Evaluation of acrosomal status of bovine spermatozoa using concanavalin a lectin

We report here that fluorescein isothiocyanate-conjugated concanavalin A (FITC-ConA) specifically labels the acrosomal region of acrosome-reacted bovine spermatozoa. This labeling is found to be useful in evaluating the acrosome status of bovine spermatozoa. When fresh bovine spermatozoa that had been fixed with 4% formaldehyde, smeared on glass slides and then air-dried were stained by FITC-ConA, weak fluorescence was observed on the acrosomal region, although almost all the spermatozoa appeared to be acrosome-intact. However, when fresh sperm suspensions were incubated with FITC-ConA and then mounted on glass slides, no fluorescence was observed on the acrosomal region. Therefore, in the ensuing experiments, both the fixation and the FITC-ConA staining of spermatozoa were done in suspension. When ethanol-treated spermatozoa, whose outer membrane may be permeabilized, were stained with FITC-ConA, the fluorescence was extensively observed on the inner acrosomal region. This fluorescence was inhibited in the presence of 0.2 M D-mannose, a competitive sugar, suggesting that FITC-ConA binds specifically to glycocomponents on the inner acrosomal membrane. We next tried to stain fresh or frozen-thawed spermatozoa from 3 different bulls that had been treated with the calcium ionophore A23187, which is known to induce acrosome reaction of bovine spermatozoa, with FITC-ConA. A significant correlation between the percentage of ConA-labeled spermatozoa and that of rose bengal stained negative ones at various time points during A23187 incubation was achieved. Furthermore, suitability of dual staining to distinguish between physiological acrosome reaction (acrosome-lost and live) and degenerative acrosomal loss (acrosome-lost and dead) using FITC-ConA and Hoechst bis-benzimide 33258 (H258) supravital stain was also confirmed. From these results, it was concluded that the FITC-ConA labeling procedure is a feasible and reliable method for the assessment of physiological acrosome reaction of bovine spermatozoa.     

Cryopreservation effects on domestic cat epididymal versus electroejaculated spermatozoa

Frozen-thawed epididymal spermatozoa have already been successfully used in artificial insemination in the domestic cat, proving to be a valuable resource for the reproduction of felid species, which are threatened with extinction. The aim of this study was to compare the effects of freezing and thawing on domestic cat semen collected by electroejaculation (EL) and from the epididymides (EP) and vasa deferentia. Ten adult cats were anesthetized, electroejaculated and immediately thereafter, orchiectomized. Epididymal spermatozoa were collected through the compression of caudae epididymidis and vasa deferentia. Spermatozoa were frozen-thawed following a single protocol. Sperm motility, sperm progressive status (0-5), plasma membrane integrity and morphology (light and transmission electron microscope) were assessed on two occasions, immediately after collection and after freezing and thawing. There were no significant differences between the electroejaculated and epididymal fresh or frozen-thawed spermatozoa for any of the variables. However, the incidence of acrosome defects after freezing and thawing increased by 19% based on light microscopy, whereas ultrastructural images revealed acrosome damages in most sperm cells. Since these acrosomal changes are known to affect sperm fertilising capacity, further studies are needed to optimize cryopreservation techniques for epididymal as well as electroejaculated domestic cat spermatozoa.     

The effects of cooling to 5 degrees C and freezing and thawing on the ultrastructure of bull spermatozoa.

Semen from 6 bulls was examined under the transmission electron microscope immediately after collection, after dilution and cooling to 5 degrees C and after freezing and thawing. Conception rates were determined following artificial insemination of the frozen and thawed semen. Dilution and cooling to 5 degrees C caused acrosomal swelling in about 50% of the spermatozoa. Subsequent freezing and thawing caused considerable ultrastructural changes to the acrosomes (disruption of the plasma and outer acrosomal membranes and dispersion of the acrosomal contents) and middle pieces (breakage of the plasma membrane and a reduction in the electron density of the mitochondrial matrix) of a high proportion of spermatozoa. The average non-return rate following insemination of semen from 5 of the bulls was 61.6% and higher (P greater than 0.001) than for the sixth bull (15%). Although this difference in semen viability was also demonstrated in the structural studies (acrosome, P greater than 0.05: middle piece, P greater than 0.001), more work is required to assess the relationship between structure and function of spermatozoa.     

