Relationship of tyrosine concentration to catecholamine levels in rat brain

Rats were fed a choline-free low protein diet for 12 or 26 weeks. In the 12-week group, the brain tyrosine concentration did not change. Dopamine levels were low in both the cerebral cortex and striatum. Norepinephrine level was low in the diencephalon. In the 26-week group, the tyrosine concentration was high in the brain. However, the dopamine and norepinephrine levels did not change in the cerebral cortex, striatum and hypothalamus. Furthermore, in another group of rats which were intraperitoneally injected with tyrosine, the brain tyrosine concentration was high, whereas the dopamine and norepinephrine levels in the hypothalamus were not significantly different from control levels.