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Carla J. Abbott, Kumiko A. Percival, Paul R. Martin, Ulrike Grunert; Bipolar and Amacrine Input to Midget and Parasol Ganglion Cells in the Retina of Marmosets. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1606.
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© ARVO (1962-2015); The Authors (2016-present)
To study the density and arrangement of excitatory and inhibitory synaptic input to the dendrites of midget and parasol ganglion cells in marmoset (Callithrix jacchus) retina.
Ganglion cells were retrogradely labeled (5% dextran, tetramethylrhodamine and biotin, 3000 MW "microruby") from the lateral geniculate nucleus and subsequently photo-filled (Dacey et al., 2003). Retinas containing retrogradely labeled cells were processed simultaneously with antibodies against the GluR4 subunit of the AMPA receptor to identify presumed bipolar cell synapses (excitatory input) and antibodies against gephyrin to identify presumed amacrine cell synapses (inhibitory input). Some intracellularly injected parasol cells from peripheral retina (Lin et al., 2000, Visual Neuroscience) were also used. Animals were treated in accordance with the ARVO statement for the Use of Animals in Ophthalmic and Vision Research.
Twenty midget (15 OFF, 5 ON) and 32 parasol cells (15 OFF, 17 ON) from central retina (eccentricity 0.2 to 2.5 mm), and six parasol cells (2 OFF, 4 ON) from peripheral retina (eccentricity 4.5 to 8 mm) were analyzed. Midget and parasol cells from central retina had comparable average densities of colocalized immunoreactive (IR) puncta; about 5 GluR4 IR puncta and about 6 to 7 gephyrin IR puncta per 100 µm² dendritic surface area, and for both cell types approximately 18% of gephyrin IR puncta were located within 1 µm of a GluR4 IR punctum. The density of colocalized GluR4 and gephyrin IR puncta was weakly correlated for central midget cells but strongly correlated for central parasol cells (correlation coefficients: 0.28 and 0.77). The parasol cells from peripheral retina had greater presumed inhibitory input (12 gephyrin IR puncta per 100 µm² dendritic surface area, ANOVA; P < 0.05) but comparable presumed excitatory input (8 GluR4 IR puncta per 100 µm² dendritic surface area) to those from central retina.
Inhibitory input increases in peripheral cells. Approximately one-fifth of amacrine synapses to both midget and parasol ganglion cells are likely to be involved in feed-forward synapses at dyads.
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