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 [H-3]ketanserin (B-sp) with serotonin (5HT) in brain regions of juvenile and sexually recrudescing female trout. Amounts of B-sp varied widely among brain regions and consistently differed between juvenile and sexually recrudescing females. Levels of B-sp 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). B-sp 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, B-sp 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 B-sp and 5HT were comparable in the hypothalamus and preoptic area in juvenile and sexually recrudescing females. In general, density of specific [H-3]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 B-sp (fmol/g tissue) in all brain regions, and approximately 300-fold greater than B-sp 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.