Richard H Kramer

University of California, Berkeley, Berkeley, California, United States

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Publications (67)564.59 Total impact

  • Ivan Tochitsky, Richard H Kramer
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    ABSTRACT: Retinitis pigmentosa (RP) and age-related macular degeneration (AMD) are progressive retinal diseases that result from the death of rod and cone photoreceptors, ultimately leading to blindness. The only currently approved vision restoration treatment employs an implanted retinal 'chip' as a prosthetic device to electrically stimulate retinal neurons that survive after the photoreceptors are gone, thereby restoring light-driven neural signaling to the brain. Alternative strategies have been proposed, which would utilize optogenetic or optopharmacological tools to enable direct optical stimulation of surviving retinal neurons. Here, we review the latest studies evaluating the feasibility of these molecular tools as potential therapeutics for restoring visual function in human blinding disease. Copyright © 2015. Published by Elsevier Ltd.
    Current Opinion in Neurobiology 02/2015; 34C:74-78. DOI:10.1016/j.conb.2015.01.018 · 6.77 Impact Factor
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    ABSTRACT: Optogenetics has become an emerging technique for neuroscience investigations owing to the great spatiotemporal precision and the target selectivity it provides. Here we extend the optogenetic strategy to GABAA receptors (GABAARs), the major mediators of inhibitory neurotransmission in the brain. We generated a light-regulated GABAA receptor (LiGABAR) by conjugating a photo-switchable tethered ligand (PTL) onto a mutant receptor containing the cysteine-substituted α1-subunit. The installed PTL can be advanced to or retracted from the GABA-binding pocket with 500-nm and 380-nm light, respectively, resulting in photo-switchable receptor antagonism. In hippocampal neurons, this LiGABAR enabled a robust photoregulation of inhibitory postsynaptic currents. Moreover, it allowed reversible photocontrol over neuron excitation in response to presynaptic stimulation. LiGABAR thus provides a powerful means for functional and mechanistic investigations of GABAAR-mediated neural inhibition.
    ACS Chemical Biology 05/2014; 9(7). DOI:10.1021/cb500167u · 5.36 Impact Factor
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    ABSTRACT: Retinitis pigmentosa (RP) and age-related macular degeneration (AMD) are blinding diseases caused by the degeneration of rods and cones, leaving the remainder of the visual system unable to respond to light. Here, we report a chemical photoswitch named DENAQ that restores retinal responses to white light of intensity similar to ordinary daylight. A single intraocular injection of DENAQ photosensitizes the blind retina for days, restoring electrophysiological and behavioral responses with no toxicity. Experiments on mouse strains with functional, nonfunctional, or degenerated rods and cones show that DENAQ is effective only in retinas with degenerated photoreceptors. DENAQ confers light sensitivity on a hyperpolarization-activated inward current that is enhanced in degenerated retina, enabling optical control of retinal ganglion cell firing. The acceptable light sensitivity, favorable spectral sensitivity, and selective targeting to diseased tissue make DENAQ a prime drug candidate for vision restoration in patients with end-stage RP and AMD.
    Neuron 02/2014; 81(4):800-13. DOI:10.1016/j.neuron.2014.01.003 · 15.98 Impact Factor
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    Tzu-Ming Wang, Lars C Holzhausen, Richard H Kramer
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    ABSTRACT: The reciprocal synapse between photoreceptors and horizontal cells underlies lateral inhibition and establishes the antagonistic center-surround receptive fields of retinal neurons to enhance visual contrast. Despite decades of study, the signal mediating the negative feedback from horizontal cells to cones has remained under debate because the small, invaginated synaptic cleft has precluded measurement. Using zebrafish retinas, we show that light elicits a change in synaptic proton concentration with the correct magnitude, kinetics and spatial dependence to account for lateral inhibition. Light, which hyperpolarizes horizontal cells, causes synaptic alkalinization, whereas activating an exogenously expressed ligand-gated Na(+) channel, which depolarizes horizontal cells, causes synaptic acidification. Whereas acidification was prevented by blocking a proton pump, re-alkalinization was prevented by blocking proton-permeant ion channels, suggesting that distinct mechanisms underlie proton efflux and influx. These findings reveal that protons mediate lateral inhibition in the retina, raising the possibility that protons are unrecognized retrograde messengers elsewhere in the nervous system.
    Nature Neuroscience 01/2014; DOI:10.1038/nn.3627 · 14.98 Impact Factor
  • Biophysical Journal 01/2014; 106(2):629a. DOI:10.1016/j.bpj.2013.11.3481 · 3.83 Impact Factor
  • Biophysical Journal 01/2014; 106(2):381a-382a. DOI:10.1016/j.bpj.2013.11.2159 · 3.83 Impact Factor
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    Richard H Kramer, Alexandre Mourot, Hillel Adesnik
