Alapakkam Sampath Laboratory

Phototransduction and Synaptic Transmission

Understanding visual processing in the retina

Alapakkam Sampath, Ph.D.

Professor

Grace and Walter Lantz Endowed Chair in Ophthalmology

Departments of Ophthalmology and Neurobiology

Associate Director of Research

Jules Stein Eye Institute

asampath@jsei.ucla.edu Faculty Profile

The goal of the Sampath laboratory is the elucidation of fundamental mechanisms of visual processing. We have focused on generating a deeper understanding of development and signaling between photoreceptor cells—the rods and cones—and their synaptic partners, the bipolar cells, to determine how information is formed and processed within retinal circuits.

Our research focuses on the following questions:

How can rod photoresponses in the mammalian retina provide such an enormous range of rod vision - from single-photon responses in few rods to light bright enough to activate thousands or tens of thousands of rhodopsin pigment molecules per second?
How do the many mechanisms of pigment regeneration influence photoreceptor and circuit-level sensitivity in steady light?
What are the molecules that determine the specificity of synaptic connections between photoreceptors and bipolar cells during development? How are rod and cone photoresponses integrated in the outer retina to provide a seamless shift from rod vision to cone vision as the light intensity increases?
What is the role of retinal remodeling in controlling visual sensitivity during photoreceptor degeneration? How is this remodeling affected when vision is restored with gene therapy?
How is retinal structure and function altered or conserved across the animal kingdom? What are the implications of these similarities and differences for the evolution of the vertebrate retina?

These questions remain of great interest because of the large proportion of visual deficits arising from abnormal signaling, either within the phototransduction cascade or in synaptic transmission from photoreceptor terminals to bipolar cells. To answer these questions, we employ classical (but still state-of-the-art) physiological techniques to measure light-evoked responses of photoreceptors, bipolar cells, and ganglion cells, which let us determine how the functional properties of responses are constructed by the retinal circuitry.

Selected Publications

Cones and cone pathways remain functional in advanced retinal degeneration

Ellis EM, Paniagua AE, Scalabrino ML, Thapa M, Rathinavelu J, Jiao Y, Williams DS, Field GD, Fain GL, Sampath AP

Current Biology (2023) • New citations

View Publication

Rod photoreceptors avoid saturation in bright light by movement of the G protein transducin

Frederiksen R, Morshedian A, Tripathy SA, Zhou T, Travis GH, Fain GL, Sampath AP

Journal of Neuroscience (2021) • 12 citations

View Publication

Elevated energy requirements of cone photoreceptors: Implications for retinal dysfunction

Ingram NT, Fain GL, Sampath AP

Proceedings of the National Academy of Sciences USA (2020) • 15 citations

View Publication

Activation of rod input in a model of retinal degeneration reverses retinal remodeling and induces formation of functional synapses and recovery of visual signaling in the adult retina

Wang T, Pahlberg J, Cafaro J, Sampath AP*, Field GD*, Chen J*

Journal of Neuroscience (2019) • 25 citations

View Publication