title: Inhibitory masking controls the threshold sensitivity of retinal ganglion cells.
abstract: Retinal ganglion cells (RGCs) in dark-adapted retinas show a range of threshold sensitivities spanning ∼3 log units of illuminance. Here, we show that the different threshold sensitivities of RGCs reflect an inhibitory mechanism that masks inputs from certain rod pathways. The masking inhibition is subserved by GABACreceptors, probably on bipolar cell axon terminals. The GABAergic masking inhibition appears independent of dopaminergic circuitry that has been shown also to affect RGC sensitivity. The results indicate a novel mechanism whereby inhibition controls the sensitivity of different cohorts of RGCs. This can limit and thereby ensure that appropriate signals are carried centrally in scotopic conditions when sensitivity rather than acuity is crucial.
  
  
  
  The responses of rod photoreceptors, which subserve dim light vision, are carried through the retina by three independent pathways. These pathways carry signals with largely different sensitivities. Retinal ganglion cells (RGCs), the output neurons of the retina, show a wide range of sensitivities in the same dark-adapted conditions, suggesting a divergence of the rod pathways. However, this organization is not supported by the known synaptic morphology of the retina. Here, we tested an alternative idea that the rod pathways converge onto single RGCs, but inhibitory circuits selectively mask signals so that one pathway predominates. Indeed, we found that application of GABA receptor blockers increased the sensitivity of most RGCs by unmasking rod signals, which were suppressed. Our results indicate that inhibition controls the threshold responses of RGCs under dim ambient light. This mechanism can ensure that appropriate signals cross the bottleneck of the optic nerve in changing stimulus conditions.
authors.affiliation: Department of Biological and Vision Sciences, State University of New York College of Optometry, New York, NY, USA.|Current address: School of Optometry, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
authors.forename: Feng
authors.initials: F
authors.lastname: Pan
authors.affiliation: Department of Biological and Vision Sciences, State University of New York College of Optometry, New York, NY, USA.
authors.forename: Abduqodir
authors.initials: A
authors.lastname: Toychiev
authors.affiliation: F. M. Kirby Neurobiology Center, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Sport Biology, Janos Szentagothai Research Center, University of Pécs, Pécs, Hungary.
authors.forename: Tamas
authors.initials: T
authors.lastname: Atlasz
authors.affiliation: Department of Biological and Vision Sciences, State University of New York College of Optometry, New York, NY, USA.
authors.forename: Hariharasubramanian
authors.initials: H
authors.lastname: Ramakrishnan
authors.affiliation: Department of Biological and Vision Sciences, State University of New York College of Optometry, New York, NY, USA.
authors.forename: Kaushambi
authors.initials: K
authors.lastname: Roy
authors.affiliation: Department of Sport Biology, Janos Szentagothai Research Center, University of Pécs, Pécs, Hungary.|Department of Experimental Zoology and Neurobiology, Janos Szentagothai Research Center, University of Pécs, Pécs, Hungary.
authors.forename: Béla
authors.initials: B
authors.lastname: Völgyi
authors.affiliation: Department of Biological and Vision Sciences, State University of New York College of Optometry, New York, NY, USA.
authors.forename: Abram
authors.initials: A
authors.lastname: Akopian
authors.affiliation: Department of Biological and Vision Sciences, State University of New York College of Optometry, New York, NY, USA.
authors.forename: Stewart A
authors.initials: SA
authors.lastname: Bloomfield
mesh_terms: D000818:Animals; D018756:GABA Antagonists / Q000494:pharmacology*; D008027:Light; D008564:Membrane Potentials / Q000187:drug effects*; D051379:Mice; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D010775:Photic Stimulation / Q000379:methods; D018079:Receptors, GABA / Q000378:metabolism; D012160:Retina / Q000187:drug effects / Q000378:metabolism*; D012165:Retinal Ganglion Cells / Q000187:drug effects* / Q000378:metabolism; D017948:Retinal Rod Photoreceptor Cells / Q000187:drug effects / Q000378:metabolism; D013569:Synapses / Q000378:metabolism; D014795:Visual Pathways / Q000187:drug effects / Q000378:metabolism
chemical_list: D018756:GABA Antagonists; D018079:Receptors, GABA
keywords: Adaptation; gaba; inhibition; retinal ganglion cell; vision