Prenatal ontogenesis of brain phenolamines and catecholamines in relation to their metabolizing enzymes in Roman avoider strains of rats.

Phenolamines, particularly octopamines, are of special importance in avoidance behavior. In the Roman low avoidance (RLA) strain, p-octopamine can induce locomotor behavioral activity that is normally observed in the Roman high avoidance (RHA) strain. For these reasons, the levels of prenatal octopamines (para and meta isomers) have been studied in relation to noradrenaline and dopamine levels. In the hypothalamus and brainstem of RHA, a maximum level of the para isomer is observed at 15 days of embryonic development but, unlike in controls and RLA animals, this level remains almost constant until 20 days. For the meta-isomer and catecholamines, there is a 1-2 day delay in detection between controls and RLA or RHA. The study of related enzyme activities reveals that tyrosine hydroxylase displays a 2-day delay in RHA when compared to the control value at 19 days of fetal life. These results are discussed in terms of the role of p-octopamine in avoidance conditioning and of the possible delayed expression of the tyrosine hydroxylase gene in Roman strains of rats.