Cold-induced ultrastructural changes in bull and boar sperm plasma membranes

Novel gamete storage

The aim of this review is to outline recent advances in gamete storage that are beneficial for rescuing endangered species or for the breeding of companion animals. Much more information is available on the technical resolutions and practical applications of sperm cryopreservation in various species than of female gametes, reproductive tissues or organs. Mammalian sperm cryopreservation often works relatively efficiently; however, the ability of female gametes to be cryopreserved and still be viable for fertilisation is also essential for rescuing endangered species. For a proper evaluation of gamete cryopreservation possibilities in a given species, it is essential to understand the basic mechanism affecting the survival of cryopreserved cells, the technical and physical limitations, the available techniques and the new avenues to resolve the specific problems in that species. This paper is aimed to provide some help for this process. The limited length of this paper resulted in the omission of information on many important areas, including most data on teleosts, amphibian and insect cryopreservation.

Cryopreservation of bull spermatozoa alters the perinuclear theca

The perinuclear theca (PT) is involved in several important sperm functions leading to fertilization. The objective of this study was to investigate the effect of cryopreservation of bull spermatozoa on the integrity of the PT and the relationship between PT integrity and semen characteristics. Semen from seven bulls was evaluated before and after cryopreservation, comparing the integrity of the plasma membrane (hypo-osmotic test), percentage of live and dead spermatozoa (triple stain), acrosome integrity (triple stain) and the integrity of the PT (negative stain by electron microscopy). Cryopreservation of bull semen caused substantial damage to the PT; the proportion of spermatozoa with a damaged PT was 15.2% versus 52.5% (P<0.05) in fresh versus frozen-thawed spermatozoa, respectively. Furthermore, on average, 67.4% (range, 64-72%) of fresh spermatozoa were live, compared to 53.1% (range, 49-58%) for frozen-thawed spermatozoa; there was an inverse correlation between the percentage of live spermatozoa and the percentage with damage to the PT. Although 59.1% of frozen-thawed spermatozoa had an intact acrosome, only 43.7% of them still remained alive. In frozen-thawed semen, there was a high correlation (r=0.69) between live spermatozoa with an intact acrosome and spermatozoa that maintained an intact PT. In conclusion, freezing/thawing of bull spermatozoa altered the PT and maintaining PT integrity may be necessary to maintain acrosome integrity.

Structure of mammalian spermatozoa in respect to viability, fertility and cryopreservation

Morphological assessment of spermatozoa has a long history and it is generally accepted that specific morphologic structural deviations correlate with male sub- and infertility. Although many different and also new methods are used in semen analysis, light microscopy is still used for routine morphological evaluation. This paper gives an overview about the detailed structure of physiological mammalian spermatozoa as well as the most common morphological deviations in correlation to fertility. This should be the basis for explanation of problems resulting from semen cryopreservation. General aspects of semen cryopreservation should be regarded before to facilitate the understanding of methods and mechanisms.

Influence of cooling rates and addition of Equex pasta on cooled and frozen-thawed semen of generic gray (Canis lupus) and Mexican gray wolves (C. l. baileyi)

A current priority for the preservation of the endangered Mexican gray wolf (Canis lupus baileyi) is the development of a sperm-based genome resource bank for subsequent use in artificial insemination. To optimize the quality of cryopreserved sperm, the procedures involved in processing semen before and during freezing need to be improved. The aim of this study were to examine the effects of: (i) different cooling periods before freezing and (ii) addition of Equex pasta (Minitüb, Tübingen, Germany) on the characteristics of sperm from the generic gray wolf and the Mexican gray wolf after cooling and cryopreservation. For Mexican wolf sperm, cooling for 0.5 and 1.0 h had a less detrimental effect on cell morphology than cooling for 2.5 h, whereas the slower cooling rate (2.5 h) had a less detrimental effect on functional parameters and seemed to cause less damage to plasma membrane and acrosome integrity than 0.5 and 1.0 h. For the generic gray wolf, cooling semen for 2.5 h had less detrimental effect on plasma membrane integrity and viability; together with the 0.5 h cooling time, it yielded the highest percentages of intact acrosomes. As previously shown in the domestic dog, Equex pasta had no beneficial effect on sperm characteristics in either wolf species.

Improvement of parameters of freezing medium and freezing protocol for bull sperm using two osmotic supports

The aim of this study was to improve the freezing protocol of bull sperm, by investigating the influence on sperm viability after freeze/thawing of different freezing medium components, as well as the effect of cooling rates in the different stages of the cooling protocol, in single factor experiments. The experimental variables were: (1) salt-based versus a sugar-based medium (Tris versus sucrose); (2) glycerol concentration; (3) detergent (Equex) concentration; (4) presence of bicarbonate; (5) rate of cooling from 22 degrees C to holding temperature (CR1); (6) holding temperature (HT); (7) rate of cooling from holding temperature to -6 degrees C (CR2); (8) rate of cooling from -10 to -100 degrees C (CR3). All experiments were performed using five bulls per experiment (three ejaculates per bull). Sperm motility after freezing and thawing was assessed by CASA system, and sperm membrane integrity was assessed by flow cytometry. Sucrose-based medium did not offer a clear significant benefit compared to Tris medium. The concentration of Equex that gave the best results in Tris-based media group and sucrose-based media group was in a range between 2-7 and 4-7 g/l, respectively. In both media groups, a glycerol concentration of 800 mM was the best in any post-thaw viability parameters. In the Tris media group, the presence of bicarbonate had a negative effect on sperm viability. CR1 and CR2 had no significant effect on any of the post-thaw sperm viability parameters, but a CR1=0.2 degrees C/min and CR2=4 degrees C/min appeared to give better results in both media. The holding temperature (HT) that gave the best results was found to be in the range of 5-9 degrees C. There was a significant disadvantage of using a low CR3 of 10 degrees C/min, while 150 degrees C/min appeared to be the best cooling rate for either medium.

Ultrastructural alterations of frozen-thawed Asian elephant (Elephas maximus) spermatozoa

Intact plasma and acrosome membranes and functional mitochondria following cryopreservation are important attributes for the fertilizing ability of spermatozoa. In the present study, functional and ultrastructural changes of Asian elephant spermatozoa after cryopreservation either in TEST + glycerol or HEPT + dimethyl sulphoxide (DMSO) were evaluated by fluorescent techniques and electron microscopy. Sperm frozen in TEST + glycerol had higher proportion of sperm with intact plasma (49.1 +/- 9.2% vs. 30.9 +/- 3.9%) and acrosomal (53.7 +/- 4.9% vs. 35.8 +/- 6.1%) membranes, as well as active mitochondria (57.0 +/- 7.2% vs. 42.0 +/- 5.0%) than those cryopreserved in HEPT + DMSO. The results obtained from electron microscopy were similar to those obtained by fluorescence microscopy. The percentage of normal spermatozoa was higher when spermatozoa were frozen in TEST + glycerol than those frozen in HEPT + DMSO (31.8 +/- 5.6 vs. 28.5 +/- 6.4). The ultrastructural alterations revealed by transmission electron microscopy could be classified as (i) distension of plasma membrane, while the acrosome was swollen; (ii) disruption or loss of plasma membrane, while acrosome was swollen with distended outer acrosomal membrane; (iii) disruption or loss of plasma and outer acrosomal membrane with leakage of acrosome content; (iv) extensive vesiculation of plasma and outer acrosomal membrane and leakage of acrosome content; (v) a complete loss of both plasma membrane and outer acrosomal membrane; and (vi) swelling of mitochondria. These findings suggest that the freezing and thawing procedure caused structural damage to elephant spermatozoa, especially in the plasma membrane, acrosome and mitochondria. Fluorescence and electron microscopic evaluations are potentially a powerful tool in the analysis of elephant spermatozoa after freezing and thawing.

Equine sperm membrane phase behavior: the effects of lipid-based cryoprotectants

The plasma membrane of sperm can undergo lipid phase separation during freezing, resulting in irreversible damage to the cell. The objective of our study was to examine the membrane phase behavior of equine spermatozoa in the absence and presence of lipid-based cryoprotectants. Biophysical properties of sperm membranes were investigated with Fourier-transform infrared spectroscopy. Compared to fresh untreated sperm, postthaw untreated sperm showed extensive lipid phase separation and rearrangement. In contrast, postthaw sperm that were cryopreserved in egg phosphatidylcholine (egg PC)- or soy phosphatidylcholine (soy PC)-based diluents showed similar lipid phase behavior to that of fresh, untreated sperm. Studies with a deuterium-labeled PC lipid (POPCd-31) suggest that exogenous lipid from the diluents are strongly associated with the sperm membrane, and scanning electron microscopy images of treated sperm show the presence of lipid aggregates on the membrane surface. Thus, the exogenous lipid does not appear to be integrated into the sperm membrane after cryopreservation. When compared to a standard egg-yolk-based diluent (INRA 82), the soy and egg PC media preserved viability and motility equally well in postthaw sperm. A preliminary fertility study determined that sperm cryopreserved in the soy PC-based medium were capable of fertilization at the same rate as sperm frozen in the conventional INRA 82 medium. Our results show that pure lipid-based diluents can prevent membrane damage during cryopreservation and perform as well as a standard egg-yolk-based diluent in preserving sperm viability, motility, and fertility.

