Seasonal effects of pinealectomy on the locomotor activity rhythm in the lizard Sceloporus torquatus

Abstract

Adult lizards (Sceloporus torquatus) were used to test whether seasonal differences in the effects of pinealectomy upon the locomotor activity rhythm exist. Animals were field collected and exposed to artificial light – dark cycles and constant temperature in winter and summer. Free running circadian rhythms under constant temperature and dim red light were monitored using infrared light-crossings. The effects of pinealectomy were assessed by analysing the circadian parameters of free running period and activity – rest ratio in constant darkness or light – dark cycles. Results obtained indicate that pinealectomy changes the free running period of locomotor activity rhythm, irrespective of season, while seasonal differences in activity–rest ratio were detected. Our findings support the hypothesis that seasonal regulation of circadian rhythms in lizards is accomplished, in part, via the output of the pineal gland.