Abstract
The nature and intensity of visual stimuli have changed in recent years because of television and other dynamic light sources. Although light stimuli accompanied by contrast and strength changes are thought to have an influence on visual system development, little information is available on the effects of dynamic light stimuli such as a strobe light on visual system development. Thus, this study was designed to evaluate changes caused by dynamic light stimuli during retinal development. This study used 80 Sprague-Dawley rats. From eye opening (postnatal day 14), half of the rats were maintained on a daily 12-h light/dark cycle (control group) and the remaining animals were raised under a 12-h strobe light (2 Hz)/dark cycle (strobe light-reared group). Morphological analyses and electroretinogram (ERG) were performed at postnatal weeks 3, 4, 6, 8, and 10. Among retinal neurons, tyrosine hydroxylase-immunoreactive (TH-IR, dopaminergic amacrine cells) cells showed marked plastic changes, such as variations in numbers and soma sizes. In whole-mount preparations at 6, 8, and 10 weeks, type I TH-IR cells showed a decreased number and larger somata, while type II TH-IR cells showed an increased number in strobe-reared animals. Functional assessment by scotopic ERG showed that a-wave and b-wave amplitudes increased at 6 and 8 weeks in strobe-reared animals. These results show that exposure to a strobe light during development causes changes in TH-IR cell number and morphology, leading to a disturbance in normal visual functions.
Highlights
Changes in the visual environment affect visual system development
We studied morphology and retinal function after rearing rats in stroboscopic illumination
Dopaminergic retinal neurons depend on a light stimulus for complete development
Summary
Changes in the visual environment affect visual system development. Dark rearing is thought to decrease the intensity of immunohistochemical staining for dopaminergic cells (Kato et al 1980), reduce storage of dopamine (Parkinson and Rando 1983), and block both maturational loss of ON–OFF responsive retinal ganglion cells and the pruning of their dendrites (Tian and Copenhagen 2003). Abnormal horizontal cell processes were found in mice reared in a no-contrast environment (Lee et al 2008). American preschool children spend more than 31 h per week watching television and more than 5 h per week exposed to other media such as videogames and computers (Lee et al 2009). These visual stimuli occasionally may result in unexpected events such as myopia, asthenopia, exophoria, and convergence insufficiency (Gratton et al 1990; Murata et al 1991; Basso et al 2006; Takada et al 1999)
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