Decrease in reproductive performance in male rats by frequent mating was investigated under various male to female ratio and different diucpeion of cohabitation. Major parameters for assess-ment were incidence of pregnancy, number of implantation site in the female, and weight and histo-logy of the reproductive organs in the male.
In case of one day pairmating, fertility was close to 100% and number of implantation was 14.8±1.7 (mean±sD). By replacing the female partner every day for five consecutive day, or by prolonged polygamy, the values decreased significantly.
It is clear that when a single male rat was tempted to mate frequently, his reproductive perfor-mance is impaired quickly and, even in vivid sire, 4-5 days of rest is required for recovery. This admonishes that mating schedule in rats should be regulated for assessment of drug effects for repro-duction.

View full abstract

With the aim of using calcium ionophore A23187 (I-A) for pretreating goat spermatozoa in the study of in vitro fertilization, experiments were conducted to assess optimum pretreating conditions of spermatozoa with I-A. Penetration of spermatozoa into zona-free hamster eggs in vitro was used as a parameter to evaluate the pretreatment effects. Ejaculated goat spermatozoa from Japanese native breed were washed, resuspended in a modified Tyrode's solution (BRACKETT & OLIPHANT, 1975; isotonic BO medium) containing 0 to 10 mm caffeine but without bovine serum albumin (BSA) and then admixed with 0.1 to 1.0μm I-A for 0.5 to 3.0 min. Zona-free hamster eggs in 350μl BO medium, which contained the same concentrations of caffeine and 3 mg BSA/ml, were inseminated by intro-ducing 50 μl sperm suspension pretreated with I-A. Eggs and sperm were incubated at 37.5°C under 5% CO₂ in air.
The proportions of penetrated eggs differed according to caffeine concentration, to I-A concentra-tion, to pretreating time with I-A, to sperm concentration at the time of I-A treatment and to in-cubation times after insemination. Majority of the eggs, 73.8 to 94.4%, were penetrated when sper-matozoa were pretreated with 0.5 μm I-A for 2 min at sperm concentration of 25 x 10⁶ cells/ml in the medium containing 2 mm caffeine, Sperm penetration into the eggs was inferred to be accomplished within 3 h after insemination. The selection of males with good sperm motility was also indicated to be an important factor for obtaining high proportions of penetrated eggs.

View full abstract

Bovine morulae, collected from the superovulated heifers 6 days after the estrus, were bisected with a fine glass blade. After the bisection, the monozygotic pairs were either cultured or trans-ferred nonsurgically to recipient heifers. In Group A, one half of the demi-embryos was encased in its own zona pellucida while the other half was left naked. In Group B, both halves were cultured or transferred without zona-pellucida. Six out of 16 demi-embryos (8 monozygotic pairs) in Group A and 7 out of 28 (14 pairs) in Group B developed into normal blastocysts after culture in BMOC-3 for 40 to 46 h. However, there was only one monozygotic pair of normal blastocysts in each of the groups. Twenty-eight demi-embryos (14 pairs) were transferred to 28 recipient animals in Group A, and 4 normal calves, including one pair of monozygotic twin were obtained. In Group B, 3 normal calves were born after the transfer of 16 demi-embryos (8 pairs), but there was no monozygotic twin. These data indicate that the zona pellucida is not absolutely necessary for the normal development of demi-embryo produced from the morula.

View full abstract

The viabilities of bisected hatched blastocysts in the sheep were examined by transferring them to recipients. Embryos were collected surgically on day 7 (onset of estrus: day 0) from a superovulate-ed ewe. Hatched blastocysts were bisected using a micro-blade made from a razor. Four embryos were successfully bisected into 4 pairs of identical half embryos.
These embryos were then transported from National Institute of Animal Industry to Saitama Prefectural Livestock Experiment Station and transferred to recipient ewes immediately after arrival or after frozen-storage.
Two pairs of fresh half embryos were transferred to 2 recipients. Both of the recipients were pregnant. One of them delivered a pair of identical twins and the other did a single lamb. A pair of frozen-thawed half embryos was transferred to a recipient but none developed into lambs.

