Effect of inhibition of catecholamine synthesis on central catecholamine‐containing neurones in the developing albino rat

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Abstract
1 Tyrosine hydroxylase is thought to be the rate limiting enzyme step in catecholamine biosynthesis. Inhibition of this enzyme using α-methyl-p-tyrosine resulted in a time dependent depletion (and repletion) of formaldehyde induced fluorescence in catecholamine-containing neurones of the central nervous system in developing and adult rats. 2 Dopamine-containing neurones were depleted faster and more completely than noradrenaline-containing neurones. 3 The extent of depletion caused by α-methyl-p-tyrosine in the initial 6–9 h period was more or less comparable in young and adult rats from the age of 1 week onwards; this suggests that catecholamine turnover increases with age and parallels the increase in catecholamine levels. 4 The extent of depletion (and repletion) 18 h after administration of the inhibitor varied in animals of different age. 5 Administration of a monoamine oxidase inhibitor just before administration of α-methyl-p-tyrosine resulted in a reduction of the extent of depletion caused by the latter drug, indicating that monoamine oxidase is important for the breakdown of catecholamines in rats of all ages. 6 It is suggested that the catecholamine-containing neurones of the newborn are biochemically as well as functionally differentiated before completion of morphological differentiation.