Search PubMed⌕ Search

Biomedical subjects

S S Suarez

Publications and source records attributed to S S Suarez.

At least 37 records · Page 2Linked to original sources
PubMed1995

Ethanol and nerve growth factor effects on calcium homeostasis in cultured embryonic rat medial septal neurons before and during depolarization.

Ethanol and nerve growth factor (NGF) affect the survival of cholinergic neurons in the rat medial septum. To investigate whether calcium (Ca2+) homeostasis in these neurons is affected by ethanol or NGF treatment, changes in intracellular free Ca2+ concentration ([Ca2+]i) were studied in embryonic (E21) cultured medial septal neurons before stimulation (basal) and during stimulation with high potassium (K+). Changes in [Ca2+]i across time were measured in cultures of neurons treated without ethanol or with 100, 200, 400, or 800 mg% ethanol with NGF (+NGF) or without NGF (-NGF). Changes in [Ca2+]i were analyzed from fluorescence images, using indo-1. The effect of ethanol or NGF treatment was to reduce the rise in basal [Ca2+]i. The combination of ethanol and NGF treatment in +NGF neurons led to increases in basal [Ca2+]i with the greatest increase in basal [Ca2+]i occurring with 200 mg% ethanol. The effect of ethanol or NGF was to increase [Ca2+]i during stimulation with high K+. The greatest increases in [Ca2+]i occurred with 100 and 800 mg% ethanol. Together, ethanol and NGF treatment in +NGF-treated neurons led to significantly greater increases or decreases in K+ stimulated changes in [Ca2+]i compared to similarly treated -NGF neurons. We conclude that in medial septal neurons (before and during depolarization) changes in Ca2+ homeostasis occur in the presence of ethanol or NGF. The changes in [Ca2+]i following ethanol treatment are greater when NGF is present.

Animals↗
PubMed1995

Intracellular calcium reaches different levels of elevation in hyperactivated and acrosome-reacted hamster sperm.

Calcium plays a role in sperm motility hyperactivation and the acrosome reaction, but the relationship between cytoplasmic calcium (Ca2+in) levels in the two states was heretofore unknown. The Ca2+ indicator indo-1 was used to detect Ca2+in in moving hamster sperm in two sets of experiments. In the first experiment, activated, hyperactivated, and zona pellucida-induced acrosome-reacted/hyperactivated sperm were analyzed at the time of peak of activity for each state. In the second experiment, sperm in all states were analyzed at one time point. In both sets, mean Ca2+in in the acrosomal region, postacrosomal region, and flagellar midpiece was greater in hyperactivated sperm than in activated sperm, and in acrosome-reacted/hyperactivated sperm than in unreacted/hyperactivated sperm (P < 0.001). Ca2+in had increased to a greater extent in the midpiece than in the head in hyperactivated sperm, while the reverse was true for acrosome-reacted sperm. Oscillations at the frequency of the flagellar beat cycle were detected chiefly in the proximal flagellar midpiece of acrosome-reacted sperm, as they had been previously reported to occur in activated and hyperactivated sperm. Thus, Ca2+in may be maintained at two different elevated levels in sperm, and continues to oscillate after the acrosome reaction.

Acrosome↗
PubMed1995

Carbohydrates mediate the adherence of hamster sperm to oviductal epithelium.

The lower isthmus of the mammalian oviduct appears to serve as a reservoir for sperm that are retained by adherence to the epithelium. By inhibiting sperm binding within excised hamster oviducts and making use of carbohydrate probes, we have characterized the adherence of sperm in the reservoir and established a potential biochemical mechanism for the adherence and release of sperm. Fetuin and its terminal sugar, N-acetylneuraminic acid, interfered with the adherence of sperm to the oviductal epithelium. Labeled fetuin bound to the acrosomal region of fresh epididymal sperm, but not hyperactivated sperm, which have previously been reported to release from epithelial binding. Western blots labeled with fetuin and sialic acid-recognizing lectins identified proteins at several molecular masses that are candidates for the sperm surface component involved in adherence. Labeling of some of these candidates was reduced in samples from hyperactivated sperm. These results indicate that a sialylated oligosaccharide similar to that found on fetuin may be recognized by a sperm surface component and mediate binding to the oviductal epithelium. Release may be accomplished by loss or modification of the component during capacitation or hyperactivation.

