Background: Light-adaptation is a multifaceted process in the retina that helps adjust the visual system to changing illumination levels. Many studies are focused on the photochemical mechanism of light-adaptation. Neural network adaptation mechanisms at the photoreceptor synapse are largely unknown. We find that large, spontaneous Excitatory Amino Acid Transporter (EAATs) activity in cone terminals may contribute to cone synaptic adaptation, specifically with respect to how these signals change in differing conditions of light. EAATs in neurons quickly transport glutamate from the synaptic cleft, and also elicit large thermodynamically uncoupled Cl- currents when activated. We recorded synaptic EAAT currents from cones to study glutamate-uptake events elicited by glutamate release from the local cone, and from adjacent photoreceptors. We find that cones are synaptically connected via EAATs in dark ; this synaptic connection is diminished in light-adapted cones. Methods: Whole-cell patch-clamp was performed on dark- and transiently light-adapted tiger salamander cones. Endogenous EAAT currents were recorded in cones with a short depolarization to -10mV/2ms, while spontaneous transporter currents from network cones were observed while a local cone holding at -70mV constantly. DHKA, a specific transporter inhibitor, was used to identify EAAT2 currents in the cone terminals, while TBOA identified other EAAT subtypes. GABAergic and glycinergic network inputs were always blocked with picrotoxin and strychnine. Results: Spontaneous EAAT currents were observed in cones held constantly at -70mV in dark, indicating that the cones received glutamate inputs from adjacent photoreceptors. These spontaneous EAAT currents disappeared in presence of a strong light, possibly because the light suppressed glutamate releases from the adjacent photoreceptors. The spontaneous EAAT currents were blocked with TBOA, but not DHKA, an inhibitor for EAAT2 subtype, suggesting that a / non-EAAT 2 subtype may reside in a basal or perisynaptic area of cones, with a specialized ability to bind exocytosed glutamate from adjacent cones in dark. Furthermore, these results could be artificially replicated by dual-electrode recordings from two adjacent cones. When glutamate release was elicited from one cone, the TBOA-sensitive EAAT currents were observed from the other cone. Conclusions: Cones appear to act like a meshwork, synaptically connected via glutamate transporters. Light attenuates glutamate release and diminishes the cone-cone synaptic connections. This process may act as an important network mechanism for cone light adaptation. / by Matthew JM Rowan. / Thesis (Ph.D.)--Florida Atlantic University, 2011. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2011. Mode of access: World Wide Web.
| Identifer | oai:union.ndltd.org:fau.edu/oai:fau.digital.flvc.org:fau_3822 |
| Contributors | Rowan, Matthew JM., Charles E. Schmidt College of Science, Department of Biological Sciences |
| Publisher | Florida Atlantic University |
| Source Sets | Florida Atlantic University |
| Language | English |
| Detected Language | English |
| Type | Text, Electronic Thesis or Dissertation |
| Format | xiv, 103 p. : ill. (some col.), electronic |
| Rights | http://rightsstatements.org/vocab/InC/1.0/ |
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