Correlation between photoreceptor injury-regeneration and behavior in a zebrafish model

Direct exposure to intensive visible light can lead to solar retinopathy, including macular injury. The signs and symptoms include central scotoma, metamorphopsia, and decreased vision. However, there have been few studies examining retinal injury due to intensive light stimulation at the cellular level. Neural network arrangements and gene expression patterns in zebrafish photoreceptors are similar to those observed in humans, and photoreceptor injury in zebrafish can induce stem cell-based cellular regeneration. Therefore, the zebrafish retina is considered a useful model for studying photoreceptor injury in humans. In the current study, the central retinal photoreceptors of zebrafish were selectively ablated by stimulation with high-intensity light. Retinal injury, cell proliferation and regeneration of cones and rods were assessed at 1, 3 and 7 days post lesion with immunohistochemistry and in situ hybridization. Additionally, a light/dark box test was used to assess zebrafish behavior. The results revealed that photoreceptors were regenerated by 7 days after the light-induced injury. However, the regenerated cells showed a disrupted arrangement at the lesion site. During the injury-regeneration process, the zebrafish exhibited reduced locomotor capacity, weakened phototaxis and increased movement angular velocity. These behaviors matched the morphological changes of retinal injury and regeneration in a number of ways. This study demonstrates that the zebrafish retina has a robust capacity for regeneration. Visual impairment and stress responses following high-intensity light stimulation appear to contribute to the alteration of behaviors.

Involvement of Estrogen Receptors in the Anxiolytic-Like Effect of Phytoestrogen Genistein in Rats with 12-Weeks Postovariectomy

Phytoestrogens are natural compounds found in some vegetables, and they replicate many of the physiochemical and physiological properties of estrogens, including the regulation of mood. The phytoestrogen genistein exerts anxiolytic-like effects in rats with a chronic absence of ovarian hormones, but the mechanism involved in this effect remains to be explored. The present study explored the participation of estrogen receptor-β in the anxiolytic-like effect of genistein (1.0 mg/kg, i.p., for 4 days) in Wistar rats with 12-weeks postovariectomy, considered as experimental model of post-surgical menopause. In the light/dark test, a useful tool for anxiety study and for the screening of anxiolytic drugs, genistein reduced the latency to enter and increased the time spent in the light compartment and significantly increased the frequency and time spent exploring the light compartment compared with the control group, which is considered as an anxiolytic-like effect at experimental level. All behavioral effects produced by genistein in the light/dark test were blocked by previous tamoxifen administration (5.0 mg/kg, s.c., for 6 days), a non selective antagonist for estrogen receptor-β. The effects produced by genistein or tamoxifen in this test were not related to significant changes in general motor activity evaluated in the open field test. In conclusion, the specific contribution of present investigation was identify that estrogen receptor-β is involved in the anxiolytic-like effect produced by phytoestrogen genistein in rats with a long-term absence of ovarian hormones;supporting the hypothesis that estrogen receptor-β participates in the regulation of anxiety associated with low concentration of ovarian hormones and in the anxiolytic-like effects produced by natural estrogenic compounds such as phytoestrogens.