Turnover and synthesis of biogenic amines in discrete brainstem nuclei of the rabbit.

By use of a microtechnique and sensitive enzymatic isotopic assays norepinephrine (NE), dopamine (DA) and serotonin (5-HT) turnover rates were measured in 6 discrete brainstem regions. The results from young (3 days) and adult (1 year) rabbits were compared. In the dorsal raphe nucleus (dr) of the younger animals the slopes of disappearance of NE and 5-HT were significantly higher than in the adults. Whereas, in the dr the slope of the decline of DA was found to be significantly lower in younger animals. In the dr turnover rates of NE and 5-HT were higher in the young animals. However, higher turnover rates for DA were seen only in the LC-A6 region. The young animals had significantly lower turnover times for NE and 5-HT in the dr. The nts was the only nuclear group to reach significance for DA, and the young animals had longer turnover times when compared to adults. These results are indicative of the different roles the neurotransmitter systems play in maintaining homeostasis. The delicate balances in these systems in the brains of younger animals may contribute to their increased susceptibility to perturbations.