Endocanalicular transendothelial crossing (ETC): A novel intravasation mode used by HEK-EBNA293-VEGF-D cells during the metastatic process in a xenograft model

In cancer metastasis, intravasation of the invasive tumor cell (TCi) represents one of the most relevant events. During the last years, models regarding cancer cell intravasation have been proposed, such as the “endocanalicular transendothelial crossing” (ETC) theory. This theory describes the interplay between two adjacent endothelial cells and the TCi or a leukocyte during intravasation. Two endothelial cells create a channel with their cell membranes, in which the cell fits in without involving endothelial cell intercellular junctions, reaching the lumen through a transendothelial passage. In the present study, ten SCID mice were subcutaneously xenotransplanted with the HEK-EBNA293-VEGF-D cell line and euthanized after 35 days. Post-mortem examinations were performed and proper specimens from tumors were collected. Routine histology and immunohistochemistry for Ki-67, pAKT, pERK, ZEB-1, TWIST-1, F-actin, E-cadherin and LYVE-1 were performed followed by ultrastructural serial sections analysis. A novel experimental approach involving Computed Tomography (CT) combined with 3D digital model reconstruction was employed. The analysis of activated transcription factors supports that tumor cells at the periphery potentially underwent an epithelial-to-mesenchymal transition (EMT)-like process. Topographical analysis of LYVE-1 immunolabeled lymphatics revealed a peritumoral localisation. TEM investigations of the lymphatic vessels combined with 3D digital modelling enhanced the understanding of the endotheliocytes behavior during TCi intravasation, clarifying the ETC theory. Serial ultrastructural analysis performed within tumor periphery revealed numerous cells during the ETC process. Furthermore, this study demonstrates that ETC is an intravasation mode more frequently used by the TCi than by leukocytes during intravasation in the HEK-EBNA293-VEGF-D xenograft model and lays down the potential basis for promising future studies regarding intravasation blocking therapy.

Chronic administration of green tea extract to TRAMP mice induces the collapse of Golgi apparatus in prostate secretory cells and results in alterations of protein post-translational processing

Considering its long latency, prostate cancer (PCa) represents an ideal target for chemoprevention strategies. Green tea extract (GTE) has been proved to be one of the most promising natural substances capable of inhibiting PCa progression in animal models (transgenic adenocarcinoma of mouse prostate), as well as in humans. However, the cellular targets of the GTE action are mostly unknown. The main objective of this work was to investigate whether the endoplasmic reticulum (ER) and the Golgi apparatus (GA), known to be actively involved in sensing stress stimuli and initiating and propagating cell death signalling, may represent the subcellular targets of GTE action. To this end, 42 TRAMP mice were divided into four experimental groups: groups II and IV, received GTE in tap water (0.3 g/100 ml solution) starting at 8 weeks of age and up to the time of sacrifice. Groups I and III were respective age-matched water-fed controls. The animals were sacrificed after 4 weeks (groups I and II) or 40 weeks of treatment (groups II and IV). We also treated TRAMP-C2 cells with GTE (20 µg/ml for 7 days) to check the expression profile of clusterin (CLU), a protein involved in prostate tumourigenesis, extensively processed through ER-GA before being secreted through the plasma membrane. In vivo we found that chronic administration of GTE in TRAMP mice results in collapse of ER and GA in prostate epithelial cells. Consistently, in vitro we found that the mature, fully processed form of CLU, sCLU, is strongly reduced by GTE treatment in TRAMP-C2 cells. Taking into account the sCLU biogenesis dependence on the ER-GA integrity and the proposed anti-apoptotic role of sCLU, the possibility for GTE to counteract PCa progression by interfering with sCLU biogenesis is suggested.

The "intraendothelial canalicular formation": the route for lymphocyte diapedesis at the level of peripheral and mucosa-associated lymphoid tissue HEVs

How the lymphocyte crosses the blood endothelium during transendothelial migration is demonstrated through the study of serial sections of high endothelial venules (HEVs) of peripheral (mesenteric lymph nodes) and mucosa-associated lymphoid tissue (Peyer's patches, vermiform appendix) during normal lymphocyte homing and experimental intestinal inflammation. The sequence of serial ultrastructural features of lymphocytes englobed in the endothelial wall at different moments of transmigration made it possible to bring out that their transendothelial migration toward the extracellular matrix of lymphoid tissues occurs through an intraendothelial canalicular formation constituted by two adjacent endothelial cells that have closed interendothelial junctions. This intraendothelial canalicular formation, morphologically unlike the transcellular and paracellular migratory pathways, is an innovative model of migratory route for lymphocyte diapedesis that does not compromise the continuity of the endothelial wall. The increased presence of lymphocytes and intraendothelial canalicular formations during experimental inflammation and the metabolic hyperactivity of the spring/summer months compared to the lethargic fast in Chiropters underscores an influence on lymphocyte traffic through the HEVs of the peripheral and mucosa-associated lymphoid tissue.

