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Visual System

開催日 2014/9/11
時間 16:00 - 17:00
会場 Poster / Exhibition(Event Hall B)

Functional segregation of gap-junctionally connected retinal amacrine cells and regulation of channel opening of their electrical synapses

  • P1-166
  • 日高 聡 / Soh Hidaka:1 
  • 1:藤田保健衛生大学 / Dept.of Physiol., Fujita Health Univ.Sch.of Med. 

Electrical synapses are present in retinal neurons expressing channel subunit, connexins (Journal of Neuroscience, 2004; Journal of Intgra. Neuroscience, 2008; Brain Research, 2012). Electrical current spread through connections of cells is expected to modulate chemical synapses. Our previous studies revealed that individual amacrine cells show specific coupling patterns (Journal of Intgra. Neuroscience, 2005; Brain Research, 2012). Based on coupling patterns and dendritic morphology, six different classes of homotypic lateral connections between amacrine cells of the same cell subtype were identified. Two types of contacts, tip-contacts and cross-contacts, were found. Tip-contacts were at dendritic tips of amacrine cells in a hexagonal array, whereas cross-contacts between dendritic shanks. Recent studies revealed channel opening of gap junctions between tip-contact amacrine cells is regulated by intracellular cyclic AMP as well as intracellular Ca2+ concentration (Brain Research, 2012). In the present study, I investigated synaptic contacts of these amacrine cells by electron microscopy in order to examine functional segregation of amacrine cells. Tip-contact amacrine cells make direct chemical synapses onto dendrites of retinal ganglion cells. On the other hands, cross-contact amacrine cells make chemical output synapses only onto axon terminals of retinal bipolar cells. Then I investigated regulatory mechanisms of channel opening of electrical synapses between cross-contact amacrine cells under dual whole-cell patch clamp recordings. Gap junctions between cross-contact amacrine cells closed under intracellular high (>300nM) Ca2+ concentration. However, intracellular cyclic AMP did not suppress gap junction permeability between cross-contact amacrine cells. These results suggest that gap-junctionally connected retinal amacrine cells functionally may make differential output chemical synapses onto postsynaptic retinal neurons through electrical synapses by individual homotypic lateral connections.

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