Development of a Method for Monitoring the Locomotor and Visual Circadian Rhythms in a Free-moving Scorpion

he present study aimed to develop a method to record circadian patterns of electroretinogram (ERG) and electromyogram (EMG) simultaneously in unrestrained Egyptian yellow fat-tailed scorpion Androctonus australis under different light regimes. A specially designed aluminum "jacket" was properly fixed on the scorpion allowing its free movement during recording. The lightjacket extends along the scorpion body from the chelicerae to the metasoma. Stainless steel electrodes were implanted in the cornea of the median eyes to measure the ERG in response to brief light pulses (100 ms/30 min.), and into the patellae of each 3 leg to measure the EMG. Under entrainment (LD 12:12) as well as freerunning (DD) conditions, the circadian activities were successfully recorded for several weeks. The ERG-amplitude changed along the 24 hours. Its high level reached during subjective night, whereas its low level was during the subjective day. So, the internal central time was measured through analyzing the ERG circadian rhythm. Locomotor activity rhythm was synchronized with ERG rhythm. The scorpion started its activity at the beginning of the subjective night when the ERG-amplitude increased. Based on both EMGs recording and IR-camera monitoring, rest-state and three types of active behavioral categories were observed. The developed jacket is a suitable design for monitoring and analyzing the ERGs and EMGs circadian rhythms in a free-moving scorpion for extended periods. This facilitates series of experiments to investigate the effect of various environmental, physiological and behavioral T