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Kristensson, Charlotte, 2014. Evaluation of the retinal ON- and OFF-responses in the dog ERG. First cycle, G2E. Uppsala: SLU, Dept. of Clinical Sciences

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Abstract

The aim of the study was to examine the retinal ON- and OFF-pathways of the canine electroretinogram (ERG). The ON- and OFF-pathways are used to distinguish objects from
their backgrounds. A dark object is discernible from a lighter background using the OFFpathway and the ON-pathway is used to descry a light object upon a darker background.
This study shows that the dog ERG has both ON- and OFF-responses and that these responses can be separated by prolonging the flash duration over 50 ms. The dog OFF-response waveform was more similar to the cat OFF-response than the human OFF-response
(Frishman, 2006; Zrenner and Gouras, 1979).
In this study six female three-year-old Beagle dogs were included. Both background and flash stimuli were provided by LEDs (light emitting diodes) with a wavelength of 470 nm, a wavelength that is absorbed almost as effectively by the canine M/L-cones as by the S-cones.
These stimuli gave ERGs with both ON- and OFF-responses. It was found that a background intensity of 40-60 cd/m2 provided good ERGs with a-waves, distinct b-waves and a small positive OFF-response followed by an obvious negative OFF-response. When the relative flash intensities were varied from 12.28 to 12.8 log relative photons/m2 per 100 ms- flash, all three curves were clearly readable. Flash intensities exceeding 12.8 log relative photons/m2 reduced the negative OFF-response amplitudes.
Additional examinations ought to be made to gain knowledge about the OFF-responses of the S- and M/L-cones, respectively. This study also warrants further investigations on the cellular origin of the canine OFF-response, in particular the late negative OFF-component.

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I denna studie ingick sex treåriga beagletikar. Studiens syfte var att ytterligare undersöka
hundars retinala ON- och OFF-banor med hjälp av elektroretinografi. De retinala ON- och
OFF-vägarna används för att skilja ut ett objekt från bakgrunden. Via OFF-vägen blir ett
mörkare objekt synligt när det kontrasteras mot en ljusare bakgrund och via ON-vägen kan ett
ljust objekt bli synligt mot en mörkare bakgrund.
Studien visar att hundars elektroretinogram (ERG) har både ett ON- och ett OFF-svar, samt
att dessa svar kan separeras när blixtdurationen överstiger 50 ms. Hundens OFF-svar visade
mer likhet med det som ses hos katt än det OFF-svar som ses hos människor (Frishman, 2006;
Zrenner and Gouras, 1979).
LED-lampor (Light emitting diodes) användes till både bakgrundsljus och blixtstimulering
och dessa LEDar sände ut ljus med en medelvåglängd på ca 470 nm, en våglängd som
absorberas nästan lika effektivt av hundens M/L-tappar, som av S-tapparna. Vi fann att en
bakgrundsintensitet på 40-60 cd/m2 gav tydliga ERGn med a-vågor, tydliga b-vågor och en
liten positiv OFF-respons, som följdes av en större negativ OFF-respons. När den relativa blixtintensiteten varierades mellan 12,28 och 12,8 log fotoner/m2 kunde b-vågorna, liksom
OFF-responserna ses tydligt, men när intensiteten överskred denna nivå började amplituden hos den negativa OFF-komponenten minska.
Ytterligare studier behövs för att undersöka S- respektive M/L-tapparnas OFF-responser. Vår studie väcker dessutom frågan kring det cellulära ursprunget för hundens OFF- svar, särskilt den negativa OFF-komponenten.

Main title:Evaluation of the retinal ON- and OFF-responses in the dog ERG
Authors:Kristensson, Charlotte
Supervisor:Ekesten, Björn
Examiner:Hamlin, Helene
Series:UNSPECIFIED
Volume/Sequential designation:2014:63
Year of Publication:2014
Level and depth descriptor:First cycle, G2E
Student's programme affiliation:VY002 Veterinary Medicine Programme 330 HEC
Department:(VH) > Dept. of Clinical Sciences
Keywords:electroretinography, ERG, dog, cones, ON-response, OFF-response, elektroretinografi, hund, tappar, ON-respons, OFF-respons
URN:NBN:urn:nbn:se:slu:epsilon-s-4155
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-s-4155
Subjects:Animal physiology and biochemistry
Technology
Language:English
Deposited On:05 Mar 2015 09:55
Metadata Last Modified:05 Mar 2015 09:55

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