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Ramsés Noguez, Edgar Morales, Ataúlfo Martínez, Stephanie Thebault, Javier ledezma; BASAL ELECTRORETINOGRAM REVEALS SLOW OSCILLATORY ACTIVITY THAT IS NOT ALTERED IN OBESE MICE. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5524.
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There is a lack of knowledge about the basal or non-evoked oscillatory activity in the adult retina. We tested whether basal ERG can reveal basal oscillations, and since electroencephalogram showed altered basal oscillations in diabetic brains, we explored basal ERG oscillations in a type 2 diabetes mouse model.
ERG with no light flash was measured in both eyes of adult C57BL/6J female and male mice (1:1 ratio) that were either fed a high-fat diet (HFD, 60 % fat, N=4-5) or a standard diet (30% fat, N=3-7) for 2 weeks. Mice were dark-adapted before ketamine–xylazine anesthesia (7/3, i.p.). The pupils were dilated with tropicamide/phenylephrine (0.75 and 0.25 %); tetracaine hydrocloride was used as a cornea anesthetic; active electrodes were placed on each cornea and hydrated with 0.5 % hypromellose solution to maintain conductivity. Subdermal electrodes placed at the base of the nose (reference) and in the tail (ground). The 2-minute signal was amplified 100-fold using a differential amplifier with a 0.1–1000 Hz bandwidth. Mice were then light-adapted for 15 minutes to record basal photopic ERGs as described for scotopic measures. ERG data were then analyzed by Fast Fourier Transform to calculate spectral density. Body weight, glucemia, respiratory rhythm, glucose and insulin tolerance tests were weekly measured.
Spectral analysis of basal ERG showed two main waves with a frequency oscillation between 1-2 and 2.1-3.5 hertz. The two slow waves are present under both scotopic and photopic conditions and in both males and females, with a similar power density (p>0.05). The averaged respiratory frequency in lean mice was 4.0 ± 0.2 hertz, suggesting that it did not interfere with basal ERG oscillations. After 2 weeks of HFD, mice were overweight but they were still normoglucemic and tolerant to glucose and insulin. They also showed similar basal slow ERG oscillations than the ones of control group (p>0.05).
Our data identified basal slow oscillatory activity in adult mouse retina that shares similar circuitry in scotopic and photopic conditions. No gender difference was observed. Obese mice did not show any alterations in basal slow oscillatory activity after 2 weeks of HFD. A longer follow-up is required to determine if slow oscillatory activity in basal ERG is affected by the development of obesity-related insulin resistance.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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