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J. Zhang, C.Y. Yang; Synaptic Organization of GABAergic Amacrine Cells in the Salamander Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5176.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: GABA is a major inhibitory neurotransmitter in amacrine cells of the vertebrate retina. Physiological studies have demonstrated that GABAergic amacrine cells in the salamander retina participate in feedback inhibition to bipolar cells and feedforward inhibition to ganglion cells and other amacrine cells. However, little is known about the synaptic organization of GABAergic amacrine cells in this species. This study focused on the types and distribution of GABA-immunoreactive (GABA-IR) amacrine synapses in the IPL. Methods: Photomontages of electron micrographs covering 3618 µm2 of the IPL were obtained by using a post-embedding GABA immunogold method. Results: 1) GABA-IR amacrine synapses (N=459) were distributed throughout the IPL, with a peak at the proximal margin of sublamina a and a somewhat higher concentration in sublamina b. 2) The majority of output targets (81%) were not GABA-IR. 3) Most of the contacts (94%) were simple synapses with one postsynaptic element identified as a process of an amacrine cell (50%), bipolar cell (19%) or ganglion cell (25%); 2.6% were serial synapses and 3.4% were unidentified. 4) Of the 86 postsynaptic bipolar terminals, 63% participated in a reciprocal feedback synapse with the same presynaptic GABA-IR amacrine profile. 5) There appeared to be no preference between amacrine contacts with rod- or cone- dominant bipolar cells (9.1% vs 8.9%) or in the total number of amacrine synapses in sublaminas a and b (52% vs 47%). Conclusion: GABA-IR amacrine cells in salamander preferentially contact other amacrine cells, indicating that they are more involved in lateral inhibitory pathways. This is in contrast to mammals (cat, monkey), in which about 50% of the GABAergic amacrine output is onto bipolar cells and thereby they are more likely to exert their effects directly on the through pathway.
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