1.75 +/- 1.07 (mg/l) in control group to 5.31 +/- 0.53 (mg/l) in ZnO NPs (5 mg/kg) and 10.38 +/- 0.90 (mg/l) in cZnO (10 mg/kg) groups). Also, all doses increased serum pH (from 7.3 +/- 0.05 in control group to 8.1 +/- 0.05 in ZnO NPs (5 mg/kg) and 8.05 +/- 0.01 in cZnO (10 mg/kg) groups and kept them constant after 24 hours. Conclusion: Results indicate that the anxiolytic effect of ZnO NPs is much higher than its conventional form, but the introduction of ZnO NPs, as a new drug for treatment of anxiety disorder, needs further investigations.