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H. Hoshi, S.L. Mills; The G3 Ganglion Cell in the Rabbit Retina Is Coupled to Dorsally–Directed Amacrine Cells . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2311.
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© ARVO (1962-2015); The Authors (2016-present)
We examined a novel circuit by observing the morphology and tracer coupling patterns of a ganglion/amacrine cell tracer–coupled pair in the rabbit retina.
We stained a regular–occurring ganglion cell type in the rabbit retina termed G3 by Rockhill et al. (2002) J Neurosci. 22: 3831–3843.
Intracellular staining via Neurobiotin injection confirmed that the G3 ganglion cell (G3) ramified in sublamina a just distal to the ChAT–a band. Most G3 were asymmetrically distributed, usually extremely so, with the majority of the processes ventral to the soma in the inferior retina. Strikingly, Neurobiotin–tracer coupling also stained a single population of amacrine cells previously reported by others and sometimes termed dorsally–directed amacrine cells. These were distinguished by several processes emanating from the amacrine cell soma and coursing entirely in a narrow bundle in the dorsal direction. Many of these amacrine cell somas were located well outside the dendritic field of the ganglion cells and were presumably stained only due to their long processes ( > 2mm) which run dorsally to make contact with the ventrally–directed ganglion cell processes. There was more variability in the superior retina in that G3’s were often more nearly symmetrical and the amacrine cell dendrites were less constrained in their orientation. Tracer–coupled G3 somas were sometimes observed in the ganglion cell layer. The staining patterns suggested these were likely stained via the amacrine cell intermediaries rather than by direct dendritic contact with the injected G3. G3 ganglion cell/amacrine cell contacts were regularly immunopositive for an antibody to connexin36.
Two elements of a retinal circuit are described by virtue of Neurobiotin–tracer coupling through presumptive gap junctions. The location of the respective dendritic fields suggests that the G3 ganglion cell may have an unusual receptive field consisting of excitatory bipolar cell input mostly ventral to the soma, and a surround of even greater ventral bias arising from the amacrine cells. These amacrine cells should provide some additional excitatory (through the gap junctions) and perhaps inhibitory input via conventional synapses from the coupled amacrine cell as well, or some combination thereof.
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