Tumor cell transendothelial passage in the absorbing lymphatic vessel of transgenic adenocarcinoma mouse prostate

The distribution and fine structure of the tumor-associated absorbing lymphatic vessel in the tumor mass of prostate adenocarcinoma and of seminal vesicle metastasis in transgenic mice was studied for the purpose of understanding the modality of tumor cell transendothelial passage from the extravasal matrix into the lymphatic vessel. In the tumor mass, two main cell populations were identified: stromal tumor cells and the invasive phenotype tumor (IPT) cells, having characteristics such as a highly electron-dense matrix rich in small granules lacking a dense core and massed nuclear chromatin, which is positive to immunostaining with anti-SV40 large T antigen antibody. Based on the ultrastructural pictures of different moments of the IPT cell transendothelial passage by ultrathin serial sections of the tumor-associated absorbing lymphatic vessel, the manner of its transendothelial passage through the intraendothelial channel, without involving intercellular contacts, was demonstrated. The presence of IPT cells in the parenchyma of satellite lymph node highlights its significant role in metastatic diffusion. The intraendothelial channel is the reply to the lack of knowledge regarding the intravasation of the tumor cell into the lymphatic circulation. The lymphatic endothelium would organize this channel on the basis of tumor cell-endothelial cell-extravasal matrix molecular interactions, which are as yet unidentified.

The modality of transendothelial passage of lymphocytes and tumor cells in the absorbing lymphatic vessel

The modality of transendothelial passage of the macromolecules and cells (lymphocyte and cancer cells) in the absorbing lymphatic vessel (ALV) and the tumor-associated absorbing lymphatic (TAAL) vessel is studied. On the basis of the peculiar plasticity of the lymphatic endothelial cell of these vessels (lacking a continuous basement membrane, pores and open junctions) the endothelial wall organizes formation of the intraendothelial channel, by means of molecular interactions as yet unidentified. The remarkable finding of the intravasation of lymphocyte and experimental tumor cancer cells (T84 colon Adenocarcinoma, B16 melanoma in nude mice and spontaneous prostate adenocarcinoma in transgenic mice) should be stressed. This intravasation takes place, under both physiologic and pathological conditions, following the same transendothelial morphological modality, i.e. the intraendothelial channel - a dynamic and transient entity - is probably also induced by similar molecular interactions, a crucial point that merits future research.

On the transendothelial passage of tumor cell from extravasal matrix into the lumen of absorbing lymphatic vessel

The aim of the research is the study of ultrastructural characteristics of the absorbing lymphatic vessel and of tumor cell passage through the endothelial lymphatic wall in (a) subcutaneous xenografts of T84 colon adenocarcinoma and B16 melanoma cell lines in nude mice and (b) human colorectal cancer. It was found that the tumor-associated absorbing lymphatic (TAAL) vessel has the same ultrastructural characteristics as the absorbing lymphatic vessel in normal organs, and it is provided with an endothelial wall wholly lacking a continuous basement membrane, pores, fenestrations, and open junctions. The TAAL vessel is always missing in the studied tumor masses as far as the central stroma is concerned, whereas it is always present in the peripheral area of the tumor and in the peritumoral connective tissue. The factors of extravasal matrix that play an active role in migration process of invasive phenotype tumor (IPT) cell after its detachment from tumor mass, as well as the role of cytoplasmic protrusions (pseudopod-like) in lymphatic recognition, were considered. For the first time, this study demonstrated the transendothelial passage of IPT cell inside the TAAL vessel lumen, which takes place by means of the intraendothelial channel (approximately 1.8-2.1 mum in diameter and 6.8-7.2 microm in length). This channel is to be considered a transient morphological entity organized by TAAL vessel endothelium by means of still unidentified molecular mechanisms. Therefore, it appears to be ascertained that the intraendothelial channel represents a step forward in the knowledge of the drainage into lymphatic circulation of interstitial fluid and the answer to the lack of knowledge expressed till today by researchers concerning the modality of passage of the tumor cell through the endothelial wall of the TAAL vessel.

