Canine cone electroretinograms in response to visible and ultraviolet lights

Abstract: Although ultraviolet (UV-) sensitivity has long been known to be widespread amonginvertebrates, bi s and some rodents, recent studies have revealed that the ocular media ofmost mammals (unlike man) transmits a large amount of the UV-A wavelengths. In addition torod cells, the domestic dog has two discrete types of cone photoreceptors. The peak sensitivityof the short wavelength-sensitive cones (S-cones) is in the blue to violet spectral range and themedium- to long-wavelength-sensitive cones have their peak sensitivity in the red to green partof the spectrum. In addition to the peak sensitive range (the α-band), the photosensitive conepigment will to some degree also absorb photons of shorter wavelengths: ꞵ-band absorption.This extends the visible spectrum, theoretically reaching into the UV-part of the spectrum. Full-field, flash electroretinography (fERG) is a non-invasive procedure that can be used toevaluate electrophysiological responses from the retinal cells. The fERG produces a twodimensional waveform, which can be analyzed according to established guidelines. Bystimulating the retina with wavelengths near the peak sensitivity of the S- or M/L-type conesalong with continuous chromatic background illumination that desensitizes the responses fromthe rods and other type of cone (selective chromatic adaptation), it is possible to separate theresponses from specific cell types. This study details ERG exams performed on 9 healthy research dogs at the Swedish Universityof Agricultural Sciences to evaluate the UV-sensitivity of the canine cone photoreceptors.Using visible short- and long wavelengths, ERG recordings of S- and M/L- responses intendedas a comparative baseline were obtained before also using UV-stimuli. Our results show thatresponses to different colored stimuli on a rod saturating and selective chromatic backgroundcan be used to obtain exclusive ML-cone driven responses and predominantly S-cone drivenresponses, respectively and indicate that both the S- and the M/L-cones are sensitive to stimuliin the UVA-range, although to different degrees.