Storage of spermatozoa in the female genital tract of the vespertilionid bat, Scotophilus heathi

Sperm storage by females across the animal phyla: A survey on the occurrence and biomolecules involved in sperm storage

Long-term sperm storage by females in various regions of the oviduct is documented across many invertebrate and vertebrate species. Although, many reports emphasize on the histology, histochemistry and ultrastructural features of sperm storage, very little is known about the mechanisms underlying the sperm storage. The current review documents the occurrence of sperm storage by females in a wide array of invertebrate and vertebrate species. This review also provides an insight on the presence of various molecular factors of the sperm storage tubules presumably responsible for the prolonged sperm storage with an emphasis on a model reptile, the Indian garden lizard, Calotes versicolor which contains a unique approximately 55-kDa protein in its utero-vaginal lavage and found to inhibit washed epididymal sperm motility in a concentration and time-dependent manner in a reversible fashion.

Sperm Storage in the Female Reproductive Tract

The capacity for sperm storage within the female reproductive tract occurs widely across all groups of vertebrate species and is exceptionally well developed in some reptiles (maximum duration seven years) and fishes (maximum duration >1 year). Although there are many reports on both the occurrence of female sperm storage in diverse species and its adaptive benefits, few studies have been directed toward explaining the mechanisms involved. In this article we review recent findings in birds and mammals in an effort to develop hypotheses that could be translated into research applications in animal breeding technologies. There are pockets of evidence to suggest that the local epithelial cells, sometimes arranged as sperm storage tubules, can respond to spermatozoa by producing heat shock proteins as well as providing an environment rich in antioxidants. Moreover, the local immune system seems to tolerate the arrival of spermatozoa, while retaining the ability to combat the arrival of infectious microorganisms.

Changes in glucose and carnitine levels and their transporters in utero-tubal junction in relation to sperm storage in the vespertilionid bat, Scotophilus heathi

Prolonged sperm storage over winter is a common feature of reproduction in some bats. In order to understand how sperm storage in the female genital tract of the vespertilionid bat, Scotophilus heathi (Greater yellow bat), is controlled, we compared concentrations of glucose and the fatty-acid carrier carnitine in the blood, and carnitine concentrations and levels of expression of the glucose transporters (GLUTs) and the carnitine transporter OCTN2 in the utero-tubal junction of females during non-storage (early winter) and sperm-storage periods (late winter-early spring). During the sperm-storage period (December-January) blood glucose concentrations declined, as did the expression of GLUT3 and GLUT5 in the utero-tubal junction. At the same time there were increases in the concentration of carnitine, and expression of OCTN2 and hormone-sensitive lipase (HSL) in the utero-tubal junction. These results suggest that prolonged sperm storage is enhanced by decreased glucose availability but increased free fatty acid availability at the site of sperm storage. Increases in expression of GLUT4 and GLUT8 in late winter suggest a role for these GLUTs in increasing sperm motility prior to fertilization.

Changes in the expression of HSL and OCTN2 in the female reproductive tract of the bat, Scotophilus heathii in relation to sperm storage

The aim of this study was to compare the changes in the expression of hormone sensitive lipase (HSL) and organic cation transporter 2 (OCTN2) in different regions of the female reproductive tract of bats (Scotophilus heathii) during the period of sperm storage. Western blot analysis revealed that both HSL and OCTN2 showed elevated expression in the utero-tubal junction, the site of sperm storage, compared to the vagina, cervix and uterus. An immunohistochemical study showed localization of HSL and OCTN2 in the cytoplasm of luminal epithelial cells in the utero-tubal junction of S. heathii, which suggests a role of fatty acids metabolism at the site of sperm storage. Furthermore, this study showed the presence OCTN2 immunostaining in the tail of stored sperm, which suggests a direct role of carnitine in sperm physiology. However, the role of carnitine in sperm storage needs further investigation. It is hypothesized that the utero-tubal junction may be finely tuned with fat depletion to support sperm storage in the female genital tract of S. heathii.

Mechanisms of sperm storage in the female reproductive tract: an interspecies comparison

Once semen has been collected for artificial insemination, it is diluted into extenders designed to prevent its deterioration over the period prior to insemination. If the semen is not frozen, the extenders provide protection for a period of a few hours to a few days, depending on species. Despite the efforts of biotechnologists to increase the duration of storage without compromising fertility, there has been relatively little progress for many years. However, comparative studies in diverse species have revealed that long-term sperm storage (up to months and years) within the female reproductive tract is relatively commonplace in reptiles, fishes, birds and amphibians. Even among mammals, some species of bat have evolved mechanisms for storing spermatozoa for several months in the uterus or oviduct so that they can mate in the autumn but postpone fertilization until the spring. We currently know little about the mechanisms that support such long-term sperm storage, mainly because evidence from such species is either absent or fragmentary. Nevertheless, parallels between mammalian and other systems, where spermatozoa are sequestered in sperm storage tubules, suggest that the enclosure of spermatozoa within pockets of epithelial cells may be sufficient to achieve long-term sperm storage. In addition, recent evidence from sperm-storing bats has suggested an alternative, or additional, hypothesis that the modulation of apoptosis within epithelial cells is important in controlling sperm survival. Despite a lack of direct experimental evidence from a wide variety of species, I propose that there is now enough evidence to warrant investigation of these hypotheses.

