Impact on hyperactivated motility of cryopreserved mouse sperm from pretreatment with Thimerosal

Hyperactivated motility of sperm cells is essential to successful fertilization. This study was performed to observe the effect of Thimerosal treatment of cryopreserved mouse sperm on their hyperactivated motility and subsequent development to two-cell embryos after in vitro fertilization. Hyperactivated motility was evaluated by curvilinear velocity (VCL, the rate of travel of the sperm head) and Amplitude of Lateral Head Displacement (ALH, degree of side-to-side head movement measured as the mean width of head oscillations) of cells using Computer-assisted Sperm Analysis (CASA). The fresh sperm had higher VCL and ALH than frozen-thawed sperm (p<0.05). Following In Vitro Fertilization (IVF), fertilization rate from frozen-thawed sperm was significantly lower than that from fresh sperm (71.6, 94.4%) (p<0.05). Neither VCL nor ALH differed significantly between fresh sperm and frozen-thawed sperm not treated with Thimerosal. The decreased hyperactivated motility of mouse sperm due to cryopreservation may contribute to reduced fertilization rate compared to that achieved with fresh sperm. In addition because Thimerosal treatment of sperm after cryopreservation enhances hyperactivated motility, its use may improve the development of cryopreserved mouse oocytes from cryopreserved sperm.