Comparative aspects of sperm membrane fatty acid composition in silver (Vulpes vulpes) and blue (Alopex lagopus) foxes, and their relationship to cell cryopreservation

Cryogenic protocols have been developed for the storage of farmed silver fox (Vulpes vulpes) spermatozoa. However, these same protocols and modifications of these protocols have failed to satisfactorily preserve spermatozoa collected from farmed blue foxes (Alopex lagopus). Because cryogenic success has been linked to membrane composition, the plasma membrane lipid composition of farmed blue fox and silver fox spermatozoa was studied. Silver fox spermatozoal membranes have significantly higher levels of docosapentaenoic acid (DPA; 22:5, n-6) compared to blue fox spermatozoa, and blue fox spermatozoal membranes have significantly higher levels of stearic acid (18:0). Silver fox spermatozoal membranes not only have a higher ratio of unsaturated/saturated membrane fatty acids, but also higher levels of membrane desmosterol and cholesterol.

Effects of hypothermic liquid storage and cryopreservation on basal and induced plasma membrane phospholipid disorder and acrosome exocytosis in boar spermatozoa

Flow cytometry was utilised to determine whether short-term (Day 1) or long-term hypothermic liquid storage (Day 5), or cryopreservation of boar spermatozoa (1) caused changes in plasma membrane phospholipid disorder (MPLD) and acrosome exocytosis (AE), indicative of an advanced stage of capacitation or acrosome status, and (2) facilitated or inhibited the induction of capacitation and the acrosome reaction. Merocyanine with Yo-Pro-1 and peanut agglutinin–fluorescein isothiocyanate with propidium iodide were used to identify MPLD and AE, respectively, in viable spermatozoa. The incidence of basal sperm MPLD and AE in fresh semen was very low (1.1 and 2.2%, respectively) and was increased (P < 0.05) only a small amount in Day 5 and cryopreserved semen (3–8%). Compared to no bicarbonate, incubation with bicarbonate increased MPLD, but the response was greatest (P < 0.05) in fresh sperm (52.3%) compared with Day 1 (36.6%), Day 5 (13.9%) and cryopreserved sperm (13.6%). Incubation with calcium ionophore A23187 increased AE in spermatozoa, but the response was less (P < 0.05) for fresh (34%) and cryopreserved (27%) semen than for Day 1 (45%) and Day 5 (57%) semen. In summary, hypothermic liquid storage and cryopreservation of boar spermatozoa did not advance capacitation or acrosome status in viable spermatozoa, but did alter their responses to induction of capacitation and the acrosome reaction.

New assays for detection and localization of endogenous lipid peroxidation products in living boar sperm after BTS dilution or after freeze–thawing

Reactive oxygen species have been implicated in sperm aberrations causing multiple pathologies including sub- and infertility. Freeze/thawing of sperm samples is routinely performed in the cattle breeding industries for semen storage prior to artificial insemination but unusual in porcine breeding industries as semen dilution and storage at 17 degrees C is sufficient for artificial insemination within 2-3 days. However, longer semen storage requires cryopreservation of boar semen. Freeze/thawing procedures induce sperm damage and induce reactive oxygen species in mammalian sperm and boar sperm seems to be more vulnerable for this than bull sperm. We developed a new method to detect reactive oxygen species induced damage at the level of the sperm plasma membrane in bull sperm. Lipid peroxidation in freshly stored and frozen/thawed sperm cells was assessed by mass spectrometric analysis of the main endogenous lipid classes, phosphatidylcholine and cholesterol and by fluorescence techniques using the lipid peroxidation reporter probe C11-BODIPY(581/591). Peroxidation as reported by the fluorescent probe, clearly corresponded with the presence of hydroxy- and hydroperoxyphosphatidylcholine in the sperm membranes, which are early stage products of lipid peroxidation. This allowed us, for the first time, to correlate endogenous lipid peroxidation with localization of this process in the living sperm cells. Cytoplasmatic droplets in incompletely matured sperm cells were intensely peroxidized. Furthermore, lipid peroxidation was particularly strong in the mid-piece and tail of frozen/thawed spermatozoa and significantly less intense in the sperm head. Induction of peroxidation in fresh sperm cells with the lipid soluble reactive oxygen species tert-butylhydroperoxide gave an even more pronounced effect, demonstrating antioxidant activity in the head of fresh sperm cells. Furthermore, we were able to show using the flow cytometer that spontaneous peroxidation was not a result of cell death, as only a pronounced subpopulation of living cells showed peroxidation after freeze-thawing. Although the method was established on bovine sperm, we discuss the importance of these assays for detecting lipid peroxidation in boar sperm cells.

Impact of storage prior to cryopreservation on plasma membrane function and fertility of boar sperm

Occasionally, boar semen must be shipped to another location for cryopreservation. We increased the initial holding time for the cooling of extended semen at 15 degrees C from 3 to 24 h to determine the effects on sperm characteristics and fertility. Thirty-one gilts and sows were inseminated once with subsequently cryopreserved and thawed semen. Increasing the holding time from 3 to 24 h had no significant effect on pregnancy rate 23 days after AI with frozen-thawed semen (64.5%) but decreased (P<0.05) embryo number from 15 to 9 and recovered embryos as fraction of CL from 73 to 47%. While the longer holding time at 15 degrees C did decrease potential litter size, the loss incurred was not too great to preclude the incorporation of a longer holding time into the cryopreservation protocol. An experiment was conducted to test the hypothesis that processing and freeze-thawing of boar semen would induce phospholipid scrambling in the plasma membrane similar to that evoked by incubation in bicarbonate-containing media. Merocyanine staining after incubation in the presence and absence of bicarbonate indicated that changes in plasma membrane phospholipid scrambling of processed and cryopreserved sperm differed from those in fresh semen undergoing bicarbonate-induced capacitation. The level of Annexin-V binding in boar spermatozoa increased from 1.6% in live spermatozoa in fresh semen to 18.7% in cryopreserved sperm. Apoptosis is unlikely to operate in mature spermatozoa. Apoptotic morphology in ejaculated spermatozoa is probably a result of incomplete deletion of apoptotic spermatocytes during spermatogenesis. Increased Annexin-V binding in thawed spermatozoa probably results from plasma membrane damage incurred during freezing and thawing.

Effects of extender composition, cooling rate and freezing on the fertilisation viability of spermatozoa of the Pacific oyster (Crassostrea gigas)

The aim of this research was to optimise protocols for freezing spermatozoa of the Pacific oyster. All the phases of the cryopreservation procedure (choice of cryoprotectant, cooling, freezing, and thawing) were studied in relation to the species of spermatozoa to restore on thawing the morphological and physiological characteristics of fresh semen. The choice of type and concentration of cryoprotectant in which semen is incubated before freezing is fundamental for a successful cryopreservation: the cryoprotectants (dimethylsulfoxide--Me(2)SO, ethylene glycol--EG, propylene glycol-PG, and glycerol in concentrations between 5 and 15%) were tested for their toxicity on the semen exposed up to 30 min at +26 degrees C (room temperature) by evaluating its ability to fertilise and the embryo development to the regular D larval stage. The best cryoprotectants, Me(2)SO, EG, and PG 5, 10, and 15% respectively, were used for the pre-cooling (adaptation/cooling) tests. Two different adaptation/cooling procedures were tested: (A) from +26 degrees C to 0-2 degrees C (2.6 degrees C/min) and (B) at +26 degrees C for 15 min. Lastly, using the cryoprotectants and the adaptation procedure (B) that had given the best results in the preceding stages of the experiment, four cooling rates were tested: 6, 11, 16, and 21 degrees C/min. It was seen that the semen that was incubated with EG 10%, adapted at +26 degrees C for 15 min, and then cooled at a rate of 6 degrees C/min showed a percentage of regular D larvae on thawing comparable to that of fresh semen (p > 0.05).

