Developmental characteristics of brain catecholamines and tyrosine hydroxylase in the rat: effects of 6-hydroxydopamine.

1. Brain noradrenaline, dopamine and tyrosine hydroxylase were found in rat brain a few days before birth and increased progressively until reaching adult values. The most rapid period of growth for these substances seemed to occur between 7 and 18 days.2. The intracisternal administration of 6-hydroxydopamine to rats 7 days of age reduced concentrations of noradrenaline, dopamine, and tyrosine hydroxylase by 72 hours.3. The concentrations of noradrenaline, dopamine or tyrosine hydroxylase in rats that received 6-hydroxydopamine at 7 or 14 days of age remained markedly reduced when determined at adulthood, indicating that fibres did not continue to develop after the administration of this compound. The rats treated at 7 days also showed diminished concentrations of noradrenaline in heart.4. Rats injected with 6-hydroxydopamine at 7 days had reduced body weight as well as a reduction of some organ weights. This growth deficit was not observed in animals that received this drug at 14 days of age.5. The administration of ovine growth hormone to rats that received 6-hydroxydopamine at 7 days did not reverse the growth deficiency in these animals.