Acrosome↗
PubMed1995

Characterization of the oviductal sperm reservoir in cattle.

A reservoir for sperm has been found in the oviductal isthmus in several species. Sperm are apparently trapped in the reservoir by binding to the oviductal epithelium, although other factors may be involved. We hypothesized that binding sites for bovine sperm are limited to the isthmus and are regulated by the hormonal state of the cow. Ipsilateral oviducts were obtained from heifers that were preovulatory (in estrus), had ovulated recently (within 12 h), or were in diestrus (Day 10). The isthmic and the ampullar epithelium were milked out and incubated separately in serum-free (SFRE-199-2) medium, at 39 degrees C in 5% CO2. Frozen-thawed sperm from bulls were added to the epithelium and coincubated for 15 min. The number of spermatozoa that bound to explants was not affected by stage of cycle or by anatomic origin of the explants (p > 0.05). In an additional experiment, oviducts were infused with sperm in vivo and then prepared for scanning electron microscopy, which revealed that sperm were associated with ciliated epithelium in both the isthmus and ampulla. Thus, bovine sperm may form a reservoir in the isthmic end of the oviduct because it is the first oviductal region that they encounter.

Animals↗
PubMed1995

Sperm motility hyperactivation facilitates penetration of the hamster zona pellucida.

These experiments were conducted to determine whether or not sperm motility hyperactivation facilities penetration of the zona pellucida of the oocyte. Two approaches were used. For the first, hamster sperm were incubated for 4.0-4.25 h in a capacitating medium that contained either 2.9 or 25.0 mM sodium bicarbonate. In these media, sperm became equally capacitated as evidenced by their ability to undergo the acrosome reaction when exposed to lysophosphatidyl choline or intact zonae pellucidae; however, sperm became hyperactivated only in the medium containing 25.0 mM bicarbonate. When these sperm were added to cumulus-free oocytes in vitro, only 2 of 88 oocytes were penetrated by sperm preincubated in 2.9 mM bicarbonate, while 31 of 86 oocytes were penetrated by sperm in 25.0 mM bicarbonate. It was found that equal numbers of sperm were bound to the oocytes and that equal numbers were acrosome-reacted on the surface of the zonae in the two media. For the second approach, sperm were incubated in a capacitating medium containing 25 mM bicarbonate. When > 70% were hyperactivated, aliquots were added to three sets of oocytes. After 10 min had been allowed for sperm to attach and acrosome-react, inhibitors of hyperactivation were added and the sperm and oocytes were incubated for an additional 20 min before fixation and examination for zona penetration. In the dishes treated with the inhibitors verapamil or Cd2+, 1 of 42 and 0 of 42 oocytes were penetrated, respectively, compared with 25 of 40 in controls. Therefore, it appears that hyperactivation facilitates penetration of the hamster zona pellucida.

Acrosome↗
PubMed1993

Intracellular calcium increases with hyperactivation in intact, moving hamster sperm and oscillates with the flagellar beat cycle.

At some time before fertilization, mammalian sperm undergo a change in movement pattern, termed hyperactivation. There is evidence that hyperactivation offers an advantage to sperm for detaching from the oviductal mucosa, for penetrating viscoelastic substances in the oviduct, and for penetrating the zona pellucida. Hyperactivation is known to require extracellular calcium, but little else is known about the mechanisms by which calcium affects sperm movement. The calcium-sensitive fluorescent dye indo-1 was used to follow intracellular calcium levels ([Ca2+]i) in individual moving sperm. Sperm were loaded with 10 microM of the acetoxymethyl ester form of the dye and then rinsed. The dye was excited at 340 nm by using a filtered xenon stroboscope, and images at the 405-nm and 490-nm excitation maxima were simultaneously digitized at 30 per sec for 2.1 sec. [Ca2+]i was significantly higher in the acrosomal and postacrosomal regions of the head and in the flagellar midpiece (the principal piece could not be measured) in hyperactivated than in nonhyperactivated sperm (P < 0.0001). [Ca2+]i oscillations were detected in the proximal half of the midpiece that were identical in frequency to the flagellar-beat-cycle frequency in 12 of 17 hyperactivated sperm (median, 3.5 Hz). Rapid [Ca2+]i oscillations were also detected in the acrosomal and postacrosomal regions, as well as in the distal midpiece. Oscillations were not eliminated by dampening the flagellar bending with methyl cellulose. The [Ca2+]i oscillations detected in sperm are significantly more rapid than oscillations detected in other cell types.

