Biology subjects

Chen, S.-K.

Publications and source records attributed to Chen, S.-K..

5 recordsLinked to original sources

bioRxiv2025

White eye-rings coevolved with diurnal behaviors as a trait enhancing visual appeal in rodents

Conspicuous colorations are widespread in animals, yet their adaptive functions remain unclear, particularly in mammals. White eye-rings (WER), the bright-colored pelage encircling eyes, are prevalence in rodents (Mammalia: Rodentia). Phylogenetic analyses across 601 rodents show that WER has repeatedly emerged with transitions to diurnalism and disappeared with reversions to nocturnalism during rodent evolution. To explore WERs function, we performed behavioral tests on the Nile rat (Arvicanthis niloticus, diurnal with WER) and the house mouse (Mus musculus, nocturnal without WER), and found that WER enhances visual appeal (the ability to attract attention or preference), likely by accentuating facial bilateral symmetry. This effect is neither associated with sexual selection nor species recognition and was absent in mice. Thus, WER appears selectively favored in diurnal rodents capable of perceiving and responding to it, but is constrained in nocturnal species. These findings illustrate how ecological factors and shared sensory preferences shape conspicuous color patterns.

evolutionary biology↗

bioRxiv2024

Discrete photoentrainment of mammalian central clock is regulated by bi-stable dynamic network in the suprachiasmatic nucleus.

The circadian clock, an evolutionarily conserved mechanism regulating the majority of physiological functions in many organisms, is synchronized with the environmental light-dark cycle through circadian photoentrainment. This process is mediated by light exposure at specific times, leading to a discrete phase shift including phase delays during early subjective night, phase advances during late subjective night, and no shift at midday, known as the dead zone. In mammals, such as mice, the intrinsically photosensitive retinal ganglion cells (ipRGCs) are crucial for conveying light information to the suprachiasmatic nucleus (SCN), the central clock consisting of approximately 20,000 neurons. While the intracellular signaling pathways that modulate clock gene expression post-light exposure are well-studied, the functional neuronal circuits responsible for the three discrete light responses are not well understood. Utilizing in vivo two-photon microscopy with gradient-index (GRIN) endoscopes, we have identified seven distinct light responses from SCN neurons. Our findings indicate that light responses from individual SCN neurons are mostly stochastic from trial to trial. However, at the population level, light response composition remains similar across trials, with only minor variations between circadian times, suggesting a dynamic populational coding for light input. Additionally, only a small subset of SCN neurons shows consistent light responses. Furthermore, by utilizing the targeted recombination in active populations (TRAP) system to label neurons that respond to light during early subjective night, we demonstrate that their activation can induce phase delays at any circadian time, effectively breaking the gate that produce photoentrainment dead zone typically observed at midday. Our results suggest the existence of at least two separate time-dependent functional circuits within the SCN. We propose a dynamic bi-stable network model for circadian photoentrainment in the mammalian central clock, where a shifting clock is driven by a dynamic functional circuit utilizing population coding to integrate information flow similar to proposed cortical computational network, rather than a simplistic, consistent linear circuit.

neuroscience↗

bioRxiv2022

Environmental luminance impairs socio-sexual recognition memory through a succinct retina to supraoptic nucleus circuit

Social memory between the same gender or even different gender is a complex and heavily modulated process in the nervous system. It is important for an individual to form social memory between the opposite sex to either increase mating opportunities with multiple partners or form monogamous pair bonding. Therefore, a specific neuronal circuit to regulate social sexual memory may enhance the mating opportunity for an individual. It has been shown that both the auditory and somatosensory systems could increase the activity of oxytocin neurons in the paraventricular nucleus to regulate social behaviors. Although light exposure could influence various forms of memory, such as fear and object memory, how luminance signals modulate social recognition memory remains unclear. Here, we show that acute light exposure could impair the socio-sexual recognition memory (SSRM) in male mice. Contrary to sound and touch, light stimulation could inhibit oxytocin neurons in the SON (SONOT) through M1 SON-projecting ipRGCs and GABAergic neurons in the peri-SON (pSONGABA). Optogenetic activation of SONOT neurons with channelrhodopsin is sufficient to enhance the SSRM performance in male mice, even under light conditions. Our results show that the visual system could modulate SSRM through a succinct ipRGCs-pSONGABA-SONOT neuronal circuitry. Together, we demonstrate a dedicated neuronal circuit of how luminance affects memory formation for an individual toward different sex through the oxytocin system, a powerful modulatory neurohormone in the central nervous system.

neuroscience↗

bioRxiv2020

External light dark cycle shapes gut microbiota through intrinsically photosensitive retinal ganglion cells

Gut microbiota has been shown to involve in many physiological functions such as metabolism, brain development, and neuron degeneration disease. Intriguingly, many microbes in the digestive tract do not maintain a constant level of their relative abundance but show daily oscillations under normal conditions. Recent evidence indicates that chronic jetlag, constant darkness, or deletion of the circadian core gene can alter the composition of gut microbiota and dampen the daily oscillation of gut microbes. These studies suggest that the interaction between the host circadian clock and the light-dark cycle plays an important role in gut homeostasis and microbiota. However, how or whether environmental factors such as the light-dark cycle could modulate gut microbiota is still poorly understood. Using genetic mouse models and 16s rRNA metagenomic analysis, we found that light-dark cycle information transmitted by the ipRGC-sympathetic circuit was essential for daily oscillations of gut microbes under temporal restricted high fat diet condition. Furthermore, aberrant light exposure such as dim light at night (dLAN), acting through intrinsically photosensitive retinal ganglion cells (ipRGCs), could alter the composition, relative abundance, and daily oscillations of gut microbiota. Together, our results indicate that external stimulation, such as light-dark cycle information, through the sensory system can modulate gut microbiota in the direction from the brain to the gut.

neuroscience↗

bioRxiv2020

Dual GRIN lens two-photon endoscopy for high-speed volumetric and deep brain imaging

Studying neural connections and activities in vivo is fundamental to understanding brain functions. Given the cm-size brain and three-dimensional neural circuit dynamics, deep-tissue, high-speed volumetric imaging is highly desirable for brain study. With sub-micrometer spatial resolution, intrinsic optical sectioning, and deep-tissue penetration capability, two-photon microscopy (2PM) has found a niche in neuroscience. However, current 2PM typically relies on slow axial scan for volumetric imaging, and the maximal penetration depth is only about 1 mm. Here, we demonstrate that by integrating two gradient-index (GRIN) lenses into 2PM, both penetration depth and volume-imaging rate can be significantly improved. Specifically, an 8-mm long GRIN lens allows imaging relay through a whole mouse brain, while a tunable acoustic gradient-index (TAG) lens provides sub-second volume rate via 100 kHz [~] 1 MHz axial scan. This technique enables the study of calcium dynamics in cm-deep brain regions with sub-cellular and sub-second spatiotemporal resolution, paving the way for interrogating deep-brain functional connectome.

bioengineering↗