Alapakkam Sampath, Ph.D.

Research interest:

Research

Dr. Sampath is an internationally known visual neuroscientist who is recognized as a leader in the study of cellular and circuit level visual processing. His work focuses on signal transmission between photoreceptor cells, the rods and cones, and bipolar cells to determine how information is processed within retinal circuits and gives rise to visual perceptual sensitivity. Not only is his work of broad fundamental scientific interest, it has significant implications for our understanding of visual blinding diseases such as night blindness.

Publications

Majumder Anurima, Pahlberg Johan, Boyd Kimberly K, Kerov Vasily, Kolandaivelu Saravanan, Ramamurthy Visvanathan, Sampath Alapakkam P, Artemyev Nikolai O Transducin translocation contributes to rod survival and enhances synaptic transmission from rods to rod bipolar cells Proceedings of the National Academy of Sciences of the United States of America, 2013; 110(30): 12468-73.

Chen Shih-Kuo, Chew Kylie S, McNeill David S, Keeley Patrick W, Ecker Jennifer L, Mao Buqing Q, Pahlberg Johan, Kim Bright, Lee Sammy C S, Fox Michael A, Guido William, Wong Kwoon Y, Sampath Alapakkam P, Reese Benjamin E, Kuruvilla Rejji, Hattar Samer Apoptosis regulates ipRGC spacing necessary for rods and cones to drive circadian photoentrainment Neuron, 2013; 77(3): 503-15.

Mao Wen, Miyagishima K J, Yao Yun, Soreghan Brian, Sampath Alapakkam P, Chen Jeannie Functional comparison of rod and cone Gα(t) on the regulation of light sensitivity The Journal of biological chemistry, 2013; 288(8): 5257-67.

Arman A Cyrus, Sampath Alapakkam P Dark-adapted response threshold of OFF ganglion cells is not set by OFF bipolar cells in the mouse retina Journal of neurophysiology, 2012; 107(10): 2649-59.

Cho Alice K, Sampath Alapakkam P, Weiland James D Physiological response of normal and RD mouse retinal ganglion cells to electrical stimulation Conference proceedings : … Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference, 2012; 2012(10): 2985-8.

Cao Yan, Pahlberg Johan, Sarria Ignacio, Kamasawa Naomi, Sampath Alapakkam P, Martemyanov Kirill A Regulators of G protein signaling RGS7 and RGS11 determine the onset of the light response in ON bipolar neurons Proceedings of the National Academy of Sciences of the United States of America, 2012; 109(20): 7905-10.

Farley Robert A, Sampath Alapakkam P Perspectives on: information coding in mammalian sensory physiology The Journal of general physiology, 2011; 138(3): 281-2.

Doroudchi M Mehdi, Greenberg Kenneth P, Liu Jianwen, Silka Kimberly A, Boyden Edward S, Lockridge Jennifer A, Arman A Cyrus, Janani Ramesh, Boye Shannon E, Boye Sanford L, Gordon Gabriel M, Matteo Benjamin C, Sampath Alapakkam P, Hauswirth William W, Horsager Alan Virally delivered channelrhodopsin-2 safely and effectively restores visual function in multiple mouse models of blindness Molecular therapy : the journal of the American Society of Gene Therapy, 2011; 19(7): 1220-9.

Pahlberg Johan, Sampath Alapakkam P Visual threshold is set by linear and nonlinear mechanisms in the retina that mitigate noise: how neural circuits in the retina improve the signal-to-noise ratio of the single-photon response BioEssays : news and reviews in molecular, cellular and developmental biology, 2011; 33(6): 438-47.

Okawa Haruhisa, Pahlberg Johan, Rieke Fred, Birnbaumer Lutz, Sampath Alapakkam P Coordinated control of sensitivity by two splice variants of Gα(o) in retinal ON bipolar cells The Journal of general physiology, 2010; 136(4): 443-54.

