Calcium binding proteins neuroplasticity in vertebrate retinas exposed to dim light

Abstract

 

Purpose

 

The aim of this work was to study different subtypes of calcium binding proteins (CBPs) and their networks in the chicken retina. We have analyzed how calbindin, calretinin, and visinin are modified along postnatal development after rearing animals in dim light conditions. We have also investigated the expression pattern of a transmembrane secretory vesicle protein (SV2) and some downstream targets proteins of these CBPs.

 

Methods

 

Control animals were reared with cycles of 12 hs white cool light (200 lux) and 12 hs darkness. Dim-light animals, were reared from hatching to P12 with cycles of 12 hs with a white dim-light (0,2 lux) and 12 hs darkness. Experiments were performed at P6, P9 and P12. Tissue was fixed, frozen and then sectioned in a cryostat in order to obtain retinal sections for immunohistochemistry. The morphometric analysis was done and results were statistically analyzed using two-tailed Student’s t-test. Also, western blot analyses were performed on crude retinal membrane fraction.

 

Results

 

Densitometric inmmunohistochemistry and Western blot analysis results showed a decrease in calbindin D28k networks , between normal and dim-light reared group of animals, demonstrating significant differences at P9 and P12 (p<0.05). In addition, we found that the calbindin D28k immunoreactive doble-cone pedicle was smaller and the cone height was largest. Also, visinin and SV2 have a lowest concentration in the dim-light group at P9 and P12 (p<0.05).

 

Conclusions

 

Our results shows that dim-light conditions modify the global CBPs expression in the chicken retina. These changes, not only affect its concentrations, but also the organization of CBPs networks. Size and width of the double-cones pedicles, its longitude, arborization and the dendritic pattern in the inner plexiform layer are examples of the structural changes that we found in a close relationship with the environmental cues -dim light rearing- and this could be interpreted as neuroplastic changes.

 

 

A: CB-reactive retinas from P9 and B: P12. Indicated sublayers at IPL was measured. Integrated optic density (IOD) of all the CB-reactive plexi was greater in normo-stimulated retinas. (*) p=<0.05, (**) p=<0.001. C: CR-reactive retinas from P9 and D: P12.IOD fail to show any pattern of expression or any statistical significance in all the CR-reactive plexi. Scale bar = 20µm.

 

 

Double-cone morphology at P12. Cone pedicles are smaller in DIM group.

 

Keywords: 439 calcium • 698 retinal development • 650 plasticity