Figure 1. Restoration of brain tyrosine levels in BH₄-deficient Spr ^−/− mice after the dietary tyrosine supplementation.

Concentrations of phenylalanine and tyrosine in the cerebra separated from brains of Spr ^+/+ or Spr ^−/− mice either fed a normal diet (ND) or the tyrosine diet (+Tyr) for 10 days are shown (n ≥5 for each experimental group). Data represent mean ± SD. Statistical significance was determined by Student’s t test, * P<0.05, ** P<0.01, *** P<0.001.