Seminar: Maarten Kamermans, theme Sensory disorders

Inhibition in the outer retina. Intriguing synaptic mechanisms with unexpected players

Date:
8 October 2015 12:30 hrs. - 13:30 hrs.
Location:
Figdor Lecture Theatre, 8th floor RIMLS Building, Geert Grooteplein 26-28, route 289
Title:
Inhibition in the outer retina. Intriguing synaptic mechanisms with unexpected players
Speaker(s):

Maarten Kamermans, Netherlands Institute for Neuroscience of the Royal Netherlands Academy of Arts and Sciences and Academic Medical Center; University of Amsterdam, NL

Host(s):

Margo Dona, Dept. of Human Genetics, Radboudumc

08-10-2015 12:30:0008-10-2015 13:30:00Europe/AmsterdamInhibition in the outer retina. Intriguing synaptic mechanisms with unexpected players Figdor Lecture Theatre, 8th floor RIMLS Building, Geert Grooteplein 26-28, route 289Rimlsrimls@radboudumc.nl

Remarks / more information:

undefinedNeuronal computations strongly depend on inhibitory interactions. The timing of these inhibitory interactions is crucial for their computational effect. One example of such an inhibitory interaction occurs at the first retinal synapse, where horizontal cells (HC) inhibit photoreceptors. This interaction generates the centre/surround organization of bipolar cell (BC) receptive fields and is crucial for contrast enhancement1,2 and possibly colour constancy3. There are two competing hypotheses for the underlying mechanism: an ephaptic mechanism1,4 and a proton-mediated mechanism5,6.

Here we show that HCs feed back to photoreceptors via an unexpected synthesis of both mechanisms; a very fast ephaptic mechanism with no synaptic delay and a relatively slow mechanism with a time constant of about 160 ms. The first component is one of the fastest inhibitory processes known. The second component is a fully novel form of synaptic modulation, with involves Pannexin 1 channels, ATP release and the ectoATPse NTDPase16. We anticipate that this novel form of synaptic modulation is a general phenomenon occurring also at synapses outside the retina.

These two feedback pathways together form a very efficient computational unit. To reduce spatial redundancies in the visual scene, the mean activity of all cones within the large receptive field of HCs is subtracted from the output of individual cones. If this process was not extremely fast, the surround of BC receptive fields would lag behind the centre when responding to moving stimuli. Conversely, reducing temporal redundancies requires a slow mechanism, so lasting activity can be subtracted from the cone output. The slow component of feedback, we described here, is especially suitable for this role.

  1. Lauw J. Klaassen, Ziyi Sun, Marvin N. Steijaert, Petra Bolte, Iris Fahrenfort, Trijntje Sjoerdsma, Jan Klooster, Yvonne Claassen, Colleen R. Shields, Huub M. M. Ten Eikelder, Ulrike Janssen-Bienhold, Georg Zoidl, Douglas G. McMahon, Maarten Kamermans, "Synaptic transmission from horizontal cells to cones is impaired by loss of connexin hemichannels," PLoS. Biol. 9(7), e1001107 (2011).
  2. L. M. Chalupa and J. S. Werner, the visual neurosciences (A Bradford Book, The MIT Press, Cambridge, Massachusetts; London, England, 2003).
  3. Maarten Kamermans, Dick A. Kraaij, and Henk Spekreijse, "The cone/horizontal cell network: a possible site for color constancy," Vis. Neurosci. 15(5), 787 (1998).
  4. Maarten Kamermans, Iris Fahrenfort, Konrad Schultz, Ulrike Janssen-Bienhold, Trijntje Sjoerdsma, Reto Weiler., "Hemichannel-mediated inhibition in the outer retina," Science. 292, 1178 (2001).
  5. H. Hirasawa and A. Kaneko, "pH changes in the invaginating synaptic cleft mediate feedback from horizontal cells to cone photoreceptors by modulating Ca2+ channels," J. Gen. Physiol. 122(6), 657 (2003).
  6. Rozan Vroman, Lauw J. Klaassen, Marcus H.C. Howlett, Valentina Cenedese, Jan Klooster, Trijntje Sjoerdsma, Maarten Kamermans, Ëxtracellular ATP hydrolisis inhibits synaptic transmission by increasing pH buffering in the synaptic cleft”, PLoS Biol. 12(5),e1001864 (2014).undefined


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