View full abstract

The present study was undertaken to confirm the report of MCGRATH & SOLTER (1983) who sucess-fully transplanted single pronucleus between one-cell stage eggs using inactivated sendai virus (HVJ).
One or two pronucleus was removed and discarded in a manner which the pipette did not pene-trate the ovum plasma membrane (recipient egg). The pronucleus (ei) was also removed from donor egg in the same way, then a small volume of HVJ was drawn into the pipette.
The recipient egg was held by a suction pipette with the previous site of encleation, and HVJ and karyoplast were in-jected into perivitelline space. The results obtained are as follows.
1) The proportion of fused eggs with karyoplast were 92% and 90% for single or both pronuclei transplantation.
2) The proportion of eggs developed to morula or blastocyst stage was 78 to 87%.
3) The proportion of single and both pronuclei transplant eggs that successfully developed to term was 11% and 19%, respectively.
So far as we know, the present study was the first report for successful pronucler transplanta-tion in mammalian eggs in Japan.

View full abstract

The effect of neonatal thymectomy upon the reproductive function was examined infemale Wistar rats. After female pups were thymectomized within 48 hours of birth, the somatic growth was not inferior to that of controls after 18 days of age, but less than controls from 3 to 15 days of age (P<0.01 or 0.05). The day of vaginal opening in thymectomized rats (41.2±1.02) was similar to that of intact rats (39.9±0.78). The results of incidences of vaginal estrous and proestrous stageor estrous stage alone at 20-day in-tervals from 50 to 169 days of age in thymectomized rats indicated that the ovarian func-tion appeared to decline progressively after 90 days of age. Between thymectomized and intact rats, there was no significant difference in the weight of ovaries, uteri, pituitary gland, thyroid glands and spleen, except the weight of adrenal glands (P> 0.05) at 180 days of age. Histological findings in thymectomized rats indicated the hyperplasia of theinter-stitial cell elements and degeneration of follicles in the ovary and formation of marked cytoplasmic haloes in the basophilic cells of the pituitary gland.

View full abstract

The effect of repeated treatments of PMSG and hCG on the ovulatory response and the number of follicles were determined using Wistar-Imamichi rats. At 75 (±2) day-old, animals received the 1st treatment with each 20 or 40 IU of PMSG and hCGat 16 (±2) days interval.
When rats were treated with 20 (or 40) IU of PMSGandhCG, the number of ova shed per rat decreased markedly from 23.5 (48.4) by the 1st treatment to 9.3 (8.2) by the 3rd treatment (P<0.01 or 0.001). The number of healthy follicles decreased markedly from 336.2 (360.6) to 187.5 (140.3) after the 3rd treatment with 20 (or 40) IU of PMSG (P<0.01 or 0.001). After the 2nd, 3rd or 4th treatment, the number of healthy follicles was signi-ficantly fewer than that in untreated rats at the same ages (P<0.05 to 0.001), except after the 3rd treatment with 20 IU of PMSG and hCG. The number of healthy follicles in un-treated rats decreased with the advance of age. In both untreated and gonadotropin-treated rats, the decrease was more evident in smaller sized healthy follicles.
It is suggested that the low ovulatory response following repeated treatmentswith PMSG and hCG is partly due to a poor recruitment of follicles which are responsive to PMSG.

View full abstract

Accessory spermatozoa were observed in 29 out of 220 (13.2%) chromosomal preparations of mouse blastocysts. No significant difference in the mitotic index was found between the blastocysts with and without spermatozoa. Polyploidy was detected in only one blastocyst with accessory spermatozoa.
Epon semi-thin sections showed the presence of accessory spermatozoa with sperm heads in the perivitelline space in 4 out of 30 blastocysts.
Transmission electron microscopy showed the presence of accessory spermatozoa in 2 out of 15 blastocysts. In one blastocyst, a sperm head was observed in the perivitelline space. In the other blastocyst, a middlepiece in the blastocoele and a sperm tail in the perivitelline space, blastocoele and trophectoderm were observed. The cell membrane of these spermatozoa was degenerated. There was no abnormality in the morphology of the nuclei, cytoplasmic organelles and cell membrane in these blastocysts. Spermatozoa which were attached to or penetrated into the zona pellucida were not detected under the light and electron microscope.

View full abstract

[in Japanese]

View full abstract