Animals↗
PubMed1993

Distribution of lectin binding sites in the oviducts of cycling and hormone-treated pigs.

Gamete transport, fertilization, and early embryonic development take place in different regions of the oviduct and under different hormonal conditions. The objective of this study was to use lectins to detect variation in the distribution of glycosylated molecules on the surface of the epithelia that influence these events. Oviducts were collected from gilts on day 1 (estrus) and day 16 (diestrus) of the estrous cycle, and from gilts that were bilaterally ovariectomized on day 4 of the estrous cycle, and were subsequently treated with estradiol valerate (100 micrograms/day), progesterone (200 mg/day), or corn oil vehicle for 11 days. Six biotinylated lectins, Triticum vulgaris (WGA), Arachis hypogaea (PNA), Ulex europeus (UEA-I), Dolichos biflorus (DBA), Ricinus communis (RCA-I), and Canavalia ensiformis (Con A), were used to probe tissue from the isthmus and ampulla using peroxidase-conjugated avidin as the marker. In cyclic gilts, WGA and DBA stained more strongly in the isthmus than the ampulla on both cycle days. Staining with PNA was patchy, but greater on the apical surface of isthmic epithelium on day 16 than day 1. With UEA-I, staining was more intense in the ampulla on day 16 than day 1. Staining by PNA and UEA-I was suppressed in both the ampulla and isthmus with estradiol treatment. DBA staining was suppressed in the isthmus with both estradiol and progesterone treatments. Cilia were labelled by all lectins except WGA and PNA. Thus glycosylation patterns vary in the porcine oviduct with region and hormonal state, reflecting the variety of events that may be influenced.

Animals↗
PubMed1992

Hyperactivation enhances mouse sperm capacity for penetrating viscoelastic media.

A movement pattern known as hyperactivation has been observed among sperm recovered from the periovulatory oviduct of several species. In culture medium, hyperactivated sperm swim in a pattern that is far less progressive than that of freshly ejaculated sperm. In the oviduct, sperm encounter highly viscoelastic substances, such as mucus and the cumulus matrix. We have previously reported that hyperactivated hamster sperm become more progressive in vitro when the viscosity of medium is increased. In the present study, we tested the effect of increasing the viscosity and viscoelasticity of the medium on the swimming progressiveness of mouse sperm. Caudal epididymal sperm were incubated in a medium that produced hyperactivated motility in 60 min. Swimming velocities of sperm incubated for 60 min were compared with those of fresh sperm after addition of one of the following to culture medium: solutions of 1.8% methylcellulose (high viscosity), 1.8% long chain polyacrylamide (high viscoelasticity), or culture medium alone (low viscosity). In culture medium, hyperactivated sperm had significantly lower mean straight-line velocities than fresh sperm (p = 0.004); this difference disappeared in methylcellulose (p = 0.085) and was reversed in polyacrylamide (p = 0.004). This and other velocity measurements indicated that hyperactivated mouse sperm penetrate viscoelastic media more efficiently than fresh sperm and therefore may be more efficient at penetrating oviductal mucus and cumulus matrix in vivo.

Animals↗
PubMed1992

Hyperactivated sperm progress in the mouse oviduct.

