The circadian system regulates daily rhythms of physiology and behavior. Although extraordinary advances have been made to elucidate the brain mechanisms underlying the circadian system in nocturnal species, less is known in diurnal species. Recent studies have shown that retinorecipient brain areas such as the intergeniculate leaflet (IGL) and olivary pretectal nucleus (OPT) are critical for the display of normal patterns of daily activity in diurnal grass rats (Arvicanthis niloticus). Specifically, grass rats with IGL and OPT lesions respond to light in similar ways to intact nocturnal animals. Importantly, both the IGL and OPT project to one another in nocturnal species, and there is evidence that these 2 brain regions also project to the superior colliculus (SC). The SC receives direct retinal input, is involved in the triggering of rapid eye movement sleep in nocturnal rats, and is disproportionately large in the diurnal grass rat. The objective of the current study was to use diurnal grass rats to test the hypothesis that the SC is critical for the expression of diurnal behavior and physiology. We performed bilateral electrolytic lesions of the SC in female grass rats to examine behavioral patterns and acute responses to light. Most grass rats with SC lesions expressed significantly reduced activity in the presence of light. Exposing these grass rats to constant darkness reinstated activity levels during the subjective day, suggesting that light masks their ability to display a diurnal activity profile in 12:12 LD. Altogether, our data suggest that the SC is critical for maintaining normal responses to light in female grass rats.

中文翻译：

---

昼夜草大鼠（天牛）的上层眼球病变导致对光的反应中断。

昼夜节律系统调节生理和行为的日常节律。尽管在阐明夜间物种中昼夜节律系统的大脑机制方面已取得了非凡的进步，但在昼夜物种中却知之甚少。最近的研究表明，视网膜受体的大脑区域，如间质小叶（IGL）和橄榄核前盖核（OPT），对于日间草大鼠（Arvicanthis niloticus）日常活动的正常显示至关重要。具体而言，具有IGL和OPT病变的草鼠对光的反应与完整的夜间动物相似。重要的是，IGL和OPT都在夜间物种中相互投射，并且有证据表明这两个大脑区域也投射到上丘（SC）。SC接收直接的视网膜输入，参与夜间大鼠快速眼动睡眠的触发，在昼间草大鼠中比例过大。当前研究的目的是使用昼夜草鼠来检验以下假设：SC对昼夜行为和生理的表达至关重要。我们在雌性草大鼠中进行了SC的双侧电解损伤，以检查行为模式和对光的急性反应。大多数有SC损伤的草鼠在光照下均表现出明显降低的活性。在主观的一天中，将这些草鼠暴露于恒定的黑暗中，恢复了活动水平，这表明光掩盖了它们在LD 12:12中表现出昼夜活动特征的能力。总之，我们的数据表明，SC对于维持雌性草大鼠对光的正常反应至关重要。