Seasonal variations of serotonin content in the pineal complex and the lateral eye of Lampetra planeri (cyclostoma, petromyzontidae).

Serotonin concentrations were measured by spectrofluorimetry in the pineal complex and the lateral eyes of Lampetra planeri, living in a natural environment, throughout two consecutive years. Large seasonal fluctuations with bimodal annual patterns of variations were observed in both the pineal complex and the lateral eyes. In the pineal complex, peak values occurred in February and August and low values in April and November. In the lateral eyes, peak values occurred in March and September. Comparison of the serotonin concentrations between the pineal complex and the lateral eyes showed that in ammocoetes the serotonin concentrations were similar in these organs, while in metamorphosing forms and adults the serotonin concentrations were significantly higher in the lateral eyes. The physiological significance of the seasonal variations of serotonin observed in both the pineal organ and the lateral eyes and the importance of environmental factors in their control remain to be determined and need further investigations.