No abstract

Daily oscillation of the immune system follows the central biological clock outputs control such as melatonin produced by the pineal gland. Despite the literature showing that melatonin is also synthesized by macrophages and t lymphocytes, no information is available regarding the temporal profile of the melatonergic system of immune cells and organs in steady-state. Here, the expression of the enzymes arylalkylamine-n-acetyltransferase (AA-nAt), its phosphorylated form (p-AA-nAt) and acetylserotonin-O-methyltransferase (ASMT) were evaluated in phagocytes and T cells of the bone marrow (BM) and spleen. We also determined how the melatonergic system of these cells is modulated by LPS and the cytokine IL-10. The expression of the melatonergic enzymes showed daily rhythms in BM and spleen cells. Melatonin rhythm in the BM, but not in the spleen, follows P-AA-NAT daily variation. In BM cells, LPS and IL10 induced an increase in melatonin levels associated with the increased expressions of P-AA-NAT and ASMT. In spleen cells, LPS induced an increase in the expression of P-AA-NAT but not of melatonin. Conversely, IL10 induced a significant increase in melatonin production associated with increased AA-NAT/P-AA-NAT expressions. In conclusion, BM and spleen cells present different profiles of circadian production of local melatonin and responses to immune signals.Organs and cells of the immune system present daily variations regulated by oscillators present in each cell 1-6 . The intrinsic circadian clock of most of the immune cells imposes circadian expression of downstream genes and functions 4 . This is the case for the expression of pattern-recognition receptors and cytokines, the recruitment to tissues and the phagocytic activity of monocytes, macrophages and microglia 7-10 . Clock genes are also circadian expressed in mouse lymph nodes 10,11 and in B splenic cells 12 , where they control the activity of the cells 4,11 . Besides the intrinsic rhythmicity of cells and organs, there is a central synchronization that relies on neural and hormonal signaling controlled by the central clock in the suprachiasmatic nuclei 13,14 . After a sympathetic input, the darkness hormone melatonin, prolactin and glucocorticoids impose, for example, a daily rhythm in the migration of leukocytes to peripheral tissues 6 .In vertebrates, melatonin is known to be produced in a rhythmic manner by the pineal gland and retina, constitutively by the gastrointestinal tract and on demand by some immunocompetent cells 15,16 . Activated monocytes/macrophages/microglia and T lymphocytes expressed the enzymes arylalkylamine-N-acetyltransferase (AA-NAT), its active phosphorylated form (P-AA-NAT) and acetylserotonin-O-methyltransferase (ASMT) and melatonin 17-21 . In the spleen and in the bone marrow (BM), some works have shown the expression and activity of the melatonergic enzymes 22-24 , however, whether the immune cells of these organs also present www.nature.com/scientificreports www.nature.com/scientificreports/ circadian variations of the melaton...

Objective: Circadian disturbances common to modern lifestyles have been associated with mood disorders. Animal models that mimic such rhythm disturbances are useful in translational research to explore factors contributing to depressive disorders. This study aimed to verify the susceptibility of BALB/c, C57BL/6N, and CF1 mice to photoperiod changes. Methods: Thermochron iButtons implanted in the mouse abdomen were used to characterize temperature rhythms. Mice were maintained under a 12:12 h light-dark (LD) cycle for 15 days, followed by a 10:10 h LD cycle for 10 days. Cosinor analysis, Rayleigh z test, periodograms, and Fourier analysis were used to analyze rhythm parameters. Paired Student's t test was used to compare temperature amplitude, period, and power of the first harmonic between normal and shortened cycles. Results: The shortened LD cycle significantly changed temperature acrophases and rhythm amplitude in all mouse strains, but only BALB/c showed altered period. Conclusion: These findings suggest that BALB/c, the preferred strain for stress-induced models of depression, should also be favored for exploring the relationship between circadian rhythms and mood. Temperature rhythm proved to be a useful parameter for characterizing rhythm disruption in mice. Although disruption of temperature rhythm has been successfully documented in untethered mice, an evaluation of desynchronization of other rhythms is warranted.

Circadian rhythm disturbances are among the risk factors for depression, but specific animal models are lacking. This study aimed to characterize the effects of acute rhythm disruption in mice and investigate the effects of imipramine and N-acetylcysteine (NAC) on rhythm disruption-induced changes. Mice were exposed to 12:12-hour followed by 10:10-hour light:dark cycles (LD); under the latter, mice were treated with saline, imipramine or NAC. Rhythms of rest/activity and temperature were assessed with actigraphs and iButtons, respectively. Hole-board and social preference tests were performed at the beginning of the experiment and again at the 8th 10:10 LD, when plasma corticosterone and IL-6 levels were also assessed. Actograms showed that the 10:10 LD schedule prevents the entrainment of temperature and activity rhythms for at least 13 cycles. Subsequent light regimen change activity and temperature amplitudes showed similar patterns of decline followed by recovery attempts. During the 10:10 LD schedule, activity and temperature amplitudes were significantly decreased (paired t test), an effect exacerbated by imipramine (ANOVA/SNK). The 10:10 LD schedule increased anxiety (paired t test), an effect prevented by NAC (30 mg/kg). This study identified mild but significant behavioral changes at specific time points after light regimen change. We suggest that if repeated overtime, these subtle changes may contribute to lasting behavioral disturbancess relevant to anxiety and mood disorders. Data suggest that imipramine may contribute to sustained rhythm disturbances, while NAC appears to prevent rhythm disruption-induced anxiety. Associations between sleep/circadian disturbances and the recurrence of depressive episodes underscore the relevance of potential drug-induced maintenance of disturbed rhythms.