Activities of monoamine oxidase-A and -B are altered in the brains of congenitally hyperammonemic sparse-fur (spf) mice.

Activities of monoamine oxidases, MAOA and MAOB, were measured using radiometric assays in different brain regions of the sparse-fur (spf/Y) mouse, a model of congenital hyperammonemia resulting from an X-chromosomal defect of ornithine transcarbamylase. MAOA activities were decreased in cerebellum (by 23%, P < 0.05) and brainstem (by 16%, P < 0.05) of spf mice; activities of MAOB were concomitantly increased in cerebellum (by 22%, P < 0.05), brainstem (by 20%, P < 0.05) and cerebral cortex (by 22%, P < 0.05). These findings offer a rational explanation for previous findings of increased acidic metabolites of monoamines in the brain of spf mice. Altered monoaminergic function could be a key factor in the pathogenesis of neurological dysfunction in congenital hyperammonemias.