May 2007
Volume 48, Issue 13
ARVO Annual Meeting Abstract  |   May 2007
Effects of Nitrate on Starburst Amacrine and Ganglion Cell Light Responses in the Rabbit Retina
Author Affiliations & Notes
  • K. E. Gavrikov
    Neuroscience, Ohio State Univ, Columbus, Ohio
  • S. C. Mangel
    Neuroscience, Ohio State Univ, Columbus, Ohio
  • Footnotes
    Commercial Relationships K.E. Gavrikov, None; S.C. Mangel, None.
  • Footnotes
    Support NEI Grant EY014235 to S.C.M.
Investigative Ophthalmology & Visual Science May 2007, Vol.48, 5963. doi:
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      K. E. Gavrikov, S. C. Mangel; Effects of Nitrate on Starburst Amacrine and Ganglion Cell Light Responses in the Rabbit Retina. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5963.

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

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Purpose:: Directionally selective (DS) light responses occur first in the retina in the dendrites of starburst amacrine cells (SACs), which depolarize to stimuli that move centrifugally through the receptive field (RF) surround and hyperpolarize to stimuli that move centripetally through the surround (Gavrikov et al., 2003). We have recently reported that these DS responses are highly sensitive to the activity of NKCC2 and KCC2, two subtypes of chloride (Cl-) cotransporter that determine whether GABA depolarizes or hyperpolarizes neurons, respectively. Specifically, our findings demonstrated that the differential distribution of NKCC2 on the proximal dendrites and KCC2 on the distal dendrites of SACs results in a GABA-evoked depolarization and hyperpolarization at the NKCC2 and KCC2 compartments, respectively, and underlies the DS light responses of SACs (Gavrikov et al., 2006). We have further examined whether the Cl- cotransporters mediate DS light responses by performing Cl- substitution experiments utilizing nitrate, an anion that flows through Cl- channels, but inhibits NKCC activity (Miyamoto et al., 1986; Hegde & Palfrey, 1992; Russell, 2000).

Methods:: Whole-cell patch-clamp recordings of displaced SACs and whole-cell patch-clamp and extracellular recordings of On-Off DS ganglion cells in the rabbit retina were obtained and the effects of nitrate assessed.

Results:: Substitution of nitrate (10 mM) for 10 mM Cl- in the bathing medium depolarized DS ganglion cells, increased their spontaneous activity, and eliminated their directional responses by increasing the response to movement in the null direction, but did not affect the response to RF center stimulation. In addition, substitution of nitrate (10 mM) for 10 mM Cl- in the bathing medium hyperpolarized SACs, increased response amplitude to RF center stimulation, decreased response amplitude to RF surround stimulation, and reduced or eliminated their DS light responses to moving slit stimulation. The effects of bumetanide (10 µM), a selective blocker of NKCC, on SACs and DS ganglion cells were similar to those of nitrate.

Conclusions:: These results indicate that nitrate preferentially interferes with the directional light responses of SACs and On-Off DS ganglion cells. Because nitrate inhibits NKCC activity, these results are consistent with previous reports that the Cl- cotransporters underlie GABA-dependent direction selectivity (Gavrikov et al., 2003, 2006). The results also suggest that the mechanisms that underlie direction selectivity are distinct from those that underlie the response to stationary flashing stimuli.

Keywords: amacrine cells • ion transporters • retinal connections, networks, circuitry 

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