THE USE OF BRIGHT-FIELD MICROSCOPY IN EVALUATING BOVINE ACROSOME REACTION

A novel stain for evaluating the acrosomes of bovine spermatozoa was i nvestigated. Acrosome reactions were induced by incubating spermatozoa enriched by swim-up with 1 mu mol/l calcium ionophore A23187 for 1 or 1.5 h, while control samples were incubated in modified Tyrode's medi um alone. After fixing in formaldehyde, spermatozoa were stained eithe r with naphthol yellow S plus erythrosin B (NE) or with the novel stai n, naphthol yellow S plus aniline blue (NA). The number of spermatozoa that had undergone acrosome reaction was counted and compared with re sults obtained using differential interference contrast microscopy (DI C). The correlation between the 2 staining methods was high (r=0.99), as was the correlation between NA staining and DIC (r=0.97). Slides st ained with NA showed little background staining and the preparations w ere permanent. The results indicate that NA may be a useful stain for the bright-field evaluation of the bovine acrosome.