The Effect of Electrolytic Lesions of Superior Colliculus on Circadian Rhythms and Anxiety-like Behavior in Rats

Circadian rhythms are physiological oscillations that allow organisms to maintain homeostasis. Circadian disruption can lead to negative health implications such as cardiovascular disease, hypertension, anxiety, depression, and even cancer. (AASM, 2005; Shields, 2002). Several brain structures modulate circadian rhythms, including the suprachiasmatic nucleus (SCN), and the intergeniculate leaflet (IGL), but very little is known about the role of the superior colliculus (SC). Here, we focused on how the SC modulates circadian rhythms and anxiety-like behaviors in diurnal species. Sprague Dawley (SD) rats (N = 18) were used in this study; nine rats experienced electrolytic lesions of the SC, while nine rats were controls. We then performed behavioral tests, including the open field test (OFT), elevated plus maze (EPM), sociability test, and light-dark box (LD box). Moreover, we assessed animals’ circadian rhythms by tracking their activity with infrared sensors under various lighting conditions. Our results show that in the EPM, the lesioned rats demonstrated significantly greater risk taking behavior, evidenced by the rats’ higher latency to enter the closed arm (p=.014). Moreover, animals with SC lesions spent significantly less time in the light portion of the LD box than the sham lesion group (p=.041). The data can exclude the possibility of anxiety-like behaviour, given that non-significant results were found in the OFT (p\u3e.05). Moreover, we found a non-significant difference in social interactions between the SC lesion group and and shams (p\u3e.05). Our results suggest that the SC is thus involved in modulating risk-taking ability of animals throughout the day, as well as leading to a disruption in regulating behavior to light. Therefore, the SC may be one of the main regulators of visual activity (through the modulation of sensitivity to light), suggesting that the SC may thus be a fundamental circadian rhythm-regulator