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Published on: October 13, 2016
Characterization of secretagogin-immunoreactive amacrine cells in marmoset retina
Felix Weltzien1, Stefano Dimarco, Dario A Protti
1Department of Ophthalmology and Save Sight Institute, University of Sydney, Australia; Australian Research Council Centre of Excellence in Vision Science, University of Sydney, Australia.
Insights
Researchers identified secretagogin amacrine cells in the marmoset retina, which use the neurotransmitter gamma-aminobutyric acid (GABA). These cells play a role in visual processing by potentially mediating spatial inhibition within the inner plexiform layer.
Area of Science:
- Neuroscience
- Retinal Cell Biology
- Primate Vision
Background:
- The retina has over 30 amacrine cell types, but many remain poorly understood.
- Amacrine cells are crucial for retinal information processing.
Purpose of the Study:
- To characterize a specific population of amacrine cells in the marmoset retina.
- To investigate the localization and properties of secretagogin-expressing amacrine cells.
Main Methods:
- Immunohistochemistry to localize secretagogin and glutamic acid decarboxylase (GAD).
- Spatial density measurements and cell counting.
- Intracellular injection of DiI to map dendritic fields.
Main Results:
- Secretagogin was found in regular and displaced amacrine cells in the marmoset retina.
- These cells stratify in specific layers (strata 2-4) of the inner plexiform layer.
- Secretagogin amacrine cells are GABA-ergic and have medium-sized dendritic fields (170 μm diameter).
- Their density varies with eccentricity, constituting a significant portion of displaced amacrine cells.
Conclusions:
- Secretagogin amacrine cells are a distinct population in the marmoset retina.
- They exhibit a unique combination of stratification and neurotransmitter use.
- These cells likely contribute to spatial inhibition within the central retina.
Abstract:
The retina contains at least 30 different types of amacrine cells but not many are well characterized. In the present study the calcium-binding protein secretagogin was localized in a population of regular and displaced amacrine cells in the retina of the common marmoset Callithrix jacchus. Irrespective of their soma location, the dendrites of secretagogin amacrine cells occupy strata 2, 3, and 4 of the inner plexiform layer, between the two bands formed by cholinergic amacrine cells. Segretagogin amacrine cells are also immunopositive to antibodies against glutamic acid decarboxylase, suggesting that they use γ-aminobutyric acid (GABA) as their neurotransmitter. The spatial density of secretagogin amacrine cells decreases from a peak of about 400 cells/mm(2) near 1 mm eccentricity to less than 100 cells/mm(2) in peripheral retina; these densities account for about 1% of amacrine cells in the inner nuclear layer and for up to 27% of displaced amacrine cells. The cell bodies form a regular mosaic, suggesting that they constitute a single amacrine cell population. Secretagogin cells have varicose dendrites, which are decorated with small spines. Intracellular injection of DiI into secretagogin cells revealed an average dendritic field diameter of 170 μm and an average coverage factor of 3.2. In summary, secretagogin cells in marmoset retina are medium-field amacrine cells that share their stratification pattern with narrow-field amacrine cells and their neurotransmitter with wide-field amacrine cells. They may mediate spatial inhibition spanning the centralmost (on and off) bands of the inner plexiform layer.