Selectivity in the transport of spermatozoa to oviductal reservoirs in the menstruating fruit bat, Carollia perspicillata

To better document the timing of ovulation and fertilization, female reproductive tracts were collected every 12 h from captive-bred fruit bats (Carollia perspicillata) on days 1–3 postcoitum and examined histologically. This also permitted observations on sperm transport, storage, and disposition. As the animals had previously been sexually segregated, most had been cycling and possessed menstrual uteri at the time of collection. Menstruation is periovulatory in this species. A widespread, headfirst orientation of spermatozoa to the uterine mucosa was observed in specimens apparently collected soon after insemination. Thereafter, however, this relationship was limited in most cases to the area around the entrance of each uterotubal junction (UTJ). A small number of spermatozoa also colonized the UTJs, which functioned as temporary sperm reservoirs on days 1–2. AlthoughC. perspicillatais monovular, no consistent differences were observed between the two oviducts in the pattern of sperm storage and release. Very few sperm were ever observed in the isthmus or ampulla (the site of fertilization). Menstrual debris (including fine particulate matter) and leukocytes present in the uterine cavity in most tracts did not gain access to the UTJ with the spermatozoa. Smooth muscle and abundant elastic fibers in the wall of the intramural UTJ, as well as receptors on its luminal epithelial cells, may play roles in the selective transport of spermatozoa to the fertilization site. While some spermatozoa are phagocytosed in the uterine lumen or by epithelial cells in the UTJ, the fate of most is probably expulsion into the vagina.

Evidence of androgen-dependent sperm storage in female reproductive tract of Scotophilus heathi

The aim of present study was to investigate the role of androgen in sperm storage in the female genital tract of Scotophilus heathi. Spermatozoa were observed in the distal part of oviduct and utero-tubal junction of all the female bats collected between January and early March. Increase in circulating testosterone level coincided with the arrangement of sperm with their head oriented towards the epithelial lining of reproductive tract. Immunocytochemical and Western blot analysis revealed the presence of androgen receptor (AR) only in the distal part of the oviduct and utero-tubal junction, the site of sperm storage. Localization of AR in the cytoplasm of luminal epithelial cells in utero-tubal junction of S. heathi suggests non-genomic action of androgen at the site of sperm storage. Further study showed the presence of intense immunoreactivity of androgen binding protein (ABP) in the glandular epithelial cells of utero-tubal junction. It is hypothesized that androgen creates a unique microenvironment e.g. secretion of ABP within lumen of utero-tubal junction which helps to store spermatozoa for prolonged period in the female genital tract of S. heathi.

Sperm distribution in the genital tract of the bitch following artificial insemination in relation to the time of ovulation

In the present study, sperm distribution in the genital tract of the bitch following artificial insemination (AI) in relation to the time of ovulation was investigated by histology, scanning electron microscopy (SEM) and flushing. Ten bitches were inseminated intravaginally with 500 × 106spermatozoa: three dogs before ovulation, four dogs during ovulation and three dogs after ovulation. Ovariohysterectomy was performed 24 h after AI. Half of the genital tract was divided into nine segments (cervix, corpus uteri, caudal, middle and cranial uterine horn (UTH), utero–tubal junction (UTJ), isthmus, ampulla and infundibulum), which were processed for histology and SEM. The contralateral UTH and uterine tube (UT) were flushed, and several sperm characteristics were assessed. Histology revealed that the spermatozoa were mainly located in the uterine glands and at the UTJ, while very few spermatozoa were detected in the UT. Insemination during ovulation resulted in higher percentages of glands with spermatozoa in the different parts of the uterus (P< 0.05). Evaluation by SEM showed higher numbers of spermatozoa in several parts of the uterus for bitches inseminated during ovulation (P< 0.05). The mean number of spermatozoa flushed from the UTH and the UT was low. No significant differences in the evaluated sperm quality parameters were found between the flushings of the UTH and the UT. In conclusion, based on our findings, the uterine glands and the UTJ might act as sperm reservoirs in the bitch and sperm transport in the genital tract is affected by the time of AI in relation to ovulation.

