Journal
VISUAL NEUROSCIENCE
Volume 27, Issue 1-2, Pages 19-42Publisher
CAMBRIDGE UNIV PRESS
DOI: 10.1017/S0952523810000052
Keywords
ACh; Choline acetyltransferase; GABA; Glutamic acid decarboxylase; GAT1; ChAT; GAD(65); GAD(67); Retinal waves
Categories
Funding
- Natural Science and Engineering Research Council of Canada
- Alberta Heritage Foundation for Medical Research
- Lions Sight Centre of the University of Calgary
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Starburst amacrine cells (SACs), the only acetylcholine (ACh)-releasing amacrine cells (ACs) in adult rabbit retina, contain GABA and are key elements in the retina's directionally selective (DS) mechanism. Unlike many other GABAergic ACs, they use glutamic acid decarboxlyase (GAD)(67), not GAD(65), to synthesize GABA. Using immunocytochemistry, we demonstrate the apoptosis at birth (PO) of transitory putative ACs that exhibit immunoreactivity (IR) for the ACh-synthetic enzyme choline acetyltransferase (ChAT), GAD(67), and the GABA transporter, GAT I. Only a few intact, displaced ChAT-immunoreactive SAC bodies are detected at PO. At P2, ChAT-IR is detected in the two narrowly stratified substrata of starburst dendrites in the inner plexiform layer (IPL). Quantitative analysis reveals that in the first postnatal week, only a small fraction of SACs cells express ChAT- and GABA-IR. Not until the end of the second week are they expressed in all SACs. At PO, a three-tiered stratification of GABA-IR is present in the IPL, entirely different from the adult pattern of seven substrata, emerging at P3-P4, and optimally visualized at P13. At P0, GAD(65) is detectable in normally placed AC bodies. At PI, GAD(65)-IR appears in dendrites of nonstarburst GABAergic ACs, and by P5 is robust in the adult pattern of four substrata in the IPL. GAD(65)-IR never co-localizes with ChAT-IR. In a temporal comparison of our data with physiological, pharmacological, and ultrastructural studies, we suggest that transitory ChAT-immunoreactive cells share with SACs production of stage II (nicotinic) waves of previsual synchronous activity in ganglion cells (GCs). Further, we conclude that (1) GAD(65)-immunoreaetive, non-SAC GABAergic ACs are the most likely candidates responsible for the suppression of stage III (muscarinic/AMPA-kainate) waves and (2) DS responses first appear in DS GCs, when about 50% of SACs express ChAT- and GABA-IR, and in 100% of DS GCs, when expression occurs in all SACs.
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