5-HT concentration in cat's brain.

Endogenous concentrations of TRP, 5-HT and 5-HIAA were determined in the different cortical and subcortical areas of adult cat's brain, using ion-exchange chromatography and spectrofluorimetric methods. Tryptophan is homogeneously distributed in all structures of the brain. 5-HT is mainly accumulated in the brain stem, hypothalamus and caudate nucleus, but also in cortical areas as olfactory and piriform gyrus. The ratio 5-HIAA/5-HT shows that 5-HT utilization is higher in the structures containing small amounts of 5-HT. Using the radioenzymatic assay described by Saavedra et al. (1973), the rostrocaudal distribution of 5-HT content was determined in olfactory and piriform cortex. Important concentrations of 5-HT were detected in the prepiriformis and anterior amygdaloidea areas. Using the same assay and microdissection on frozen frontal slices of the brain, the distribution of 5-HT concentration throughout the different layers of cortical areas was studied. Piriform, olfactory and sigmoid cortex present high concentrations in the superficial layers, including the molecular one. These results were confirmed by uptake studies, made on crude homogenates from frozen tissue, suggesting that 5-HT is mainly contained in the most external cortical terminals.