Step-wise dilution for removal of glycerol from fresh and cryopreserved equine spermatozoa

Osmotic stress is an important component of the damage to spermatozoa during cryopreservation. Osmotic injury, due to hyperosmolar freezing extenders, changes in relative solute concentration in the extra cellular medium during freezing and differences in the relative permeabilities of penetrating cryoprotectants, such as glycerol, and water occur when cryopreserved spermatozoa are diluted into isosmotic media or when spermatozoa are placed in the female reproductive tract. The purpose of the study reported here was to evaluate the effect of step-wise dilution for the removal of the permeating cryoprotectant, glycerol, from both fresh and cryopreserved equine spermatozoa on their motility and viability. There were significant (P < 0.05) effects of osmolality and dilution method on both total and progressive motility as well as viability in fresh spermatozoa. With the rapid, one-step dilution being significantly more detrimental to viability and motility, compared to the fixed molarity and fixed volume-dilutions. With frozen-thawed spermatozoa there were significant effects of stallion on total and progressive motility of spermatozoa after cryopreservation and thawing; however, treatment (type of dilution after thawing) did not affect post-thaw motility. These data indicate that rapid, single-step removal of glycerol from fresh equine spermatozoa results in a post-hyperosmotic stress that is characterized by a reduction in both motility and membrane integrity. This post-hyperosmotic stress can be reduced by a step-wise dilution for removal of glycerol, which improved the maintenance of both motility and membrane integrity. However a similar benefit for step-wise dilution for removal of glycerol was not observed in cryopreserved equine spermatozoa.

Liquid storage of Asian elephant (Elephas maximus) sperm at 4 °C

The Asian elephant (Elephas maximus) population in the wild has been in decline for several decades and breeding in captivity has not been self-sustaining. The use of artificial insemination (AI) can help overcome many of the difficulties associated with breeding elephants in captivity; however, the ability to store semen for extended periods of time is critical to the successful application of AI to elephants. The objective of the present study was to assess the effects of four different semen extenders and the presence of egg yolk on the viability and motility of Asian elephant semen stored at 4 degrees C. High quality ejaculates (n=4) were collected from two Asian elephant bulls by rectal massage. Aliquots of each ejaculate were extended in four different diluents (Beltsville thawing solution (BTS); Tris-citric acid (TCA)/fructose-based; Beltsville F5 (BF5); dextrose-supplemented phosphate-buffered saline (PBS)) with or without egg yolk then cooled and stored at 4 degrees C. The percentages of viable (viability) and motile (motility) sperm were evaluated at 8, 24 and 48 h following collection. The addition of egg yolk significantly reduced the percentage loss in viability from initial collection to 48 h compared to extenders without egg yolk (17.0 +/- 8.2 versus 32.6 +/- 8.9 decline in percent viable sperm in the population, respectively; P<0.05). Extender and egg yolk affected (P<0.005) total motility and percent progressively motile sperm at all evaluation times during incubation. TCA + egg yolk maintained higher (P<0.05) levels of progressive motility compared to other extenders supplemented with egg yolk. These results indicate that Asian elephant semen extended in TCA diluent supplemented with egg yolk can maintain at least 50% viability and motility when stored at 4 degrees C for 48 h.

Effects of fertilization promoting peptide, adenosine, and pentoxifylline on thawed human sperm

Fertilization promoting peptide (FPP) and adenosine were demonstrated to be potential modulators of sperm capacitation in mammals. Both FPP and adenosine, by modulating the adenylate cyclase (AC)/cAMP signaling pathway, elicit similar biphasic responses in mammalian sperm (i.e., stimulating capacitation and inhibiting spontaneous acrosome loss). Pentoxifylline, an artificial sperm stimulant, is clinically used to enhance motility of sperm from infertile men. By inhibiting phosphodiesterase, pentoxifylline increases the intracellular cAMP level of sperm, and thus contributes to capacitation, hyperactivation, and acrosome reaction in animal studies. The effects of FPP, adenosine, and pentoxifylline on thawed human sperm are stressed. Chlortetracycline (CTC) fluorescence assessment revealed that none of the 3 reagents improved fertilization ability of post-thawed sperm. Motility studies with computer-aided sperm analyzer (CASA) showed significantly smaller STR (straight-line velocity) and LIN (linearity) in the FPP-treated group at 4 h of incubation p<or=005, significantly larger VCL in the adenosine-treated group p<or=.05, and significantly larger VCL (curvilinear velocity) and smaller LIN in the pentoxifylline-treated group p<or=.05. Significant decreases in percentage motility were also noted in both FPP and adenosine-treated groups p<or=05. It would appear that FPP potentiates fertilizing ability and prevents spontaneous acrosome loss, via regulating membrane-bound Na(+)-K(+) ATPase, and/or Ca(2+) ATPase, by keeping the sperm intracellular Ca(2+) concentration within the physiological range optimal for fertilization. adenosinefertilizationFPPpentoxifyllinespermthawing

Effects of extender composition, cooling rate, and freezing on the motility of sea bass (Dicentrarchus labrax, L.) spermatozoa after thawing

A successful cryopreservation procedure for sperm must guarantee recovery of the morphological and functional characteristics of the cells following thawing so that preserved semen can to be used comparably with non-preserved semen. The aim of this work was to identify a species-specific freezing protocol for sea bass (Dicentrarchus labrax) spermatozoa by optimising all the stages in the cryopreservation procedure. In the first stage of the experiments, the cryoprotectants and the relative concentrations that had the least toxic effect on motility at room temperature were selected. The capacity of the selected cryoprotectant substances was then assessed in freezing tests as follows: dimethyl sulfoxide (Me(2)SO) 5% and 7%, ethylene glycol (EG) 7% and 10%, propylene glycol (PG) 7% and 10%. The cryoprotectant that gave the best results in this second stage of the experiments was EG 10%, and this was then used for the optimisation of the different stages in the freezing procedure: two different times of adaptation to the cryoprotectant were tested (15min and 6h), as well as the effects of adding an energy substrate (1.25mM sodium pyruvate) to assess its possible use as an energy source. Lastly, using the extender (diluent+Na-pyruvate+EG10%) and the adaptation procedure (6h at 0-2 degrees C) that had given the best results in the preceding stages of the experiments, four cooling rates were tested: 10, 12, 15, 24 degrees C/min. It was shown that the semen that was diluted immediately after collection in extender that contained the cryoprotectant (EG 10%), was equilibrated for 6h at 0-2 degrees C and then cooled at a rate of 15 degrees C/min, showed motility on thawing comparable to that of fresh semen (P=0.045).

Liquid storage of miniature boar semen

The effects of liquid storage at 15 degrees C on the fertilizing ability of miniature pig semen were investigated. Characterization of ejaculated semen from 3 miniature boars was carried out. Semen volume and pH were similar among these boars. In one of the boars, sperm motility was slightly low, and sperm concentration and total number of sperm were significantly lower than in the others (P < 0.01). Seminal plasma of the semen was substituted with various extenders (Kiev, Androhep, BTS and Modena) by centrifugation and semen was stored for 7 days at 15 degrees C. Sperm motility was estimated daily at 37 degrees C. For complete substitution of seminal plasma, Modena was significantly more efficient than the other extenders (P < 0.001) in retaining sperm motility. Semen from each of the 3 miniature boars that had been stored for 5 to 7 days at 15 degrees C in Modena was used for artificial insemination of 15 miniature sows. The farrowing rates were 100, 100 and 60%, and litter sizes were 6.4 +/- 1.5, 5.8 +/- 0.8 and 5.0 +/- 1.0 for each boar semen, respectively. The boar that sired the smallest farrowing rate was the same one that showed lower seminal quality with respect to sperm motility, sperm concentration and total number of sperm. These results suggest that miniature boar semen can be stored for at least 5 days at 15 degrees C by the substitution of seminal plasma with Modena extender.

