Adaptation (eye)

Summary

In visual physiology, adaptation is the ability of the retina of the eye to adjust to various levels of light. Natural night vision, or scotopic vision, is the ability to see under low-light conditions. In humans, rod cells are exclusively responsible for night vision as cone cells are only able to function at higher illumination levels. Night vision is of lower quality than day vision because it is limited in resolution and colors cannot be discerned; only shades of gray are seen. In order for humans to transition from day to night vision they must undergo a dark adaptation period of up to two hours in which each eye adjusts from a high to a low luminescence "setting", increasing sensitivity hugely, by many orders of magnitude. This adaptation period is different between rod and cone cells and results from the regeneration of photopigments to increase retinal sensitivity. Light adaptation, in contrast, works very quickly, w

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https://en.wikipedia.org/wiki/Adaptation_(eye)

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Constitutive differences in habituation of the glucocorticoid response to stress are related to variation in aggression and anxiety-related behaviors

Marie-Isabelle Guillot de Suduiraut, Maria del Carmen Sandi Perez, Sophie Elizabeth Walker, Olivia Zanoletti

Glucocorticoids coordinate responses that enable an individual to cope with stressful challenges and, additionally, mediate adaptation following cessation of a stressor. There are important individual differences in the magnitude of glucocorticoid responsiveness to stressors. However, whether individual differences in glucocorticoid responsiveness to stress are linked to different behavioral strategies in coping with social and non-social challenges is not easily studied, owing to the lack of appropriate animal models. To address this, we generated three lines of Wistar rats selectively bred for the magnitude of their glucocorticoid responses following exposure to a variety of stressors over three consecutive days at juvenility. Here, we present findings following observations of a high level of variation in glucocorticoid responsiveness to stress in outbred Wistar rats, and the strong response to selection for this trait over a few generations. When challenged with different stressful challenges, rats from the three lines differed in their coping behaviors. Strikingly, the line with high glucocorticoid responsiveness to stress displayed enhanced aggression and anxiety-like behaviors. In addition, these rats also showed alterations in the expression of genes within both central and peripheral nodes of the hypothalamic-pituitary-adrenal (HPA) axis and enhanced reactivity to acute stress exposure. Together, these findings strongly link differences in glucocorticoid responsiveness to stress with marked differences in coping styles. The developed rat lines are thus a promising model with which to examine the relationship between variation in reactivity of the HPA axis and stress-related pathophysiology and could be employed to assess the therapeutic potential of treatments modulating stress habituation to ameliorate psychopathology.

2017

Neural correlates of non-retinotopic visual processing and light adaptation

Yvonne Evelina Thunell

In the main part of this thesis, I investigate the neural correlates of nonretinotopic processing. We might intuitively think of the visual representation of the world as retinotopic, as is the case for the organization of most visual brain areas, but in fact our perception is usually not retinotopic. Consider for example a bicycle passing by with a reflector on one of its wheels. The reflector appears to move in a circular or prolate cycloidal orbit. It’s true motion trajectory, however, is a curtate cycloid. It seems that we perceive the reflector motion relative to the bicycle. The bicycle thus serves as a moving reference system for computing the motion of its constituent parts. Only little is known about the neural correlates of this type of non-retinotopic processing. Here, using EEG, I investigate the temporal dynamics of the encoding of non-retinotopic motion relative to a moving reference system. The results indicate that the motion of the reference system is discounted from the motion of the part already from 120 ms after stimulus onset and that the non-retinotopic representation dominates throughout the rest of the visual processing. Further, I use fMRI to show that the earliest area in the visual hierarchy holding non-retinotopic representations is the human motion processing complex (hMT+). In the second part of the thesis, the EEG correlates of light adaptation are investigated. Light adaptation is crucial for coping with the large range of ambient luminance values in our environment. We first confirm the known adaptation effect; the overall response to light flashes decreases substantially after adaption to bright light as compared to dim light. Furthermore, this adaptation effect depends on the wavelength of the light, being most pronounced for red light as compared to white, green and blue light. In addition, at short latencies (less than 100 ms) responses to light flashes are stronger after bright than after dim light adaptation for all colors except red. Our results show that even very short-latency EEG responses are differentially affected by different wavelengths of light.

EPFL2014

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Multiple enveloped RNA viruses of the family Paramyxoviridae and Pneumoviridae, like measles virus (MeV), Nipah virus (NiV), canine distemper virus (CDV), or respiratory syncytial virus (RSV), are of high clinical relevance. Each year a huge number of lives are lost as a result of these viral infections. Worldwide, MeV infection alone is responsible for over a hundred thousand deaths each year despite available vaccine. Therefore, there is an urgent need for treatment options to counteract these viral infections. The development of antiviral drugs in general stands as a huge challenge due to the rapid emergence of viral escape mutants. Here, we disclose the discovery of a small-molecule antiviral, compound 1 (ZHAWOC9045), active against several pneumo-/paramyxoviruses, including MeV, NiV, CDV, RSV, and parain-fluenza virus type 5 (PIV-5). A series of mechanistic characterizations revealed that compound 1 targets a host factor which is indispensable for viral genome replication. Drug resistance profiling against a paramyxovirus model (CDV) demonstrated no detectable adaptation despite prolonged time of investigation, thereby mitigating the rapid emergence of escape variants. Furthermore, a thorough structure-activity relationship analysis of compound 1 led to the invention of 100-times-more potent-derivatives, e.g., compound 2 (ZHAWOC21026). Collectively, we present in this study an attractive host-directed pneumoviral/paramyxoviral replication inhibitor with potential therapeutic application. IMPORTANCE Measles virus, respiratory syncytial virus, canine distemper virus, and Nipah virus are some of the clinically significant RNA viruses that threaten substantial number of lives each year. Limited to no availability of treatment options for these viral infections makes it arduous to handle the outbreaks. This highlights the major importance of developing antivirals to fight not only ongoing infections but also potential future epidemics. Most of the discovered antivirals, in clinical trials currently, are virus targeted, which consequently poses the challenge of rapid emergence of escape variants. Here, we present compound 1 (ZHAWOC9045), discovered to target viral replication in a host-dependent manner, thereby exhibiting broad-spectrum activity against several members of the family Pneumo-/Paramyxoviridae.

AMER SOC MICROBIOLOGY2021