Distribution of catecholamines and serotonin in the rat cerebral cortex: absolute levels and relative proportions.

The rat cerebral cortex was dissected in five regions and analyzed for the catecholamines noradrenaline, adrenaline and dopamine, and for the indoleamine serotonin using sensitive radioenzymatic assay methods with thin-layer chromatography. The noradrenaline concentration was highest in the ventral cortex, lateral to the hypothalamus, had intermediate values for the prefrontal, frontal and parietal cortical areas and was lowest in the occipital cortex. Dopamine levels were also highest in the cortex lateral to the hypothalamus, and moderate in the prefrontal and frontal cortical areas, with the lowest values measured for the occipital cortex. The ratios dopamine/noradrenaline further supports the hypothesis that they are independent transmitters. Traces of adrenaline were measured in all regions examined. The serotonin distribution was found to be non-homogeneous, with the highest values for the prefrontal cortex and ventral cortex lateral to the hypothalamus. The functional significance of these amines and their ratios are discussed in relation to their role as putative modulators of cortical neuronal excitability.