Sperm from naturally mated mice were observed and videotaped moving within mouse oviducts. The typical pattern of sperm progress involved intermittently breaking free and swimming a short distance, then reattaching to the epithelium. The proportion of sperm that swam freely (were not attached to the epithelium) was calculated and analyzed for effects of oviductal region, ovulation status, and sperm location relative to the lumen. A significantly higher proportion of sperm were free in the ampulla than in the isthmus (26.3% +/- 0.8% vs. 11.8% +/- 1.0%; p less than 0.0001) and in post-ovulatory than pre-ovulatory (16.2% +/- 2.0% vs. 10.6% +/- 1.6%; p less than 0.05) oviducts. Flagellar curvature ratio values showed that free sperm (0.716 +/- 0.024) had more sharply curved tails than stuck sperm (0.782 +/- 0.013). While this difference is significant (p = 0.01), the effect of attachment status interacted significantly (p less than 0.05) with the oviductal region such that there was a greater difference in the isthmus than in the ampulla. Only sperm using the more curved tail beats of hyperactivation were seen to break free from the epithelium and to progress along the oviduct. These results indicate that hyperactivation plays a role in moving sperm out of the isthmic reservoir and to the site of fertilization.

Animals↗
PubMed1991

Fertilizing capacity of bovine sperm may be maintained by binding of oviductal epithelial cells.

The ability of the bovine oviduct to maintain the motility and fertilizing capacity of bovine sperm was investigated by incubating frozen-thawed sperm with endosalpingeal epithelial cells cultured on either tissue culture plastic (nonpolarizing) or Matrigel-coated Millicell (polarizing) substrata. Sperm were also incubated in medium alone or with cultured bovine tracheal epithelial cells. Motility was determined at 6-h intervals over a 48-h period. The fertilizing capacity of sperm was evaluated after 0, 24, and 30 h of incubation by adding oocytes to the culture and determining the incidences of fertilization and polyspermy. Motility was maintained for 48 h in sperm that bound to endosalpingeal epithelial cells, but to a greater extent with polarized cells (38.4% motile) than with nonpolarized cells (0.8%). Fertilizing capacity was maintained for 30 h in sperm incubated with endosalpingeal epithelial cells on Matrigel/Millicell, but not in sperm incubated in medium alone or with tracheal cells. Only sperm incubated with oviductal cells developed hyperactivated motility. Scanning electron micrographs revealed that sperm were bound by the rostral portion of the intact acrosome to the apical surface of polarized endosalpingeal cells. These results suggest that the oviduct may not only store sperm but may also maintain sperm viability and fertilizing capacity during the preovulatory period.

Animals↗
PubMed1991

Evidence for the function of hyperactivated motility in sperm.

After insemination, mammalian sperm undergo a striking change in flagellar beat pattern, termed hyperactivation. In low-viscosity culture medium, nonhyperactivated sperm flagella generate relatively symmetrical, low-amplitude waves, while hyperactivated sperm flagella generate an asymetrical beating pattern that results in nonprogressive movement. Since sperm encounter highly viscous and viscoelastic fluids in the female reproductive tract, the progress of hyperactivated sperm was compared with that of nonhyperactivated and transitional sperm in media of increasing viscosity. Hamster sperm obtained from the caudal epididymis were incubated in a medium that promotes capacitation. After 0, 3, and 4 h of incubation, the majority of the sperm exhibited, respectively, activated, transitional, and hyperactivated motility. At each of these time points, aliquots of sperm were removed from incubation and added to solutions of 0, 5%, 10%, 20%, and 30% Ficoll in medium. Samples containing mostly hyperactivated sperm (4 h) maintained higher swimming and flagellar velocities and were able to generate greater forces in response to increased viscous loading than activated sperm (0 h). Transitional sperm (3 h) showed an intermediate response. The paths of hyperactivated sperm through solutions of 20% and 30% Ficoll were considerably straighter than those made through medium alone. This is the first demonstration that hyperactivation can confer a mechanical advantage upon sperm in the oviduct where they may encounter viscous oviductal fluid and a viscoelastic cumulus matrix.

Animals↗
PubMed1988

Hamster sperm motility transformation during development of hyperactivation in vitro and epididymal maturation.