Differences among dogs in response of their spermatozoa to cryopreservation using various cooling and warming rates

Spermatozoa collected from the caudae epididymides of 16 dogs of various breeds were suspended in an isotonic salt solution (DIMI medium) containing 0.6 M glycerol, frozen in liquid nitrogen, and their "survival" was measured after thawing. In the first experimental series, duplicate samples of spermatozoa from each of 11 dogs were cooled at rates of 0.5, 3, 11, 58, or 209 degrees C/min, stored in liquid nitrogen, and the frozen samples warmed at approximately 830 or at 33 degrees C/min. Sperm "survival" was judged by microscopic assessments of motility and of membrane integrity, the latter as assayed with Fertilight, a double fluorescent stain. Motility of frozen spermatozoa that were thawed rapidly, averaged for 11 dogs, was low at low rates, increased to a maximum at 11 degrees C/min, and then decreased significantly at higher rates (P<0.01). This inverted V-shaped curve was also observed with slow thawing, although the apparent optimum cooling rate ranged from 3 to 11 degrees C/min. The integrity of sperm plasma membranes showed a similar dependence on cooling rate, although the percentages of spermatozoa with intact plasma membranes were higher than the percentages of motile spermatozoa. Motility of spermatozoa, as a function of cooling rate, varied considerably from male to male (P<0.01), whereas membrane integrity was much more consistent among the 11 dogs. In the second experimental series with spermatozoa from 5 dogs, motility of spermatozoa frozen at 0.5 degrees C/min and warmed at 3.6, 33, 140, or 830 degrees C/min also exhibited an inverted V-shaped survival curve, in this case as a function of warming rate. In summary, high survival of frozen-thawed canine epididymal spermatozoa depended on both cooling and warming rates, but spermatozoa from each dog exhibited their own sensitivity to cooling and warming rates.

Cryopreservation in different concentrations of glycerol alters boar sperm and their membranes

To test the hypothesis that glycerol would concomitantly affect sperm membrane structure and the function of the intact cells, boar semen (4 ejaculates from 4 boars) was cryopreserved in an egg yolk extender with 0%, 2%, 4%, or 8% glycerol in 0.5-mL straws using previously derived optimal cooling and thawing rates. Increasing glycerol concentrations increased spermatozoal progressive motility immediately after thawing and after 2 hours at 43 degrees C, but decreased the percentage of sperm with normal acrosomal morphology. The mathematical products of the motility and acrosomal integrity scores (MOT x NAR index) were low in 0% and 8% glycerol, and significantly higher in 2% and 4% glycerol. The fluidity of sperm-head plasma membranes, a measure of molecular interaction, was assessed with the lipid probes trans-parinaric acid and cisparinaric acid (tPNA, cPNA), during a 2.5-hour incubation with or without 1 mM Ca2+. Membrane fluidity detected by each probe differed significantly, indicating the presence of at least 2 domains whose constituent molecules had unique dynamics. Behavior of each domain was radically altered by cryopreservation. Increasing glycerol concentration caused a variably faster loss of fluidity in the cPNA domain, and had highly variable effects on fluidity change over time in the tPNA domain. Normal acrosomal ridge (NAR) and the MOT x NAR index correlated significantly with the fluidity of the more mobile cPNA domain (+/- 1 mM Ca2+), supporting the hypothesis of an interrelationship of glycerol concentration during cryopreservation with sperm membrane structure and cell function. The MOT x NAR index may be a useful guide in choosing optimal cryoprotectant concentrations.

Cryopreservation-induced acrosomal vesiculation in live spermatozoa from cynomolgus monkeys (Macaca fascicularis)

BACKGROUND

Cryopreserved spermatozoa are known to undergo accelerated capacitation and require a shorter incubation time for fertilization. However, details of their acrosomal membranes following cryopreservation remain unclear.

METHODS

Percoll density gradient centrifugation was used to remove dead spermatozoa; thus >90% live spermatozoa were recovered after cryopreservation, and acrosomal status was compared among non-incubated and incubated fresh and cryopreserved spermatozoa.

RESULTS

Transmission election microscopy (TEM) using microwave methods and fluorescein isothiocyanate-conjugated Pisum sativum agglutinin (FITC-PSA) staining revealed that 21.1 and 61.6% respectively of non-incubated, cryopreserved spermatozoa were intact, whereas 97.6% (TEM) or 91.9% (FITC-PSA) of non-incubated fresh spermatozoa were intact. TEM revealed that 28.8% of the cryopreserved spermatozoa were swollen, and probably included among those counted as intact by FITC-PSA staining. The non-incubated cryopreserved spermatozoa had fused plasma and outer acrosomal membranes, and 36.4% of them had vesiculation when observed by TEM. FITC-PSA staining indicated that 22% of the live spermatozoa were acrosome reacted.

CONCLUSIONS

Acceleration of the acrosome reaction was evident by both TEM and FITC-PSA. Incubation of cryopreserved spermatozoa for 2 h accelerated vesiculation to a state similar to that of fresh spermatozoa that had been incubated for 8 h. These results reveal that in cryopreserved spermatozoa, the process of acrosome reaction begins before incubation.

Bicarbonate stimulated phospholipid scrambling induces cholesterol redistribution and enables cholesterol depletion in the sperm plasma membrane

Mammalian sperm cells are activated prior to fertilization by high bicarbonate levels, which facilitate lipoprotein-mediated cholesterol efflux. The role of bicarbonate and cholesterol acceptors on the cholesterol organization in the sperm plasma membrane was tested. Bicarbonate induced an albumin-independent change in lipid architecture that was detectable by an increase in merocyanine staining (due to protein kinase A-mediated phospholipid scrambling). The response was limited to a subpopulation of viable sperm cells that were sorted from the non-responding subpopulation by flow cytometry. The responding cells had reduced cholesterol levels (30% reduction) compared with non-responding cells. The subpopulation differences were caused by variable efficiencies in epididymal maturation as judged by cell morphology. Membrane cholesterol organization was observed with filipin, which labeled the entire sperm surface of non-stimulated and non-responding cells, but labeled only the apical surface area of bicarbonate-responding cells. Addition of albumin caused cholesterol efflux, but only in bicarbonate-responding cells that exhibited virtually no filipin labeling in the sperm head area. Albumin had no effect on other lipid components, and no affinity for cholesterol in the absence of bicarbonate. Therefore, bicarbonate induces first a lateral redistribution in the low cholesterol containing spermatozoa, which in turn facilitates cholesterol extraction by albumin. A model is proposed in which phospholipid scrambling induces the formation of an apical membrane raft in the sperm head surface that enables albumin mediated efflux of cholesterol.

Seasonal differences in ram seminal plasma revealed by partition in an aqueous two-phase system

Seminal plasma plays an important role in maturation of spermatozoa through hormonal, enzymatic and surface-modifying events. We have previously shown that adsorption of seminal plasma proteins (SPPs) to the sperm cell surface partially restores the functional characteristics of damaged spermatozoa, reproducing those of live cells. In the present report, we investigate the hypothesis that seasonal differences in seminal plasma could affect its ability to recover membrane integrity of cold-shocked sperm. The effect of seminal plasma proteins, obtained in breeding (bsSPPs) and non-breeding (nbsSPPs) season, on cold-shocked ram spermatozoa previously freed from seminal plasma, was analysed by centrifugal counter-current distribution (CCCD) in an aqueous two-phase system as well as membrane integrity determination by fluorescence markers. Cold-shock treatment greatly lowered cell viability in both breeding and non-breeding season spermatozoa. The cold-shocked sperm viability obtained was approximately 20%. The loss of heterogeneity and the decrease in viability revealed by CCCD analysis was reversed by the addition of increasing amounts of bsSPP, which induced restoration of the surface characteristics of viable-like spermatozoa, as well as an increase in the number of recovered viable sperm. However, this restoring effect was much lower when nbsSPPs were added, even in a sixfold higher concentration than used with bsSPPs. Incubation of cold-shocked cells with both kinds of proteins performed in both seasonal periods, showed that the recovering effect was related to the season when the plasma sample was obtained rather than to the semen season. The addition of bsSPPs to cold-shocked sperm accounted for a nearly 50% reversion for both studied breeding seasons. However, the reversion percentages obtained with nbsSPPs were significantly lower (P<0.05) than those found with bsSPPs in both studied seasonal periods. This different reversion capacity of bsSPPs and nbsSPPs was related to a different protein composition, as revealed by comparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. The bands of 20, 21, 24, 36 and 67 kDa of the bsSP sample profile decreased in winter-spring SP, and were even less intensely stained in summer SP. Densitometric analysis of the stained gel patterns allows automatic comparison among the separated bands, and revealed an important decrease in the content of several bands. The 21.5 kDa band showed the highest decrease, lowering to 14% in June-August plasma with respect to the value obtained in September-December plasma.