Transendothelial transport and migration in vessels of the apparatus lymphaticus periphericus absorbens (ALPA)

The vessel of the apparatus lymphaticus periphericus absorbens (ALPA) represents the sector with high absorption capacity of the canalization of the lymphatic vascular system. It plays a basic role in preserving tissue homeostasis and in directing interstitial capillary filtrate back to the bloodstream. ALPA lymphatic endothelium differs from the endothelia of conduction and flowing vessels (precollectors, prelymph nodal and postlymph nodal collectors, main trunks), since it presents a discontinuous basement membrane, which is often absent, and lacks pores and fenestrations. The mesenchymal origin of the ALPA lymphatic vessel, morphological and ultrastructural aspects, intrinsic contractile properties, the presence of valves, innervation, and specific lymphatic markers that reliably distinguish it from blood capillaries are studied. Furthermore, its role in lymph formation through different mechanisms (hydrostatic pressure and colloidal osmotic-reticular mechanisms, vesicular pathway, and intraendothelial channel) is investigated. We have studied morphological and biomolecular mechanisms that control the transendothelial migration, from the extracellular interstitial matrix into the lumen of the lymphatic vessel, of cells involved in immune response and resistance (lymphocyte recirculation, etc.) and in the tumoral metastatic process via the lymphatic system. Finally, future research prospects, clinical implications, and therapeutic strategies are considered.

Structure, lymphatic vascularization and lymphocyte migration in mucosa-associated lymphoid tissue

In this review, we consider the morphological aspects and topographical arrangement of gut-associated lymphoid tissue (GALT) (solitary and aggregate lymph nodules or Peyer's patches) and of vermiform appendix in the human child and in some mammals. The spatial arrangement of the vessels belonging to apparatus lymphaticus periphericus absorbens (ALPA) and of blood vessels within each lymphoid follicle as well as the ultrastructural characteristics of the lymphatic endothelium with high absorption capacity are considered. Particular attention is also paid to the morphological and biomolecular mechanisms inducing lymphocyte transendothelial migration to the bloodstream by means of lymphatic vessels as well as their passage from blood into lymphoid tissue through the high endothelial venules (HEVs). The preferential transendothelial passage of lymphocytes and polymorphonuclear neutrophils within ALPA vessels of the interfollicular area does not occur following the opening of intercellular contacts, but rather it occurs by means of 'intraendothelial channels'. In HEVs, on the contrary, the hypothesis is plausible that lymphocyte transendothelial migration into lymphoid tissue occurs through a channel-shaped endothelial invagination entirely independent of interendothelial contacts. The lymph of ALPA vessels of the single Peyer's patch is conveyed into precollector lymphatic vessels and into prelymph nodal collectors, totally independent of the ALPA vessels of the gut segments devoid of lymphoid tissue. The quantitative distribution of T lymphocytes in the lymph of mucosal ALPA vessels suggests a prevalent function of fluid uptake, whereas a reservoir and supply function is implicated for the vessels of interfollicular area. The precollector lymphatic vessels and prelymph nodal collectors are considered to be vessels with low absorption capacity, whose main function is lymph conduction and flow.

Ultrastructural aspects of the follicular cells of the pars tuberalis in bats related to the seasonal cycle

The topography and structure of the follicular cells and the follicular cavity of the hypophyseal pars tuberalis (PT) were studied in adult hibernating bats (Pipistrellus pipistrellus and Rhinolophus ferrumequinum) of both sexes, during the annual seasonal cycle and the reproductive cycle. The follicular cells were found to be organized around a central cavity. They showed a polyhedral shape and apical microvilli protruding into central cavities. During hibernation, the follicular cells showed active cytoplasmic organelles, clusters of glycogen particles, and lipid droplets. In the supranuclear cytoplasm, 9+2 type cilia, some dense bodies, microvesicular vacuoles, and thin actin-like filaments (rather scarce during autumn) were detected. The contents of the follicular cavity showed well-defined ultrastructural seasonal characteristics, with a colloid-like aspect during awakening and a strongly granular aspect during autumn oestrus and mating. Positive staining for PAS and paraldehyde fuchsin, and a marked reaction to lectins PHA-L4, MAM, and RCA 60 suggested the presence of sialo-glycoproteins in the follicular cavities. Both follicular and endocrine PT-specific cells appeared to mark the boundary of follicular cavities. This finding suggests that the follicular cavity contents are comprised of both types of cells, rather than by cell fragmentation or degeneration products.

