Levels of specifically bound [3H]ketanserin compared with levels of serotonin (5HT) in the brain regions of juvenile and sexually recrudescing female rainbow trout, Oncorhynchus mykiss

This study compared the distribution of specifically bound 3H]ketanserin (Bsp) with serotonin (5HT) in brain regions of juvenile and sexually recrudescing female trout. Amounts of Bsp varied widely among brain regions and consistently differed between juvenile and sexually recrudescing females. Levels of Bsp were significantly greater in the hypothalamus than the olfactory lobe, which were at least threefold greater than in all other tissues examined (Kruskal-Wallis test, p < 0.05). Bsp densities in the hypothalamus, preoptic area, and optic lobe were significantly greater in juveniles compared with corresponding tissues from sexually recrudescing females (Mann-Whitney U test, p < 0.05); in contrast, Bsp in olfactory lobe and spinal cord did not differ significantly between the two classes of fish. 5HT concentration was determined by high performance liquid chromatography - electrochemical detection (HPLC-EC) analysis. Biogenic amine standards eluted in a stereotypic pattern, with peaks consistently separable in time. 5HT concentration was significantly greater in hypothalamus than in olfactory lobe and undetectable in the pituitary (Kruskal-Wallis test, p < 0.05). Trends in distribution of Bsp and 5HT were comparable in the hypothalamus and preoptic area in juvenile and sexually recrudescing females. In general, density of specific 3H]ketanserin binding sites was directly related to 5HT content of brain regions in juvenile and sexually recrudescing females. 5HT concentrations (pmol/g tissue) were approximately 900-fold greater than Bsp (fmol/g tissue) in all brain regions, and approximately 300-fold greater than Bsp in the olfactory lobe. These results suggest important regulatory role(s) for 5HT in the trout preoptic-hypothalamo-hypophysial axis, which may differ from 5HT role(s) in trout olfactory lobe.