Semen plasma proteins prevent cold-shock membrane damage to ram spermatozoa

Although the effect of semen plasma on the function of spermatozoa has been widely studied, results are contradictory. We showed that semen plasma proteins are adsorbed onto the cold-shocked ram sperm surface, and that this adsorption is able to reverse the membrane alterations induced by cold-shock. In the present study we evaluate whether the addition of semen plasma proteins before the cold-shock would prevent membrane damage and maintain ram sperm viability. Ram spermatozoa freed from semen plasma by a dextran/swim-up procedure were strongly affected by the cold-shock treatment, lowering cell viability (membrane integrity by fluorescence markers) from 72.2+/-3.4% to 24.6+/-2.1%. Adding semen plasma proteins (> 3 kDa) to the medium before the cold treatment had an immediate beneficial effect on sperm survival in all samples. This effect was concentration-dependent, since the percentage of membrane-intact spermatozoa increased significantly with increased protein concentration in the incubation medium. The highest concentration of proteins (2.1 mg) continued to protect the membranes after 1 h of incubation at 20 degrees C while lower concentrations (0.7 and 1.4 mg) showed a slight decline. Inclusion of linoleic-oleic acids had a beneficial effect on preserving sperm viability when 25, 37 or 75 microM linoleic-oleic acids were added. There was a positive interaction between fatty acids and semen plasma proteins. Thus, the addition of 25 microM oleic-linoleic acid in the presence of 2.1 mg semen plasma proteins accounted for an increase in viability up to 50.7% significance (P < 0.001) relative to the control sample (25%). Likewise, semen plasma proteins significantly promoted the ability of Vitamin E (alpha-tocopherol phosphate) to improve sperm survival. A 26% viability value obtained after cold-shock in the control sample significantly increased (P < 0.001) up to 57% in the sample with 1.6 mM Vitamin E phosphate and 2.1 mg semen plasma proteins (0 h). This study demonstrates that impaired function of cold-shocked ram spermatozoa freed from semen plasma could be prevented by addition of semen plasma proteins, resulting in higher maintained viability values. Inclusion of either linoleic-oleic acids or vitamin E together with semen plasma proteins would increase the improvement in ram spermatozoa survival.

A short hypoosmotic swelling test for the prediction of boar sperm fertility

This study was designed to explore the relationship between the ejaculate response to a hypoosmotic swelling test (HOST) and in vivo fertility in a group of 38 boars The hypoosmotic test used was a modification of the HOST that involves a shorter incubation time (5 vs 120 min) and lower osmotic pressure (75 vs 150 mOsm/kg). Ejaculates containing less than 20% abnormal spermatozoa were selected and checked for percentage of motility, percentage of normal acrosomes, percentage of short ORT and percentage of cells showing positive short HOST (sHOST) results Two hundred eightyeight sows were inseminated to obtain in vivo fertility and prolificacy data. No differences were shown between technicians in the sHOST results obtained. Significant differences were recorded between boars in sHOST results (p < 0.002). Only the sHOST result presented a significant correlation with in vivo fertility (r = 0.43, p < 0.01). Short HOST data significantly improved fertility prediction of routine semen analysis tests. Unlike motility and acrosomal status, sHOST values showed a significant decrease when fresh ejaculates (37 degrees C) were stored for 24 h at 15 degrees C, indicating possible damage due to cold shock.

Is cryopreservation a homogeneous process? Ultrastructure and motility of untreated, prefreezing, and postthawed spermatozoa of Diplodus puntazzo (Cetti)

This study subdivides the cryopreservation procedure for Diplodus puntazzo spermatozoa into three key phases, fresh, prefreezing (samples equilibrated in cryosolutions), and postthawed stages, and examines the ultrastructural anomalies and motility profiles of spermatozoa in each stage, with different cryodiluents. Two simple cryosolutions were evaluated: 0.17 M sodium chloride containing a final concentration of 15% dimethyl sulfoxide (Me(2)SO) (cryosolution A) and 0.1 M sodium citrate containing a final concentration of 10% Me(2)SO (cryosolution B). Ultrastructural anomalies of the plasmatic and nuclear membranes of the sperm head were common and the severity of the cryoinjury differed significantly between the pre- and the postfreezing phases and between the two cryosolutions. In spermatozoa diluted with cryosolution A, during the prefreezing phase, the plasmalemma of 61% of the cells was absent or damaged compared with 24% in the fresh sample (P < 0.001). In spermatozoa diluted with cryosolution B, there was a pronounced increase in the number of cells lacking the head plasmatic membrane from the prefreezing to the postthawed stages (from 32 to 52%, P < 0.01). In both cryosolutions, damages to nuclear membrane were significantly higher after freezing (cryosolution A: 8 to 23%, P < 0.01; cryosolution B: 5 to 38%, P < 0.001). With cryosolution A, the after-activation motility profile confirmed a consistent drop from fresh at the prefreezing stage, whereas freezing and thawing did not affect the motility much further and 50% of the cells were immotile by 60-90 s after activation. With cryosolution B, only the postthawing stage showed a sharp drop of motility profile. This study suggests that the different phases of the cryoprocess should be investigated to better understand the process of sperm damage.

Effect of cooling rate and partial removal of yolk on the chilling injury in zebrafish (Danio rerio) embryos

High chilling sensitivity is one of the main obstacles to successful cryopreservation of zebrafish embryos. So far the nature of the chilling injury in fish embryos has not been clear. The aim of this study is to investigate the effect of cooling rate and partial removal of yolk on chilling injury in zebrafish embryos. Zebrafish embryos at 64-cell, 50%-epiboly, 6-somite and prim-6 stages were cooled to either 0 degrees C or -5 degrees C at three different cooling rates: slow (0.3 degrees C/min or 1 degree C/min), moderate (30 degrees C/min), and rapid (approximately 300 degrees C/min). After chilling, embryos were warmed in a 26 degrees C water bath, followed by 3-day culturing in EM at 26 +/- 1 degrees C for survival assessment. When embryos were cooled to 0 degrees C for up to 30 min, 64-cell embryos had higher survival after rapid cooling than when they were cooled at a slower rate. When 64-cell embryos were held at -5 degrees C for 1 min, their survival decreased greatly after both slow and rapid cooling. The effect of cooling rate on the survival of 50%-epiboly and 6-somite embryos was not significant after 1 h exposure at 0 degrees C and 1 min exposure at -5 degrees C. However, rapid cooling resulted in significantly lower embryo survival than a cooling rate of 30 degrees C/min or 1 degree C/min after 1 h exposure to 0 degrees C for prim-6 stage or 1 h exposure to -5 degrees C for all stages. Chilling injury in 64-cell embryos appears to be a consequence of exposure time at low temperatures rather than a consequence of rapid cooling. Results also indicate that chilling injury in later stage embryos (50%-epiboly, 6-somite and prim-6) is a consequence of the combination of rapid cooling and exposure time at low temperatures. Dechorionated prim-6 embryos were punctured and about half of yolk was removed. After 24 h culture at 26 +/- 1 degrees C after removal of yolk, the yolk-reduced embryos showed higher embryo survival than did control embryos after rapid cooling to -5 degrees C for 10 to 60 min. Results suggest that cold shock injury after rapid cooling can be mitigated after partial removal of yolk at the prim-6 stage. These findings help us to understand the nature of chilling sensitivity of fish embryos and to develop protocols for their cryopreservation.

Dynamics of the mammalian sperm plasma membrane in the process of fertilization

Sexual reproduction requires the fusion of sperm cell and oocyte during fertilization to produce the diploid zygote. In mammals complex changes in the plasma membrane of the sperm cell are involved in this process. Sperm cells have unusual membranes compared to those of somatic cells. After leaving the testes, sperm cells cease plasma membrane lipid and protein synthesis, and vesicle mediated transport. Biophysical studies reveal that lipids and proteins are organized into lateral regions of the sperm head surface. A delicate reorientation and modification of plasma membrane molecules take place in the female tract when sperm cells are activated by so-called capacitation factors. These surface changes enable the sperm cell to bind to the extra cellular matrix of the egg (zona pellucida, ZP). The ZP primes the sperm cell to initiate the acrosome reaction, which is an exocytotic process that makes available the enzymatic machinery required for sperm penetration through the ZP. After complete penetration the sperm cell meets the plasma membrane of the egg cell (oolemma). A specific set of molecules is involved in a disintegrin-integrin type of anchoring of the two gametes which is completed by fusion of the two gamete plasma membranes. The fertilized egg is activated and zygote formation preludes the development of a new living organism. In this review we focus on the involvement of processes that occur at the sperm plasma membrane in the sequence of events that lead to successful fertilization. For this purpose, dynamics in adhesive and fusion properties, molecular composition and architecture of the sperm plasma membrane, as well as membrane derived signalling are reviewed.