The effect of cryopreservation on sperm head morphometry in Florida male goat related to sperm freezability

The Sperm Class Analyzer was used to investigate the effect of freeze-thawing procedure on Florida buck sperm head morphometry, and to relate possible changes in sperm head dimensions to cryopreservation success. Semen samples (n=76) were frozen with tris and milk-based extenders and thawed. Sperm quality samples (motility, morphology, acrosome), and sperm head morphometric values (length, width, area, perimeter, ellipticity) were compared between fresh and frozen-thawed samples. Sperm freezability was judged according to the sperm quality parameters assessed. Fertility data was obtained after artificial insemination with cryopreserved semen. Cryopreservation success was different between freezing methods. Sperm head dimensions were significantly (p<0.05) smaller in cryopreserved tris and milk spermatozoa respectively than in those of the fresh samples. The sperm head morphometric parameters that had changed after cryopreservation were lower in suitable semen samples after thawing and with successful pregnancies after artificial insemination. These data suggest that changes in sperm head morphometry might reflect spermatozoa injury occurred during cryopreservation.     

Effect of semen collection method on pre- and post-thaw Guirra ram spermatozoa

In this study, we evaluated the potential effect of the method of recovery (artificial vagina or electroejaculation) on the production and quality of Guirra ram spermatozoa cryopreserved for the possible constitution of a sperm bank. In order to address this question, we evaluated the effect of semen collection method on fresh semen quality parameters, including: volume, concentration, production, microscopic analysis (abnormal sperm and intact apical ridge) and sperm motility parameters determined by CASA system. For frozen-thawed semen, we evaluated motility parameters by CASA and intact apical ridge, acrosomal status, assessed by dual staining by IP and FITC-PNA and capacitation status, assessed by M540 and Yo-pro1, using flow cytometry. The main findings from this study were: (i) that electroejaculation resulted in a lower recovery efficiency (80% of the cases), as a consequence of contamination with urine or lack of response to the electrical stimulation; (ii) the fresh seminal quality was not significantly different between recovery methods, except for the concentration of spermatozoa, but total number of spermatozoa and the consequent number of possible seminal doses for artificial insemination were similar; and, (iii) a higher number of stable and functional spermatozoa (higher number of live non-capacitated cells, higher live acrosome intact cells and live acrosome reacted cells) were found for frozen-thawed spermatozoa collected by electro ejaculation than by artificial vagina. According to our results, we are able to develop both methodologies in the creation of the Guirra sperm bank. Assuming the advantages and limitations of both methodologies, in Guirra breed, would enable the rapid constitution of a sperm bank including samples from a large number of non-trained rams in a short period of time, which will increase the genetic variability, and so guarantee the conservation of this breed.     

Apoptotic-like changes in the spermatozoa of fresh and stored boar semen and the quality of embryos produced in vivo

The aim of this study was to determine the apoptotic-like changes in the spermatozoa of fresh and stored boar semen and to investigate the relationship between this phenomenon and the quality of embryos produced in vivo. The experiments were divided into two series. In the first series, ten ejaculates were collected from five boars, which were crossbreeds of the Polish Landrace and Large White breeds. The semen was stored as a liquid until Day A (the day on which sperm motility decreased to 30%). Three fluorescence methods were used to evaluate semen quality: an assay to assess the early changes in sperm membrane integrity using the fluorophore YO-PRO-1, an assay for phosphatidylserine (PS) translocation across the plasma membrane using fluorescein-labeled annexin-V and the mitochondrial-specific probe JC-1 (5,5',6,6'-tetrachloro-1,1',3,3' tetraethylbenzimidazolylcarbocyanine iodide) for measuring changes in mitochondrial membrane potential. Our results showed that liquid preservation of boar semen causes apoptotic-like changes in the sperm, and a significant increase in both: apoptotic sperm (YO-PRO-1(+)/PI(-)) and early apoptotic sperm (annexin-V(+)/PI(-)) were observed between Day 0 (fresh semen) and Day A only in semen from three of the five boars. In the second series of experiments, the semen from boar nos. 1, 2, and 3 was selected for insemination of superovulated gilts. The fertilizing capacity of fresh and stored semen with different levels of apoptotic spermatozoa was measured based on the morphology and the number of cells of embryos that were obtained after insemination with this semen. Our studies indicated no significant differences in the fertilization rate of gilts after insemination with fresh and stored semen with increased levels of apoptotic spermatozoa. After insemination with stored semen, a significantly greater number of degenerated embryos were observed, but the morphologically normal blastocysts obtained after insemination with either fresh or stored semen had a similar number of nuclei.     

