Yusuke Kuroda

A Comparison of the Histological Structure of the Placenta in Experimental Animals

The primary function of the placenta is to act as an interface between the dam and fetus. The anatomic structure of the chorioallantoic placenta in eutherian mammals varies between different animal species. The placental types in eutherian mammals are classified from various standpoints based on the gross shape, the histological structure of the materno-fetal interface, the type of materno-fetal interdigitation, etc. Particularly, the histological structure is generally considered one of the most useful and instructive classifications for functionally describing placental type. In this system, three main types are recognized according to the cell layers comprising the interhemal area: (1) epitheliochorial type (horses, pigs and ruminants), (2) endotheliochorial type (carnivores) and (3) hemochorial type (primates, rodents and rabbits). The number of cell layers in the interhemal area is considered to modify the transfer of nutrients between maternal and fetal blood and is one of the important factors with respect to the difference in placental permeability between animal species. Therefore, in reproductive and developmental toxicity studies, careful attention should be paid to the histological structure of the interhemal area when extrapolating information concerning placental transfer characteristics to different animal species.

Background Data on Developmental Parameters During the Gestation Period in Rats

Background data during the gestation period were obtained from 128 Wistar Hannover GALAS rats and 26 Crl:CD(SD) pregnant rats in the control groups of our previous toxicity studies. The body weights of dams in the Wistar Hannover GALAS rats were significantly lower throughout the gestation period than those in the Crl:CD(SD) rats. In contrast, the time-dependent change in the body weight gain (%) of dams showed very similar trends in both strains. The mean number of live embryos/fetuses in the Wistar Hannover GALAS rats was 12.0, and was lower than that (14.5) in the Crl:CD(SD) rats. The placental weights gradually increased with pregnancy progression and reached a plateau on gestation day (GD) 19, although the embryo/fetal weights rapidly increased from GD 17 to GD 21. The embryo/fetal weights in the Wistar Hannover GALAS rats were significantly lower on only GD 21 than those in the Crl:CD(SD) rats. It is considered that this fetal weight difference between the strains develops during the fetal period, but not during the organogenesis period. In contrast, there were no differences in the placental weights between the two strains. Microscopically, the thickness of the labyrinth zone in the Wistar Hannover GALAS rats was thicker throughout the gestation period than that in the Crl:CD(SD) rats.

Effect of estrogen on rat placental development depending on gestation stage

We examined the sequential histopathological changes in the placenta from rats exposed to estrogen. 17 β-estrogiol-3-benzoate was intraperitoneally administered at 100 μg/animal/day during GD 6 to GD 8 (GD6-8 treated group), GD 9 to GD 11 (GD9-11 treated group) and GD 12 to GD 14 (GD12-14 treated group), and the placentas were sampled on GDs 11, 13, 15, 17, and 21. Fetal mortality rates were increased up to approximately 50% in the GD6-8 and 9-11 treated groups, but there was no change of fetal weight on GD 21. An increase in placental weight and a reduction in fetal/placental weight ratio were detected during GD 17 to GD 21 in the GD6-8 treated group. Histopathologically, hypoplasia of metrial gland was detected with defective development of spiral arteries in the GD6-8 and GD9-11 treated groups. A decrease in the thickness of metrial gland was observed from GD 11 onwards in the GD6-8 treated group and from GD 13 onwards in the GD9-11 treated group. The endovascular trophoblasts invaded into the spiral arteries in the deep part of metrial gland in these treated groups. The number of phospho-histone H3 positive cells was decreased on GD 11 or GD 13 in these groups. In the decidua basalis, transitory necrosis was observed with hemorrhage on GD 13 in the GD6-8 and GD9-11 treated groups. In the labyrinth zone, cystic dilatation of the sinusoid was observed with congestion in the GD6-8 treated group, resulting in an increased placental weight. Therefore, we consider that estrogen inhibits the proliferation of decidualized endometrial stromal cells in the metrial gland, and leads to metrial gland hypoplasia with less development of the spiral arteries. The reduced utero-placental blood flow is supposed to be one of the important factors for poor reproductive performance.

Histopathology of a wavy medaka

Wavy medakas are medakas that exhibit spinal curvature characterized by dorsoventrally curved vertebrae. We found a spontaneous wavy medaka in our experimental stock and subjected it to a histopathological examination. Macroscopically, the wavy medaka’s spine formed an M shape, and its vertebrae displayed a dorsoventral curvature that started at the third vertebral bone. Microscopically, the vertebral cavities were filled with fibrous tissue, which was similar to that seen in the central parts of the intervertebral discs of a normal medaka. The vertebral joints were composed of vacuolated notochord cells without intervertebral disc formation. These changes were also observed in the caudal region, which exhibited less curvature. In the normal medaka, the intervertebral discs form via the regression of the notochord that plays a key role in the development of vertebrae and disc formation. We concluded that notochordal subinvolution had induced intervertebral disc dysplasia, leading to lordokyphosis, in the wavy medaka.

Histomorphological comparison of rat placentas by different timing of chlorpromazine-administration.

