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The role of NMDA and non-NMDA excitatory amino acid receptors in the functional organization of primate retinal ganglion cells
- Ethan D. Cohen, Robert F. Miller
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- Journal:
- Visual Neuroscience / Volume 11 / Issue 2 / March 1994
- Published online by Cambridge University Press:
- 02 June 2009, pp. 317-332
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The role of excitatory amino acid (EAA) receptors in primate retinal ganglion cell function was analyzed in a superfused retina-eyecup preparation using single-unit, extracellular recording techniques. The effects of bath applied L-2–amino-4–phosphonobutyrate (APB), N-methyl-D-aspartate (NMDA), and non-NMDA EAA receptor agonists and antagonists were examined on the light-evoked responses and resting firing rates of ganglion cells. APB (30–100 μM) reduced or blocked the light-evoked responses and resting firing rates of all ON-center ganglion cells; higher doses of APB (100 μM) were required to block the light-evoked responses of ON-transient cells. In contrast, an increase in resting firing rates was observed when L-APB was applied to some OFF-center ganglion cells. The EAA agonists kainate (KA) (10–20 μM) and NMDA (200–350 μM) increased the firing rate of virtually all ganglion cells examined. Quisqualate (10–20 μM) increased firing in most cells, but occasionally (4/13 cases) produced inhibition. The NMDA antagonist D-amino-phosphono-heptanoic acid (D-AP7) (200–250 μM) reduced the light-evoked responses of ganglion cells by an average of 12% from control levels, while resting firing rates declined 37%. In the presence of D-AP7, the basic receptive-field characteristics of cells were not significantly altered. In contrast, two non-NMDA receptor antagonists, NBQX (2,3–Dihydroxy-6–nitro-7–sulfamoyl-benzo-(F)-quinoxalinedione) and DNQX (6,7–dinitro-quinoxaline-2,3–dione), produced substantial reductions in the light-evoked responses (82%) and resting firing rates (87%) of all ganglion cell classes. A striking observation in some neurons was the recovery of a persistent transient light-evoked response in the presence of NBQX. This NBQX-insensitive, light-evoked response was always blocked by adding D-AP7. Thus, neurotransmission from bipolar to ganglion cells in primates is mediated predominantly by non-NMDA EAA receptors, with NMDA receptors forming a minor component of the light-evoked response.
A morphological classification of ganglion cells in the zebrafish retina
- WELLS I. MANGRUM, JOHN E. DOWLING, ETHAN D. COHEN
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- Journal:
- Visual Neuroscience / Volume 19 / Issue 6 / November 2002
- Published online by Cambridge University Press:
- 30 January 2003, pp. 767-779
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We examined the distribution and morphological types of ganglion cells in the retina of the zebrafish, a model vertebrate genetic organism. Using cresyl violet and methylene blue staining, a prominent central area was observed in the ventral temporal retina. The density of ganglion cell layer neurons averaged from ∼12,000/mm2 in the dorsal-nasal retina to a peak of ∼37,000/mm2 in the ventral-temporal retina. Individual zebrafish ganglion cells were labeled by backfilling with DiI through the optic nerve followed by reconstruction using confocal microscopy. The dendritic stratification and branching pattern of each labeled ganglion cell was examined in relation to the borders of the inner plexiform layer (IPL). We identified 11 different morphological types of ganglion cell. The most commonly labeled ganglion cells were two types termed Type III or IV, which displayed highly stratified dendritic arborizations in their respective ON-, OFF-sublaminae of the IPL. Their dendritic branching patterns were highly asymmetric with many thorn-like varicosities that profusely filled the area of arborization. In contrast, Type V cells formed a small simply branching dendritic field in the innermost portion of the ON-sublamina of the IPL. Two large ganglion cell types (Types I and II) with wide monostratified dendritic fields were found in both the ON- and OFF-sublamina of the IPL. Three different types of multistratified/bistratified ganglion cells were found (Types, IX, X, and XI.) whose dendrites occupied different regions of the IPL. The multistratified dendrites of IX cells occupied the whole width of the IPL, while the dendrites of Type XI cells formed vertical claw-like endings in only the ON-sublamina of the IPL. We conclude that zebrafish ganglion cells display a rich variety of types and branching patterns. This study establishes a series of baseline measurements of zebrafish ganglion cells to facilitate examination of genes playing a role in the specification and stratification of ganglion cell types.
Voltage-gated calcium and sodium currents of starburst amacrine cells in the rabbit retina
- ETHAN D. COHEN
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- Journal:
- Visual Neuroscience / Volume 18 / Issue 5 / September 2001
- Published online by Cambridge University Press:
- 20 May 2002, pp. 799-809
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The voltage-gated calcium and sodium currents of starburst amacrine cells were examined in slices of the adult rabbit retina. ON-center starburst amacrine cells were targeted for whole-cell recording by prelabeling the retina with the nuclear dye 4′-6-diamidino-2-phenylindole hydrochloride (DAPI). Calcium currents were isolated using an external Ringer that contained tetrodotoxin to block sodium currents and barium to block potassium channels. When starburst amacrine cells were stepped to holding potentials positive to −50 mV, a series of voltage-dependent calcium currents were activated. The calcium current peaked at −10 mV. The calcium currents kinetics were mainly sustained in nature, showing only a small amount of slow inactivation. Nickel (100 μM), a T-type channel blocker, had no effect on the calcium current. Application of the L-type channel agonist BAY K8644 (1–2.5 μM) had small variable effects on the calcium current while the L-type channel antagonist nifedipine (10 μM) had no effect. However, addition of a reported N-type calcium channel antagonist, omega-conotoxin G6A (1 μM), blocked a large portion of the calcium current, as did a more nonselective antagonist, omega-conotoxin M7C (200 nM). Agatoxin 4A (500 nM) reduced a smaller sustained calcium current component, implying a P/Q-type calcium channel was present on these neurons. In addition to the calcium currents, a fast voltage-gated sodium current was observed in many starburst cells. This current could be blocked by tetrodotoxin (200–500 nM). The differing kinetics and durations of the sodium and calcium currents could play important roles in the regulation of synaptic release and in the coordination of spiking by starburst amacrine cell dendrites during retinal development and in the encoding of motion across the retinal surface.