Abnormal c-fos-like immunoreactivity in the superior colliculus and other subcortical visual centers of pigmented Royal College of Surgeons rats.
Neurons in the central nervous system often show a transient up-regulation of expression of the immediate early gene c-fos when presented with precise novel stimuli. In normal rats, neurons in most subcortical visual centers show low levels of fos-like immunoreactivity (FLI) expression, but there is a substantial and transient increase in FLI expression if the animal is exposed to a flashing light. This is especially evident in the superior colliculus (SC). We have examined here FLI expression in the subcortical visual centers of the Royal College of Surgeons rat, focusing specifically on the SC. In this animal, as a result of a genetic defect, there is early loss of rod photoreceptors over the first few months of life, along with slower disappearance of cones. Although light stimulation showed that FLI expression was very similar to that seen in normal rats, the basal levels of FLI expression under dark-maintained conditions were much higher than normal, even exceeding the levels seen after visual stimulation. In the SC, the elevation of FLI expression was already evident by 6 weeks of age and reached a plateau by 17 weeks. Other subcortical visual centers also showed elevated basal levels of FLI expression, although in general the increases were less dramatic than the increase in the SC. The elevated FLI expression in dark-maintained condition seen in the SC was abolished by contralateral optic nerve section. It was also severely diminished by subretinal cell transplantation at 3 weeks of age with the objective of limiting photoreceptor loss over part of the retina. These results suggest that the elevated basal FLI expression is a retina-driven event. Although it correlates with the loss of rod photoreceptors, it is unlikely to reflect reduced photoreceptor drive but rather some form of bursting activity generated in the inner retina, as a result of circuit reorganization or receptor up-regulation.
Lu
Bin
B
Department of Ophthalmology and Visual Science, Moran Eye Center, University of Utah Health Science Center, Salt Lake City, Utah 84132, USA.
Coffey
Peter
P
Wang
Shaomei
S
Ferrari
Renata
R
Lund
Raymond
R
D000818:Animals; D016762:Genes, fos / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D010786:Photoreceptor Cells / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D011922:Rats, Mutant Strains; D012160:Retina / Q000737:chemistry / Q000378:metabolism; D013477:Superior Colliculi / Q000737:chemistry* / Q000378:metabolism*