The transformation of hamster sperm motility during capacitation in vitro and during maturation in the caudal epididymis was analyzed and compared using videomicrography. Sperm recovered from the distal portion of the caudal epididymis, as well as ejaculated sperm recovered from the uterus exhibited low amplitude, planar flagellar beating. By 3 hr of incubation under capacitating conditions, the caudal epididymal sperm were swimming in helical patterns apparently produced by significantly increased acuteness of flagellar bending and by torsion seen as abrupt, periodic turning of the head. By 4 hr, most sperm were hyperactivated, swimming in circles resulting from asymmetrical, planar flagellar bending that was significantly more acute than the preceding patterns. When motility parameters of fresh sperm were compared with those of sperm swimming in the transitional helical pattern and with hyperactivated sperm, transitional sperm had significantly higher net and average path velocities than the others, indicating that they covered space at the greatest rate. This suggests that the transitional phase plays an important role in sperm transport. Sperm recovered from the proximal region of the caudal epididymis, near the corpus, swam in either the helical or hyperactivated patterns, or a mixture of the two. The means of their flagellar curvature ratios and linear indices were intermediate between helical and hyperactivated mean values. Thus, sperm undergoing final maturation in the caudal epididymis reverse the pattern of development of hyperactivation. Also, the development of hyperactivated motility must therefore entail induction of a preexisting potential for flagellar movement, rather than a maturational process.

Acrosome↗
PubMed1987

Hyperactivated motility induced in mouse sperm by calcium ionophore A23187 is reversible.

The reversibility of hyperactivated motility was tested in caudal epididymal mouse sperm by treating them with 1 microM calcium ionophore A23187 in dimethyl sulfoxide (DMSO), followed 2 min later by the addition of medium containing high levels of bovine serum albumin (BSA) (final concentrations: 0.5 microM A23187, 22 mg/ml BSA). Controls received DMSO alone, followed by BSA. Immediately following treatment with A23187, motility was weak and vibratory. Two minutes after the addition of high levels of BSA, motility was hyperactivated, as determined by videotape analysis of linearity of trajectory and acuteness of flagellar bending. Ten minutes after the addition, the movement pattern returned to that of fresh, uncapacitated epididymal sperm. Control sperm retained the linear swimming pattern of fresh caudal epididymal sperm during the 10 min of observation. Ninety minutes later, however, both control and treated sperm became hyperactivated. The percentage of motile sperm was not affected by treatment or time. Thus, ionophore-induced hyperactivation is reversible and does not interfere with the normal development of hyperactivation during incubation under capacitating conditions in vitro.

Analysis of Variance↗
PubMed1987

Sperm transport and motility in the mouse oviduct: observations in situ.

Sperm transport and motility were studied through the transparent walls of the mouse oviduct by direct microscopic observation and videomicrography. Observations were made on excised female tracts 1-2 h post-coitus (pc) and 1-2 h before and after the approximate time of ovulation. Motile sperm were seen at the uterine entrance to the uterotubal junction (UTJ) in all females at 1-2 h pc, but in fewer females at later times. The intramural UTJ was usually constricted and held few sperm. The extramural UTJ and adjacent lower isthmus contained many motile sperm at 1-2 h pc. Apparently, the column of sperm moved upwards because in some females, sperm were found in the upper isthmus and not in the UTJ at the later time points. Few sperm were seen in the ampulla in the periovulatory period, and none at 1-2 h pc. There appeared to be two mechanisms retaining sperm in the lower oviduct: immobilization and adherence to the epithelium. Columns of immotile sperm were seen in the lower isthmus of some females. Motile sperm usually appeared to adhere by their heads to the oviductal epithelium, only occasionally breaking free to move vigorously about the lumen.

Animals↗
PubMed1983

Movement characteristics and acrosomal status of rabbit spermatozoa recovered at the site and time of fertilization.

