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Jason Charng, Zheng He, Algis J. Vingrys, Bang V. Bui, Rebecca L. Fish, Dewi Roberts, Rachel Gurrell, Christine T. Nguyen; Longitudinal Stability Of Conscious And Anaesthetised Wireless Telemetry Electroretinography Recordings In Rats. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2466.
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© ARVO (1962-2015); The Authors (2016-present)
Electroretinogram (ERG) recordings in rats are commonly achieved under general anaesthesia, which can modify the retinal responses. We aim to develop conscious wireless ERG recordings with telemetry implantation. Here we assess the repeatability of wireless ERGs and compare conscious against anaesthetised ERG recordings collected in the same animals.
Physiotel transmitters (F50-EEE, Data Sciences International, U.S.A.) were implanted intraperitoneally in Long-Evans rats (n=7). The active electrode was sutured onto the superior sclera (1mm behind the limbus) with the reference anchored 5mm rostral to bregma. An energy response series (-5.60 to 1.52 logcd.s.m-2) was recorded in conscious animals 7, 10 and 14 days after surgery. On day 7, using the same telemetry montage, ERGs were recorded under anaesthesia (intramuscular, ketamine:xylazine, 60:5 mg/kg). Data for a-wave (minimum), b-wave (trough-to-peak) and scotopic threshold response (STR) are expressed as mean (± SEM).
Wireless telemetry returned ERGs with a-wave and b-wave amplitudes of -12.8(±1.5μV) and 46.0(±7.9μV), respectively. At the dimmest light level conscious ERGs had a signal-to-noise ratio of 2.9(±0.6), increasing to a maximum of 26.8 (±2.6) at brighter light levels. The a-wave (d7 -13.5±1.5; d10 -12.8±1.8; d14 -13.5±1.6 μV, all p>0.05), b-wave (d7 47.2±5.5; d10 46.4±8.8; d14 48.0±10.9 μV) and STR (d7 1.3±0.2; d10 1.2±0.2; d14 1.5±0.3 μV) did not change significantly across from day 7 to 14. Coefficients of variation for the a-wave, b-wave and STR were 21, 30 and 28%, respectively. Under anaesthesia, the b-wave was 21% slower compared to the conscious state (p<0.05). Other parameters were not different between conscious and anaesthetised conditions.
This is the first study to successfully use telemetry for wireless ERG recordings in conscious rats. We show that ERGs can be recorded across 7 log units of luminous energy. The dimmest stimuli, which elicits a scotopic threshold response coincides with behavioural threshold for rats. We show that implantation is stable for at least 2 weeks, and returns excellent signal to noise characteristics. This technology has implications for improved translatability of functional assessment from animal models to humans.
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