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Michael B Manookin, Christian Puller, Fred Rieke, Maureen Neitz, Jay Neitz; A non-spiking, wide-field amacrine cell that rapidly integrates visual signals over long distances in the primate. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2640.
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© ARVO (1962-2015); The Authors (2016-present)
Stimulation outside of the classical receptive field produces clear and significant effects on visual processing, but little is known about the mechanisms mediating these long-range effects. Wide-field amacrine cells are a likely culprit, but, with a few exceptions, the function of these cells remains uncertain. Particularly little is known about wide-field amacrine cells in the primate. Here, we studied the physiology of a class of primate amacrine cells whose extensive dendritic arbor is well suited for integrating visual signals over broad regions of space.
We recorded from a class of displaced amacrine cells in an in vitro, whole-mount preparation of macaque retina. Responses were recorded to various light stimuli including spatio-temporal noise, which was used to characterize a cell’s receptive field (Chichilnisky, 2001 Network). We performed recordings in current-clamp with a K-based pipette solution that included lucifer yellow so we could recover the cells’ morphology after recording. Recordings were performed at an eccentricity of ~4-8 mm from the fovea.
Recorded amacrine cells appeared to constitute a single class based on their light responses, cellular morphology, and stratification pattern. Cells showed on average nine straight, smooth dendrites that extended 0.8-1.2 mm from the soma. These dendrites exhibited putative synaptic varicosities along their full length but lacked spines and axonal processes. This class of amacrine cells comprised OFF and ON types, stratifying in the outer and inner sublamina of the inner plexiform layer, respectively. The OFF type depolarized at light offset and the ON type depolarized at light onset; neither type exhibited a classical center-surround receptive field. Action potentials were not observed to either light stimulation or current injection despite depolarizations of >20 mV. Nonetheless, visual inputs located >0.5 mm from the cell body were effective in producing changes in somatic voltage.
The morphology of the wide-field amacrine cells characterized here is consistent with the wiry-type amacrine cells described by Mariani (1990, J Comp Neuro) in macaque retina. These cells appear well suited for rapidly integrating and communicating over distances.
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