The effects of chlorpromazine-treatment timing on the development of the placenta in pregnant rats were examined. Chlorpromazine was administered intraperitoneally at 100mg/kg on gestation day (GD) 11 (GD11-treated group), GD 13 (GD13-treated group) or GD 15 (GD15-treated group) into pregnant rats. All treated dams exhibited decreased body weight, prone position, hypothermia, loss or decrease of locomotor activity, etc. The fetal mortality rates were increased up to 42.9% in the GD11- and GD13-treated groups and up to 16.7% in the GD15-treated group. The embryo/fetal weight was on a declining trend from GD 16 onward, and the intrauterine growth retardation (IUGR) rates on GD 21 were increased in all treated groups. The placental weight showed a declining trend from GD 15 onward in all treated groups. Histopathologically, apoptosis was detected 1 or 2 days after treatment, and led to hypoplasia in the labyrinth zone and metrial gland, and cystic degeneration in the basal zone on GD 21 in all treated groups. There was no difference in the histopathological lesions on GD 21 among the treated groups. Thus, it is considered that chlorpromazine-induced placental toxicity is characterized in that there is no obvious specific sensitive period from GD 11 to GD 15. Chlorpromazine induced a non-specific transient development retardation of the placenta by apoptosis independently of the cell proliferation period in each part/zone.

Effect of chlorpromazine on rat placenta development

We examined the sequential histopathological changes in the placentas from rats exposed to chlorpromazine. Chlorpromazine was intraperitoneally administered on GD 14 at 50 and 100 mg/kg and the placentas were sampled on GDs 14.5, 15, 17 and 21. The incidence of dams with complete fetal resorption was increased from GD 17 up to 20% at 50 mg/kg and 44.4% at 100 mg/kg. The embryo/fetal weights reduced on GDs 15 and 17 at 50 mg/kg and during GDs 15-21 at 100 mg/kg. The placental weights reduced on GD 17 at 50 mg/kg and during GDs 14.5-21 at 100 mg/kg. Histopathologically, in the labyrinth zone, apoptotic cells were scattered in the trophoblastic septa without inhibition of cell proliferation on GDs 14.5 and 15 at 50 and 100 mg/kg in a dose-dependent manner. A decrease in trophoblasts led to labyrinth zone hypoplasia. In the basal zone, apoptotic cells were scattered on GDs 14.5 and 15 at 100 mg/kg, and most of them appeared to be glycogen cells. A decrease in glycogen cells induced the delayed development of glycogen cell islands and the subsequent remaining glycogen cell islands, and led to the cystic degeneration of glycogen cells. In addition, failure of development of the glycogen cell islands led to the impaired interstitial invasion of the glycogen cells, and then metrial gland hypoplasia occurred.

Effect of dibutyltin on placental and fetal toxicity in rat

In order to elucidate the effect of chorioallantoic and yolk sac placenta on the embryonic/fetal toxicity in dibutyltin dichloride (DBTCl)-exposed rats, we examined the histopathological changes and the tissue distribution of dibutyltin in the placentas and embryos. DBTCl was orally administered to the groups at doses of 0 mg/kg during gestation days (GD)s 7-9 (control group) and 20 mg/kg during GDs 7-9 (GD7-9 treated group), and GDs 10-12 (GD10-12 treated group). The total fetal mortality was increased, and malformations characterized by craniofacial dysmorphism were detected in the GD7-9 treated group. The embryonic/fetal weight and placental weight showed a decrease in both DBTCl-treated groups. Histologically, some embryos on GD 9.5 in the GD7-9 treated group underwent apoptosis without any changes of yolk sac. In the laser ablation-inductively coupled plasma-mass spectrometry analysis (LA-ICP-MS), tin was detected in the embryo, allantois, yolk sac, ectoplacental cone and decidual mass surrounding the conceptus on GD 9.5 in the GD7-9 treated group. Thus, it is considered that the embryo in this period is specifically sensitive to DBTCl-induced apoptosis, compared with other parts. The chorioallantoic placentas in both DBTCl-treated groups showed the developmental delay and hypoplasia in the fetal parts of placenta, resulting from apoptosis and mitotic inhibition. Thus, it was speculated that the DBTCl-induced malformations and fetal resorption resulted from the apoptosis in the embryo caused by the direct effect of DBTCl. The DBTCl-induced lesions in the chorioallantoic placenta were a non-specific transient developmental retardation in the fetal parts of placenta, leading to intrauterine growth retardation.

Pancreatic Ductal Adenocarcinoma in a Wistar Hannover GALAS Rat

There are no reported spontaneous cases of pancreatic ductal adenocarcinoma (PDAC), and there are few reports about chemically-induced PDAC in rats. We encountered a PDAC in a Wistar Hannover GALAS rat that had been subjected to a medium-term multiorgan carcinogenicity bioassay. This article describes the histological and histochemical findings of the tumor. The tumor was located in the pancreatic tissue and had not invaded the liver parenchyma or the mucosal layer of the alimentary tract. The tumor cells were atypical and were mainly arranged in small tubules. In addition, abundant stroma and mucus production were observed in the tumor. In an immunohistochemical examination, the tumor cells were positive for cytokeratin, Sox9 and pancreas duodenum homeobox 1 and negative for amylase 2A and insulin. Therefore, the tumor was diagnosed as a PDAC based on its histological and histochemical findings. We considered that the tumor was caused by the carcinogens administered during the abovementioned bioassay.