Photoelectron imaging of guinea-pig, hamster and human spermatozoa

Photoelectron images of mammalian spermatozoa were obtained by subjecting the specimens to u.v.-irradiation and focussing the emitted electrons by electron optics (photoelectron microscopy). Guinea-pig, hamster and human spermatozoa were fixed in glutaraldehyde, deposited on conductive glass discs, and dehydrated. Sufficient quantities of photoelectrons were released from the surface of spermatozoa to produce images without staining, coating or metal shadowing. The large planar heads of guinea-pig spermatozoa were easily resolved with good delineation of acrosomal and postacrosomal regions. Residual vesicles could be visualized on the surface of the inner acrosomal membrane of spermatozoa that had undergone the acrosome reaction. Also detectable in these photoelectron images were finer membrane surface details, periodicities in the midpiece region of the tail which coincided with the distribution of mitochondria, and periodicities in the principal piece which appeared to be related to fibrous sheath components. Hamster spermatozoa were similarly well resolved but human spermatozoa were more difficult to image because of their increased surface curvature. The mechanism responsible for detection of these surface details is primarily topographical contrast rather than material contrast, since spermatozoa coated with a thin layer of gold or platinum exhibited similar features, although at reduced resolution, as the uncoated specimens.