Altimus Cara M, Güler Ali D, Alam Nazia M, Arman A Cyrus, Prusky Glen T, Sampath Alapakkam P, Hattar Samer Rod photoreceptors drive circadian photoentrainment across a wide range of light intensities Nature neuroscience, 2010; 13(9): 1107-12.

Okawa Haruhisa, Miyagishima K Joshua, Arman A Cyrus, Hurley James B, Field Greg D, Sampath Alapakkam P Optimal processing of photoreceptor signals is required to maximize behavioural sensitivity The Journal of physiology, 2010; 588(Pt 11): 1947-60.

Matthews Hugh R, Sampath Alapakkam P Photopigment quenching is Ca2+ dependent and controls response duration in salamander L-cone photoreceptors The Journal of general physiology, 2010; 135(4): 355-66.

Singer Joshua H, Glowatzki Elisabeth, Moser Tobias, Strowbridge Ben W, Bhandawat Vikas, Sampath Alapakkam P Functional properties of synaptic transmission in primary sense organs The Journal of neuroscience : the official journal of the Society for Neuroscience, 2009; 29(41): 12802-6.

Miyagishima Kiyoharu J, Cornwall M Carter, Sampath Alapakkam P Metabolic constraints on the recovery of sensitivity after visual pigment bleaching in retinal rods The Journal of general physiology, 2009; 134(3): 165-75.

Mayank Mehta, Ph.D.

Research

The mind is thought to be the emergent property of the activities of ensembles of neurons. The nature of these emergent properties and how they arise are unknown. This is the focus of our research. In particular, our current research addresses the following fundamental questions in Neurophysics: 1. How is information about the physical world represented by ensembles of neurons? In particular, what are the neural mechanisms of perceiving space-time? 2. How do the neural representations evolve with learning? 3. What is the role of brain rhythms in learning and memory? 4. How does sleep influence learning? To address these questions we use both experimental and theoretical approaches as follows: 1. Develop hardware to measure and manipulate neural activity and behavior. 2. Measure the activity of ensembles of well isolated neurons from many hippocampal and neocortical areas simultaneously during learning and during sleep. 3. Develop data analysis tools to decipher the patterns of neural activity and field potentials, and their relationship to behavior. 4. Develop biophysical theories of synapses, neurons and neuronal networks that can explain these experimental finding, relate them to the underlying cellular mechanisms, and make experimentally testable predictions. The results would not only provide fundamental understanding of neural ensemble dynamics but also point to novel ways of treating learning and memory disorders.

Publications

Jason J. Moore, Pascal M. Ravassard, David Ho, Lavanya Acharya, Ashley L. Kees, Cliff Vuong, Mayanak R. Mehta.  Dynamics of Cortical Dendritic Membrane Potential and Spikes in Freely Behaving Cats.  Science, vol 335, issue 6331, 1281 (2017), 24 March 2017.

Acharya Lavanya, Aghajan Zahra M, Vuong Cliff, Moore Jason J, Mehta Mayank R Causal Influence of Visual Cues on Hippocampal Directional Selectivity Cell, 2016; 164(1-2): 197-207.

Mehta Mayank R From synaptic plasticity to spatial maps and sequence learning Hippocampus, 2015; 25(6): 756-62.

Aghajan Zahra M, Acharya Lavanya, Moore Jason J, Cushman Jesse D, Vuong Cliff, Mehta Mayank R Impaired spatial selectivity and intact phase precession in two-dimensional virtual reality Nature neuroscience, 2015; 18(1): 121-8.

Ravassard Pascal, Kees Ashley, Willers Bernard, Ho David, Aharoni Daniel, Cushman Jesse, Aghajan Zahra M, Mehta Mayank R Multisensory control of hippocampal spatiotemporal selectivity Science (New York, N.Y.), 2013; 340(6138): 1342-6.

