Regional changes in monoamine synthesis in the developing rat brain during hypoxia

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Abstract
Rats (4, 14 and 28 days old) were exposed to a hypoxic environment of 6% O2-94% N2 for 30 min. Tyrosine hydroxylase and tryptophan hydroxylase activity was studied in different brain regions (hemispheres, striatum, midbrain and brainstem) in vivo by measuring the accumulation of dihyroxyphenylalanine (DOPA) and 5-hydroxytryptophan (5-HTP) respectively, after inhibition of aromatic L-amino acid decarboxylase with NSD 1015 [3-hydroxybenzylhydrazine fumarate]. Tyrosine and tryptophan levels in the different brain regions were measured simultaneously. The tyrosine and tryptophan levels in the various brain parts were generally not influenced during exposure to hypoxia. Tyrosine hydroxylase activity decreased in most areas in the 4 and 14 days old rats, and all brain areas studied in the 28 day old rats. Tryptophan hydroxylase activity decreased markedly in all brain areas at all ages studied. The enzymes tyrosine hydroxylase and tryptophan hydroxylase seem to be equally affected during hypoxia in the different brain regions studied.