University of Southern California

USC Neuroscience

Alapakkam P. Sampath

Associate Professor
Department of Physiology & Biophysics
Zilkha Neurogenetic Institute
Keck School of Medicine
Co-Associate Director, Neurosciences Graduate Program

Research Topics

  1. Cellular Neurobiology
  2. Signal Transduction
  3. Vision Research
  4. Rod and Cone Phototransduction
  5. G-Protein Coupled Signaling Pathways
  6. Retinal Physiology and Signal Processing.

Research Overview

The Sampath laboratory is interested in understanding the molecular mechanisms underlying early visual processing to gain insight into the following questions. (1) How are G-protein-coupled signaling pathways in the retina controlled, and what are their functional properties? (2) How do these signaling pathways contribute to vision at low light levels? (3) How do alterations in retinal physiology influence visually guided behavior?

To answer these questions we use electrophysiological and optical techniques to measure the light-evoked activity of neurons in the retina. We are interested in rod and cone phototransduction, in particular how these photoreceptors achieve such different response properties despite having similar G-protein signaling pathways. In addition, we are interested in how the second order retinal cells , the bipolar cells, interpret the rod and cone signals and ultimately how these signals are encoded at the retinal output, the ganglion cells. By following the light responses in each of these neurons we can gain insights into how light-evoked signals are procesed by the retina.

We are ultimately interested in the causal relationship between retinal physiology and behavior for rod-mediated vision. We use a water maze to characterize visual threshold in transgenic mice with altered retinal protein expression. Our goal is to correlate the physiological properties of the retina with changes in visually guided behavior. This work will provide insights into how the retina shapes signals that are functionally relevant for vision.

Contact Information

Web Sites:
Zilkha Neurogenetic Institute
PIBBS
Lab Website
E-mail:
asampath@usc.edu
Mailing Address:
Zilkha Neurogenetic Institute
USC Keck School of Medicine
1501 San Pablo St., ZNI 435
Los Angeles, CA 90089
Office Location:
ZNI 435
Office Phone:
(323) 442-4413
Fax:
(323) 442-2448

Education

  • University of California, Berkeley, B.A., 1994
  • University of California, Los Angeles, Ph.D., 1999
  • Stanford University, Postdoctoral Fellowship, 2001
  • University of Washington, Postdoctoral Fellowship, 2004

Research Images

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Selected Publications

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Cao Y, Pahlberg J, Sarria I, Kamasawa N, Sampath AP*, Martemyanov KA*. (2012) Regulators of G protein signaling RGS7 and RGS11 determine the onset of the light response in ON bipolar neurons. Proc Natl Acad Sci USA 109: 7905-7910.

-PubMed

Arman AC, Sampath AP. (2012) Dark-adapted response threshold of OFF ganglion cells is note set by OFF bipolar cells in the mouse retina. J Neurophys 107: 2649-2659.

-PubMed

Pahlberg J,  Sampath AP. (2011) Visual threshold is set by linear and nonlinear mechanisms in the retina that mitigate noise. Bioessays 33:438-447. -PubMed

Doroudchi MM, Greenberg KP, Liu J, Silka KA, Boyden ES, Lockridge JA, Arman AC, Janani R, Boye, SE, Boye SL, Gordon GM, Matteo BC, Sampath AP*, Hauswirth WW*, Horsager, A*  (2011) Virally delivered channelrhodopsin-2 safely and effectively restores visual function in multiple mouse models of blindness. Mol Ther. Apr 19, advance online. -PubMed

Okawa H, Miyagishima KJ, Arman AC, Hurley JB, Field GD, Sampath AP. (2010) Optimal processing of photoreceptor signals is required to maximize behavioural sensitivity. J Physiol 588:1947-1960. -PubMed

Okawa H, Miyagishima KJ, Arman AC, Hurley JB, Field GD, Sampath AP. (2010) Coordinated control of sensitivity by two splice variants of Gao in retinal ON bipolar cells . J Gen Physiol 136: 443-454. -PubMed

Miyagishima KJ, Cornwall MC, Sampath AP. (2009) Metabolic constraints on the recovery of sensitivity after visual pigment bleaching in retinal rods. J Gen Physiol 134:165-175. -PubMed

Altimus, CM, Guler AD, Alam NM, Arman AC, Prusky GT, Sampath AP*, Hattar S*. (2010) Rod photoreceptors drive circadian photoentrainment across a wide range of light intensities Nat Neurosci. 13: 1107-1112. -PubMed

Field GD, Sampath AP, Rieke F. (2005) Retinal processing near absolute threshold: from behavior to mechanism. Annu Rev Physiol. 67:491-514. -PubMed

Sampath AP, Rieke F. (2004) Selective transmission of single photon responses by saturation at the rod-to-rod bipolar synapse. Neuron. 41(3):431-43. -PubMed