Abstract
Purpose: :
It has been well documented that the length of rod outer segments (ROS) is influenced by light history. Animals reared in total darkness have longer ROS, and those in bright habitat light have shorter ROS. In the present work, we studied the influence of habitat light on the length of cone outer segments (COS).
Methods: :
Adult balb/c mice were housed in 50 lux in-cage illumination on a 12:12 light:dark cycle. One group of animals were kept in total darkness for 10 days and another group were kept in 400 lux (12:12 light:dark) for 10 days. Eyes were collected and cut to obtain thick sections of 100 µm on a vibratome. COS were identified by immunostaining with antibodies against either red/green opsin, or blue opsin, and examined by confocal microscopy.
Results: :
COS lengths in control animals are 14.96± 1.29 µm (blue cones, mean±SD, n=90) and 15.15±1.85 µm (red/green cones, n=87). Significant increases in COS length in both blue cones (29.1%, P<0.001) and red/green cones (25.4%, P<0.001) are found in retinas from animals after 10 days in total darkness, compared with controls in 50 lux habitat light. On the other hand, exposure to 400 lux habitat light for 10 days induced significant decreases in COS length in blue cones (34.7%, P<0.001) and in red/green cones (37.6%, P<0.001), compared with controls.
Conclusions: :
Our data demonstrate that the length of cone outer segments is regulated by light history in the same way as rod outer segments. In a separate study, we found that CNTF also regulates the length of cone outer segments. Together, these data suggest a same underlying mechanism that mediates light-induced cone plasticity and CNTF-induced changes in cone outer segments
Keywords: photoreceptors • plasticity • retina