Scanning elctron microscopy of rat ova at early stages of fertilization

Abstract

Surface ultrastracture has been studied in rat ova at early stages of fertilization after natural mating, comparing with the results of phase contrast microscopy.
The ova were recovered 5 : 00 to 9 : 30 hours of estrus rat mated at 24 : 00 in proestrus. The ova were fixed for 90120 min. at room temperature (1820°C) in 2.5% glutaraldehyde solution buffered to pH 7.4 with 2 M Na₂HPO₄ and NaH₂PO₄ (1 : 1) and then immersed in 13% sucrose solution. The ova were washed 3 times in distilled water and then treated with 60% and 70% alcohol. The eggs were mounted on brass cylinder and dryed in room temperature.
An information obtained with the scanning electron microscope is unobtainable by other methods.
An effective depth and many microvilli can be seen on surface of rat ovum in zona free (Fig. 1).
The process of sperm penetration into ooplasma was observed and sperm head attached to surface of ovum, intiating membrane fusion of anterior of the post-nuclear cap region to microvilli (Fig. 2-A. B.).
Also, specific mode of incorporation of sperm tail was observed (Fig. 2-C. D.). The present photomicrographs confirm the conclusion for entry of sperm head drawn from transmisson electron microscopy.