Effects of dietary protein and tyrosine on behavior of diabetic rats

Streptozotocin-diabetic and nondiabetic control male rats were fed synthetic diets varying in macronutrient content (experiment 1) or diets with or without added tyrosine (experiments 2 and 3). All rats were evaluated for stereotyped behaviors after administration of apomorphine (1 mg/kg) and amphetamine (3 and 5 mg/kg). At the end of experiments 2 and 3, rates of tyrosine hydroxylation in hypothalamus, nucleus accumbens, and striatum were determined by measuring L-3,4-dihydroxyphenylalanine concentrations after decarboxylase inhibition. In experiment 3 the ratios of tyrosine to dopamine were also measured in striatum and nucleus accumbens. Diabetic rats fed a standard high-carbohydrate diet showed decreased stereotypy relative to controls. Neither systematic alterations of fat or protein content of the diet nor selective tyrosine enrichment affected this attenuation of stereotypy in diabetics. L-3,4-dihydroxyphenylalanine concentration in nucleus accumbens was increased by dietary tyrosine enrichment in experiment 2 but not in experiment 3. However, brain tyrosine levels were elevated in rats fed tyrosine-enriched diets. These results argue against a significant contribution of precursor elevation to catecholamine function and behavior in experimental diabetes.