Under light dark cycles all tuco tucos displayed

Under light/dark cycles, all tuco-tucos displayed very robust 24h rhythms, with wheel-running activity concentrated in the dark phase (Fig. 1A). An unusual event of rhythm disruption was registered in several individuals: On October 22th 2008, one of the females (captured in July of the same year) gave birth to two pups in the animal facility. The female abandoned the pups, which wandered around the cage for two days until perishing. This event caused an unusual response in several other animals present in the room: out of 13 animals, seven females ran during the whole day and night (animals # 9, 19, 21, 23, 27, 29 and 24, the female with pups), displaying “around-the-clock” activity for one entire day. One male (# 10) also displayed this continuous 24h activity but then totally interrupted activity for three continuous days. Two other males displayed long-term arrythmicity that lasted for at least 14 days (# 20 and 26) and rhythmicity was then restored without an observable phase shift (data not presented). One female died after running all day and night (# 28). Only two females maintained intact nocturnal rhythmicity (# 15 and 18 Fig. 1A) and these were notably those whose cages were farthest (340–300cm away) from the pups (see Fig. 1B).
Experiment: effect of acoustic cues on activity rhythms
Discussion
Concluding remarks
Acknowledgements
Introduction Delirium is a neuropsychiatric syndrome characterized by a fluctuating mental and behavioral condition. It can include reduced alertness, global cognitive decline, delusional-hallucinatory phenomena, mood swings and gross disturbances of behavior [1]. Delirium has a higher prevalence among older patients, with a proportion of 11–42% [2]. Symptoms of delirium are tightly related with circadian rhythm and sleep disruption. In patients developing delirium, the sleep/wake jak stat pathway is reversed and patients are drowsy and take naps during the day, while nighttime sleep is short and fragmented [3]. Overall, 73% of delirious patients have at least moderate alterations of sleep/wake cycle [4]; while in older patients these alterations reach up to 98% [5]. The integrity of the sleep/wake cycle and the temporal order for a variety of physiological and behavioral functions, including melatonin, are driven by the circadian system. The synthesis and release of melatonin is dependent on the adequate internal synchronization between the suprachiasmatic nuclei and the pineal gland. Moreover, as melatonin receptors are present in components of the circadian system including the suprachiasmatic nucleus, the reproductive system, renal and immune systems, among others [6,7], melatonin is suggested to function as an internal signal of circadian synchronization [8,9]. This feature points out the relevance of studying melatonin as a reliable indicator of the timing in the circadian system. Several studies have suggested that delirium is accompanied by a loss of temporal variation in plasma melatonin. In patients that underwent major abdominal surgery and developed postoperative delirium, plasma levels of melatonin were reduced and suffered sleep disturbances, including delayed sleep phase disorder or reversal of the sleep-wake cycle [10]. A different study reported cases of delirium in ICUs that presented a loss of melatonin circadian rhythms [11]. Other indicators of melatonin secretion are also altered in delirious patients, like urinary levels of the metabolite of melatonin; 6-sulphatoxymelatonin (6-SMT), which are mainly elevated in hypoactive patients and decreased in hyperactive patients [12].
Subjects and methods This study was conducted in the inpatient service of the Department of Internal Medicine at general hospital “Dr. Manuel Gea González” in Mexico City. All patients (>65 years) admitted between 2012 December to 2013 February who signed informed consent forms were included; patients who were taking drugs that entrain circadian rhythms were excluded. All participants underwent a daily evaluation of delirium risk based on the DSM-IV-TR diagnostic criteria, and provided daytime and nighttime melatonin samples. Due to budget constraints, two investigators that were trained for the collection of samples of salivary melatonin and diagnosis of delirium and blinded to the patients\' condition, analyzed the samples of 7 patients who developed delirium (D), from 3 days prior to 3 days after its setting. The mean day of delirium onset in these patients was the fourth day of hospitalization, therefore, 6 patients who didn\'t develop delirium (ND) until discharges were randomly selected, and their melatonin levels analyzed from days 1 through 7 of hospitalization. The study was approved by the ethical committee of the “Dr. Manuel Gea González” Hospital; No.14-82-2012. Patients received their food at 8:00 and 19:00h.