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Hanna Heikkinen, Frans Vinberg, Marja Pitkänen, Bertel Kommonen, Ari Koskelainen; The Sensitivity And Kinetics Of Mouse Rod Photoreceptors Recorded With Erg In Vivo And Across The Isolated Retina. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6579.
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We examined the amplification and kinetics of murine rod photoresponses from the ERG flash responses recorded in vivo and ex vivo.
Dark-adapted ERG responses to full-field flashes of green light wererecorded from live anesthetized (ketamine/xylazine) C65BL/6N mice. ERG flash responses to homogenous light stimuli arriving from the photoreceptor side were then recorded ex vivo from the same retinas, isolated and perfused with modified Ringer’s or Ames solution at 37°C. The responses were analyzed regarding to 1. the a-wave kinetics, quantified with the Lamb-Pugh activation model and 2. the estimated flash sensitivity and kinetics of the rod responses derived with the paired flash protocol. The data was low pass filtered with fc = 1 kHz and digitized with f = 10 kHz in both setups.
The a-waves measured in vivo and from the isolated retina were of comparable size, sensitivity and kinetics, while the synaptic transmission (as assayed by the onset of the b-wave) was delayed and oscillatory potentials either attenuated or absent ex vivo. The Lamb-Pugh activation constants were of the same order for both preparations. Activation constant obtained from individual flash responses decreased progressively with increasing stimuli. This attenuation of activation with bright stimuli was stronger in the isolated retina. The kinetics of the derived photoreceptor responses were similar in both conditions, although the responses were slightly slower ex vivo. Flash sensitivity was consistently lower in the isolated retina, although this estimate is subject to uncertainties in conversions of flash intensity to R* in the different geometries. The correspondence of the ERG responses in vivo and ex vivo was strongly dependent on the preparation of the tissue, choice of perfusion medium and optimization of the experimental conditions regarding pH buffering and perfusion flow rate.
We emphasize the importance of assaying the physiological state of neural tissues under electrophysiological investigation, especially when the neural function and adaptation beyond the first input stage is assessed.
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