The major focus of this application is to explore the intracellular Ca2+-dependent mechanisms which control the light-induced membrane conductance changes that underlie the spiking patterns of retinal ganglion cells. Multiple types of voltage-gated conductances are involved in the generation of somatic action potentials and the regulation of the frequency of spike firing in ganglion cells. Although light exerts an important influence on the regulation of the frequency of ganglion cell firing by triggering direct, ionotropic excitatory and inhibitory synaptic inputs, it is often overlooked that both ligand- and voltage-activated conductances are subject to modulation by neuromodulators, which alter the electrical characteristics of channels through various intracellular processes. The experimental hypothesis of this application is that certain Ca2+-dependent intracellular processes, triggered by activation of neurotransmitter receptors, modify the input/output relation of ganglion cells by modulating both intrinsic ion channels and synaptically-gated channels. To test my hypothesis, I will study ganglion cells in turtle retinal slices. Both electrically- and synaptically-evoked responses will be recorded, whereby the contribution of excitatory inputs, as well as different types of voltage-gated K+ currents to the spiking patterns of the ON, OFF and ON-OFF ganglion cells will be evaluated. The interrelationship between light-activated excitatory synaptic inputs, intracellular Ca2+-dependent processes, and ganglion cell spiking responses will be investigated by manipulating intracellular Ca2+, and using selective inhibitors of Ca2+-calmodulin-dependent enzymes. To supplement results obtained by patch clamp experiments, Ca2+-imaging technique will be used to test directly whether glutamate raises intracellular Ca2+ in ganglion cells, to identify the type of glutamate receptor responsible for [Ca2+]i increase, and the pathways of [Ca2+ ]i elevation (e.g., influx through receptor- or voltage-activated channels, or release from internal stores). The effect of intracellular Ca2+ on the functioning of glutamate receptors, and on activation/inactivation properties of voltage-gated currents will be studied under whole-cell and perforated versions of patch clamp.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Research Project (R01)
Project #
1R01EY012497-01A1
Application #
6087494
Study Section
Visual Sciences C Study Section (VISC)
Program Officer
Hunter, Chyren
Project Start
2000-05-01
Project End
2004-04-30
Budget Start
2000-05-01
Budget End
2001-04-30
Support Year
1
Fiscal Year
2000
Total Cost
$224,601
Indirect Cost
Name
New York University
Department
Ophthalmology
Type
Schools of Medicine
DUNS #
City
New York
State
NY
Country
United States
Zip Code
10016
Xing, Wei; Akopian, Abram; Križaj, David (2012) Trafficking of presynaptic PMCA signaling complexes in mouse photoreceptors requires Cav1.4 ?1 subunits. Adv Exp Med Biol 723:739-44
Busquet, Perrine; Nguyen, Ngoc Khoi; Schmid, Eduard et al. (2010) CaV1.3 L-type Ca2+ channels modulate depression-like behaviour in mice independent of deaf phenotype. Int J Neuropsychopharmacol 13:499-513
Mizuno, Fengxia; Barabas, Peter; Krizaj, David et al. (2010) Glutamate-induced internalization of Ca(v)1.3 L-type Ca(2+) channels protects retinal neurons against excitotoxicity. J Physiol 588:953-66
Cristofanilli, Massimiliano; Mizuno, Fengxia; Akopian, Abram (2007) Disruption of actin cytoskeleton causes internalization of Ca(v)1.3 (alpha 1D) L-type calcium channels in salamander retinal neurons. Mol Vis 13:1496-507
Cristofanilli, Massimiliano; Akopian, Abram (2006) Calcium channel and glutamate receptor activities regulate actin organization in salamander retinal neurons. J Physiol 575:543-54
Akopian, A; Szikra, T; Cristofanilli, M et al. (2006) Glutamate-induced Ca2+ influx in third-order neurons of salamander retina is regulated by the actin cytoskeleton. Neuroscience 138:17-24
Schubert, T; Akopian, A (2004) Actin filaments regulate voltage-gated ion channels in salamander retinal ganglion cells. Neuroscience 125:583-90
Witkovsky, Paul; Veisenberger, Eleonora; Haycock, John W et al. (2004) Activity-dependent phosphorylation of tyrosine hydroxylase in dopaminergic neurons of the rat retina. J Neurosci 24:4242-9
Akopian, Abram (2003) Differential modulation of light-evoked on- and off-EPSCs by paired-pulse stimulation in salamander retinal ganglion cells. Brain Res 967:235-46
Akopian, Abram; Galoyan, Armen (2003) Effect of hypothalamic proline-rich-polypeptide on voltage-gated Ca2+ currents in retinal ganglion cells. Neurochem Res 28:1867-71

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