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    ABSTRACT: The optical neuroscience revolution is transforming how we study neural circuits. By providing a precise way to manipulate endogenous neuronal signaling proteins, it also has the potential to transform our understanding of molecular neuroscience. Recent advances in chemical biology have produced light-sensitive compounds that photoregulate a wide variety of proteins underlying signaling between and within neurons. Chemical tools for optopharmacology include caged agonists and antagonists and reversibly photoswitchable ligands. These reagents act on voltage-gated ion channels and neurotransmitter receptors, enabling control of neuronal signaling with a high degree of spatial and temporal precision. By covalently attaching photoswitch molecules to genetically tagged proteins, the newly emerging methodology of optogenetic pharmacology allows biochemically precise control in targeted subsets of neurons. Now that the tools for manipulating endogenous neuronal signaling proteins are available, they can be implemented in vivo to enhance our understanding of the molecular bases of brain function and dysfunctions.
    Nature Neuroscience 06/2013; 16(7):816-823. DOI:10.1038/nn.3424 · 14.98 Impact Factor
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    Alexandre Mourot, Ivan Tochitsky, Richard H Kramer
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    ABSTRACT: Ion channels are transmembrane proteins that control the movement of ions across the cell membrane. They are the molecular machines that make neurons excitable by enabling the initiation and propagation of action potentials (APs). Rapid signaling within and between neurons requires complex molecular processes that couple the sensing of membrane voltage or neurotransmitter release to the fast opening and closing of the ion channel gate. Malfunction of an ion channel's sensing or gating module can have disastrous pathological consequences. However, linking molecular changes to the modulation of neural circuits and ultimately to a physiological or pathological state is not a straightforward task. It requires precise and sophisticated methods of controlling the function of ion channels in their native environment. To address this issue we have developed new photochemical tools that enable the remote control of neuronal ion channels with light. Due to its optical nature, our approach permits the manipulation of the nervous system with high spatial, temporal and molecular precision that will help us understand the link between ion channel function and physiology. In addition, this strategy may also be used in the clinic for the direct treatment of some neuronal disorders.
    Frontiers in Molecular Neuroscience 03/2013; 6:5. DOI:10.3389/fnmol.2013.00005
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    Alexandre Mourot, Timm Fehrentz, Richard H Kramer
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    ABSTRACT: Voltage-gated potassium (K v) channels are membrane proteins that open a selective pore upon membrane depolarization, allowing K(+) ions to flow down their electrochemical gradient. In neurons, K v channels play a key role in repolarizing the membrane potential during the falling phase of the action potential, often resulting in an after hyperpolarization. Opening of K v channels results in a decrease of cellular excitability, whereas closing (or pharmacological block) has the opposite effect, increased excitability. We have developed a series of photosensitive blockers for K v channels that enable reversible, optical regulation of potassium ion flow. Such molecules can be used for remote control of neuronal excitability using light as an on/off switch. Here we describe the design and electrophysiological characterization of photochromic blockers of ion channels. Our focus is on K v channels but in principle, the techniques described here can be applied to other ion channels and signaling proteins.
    Methods in molecular biology (Clifton, N.J.) 01/2013; 995:89-105. DOI:10.1007/978-1-62703-345-9_7 · 1.29 Impact Factor
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    ABSTRACT: Retinitis pigmentosa (RP) and age-related macular degeneration (AMD) are degenerative blinding diseases caused by the death of rods and cones, leaving the remainder of the visual system intact but largely unable to respond to light. Here, we show that AAQ, a synthetic small molecule photoswitch, can restore light sensitivity to the retina and behavioral responses in vivo in mouse models of RP, without exogenous gene delivery. Brief application of AAQ bestows prolonged light sensitivity on multiple types of retinal neurons, resulting in synaptically amplified responses and center-surround antagonism in arrays of retinal ganglion cells (RGCs). Intraocular injection of AAQ restores the pupillary light reflex and locomotory light avoidance behavior in mice lacking retinal photoreceptors, indicating reconstitution of light signaling to brain circuits. AAQ and related photoswitch molecules present a potential drug strategy for restoring retinal function in degenerative blinding diseases.
    Neuron 07/2012; 75(2):271-82. DOI:10.1016/j.neuron.2012.05.022 · 15.98 Impact Factor
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    ABSTRACT: Selective ligands are lacking for many neuronal signaling proteins. Photoswitched tethered ligands (PTLs) have enabled fast and reversible control of specific proteins containing a PTL anchoring site and have been used to remote control overexpressed proteins. We report here a scheme for optical remote control of native proteins using a "photoswitchable conditional subunit" (PCS), which contains the PTL anchoring site as well as a mutation that prevents it from reaching the plasma membrane. In cells lacking native subunits for the protein, the PCS remains nonfunctional internally. However, in cells expressing native subunits, the native subunit and PCS coassemble, traffic to the plasma membrane, and place the native protein under optical control provided by the coassembled PCS. We apply this approach to the TREK1 potassium channel, which lacks selective, reversible blockers. We find that TREK1, typically considered to be a leak channel, contributes to the hippocampal GABA(B) response.
