title: Enhancement of ON-bipolar cell responses of cone electroretinograms in rabbits with the Pro347Leu rhodopsin mutation.
abstract: OBJECTIVE
  To determine how the different stages of retinal processing change after photoreceptor degeneration in rabbits carrying the Pro347Leu rhodopsin mutation (Tg rabbits).
  
  
  METHODS
  Cone electroretinograms (ERGs) were elicited by 150-ms duration stimuli from 13 Tg rabbits at 12 and 24 weeks of age. The ERG recordings were made before and after an intravitreal injection of tetrodotoxin citrate (TTX) plus N-methyl-dl-aspartic acid (NMDA), with the addition of 2-amino-4-phosphonobutyric acid (APB) and then cis-2,3-piperidine-dicarboxylic acid (PDA) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Digital subtraction of the ERG after the injection from the ERG before the injection was used to extract the components that were blocked by these drugs. Thirteen age-matched, wild-type (WT) rabbits were studied with the same protocol.
  
  
  RESULTS
  In Tg rabbits, the cone ERGs elicited by intermediate intensities had a depolarizing pattern. At 12 weeks of age, the photoreceptor and OFF-bipolar/horizontal cell responses reflected in the ERG in the Tg rabbits did not differ significantly from those in the WT rabbits. The ON-bipolar cells and the third-order neuronal responses recorded after pharmacologic blockade were significantly enhanced in the Tg rabbits compared with those recorded in the WT rabbits. At 24 weeks of age, the ERG waveforms representing the photoreceptors and OFF-bipolar/horizontal cell responses were significantly decreased, but those representing the ON-bipolar cell and third-order neuronal responses were still preserved in the Tg rabbits.
  
  
  CONCLUSIONS
  A depolarizing pattern of the cone ERG responses was seen in Pro347Leu Tg rabbits. The enhancement or preservation of the ON-bipolar cell response in the ERGs contributed to shaping the waveform in the Tg rabbits. In this model, the functional alterations in the ON-pathway took place before the deterioration of cone photoreceptor function.
authors.affiliation: Department of Ophthalmology, Iwate Medical University School of Medicine, Iwate, Japan.
authors.forename: Tomoharu
authors.initials: T
authors.lastname: Nishimura
authors.forename: Shigeki
authors.initials: S
authors.lastname: Machida
authors.forename: Mineo
authors.initials: M
authors.lastname: Kondo
authors.forename: Hiroko
authors.initials: H
authors.lastname: Terasaki
authors.forename: Daisuke
authors.initials: D
authors.lastname: Yokoyama
authors.forename: Daijiro
authors.initials: D
authors.lastname: Kurosaka
mesh_terms: D000613:Aminobutyrates / Q000633:toxicity; D000818:Animals; D030801:Animals, Genetically Modified; D004195:Disease Models, Animal; D004596:Electroretinography / Q000187:drug effects*; D018690:Excitatory Amino Acid Agonists / Q000633:toxicity; D018691:Excitatory Amino Acid Antagonists / Q000633:toxicity; D058449:Intravitreal Injections; D017354:Point Mutation; D011817:Rabbits; D051245:Retinal Bipolar Cells / Q000502:physiology*; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology*; D012162:Retinal Degeneration / Q000235:genetics / Q000503:physiopathology*; D012243:Rhodopsin / Q000235:genetics*; D013779:Tetrodotoxin / Q000633:toxicity; D014785:Vision, Ocular
chemical_list: D000613:Aminobutyrates; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D013779:Tetrodotoxin; D012243:Rhodopsin; C012729:2-amino-4-phosphonobutyric acid