The Superior Colliculus (SC) is Necessary for the Normal Display of Diurnal Behavior in Nile Grass Rats
Dr. Andrew Gall, Department of Psychology
The circadian system regulates daily rhythms of physiology and behavior and thus, it affects many aspects of daily life. Although there has been tremendous progress elucidating the mechanisms responsible for the workings of the circadian system in nocturnal species, little is known about the mechanisms that support a diurnal profile of activity in species like our own. Recent data has 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) (Gall et al., 2013, 2014). Specifically, grass rats with IGL and OPT lesions behave in ways similar to nocturnal animals. Importantly, both the IGL and OPT project to one another in nocturnal species, and there is evidence that these two brain regions also project to the superior colliculus (SC). The superior colliculus (SC) receives direct retinal input, is involved in the triggering of REM sleep in nocturnal rats (Miller et al., 1998), and is disproportionately large in the diurnal grass rat (Gaillard et al., 2013). 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 to examine the diurnal behavioral patterns and acute responses to light in these animals. The majority of grass rats with SC lesions expressed significantly reduced activity in the presence of light. Exposing the 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 diurnal behavior. This research has implications for understanding Alzheimer’s Disease (AD) and Parkinson’s Disease (PD), neurological disorders in which diurnal behavior is severely disrupted.
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