Cushman Jesse D, Aharoni Daniel B, Willers Bernard, Ravassard Pascal, Kees Ashley, Vuong Cliff, Popeney Briana, Arisaka Katsushi, Mehta Mayank R Multisensory control of multimodal behavior: do the legs know what the tongue is doing? PloS one, 2013; 8(11): e80465.

Ghorbani Maryam, Mehta Mayank, Bruinsma Robijn, Levine Alex J Nonlinear-dynamics theory of up-down transitions in neocortical neural networks Physical review. E, Statistical, nonlinear, and soft matter physics, 2012; 85(2 Pt 1): 021908.

Ahmed Omar J, Mehta Mayank R Running speed alters the frequency of hippocampal gamma oscillations The Journal of neuroscience : the official journal of the Society for Neuroscience, 2012; 32(21): 7373-83.

Hahn Thomas T G, McFarland James M, Berberich Sven, Sakmann Bert, Mehta Mayank R Spontaneous persistent activity in entorhinal cortex modulates cortico-hippocampal interaction in vivo Nature neuroscience, 2012; 15(11): 1531-8.

Resnik Evgeny, McFarland James M, Sprengel Rolf, Sakmann Bert, Mehta Mayank R The effects of GluA1 deletion on the hippocampal population code for position The Journal of neuroscience : the official journal of the Society for Neuroscience, 2012; 32(26): 8952-68.

Mehta Mayank R Contribution of Ih to LTP, place cells, and grid cells Cell, 2011; 147(5): 968-70.

McFarland James M, Hahn Thomas T G, Mehta Mayank R Explicit-duration hidden Markov model inference of UP-DOWN states from continuous signals PloS one, 2011; 6(6): e21606.

Kumar Arvind, Mehta Mayank R Frequency-Dependent Changes in NMDAR-Dependent Synaptic Plasticity Frontiers in computational neuroscience, 2011; 5(5): 38.

Chen Zhiping, Resnik Evgeny, McFarland James M, Sakmann Bert, Mehta Mayank R Speed controls the amplitude and timing of the hippocampal gamma rhythm PloS one, 2011; 6(6): e21408.

Ahmed Omar J, Mehta Mayank R The hippocampal rate code: anatomy, physiology and theory Trends in neurosciences, 2009; 32(6): 329-38. Mehta Mayank R Cortico-hippocampal interaction during up-down states and memory consolidation Nature neuroscience, 2007; 10(1): 13-5.

Hahn Thomas T G, Sakmann Bert, Mehta Mayank R Differential responses of hippocampal subfields to cortical up-down states Proceedings of the National Academy of Sciences of the United States of America, 2007; 104(12): 5169-74.

Hoffman Kari L, Battaglia Francesco P, Harris Kenneth, MacLean Jason N, Marshall Lisa, Mehta Mayank R The upshot of up states in the neocortex: from slow oscillations to memory formation The Journal of neuroscience : the official journal of the Society for Neuroscience, 2007; 27(44): 11838-41.

Hahn Thomas T G, Sakmann Bert, Mehta Mayank R Phase-locking of hippocampal interneurons’ membrane potential to neocortical up-down states Nature neuroscience, 2006; 9(11): 1359-61.

Mehta Mayank R Role of rhythms in facilitating short-term memory Neuron, 2005; 45(1): 7-9.

Mehta Mayank R Cooperative LTP can map memory sequences on dendritic branches Trends in neurosciences, 2004; 27(2): 69-72.

Petersen Carl C H, Hahn Thomas T G, Mehta Mayank, Grinvald Amiram, Sakmann Bert Interaction of sensory responses with spontaneous depolarization in layer 2/3 barrel cortex Proceedings of the National Academy of Sciences of the United States of America, 2003; 100(23): 13638-43.

Baljit Khakh, Ph.D.