Semen assessment, fertility and the selection of Hereford bulls for use in AI

Nineteen young Hereford bulls were used to study the relationship between semen characteristics and fertility in artificial insemination following 15 320 inseminations. Seven measures of sperm motility, morphological abnormalities, the release of hyaluronidase, ATP content and sperm head measurements were examined as predictors of fertility (49-day fixed-interval non-return rate). Two assessments of motility, three categories of abnormal spermatozoa, acrosomal changes and the release of hyaluronidase had predictive power. Multiple regression analysis showed that a combination of sperm motility after dilution in saline, motility after thawing and the proportion of coiled tails and proximal protoplasmic droplets provided the best prediction of fertility and allowed bulls to be ranked in order of observed non-return rate (%) with a Spearman correlation better than +0.80.     

Cryopreservation of epididymal sperm obtained at necropsy from goats

In the field of transgenic production, the ability to carry a male's genetic contribution beyond its natural life span is remarkably important. The ability to successfully collect and cryopreserve sperm from the epididymis at necropsy may prove to be a useful technique for preserving valuable genes. Thirty-two bucks ranging in age from 13 days to 7 years were examined in this study and 25 had epididymal sperm extracted at necropsy. Seven bucks yielded clear fluid with no spermatozoa; all were under four months of age. Testes were removed from the scrotal sac, small lateral incisions made across the convoluted tubules, pressure applied to the tail of the epididymis and small droplets of sperm pipetted into equilibrated extender. The average initial analysis of wave motion (0 to 5, 5 being rapid wave motion), live/dead sperm percentage and acrosomal integrity of 25 fresh epididymal samples were 5.0, 92%, and 100%, respectively. By comparison, the same parameters obtained from 206 fresh ejaculated samples were 3.0, 86%, and 95%, respectively. After being cryopreserved in liquid nitrogen, one straw from each sample was thawed after 3 to 60 days of cryostorage. Results of post-thaw analysis of 25 cryopreserved epididymal sperm samples for live/dead percentage and acrosomal integrity were 82% and 84%, respectively. By comparison, results of post-thaw analysis of 206 cryopreserved ejaculated sperm samples for live/dead percentage and acrosomal integrity were 60% and 89%, respectively. To assess the competence of the frozen epididymal sperm, IVF and AI were performed. In parallel IVF experiments, 40% of the oocytes showed cleavage patterns, with 6% developing to the blastocyst stage using frozen epididymal sperm, while 37% of the oocytes showed cleavage patterns and 4% developed into blastocysts using frozen ejaculated sperm. One artificial insemination out of 20 resulted in a pregnancy using frozen epididymal sperm, while 7 of 18 artificial inseminations resulted in a pregnancy using frozen ejaculated sperm. This data documents the successful collection and cryopreservation of epididymal sperm from the goat and its use for in vitro fertilization and artificial insemination.     

In vitro phagocytosis of boar spermatozoa by neutrophils from peripheral blood of sows

A considerable number of spermatozoa are used in each sow in routine artificial insemination. However, within a few hours after insemination, many spermatozoa are phagocytosed by polymorphonuclear leucocytes. Some aspects of sperm transport in the female genital tract in the sow have been thoroughly investigated, whereas little is known about the mechanisms involved in the phagocytosis of spermatozoa, or about which spermatozoa (fresh, capacitated or dead) are the most susceptible to ingestion by polymorphonuclear leucocytes. In this study, phagocytosis was investigated by use of an in vitro phagocytosis assay. Polymorphonuclear leucocytes were challenged with either untreated, cold-shocked or frozen-thawed spermatozoa, or with spermatozoa that had been treated to induce capacitation in vitro. The influence of serum on phagocytosis was also investigated. Treatment of the semen to induce capacitation in vitro considerably reduced the phagocytosis of spermatozoa, whereas crude treatments like cold-shock or freezing and thawing reduced phagocytosis only in the first 15-30 min of incubation with polymorphonuclear leucocytes. Viable spermatozoa were phagocytosed mainly through a pathway that was independent of complement or other serum components (for example, antibodies). Complement had little effect on phagocytosis of spermatozoa, but did cause acrosomal exocytosis and cell death.     

