Chemogenetic Activation of Melanopsin Retinal Ganglion Cells Induces Signatures of Arousal and/or Anxiety in Mice

Abstract

SummaryFunctional imaging and psychometric assessments indicate that bright light can enhance mood, attention, and cognitive performance in humans. Indirect evidence links these events to light detection by intrinsically photosensitive melanopsin-expressing retinal ganglion cells (mRGCs) [1, 2, 3, 4, 5, 6, 7, 8, 9]. However, there is currently no direct demonstration that mRGCs can have such an immediate effect on mood or behavioral state in any species. We addressed this deficit by using chemogenetics to selectively activate mRGCs, simulating the excitatory effects of bright light on this cell type in dark-housed mice. This specific manipulation evoked circadian phase resetting and pupil constriction (known consequences of mRGC activation). It also induced c-Fos (a marker of neuronal activation) in multiple nuclei in the hypothalamus (paraventricular, dorsomedial, and lateral hypothalamus), thalamus (paraventricular and centromedian thalamus), and limbic system (amygdala and nucleus accumbens). These regions influence numerous aspects of autonomic and neuroendocrine activity and are typically active during periods of wakefulness or arousal. By contrast, c-Fos was absent from the ventrolateral preoptic area (active during sleep). In standard behavioral tests (open field and elevated plus maze), mRGC activation induced behaviors commonly interpreted as anxiety like or as signs of increased alertness. Similar changes in behavior could be induced by bright light in wild-type and rodless and coneless mice, but not melanopsin knockout mice. These data demonstrate that mRGCs drive a light-dependent switch in behavioral motivation toward a more alert, risk-averse state. They also highlight the ability of this small fraction of retinal ganglion cells to realign activity in brain regions defining widespread aspects of physiology and behavior.

Chemogenetic Activation of ipRGCs Drives Changes in Dark-Adapted (Scotopic) Electroretinogram

“…Experiments were performed in adult (3–6 months old) Opn4 Cre/+ mice. 13 Unilateral intravitreal injections of AAV2-hSyn-DIO-hM3Dq-mCherry vector (2.3 × 10 13 genomic particles/mL; the Vector Core, University of North Carolina at Chapel Hill, NC, USA) were performed as previously reported 11 and used hyaluronan lyase and heparinase III (200 U each) to maximize retinal penetration (total volume, 2.5 μL injected over 1 minute). 14 Control mice underwent the same procedure, with injections including glycosydic enzymes and the virus-lacking hM3Dq receptor AAV2-hSyn-DIO-mCherry vector (1.2 × 10 13 genomic particles/mL; UNC Vector Core).…”

“…Immunohistochemistry was performed as previously described 11 in retinal wholemounts in methanol-free 4% paraformaldehyde. The primary antibodies used in these studies included rabbit anti-dsRed (product 632496; 1:1000 dilution; Clontech, Saint-Germain-en-Laye, France) and chicken anti-GFP (product ab13970; 1:1000 dilution; Abcam).…”

“…We previously used this strategy in vivo to selectively excite ipRGCs. 11 Using that approach in this study enabled us to specifically activate ipRGCs, independently of any light stimulation, and hence examine the impact of ipRGC activity on the scotopic ERG. We found that selective activation of ipRGCs suppressed both a- and b-wave amplitude and caused a shift in b-wave sensitivity.…”

Modulation of recognition memory performance by light requires both melanopsin and classical photoreceptors

“…However, the change in freezing in wild-type (WT) mice could be due to retrieval of a stronger associative memory (leading to better performance), but it could also be the result of a general increase in anxiety in response to light inputs [12]. This latter effect has been demonstrated in a recent study in which chemogenetic activation of OPN4-expressing pRGCs elevates the level of anxiety/arousal in the open field and elevated–plus maze tests [21]. These findings complicate interpretation of the role of the melanopsin in regulating memory performance.…”

Unconventional Roles of Opsins

“…These include photoentrainment of circadian rhythms (Freedman et al 1999, Panda et al 2002), light-induced pupillary constriction (Lucas et al 2003, Xue et al 2011), suppression of pineal melatonin (Lucas et al 1999), light aversion (Johnson et al 2010, Semo et al 2010), control of sleep states (Altimus et al 2008, Hubbard et al 2013, Lupi et al 2008, Milosavljevic et al 2016, Pilorz et al 2016, Tsai et al 2009), and other functions (Atkinson et al 2013, Esquiva et al 2016, Rao et al 2013, Reifler et al 2015, Zhang et al 2008). The discoveries of melanopsin and its myriad of non-image and rudimentary image forming functions in the eye are covered in detail in other reviews (Do & Yau 2010, Hankins et al 2008, Hughes et al 2016, Lucas 2013, Matynia 2013, Schmidt et al 2011).…”