April 2009
Volume 50, Issue 13
ARVO Annual Meeting Abstract  |   April 2009
Rods and Cones Drive Lateral Feedback to Mb Bipolar Cell Terminals With Different Characteristics
Author Affiliations & Notes
  • J. Vigh
    Biomedical Sciences, Colorado State University, Fort Collins, Colorado
  • H. von Gersdorff
    Vollum Institute, Oregon Health and Sciences University, Portland, Oregon
  • Footnotes
    Commercial Relationships  J. Vigh, None; H. von Gersdorff, None.
  • Footnotes
    Support  CSU VMBMS College Research Council Grant
Investigative Ophthalmology & Visual Science April 2009, Vol.50, 1629. doi:
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      J. Vigh, H. von Gersdorff; Rods and Cones Drive Lateral Feedback to Mb Bipolar Cell Terminals With Different Characteristics. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1629.

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      © ARVO (1962-2015); The Authors (2016-present)

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Purpose: : Bipolar cell axon terminals in the inner plexiform layer (IPL) receive reciprocal (feedback) and lateral (feed-forward) inhibition from amacrine cells (ACs). When the connection between an Mb axon terminal and its cell body has been severed, light information can reach axotomized Mb terminals only via ACs. Thus, the light- evoked signals in axon severed Mb terminals are most likely due to be pure lateral, feed-forward inhibition. Our goal was to characterize this lateral inhibition targeting Mb bipolar cell axon terminals in the goldfish retina.

Methods: : Patch clamp recordings of full-field illumination-evoked (555 nm LED, 100 nW/cm2-1.4 microW/cm2) membrane currents were made directly from axotomized terminals of Mb bipolar cells in retinal slices made from goldfish retina (Carassius auratus). Preparation was performed under infrared illumination. Light intensity was controlled by the LED voltage and calibrated with an optical power meter.

Results: : Light triggered ON-OFF inhibition in dark adapted, large, axotomized Mb terminals located in the ON sublamina of the IPL. Within our light intensity range the ON component quickly saturated with increasing intensities whereas the OFF did not. The ON component was not blocked by APB (50 microM), but was sensitive to the EAAT blocker TBOA (100 microM). Moreover, TBOA enhanced the OFF component. Both ON and OFF components of the lateral feedback signals were sensitive to the GABAA specific blocker SR95503 (25 microM) and to the GABAC specific blocker TPMPA (100 microM). A combination of both blockers or application of picrotoxin (100 microM), eliminated the lateral ON-OFF feedback completely.

Conclusions: : The ON-OFF lateral inhibitory signals targeting the Mb axon terminals were GABAergic, with contribution from both GABA A and C receptors. Saturation of the ON component amplitude with intensity suggests that this part had rod origin. Thus our results indicate that in the goldfish retina both rods and cones mediate the GABAergic lateral inhibition, albeit with different characteristics: a saturable, rod-mediated pathway provides ON inhibition, while cone signals drive inhibition at light OFF in Mb axon terminals.

Keywords: bipolar cells • retinal connections, networks, circuitry • retina: proximal (bipolar, amacrine, and ganglion cells) 

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