Quantitative changes of Ricinus communis agglutinin I and Helix pomatia lectin binding sites in the acrosome of rat spermatozoa during epididymal transit.

During passage through the epididymis, spermatozoa undergo a number of changes which result in their acquisition of fertility and motility. Some of the changes that occur include loss of the cytoplasmic droplet and changes in sperm morphology, metabolism and properties of the nucleus and plasma membrane. Changes have also been reported in the acrosomic system of mammalian spermatozoa during their transit through the epididymis. In the present study, the quantitative changes of the glycoconjugate content in the acrosome of rat spermatozoa were examined during their passage through the epididymis using lectin-colloidal gold cytochemistry. Various regions of the epididymis (initial segment, caput, corpus and cauda epididymidis) were fixed by perfusion with 1% or 2% glutaraldehyde buffered in sodium cacodylate (0.1 M), dehydrated in ethanol and embedded without osmication in Lowicryl K4M. Lectin-colloidal gold labeling was performed on thin sections using Ricinus communis agglutinin I (RCA I) or Helix pomatia lectin (HPL) to detect D-galactose- and N-acetyl-D-galactosamine-containing glycoconjugates, respectively. The labeling density over the acrosome of the acrosomic system was evaluated as the number of gold particles per microns 2 of profile area using a Zeiss MOP-3 image analyzer. The overall mean labeling densities over the acrosome of spermatozoa for each lectin was estimated from 4 rats and over the four distinct epididymal regions. The mean labeling density of the acrosome with RCA I and HPL showed a similar pattern along the epididymis, although RCA I revealed approximately twice as many gold particles per epididymal region. In either case, there was a significant decrease in the labeling density of the acrosome of spermatozoa between the initial segment or caput epididymidis and cauda epididymidis (p less than 0.01). A similar decrease was also noted between the initial segment and corpus epididymidis (p less than 0.01). No change was found between the initial segment and caput epididymidis. Controls showed a virtual absence of labeling. These results suggest that in addition to a multitude of changes occurring to spermatozoa during epididymal transit, there are also significant quantitative changes in the glycoconjugate content within the acrosome.     

A scanning electron microscopic study of rabbit spermatozoa in the female reproductive tract following coitus

The surface morphology of rabbit spermatozoa, fixed in situ (female reproductive tract) and prepared for scanning electron microscopy by critical point drying, was studied for as many as 36 hours post coitum. The findings demonstrate that 1) spermatozoa in the reproductive tract following coitus exist as a heterogenous, morphological population and 2) with time, shifts within this population from one predominant morphology to another take place. In the fresh ejaculate, most spermatozoa have intact surfaces free of membranous disruptions. With time, a process of labilization (denudation) of the membranes covering the acrosomal region occurs in a progressively larger proportion of spermatozoa. The labilization originates by a process of vesiculation and/or vacuolation and leads to the appearance of a series of small fenestrations of perforations of the surface membranes. The perforations coalesce, and gradually larger areas of the surface membranes are eroded such that by 15 hours post coitum, the outer acrosomal membrane, as well as other acrosomal areas, are to varying degrees, directly exposed to the uterine milieu. Secretory granules, picked up by cilia and transferred to the spermatozoa become localized over the acrosomal region shortly after coitus. The possible significance of these time-dependent morphological events with the phenomena of capacitation and the "true" and "false" acrosome reactions are discussed.     

Morphological and functional changes of stallion spermatozoa after cryopreservation during breeding and non-breeding season

