Conclusion: This new parenteral amino acids mixture is safe and more efficient for the treatment of acute MSUD decompensation than classic enteral feeding. Background: Tyrosine levels are abnormally elevated in tissues and physiological fluids of patients with inborn errors of tyrosine catabolism, especially in tyrosinemia type II, which is caused by deficiency of tyrosine aminotransferase. Hypertyrosinemia is associated with neurologic and development difficulties in several patients and the mechanisms of brain damage in this disorder are poorly known. Objectives: We investigated the effect of L-tyrosine administration on acetylcholinesterase activity in hippocampus, striatum, cerebral cortex and serum of rats. Methods: For acute administration, 10-and 30-day-old Wistar rats were killed one hour after a single intraperitoneal injection of L-tyrosine (500 mg/kg) or saline. For chronic administration, two injections (at 12 h interval) of L-tyrosine (500 mg/kg) or saline were given starting at postnatal day 7 for 21 days; twelve hours after the last injection, the animals were killed. Brain was removed and serum was collected for acetylcholinesterase activity evaluation. Results: We observed that acute (10-and 30-day-old) and chronic administration of L-tyrosine increased acetylcholinesterase activity in hippocampus, striatum, cerebral cortex and serum, as compared to control group. Conclusions: These results suggest that L-tyrosine administration may alter cholinergic synapses, and this may be involved in the pathophysiology of brain damage found in patients affected with hypertyrosinemia. Background: Maple syrup urine disease (MSUD) is an inherited aminoacidopathy resulting from dysfunction of the branched-chain keto acid dehydrogenase complex, leading to accumulation of the branched-chain amino acids (BCAA) leucine, isoleucine and valine. Affected patients usually present CNS disturbances. Thus, we investigated BDNF levels in brain of rats submitted to an animal model of MSUD. Methods: For acute administration, three injections (1 h interval) of BCAA pool or saline were given subcutaneously to rats on postnatal day (PD) 10 or 28. For chronic administration, two injections (12 h interval) of BCAA pool or saline were given subcutaneously starting at PD 7 for 21 days. One hour (acute) or twelve hours (chronic) after the last injection, the animals were killed by decapitation and the brain was removed; BDNF levels were measured using a sandwich enzyme-linked immunosorbent assay.