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Melanopsin retinal ganglion cell loss in diurnal grass rats

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Melanopsin retinal ganglion cell loss in diurnal grass rats

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Project Description:

Light influences behavior and physiology in mammals by entraining circadian rhythms (Daan and Pittendrigh, 1976) and also through direct and acute inhibition or stimulation of activity, a process called masking (Redlin, 2001). Although there has been substantial progress elucidating the mechanisms responsible for the workings of the circadian system in nocturnal species, less is known about the mechanisms that support the diurnal profile of activity of mammals (Smale et al., 2003). We recently showed that the intergeniculate leaflet (IGL) is critical for the display of normal patterns of daily activity in diurnal grass rats (Arvicanthis niloticus) (Gall et al., 2013). Specifically, IGL lesions reversed the activity patterns of these animals such that they became nocturnal (Figure 1); this occurred through their effects on both circadian mechanisms and masking (Figure 2). The IGL is a thalamic structure that receives direct inputs from the melanopsin containing intrinsically photosensitive retinal ganglion cells (known as ipRGCs) (Chen et al., 2011), and has reciprocal connections with the olivary pretectal nucleus (OPT) (Klooster et al., 1995, Moore et al., 2000) and the superior colliculus (SC) (Moore et al., 2000); the OPT and SC also receive inputs from ipRGCs (Hattar et al., 2006). Grass rats with OPT and SC lesions also respond to acute presentations of light in an opposite manner. Importantly, the IGL, OPT, and SC connect with each other in nocturnal and diurnal species. Our unique diurnal animal model provides us the opportunity to examine these mechanisms in an unprecedented fashion. We propose to use diurnal grass rats to test the novel hypothesis that melanopsin is critical for the expression of diurnal behavior and physiology, and is involved in masking responses to light. We will achieve this goal by destroying the melanopsin cells within the retina, and examining behavior following this experimental manipulation. Undergraduates will be involved in every step of the scientific process, including designing experiments, collecting and analyzing data, writing manuscripts, and presenting at conferences.

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