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N. Swaminithan, T. Park, E. Nevo, J. Hetling; Electroretinography in Micropthalmic Eyes: Blind and Zambian Mole–Rats . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3089.
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Several subterranean rodent species possess microphthalmic eyes (∼1 mm dia) that lie beneath thick lids or beneath skin with no lids. Electroretinographic (ERG) recording from these animals requires a specialized electrode and light delivery system. To measure the ERG from Zambian and blind mole–rats, such a system was developed, characterized, and tested.
To electrically couple the recording amplifier with the cornea, a 1.5 mm glass capillary tube was filled with a 3% Agar–KCl gel; one end of the capillary contacted the cornea, the other end was held in a modified capillary electrode holder (WPI) containing a Ag/AgCl pellet and right–angle pin contact. The back end of this holder was machined to accept a super–bright white LED. The capillary tube was used to hold open the eye lids (or skin flaps following a small surgical incision in the case of the blind mole–rat), and light from either the LED or an external xenon flash source was coupled to the capillary which approximated a light guide. Stimulus strength and signal to noise ratio (SNR) were characterized using bench–testing and physiological recording in gerbil. The stimulus/recording system was then used to make ERG recordings in two species of microphthalmic mole–rats.
When driven with maximum current, the ERG a–wave response to the LED stimulus was ∼ 20% of that generated by a saturating full–field stimulus in gerbil. When the xenon flash source was coupled to the capillary electrode, a saturating response was elicited. SNR levels were as good or better than conventional wire electrodes used in rodent ERG recording. Using maximum stimulus strengths available and averaging 10–40 records, no ERG response with SNR > 1 was obtained from the blind or Zambian mole–rats.
An ERG stimulus/recording system optimized for microphthalmic rodent eyes was developed. The two subterranean rodents investigated exhibited no recordable response to light stimuli that were of sufficient strength to elicit a saturating response in a normally–sighted terrestrial rodent (gerbil).
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