Pregerminated Brown Rice Enhanced NMDA Receptor/CaMKIIα Signaling in the Frontal Cortex of Mice

We previously reported that the continuous feeding of mice with pellets of pregerminated brown rice (PGBR; Hatsuga genmai in Japanese) enhances their spatial learning. Here, we show the possible relationships of the enhancement of learning and memory with the glutamatergic system in the brain of PGBR-pellet-fed mice. The enhancement of learning and memory in the novel object recognition and Y-maze tests after 28-day-feeding of PGBR pellets was inhibited by dizocilpine (10 μg/kg s.c.), an N-methyl-D-aspartate (NMDA) receptor antagonist, whereas the extracellular glutamate level and the glutamate content were not affected in the frontal cortex and hippocampus. In the frontal cortex of mice fed PGBR pellets, the phosphorylation of calcium calmodulin kinase IIα (CaMKIIα), one of the important events after NMDA receptor activation, was facilitated compared with that of mice fed control pellets. This facilitation was inhibited by dizocilpine (10 μg/kg s.c.), whereas the phosphorylation of extracellular signal-regulated protein kinases (ERKs), another index of memory formation was not affected by PGBR pellets. On the other hand, in the hippocampus, there was no significant difference in the phosphorylation of CaMKIIα and ERKs between the control and PGBR pellets-fed mice. Taken together, these results suggest that PGBR enhances the NMDA receptor/CaMKIIα signaling in the frontal cortex, leading to enhanced learning and memory in mice. Materials and Methods Animals and foods Five-week-old male ICR mice (Nihon SLC Co., Shizuoka, Japan) were purchased. We received the mice from 11h00 and 13h00, then put them into the home cage and gave adequate food pellets (day 0). The animals were housed in a controlled environment (23 ± 1°C, 50 ± 5% humidity) and given access to water ad libitum. Room lights were on between 7:30 and 19:30. We used commercial pellets (AIN93G; Oriental Yeast, Tokyo, Japan) as the control, the ingredients of which are as follows: 39.7% cornstarch, 20% casein, 0.3% L-cystine, 13.2% α-cornstarch, 10% sucrose, 7% bean oil, 5% cellulose powder, 3.5% minerals, 1% vitamins, 0.25% choline bicitrate, and 0.0014% butylhydroquinone. The rice we used was grown in Hokkaido area in Japan [Oryza sativa subsp. japonica (Hoshino-yume)]. PGBR was prepared at 25–30% water content to induce germination and dried to 15% according to a patented procedure (Patent No. 3738025, JP, November 4, 2005). PGBR was manufactured as powdered feed by Oriental Yeast. The nutrients in the PGBR pellets were the same as those in AIN-93G, except that cornstarch was replaced with PGBR, as reported previously [1,9]. All experiments were conducted in accordance with the Guidelines for Animal Experiments of Meijo University (Approval number: Yaku-Jitsu-12) and the Guiding Citation: Mamiya T, Morikawa K, Kise M (2014) Pregerminated Brown Rice Enhanced NMDA Receptor/CaMKIIα Signaling in the Frontal Cortex of Mice. J Rice Res 2: 123. doi: 10.4172/jrr.1000123