Flagellar movement of human spermatozoa held by their heads with a micropipette was recorded by means of a video‐strobe system. Spermatozoa were studied in normal Hanks' solution, Hanks' solution with increased viscosity, cervical mucus, and hyaluronic acid. When flagellar movement in normal Hanks' solution was observed from the direction parallel to the beating plane, segments of the flagellum in focus did not lie on a straight line but on two diverging dashed lines. The distance between the two dashed lines was about 20% of the bend amplitude in the major beating plane. These observations indicate that flagellar beating of human spermatozoa in normal Hanks' solution is not planar. In contrast, segments of the flagellum in focus lay on a straight line when the spermatozoa were observed in Hanks' solution with increased viscosity, cervical mucus, or hyaluronic acid. In normal Hanks' solution, free swimming spermatozoa rotated constantly around their longitudinal axes with a frequency similar to the beat frequency, whereas little or no rotation of spermatozoa occurred in Hanks' solution with increased viscosity, in cervical mucus, or in hyaluronic acid. We conclude that human spermatozoa in normal Hanks' solution beat with a conical helical waveform having an elliptical cross section, the semiaxes of which have a ratio of 0.2. The three‐dimensional geometry of the flagellar movement is responsible for the rotation of the sperm around their longitudinal axes.

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Caudal epididymal spermatozoa of golden hamsters were incubated in capacitation medium. Their movement patterns changed as they became hyperactivated and underwent the acrosome reaction. To understand the basic mechanism by which changes in movement pattern are brought about, digital image analysis was carried out on the flagellar movements recorded with a video system. The degree of flagellar bending increased with incubation time, especially in the proximal midpiece. The hyperactivated spermatozoa had remarkably asymmetrical flagellar waves of large amplitude because either the bends in the same direction as the hook of the head (referred as the "pro-hook bend") or the bends in the opposite direction to the hook of the head (referred as the "anti-hook bend") extremely increased their curvature; whereas, the acrosome-reacted spermatozoa had relatively symmetrical flagellar waves of large amplitude because both the pro- and anti-hook bends remarkably increased their curvature. Beat frequency significantly decreased while wavelength of flagellar waves increased after hyperactivation and further after the acrosome reaction. These results suggest that both extreme pro- and anti-hook bends are essential in the acrosome-reacted spermatozoa even though beat frequency decreased markedly.

Abstract. We have used the technique of fluorescence recovery after photobleaching to measure the diffusibility of the fluorescent lipid analogue, 1,1 '-dihexadecyl 3,3,3',3'-tetramethylindocarbocyanine perchlorate on the morphologically distinct regions of the plasma membranes of mouse spermatozoa, and the changes in lipid diffusibility that result from in vitro hyperactivation and capacitation with bovine serum albumin.We found that, as previously observed on ram spermatozoa, lipid analogue diffusibility is regionalized on mouse spermatozoa, being fastest on the flagellum. The bovine serum albumin induced changes in diffusibility that occur with hyperactivation are also regionalized. Specifically, if we compare serum incubated in control medium, which maintains normal motility, with those hyperactivated in capacitating medium, we observe with hyperactivation an increase in lipid analogue diffusion rate in the anterior region of the head, the midpiece, and tail, and a decrease in diffusing fraction in the anterior region of the head. IN general, ejaculated mammalian spermatozoa cannot fertilize ova. They gain this capacity from contact with the fluids of the female reproductive system, in particular with the ampullary fluid in the fallopian tube (l, 9; for more recent reviews see references 2, 6, and 40). Capacitation (9) results in two dramatic changes in sperm physiology: hyperactivation and acquisition of the ability to undergo the acrosome reaction and fertilize an oocyte. The midpieces of ejaculated spermatozoa are relatively inflexible. Their flagella exhibit low amplitude symmetric beating, which results in linear swimming patterns. In contrast, the midpieces of hyperactivated spermatozoa are highly flexible. Their flagella exhibit large amplitude, often asymmetric, beating, which results in circular swimming patterns. Often hyperactivation also results in altered beat frequency. The acrosome reaction refers to a fusion and vesiculation between the sperm plasma membrane in the anterior region of the head and the underlying acrosome. This results in a release of the acrosomal vesicle contents both lytic components and adhesion proteins (for review see reference 61) involved in fertilization, and exposes the inner acrosomal membrane. In most mammals, subsequent fusion of egg and sperm plasma membranes occurs at the equatorial region of the sperm surface (7). The precise molecular mechanism of this process of capacitation remains unknown. However, capacitation results in dramatic changes in plasma membrane lipid and protein composition as well as in the lateral distribution or regionalization of these components (5,16,21,25,29,35,39,46,51). Indeed, it has been suggested that lipid redistributions that result from capacitation provide the fusogenic domains required for vesiculation during the acrosome reaction (5).In vitro capacitation can in some species be effected by incubation of spermatozoa in serum albumin (30). Once again, the precise molecular mechanism of this in vitro capacitation remains unknown. ...

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