Figure 5. TUNEL labeling of pineal and retinal sections of metronidazole-treated and untreated transgenic (Tg) and wild-type (AB) zebrafish (8 months old).

(A, B) Pineal and retinal sections of untreated transgenic fish. No obvious cell death was detected. (C, D) Pineal and retinal sections of transgenic zebrafish after 4 metronidazole treatments. In the pineal gland, TUNEL-positive cells were detected (arrows). No cell death was seen in the retina. (E–H) Pineal and retinal sections from untreated and metronidazole-treated wild-type zebrafish. No cell death was seen in the pineal gland or retina. Dashed lines outline the retina.