Neurochemical characteristics of cerebral catecholamine neurons during the postnatal development in the rat.

The development of cerebral dopamine (DA) and noradrenaline (NA) neurons was studied biochemically in 1- to 28-day-old rats. The precursor amino acid tyrosine increased to a steady state level in the whole brain during early postnatal age. After 14 days, however, there was a marked drop in the brain tyrosine level. In general, regional tyrosine levels also decreased between 4 and 28 days. DOPA accumulation was measured in whole brain and regional brain areas after inhibition of L-aromatic amino acid decarboxylase with NSD 1015. This is a well recognized method for estimating the in vivo rate of tyrosine hydroxylase activity. Whole brain DOPA accumulation after NSD 1015 increased progressively during postnatal life, and between 1 and 28 days a more than 3-fold increase was noted. Similar increases were also found in whole brain DA and NA levels during the corresponding period. Regional DA and NA levels generally increased with advancing age, with the highest DA levels in the striatum region and NA levels in the midbrain region. Regional DOPA accumulation after NSD 1015, reflecting in vivo tyrosine hydroxylase activity, increased in a similar fashion as the endogenous neurotransmitter levels. Measurements of DA and NA disappearance after alpha-methyltyrosine indicated the existence of an adult-like nerve impulse activity in DA neurons in the striatum and midbrain regions and in NA neurons in the hemispheres region of the 4-day-old rats. Gammahydroxybutyric acid (GHBA), which causes an inhibition of nerve impulse activity, was given to 4- and 28-day-old rats. This induced an initial increase in CA synthesis as measured by the NSD 1015 method at both ages. The results from this investigation show that the age-related regional increases in endogenous DA and NA levels closely follow the increase in regional tyrosine hydroxylase activity measured in vivo. Furthermore, the study also supports the view that feed-back mechanisms, resulting in an increased transmitter synthesis, exist in DA neurons after nerve impulse inhibition by GHBA at an early postnatal age.