Fine structure and photoperiodical seasonal changes in Pars tuberalis of hibernating bats

In Pars tuberalis (PT) of pituitary gland of hibernating bats, extending cranially along the ventral face of the hypothalamic median eminence, around the hypophyseal stalk, and caudally continuing in the Pars distalis (PD), pt specific cells, follicular cells and gonadotropic cells were distinguished. Pt specific cells contain peculiar secretory granules positive to lectin WGA and negative to lectins LFA and PNA, positive to S-100 protein labeling and to PD hormones antisera. During hibernation they present a low numerical density of both secretory granules and melatonin binding sites. After light exposure, on the other hand, the latter increase in density and are associated with marked secretion synthetic activity and exocytosis. These aspects result to be more balanced in animals sacrificed during summer. These changes seem to support the hypothesis of marked annual changes even in animal species with seasonal rhythmicity of metabolisms and gonads. Follicular cells, organized in closed follicles, have slightly developed RER and Golgi apparatus during hibernation, whereas they seem to show an increased secretory activity after light exposure and during summer. In perinuclear and supranuclear cytoplasm, glycogen particles clusters (peculiar of hibernation), cilia 9+2 and multivesicular bodies were identified. Concerning FSH cells, a reduced numerical density during hibernation, the secretory granules morphological characteristics and their probable involvement in photoperiod-linked reproductive functions are investigated.

Ultrastructure of absorbing peripheral lymphatic vessel (ALPA) in guinea pig Peyer's patches

Corrosion casts from neoprene direct injection of lymphatic and blood vessels in guinea pig gut-associated lymphoid tissue, that is, solitary lymphoid follicles and Peyer's patches, have shown both their numerical density and their topographical arrangement in physiological conditions, after starvation and lymphatic stasis. The absorbing peripheral lymphatic vessel (ALPA) begins with the lacteal vessel, which continues in the mucosal lymphatic network. The latter is formed by subepithelial and interfollicular vessels wrapping single lymphoid follicles like a basket. Interfollicular vessels drain in the submucosal network, which flows into muscular tunica vessels with nonsegmentary bicuspid valves. They in turn drain lymph in subserosal precollectors and then in prelymphonodal collectors with conduction function. The follicles' germinal center and dome are completely devoid of ALPA vessels, while they are rich in blood vessels. Ultrastructurally, the ALPA vessel wall consists of a monolayer of endothelial cells devoid of pores, fenestrations, and open junctions and lacking a continuous basal lamina. Endothelial cells are joined by overlapping and interdigitating intercellular contacts, while end-to-end contacts are rare. They have a sizeable cell body, containing the nucleus and the common endocytoplasmic organelles, and a peripheral cytoplasm with actin-like filament bundles, free microvesicles or forming channels and a few rough-surfaced encloplasmic reticulum (RER) canaliculi. The presence of intraendothelial channels crossed by lymphocytes can often be detected within the endothelial wall during the different phases of cell transendothelial migration from lymphoid tissue to lymphatic vessel lumen. These channels undergo a numerical increase during starvation, while they are scarce during lymphatic stasis. We have quantitatively evaluated the prevalence of T lymphocytes in the lymph of interfollicular ALPA vessels and of prelymphonodal collectors draining the small intestine tract with or without Peyer's patches, under physiological and experimental conditions (starvation, lymphatic stasis).

NK-active cytokines IL-2, IL-12, and IL-15 selectively modulate specific protein kinase C (PKC) isoforms in primary human NK cells

Natural killer (NK) cell function is largely modulated by growth factors and cytokines. In particular, interleukin (IL)-2, IL-12, and IL-15 have major effects on the proliferative and cytotoxic activities of NK cells against tumor and virus-infected cells. It is thought that the members of the protein kinase C (PKC) family of serine/threonine kinases play an important role in mediating the pleiotropic effects of cytokines on their target cells. We have investigated the downstream effects generated in purified human NK cells by IL-2, IL-12, and IL-15 on PKCalpha and PKCepsilon--a canonical and a novel isoform of PKC, respectively. By means of Western blotting, PKC activity assays, and immunofluorescence performed on highly purified preparations of primary human NK cells, we demonstrate that: 1) the three cytokines have similar effects on PKCalpha and PKCepsilon activities; 2) whereas PKCepsilon activity is induced by cytokine stimulation, PKCalpha activity is inhibited; and 3) both the induction of PKCepsilon and the inhibition of PKCalpha functional activity are relatively early events in NK cells, while longer cytokine stimulations do not generate significant variations in enzyme activity, suggesting that the activation of both the canonical and novel isoforms of PKC are events required in the early phases of cytokine-induced NK cell stimulation.