Research

Astrocyte biology and biophysics. Astrocytes are a type of brain glial cell discovered by early neuroanatomists over a century ago. Captivated by their elaborate shapes, these pioneers documented the close spatial relationships between astrocytes and neurons. Subsequent work showed that fine astrocyte processes form connections with as many as 100,000 synapses and that individual astrocytes are tiled, as though they “know” not to invade each others territories. These studies raise the exciting possibility that individual astrocytes may regulate subsets of neurons and contribute to the operation of neuronal circuits. The lab seeks to investigate this possibility. ATP signaling. One reason the body can function in a regulated manner is due to the ability of cells to communicate with other cells in a precise way over different scales of time and distance. A major advance has been the realization that ATP, which is the energy source for reactions within cells, also plays major roles as a communicator between cells by activating P2X ion channels which are cell surface ATP receptors. By understanding P2X channel physiology in neurons and glia we seek to decipher how ATP shapes excitability and signaling over broad spatial and temporal scales.

Publications

Tong Xiaoping, Shigetomi Eiji, Looger Loren L, Khakh Baljit S Genetically encoded calcium indicators and astrocyte calcium microdomains The Neuroscientist : a review journal bringing neurobiology, neurology and psychiatry, 2013; 19(3): 274-91.

Shigetomi Eiji, Jackson-Weaver Olan, Huckstepp Robert T, O’Dell Thomas J, Khakh Baljit S TRPA1 channels are regulators of astrocyte basal calcium levels and long-term potentiation via constitutive D-serine release The Journal of neuroscience : the official journal of the Society for Neuroscience, 2013; 33(24): 10143-53.

Shigetomi Eiji, Bushong Eric A, Haustein Martin D, Tong Xiaoping, Jackson-Weaver Olan, Kracun Sebastian, Xu Ji, Sofroniew Michael V, Ellisman Mark H, Khakh Baljit S Imaging calcium microdomains within entire astrocyte territories and endfeet with GCaMPs expressed using adeno-associated viruses The Journal of general physiology, 2013; 141(5): 633-47.

Hamby Mary E, Coppola Giovanni, Ao Yan, Geschwind Daniel H, Khakh Baljit S, Sofroniew Michael V Inflammatory mediators alter the astrocyte transcriptome and calcium signaling elicited by multiple G-protein-coupled receptors The Journal of neuroscience : the official journal of the Society for Neuroscience, 2012; 32(42): 14489-510.

Khakh Baljit S, North R Alan Neuromodulation by extracellular ATP and P2X receptors in the CNS Neuron, 2012; 76(1): 51-69. E. Shigetomi, X. Tong, K. Kwan, D.P. Corey, & B.S. Khakh TRPA1 channels regulate astrocyte resting calcium and inhibitory synapse efficacy via GAT-3 Nature Neuroscience, 2012; 15: 70-80.

Toulme Estelle, Khakh Baljit S Imaging P2X4 receptor lateral mobility in microglia: regulation by calcium and p38 MAPK The Journal of biological chemistry, 2012; 287(18): 14734-48.

Shigetomi Eiji, Tong Xiaoping, Kwan Kelvin Y, Corey David P, Khakh Baljit S TRPA1 channels regulate astrocyte resting calcium and inhibitory synapse efficacy through GAT-3 Nature neuroscience, 2012; 15(1): 70-80.

Richler Esther, Shigetomi Eiji, Khakh Baljit S Neuronal P2X2 receptors are mobile ATP sensors that explore the plasma membrane when activated The Journal of neuroscience : the official journal of the Society for Neuroscience, 2011; 31(46): 16716-30.

Reeves AM, Shigetomi E, Khakh BS. Bulk loading of calcium indicator dyes to study astrocyte physiology: key limitations and improvements using morphological maps J Neurosci, 2011; 22: 9353-8.

Richler E, Shigetomi E, Khakh BS. Neuronal P2X2 Receptors Are Mobile ATP Sensors That Explore the Plasma Membrane When Activated J Neurosci, 2011; 31: 16716-30.