Seminal plasma proteins revert the cold-shock damage on ram sperm membrane

Ejaculated ram spermatozoa, freed from seminal plasma by a dextran/swim-up procedure and exposed to cold shock, were incubated with ram seminal plasma proteins and analyzed by fluorescence markers and scanning electron microscopy. Seminal plasma proteins bound to the sperm plasma membrane modified the functional characteristics of damaged spermatozoa, reproducing those of live cells. Scanning electron microscopy showed that the dramatic structural damage induced by cooling reverted after incubation with seminal plasma proteins. Assessment of membrane integrity by fluorescence markers also indicated a restoration of intact-membrane cells. This protein adsorption is a concentration-dependent process that induces cell surface restoration in relation to the amount of protein in the incubation medium. Fractionation of ram seminal plasma proteins by exclusion chromatography provided three fractions able to reverse the cold shock effect. Scanning electron microscopy also confirmed the high activity of one fraction, because approximately 50% of cold-shocked sperm plasma membrane surface was restored to its original appearance after incubation. Differences in composition between the three separated fractions mainly resulted from one major band of approximately 20 kDa, which must be responsible for recovering the sperm membrane permeability characteristic of a live cell.

Basic aspects of frozen storage of semen

Basic concepts of cryopreservation and the causes of cryoinjury are reviewed. The possible roles of cryoprotectants and additives are considered in the context of their putative interactions with the sperm plasma membrane. Modern approaches to the laboratory assessment of spermatozoa after freeze-thawing are also briefly discussed.

Effect of differential addition of glycerol and pyruvate to extender on cryopreservation of Mediterranean buffalo (B.bubalis) spermatozoa

The composition of the extender in which semen is diluted before freezing plays a major role in successful cryopreservation of spermatozoa. Substances of high osmolarity, like glycerol, protect sperm cells during the freezing process and energy-rich compounds, like pyruvate provide extra energy during capacitation and fertilization. Since cryopreservation procedures for Buffalo spermatozoa have not been adequately defined, the aim of the study was to improve the survival rate of buffalo (Bubalus bubalis) spermatozoa after cryopreservation by optimizing the timing for adding glycerol and by enriching the cryoprotectant extender with an energy source substrate. Semen was collected with an artificial vagina from 5 bulls and the ejaculates were immediately evaluated for motility, forward progressive motility and for viability, pooled and held at room temperature (28 degrees C) for 1 h. Then aliquots of pooled semen were subjected to dilution and equilibration in triplicate as follows: Experiment 1. Glycerol (3%) in a commercial extender was added to the semen at 28 degrees C and cooled to 5 degrees C for 1 h; then extender with 11% glycerol was added before further equilibration (initial glycerol addition; IGA) and the samples held at 5 degrees C for 1, 3 or 5 additional hours (IGA 1, n = 24; IGA 3, n = 24; IGA 5, n = 24) before freezing. Experiment 2. Glycerol (3%) was added and the mixture brought to 5 degrees C as described above. Then extender with 11% glycerol was added (late glycerol addition; LGA) and after equilibration for 1, 3 and 5 h (LGA 1, n= 24; LGA 3, n = 24; LGA 5, n = 24) the samples were frozen. In Experiments 3 and 4 Na pyruvate (1.25 mM) was added to the extender as described for IGA and LGA above (IPA and LPA samples). The effect of addition time (initial vs late) of glycerol and pyruvate was evaluated by measuring sperm motility, progressively forward motility and viability. After freezing-thawing the percentage of motile spermatozoa was significantly higher (0.001<P<0.01) after a late addition of glycerol and pyruvate (LGA 5 and LPA 5). The optimizing of the timing of the glycerol addition and the presence in the extender of an energy source rendered a higher efficiency in thawed spermatozoa.

The causes of reduced fertility with cryopreserved semen

Cryopreserved mammalian semen is generally acknowledged to have an impaired fertility by comparison with fresh semen. The reduction arises from both a lower viability post-thaw and sublethal dysfunction in a proportion of the surviving subpopulation. The reasons for the loss of fertility are various. In this paper, factors affecting the proportion of survivors (e.g., cold shock susceptibility, cooling rate, diluent composition and osmotic stress) and factors influencing functional status of survivors (e.g., membrane stability, oxidative damage, membrane receptor integrity, nuclear structure) are briefly reviewed. The possible effects of cryopreservation on the role of spermatozoa in the early stages of embryogenesis are considered. In the light of this review, indications for new approaches for improving the performance of cryopreserved semen are offered.

Detection of calcium ionophore induced membrane changes in dog sperm as a simple method to predict the cryopreservability of dog semen

The sensitivity of dog sperm cells for extracellular Ca(2+)/Ca(2+)-ionophore challenge was compared to the detrimental effects of an optimized freeze/thawing protocol. Three sperm-rich fractions of ejaculates from 9 dogs were obtained, and one aliquot of each ejaculate was washed in a modified Tyrode's medium (HBT containing 0.1 mM Ca(2+)), without (control sample) and with 2.5 microM Ca(2+)-ionophore (induced sample) and incubated for 60 min at 38 degrees C in humidified atmosphere. Another aliquot from the same semen fractions was diluted, washed in a Tris buffer, and packed into 0.5-ml straws with a Tris buffer containing 7.5 vol % glycerol. The samples were stored for 1 week in liquid nitrogen after a computer-driven three-step freeze protocol and subsequently thawed for 50 sec in a 37 degrees C water bath and reconstituted into HBT. The acrosome integrity was determined using fluorescein-conjugated peanut agglutinin (PNA-FITC) as an acrosomal marker, while the vitality of the sperm cells was simultaneously assessed with the membrane impermeable DNA supravital stain ethidium homodimer 1 (EthD-1) using fluorescence microscopy and flow cytometry. The motility of frozen/thawed sperm samples was evaluated by microscopic as well as computerized motility analyses. Remarkably, the percentage sperm cells that underwent acrosome reactions induced by Ca(2+)-ionophore correlated very positively (r = 0.93) with the amount of acrosome damage observed in cryopreserved sperm samples. Furthermore, the degree of cellular damage induced by Ca(2+)-ionophore treatment correlated very negatively (r = -0.99) with the relative amount of sperm cells that remained motile after cryopreservation. Such clear correlations between Ca(2+)-ionophore induced acrosome reaction and motility parameters for frozen/thawed dog sperm cells were not found, suggesting that the generation of acrosome leakage and sperm immotility are two independent detrimental processes occurring during cryopreservation. From these results it can be concluded that Ca(2+)-ionophore treatment followed by simultaneous determination PNA-FITC and EthD-1 staining can be used to predict the cryopreservability of ejaculates from individual dogs used as donors.

Effect of sperm diluents on the acrosome reaction in canine sperm

In this study we investigated the influence of sperm diluting media and temperature on the incidence of the acrosome reaction in dog sperm. Ejaculates were collected from 5 dogs, diluted with six different media and then incubated at 37 degrees C and 20 degrees C. Fluorescein isothiocynate conjugated peanut agglutinin (FITC-PNA) and ethidium homodimer as a vital stain were used in combination to determine the acrosomal status of viable spermatozoa, the technique was validated using electron microscopy. The outer acrosomal membrane of dog spermatozoa was shown to be the specific binding site for FITC-PNA. After 6 h of incubation, ejaculates diluted in media with a high Ca2+ concentration showed a significantly higher percentage (means +/- SD) of acrosome reacted spermatozoa [64 +/- 7 and 58 +/- 9 in sperm capacitation medium with (SP-TALP-1) and without BSA (SP-TALP-2), respectively] than those diluted in media with a low Ca2+ concentration [36 +/- 5, 39 +/- 4, 18 +/- 2 and 20 +/- 4 in Canine Capacitation Medium (CCM), Egg Yolk Tris dog semen extender (EXT-1), Modified Egg Yolk Tris extender (EXT-2) and Modified CCM (MCCM), respectively]. The increase in the percentage of acrosome reaction (AR) was slower at 20 degrees C than at 37 degrees C. In addition, the percentage of viable acrosome reacted spermatozoa increased significantly from 19 +/- 5 and 22 +/- 3 in non-bound sperm to 27 +/- 4 and 30 +/- 6 in zona pellucida bound sperm (diluted in EXT-2 and MCCM, respectively). We conclude that the composition of the spermatozoa diluent has a marked effect on the incidence of the acrosome reaction. Therefore, both the media used to dilute dog sperm and the temperature at which the spermatozoa are handled are important factors to consider when processing spermatozoa for artificial insemination, IVF procedures or preservation.

