Effects of visible light and room temperature on the ultrastructure of preimplantation rabbit embryos: a time course study.

In a time course study (4-20 h) rabbit early cleavage stages (day 1 p.c.) and compacted morulae (day 3 p.c.) were exposed to visible light or room temperature (23 degrees C), respectively. An 8 h light exposure of day 1 embryos caused alterations in nuclear morphology (lobulated nuclei, loss of nucleolar differentiation), an increased electron density of the cytoplasm, and cellular fragmentation leading to a considerable degeneration of blastomeres (central clustering of organelles, loss of cell surface differentiation) after a 20 h exposure. Room temperature exposure (compacted Day 3 morulae) led to decompaction and a cleavage delay after 8 h. After 10 h, arrested metaphases occurred in all examined morulae. Even after 20 h at 23 degrees C, day 3 embryos were at the decompacted morula stage, and showed metaphase-arrested blastomeres. The general morphology of the blastomeres was unaffected at this temperature, except for vacuolated ser- and cis-side vesicles of the Golgi complex at 8, 12 and 20 h, respectively.