Bano Otalora, B. | Search bioRxiv

bioRxiv2026

Parallel visual processing in the suprachiasmatic region of a diurnal mammal.

Light shapes mammalian physiology and behaviour through hypothalamic pathways, yet how these pathways process visual information in day-active species remains poorly understood. Based largely on work in nocturnal rodents, the suprachiasmatic nucleus (SCN) is classically viewed as a retinal target that encodes ambient illumination for circadian entrainment. We combine anatomical tracing, light-evoked c-Fos mapping and high-density silicon-probe electrophysiology to define visual processing in the suprachiasmatic region of the diurnal murid Rhabdomys pumilio. We find that retinal input and light-evoked activity extend beyond the SCN into rostral and lateral peri-SCN hypothalamus. Within the SCN, neurons encode irradiance with graded changes in maintained firing broadly similar to those observed in parallel recordings of nocturnal Mus domesticus. Across the wider suprachiasmatic region, Rhabdomys neurons show selectivity for more dynamic visual stimuli, including luminance transitions, contrast and temporal structure. Unsupervised clustering identifies five functionally distinct hypothalamic visual response classes with different anatomical distributions. These findings reveal an expanded hypothalamic visual network in a diurnal mammal, placing SCN irradiance coding within a broader system for processing dynamic visual features.

neuroscience↗

bioRxiv2020

Daily electrical activity in the master circadian clock of a diurnal mammal

Daily or circadian rhythms in mammals are orchestrated by a master circadian clock within the hypothalamic suprachiasmatic nuclei (SCN). Here, cell-autonomous oscillations in gene expression, intrinsic membrane properties, and synaptic communication shape the electrical landscape of the SCN across the circadian day, rendering SCN neurons overtly more active during the day than at night. This well-accepted hallmark bioelectrical feature of the SCN has overwhelmingly emerged from studies performed on a small number of nocturnal rodent species. Therefore, for the first time, we investigate the spontaneous and evoked electrical activity of SCN neurons in a diurnal mammal. To this end, we measured the electrical activity of individual SCN neurons during the day and at night in brain slices prepared from the diurnal murid rodent Rhabdomys pumilio and then developed cutting-edge data assimilation and mathematical modelling approaches to uncover the underlying ionic mechanisms. We find that R. pumilio SCN neurons were more excited in the day than at night, recapitulating the prototypical pattern of SCN neuronal activity previously observed in nocturnal rodents. By contrast, the evoked activity of R. pumilio neurons included a prominent suppressive response that is not present in the SCN of nocturnal rodents. Our computational modelling approaches reveal transient subthreshold A-type potassium channels as the primary determinant of the suppressive response and highlight a key role for this ionic mechanism in tuning excitability of clock neurons and optimising SCN function to accommodate R. pumilios diurnal niche.

neuroscience↗