Functional changes in rod and cone pathways after photoreceptor loss in light-damaged rats.
OBJECTIVE
To determine the functional changes in the rod and cone pathways after photoreceptor loss by continuous light exposure.


METHODS
Fifty-four male Sprague-Dawley rats were exposed to diffuse fluorescent light of 2000 lux for 24 or 48 hr. Two weeks after the light exposure, full-field scotopic and photopic electroretinograms (ERGs) were elicited by different stimulus intensities with a maximum luminance of 0.84 log cd-s/m2. The amplitudes of the a- and b-waves of the scotopic ERGs and the b-wave of the photopic ERGs were measured. The animals were sacrificed after the ERG recordings, and the number of surviving rod and cone nuclei in the outer nuclear layer was counted.


RESULTS
The logarithm (log) of the amplitudes of the maximum rod a-wave (rod Va(max)) and b-wave (rod Vb(max)) was reduced monotonically with a decrease in the rod nucleus counts (p < 0.0001). The regression line for the rod Va(max) decrease was significantly steeper than that for the rod Vb(max) (p < 0.005). The maximum b-wave amplitudes of the photopic ERGs (cone Vb(max)) were significantly correlated with the number of cone nuclei in a log-linear fashion. The slopes of the regression lines for the rod Vb(max) and cone Vb(max) were 0.0067 and 0.0140, respectively, which indicates that the amplitude of the cone b-wave was more severely affected than that of the rod b-waves by light-induced photoreceptor degeneration (p < 0.005).


CONCLUSIONS
The amplitudes of the rod and cone ERGs were correlated with rod and cone nuclei counts in a log-linear fashion in light-damaged rats. The functional loss from the photoreceptor death had a greater effect on the cone pathway than on the rod pathway when the retinal function was assessed by the b-wave.
Takahashi
Tomomi
T
Department of Ophthalmology, Iwate Medical University, School of Medicine, Morioka, Iwate, Japan.
Machida
Shigeki
S
Masuda
Tomoyuki
T
Mukaida
Yasuko
Y
Tazawa
Yutaka
Y
D000818:Animals; D002452:Cell Count; D016923:Cell Death; D004596:Electroretinography; D018698:Glutamic Acid / Q000633:toxicity; D007395:Interneurons / Q000502:physiology; D008027:Light / Q000009:adverse effects; D008297:Male; D020419:Photoreceptor Cells, Vertebrate / Q000502:physiology*; D011833:Radiation Injuries, Experimental / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012160:Retina / Q000503:physiopathology / Q000528:radiation effects*; D012162:Retinal Degeneration / Q000503:physiopathology*; D014795:Visual Pathways / Q000503:physiopathology*; D014822:Vitreous Body
D018698:Glutamic Acid