Transneuronal Degeneration in the Visual Pathway of Rats following Acute Retinal Ischemia/Reperfusion

Figure 3

Ultrastructure changes of neurons in the retina after RI/R injury. ①–③: ultrastructure changes in each layer of the retina under 1000× TEM ( μm). ① Control group. The boundaries between different layers were clear. The nucleus in ONL and INL was neatly arranged with a polygonal cross-section. ② Ultrastructure of each layer in the retina at 12 hours post-RI/R injury. Layer demarcation becomes unclear, and the arrangement of cells becomes loose, and obvious macular edema was observed. ③ Ultrastructure of each layer in the retina at 3 days post-RI/R injury. The macular edema showed a slight trace of recovery, but cell morphology becomes irregular, and nuclear chromatin became condensed. (a–l) Ultrastructure changes in each layer of the retina under 10000× TEM ( μm). I/R-12 h: rats euthanized 12 hours post-RI/R injury; I/R-3 d: rats euthanized 3 days post-RI/R injury; I/R-7 d: rats euthanized 7 days post-RI/R injury. (a) Nucleus in ONL was neatly arranged with a polygonal cross-section. (e) Outside the ONL are the inner segments (ISs) of photoreceptor (PR) cells, and they were narrow and long, with a long spindle shape, were arranged orderly, and rich in mitochondria at the peripheral portion of the soma. (l) Outer segment (OS) of photoreceptor (PR) cells contained many flattened membranous structures called discs. In the normal state, the disc is neatly folded inside, with few gaps in between. (b, f, j) I/R-12 h group. (b) Some nucleus in ONL was replaced by vacuoles. (f) Edema in the IS made cells’ volume increased significantly which decreased intercellular space. Mitochondria (Mi) were significantly increased and swelled. (j) OS swelled, the arrangement of membranous discs becomes disordered, and the space between membranous discs became widened. (c, g, k) I/R-3 d group. (c) Gliocyte proliferation in ONL (red star), cell edema, and chromatin aggregation allowed the nucleus to be deeply stained. (g) The edema in the IS showed a slight trace of recovery compared to the I/R-12 h group, while mitochondria continue to proliferate and hypertrophy (Mi). (k) The edema in the OS showed a slight trace of recovery. (d, h, l) I/R-7 d group. (d) Nucleus in ONL was lysed, and the number reduced. (h) Organelle was lysed, and the membrane was discontinuous in IS. (o) The membrane disc was loose, dissolved, and shrunk.