DISTRIBUTION OF TYROSINE HYDROXYLASE ACTIVITY IN ADULT AND DEVELOPING BRAIN

Abstract

The distribution of tyrosine hydroxylase activity in various areas of brain was studied in mature rats, rabbits, cats, and in kittens of various ages. Distribution was closely similar in all species. Areas known to have high concentrations of catecholinergic nerve endings, such as the caudate, septal area and pineal, showed very high adult levels and sharp increases during the neonatal period. Areas such as the pons–medulla and midbrain, known to contain predominantly catecholinergic cell bodies, showed, on the other hand, relatively low adult levels and little or no change in the neonatal period. Developmental data correlate with known neonatal changes in endogenous catecholamine levels and adult distributions correlate with known turnover rates. The results are in conformity with previous findings that tyrosine hydroxylase is concentrated largely in nerve endings and suggest that measurement of this enzymic activity may provide a more convenient and more sensitive index of catecholinergic nerve activity under various conditions than is provided by measurement of the amines themselves.