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Hung-Ya Tu, Chuan-Chin Chiao; Functional AII Amacrine Cell Coupling Through Cx36-containing Gap Junction during Postnatal Development of the Rabbit Retina. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4562.
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AII amacrine cells (AII ACs) play an important role in the primary rod pathway by bridging rod bipolar cells (BCs) with ON cone BCs through Connexin 36 (Cx36) gap junction channels. AII ACs are also electrically coupled with each other in the mammalian retina. Given the importance of AII AC coupling in the adult retina, it is of great interest to study the maturation of the primary rod pathway by examining the functional expression of the Cx36 gap junctions in the developing retina.
The retinas of New Zealand White rabbits from various postnatal stages were used in this study. The animals were dark-adapted for at least one hour before enucleation under dim red light. The somata of potential AII ACs under DAPI staining were targeted for Neurobiotin injection. The injected cells were recognized as AII ACs by the presence of the conventional bistratified dendritic morphology and varicosities at the process ends. The identities of the injected and tracer-coupled cells were further confirmed with the positive calretinin immunoreactivity.
In consistent with our previous observations that the Cx36 protein expression in the inner plexiform layer started to increase rapidly a few days before eye-opening and reached the adult level after the third postnatal week, the present study found that AII ACs showed adult-like coupling patterns at P21. However, no tracer coupling pattern was observed when AII ACs were injected around eye-opening.
Our result that the AII ACs remain uncoupled during the retinal development until the third postnatal week indicates that the early expressed Cx36 proteins around eye opening do not form sufficient intercellular connections with other AII ACs and ON cone BCs. This suggests that the primary rod pathway develops much slower than the cone pathway, and the coupling among AII ACs does not contribute in retinal circuit maturation.
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