Abstract
Abstract: :
Purpose: Cholinergic mechanisms initiate activity–dependent wiring of the vertebrate retina (ref. 1). Here, we have tested whether acetylcholinesterase (AChE) is involved in early structural wiring as well as the long–term maintenance of retinal functioning. Methods: The postnatal retinal development was investigated in AChE–deficient knockout mice (AChE–/–; ref. 2) first from postnatal days 1–20 (P1–20), and then during the degeneration of these retinae until P266 by enzyme histochemistry (AChE, BChE), immunohistochemistry towards calcium binding proteins calbindin (CB), calretinin (CR), parvalbumin (PV), Müller cell antigens and photoreceptors (rho4D2), DAPI–staining, electron microscopy, and TUNEL–staining. Results: Sizes of layers of the AChE–/– retina as determined from DAPI stained sections were only slightly changed. From P9 onwards, development of outer segments (OS) was delayed. From P1–3 onwards a delayed development of IPL sublaminae was revealed by calbindin (CB) and calretinin (CR) immunostainings. In particular, CR+ processes of amacrine and ganglion cells erroneously criss–crossed throughout the IPL; a near–normal sublaminar pattern was achieved only after P20. Processes from PA+ cells became regularly arranged within two "novel" sublaminae in the AChE–/– mouse from P30 onwards. Following P19 to P266 a sequential regression of retinal cells was observed. The outer nuclear layer (ONL) completely, and then the inner nuclear layer (INL) partially regressed by apoptosis. Noticeably, the width of the inner plexiform layer (IPL) remained constant, while – due to cell migration into the GCL – the innermost layer increased slightly. After three months the photoreceptor layer (ONL) and OPL were non–existent. Conclusions: These findings document an indispensable role of AChE in both early retinal network formation and maintenance of retinal structure, not replaceable by the closely related butyrylcholinesterase. Ultimately this leads to photoreceptor degeneration (Bytyqi et al., 2003). The AChE–/– mouse could become a useful novel model for blinding diseases, and moreover, of cholinergic mechanisms for development and functioning of visual systems. References. 1.) Zhou, Z. J. (2001) Prog. Brain Res., 131, 599–613; 2.) Li, B. et al. (2000) J. Neurochem., 75, 1320–1331.
Keywords: retinal degenerations: cell biology • acetylcholine • photoreceptors