Carcinoma in situ (CIS) is the noninvasive precursor of most human testicular germ cell tumors. In normal seminiferous epithelium, specialized tight junctions between Sertoli cells constitute the major component of the blood-testis barrier. Sertoli cells associated with CIS exhibit impaired maturation status, but their functional significance remains unknown. The aim was to determine whether the blood-testis barrier is morphologically and/or functionally altered. We investigated the expression and distribution pattern of the tight junction proteins zonula occludens (ZO) 1 and 2 in normal seminiferous tubules compared to tubules showing CIS. In normal tubules, ZO-1 and ZO-2 immunostaining was observed at the blood-testis barrier region of adjacent Sertoli cells. Within CIS tubules, ZO-1 and ZO-2 immunoreactivity was reduced at the blood-testis barrier region, but spread to stain the Sertoli cell cytoplasm. Western blot analysis confirmed ZO-1 and ZO-2, and their respective mRNA were shown by RT-PCR. Additionally, we assessed the functional integrity of the blood-testis barrier by lanthanum tracer study. Lanthanum permeated tight junctions in CIS tubules, indicating disruption of the blood-testis barrier. In conclusion, Sertoli cells associated with CIS show an altered distribution of ZO-1 and ZO-2 and lose their blood-testis barrier function.

In the glandular stomach, gap junctional intercellular communication (GJIC) plays an important role in the gastric mucosal defense system, and loss of GJIC is associated with ulcer formation. In spite of the high incidence of gastric ulcers in horses, particularly at pars nonglandularis, the presence of gap junctions in the equine stomach has not yet been studied. The objective was to obtain basic data on the distribution of gap junction protein connexin 32 (Cx32) in the different regions of normal equine gastric mucosa. Samples of mucosa were taken from seven horses at cardiac, fundic, and pyloric region and pars nonglandularis. To detect Cx32, immunohistochemical staining and Western blot analysis were performed. Corresponding mRNA was shown by RT-PCR and localised in tissue sections by in situ hybridisation. Cx32 was found in the glandular regions, whereas it was not detectable in squamous mucosa. Within the glandular epithelium, Cx32 was abundant in surface and foveolar cells and decreased towards the proliferative zone of the glands. These results suggest that gap junctions develop during the maturation of surface cells. Whether the lack of Cx32 at pars nonglandularis contributes to its susceptibility for developing ulcers, has to be further elucidated.

The donkey placenta is diffuse and epitheliochorial with numerous microplacentomes consisting of a fetal microcotyledonary and a maternal microcaruncular part. The microplacentomal vasculature during the last third of pregnancy has been investigated by light microscopy in comparison to scanning electron microscopy of the materno-fetal contact surface and corrosion casts of blood vessels after plastic instillation from either the microcotyledonary or the microcaruncular side, and, for the first time in a perissodactyle, from both sides. Morphological data were semiquantitatively evaluated. The supplying parts of both, the microcotyledonary and the microcaruncular vascular system are strictly proximo-distally oriented, thus reaching the capillary systems or working parts in the shortest way possible. The straight course of the vasculature, particularly on the fetal side, suggests the occurrence of venulo-arteriolar back diffusion. The fetal capillary system consists of convolutes confronting the maternal septal capillary complexes in a countercurrent way. This materno-fetal blood flow interrelationship is highly efficient in terms of placental exchange, which is further supported (1) by dilations and increasing coiling of the fetal venular capillary limbs in particular and (2) by a decrease in the interhaemal distance from 12.5 to 7.2 microm between the two capillary systems. Besides the countercurrent blood flow interrelationship, some maternal branch arterioles reach the septal capillary system from the maternally oriented pole of the microplacentome or microcaruncle, respectively, resulting in the less efficient crosscurrent blood flow. Hence, in the donkey placenta fetal and maternal blood vessels meet in a mix of countercurrent and crosscurrent flow patterns.

Gap junctional inter‐cellular communication (GJIC) is known to be important in the maintenance of tissue homeostasis. Evidence is accumulating that GJIC plays an important role in the gastric mucosal defence system and that the loss of GJIC is associated with gastric ulcer formation. The prevalence of gastric ulceration in foals and horses is high. However, there are no studies about the presence of gap junctions in gastric mucosa of horses. The purpose of this study was to investigate the distribution pattern of the gap junction protein 32 in normal gastric mucosa of horses. Immunocytochemical observations were made with light microscopy on cryosections of fresh frozen gastric mucosa from the fundic region, pyloric region, margo plicatus and pars nonglandularis. Immunohistochemical staining was performed by standard immunoperoxidase techniques using an anti‐connexin 32 polyclonal antibody. In Situ Hybridization, Western Blot Analysis and RT‐PCR were performed to confirm the presence of connexin 32. In normal horse gastric mucosa, connexin 32 was abundant in the surface epithelium and in a decreasing staining gradient extending down to the neck of the glands. Gastric surface mucous cells are formed in the neck of the glands and migrate along the foveola toward the mucosal surface. So, immature forms of surface mucous cells are found in the generative zone and in the deep part of the foveola, whereas well‐matured ones cover the upper part of the foveola and the luminal surface of the mucosa. Therefore, these findings are in line with other studies, which described larger and more numerous gap junctions in mature surface mucous cells than in immature cells. These results show that gap junctions develop during the maturation of surface mucous cells and suggest that GJIC between gastric surface mucous cells plays an important role in the regulation of cell differentiation and in tissue homeostasis. Further studies are required to investigate the distribution pattern of connexin 32 in the gastric mucosa of horses with gastric ulcer.