Effect of quantity and quality of dietary protein on choline acetyltransferase and nerve growth factor, and their mRNAs in the cerebral cortex and hippocampus of rats

The brain protein synthesis is sensitive to the dietary protein; however, the role of dietary protein on biomarkers including choline acetyltransferase and nerve growth factor (NGF) for the function of cholinergic neurons remains unknown in young rats. The purpose of this study was to determine whether the quantity and quality of dietary protein affects the concentration of NGF and activity of choline acetyltransferase, and their mRNA levels in the brains of young rats. Experiments were carried out on five groups of young rats (4 weeks) given the diets containing 0, 5, 20% casein, 20% gluten or 20% gelatin for 10 days. The activity of choline acetyltransferase in the cerebral cortex and hippocampus declined gradually with a decrease in quantity and quality of dietary protein. The concentration of NGF in the cerebral cortex and the mRNA levels of choline acetyltransferase in the cerebral cortex and hippocampus did not differ among groups. However, the concentration and mRNA level of NGF in the hippocampus was significantly lower in rats fed with lower quantity of protein or lower quality of protein. In the hippocampus, the mRNA levels of NGF significantly correlated with the NGF concentration when the quantity (r = 0.704, P < 0.01) and quality (r = 0.682, P < 0.01) of dietary protein was manipulated. It was further found that a significant positive correlation existed between the NGF concentration and the activity of choline acetyltransferase in the hippocampus (dietary protein quantity, r = 0.632, P < 0.05; dietary protein quality, r = 0.623, P < 0.05). These results suggest that the ingestion of lower quantity and quality of dietary protein are likely to control the mRNA level and concentration of NGF, and cause a decline in the activity of choline acetyltransferase in the brains of young rats.