Regional differences in the catecholamine content of the rat brain: effects of neonatal castration and androgenization.

The long-term organizational influence of perinatal androgen manipulations upon the central noradrenergic and dopaminergic systems was investigated in the rat. Males were castrated or sham-operated upon within 24 h of birth. Newborn females received either five daily sc injections of 100 micrograms of testosterone in oil, or vehicle only. Groups of animals were then decapitated at ages ranging from 12 to 180 days. Levels of noradrenaline and dopamine were measured in six brain regions using high-performance liquid chromatography with electrochemical detection. The results confirm that the noradrenaline and dopamine content of the brain are affected by perinatal androgen exposure and show that brain catecholamine levels alter during the first six months of life, in some areas merely increasing, but in others rising and later falling. Sex differences in catecholamine levels may be apparent at particular ages, but the direction of the difference is frequently reversed as the animals grow older. In the hypothalamus and amygdala broadly similar patterns of time-related changes in catecholamine levels were observed. However, although in other regions (cerebral cortex, cerebellum, corpus striatum and corpora quadrigemina) sex differences in the noradrenaline and dopamine content were frequently detected, on most occasions they were not affected in any recognizable fashion by steroid manipulation in the newborn. Once adult patterns of gonadotropin secretion and behaviour became established in early adulthood, a functional relationship between brain catecholamine levels and the early effects of testosterone is no longer so apparent. Nevertheless, it would seem that testosterone, acting during the neonatal period, tends to accelerate the fall in brain amine levels that occurs as the animals grow older.