The postnatal ontogeny of monoamine-containing neurones in the central nervous system of the albino rat

The fluorescence histochemical technique of Falck and Hillarp was used to study the postnatal development of monoamine-containing neurones in the albino rat. The levels of monoamines were also measured biochemically. At birth the presumed dopamine-containing neurones were found to be more developed morphologically than the noradrenaline-containing neurones, and these more than the 5-HT-containing neurones. It is suggested that the increments in the biochemically measured levels of the 3 amines were paralleled (or brought about) by morphological development (mainly axon-terminal proliferation) and production of increasing amounts of synthesising enzymes and storage particles. Axon terminal proliferation was highest during the first 3 postnatal weeks in the NA- and 5-HT-containing neurones and during the first 4 weeks in the DA-containing neurones; the proliferation of nerve terminals occurred at different rates in the various parts of the central nervous system. The monoamine-containing neurones of the newborn could take up the amine precursors, and react to reserpine (which blocks the uptake-storage mechanism of storage granules) and nialamide (inhibitor of monoamine oxidase) in the same way as in the adult. These neurones, therefore, were biochemically differentiated before completion of their morphological development.