Rabbit spermatozoa were recovered from the oviductal ampullae 11 h postcoitus by an oil microflush technique. Their movement was evaluated in the ampullar fluid, or in ampullar fluid diluted with in vitro fertilization medium, in slide preparations which were approximately 25 micron or 100 micron deep. The movement of these sperm was compared with the movement of ejaculated sperm in diluted semen. Movement parameters measured from videotapes recorded by a high-speed camera were coded according to treatment and entered into a microcomputer for statistical analysis. A total of 157 spermatozoa were recovered from the oviducts of 16 does: 152 were motile and 126 were free-swimming. Nearly all of the free-swimming sperm swam in trajectories whose average paths were circular. The flagellar beat pattern of the circular swimmers was asymmetric and nearly planar, and the sperm did not roll. Spermatozoa observed in 25-micron slide preparations produced smaller flagellar bends than sperm swimming in 100-micron preparations and tended to swim in larger circles which were oriented in the plane of the slide. Spermatozoa observed within the cumulus matrix moved in a slow, erratic, sinuous manner, but resumed rapid circling upon leaving the matrix. It was concluded that the ampullar sperm were hyperactivated, retaining this physiological condition as they entered the cumulus. The movement qualitatively resembled that of hyperactivated guinea pig and hamster spermatozoa because these species effectively swim in circles. In contrast, 80% of the ejaculated spermatozoa swam in linear trajectories, resulting from relatively symmetrical, flagellar beat patterns. The percentage of rolling spermatozoa and the rolling frequencies were less in the 25-micron than the 100-micron slide preparations. Thus, the movement parameters of both ampullar and ejaculated spermatozoa were affected by the geometry of their observation chambers. This influence should be taken into account when observing sperm motility in vitro. It could also be important in vivo, where changes in sperm movement in response to epithelial surfaces might provide an advantage for reaching the cumulus mass. Ninety-eight percent of the motile ampullar sperm were observed to have acrosomes, including all spermatozoa found within the cumulus matrix.

Acrosome↗
PubMed1982

Interaction of rabbit spermatozoa and serum complement components.

Unheated rabbit and human sera were found to induce acrosomal loss in rabbit spermatozoa, while similar concentrations of heated sera did not. In addition, human serum did not induce acrosomal loss when pretreated with antiserum to complement component C8, suggesting that acrosomal loss in unheated serum is caused by the membrane attack complex of complement. Human serum complement anaphylatoxins did not induce acrosomal loss, although they are known to induce exocytosis of secretory granules in other cell types. When incubated directly in human or rabbit sera, rabbit spermatozoa fixed complement; i.e., reduced the potential hemolytic activity of the sera. Fixation was suppressed by adding EGTA to reduce free calcium. This indicates that rabbit spermatozoa fix complement by initiating the classical pathway to complement activation. Initiation requires the presence of cell-bound immunoglobulins and the subsequent binding of complement component C1q. Immunoglobulins were detected in detergent extracts of washed ejaculated spermatozoa by a solid-phase radioimmunoassay, and the binding of 125 I-human C1q was detected on samples of living ejaculated spermatozoa. Seminal plasma was found to inhibit complement-induced hemolysis of erythrocytes. These results suggest that, in the absence of seminal plasma, spermatozoa may activate complement where it is present in the male or female tract.

Acrosome↗
PubMedDate not supplied

Movement characteristics of boar sperm obtained from the oviduct or hyperactivated in vitro.

The objectives of this study were to describe hyperactivated motility in boar sperm and to determine the incidence of hyperactivation among boar sperm flushed from the oviduct. Oviducts were surgically removed from 13 gilts 32 hours after mating them to fertile boars. The majority of the sperm flushed from the oviducts was immotile, weakly motile, or stuck to mucus or cellular debris. The mucus could not be penetrated by the sperm. The remaining 3% to 19% of the flushed sperm was free-swimming. Only five hyperactivated sperm were recovered, all from the ampulla of the oviduct. The remainder of the free-swimming sperm travelled in linear trajectories and possessed significantly higher flagellar curvature ratios (the flagella were less bent) than boar sperm measured in diluted semen. Hyperactivated motility was induced in washed ejaculated boar sperm, using a 1-minute pulse of 4 mumol/L calcium ionophore A23187. The ionophore-treated sperm had significantly lower straight-line velocities, linearities, and flagellar curvature ratios than controls, as would be expected for hyperactivated sperm. They were vigorous and swam in circles. It was concluded that, although few hyperactivated boar sperm could be recovered from the oviduct, boar sperm are capable of undergoing hyperactivation.

Animals↗