Locomotor activity and serum tryptophan and serotonin in goats: daily rhythm

The goal of the present study was to investigate the daily amount of motor activity and the daily rhythm of tryptophan and serotonin in goats housed in individual boxes under a 12/12 light/dark cycle. We equipped six Girgentana breed goats with Actiwatch-Mini® (Cambridge Neurotechnology Ltd., UK), actigraphy-based data loggers that record a digitally integrated measure of motor activity. Also blood samples were collected at four-hour intervals over a 48 h period via an intravenous cannula inserted into the jugular vein. The concentration of tryptophan (TRP) and serotonin (5-HT) were assessed by the high-performance liquid chromatography (HPLC) method. Our results outline a diurnal pattern of motor activity and levels of tryptophan in the serum, and a nocturnal pattern of levels of serotonin in the serum, which underline the impact of endogenous serotoninergic activity on the behavioural aspects of the circadian response to light.