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Raymond H. Farmen, Timothy J. Schuchardt, James J. Vrbanac, David M. Linn, Kazuhiro Iwamoto, Cindy L. Linn; Determination of Neurotransmitter levels in Rodent Retina. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5629.
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© ARVO (1962-2015); The Authors (2016-present)
The rat retina is the preferred model for many ocular efficacy studies. Therefore, quantification of neurotransmitter levels in control rat retina would be essential prior to conducting efficacy studies where levels may be altered. The purpose of this study was to quantify the levels of two excitatory neurotransmitters and two inhibitory neurotransmitters in the rat retina.
Retina from Long-Evan rats was collected at a body weight of 285g-589g. Retinas were placed in analysis tubes and stored at -20 °C until the time of analysis. Quantitative analysis of neurotransmitter levels in retina was by LC-MS-MS, and chromatography and mass spectrometry conditions will be described. The neurotransmitters examined in this study were glutamate, glycine, GABA and acetylcholine (ACh).
Glutamate is considered as the predominant excitatory neurotransmitter in the mammalian retina. As expected, glutamate was the most abundant analyte with an average of 313,000 ng/g (2120 µM). Glycine and GABA are considered the two main inhibitory neurotransmitters in the mammalian retina and they were found in approximately equal amounts. Glycine was determined to be at 173,000 ng/g (2310 µM) and GABA was found to be at 161,000 ng/g (1570 µM). ACh is localized to a subset of amacrine cells in the retina and could be considered as a secondary excitatory neurotransmitter relative to glutamate. ACh was calculated to be present in the amount of 752 ng/g (5.14 µM).
Glutamate was found to be the most abundant neurotransmitter examined in the rat retina. This is consistent with the hypothesis that glutamate is the predominant neurotransmitter in the retina. The two predominant inhibitory neurotransmitters, glycine and GABA, were calculated to be present at approximately half the amount of glutamate respectively. This is also consistent with the hypothesis that both inhibitory neurotransmitters are found equally in the retina. The levels of ACh in the rat retina were found to be significantly lower than glutamate, glycine or GABA; but well within limits of detection. This is also consistent with the concept that ACh is much less abundant than glutamate in the mammalian retina. Overall, our study indicates that changes in the neurotransmitter system of the rat retina (possibly associated with neurodegenerative diseases) should be well within current limits of detection.
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