Dynamics in the membrane organization of the mammalian sperm cell and functionality in fertilization

The capacitation process of sperm cells involves complex changes in the composition and orientation of molecules at the surface of the sperm cell. Here we focus on the lipid architecture in the sperm plasma membrane and demonstrate that the sperm plasma membrane is not static but is an extremely dynamic structure. Advanced fluoroscopic techniques enabled continuous monitoring of lipid organization in living cells and extremely rapid lipid movements were observed. The orientation of lipids in the sperm plasma membrane changed under capacitative treatments, was found to be sensitive for temperature and also changed upon binding of sperm cells to the zona pellucida. The changes in membrane properties coincided with an activation of protein kinases resulting in tyrosine phosphorylation of specific plasma membrane proteins. The detected membrane changes relate to intrinsic membrane properties such as fluidity, permeability, adhesiveness and fusibility. We think that these results may provide a physiological basis for new assays, able to discriminate between functional and non-physiological sperm cells.

Effect of cooling rates on post-thaw sperm motility, membrane integrity, capacitation status and fertility of dairy bull semen used for artificial insemination in Sweden

We studied the effects of 2 different cooling rates during equilibration of semen from room temperature to 4 degrees C, at 4.2 degrees C/min (control split sample) or at 0.1 degree C/min (treatment split sample) on in vitro sperm viability post thawing and fertility after AI. Forty batches of split-frozen semen from 14 dairy bulls (Swedish Red and White breed) aged 14 to 16 m.o. or 66 to 79 m.o. were evaluated post-thawing for sperm motility (visual and computer-assisted sperm analysis [CASA], membrane integrity (fluorescent microscopy and flow cytometry post-loading with the combined fluorophores Calcein AM/EthD-1 and SYBR-14/PI); acrosomal status (with Pisum sativum agglutinin [PSA] staining); and capacitation status (CTC-assay). Fertility values (56-d nonreturn rate) of the slow cooling batches (treatment) were 0.4% units higher than for faster cooled (control) batches, but the difference was not statistically significant. Fertility values for the older bulls were 1.6% units higher than for the group of younger sires. No statistically significant correlations were found between semen viability parameters assessed in vitro and 56-d nonreturn rate. Visually assessed sperm motility, membrane integrity, capacitation and acrosomal status post-thawing did not differ significantly between cooling procedures, however the percentage of motile spermatozoa and the kinetic characteristics of spermatozoa--average path velocity (VAP), straight path velocity (VSL) and curvilinear velocity (VCL)--assessed by CASA differed significantly between cooling procedures. The results indicate that most of the in vitro sperm viability parameters post-thawing and the fertility results for bulls after AI did not differ significantly between the 2 semen cooling procedures tested.

Substantial decrease of heat-shock protein 90 precedes the decline of sperm motility during cooling of boar spermatozoa

The decline in boar semen quality after cryopreservation may be attributed to changes in intracellular proteins. Thus, the aim of the present study was to evaluate the change of protein profiles in boar spermatozoa during the process of cooling and after cryopreservation. A total of 9 sexually mature boars (mean age = 25.5+/-12.3 mo) was used. Samples for protein analysis were collected before chilling, after cooling to 15 degrees C, after cooling to 5 degrees C, following thawing after freezing to -100 degrees C, and following thawing after 1 wk of cryopreservation at -196 degrees C. Semen characteristics evaluated included progressive motility and the percentage of morphologically normal spermatozoa. Total proteins from 5x10(6) spermatozoa were separated and analyzed by SDS-PAGE. The results revealed that there was a substantial decrease of a 90 kDa protein in the frozen-thawed spermatozoa. Western blot analysis demonstrated that this protein was 90 kDa heat-shock protein (HSP90). Time course study showed that the decrease of HSP90 in spermatozoa initially occurred in the first hour during cooling to 5 degrees C. When compared with the fresh spermatozoa before chilling, there was a 64% decrease of HSP90 in spermatozoa after cooling to 5 degrees C. However, the motility and percentage of normal spermatozoa did not significantly decrease during this period of treatment. Both declined substantially as the semen was thawed after freezing from -100 degrees C. The results indicated that the decrease of HSP90 precedes the decline of semen characteristics. The length of time between a decrease of HSP90 and the decline in sperm motility was estimated to be 2 to 3 h. Taken together, the above results suggested that a substantial decrease of HSP90 might be associated with a decline in sperm motility during cooling of boar spermatozoa.

Effect of cryopreservation on the fine structure of spermatozoa of rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta F. fario)

Freeze-fracture electron microscopy has revealed that changes are induced in the organization of the plasma membranes of spermatozoa of rainbow and brown trout when they are cryopreserved. Electron-micrographic images of spermatozoa that had not been exposed to cryopreservation showed a protoplasmic surface with particles homogeneously distributed. The concentration of the particles was low. In the median portion of the tail the authors observed longitudinal strips, consisting of particles located along the bands. In the neck of the spermatozoon the particles were aggregated in a chaotic manner. Electron micrographs of trout spermatozoa that had been cryopreserved showed particles grouped in rounded clusters on the protoplasmic surfaces of both the head and the tail. In some spermatozoa, folding of the protoplasmic membrane, with the particle-free sites, were found. The dimensions of the clusters and the spaces that were free of particles suggest that, after thawing, the spermatozoa of the brown trout is likely to experience greater difficulty in restoring their physiological integrity than those of the rainbow trout. These results suggest that the membrane proteins of spermatozoa of the species of trout that were studied possess high motility and diffuse, with the formation of clusters, in very short periods of time (about 30 s). The changes in membrane structure of the trout spermatozoa following cryopreservation appear to indicate high lability. Copyright 1998 Academic Press.

Characterization of lower temperature storage limitations of fresh-extended porcine semen

Irreversible damage caused by cold shock has been assumed to occur when boar semen is exposed to temperatures below 15 degrees C. Identification of the lower critical temperature at which extended boar semen undergoes cold shock, however, has yet to be defined. The aims of this study were to 1) identify the cold-shock critical temperature and time on extended boar semen as assessed by sperm motility and morphology, and 2) determine the effects on fertility of using extended porcine semen exposed to this critical temperature and time. For Objective 1, ejaculates from 18 boars were collected, analyzed and extended in Androhep to 50 x 10(6) sperm/mL. Doses (4 x 10(9) sperm) from each ejaculate were exposed to 5 storage temperatures (8, 10, 12, 14 and 17 degrees C). Sperm motility and morphology (including acrosomes) were assessed following collection and at 12-h intervals for 48-h. Decreases in sperm motility occurred within the first 12-h at all temperatures. Sample motility dropped below 70% within 12-h in the 8 degrees C group and by 48-h in the 10 degrees C group. Sample motility was > 75% in the 12, 14 and 17 degrees C (control) groups throughout the trial. The percentage of morphologically abnormal sperm cells, including acrosomes, did not change within or between treatment groups over the 48-h storage period. In Objective 2, boar ejaculates (n = 9) were handled as in the first objective and were equally divided into treated (12 degrees C for < or = 60-h) and control (17 degrees C for < or = 60-h) groups. Using a timed, double insemination technique, 135 sows were bred by AI using either 12 degrees C (n = 74) or 17 degrees C (n = 61) extended, stored semen. No differences were observed in the farrowing rate (93 vs 95%), total offspring born (11.58 vs 11.61) or number live born (10.68 vs 10.63) between 12 and 17 degrees C groups, respectively. The results demonstrate that acceptable fertility can be obtained with Androhep extended boar semen exposed to temperatures as low as 12 degrees C for up to 60-h, and that cold shock appears to occur in vitro when extended boar semen is exposed to storage temperatures below 12 degrees C.

Loss of plasma membrane proteins of bull spermatozoa through the freezing-thawing process

The widespread application of A. I. and realization of its full potential depends largely on the use of frozen semen. However, fertility resulting from A. I. is poorer than that from fresh semen in most species. The objective of this study was to compare the protein composition of fresh and frozen-thawed bull sperm plasma membrane surface. The effect of Tween 20 on protein removal from fresh and frozen sperm plasma membrane surface was studied and compared. The effect of incubation with different detergent concentrations on sperm motility and viability was examined. Approximately 2 x 10(8) frozen-thawed bull spermatozoa washed through a discontinuous Percoll gradient were incubated for 15 min at 20 degrees C with 0.01, 0.03 and 0.05% Tween 20. Sperm motility was completely eliminated at all 3 assayed detergent concentrations, while the initial sperm viability of 52% was decreased to 26, 10 and 5%, respectively, at the 3 concentrations. The removal of sperm plasma membrane proteins also increased from 0.72 mg to 2 mg with 0.05% Tween 20. Similar results were found with fresh semen samples. Although the amount of extracted proteins was significantly lower than that obtained with frozen spermatozoa, fresh sperm motility was likewise eliminated by the detergent treatment, and sperm viability was decreased. A semen sample with an initial sperm viability of 59% had a value of only 8% after treatment with 0.05% Tween 20. Comparative SDS-PAGE analysis of the extracted fractions from fresh and frozen-thawed semen treated with Tween 20 showed that the higher amount of extracted proteins in the frozen semen samples corresponded to the egg yolk lipoproteins in the cryoprotectant medium. However, it is worth noting that 4 more bands were found in the sample obtained from fresh semen than from frozen semen. These results indicate that some cell membrane proteins are lost through the freezing-thawing process.