The study compared quality and freezability of stallion semen during breeding and non-breeding seasons. Ejaculates were collected twice per week from four stallions during May (n = 24) and December (n = 24). The semen was mixed with skim milk extender, centrifuged and resuspended in fresh extender. Aliquots of this sperm suspension were separated from extender and diluted in TALP medium for sperm evaluation or with cryoextender (type "Gent" or a combination of Triladyl and skim milk). Samples of 0.5ml were cryopreserved in straws using a programmed freezer. Parameters of sperm quality were evaluated before and after freezing/thawing. These included percentages of motile spermatozoa and of morphological intact sperm. Typical injuries were demonstrated by scanning electron microscopy (S.E.M.). The acrosomal status was visualised using FITC-conjugated peanut agglutinin, and the acrosome reaction was induced by calcium ionophore A 23187. The chromatin stability was estimated by acridine orange test.In winter, the average percentages of motile and morphologically normal sperm (67 and 74.3%, respectively) were higher than during the breeding season in May (59 and 65.9%; P < 0.05). After freezing/thawing the proportions of vital and intact sperm decreased significantly. The number of motile sperm declined to 15 and 18% in May and December (range 5-40%), and of morphologically intact sperm to 51% in both seasons. Results of S.E.M. showed typical membrane ruptures in the acrosomal region and some sperm with abnormal necks. The proportion of frozen sperm with spontaneous acrosome reaction was higher during winter (86.5 versus 77.0%), suggesting a higher degree of membrane reactivity. Percentages of spermatozoa with denaturated chromatin were minimal and showed minimal differences between fresh and frozen state, stallions or seasons. An additional decondensation treatment with papain and DTE revealed a slightly enhanced number of spermatozoa with denaturable DNA after cryopreservation, especially in December (5.4 +/- 1.3%). The influence of cryoextenders was not significant for most sperm parameters, but there was a high variability between the stallions. Altogether, the influence of factors on the quality of spermatozoa has the following rank order: cryopreservation > stallion > season. Different cellular structures seem to have different susceptibilities to physicochemical stress. The cryopreservation of sperm during December results in survival rates similar to those measured during the breeding season, even more important for successful preservation is the selection of suitable semen donors.     

Analysis of selected sperm by density gradient centrifugation might aid in the estimation of in vivo fertility of thawed ram spermatozoa

The aim of the present study was to evaluate the effect of selecting a sperm subpopulation by means of a discontinuous density gradient centrifugation (DGC) on the quality of ram thawed semen, and the relationships between sperm parameters assessed in unselected and in selected sperm samples with in vivo fertility after intrauterine artificial insemination (IUI) using unselected sperm samples. Semen samples from twenty males were collected by artificial vagina and cryopreserved following a standard protocol. After thawing, unselected sperm samples were used in an in vivo fertility trial and sperm motility (subjective and objective, assessed by means of CASA) and membrane and acrosomal integrities (microscopy) were evaluated on unselected and selected sperm samples. In addition, plasmalemma integrity (YO-PRO-1/PI), membrane fluidity (Merocyanine 540/YO-PRO-1), mitochondrial activity (Mitotracker Deep Red/YO-PRO-1), and DNA fragmentation index (%DFI) assessed by Sperm Chromatin Structure Assay (SCSA^®) were evaluated by flow cytometry before and after sperm processing using DGC. Results showed that DGC improved all sperm parameters significantly, except the %DFI, which increased after the selection procedure. No relationships were found between sperm parameters evaluated in unselected sperm samples and in vivo fertility. However, we found a positive correlation between spermatozoa with high membrane fluidity within the viable sperm population (VIABMerocyanine+) evaluated in selected sperm samples and in vivo fertility (r = 0.370, P = 0.019). In conclusion, our results suggest that selected spermatozoa represent a sperm subpopulation different to the unselected one that could be related with the in vivo fertility.     

Surface mapping of binding of oviductin to the plasma membrane of golden hamster spermatozoa during in vitro capacitation and acrosome reaction

Oviductins are high-molecular-weight glycoproteins synthesized and secreted by nonciliated oviductal epithelial cells and have been shown to play a role in fertilization and early embryo development. The present study was carried out to examine the in vitro binding capacity of hamster oviductin to homologous sperm and to determine the sites of its localization in untreated, capacitated, and acrosome-reacted spermatozoa. Freshly prepared epididymal and capacitated sperm as well as acrosome-reacted sperm were incubated with oviductal fluid prepared from isolated hamster oviducts, fixed and then probed with a monoclonal antibody against hamster oviductin. Results obtained with pre-embedding immunolabeling experiments revealed binding of oviductin to the acrosomal cap and the apical aspect of the postacrosomal region. Immunolabeling of both regions appeared to be more intense in capacitated spermatozoa. Acrosome-reacted sperm showed an immunoreaction of moderate intensity over the postacrosomal region. The plasma membrane overlying the equatorial segment also exhibited a weak labeling. Quantitative analysis obtained with the surface replica technique indicated that oviductin had a higher binding affinity for the acrosomal cap than the postacrosomal region and that the binding of oviductin to the latter plasma membrane domain was enhanced during capacitation. Binding of oviductin to the postacrosomal region, however, was attenuated after acrosome reaction. Immunolabeling for oviductin was found to be the weakest over the equatorial segment regardless of the experimental conditions. The binding of hamster oviductin to specific membrane domains of the homologous sperm and the changes in its distribution during capacitation and acrosome reaction may be important for the function of hamster oviductin preceding and during fertilization.     

