Mechanisms of Adaptation to Mean Light Intensity in the Chick Retina

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Through adaptation, animals can function visually under an enormous range of light intensities. Adaptation to changes in light intensity takes place early, in the retina. One role of adaptation is to regulate the spatiotemporal tuning of retinal outputs via retinal ganglion cells. In my project, I used the optokinetic response (OKR) to characterize contrast sensitivity (CS) in the chick retina as a function of spatial frequency and temporal frequency at different mean light intensities. I first found that adaptation from light to dark caused a shift in tuning preference of CS (Chapter 2). In the daytime, photopic CS of the chick was tuned to spatial frequency; whereas in the nighttime, scotopic CS was tuned to temporal frequency. Later, I explored mechanisms that modulated spatiotemporal CS under different adaptational conditions (Chapter 3). Since dopamine (DA) and nitric oxide (NO) are putative light-adaptation messengers in the retina, I injected agents affecting DA and NO actions and gap junction coupling into the eyes (vitreous bodies) of dark- or light-adapted chicks. Finally, I investigated the role of cell-cell coupling, a downstream mediator of DA or NO actions in the retina, in adaptation. I demonstrated that the chick uses a similar strategy to that used by mammals, to adapt to ambient illumination; and that DA, NO, as well as cell-cell coupling are adaptation-sensitive modulators of spatiotemporal visual processing in the retina. Optokinetic CS is a rapid and noninvasive method for assessing retinal function, which can be manipulated rapidly, conditionally and reversibly by intravitreal injection of specific pharmacological agents. The chick’s large eyes, and the similarities of control of light adaptation in chick and other species (e. g., mouse), make the chick a powerful new model for retinal research.
Shi, Q. (2014). Mechanisms of Adaptation to Mean Light Intensity in the Chick Retina (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from doi:10.11575/PRISM/26863