title: Chemogenetic Activation of ipRGCs Drives Changes in Dark-Adapted (Scotopic) Electroretinogram.
abstract: The purpose of this study was to investigate the impact of activating melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs) on dark-adapted (scotopic) electroretinograms (ERG).
  
  
  
  We used mice (Opn4Cre/+) expressing cre recombinase in melanopsin-expressing cells for a targeted gene delivery of a chemogenetic Gq-coupled receptor, hM3Dq, to ipRGCs. Intraperitoneal injection of clozapine N-oxide (CNO) at 5 mg/kg was used for acute activation of hM3Dq and thus excitation of ipRGCs in darkness. Dark-adapted flash ERGs were recorded across a 9-fold range of irradiances from hM3Dq Opn4Cre/+ and control Opn4Cre/+ mice before and after intraperitoneal injection of CNO. A- and b-wave amplitudes and implicit times and oscillatory potentials (OPs) were analyzed. Paired-flash stimuli were used to isolate cone-driven responses.
  
  
  
  Clozapine N-oxide application suppressed a- and b-wave amplitudes of the dark-adapted ERG across the flash intensity range in hM3Dq Opn4Cre/+ mice compared to control mice. Examination of the normalized irradiance-response functions revealed a shift in b-wave but not a-wave sensitivity. No changes in a- and b-wave implicit times were detected. Total OP amplitudes were also reduced in hM3Dq Opn4Cre/+ mice compared to controls following CNO administration. The paired-flash method revealed reduction in both the first (rods and cones) and second (cones only) flash response.
  
  
  
  Acute and selective activation of ipRGCs modulates the amplitude of both a- and b-waves of the scotopic ERG, indicating that the influence of this ganglion cell class on the retinal physiology extends to the photoreceptors as well as their downstream pathways.
authors.affiliation: Faculty of Biology, Medicine and Health, the University of Manchester, Manchester, United Kingdom.
authors.forename: Nina
authors.initials: N
authors.lastname: Milosavljevic
authors.affiliation: Faculty of Biology, Medicine and Health, the University of Manchester, Manchester, United Kingdom.
authors.forename: Annette E
authors.initials: AE
authors.lastname: Allen
authors.affiliation: Centre for Ophthalmology and Vision Sciences, Institute of Human Development, the University of Manchester, Manchester, United Kingdom.
authors.forename: Jasmina
authors.initials: J
authors.lastname: Cehajic-Kapetanovic
authors.affiliation: Faculty of Biology, Medicine and Health, the University of Manchester, Manchester, United Kingdom.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Lucas
mesh_terms: D000818:Animals; D003024:Clozapine / Q000031:analogs & derivatives / Q000494:pharmacology; D003623:Dark Adaptation / Q000187:drug effects / Q000502:physiology*; D004596:Electroretinography / Q000187:drug effects / Q000379:methods*; D007150:Immunohistochemistry; D019426:Integrases / Q000096:biosynthesis*; D051379:Mice; D018345:Mice, Knockout; D023421:Models, Animal; D010775:Photic Stimulation; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology; D012165:Retinal Ganglion Cells / Q000187:drug effects / Q000502:physiology*; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology; D017299:Rod Opsins / Q000378:metabolism; D000099210:Melanopsin
chemical_list: D003024:Clozapine; D019426:Integrases; D017299:Rod Opsins; D000099210:Melanopsin; C045073:Cre recombinase; C079149:clozapine N-oxide