title: Direct rod input to cone BCs and direct cone input to rod BCs challenge the traditional view of mammalian BC circuitry.
abstract: Bipolar cells are the central neurons of the retina that transmit visual signals from rod and cone photoreceptors to third-order neurons in the inner retina and the brain. A dogma set forth by early anatomical studies is that bipolar cells in mammalian retinas receive segregated rod/cone synaptic inputs (either from rods or from cones), and here, we present evidence that challenges this traditional view. By analyzing light-evoked cation currents from morphologically identified depolarizing bipolar cells (DBCs) in the wild-type and three pathway-specific knockout mice (rod transducin knockout [Tralpha(-/-)], connexin36 knockout [Cx36(-/-)], and transcription factor beta4 knockout [Bhlhb4(-/-)]), we show that a subpopulation of rod DBCs (DBC(R2)s) receives substantial input directly from cones and a subpopulation of cone DBCs (DBC(C1)s) receives substantial input directly from rods. These results provide evidence of the existence of functional rod-DBC(C) and cone-DBC(R) synaptic pathways in the mouse retina as well as the previously proposed rod hyperpolarizing bipolar-cells pathway. This is grounds for revising the mammalian rod/cone bipolar cell dogma.
authors.affiliation: Cullen Eye Institute, Baylor College of Medicine, Houston, TX 77030, USA.
authors.forename: Ji-Jie
authors.initials: JJ
authors.lastname: Pang
authors.forename: Fan
authors.initials: F
authors.lastname: Gao
authors.forename: Janis
authors.initials: J
authors.lastname: Lem
authors.forename: Debra E
authors.initials: DE
authors.lastname: Bramblett
authors.forename: David L
authors.initials: DL
authors.lastname: Paul
authors.forename: Samuel M
authors.initials: SM
authors.lastname: Wu
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D048430:Cell Shape; D017630:Connexins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018408:Patch-Clamp Techniques; D010775:Photic Stimulation; D051245:Retinal Bipolar Cells / Q000166:cytology / Q000502:physiology; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology / Q000502:physiology*; D017948:Retinal Rod Photoreceptor Cells / Q000166:cytology / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology; D015293:Transducin / Q000235:genetics / Q000378:metabolism; D014795:Visual Pathways / Q000033:anatomy & histology / Q000502:physiology; D000097004:Gap Junction delta-2 Protein
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D017630:Connexins; D015293:Transducin; D000097004:Gap Junction delta-2 Protein; C455509:Bhlhb4 protein, mouse