5-Hydroxytryptamine metabolism in the damselfly, Ischnura graellsii, in relation to sex and larval-adult period.

Changes in total serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were investigated by HPLC EC in Ischnura graellsii over a larval-adult period including both sexes. Variationsof tryptophan (Trp) and protein levels were also studied. Significant higher levels of 5-HT were found in head portion for both sexes over the period studied, with mean values (in ng/mg protein) of 12.19-27.46 (head) and 2.63-6.06 (body) for males, and mean values of 3.13-26.48 (head) and 1.84-4.03 (body) for females. 5-HIAA concentration was also significantly higher in head portion for both sexes; mean values (in ng/mg protein) of 4.45-24.19 (head) and 0.87-8.63 (body) were observed for males, and mean values of 0.76-16.87 (head) and 1.18-7.12 (body) for females. The levels of the four compounds studied were significantly affected by the factor Instar. It is noticeable that significant differences between sexes for head Trp, 5-HT and 5-HIAA were observed in the last larval instar (F0), males showing higher values of 5-HT and 5-HIAA, and females higher values of Trp. In all cases, 5-HIAA/5-HT ratio decreased down to F0 and increased in adult stage. A positive correlation between 5-HT and 5-HIAA in both males (P < 0.0005) and females (P < 0.0001) was also observed. Our data suggest that oxidative deamination of serotonin in Ischnura may have higher importance than in other insects.