Objective evaluation of hyperactivated motility in rat spermatozoa using computer-assisted sperm analysis*

The aim of this study was to use computer-assisted sperm analysis (CASA) to examine changes in motion parameters of rat spermatozoa incubated under culture conditions that support IVF. Rat cauda epididymal spermatozoa were evaluated in six replicate experiments, at 0 and 4h of incubation. CASA was conducted at 60 Hz on digital 1s tracks ( approximately 100 spermatozoa/rat). Mean values of CASA parameters that describe the vigour of spermatozoa [curvilinear velocity (VCL), amplitude of lateral head displacement (ALH) and beat cross frequency (BCF)] increased, while those indicating progressiveness [straight line velocity (VSL), linearity (LIN) and straightness (STR)] decreased between 0 and 4 h. Visual inspection of sperm tracks after 4 h of incubation revealed classical hyperactivation patterns. Bivariate models were evaluated to objectively define the subpopulation of hyperactivated (HA) spermatozoa. Of all models considered, ALH and LIN, VCL and LIN, BCF and LIN, VCL and BCF, and VCL and ALH showed significant changes in the percentage of HA spermatozoa after the 4 h incubation period. The efficacy of detecting HA spermatozoa was evaluated using sperm tracks that were visually classified as HA or progressive. VCL and LIN provided the most accurate prediction of HA spermatozoa. It was concluded that analysis of CASA data using bivariate models could be used to detect and monitor hyperactivation in rat spermatozoa.