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A. J. Valjakka, J. Ahonen, M. Itkonen, L. Pitkänen, A. Urtti; Comparison of ERG Records From Anaesthetized versus Freely Behaving Rats. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1286.
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To evaluate how the electroretinogram (ERG) responses to light stimulation are recordable from the anesthetized versus freely behaving rats using the novel ball-electrode as permanently implanted in the eye. The plausible differences in ERG inductions between the two conditions would point to the need of acquiring ERGs from conscious non-drugged animals for estimating the natural visual capacity.
The ball electrodes were bilaterally implanted in the eyes of Wistar rats, under anaesthesia. Electrodes were positioned against the laterotemporal and mediotepomporal sclera surfaces of the eye globe. Responses to white-light flashes of different intensities were recorded from the freely behaving [spontaneous alert immobility] vs. anesthetized [anaesthetic: Dormicum & Hypnorm] rats, under the background light of 1 Lx.
ERG responses were practically similar in their waveforms in the freely behaving vs. anesthetized rats. Response[b-wave amplitude]-intensity functions for the two different conditions had relatively the same degrees of data variation. Anaesthesia changed notably the forms of amplitude-intensity functions as compared to the normal behavioural situation. With the anaesthesia the threshold responses were inducible by about 3 log-unit flashes while the response amplitudes reached plateaus with about 7 log-units. Naturally behaving animals had response threshold intensity slightly greater than 1 log-unit and showed response amplitude saturations by about 6 log-unit flashes. Within the flash intensity range of 1-6 log-units the area integral of the amplitude-intensity was approximately halved because of the anaesthesia, as compared to the free-behaviour (conscious) condition.
The data show that ERG light responses are recordable with the equal reliability from the anaesthetized vs. freely behaving rats with the use of the described novel method. The estimation of natural visual capacity as regards both the retinal and optic nerve function arguably necessitates the investigation of ERGs from conscious animals, which is made possible by the presently reported novel ERG recording technique.
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