    Neuron 06/2012; 74(6):1005-14. DOI:10.1016/j.neuron.2012.04.026 · 15.98 Impact Factor
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    Miao Tian, C Shan Xu, Rachel Montpetit, Richard H Kramer
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    ABSTRACT: Rab3A is a synaptic vesicle-associated protein found throughout the nervous system, but its precise function is unknown. Genetic knock-out studies show that Rab3A is not necessary for vesicular release or replenishment at conventional synapses in the brain. Here we explore the function of Rab3A at ribbon synapses in the retina of the tiger salamander (Ambystoma tigrinum). Fluorescently labeled Rab3A, delivered into rods and cones through a patch pipette, binds to and dissociates from synaptic ribbons. Experiments using nonphosphorylatable GDP analogs and a GTPase-deficient Rab3A mutant indicate that ribbon binding and dissociation are governed by a GTP hydrolysis cycle. Paired recordings from presynaptic photoreceptors and postsynaptic OFF-bipolar cells show that the Rab3A mutant blocks synaptic release in an activity-dependent manner, with more frequent stimulation leading to more rapid block. The frequency dependence of block by exogenous Rab3A suggests that it acts competitively with synaptic vesicles to interfere with their resupply to release sites. Together, these findings suggest a crucial role of Rab3A in delivering vesicles to Ca²⁺-dependent release sites at ribbon synapses.
    The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 05/2012; 32(20):6931-6. DOI:10.1523/JNEUROSCI.0265-12.2012 · 6.75 Impact Factor
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    ABSTRACT: Rattling the cage: The two γ-aminobutyric acid (GABA) derivatives 1 and 2 exhibit efficient and rapid (<5×10(-6)  s) GABA photorelease upon one-photon excitation combined with two-photon uncaging cross-section at λ=800 nm. Compounds 1 and 2 were successfully used for two-photon GABA release in intact brain tissue, thus offering attractive perspectives in chemical neurosciences.
    Angewandte Chemie International Edition 02/2012; 51(8):1840-3. DOI:10.1002/anie.201106559 · 11.34 Impact Factor
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    ABSTRACT: Local anesthetics effectively suppress pain sensation, but most of these compounds act nonselectively, inhibiting activity of all neurons. Moreover, their actions abate slowly, preventing precise spatial and temporal control of nociception. We developed a photoisomerizable molecule, quaternary ammonium-azobenzene-quaternary ammonium (QAQ), that enables rapid and selective optical control of nociception. QAQ is membrane-impermeant and has no effect on most cells, but it infiltrates pain-sensing neurons through endogenous ion channels that are activated by noxious stimuli, primarily TRPV1. After QAQ accumulates intracellularly, it blocks voltage-gated ion channels in the trans form but not the cis form. QAQ enables reversible optical silencing of mouse nociceptive neuron firing without exogenous gene expression and can serve as a light-sensitive analgesic in rats in vivo. Because intracellular QAQ accumulation is a consequence of nociceptive ion-channel activity, QAQ-mediated photosensitization is a platform for understanding signaling mechanisms in acute and chronic pain.
    Nature Methods 02/2012; 9(4):396-402. DOI:10.1038/nmeth.1897 · 25.95 Impact Factor
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    ABSTRACT: Advances in synthetic chemistry, structural biology, molecular modelling and molecular cloning have enabled the systematic functional manipulation of transmembrane proteins. By combining genetically manipulated proteins with light-sensitive ligands, innately 'blind' neurobiological receptors can be converted into photoreceptors, which allows them to be photoregulated with high spatiotemporal precision. Here, we present the optochemical control of neuronal nicotinic acetylcholine receptors (nAChRs) with photoswitchable tethered agonists and antagonists. Using structure-based design, we produced heteromeric α3β4 and α4β2 nAChRs that can be activated or inhibited with deep-violet light, but respond normally to acetylcholine in the dark. The generation of these engineered receptors should facilitate investigation of the physiological and pathological functions of neuronal nAChRs and open a general pathway to photosensitizing pentameric ligand-gated ion channels.
    Nature Chemistry 02/2012; 4(2):105-11. DOI:10.1038/nchem.1234 · 23.30 Impact Factor
  • Biophysical Journal 01/2012; 102(3):111-. DOI:10.1016/j.bpj.2011.11.626 · 3.83 Impact Factor
  • Christian Herold, Alexandre Mourot, Richard H. Kramer
    Biophysical Journal 01/2012; 102(3):137-. DOI:10.1016/j.bpj.2011.11.756 · 3.83 Impact Factor

Publication Stats

3k Citations
564.59 Total Impact Points

Institutions

  • 2001–2015
    • University of California, Berkeley
      • • Department of Molecular and Cell Biology
      • • Department of Chemistry
      • • Division of Neurobiology
      Berkeley, California, United States
  • 2009
    • Icahn School of Medicine at Mount Sinai
      Borough of Manhattan, New York, United States
  • 2006
    • University of Berkley
      Berkley, Michigan, United States
  • 1998–2001
    • University of Miami Miller School of Medicine
      • Department of Molecular and Cellular Pharmacology
      Miami, FL, United States