The overall objective of our research is to understand the detailed cellular and synaptic mechanisms underlying center and surround responses of retinal bipolar cells (BCs). Specifically, we will look at how neurons that mediate BC center and surround inputs in the outer retina (photoreceptors and horizontal cells (HCs)) interact with one another, and how adaptation, neuromodulators and the circadian clock regulate these cell-cell interactions and, consequently, BC receptive fields. We plan to use dual voltage clamp techniques to study cell-cell interactions at the photoreceptor, BC and HC levels, and use microelectrode voltage recording techniques to study receptive field properties of various types of cones, BCs and HCs. These two complementary approaches, along with the new knowledge and technical advances developed during the past years, will be applied to the salamander retina model system to study mechanisms underlying photoreceptor, HC and BC coupling and HC feedback/feedforward synaptic inputs to cones and BCs. These are common features of synaptic organization found in most vertebrate retinas. However, experiments involved in studying these features are technically difficult, if not impossible, to be carried out in many other vertebrates, including the mouse (thus issues to be addressed here complement, but do not overlap with our mouse grant). In this competing renewal application, we plan to continue our studies by focusing on 4 specific aims: (1) properties and modulation of electrical synapses between various pairs of photoreceptors (2 types of rods and 4 types of cones), (2) mechanisms underlying the sign-inverting, rod->cone transient signaling pathways in cones;(3) mechanisms underlying the depolarizing surround (feedback from HCs) responses in various types of cones; and (4) properties and modulation of HC and BC coupling and roles of cell-cell interaction in shaping BC and HC receptive fields. Results obtained will provide a detailed description of cell-cell interactions between neurons in the outer retina that are responsible for mediating the center and surround synaptic inputs in various types of BCs. Because of the similarities in outer retinal synaptic organizations between salamander and other vertebrates, knowledge obtained from this project will facilitate our understanding of how electrical/chemical synapses and BC receptive fields in mammalian and human retinas are organized, and provide important clues for developing animal models for various retinal diseases.

Public Health Relevance

Understanding how electrical and chemical synapses mediating receptive field organization in the outer retina is a fundamental and essential step for unraveling mechanisms of visual perception and brain operation. Results obtained from this project will provide crucial information on how specific defects in photoreceptor, bipolar cell and horizontal cell synapses are responsible for the onset of eye diseases, such as retinitis pigmentosa, macular degeneration, and congenital stationary night blindness.

National Institute of Health (NIH)
National Eye Institute (NEI)
Research Project (R01)
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Biology and Diseases of the Posterior Eye Study Section (BDPE)
Program Officer
Greenwell, Thomas
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Baylor College of Medicine
Schools of Medicine
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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; Wu, Samuel M (2012) Physiological characterization and functional heterogeneity of narrow-field mammalian amacrine cells. J Physiol 590:223-34
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; Wu, Samuel M (2011) Morphology and immunoreactivity of retrogradely double-labeled ganglion cells in the mouse retina. Invest Ophthalmol Vis Sci 52:4886-96
Yu, Yongchun; Satoh, Hiromasa; Vila, Alejandro et al. (2011) Effects of histamine on light responses of amacrine cells in tiger salamander retina. Neurochem Res 36:645-54
Simons, David L; Boye, Sanford L; Hauswirth, William W et al. (2011) Gene therapy prevents photoreceptor death and preserves retinal function in a Bardet-Biedl syndrome mouse model. Proc Natl Acad Sci U S A 108:6276-81

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