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J. Johnson, R.T. Fremeau, J. Burman, R.H. Edwards, D.R. Copenhagen; Evidence for a Glutamatergic Amacrine Cell: Vesicular Glutamate Transporter 3 (VGLUT3) is Expressed in a Subset of Amacrine Cells in the Rodent Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2069.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The predominant excitatory neurotransmitter in the retina is glutamate, which is the neurotransmitter used by photoreceptors and bipolar cells. Vesicular glutamate transporters sequester glutamate into synaptic vesicles, and their expression determines the type and kind of neurotransmitter released onto post-synaptic neurons. A recently identified vesicular glutamate transporter 3 (VGLUT3) has been shown to be expressed in neurons in the brain that are not classically thought to release glutamate. We investigated the expression of VGLUT3 in the rodent retina. Methods: We used immunohistochemistry and confocal imaging to study the expression of VGLUT3 in adult rat and mouse retina. We used a polyclonal antibody raised against the C terminus of VGLUT3. Results: There was no VGLUT3 immunostaining when retinal tissue was preadsorbed with 20 µg/ml GST-VGLUT3 peptide. The preadsorption with GST-VGLUT1 or GST-VGLUT2 peptides did not alter the VGLUT3 immunostaining. VGLUT3 was localized to sparsely occurring amacrine cell bodies in the inner nuclear layer. In addition, extensive VGLUT3 immunoreactive processes were observed in the inner plexiform layer. The expression pattern for VGLUT3 was identical in rat and mouse retina. VGLUT3 immunolabeling did not colocalize with the cholinergic marker choline acetyltransferase (CHAT). VGLUT3 immunostained processes were mainly observed in between CHAT immunostained processes. VGLUT3 immunoreactive cell bodies did not colocalize with the GABAergic marker GAD6, or with the dopaminergic marker tyrosine hydroxylase. VGLUT3 immunoreactive processes did not colocalize with the bipolar cell marker PKC, indicating that VGLUT3 is not expressed in rod bipolar terminals. Conclusions: We conclude that VGLUT3 is expressed in sparsely occurring amacrine cells, which are not GABAergic, cholinergic, or dopaminergic. These results indicate that a subset of amacrine cells can release glutamate as their neurotransmitter.
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