Photoperiod integration in C3H rd1 mice

Abstract

In mammals, the suprachiasmatic nuclei (SCN) constitute the main circadian clock, receiving input from the retina which allows synchronization of endogenous biological rhythms with the daily light/dark cycle. Over the year, the SCN encodes photoperiodic variations through duration of melatonin secretion, with abundant nocturnal levels in winter and lower levels in summer. Thus, light information is critical to regulate seasonal reproduction in many species and is part of the central photoperiodic integration. Since intrinsically photosensitive retinal ganglion cells (ipRGCs) are vital for circadian photoentrainment and other nonvisual functions, we studied the contribution of ipRGCs in photoperiod integration in C3H retinal degeneration 1 (rd1) mice. We assessed locomotor activity and melatonin secretion in mice exposed to short or long photoperiods. Our results showed that rd1 mice are still responsive to photoperiod variations in term of locomotor activity, melatonin secretion, and regulation of the reproductive axis. In addition, retinas of animals exposed to short photoperiod exhibit higher melanopsin labeling intensity compared with the long photoperiod condition, suggesting seasonal-dependent changes within this photoreceptive system. These results show that ipRGCs in rd1 mice can still measure photoperiod and suggest a key role of melanopsin cells in photoperiod integration and the regulation of seasonal physiology.

Homeostatic crosstalk among gut microbiome, hypothalamic and hepatic circadian clock oscillations, immunity and metabolism in response to different light–dark cycles: A multiomics study

“…[24][25][26] The total of 240 mice, comprising both the CD and ABX groups, were randomly allocated to 10 distinct subgroups, each exposed to a specific LD cycle as outlined in Figure 1B 1D), in accordance with previously documented protocols. [19][20][21][22] Each individual mouse was housed in a separate cage within a temperature-and humidity-controlled warehouse, adhering to regulatory guidelines. LD cycles were carefully manipulated using a LED light strip emitting a brightness of 150-200 lx, and a temperature range of 4500-5000 K. In the LD12/12 condition, lights were activated at Zeitgeber time 0 (ZT0) and deactivated at ZT12 (ZT0 representing lights-on).…”

“…4,18 Recent findings have further highlighted the profound effects of extreme LD cycle alterations, such as constant darkness (LD0/24) and constant light (LD24/0), on the daily oscillations of physiological functions and GM. [19][20][21] Moreover, minor LD cycle alterations, including short light (LD8/16) and long light (LD16/8), have been extensively studied as models of circadian disorder in jet lag or shift workers. 21,22 Hence, in our study, we selected these four irregular LD cycles, along with the normal LD cycle (LD12/12), to investigate their regulation of the homeostatic crosstalk among the GM, oscillation of hypothalamic and hepatic CCs, and immunity and metabolism.…”

“…[19][20][21] Moreover, minor LD cycle alterations, including short light (LD8/16) and long light (LD16/8), have been extensively studied as models of circadian disorder in jet lag or shift workers. 21,22 Hence, in our study, we selected these four irregular LD cycles, along with the normal LD cycle (LD12/12), to investigate their regulation of the homeostatic crosstalk among the GM, oscillation of hypothalamic and hepatic CCs, and immunity and metabolism. Our hypothesis posited that different environmental LD cycles might influence the oscillatory expression of central and peripheral rhythm genes, as well as immunity and metabolism, to varying degrees.…”

Normal Light-Dark and Short-Light Cycles Regulate Intestinal Inflammation, Circulating Short-chain Fatty Acids and Gut Microbiota in Period2 Gene Knockout Mice

“…In addition, sleep and wake cycle abnormalities of shift workers increase food intake at night and reduce light exposure, which in turn triggers metabolic disorders due to inadaptability to circadian rhythms, leading to a significant increase in the incidence of obesity, diabetes, and coronary heart disease (12). It is reported that the intrinsically photosensitive retinal ganglion cells (ipRGCs) can sensitively respond to the changes in the external light cycle, which adjusts the SCN to receive the signal input from the retina to synchronize the circadian rhythm with the LD cycles (13,14).…”

Impacts of Circadian Gene Period2 Knockout on Intestinal Metabolism and Hepatic Antioxidant and Inflammation State in Mice

“…At present, many circadian clock genes have been identified in animals including period circadian clock 1/2/3 ( Per1/2/3 ), cryptochrome 1/2 ( Cry1/2 ), brain and muscle ARNT-like 1 ( Bmal1 ), and circadian locomotor output cycle kaput ( Clock ) [ 3 , 4 ]. A central circadian clock located in the suprachiasmatic nucleus (SCN) coordinates the oscillation of the peripheral circadian clock, while the intrinsically photosensitive retinal ganglion cells (ipRGCs) send light signals into SCN to guide the central clock to periodically oscillate and output rhythmic behaviors consistent with daily changes [ 5 ]. The circadian clock is produced by the transcriptional-translational feedback loops (TTFLs) of circadian genes [ 6 , 7 ].…”