5-FLUOROURACIL REDUCES PROLIFERATING CELL NUCLEAR ANTIGEN IMMUNOREACTIVE CELLS IN GOLDFISH RETINA

A pyrimidine analogue, 5-fluorouracil (5-FU), was injected intravitrea lly into one eye of the goldfish, either alone, or before or after inj ection of the same eye with the dopaminergic neurotoxin, 6-hydroxydopa mine (6-OHDA). Effects of these agents were explored by measuring thei r actions on numbers of proliferating cell nuclear antigen-immunoreact ive (PCNA-ir) cells, representing mitotically active rod precursor cel ls (RPCs) in normal conditions, in both treated and untreated retinas. At various intervals (5-45 days after the first injection of drug), t he retinas (n=6 for each treatment group) were isolated and processed as wholemounts by an indirect immunohistochemical method fbr PCNA. Som e retinas were cryosectioned and processed for certain immunoreactive cells other than PCNA. Changes in the mean density of PCNA-ir cells, f ollowing intravitreal 5-FU (10 mu g/2 mu l saline on 3 consecutive day s) alone or in combination with intravitreal 6-OHDA (2.5 mu g/2 mu l, were statistically compared for interval vs. day 0 (control from intac t retinas) and for treated vs, contralateral (untreated or treated) re tinas, in both outer and inner nuclear layers (ONL and INL, respective ly). 5-FU at this dose drastically reduced the densities of endogenous and 6-OHDA-induced PCNA-ir cells in the ONL of treated retinas, but t ransiently increased them in the contralateral untreated retinas, prob ably reflecting an injury influence from the treated retina. The densi ty of PZNA-ir cells at the retinal margin was also greatly reduced in treated retinas. Such changes peaked on days 10-15, and gradually disa ppeared over days 30-45. In the INL, on the other hand, 5-FU did not c ause a significant change of the PCNA-ir cell density in either treate d or untreated retinas. As expected, 5-FU appeared not to act upon ret inal cells immunoreactive to certain phenotype-specific antibodies oth er than PCNA. The results indicate that 5-FU strongly prevents prolife ration of RPCs in the ONL and of neuroblasts at the retinal margin, bu t negligibly influences unidentified PCNA-ir cells in inner retina. Th ey showed also that clustering of PCNA-ir cells and the marked increas e of their density, seen in 6-OHDA-intoxicated retinas, are due to vig orous proliferation of neuroblast cells in the fish retina.