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Nicholas Brecha, Alex Solomon, Allen Rodriguez, Helen Vuong, Luis Pérez de Sevilla Müller, Belinda Wong, Steven A Barnes; VIP-expressing amacrine cells in mouse retina: Multiple subtypes with heterogeneous properties. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4174.
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© ARVO (1962-2015); The Authors (2016-present)
Amacrine cells form a large and heterogeneous group of inhibitory interneurons with specific roles in distinct retinal microcircuits. Our goal is to define the function of the amacrine cell subclasses expressing vasoactive intestinal peptide (VIP) by understanding the morphological and electrophysiological properties of this cell population in the mouse retina.
VIP-tdTomato and VIP-Brainbow mouse lines were generated by crossing a VIP-Cre transgenic mouse line (JAX #10908) with a Cre-dependent tdTomato (Ai9, JAX #7909) or Brainbow2.1 (JAX #13731) reporter mouse line. Retinal sections and whole-mounts were evaluated using immunohistochemistry and intracellular tracer injection. VIP-tdTomato cells were recorded with whole cell patch clamp techniques in retinal slices.
VIP-tdTomato fluorescent cell bodies in the inner nuclear layer (INL) and their processes were distributed to laminae 1, 3, 4 and 5 of the inner plexiform layer (IPL). Brainbow fluorescence was confined to individual cells with well-defined processes and these formed multiple types based on the ramification of their processes in the IPL. There were also occasional VIP-tdTomato cell bodies in the ganglion cell layer (GCL). Neurobiotin injection of VIP-tdTomato cells in the INL revealed coupling to numerous other amacrine and ganglion cells. VIP-tdTomato cells in the GCL showed no tracer coupling. VIP-tdTomato cells in the INL were found in all retinal regions, while those in the GCL were found mainly in superior-temporal retina. Cell density in the INL was ~610 cells/mm2 and the highest cell density in the GCL was ~28 cells/mm2. All tdTomato fluorescing cells contained VIP immunoreactivity, and all VIP immunoreactive cells contained tdTomato fluorescence. Every VIP-tdTomato cell also contained GABA immunoreactivity and none contained glycine immunoreactivity. No VIP-tdTomato cells expressed the ganglion cell marker RBPMS. Voltage clamp of VIP-tdTomato cells revealed differential expression of Na and BK channels between morphological subtypes. Under current clamp, action potentials were absent but spikelets were frequently observed.
We have identified a novel amacrine cell population consisting of several subtypes that are characterized by VIP expression. These findings provide the foundation for functional studies to define the roles of these amacrine cells in visual information processing.
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