Fundamentals and recent development in cryopreservation of bull and boar semen

This paper describes some of the effects of cryopreservation on living sperm, and some recent results for bull and boar semen. During freezing and thawing of semen, the sperm can be damaged by the rapid and dramatic changes in the physicochemical conditions during cooling and ice formation. The rate and extent of these changes, and their impact on the cells, are strongly affected by the cooling rate and the medium composition. For many species, including humans and several farm animals, the optimal cooling rate has been determined, sometimes in combination with the cryoprotectant concentration. Recent results indicate that the cryopreservation of bull semen at the AI station could be improved by using controlled freezing at a cooling rate of about 100 degrees C/min, and by changing the composition of the freezing medium. An interaction between glycerol concentration and cooling rate has been described for boar semen. Current cryopreservation methods for boar semen based on an optimal combinations of these two factors allow consistent sperm survival in the frozen semen of AI boars, with acceptable variation among boars. The fertility results for semen processed in this fashion seem to be adequate for special applications, such as export, or long-term storage.

Capacitation-like changes occur in mouse spermatozoa cooled to low temperatures

Previously we showed that >70% of mouse spermatozoa cooled slowly from 37 degrees C to 4 degrees C and warmed have undergone capacitation-like changes as examined by a chlortetracycline staining assay. These membrane changes are reflected in the ability of cooled spermatozoa to achieve fertilization rates in vitro similar to those of uncooled controls when added to oocytes immediately upon warming. The aim of this study was to determine the nature of these membrane changes. We found they were not dependent upon the rate of cooling to 4 degrees C and similar changes were observed when spermatozoa were cooled to higher temperatures (10 degrees and 20 degrees C), but it took longer for 50% of the spermatozoa to undergo such changes (3, 18, and 27 min for spermatozoa held at 4 degrees, 10 degrees, and 20 degrees C, respectively). Mixing cooled spermatozoa with oocytes immediately upon warming produced fertilization rates similar to fresh spermatozoa capacitated in vitro for 90 min before the oocytes were added. The rate of sperm penetration as determined by the fluorescent DNA stain Hoescht 33258 was also similar. However, the penetration time for cooled spermatozoa was significantly shortened when they were preincubated for 90 min before being added to oocytes. We conclude that membrane changes resembling capacitation (1) occur during cooling to temperatures above freezing, (2) are independent of cooling rate, (3) proceed faster at lower temperatures, and (4) obviate the need for prior capacitation in vitro before mixing with oocytes.

Visualization and quantification of glycolipid polarity dynamics in the plasma membrane of the mammalian spermatozoon

Seminolipid (sulphogalactosylalkylacylglycerol), the glycolipid that is specific for mammalian germ cells, is located exclusively in the outer leaflet of the sperm plasma membrane. In this study the lateral distribution of seminolipid on sperm heads has been investigated by indirect immunofluorescence labelling and detection with digital imaging fluorescence microscopy. In freshly ejaculated sperm cells this glycolipid was present primarily at the apical ridge subdomain of the plasma membrane of the sperm head. After binding the sperm cells to zona-coated coverslips seminolipid migrated, in 40 minutes, from the apical ridge to the equatorial subdomain of the plasma membrane. A similar redistribution of seminolipid was observed during capacitation of sperm cells in vitro induced by Ca2+ or bovine serum albumin. Comparable migration of seminolipid was also found after prolonged storage of ejaculated sperm cells, albeit at a much slower rate. Addition of arylsulphatase A, an enzyme present in seminal plasma that desulphates seminolipid, significantly enhanced the migration of seminolipid during storage of sperm cells. Its breakdown product desulphoseminolipid (galactosylalkylacylglycerol) appeared highly specifically at the equatorial segment. The measured fluorescence intensity over the sperm head surface correlated linearly with the spatial probe distribution as was checked by fluorescence lifetime imaging microscopy. This paper demonstrates and quantifies for the first time the polarity of seminolipid on the surface of the sperm cell and the dynamic alterations that occur in this polarity during post-ejaculatory events.

Assessment of acrosomal integrity of vervet monkey spermatozoa after cryopreservation

Cryopreservation of Vervet monkey semen caused a highly significant reduction in the percentage of normal acrosomes and a highly significant increase in the percentage of mildly damaged, severely damaged, and lost acrosomes. This was demonstrated by staining ten post-thaw semen samples, which enabled a visualization of the acrosomal damage. The incidence of post-thaw intact acrosomes in this cryopreservation method was found to be similar to that reported for man and cynomolgus monkey semen.

Membrane damage during dilution, cooling and freezing-thawing of boar spermatozoa packaged in plastic bags

The objective of the present investigation was to determine the degree of membrane damage in boar spermatozoa during the course of a cryopreservation procedure, including thawing. Ejaculates from four fertile Swedish Yorkshire boars were frozen under controlled conditions in Teflon-plastic bags (2.5 ml) using 3% glycerol as cryoprotectant. Membrane integrity was monitored using supravital fluorescent dyes and confirmed by scanning electron microscopy. The results show that cooling to +5 degrees C significantly affected the permeability of the plasmalemma. Supercooling (-6 degrees C) during the freezing program did not further deteriorate the integrity of the spermatozoal membrane. The thawing procedure however, dramatically increased the frequency of spermatozoa with damaged plasma membranes. Thus particular attention must be paid on designing a better thawing procedure when dealing with boar semen frozen in plastic bags.

Sperm cell heterogeneity revealed by centrifugal counter-current distribution in an aqueous two-phase system

In recent years, partitioning in aqueous two-phase systems has been developed as a mild separation procedure of high selectivity for studying cell surface properties. This work was undertaken to study the surface heterogeneity of bull and ram sperm cells by using centrifugal counter-current distribution in dextran-poly(ethylene glycol) two-phase systems. The revealed heterogeneity appears to be associated with different viability states of the fractionated cells. Various strands of evidence support this conclusion: (a) assessment of viability by fluorescence probes showed a different enrichment of live cells in the different fractions tested, dead spermatozoa showing enhanced affinity to the dextran-rich phase; (b) freezing or thermic shock of sperm cells, known methods of promoting loss of viability, provoked an increase in the number of cells with enhanced affinity to this phase; (c) the same effect was observed when sperm cells were obtained from ejaculates after longer periods of abstinence. The results presented here strongly suggest that loss of semen viability results in a decreased hydrophobicity of the cell surface. Thus this may be suitable for detecting sperm surface changes and to separate spermatozoa populations enriched in some functional and/or structural surface features.

Fertility of bull spermatozoa frozen in whole milk extender with trehalose, taurine, or blood serum

Fertility of bull semen processed in heated whole milk-glycerol control semen extender with various additives was compared in six field trials. The additive in field trials 1 and 2 was 25.6 g of trehalose/L of the glycerol fraction of whole milk. Whole milk was heated to 95 degrees C for 10 min, cooled, and filtered 1 d before use (trial 1) or 3 d before use (trial 2). In field trial 3, 3.0 g/L of taurine were added to the glycerol fraction of whole milk. In field trial 4, specially prepared bovine serum (15% vol/vol) was included in the glycerol fraction of whole milk. Field trials 5 and 6 were larger fertility studies with trehalose in extenders prepared the day before use (trial 5) and 1 and 3 d before use (trial 6). Control and treated semen were coded and distributed randomly over a large group of professional inseminators. The 59-d nonreturn rates for control and treated semen, respectively, were as follows: trial 1, 74.1 and 73.7%; trial 2, 71.3 and 73.1%; trial 3, 74.9 and 70.9%; and trial 4, 75.1 and 71.6%. No significant differences resulted in trials 1 to 3, but bovine serum decreased the non-return rate in trial 4. Trials 5 and 6 resulted in nonsignificant improvement in fertility with added trehalose. Thus, these additives, useful as cryopreservatives or membrane protectors in other systems, did not enhance the fertility of sperm frozen in whole milk.