Characteristics of circadian rhythm of wheel-running activity and drinking behavior in Mongolian gerbils

Circadian patterns of wheel-running activity and drinking behavior of Mongolian gerbils were investigated under a 24-h light-dark cycle (LD, 12: 12). Although the circadian pattern of drinking behavior was less clear than that of the wheel-running activity, the two behaviors tended to alter in parallel with each other in 5 out of 10 gerbils. However, the other 5 gerbils exhibited less synchronization between these circadian patterns. Furthermore, there were marked individual differences in the gerbils' circadian patterns, demonstrating not only nocturnal, boundary (showing a peak around the time-of-day of the changing from light period to dark period), and/or diurnal patterns, but also a free-running pattern during the observation period of 79 days. The present result may be due to behavioral characteristics that indicate the gerbils may still be wild type. It is therefore important to know behavioral characteristics of Mongolian gerbils in preclinical evaluation of psychotropic drugs.