Melatonin rhythm and other outputs of the master circadian clock in the desert goat (Capra hircus) are entrained by daily cycles of ambient temperature

Abstract

In desert areas, mammals such as camel and goat are exposed to harsh environmental conditions. The ambient temperature (Ta) cycles have been shown to entrain the circadian clock in the camel. In the present work, we assumed that, in the goat living in a desert biotope, Ta cycles would have the same synchronizing effect on the central clock. Therefore, the effects of Ta cycles on body temperature (Tb), locomotor activity (LA) and melatonin (Mel) rhythms as outputs of the master circadian clock have been studied. The study was performed on bucks kept first under constant conditions of total darkness (DD) and constant Ta, then maintained under DD conditions but exposed to Ta cycles with heat period during subjective day and cold period during subjective night. Finally, the Ta cycles were reversed with highest temperatures during the subjective night and the lowest temperatures during the subjective day. Under constant conditions, the circadian rhythms of Tb and LA were free running with an endogenous period of 25.3 and 25.0 hours, respectively. Ta cycles entrained the rhythms of Tb and LA to a period of exactly 24.0 hours; while when reversed, the Ta cycles led to an inversion of Tb and LA rhythms. Similarly, Ta cycles were also able to entrain Mel rhythm, by adjusting its secretion to the cooling phase before and after Ta cycles inversion. All together, these results show that the Ta cycles entrain the master circadian clock in the goat.

Effects of general versus subarachnoid anaesthesia on circadian melatonin rhythm and postoperative delirium in elderly patients undergoing hip fracture surgery: A prospective cohort clinical trial

“…In this study, we controlled external factors (light, meal, activity, temperature, the start time of surgery, and preoperative medication use) known to influence melatonin secretion [17,43,44]. Our results support that GA influences postoperative melatonin secretion as reported by others [17,18].…”

Entrainment of circadian rhythms of locomotor activity by ambient temperature cycles in the dromedary camel

“…Recently, heterothermy has also been reported to occur, to some extent, in other desert ungulates like oryx and goat 55,56 . This could explain why the circadian system of the desert black Moroccan goat 15 , displays similar entrainment of T a as is seen in the camel. Accordingly, three outputs of the goat's central circadian clock, namely the T b , LA and Mel rhythms are entrained by T a cycle.…”

“…To date the T a cycle entrainment ability of the circadian master clock has been described in only two mammalian species, the camel 14 and recently in the desert goat 15 . The results of the present work show clearly that locomotor activity, another output of the master circadian clock, is also entrained in the camel by the daily T a cycles.…”

“…In the present work, the circadian nature of LA rhythm and its entrainment by the LD and T a cycles in dromedary camel have been demonstrated unambiguously. Other studies have demonstrated the existence of a circadian clock driving the LA rhythm in some domestic mammals including goat 15 , ram 16 , cat 17 and rabbit 18 . Such experimental demonstrations are rather well characterized and numerous in laboratory and wild rodents, marsupials, bats and non-human primates [19][20][21][22][23][24][25] .…”

“…The rhythm of LA was recorded individually in camels using a validated video-locomotion scoring technique 15 . The recorded video sequences were visually analyzed by two well-trained evaluators who assigned 6 scores to each activity state following a predefined scale where: Score 0 correspond to a camel in a sitting position and not moving.…”