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C. Yang, Y. Fernandez; The Expression of Vesicular Gaba Transporter in Gabaergic Neurons of the Salamander Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5157.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The vesicular GABA transporter (VGAT) is responsible for GABA uptake into synaptic vesicles of GABAergic neurons. There is mounting evidence that populations of horizontal, bipolar and amacrine cells in salamander retina are GABAergic. This study focused on the expression of VGAT on these inhibitory neurons with the aim of obtaining information regarding vesicular or non-vesicular GABA release from these neurons. Methods: Double-label immunofluorescence was performed on frozen sections of tiger salamander retina and observed under a confocal microscope. Results: VGAT immunoreactivity (VGAT-IR) was present in the outer plexiform layer (OPL), inner plexiform layer (IPL) and somas in the inner nuclear layer (INL). Double labeling for VGAT-IR and specific cellular and subcellular markers showed that VGAT-IR was in close apposition to cone pedicles that were identified with calbindin-IR or synaptic vesicle protein 2-IR. The VGAT-immunoreactive processes near the cone terminals were identified as horizontal cell dendrites because VGAT-IR co-localized with glutamic acid decarboxylase (GAD)- and GABA-immunoreactive horizontal cells in the distal INL as well as calretinin-immunoreactive processes of horizontal cells. Some calretinin-immunoreactive bipolar cells in the distal INL showed VGAT-IR. GAD- and GABA-immunoreactive amacrine cell bodies in the mid and proximal INL and their processes across the whole depth of the IPL were VGAT-immunoreactive. The punctate labelings on the processes in the IPL were likely to be amacrine cell butons because VGAT-IR co-localized with synapsin I-IR, a marker for conventional synapses. Conclusions: The presence of VGAT-IR in distal process of GABAergic horizontal cells raises the issue that GABA release from horizontal cells maybe by vesicular exocytosis. VGAT-IR in GABAergic conventional synapses in the IPL further supports the idea for vesicular GABA release from amacrine cells. Further study is needed to identify the GABAergic bipolar terminals expressing VGAT.
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