Effect of various capacitation systems on bovine sperm motion characteristics, acrosome integrity, and induction of hyperactivation

Sperm Subpopulations in Iberian Red Deer Epididymal Sperm and Their Changes Through the Cryopreservation Process1

We have applied a statistical protocol based on principal component analysis, clustering methods, and discriminant analysis for the identification of sperm subpopulations in computer-assisted sperm analysis (CASA) data. Samples were obtained from the cauda epididymis of 11 Iberian red deer and cryopreserved following a standard protocol. Motility by CASA was analyzed just after sperm recovery, just before freezing, and after thawing, and eight motility descriptors for each individual spermatozoon were recorded. Sperm viability and acrosomal status were also assessed. Subpopulation analysis was performed in four sequential steps: principal component analysis using the eight motility descriptors; nonhierarchical clustering analysis (k-means) using the first two principal components; hierarchical clustering analysis (UPGMA); and selection of the final number of clusters. Three clusters were obtained for each motility analysis: slow and nonlinear; rapid and linear; and rapid, high ALH, nonlinear. We detected variations in the clusters between treatments (initial, prefreezing and postthawed). Indeed, motility increased and linearity decreased in the prefreezing analysis. A discriminant analysis isolated three descriptors that were used again in the same statistical analysis, giving four clusters that resembled the pattern found in the first classification. We also performed a clustering analysis of the males according to prefreezing/postthawed variation of total motility, viability, and acrosomal status. The proportion of the linear subpopulations in the prefreezing treatment, in both clustering analyses, correlated positively with postthawed viability recovery. Our results show that clustering analysis of CASA data gives useful and practical information that is not obtained by conventional sperm analysis.

Effect of buffering systems on post-thaw motion characteristics, plasma membrane integrity, and acrosome morphology of buffalo spermatozoa

This study was carried out to identify the suitable buffer for cryopreservation of buffalo semen. Semen was collected with artificial vagina (42 degrees C) from four buffalo bulls. Split pooled ejaculates (n=5), possessing more than 60% visual sperm motility, were extended at 37 degrees C either in tri-sodium citrate (CITRATE), Tris-citric acid (TCA), Tris-Tes (TEST) or Tris-Hepes (HEPEST). Semen was cooled to 4 degrees C in 2 h, equilibrated at 4 degrees C for 4 h, filled in 0.5 ml straws and frozen in a programmable cell freezer before plunging into liquid nitrogen. Thawing of frozen semen was performed after 24 h at 37 degrees C for 15 s. Sperm motion characteristics, plasma membrane integrity, and acrosome morphology of each semen sample were assessed by using computer-assisted semen analyzer (CASA), hypo-osmotic swelling (HOS) assay, and phase-contrast microscope, respectively. Analysis of variance revealed that percent post-thaw visual motility tended (P=0.07) to be higher in HEPEST (61.0+/-2.9) and lowest in CITRATE (48.0+/-2.5). Computerized motility did not vary due to buffering system. Percent post-thaw linear motility tended (P=0.09) to be higher in TCA (78.2+/-5.5) and lower in TEST (52.0+/-6.9). Circular motility (%) was significantly lower (P<0.05) in TCA (11.6+/-2.8) and higher in TEST (29.8+/-5.6). Curvilinear velocity (microm s(-1)) was lower (P<0.05) in TCA (69.4+/-2.0) than in CITRATE (79.0+/-5.8), TEST (87. 2+/-1.6) and HEPEST (82.6+/-3.0). Lateral head displacement (microm) was lowest (P<0.05) in TCA (1.7+/-0.2) and highest in TEST (3.7+/-0. 6). Plasma membrane integrity and normal acrosomes of buffalo spermatozoa did not differ due to buffering system and averaged 40. 0+/-2.7% and 61.4+/-4.6%, respectively. Based upon lower circular motility, curvilinear velocity, and lateral head displacement, it is concluded that post-thaw quality of buffalo semen can be improved using the Tris-TCA buffering system.

Computer-assisted sperm motion analysis of bovine sperm treated with insulin-like growth factor I and II: implications as motility regulators and chemokinetic factors

The effects of insulin-like growth factors (IGFs) I and II on motility of bovine sperm were examined using a computer-assisted sperm motion analyzer (CASA). The following kinematic parameters were examined: percentage of rapidly moving cells, straight-line velocity , curvilinear velocity, average path velocity, amplitude of lateral head displacement, and beat cross frequency. Sperm were treated with IGF-I (100 ng/mL) or IGF-II (250 ng/mL) and compared to sperm in modified Tyrodes' medium only (control) at 90, 180, and 360 min using CASA. Insulin-like growth factor I and II increased the percentage of rapidly moving cells, straight-line velocity, curvilinear velocity, average path velocity, amplitude of lateral head displacement, and beat cross frequency compared to the control treatment. These results indicate that IGFs may be involved in initiation and maintenance of bovine sperm motility.

