Effects of Nanoparticle and Conventional-Size Suspensions of MgO and ZnO on Recognition Memory in Mice

Abstract

We examined the effects of nano forms of magnesium oxide (nano-MgO) and zinc oxide (nano-ZnO) on recognition memory in mice and also the levels of Mg2+ and Zn2+ ions in the blood serum and cerebral tissue of the animals. Adult male NMRI mice were divided into control groups and those treated with suspensions of the above nano- and also conventional forms of the above oxides (1 and 5 mg/kg). The components were injected i.p. once in the test day or three times during the training days. The novel object recognition test was used for evaluating the memory. The levels of Mg2+and Zn2+ were measured in the serum and brain hemispheres of animals at the end of the test. Nano-MgO (5 mg/kg) improved recognition memory more markedly than conv-MgO injection on the test day and during the training sessions, with increasing Mg2+ levels in the brain hemispheres. Nano- and conv-ZnO increased recognition memory only at administration in the test day, while the Zn2+ level in the brain hemispheres significantly increased in the presence of all doses of conv-ZnO and nano-ZnO injected in the test day and during the training session. In the serum, the Zn2+ concentration significantly increased after injections of conv-ZnO or nano-ZnO (1 and 5 mg/kg) in comparison with that in the saline group injected in the test day. Thus, the ability of nano-MgO and nano-ZnO to increase the levels of Mg2+ and Zn2+ in the brain hemispheres is greater than that of their conventional forms, and this factor may affect results of the recognition memory test.