The human cumulus matrix during "in vitro" fertilization. Ultrastructural observations

The real three-dimensional architecture of the human cumulus extracellular matrix and its relationships with spermatozoa during "in vitro" fertilization was studied with high resolution scanning electron microscopy. using the saponin, ruthenium red and osmium tiocarbohydrazide technique. Our observations demonstrate that the cumulus matrix in mature post-ovulatory oocytes possesses a highly complex structure and that culture conditions do not disrupt its fine architecture. In addition, it was demonstrated that the passage of the spermatozoon occurs as consequence of its active movement capable of creating a channel into the matrix instead of using pre-existent structures. A complex specific interaction between spermatozoa and cumulus glycoproteins is suggested.