Reeves Alexander M B, Shigetomi Eiji, Khakh Baljit S Bulk loading of calcium indicator dyes to study astrocyte physiology: key limitations and improvements using morphological maps The Journal of neuroscience : the official journal of the Society for Neuroscience, 2011; 31(25): 9353-8.

Shigetomi Eiji, Kracun Sebastian, Khakh Baljit S Monitoring astrocyte calcium microdomains with improved membrane targeted GCaMP reporters Neuron glia biology, 2010; 6(3): 183-91.

Shigetomi E, Kracun S, Sofroniew MV, Khakh BS. A genetically targeted optical sensor to monitor calcium signals in astrocyte processes Nature Neuroscience, 2010; 13: 759-66.

Shigetomi Eiji, Kracun Sebastian, Sofroniew Michael V, Khakh Baljit S A genetically targeted optical sensor to monitor calcium signals in astrocyte processes Nature neuroscience, 2010; 13(6): 759-66.

Toulme Estelle, Garcia Angie, Samways Damien, Egan Terrance M, Carson Monica J, Khakh Baljit S P2X4 receptors in activated C8-B4 cells of cerebellar microglial origin The Journal of general physiology, 2010; 135(4): 333-53.

Kracun Sebastian, Chaptal Vincent, Abramson Jeff, Khakh Baljit S Gated access to the pore of a P2X receptor: structural implications for closed-open transitions The Journal of biological chemistry, 2010; 285(13): 10110-21.

Kracun Sebastian, Chaptal Vincent, Abramson Jeff, Khakh Baljit S Gated access to the pore of a P2X receptor: structural implications for closed-open transitions The Journal of biological chemistry, 2010; 285(13): 10110-21.

Shigetomi Eiji, Khakh Baljit S Measuring near plasma membrane and global intracellular calcium dynamics in astrocytes Journal of visualized experiments : JoVE, 2009; 301(26): .

Singh Harpreet, Warburton Sarah, Vondriska Thomas M, Khakh Baljit S Proteomics to identify proteins interacting with P2X2 ligand-gated cation channels Journal of visualized experiments : JoVE, 2009; 301(27): .

Khakh Baljit S, Burnstock Geoffrey The double life of ATP Scientific American, 2009; 301(6): 84-90, 92.

Khakh Baljit S ATP-gated P2X receptors on excitatory nerve terminals onto interneurons initiate a form of asynchronous glutamate release Neuropharmacology, 2009; 56(1): 216-22.

Chaumont Severine, Compan Vincent, Toulme Estelle, Richler Esther, Housley Gary D, Rassendren Francois, Khakh Baljit S Regulation of P2X2 receptors by the neuronal calcium sensor VILIP1 Science signaling, 2008; 1(41): ra8.

E. Richler, S. Chaumont, E. Shigetomi, A. Sagasti & BS. Khakh. Tracking transmitter-gated P2X cation channel activation in vitro and in vivo, Nature Methods, 2008; 5: 87-93.

D.N. Bowser & BS. Khakh Two forms of astrocyte single vesicle exocytosis imaged with total internal reflection fluorescence microscopy, Proc Natl Acad Sci USA, 2007; 104: 485-91.

Khakh, B. S. North, R. A. P2X receptors as cell surface ATP sensors in health and disease, Nature, 2006; 442: 527-532. Khakh, B. S. Molecular physiology of P2X receptors and ATP signalling at synapses Nat Rev Neurosci, 2001; 2(3): 165-74.

Khakh, B.S. Zhou, X. Sydes, J. Galligan, J.J. Lester, H.A. State-dependent cross-inhibition between transmitter-gated cation channels, Nature, 2000; 406: 405-410.

Khakh, B.S. Lester, H.A. Dynamic Selectivity Filters in Ion Channels, Neuron, 1999; 23: 653-658.

Khakh, B.S. Bao, X. Labarca, C. Lester, H.A. Neuronal P2X receptor-transmitter-gated cation channels change their ion selectivity in seconds, Nat Neurosci, 1999; 2(4): 322-330.