Identification of insulin-like growth factor I in bovine seminal plasma and its receptor on spermatozoa: influence on sperm motility

Insulin-like growth factor I (IGF-I) has been identified in human seminal plasma. This study was conducted to determine whether IGF-I is present in bovine seminal plasma, whether sperm cells express the IGF-I receptor (IGF-IR), and whether IGF-I affects sperm motility. Semen samples were collected from bulls by electroejaculation and maintained at 37 degrees C, and motility of sperm was assessed. After centrifugation to separate sperm cells from seminal plasma, the seminal plasma was submitted to a validated heterologous RIA for IGF-I. Significant concentrations of IGF-I (116.29 +/- 40.83 ng/ml expressed as mean +/- SD) were measured in bovine seminal plasma. Sperm cells were washed with buffer and subjected to either radioreceptor assay (RRA) or immunocytochemistry (IC). RRA revealed a single high affinity for the IGF-IR with a Kd of 0.83 nM as determined by the computer program LIGAND. IC, using three monoclonal antibodies, localized the IGF-IR to the acrosomal region of the sperm. Computer-assisted sperm-motion analysis was used to determine the effects of IGF-I and IGF-II on bovine sperm motility parameters. Both IGF-I and IGF-II increased sperm motility and straight-line velocity (p < 0.05) relative to the control. The presence of IGF-IR on sperm, the presence of IGF-I in semen, and the ability of IGF-I to stimulate sperm motility provide evidence that the IGF system may be involved in the fertilization process in the bovine species.

Computer-assisted sperm analysis for assessing initial semen quality and changes during storage at 5 degrees C

Computer-assisted sperm analysis equipment was used to evaluate bull sperm initially in a modified Tyrode's solution, in Cornell University extender, and in egg yolk-glycerol-Tris extender (following cooling and storage in the latter two extenders). Two ejaculates of semen were collected from each of eight bulls. Semen was divided into aliquots using a factorial arrangement. The semen, diluted to approximately 20 x 10(6) sperm/ml, was loaded into two 20-micron chambers, and six microscope fields from each chamber were videotaped for each treatment of each ejaculate of semen. Eight sperm characteristics analyzed with the Hamilton Thorne integrated visual optical system (Hamilton Thorne, Beverly, MA) were reported, and some of these characteristics differed significantly among bulls. The initial values of motile sperm in modified Tyrode's solution, Cornell University extender, and egg yolk-glycerol-Tris extender were 87, 79, and 66%; little change followed cooling and storage at 5 degrees C in the latter two extenders. Also, there was a small but significant decline in sperm velocity during 3 d of storage. Hyperactive sperm increased slightly during storage. The procedures used can rapidly and accurately measure many sperm characteristics in fresh semen and in semen stored in egg yolk extenders, and differences among bulls can be detected.

Comparison of various bovine sperm capacitation systems for their ability to alter the net negative surface charge of spermatozoa

Semen was divided into five aliquots and capacitated for 4 or 6 h in calcium-free Tyrode's (37 degrees C), modified Tyrode's bovine follicular fluid (39 degrees C), modified Tyrode's heparin (39 degrees C), and TEST-yolk buffer (4 degrees C) or incubated in BSA-saline (39 degrees C). Sperm before and after capacitation were electrophoresed at 100 V of constant current for 3 and 6 min. Samples were collected, sperm were counted, and percentages of sperm migrating toward the anode at 0 h and 4 or 6 h were calculated. At 0 h, 61 to 80% of the sperm migrated with a net negative charge. After 4 or 6 h, the percentage of sperm migrating toward the anode significantly decreased in all capacitation media but not in the control. The percentage of sperm migrating toward anode was lowest in calcium-free Tyrode's (22.1%) followed by TEST (28.4%), Tyrode's follicular fluid (29.5%), and Tyrode's heparin (42.5%); these values were less than those for the control (56.0%). The movement of live sperm without the influence of current or freeze-killed sperm under the influence of electrical current (control trials) was negligible. Capacitation reduced the net negative surface charge of sperm, the magnitude of which depended on capacitation system. Net negative charge of sperm was inversely associated with efficiency in penetration of zona-free hamster oocytes.