Effects of radiographic contrast media on domestic cat epididymidal sperm

Laparoscopic artificial insemination has an important role in felid conservation but it is costly and includes surgical risk. Therefore, radiographic contrast medium combined with non-surgical transcervical AI to verify intrauterine gamete placement could be a viable alternative. Gamete-rescued fresh and frozen-thawed sperm were extended with one of two commercial contrast media (nonionic and ionic), with osmolarity adjusted to 320-330 mOsm, or feline optimized culture medium (control). Percent motility, forward progression status, and acrosomal integrity were recorded every 30 min for 4 h. Sperm penetration abilities were assessed by coincubating treated sperm with conspecific in vitro matured oocytes for 18 to 20 h, and presumptive zygotes and embryos were fixed and stained to determine sperm penetration and fertilization rate. There was reduced motility and acrosomal integrity in frozen-thawed versus fresh sperm (P < 0.05). Neither radiographic contrast medium induced adverse effects on fresh sperm motility relative to control medium (P > 0.05), but motility of frozen-thawed sperm decreased when treated with nonionic radiographic contrast medium compared to control medium (P < 0.05). There were no differences in acrosomal integrity between radiographic contrast and control media in fresh (P > 0.05) or frozen sperm (P > 0.05). Neither radiographic contrast media decreased the numbers of morphologically normal sperm (P > 0.05) or reduced the ability of domestic cat sperm to penetrate (P > 0.05) or fertilize (P > 0.05) conspecific oocytes. Ionic radiographic contrast medium can be added to fresh or frozen-thawed domestic cat sperm with no adverse effect on motility, morphology, acrosomal integrity or oocyte penetration rates, and thus may be used to facilitate further development of transcervical AI procedures.     

The status of acrosomal caps of hamster spermatozoa immediately before fertilization in vivo

Adult female golden hamsters were induced to superovulate. When they were mated several hours prior to ovulation or artificially inseminated about the time of ovulation, nearly 100% of their eggs were subsequently fertilized monospermically. During the progression of fertilization when the eggs were still surrounded by compact cumulus oophorus, the contents of the ampullary region of the oviducts were collected and spermatozoa moving in the ampullary fluid, within the cumulus and on/in the zonae pellucidae of unfertilized eggs, were examined by light and electron microscopy to evaluate the status of their acrosomal caps. Most spermatozoa swimming in the ampullary fluid had apparently intact acrosomal caps, while the vast majority moving within the cumulus had distinctly modified acrosomal caps. Most spermatozoa that had passed through the cumulus and reached the zona surfaces had remnants of their acrosomal caps (“acrosomal ghosts”). When the ghosts were present around the sperm heads on the zona, the heads pivoted about a point roughly corresponding to the places where the ghosts were located. The ghosts seemed to firmly attach to the zona surfaces, then were split open by the sperm heads and left behind as the sperm heads advanced into the zona. A few spermatozoa on the zona surfaces had no acrosomal ghosts (at least not detectable by light microscopy). In this case, the sperm head pivoted about either the inner acrosomal membrane or the equatorial segment of the acrosome. In no instance were spermatozoa with intact acrosomal caps found on zona surfaces. We infer from these observations that most spermatozoa in vivo initiate their acrosome reactions while they are advancing through the cumulus. When they arrive at the zona surfaces, acrosomal ghosts are generally present on the sperm heads. These ghosts appear to hold sperm heads to zona surfaces as well as to restrict the direction of advancement of sperm head through the zona. In a minority of cases, ghostless spermatozoa reach the zona surfaces. As these spermatozoa appear to be able to penetrate the zona successfully, structures other than the acrosomal ghost (ie, the inner acrosomal membrane and the plasma membrane over the equatorial segment of the acrosome) may also attach to zona surfaces before spermatozoa penetrate into the zona.     

