Abnormalities of the photoreceptor-bipolar cell synapse in a substrain of C57BL/10 mice.
OBJECTIVE
A preferential loss of ERG b-wave was detected in a substrain of C57BL/10 mice. Electroretinographic and histologic techniques were used to investigate this hitherto unknown retinopathy.


METHODS
ERGs were obtained from normal and affected C57BL/10. C57BL/6 mice served also as controls. a-Wave and c-wave analyses were performed. Microscopic investigations were done at two different ages.


RESULTS
In the scotopic ERG, a severe reduction of the b-wave amplitude could be observed, whereas the a-wave was only moderately attenuated ("negative ERG"). With age, the a-wave amplitude further decreased, but the rate of reduction was comparable to normals. Oscillatory potentials were severely altered, and the photopic ERG was absent. The ERG c-wave was comparable to normal. ERG a-wave analysis also revealed a reduced maximum amplitude, but no significant difference of receptor sensitivity. Light microscopy revealed a thinning of all retinal layers but mostly of the outer plexiform layer. The number of photoreceptor nuclei was reduced by one third. Electron microscopy revealed a profound loss of ribbon-shaped synapses between rod and rod-bipolar cells and severely abnormal ribbons in the case of cones.


CONCLUSIONS
The so-called negative ERG was associated with alterations in the synaptic layer between rods and rod bipolars. The absent cone ERG may be due to the altered cone-on-bipolar synapses. The overall thinning of the retina as well as the moderately reduced scotopic a-wave amplitude remain unexplained.
Ruether
K
K
UKE Eye Hospital, University of Hamburg, Germany. kreuther@uke.uni-hamburg.de
Grosse
J
J
Matthiessen
E
E
Hoffmann
K
K
Hartmann
C
C
D000818:Animals; D003623:Dark Adaptation; D004596:Electroretinography; D005260:Female; D007395:Interneurons / Q000473:pathology* / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009755:Night Blindness / Q000235:genetics / Q000473:pathology* / Q000503:physiopathology; D010375:Pedigree; D020419:Photoreceptor Cells, Vertebrate / Q000473:pathology* / Q000502:physiology; D013569:Synapses / Q000473:pathology* / Q000502:physiology