Circadian Vision in Zebrafish: From Molecule to Cell and from Neural Network to Behavior

Abstract

Most visual system functions, such as opsin gene expression, retinal neural transmission, light perception, and visual sensitivity, display robust day-night rhythms. The rhythms persist in constant lighting conditions, suggesting the involvement of endogenous circadian clocks. While the circadian pacemakers that control the rhythms of animal behaviors are mostly found in the forebrain and midbrain, self-sustained circadian oscillators are also present in the neural retina, where they play important roles in the regulation of circadian vision. This review highlights some of the correlative studies of the circadian control of visual system functions in zebrafish. Because zebrafish maintain a high evolutionary proximity to mammals, the findings from zebrafish research may provide insights for a better understanding of the mechanisms of circadian vision in other vertebrate species including humans.

Circadian rhythms in zebrafish (Danio rerio) behaviour and the sources of their variability

“…In contrast to mammals, the circadian system in zebrafish is highly decentralized, although their brain does possess the teleost equivalent of the mammalian SCN (Burrill & Easter Jr., 1994;Moore & Whitmore, 2014). There are pronounced molecular circadian oscillators in the equivalent of the SCN as well as in the retina (Moore & Whitmore, 2014;Li, 2019). However, unlike in mammals, the circadian oscillators in different zebrafish tissues can be entrained directly by light stimuli through the use of visual and non-visual peripheral photoreceptors and do not require a centralized pacemaker (Whitmore et al, 2000;Cermakian et al, 2002;Moutsaki et al, 2003;Vatine et al, 2011;Frøland Steindal & Whitmore, 2019).…”

Behavioural red-light sensitivity in fish according to the optomotor response

“…On the other hand, in fish, opsin expression and activity change during the day. It is possible that differences in expression levels due to circadian rhythms, rather than LWS opsin copy number, have had some influence on our results [56,57].…”

Diurnal changes in the efficiency of information transmission at a sensory synapse

“…In diurnal animals, the sensitivity of the retina to light is regulated both by the daily light-dark cycle and by intrinsic circadian clocks [12][13][14][15] . But the average luminance of a visual scene is not the variable driving most behaviours related to vision: navigation, finding food and avoiding predators all depend on detection of fast modulations in light intensity.…”

“…A key neuromodulator in the retina is dopamine released from amacrine cellsunder control of internal circadian clocks 12,27 as well as external signals, such as changes in luminance 14 or the appearance of food-related odours 28 . Dopamine levels are a minimum at night and increase throughout the day to modulate luminance-sensitivity 14,29 (Extended Data Figure 3). To test whether dopamine also regulates contrast sensitivity we injected agonists or antagonists of D1 receptors into the eye.…”

“…Dopamine release is controlled by the internal circadian clock as well as changes in luminance 7 or the appearance of food-related odours 4 . But other neuromodulators, are also released from amacrine cells, including melatonin 43 , Substance P 44 and somatostatin 45 and some of these can antagonize the actions of others 44 .…”