Prolonged storage of spermatozoa in the genital tract of female Mexican big-eared bats (Corynorhinus mexicanus): the role of lipid peroxidation

The results of this work support the existence of sperm storage in Corynorhinus mexicanus, a vespertilionid bat endemic to Mexico, and evidence is presented that modulation of peroxidative toxicity plays a role in the mechanism of prolonged sperm storage in Chiroptera. Spermatozoa were obtained from C. mexicanus by retrograde perfusion of the cauda epididymis, and from genital washings from previously inseminated females captured during reproductive activity. Ejaculated pig spermatozoa were simultaneously studied as controls. Lipid peroxidation was determined in both the presence and absence of genital secretions obtained from previously inseminated female C. mexicanus by measuring malondialdehyde generated during aerobic incubation of spermatozoa suspensions. The number of spermatozoa recovered from the cauda epididymis decreased steadily from November through January. Corpora lutea were observed in January. None of the female bats captured between October and January were pregnant, but some females captured in mid-February were already pregnant. Spermatozoa of C. mexicanus showed substantial lipid peroxidation activity (0.64 ± 0.11 nmol malondialdehyde was produced by 108 spermatozoa per 22 h), about half of that observed in ejaculated pig spermatozoa. Incubation of pig and C. mexicanus spermatozoa in the presence of bat female genital tract washings induced highly significant concentration-dependent inhibition of lipid peroxidation.

The relationship between testicular activity, accessory sex glands, and circulating steroid concentration during the reproductive cycle in a male Indian vespertilionid bat,Scotophilus heathi

The relationship between spermatogenesis, accessory sex glands, Leydig cell activity, and circulating concentrations of testosterone and androstenedione in male Scotophilus heathi, the greater yellow bat, was studied. Scotophilus heathi accumulated fat prior to winter dormancy at Varanasi, India. Spermatogenesis was seasonal and extended over the period November to March, with the testes becoming quiescent during winter. Monthly changes in testis and accessory sex gland masses showed two peaks, in November and January. Accessory gland secretory activity and fructose concentration showed only one peak, during January and February, which coincided with the mating period. The mass in the epididymides and their histological changes reflect the influence of testicular spermatogenesis. However, sperm were found in the cauda epididymidis during the spermatogenically quiescent period of winter dormancy. The Leydig cells showed intense side chain cleavage (SCC) enzyme activity from August to December. In late January and February, males had smaller Leydig cells and low SCC activity. Monthly changes in serum testosterone concentration included two peaks in November and January, coinciding with peak spermatogenic activity, whereas androstenedione showed only one peak, an unusually high concentration in November. The circulating serum androstenedione concentration may be responsible for the unique reproductive activity noted in this bat.

Seasonal changes in circulating serum concentration and in vitro testicular secretion of testosterone and androstenedione in the male vespertilionid bat (Scotophilus heathi)

Seasonal changes in the testicular activity were studied in the male Greater Yellow bat, Scotophilus heathi, in Varanasi, India (25 degrees N, 83 degrees E). The seasonal pattern of body weight of male bats was also recorded and compared with circulating androstenedione (A) and testosterone (T) concentration. There was a gradual increase in the body weight of the bat from September onward mainly due to accumulation of adipose tissue. Finally, body weight reached a peak level in November. Two periods of peak testicular weight and serum T concentration but only one peak of serum A concentration were observed. The first peak of T coincided closely with the peak A concentration and increased body weight. The first peak of T occurs several months before the time of mating and ovulation. The second peak of T correlated closely with the period of mating. In vitro study showed seasonal variation of the testicular responsiveness to LH stimulation. In vitro study also showed two peaks in the T but only one peak in the A production by testes in response to LH during different phases. Preliminary study showed that IGF-I but not insulin augmented hCG induced T production by testes in vitro. Our observation of an increase in serum A concentration during the period of overfeeding and weight gain and decline in A during the period of weight loss in S. heathi adds strength to the concept that nutritional status can influence hormonal function. This may be the reason for asynchrony between male and female gametic cycle found among vespertilionid bats.

Studies on prolonged spermatozoa survival in Chiroptera: a morphological examination of storage and clearance of intrauterine and cauda epididymal spermatozoa in the bats Myotis lucifugus and M. velifer

The cauda epididymidis, uterine corpus, and cornua and uterotubal junction of Myotis function to retain and preserve normal spermatozoa throughout hibernation. In none of the sites do spermatozoa show features that might account for their extended viability. Spermatozoa stored in the uterus and epididymis show no special orientation toward the epithelium lining these sites, whereas an intimate relationship is established between some sperm and the epithelial cells of the uterotubal junction which might either account for extended postcoital sperm survival or forecast their removal from further participation. Transmission and scanning electron microscopic observations do not disclose any morphological changes in stored luminal spermatozoa. A low rate of phagocytosis of sperm is evident in the female tract during hibernation. However, spermatozoa are evidently not vulnerable to being removed from the storage sites until spring arousal when ovulation occurs. Both uterotubal epithelial cells and phagocytes appear to be involved in the disposal of spermatozoa in the female, whereas epididymal spermatozoa apparently are primarily voided during urination. A mechanism that delays capacitation must underlie the ability of spermatozoa to survive in the female reproductive tract of the hibernating bat.