The overall objective of this new research project is to understand detailed synaptic mechanisms underlying rod and cone signaling pathways in the mammalian retina. Anatomical studies have suggested that rod and cone channels in the mammalian retina follow a specific set of circuitry rules: rods make synapses only on rod depolarizing bipolar cells (DBCRs), and DBCRs do not make output synapses directly on ganglion cells (GCs), but indirectly through AII amacrine cells (AIIACs). AIIACs send rod-mediated signals to ON and OFF GCs by "piggybacking" on the cone depolarizing and hyperpolarizing bipolar cells (DBCCs and HBCCs), which synapse on ON and OFF GCs, respectively. In this research proposal, we plan to systematically investigate these mammalian-specific synaptic circuits by using the mouse retina as a model system. In addition to using whole-cell voltage clamp (with dye-filling), anatomical and pharmacological techniques, we will take advantage of four strains of pathway-specific mutant mice to elucidate how mammalian rod and cone signals are transmitted to BCs, ACs and GCs, and to determine whether the mammalian-specific circuitry rules are totally valid, as recent evidence and our preliminary results suggest that the strict rod/cone input rules may not hold for all mammalian retinal neurons. We will test the overall hypothesis that "subpopulations of mouse DBCRs receive direct synaptic inputs from cones and subpopulations of mouse DBCCs and HBCCs receive direct synaptic inputs from rods, the rod- and cone-mediated signals are further mixed by AIIACs before sending to GCs, and the AC-mediated inhibitory synaptic inputs to BCs and GCs carry mixed rod/cone signals". This application has 3 specific aims focused on studying rod and cone contributions to light-evoked cation and chloride currents (?IC and ?ICl, representing glutamatergic and GABAergic/glycinergic synaptic inputs, respectively) in: (1) seven types of bipolar cells (HBCMC/Rs, HBCMCs, HBCSCs, DBCC2/MCs, DBCC1/MC/Rs, DBCR2s, DBCR1s);(2) AII amacrine cells;and (3) three types of alpha ganglion cells (ON, sOFF and tOFF ?GCs) in the dark-adapted mouse retina. Results obtained will increase our understanding of how parallel channels, such as the rod/cone signaling pathways, process, segregate and integrate information in the eye and in the brain. Since many visual disorders are associated with abnormalities in the rod and cone signaling pathways, this research project will help to identify cellular and synaptic sites responsible for the pathogenesis of these eye diseases.
The eye is the window of the brain and human eyes can register an enormous range of light intensities (from objects under starlit sky to snow under bright sun light) by dividing the labor into two parts: rod photoreceptors encode dim images and cone photoreceptors encode bright and color images. Understanding how rod and cone signals are processed by retinal synaptic pathways is a fundamental and essential step for unraveling mechanisms of visual perception and brain operation. Certain forms of macular degeneration, retinitis pigmentosa, congenital stationary night blindness and glaucoma are associated with dysfunction of the rod and cone signaling pathways, and thus results obtained from this project will provide crucial information on how specific defects in the rod and cone synaptic pathways mediate these eye disorders.
|Tse, Dennis Y; Chung, Inyoung; Wu, Samuel M (2014) Possible roles of glutamate transporter EAAT5 in mouse cone depolarizing bipolar cell light responses. Vision Res 103:63-74|
|Tse, Dennis Y; Chung, Inyoung; Wu, Samuel M (2014) Pharmacological inhibitions of glutamate transporters EAAT1 and EAAT2 compromise glutamate transport in photoreceptor to ON-bipolar cell synapses. Vision Res 103:49-62|
|Pang, Ji-Jie; Paul, David L; Wu, Samuel M (2013) Survey on amacrine cells coupling to retrograde-identified ganglion cells in the mouse retina. Invest Ophthalmol Vis Sci 54:5151-62|
|Frankfort, Benjamin J; Khan, A Kareem; Tse, Dennis Y et al. (2013) Elevated intraocular pressure causes inner retinal dysfunction before cell loss in a mouse model of experimental glaucoma. Invest Ophthalmol Vis Sci 54:762-70|
|Gao, Fan; Pang, Ji-Jie; Wu, Samuel M (2013) Sign-preserving and sign-inverting synaptic interactions between rod and cone photoreceptors in the dark-adapted retina. J Physiol 591:5711-26|
|Pang, Ji-Jie; Gao, Fan; Paul, David L et al. (2012) Rod, M-cone and M/S-cone inputs to hyperpolarizing bipolar cells in the mouse retina. J Physiol 590:845-54|
|Pang, Ji-Jie; Gao, Fan; Wu, Samuel M (2012) Physiological characterization and functional heterogeneity of narrow-field mammalian amacrine cells. J Physiol 590:223-34|
|Price, Brandee A; Sandoval, Ivette M; Chan, Fung et al. (2011) Mislocalization and degradation of human P23H-rhodopsin-GFP in a knockin mouse model of retinitis pigmentosa. Invest Ophthalmol Vis Sci 52:9728-36|
|Cai, Zhigang; Simons, David L; Fu, Xin-Yuan et al. (2011) Loss of Shp2-mediated mitogen-activated protein kinase signaling in Muller glial cells results in retinal degeneration. Mol Cell Biol 31:2973-83|
|Pang, Ji-Jie; Wu, Samuel M (2011) Morphology and immunoreactivity of retrogradely double-labeled ganglion cells in the mouse retina. Invest Ophthalmol Vis Sci 52:4886-96|
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