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 o 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.