[In vivo high-resolution imaging of rat retina with optical coherence tomography and the expression of Bcl-2, Bax, Caspase-3 mRNA during critical period plasticity]

Abstract

Objective: To observe the changes of retinal thickness during critical period plasticity in rat, and to investigate whether apoptosis participates in the structural forming of retina.

Methods: Experimental research. 50 normal newborn pups of SD rat were randomly selected in the experiment. In vivo consecutive scanning of retinal image was taken and the retinal thickness from RPE to ILM was recorded in 10 pups (20 eyes) with spectral domain optical coherence tomography (OCT) at postnatal day 14 (P14), P18, P21, P24 and P42. Bcl-2, Bax, Caspase-3 mRNA was assessed with fluorescent quantitative real-time polymerase chain reaction after total RNA extracted from 4 retinas of 2 pups at each time point from P14 to P42. Histological measurement of retinal thickness of sections with HE staining from 4 pups (8 eyes) at each time point was compared with the results of OCT scanning. TUNEL staining was used to detect the apoptotic cells in retinal cryosections of 2 pups (4 eyes) at the same time point. The data were analyzed by One-way ANOVA and Linear Regression through SPSS 11.5 software.

Results: There was significant difference between the retinal thickness measured through OCT in pups from P14 to P42 (F = 15.425, P = 0.001). And the values were (243.42 ± 13.83) µm at P14, (218.78 ± 8.21) µm at P18, (195.42 ± 8.02) µm at P21, (195.74 ± 14.85) µm at P24, (190.79 ± 11.70) um at P42. The retinal thickness measured through OCT decreased significantly during the first 3 weeks after birth. The results of OCT measurement had linear correlation with histology measurement (R = 0.794, P = 0.000). There was significant difference between mRNA expression of Bcl-2, Bax and Caspase-3 in pups from P14 to P42 (F = 18.684, F = 47.307, F = 49.611; P = 0.000). The relative expression of Bax and Caspase-3 peaked at P24 while Bcl-2 was much more stable. There were a lot of apoptotic cells in the ganglion cells layer, the inner nuclear layer and the outer nuclear layer during P18 to P24 by TUNEL staining. And the apoptosis alleviated at P42.

Conclusions: The retinal thickness decreases when the retina continues to develop during critical period plasticity. Cirrus HD-OCT can be used as an effective instrument to show the layers of retina in rat in vivo. Apoptosis participates in the course of retinal development which possibly leads to the thinning of retina.