Abstract:
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 sperm
atozoa 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, althoughat reduced resolution, as the uncoated specimens.