rhythmic changes in the serotonin content of the brain and eyestalk of crayfish during development

The present study investigated developmental circadian changes in the content of 5-hydroxytryptamine (5-HT) in two structures proposed to contain pacemakers in crayfish Procambarus clarkii: the cerebral ganglion and the eyestalks. Crayfish (N=260) from three developmental stages were divided into two groups: (1) animals subjected to 12 h:12 h light:dark cycles for 10 days and (2) animals treated as described above, then exposed to 72 h of continuous dim light. Crayfish from both groups were killed at different times of day, and the cerebral ganglion and the eyestalks of each were assayed for 5-HT by reversed-phase HPLC with electrochemical detection. In all stages of development, 5-HT content (expressed as 1 wet mass tissue) showed circadian variations in both structures analyze