Decrease in cerebral protein synthesis on a low protein diet

When rats are put on a diet that is low in protein or contains no protein, decrease in brain weight can be observed. Changes in adults are minimal. In the young there is a 10--30% decrease in cell number and protein content; the cell size (protein per cell) does not change significantly. The change is greater, the earlier the diet is started and the more severe the protein dificiency is. The longer the malnutrition period lasts, the smaller is the recovery to normal values on subsequent control diets. Amino acid incorporation in the brain decreased 10--30% under these experimental conditions; it seems the decrease was to a great extent in the more slowly metabolized protein pool. Changes in other organs were greater; for example, in liver the decrease was up to 75% under similar conditions. The changes in the brain were heterogeneous; there were regional differences, and not all proteins were affected to the same degree; choline acetyltransferase was not affected. Cellular amino acid transport as studied with incubated slices of brain was not altered under these conditions.