ZFIN ID: ZDB-PUB-201020-26
Controlling horizontal cell-mediated lateral inhibition in transgenic zebrafish retina with chemogenetic tools
Beckwith-Cohen, B., Holzhausen, L.C., Nawy, S., Kramer, R.H.
Date: 2020
Source: eNeuro   7(5): (Journal)
Registered Authors: Beckwith-Cohen, Billie, Holzhausen, Lars
Keywords: feedback inhibition, fluorescent protein, horizontal cell, lateral inhibition, photoreceptor, retina
MeSH Terms:
  • Animals
  • Membrane Potentials
  • Retina
  • Retinal Cone Photoreceptor Cells
  • Retinal Horizontal Cells*
  • Zebrafish*
PubMed: 33060180 Full text @ eNeuro
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ABSTRACT
Horizontal Cells (HCs) form reciprocal synapses with rod and cone photoreceptors, an arrangement that underlies lateral inhibition in the retina. HCs send negative and positive feedback signals to photoreceptors, but how HCs initiate these signals remains unclear. Unfortunately, because HCs have no unique neurotransmitter receptors, there are no pharmacological treatments for perturbing membrane potential specifically in HCs. Here we utilize transgenic zebrafish whose HCs express alien receptors, enabling cell-type specific control by cognate alien agonists. To depolarize HCs, we used the FMRFamide-gated Na+ channel (FaNaC) activated by the invertebrate neuropeptide FMRFamide. To hyperpolarize HCs we used PSAM-GlyR, an engineered Cl-selective channel activated by a synthetic agonist. Expression of FaNaC or PSAM-GlyR was restricted to HCs with the cell-type selective promoter for connexin-55.5. We assessed HC-feedback control of photoreceptor synapses in three ways. First, we measured presynaptic exocytosis from photoreceptor terminals using the fluorescent dye FM1-43. Second, we measured the electroretinogram (ERG) b-wave, a signal generated by postsynaptic responses. Third, we used Ca2+ imaging in retinal ganglion cells (RGCs) expressing the Ca2+ indicator GCaMP6. Addition of FMRFamide significantly increased FM1-43 destaining in darkness, whereas the addition of PSAM-GlyR significantly decreased it. However, both agonists decreased the light-elicited ERG b-wave and eliminated surround inhibition of the Ca2+ response of RGCs. Taken together, our findings show that chemogenetic tools can selectively manipulate negative feedback from HCs, providing a platform for understanding its mechanism and helping to elucidate its functional roles in visual information processing at a succession of downstream stages.SIGNIFICANCE STATEMENT Horizontal cells (HCs) are laterally projecting interneurons that share reciprocal synaptic connections with photoreceptors, an arrangement that establishes the antagonistic center/surround receptive field properties of downstream neurons in the retina and onward into the brain. HC-mediated lateral inhibition was discovered over half a century ago, yet its underlying synaptic mechanisms remain incompletely understood. This is largely because the reciprocal synapse complicates selective manipulation of HCs alone. Here, we utilize chemogenetic tools to bypass photoreceptors and directly manipulate HC membrane potential to reveal feedback effects on sequential steps in synaptic processing of visual information.
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