THE ACROSOME REACTION IN MYTILUS EDULIS : II. Stages in the Reaction,Observed in Supernumerary and Calcium-Treated Spermatozoa

Suspensions of Mytilus edulis eggs were fixed with osmium tetroxide at various intervals between 1 and 10 seconds after heavy insemination, and sectioned for electron microscopy to follow the natural process of acrosome reaction in the spermatozoa around the eggs. Sperm suspensions were also fixed after the addition of 10 per cent by volume of M/3 calcium chloride. Within the first second after the acrosome is stimulated to react, an opening appears at its apex, around which the plasma and acrosomal membranes fuse to each other, and the resulting membrane complex is reflected backward, presumably by the swelling of material lining it. At the same time the other material within the now open vesicle disappears, and the rudiment of the acrosomal process, consisting of a short axial rod loosely surrounded by the invaginated part of the acrosomal membrane, is exposed at the anterior side of the sperm head. Within another second this rudiment is extended by elongation of the axial rod and expansion of the surrounding membrane. If the spermatozoon has reacted close to the egg surface, the elongation may be very slight, whereas in suspended spermatozoa the process may reach a length of 13 µ. Possible mechanisms underlying these changes are suggested.     

Acrosome reaction in spermatozoa from hagfish (Agnatha) Eptatretus burgeri and Eptatretus stouti: acrosomal exocytosis and identification of filamentous actin

Spermatozoa of the hagfishes Eptatretus burgeri and Eptatretus stouti, caught in the sea near Japan and North America, respectively, were found to undergo the acrosome reaction, which resulted in the formation of an acrosomal process with a filamentous core. The acrosomal region of spermatozoa of E. stouti exhibited immunofluorescent labeling using an actin antibody. The midpiece also labeled with the antibody. The acrosomal region showed a similar labeling pattern when sperm were probed with tetramethylrhodamine isothyocyanate (TRITC)-phalloidin; the midpiece did not label. Following induction of the acrosome reaction with the calcium (Ca2+) ionophore ionomycin, TRITC-phalloidin labeling was more intense in the acrosomal region, suggesting that the polymerization of actin occurs during formation of the acrosomal process, as seen in many invertebrates. The potential for sperm to undergo acrosomal exocytosis was already acquired by late spermatids. During acrosomal exocytosis, the outer acrosomal membrane and the overlying plasma membrane disappeared and were replaced by an array of vesicles; these resembled an early stage of the acrosome reaction in spermatozoa of higher vertebrates in which no formation of an acrosomal process occurs. It is phylogenetically interesting that such phenomena occur in spermatozoa of hagfish, a primitive vertebrate positioning between invertebrates and high vertebrates.     

Post-coital sperm recovery and cryopreservation in the Sumatran rhinoceros (Dicerorhinus sumatrensis) and application to gamete rescue in the African black rhinoceros (Diceros bicornis)

Sumatran rhinoceros (Dicerorhinus sumatrensis) sperm samples were collected from a post-copulatory female and characterized to determine their potential for sperm preservation and future use in artificial insemination. Five samples of acceptable quality from one male were used to compare the effect of two cryoprotectants (glycerol and dimethyl sulfoxide (DMSO)) and two post-thaw protocols (untreated and glass wool column) on sperm quality. The percentage of motile spermatozoa, sperm motility index (0-100) and sperm morphology were evaluated subjectively, and viability and acrosomal status were assessed using fluorescent markers. Evaluations of frozen-thawed spermatozoa were performed over a 6 h incubation interval. Post-coital semen samples (n = 5; 104.0 +/- 9.1 ml; 2.5 +/- 0.8 x 10(9) total spermatozoa; mean +/- SEM) exhibited a sperm motility index of 56.7 +/- 3.3, and contained 40.2 +/- 6.3%, 72.0 +/- 3.2% and 79.8 +/- 6.5% normal, viable and acrosome-intact spermatozoa, respectively. Glycerol and DMSO were equally effective as cryoprotectants and, regardless of post-thaw protocol, samples retained greater than 80% of all pre-freeze characteristic values. Processing semen samples through glass wool yielded higher quality samples, but only half the total number of motile spermatozoa compared with untreated samples. High values for pre-freeze sperm characteristics were also maintained after cryopreservation of epididymal spermatozoa from one black rhinoceros (Diceros bicornis) using the same protocol. In summary, Sumatran rhinoceros spermatozoa of moderate quality can be collected from post-copulatory females. Rhinoceros sperm samples show only slight reductions in quality after cryopreservation and thawing and have potential for use in artificial insemination.