The transendothelial passage in the absorbing peripheral lymphatic vessel of the rodent diaphragm

The absorbing peripheral lymphatic vessels of rat (Wistar/Kyoto) and gerbil (Meriones unguiculatus) diaphragms were observed with SEM, TEM and three-dimensional models under normal conditions, after experimental hemorrhage and after abdominal injection of China ink and latex polystyrene particles. Superficial and deep lymphatic vessels were noted and their ultrastructural characteristics showed an endothelial wall lacking a continuous basal lamina. Moreover, "intraendothelial channels" which are dynamic, fundamental pathways for lumen migration into the lymphatic vessel for fluids, China ink and latex polystyrene particles, were also demonstrated. Concerning the transendothelial passage of the autologous erythrocytes after their migration through the stomata and submesothelium connective channel, it was observed that this passage occurs by means of a "transcellular pathway". This consists of a "migratory pore" independent from the intercellular junctions, which is formed by an active process following a probable immunological response or cellular interaction between the erythrocyte and the endothelial cell.

Ultrastructural and three dimensional aspects of the lymphatic vessels of the absorbing peripheral lymphatic apparatus in Peyer's patches of the rabbit

We studied the absorbing lymphatic peripheral vessels of the Peyer's patches of the small and large intestine of the rabbit by means of light microscopy after injection of Neoprene latex and transmission electron microscopy in order to highlight their topographical distributions to blood vessels as well as the morphologic mechanism of transendothelial passage of the lymphocytes to the lymph. The distribution of absorbing lymphatic vessels originates from the lacteal vessels and the subepithelial mucosal lymphatic network, which continue without interruptions and dilations into the vessels of the interfollicular area which are woven into basket-like networks entwining the medio-basal portion of each lymphoid follicle. The interfollicular area vessels then drain into the large vessels of the tunica submucosa, which in turn drain into the valved precollector vessels of the subserosa by way of intramuscular vessels. TEM revealed the absorbing lymphatic vessels to have a continuous endothelial wall without open junctions, fenestrations, and continuous basal lamina. We observed many lymphocytes wedged in the lymphatic endothelial wall. This underlines the different phases of their migration from the lymphoid tissue in the lumen of the lymphatic vessel. Results of ultrathin serial sections and three dimensional reconstruction of lymphatic vessel segments with included lymphocyte showed the transendothelial passage of lymphocyte, through the "intraendothelial channels."

[The fine structure of the gustatory cells of the circumvallate, foliate and fungiform papillae in hibernating bats]

The cells of vallate, foliate and fungiform papillae were studied in insectivore hibernating bats (Pipistrellus pipistrellus and Rhinolophus ferrumequinum) in the various epochs of the year in order to show cell types the seasonal changes. On the basis of the ultrastructural aspects and the relationships with nerve endings, besides the few basal cells, three types of sensorial cells can be identified: dark type I cells, light type II cells and light type III cells. All gustatory cells, long and narrow shaped, extend from the epithelial basal lamina to the gustatory canal, where they send long microvillous expansions of the apical cytoplasm. These expansions, except those of the fungiform papillae which never extend beyond the lower two thirds, usually reach the external opening of the taste pore, always completely void of dense substance. Dark type I cells are characterized by a developed RER and large granules. Light type III cells show peculiar dense core light vesicles, labelled protein A-gold particles immunoreactive to 5-HT. These cells only in the foliate and fungiform papillae also have bundles of microtubules whose function is still unknown. After comparative evaluation and discussion of topographical and ultrastructural aspects with those of other mammals and humans, the Authors states that bats are provided with a valid gustatory system and that all cell types are involved in taste transduction.

[The absorbing peripheral lymphatic apparatus and blood vessels of the vermiform appendix: the 3-dimensional and ultrastructural aspects]

We studied the lymphatic angiotectonics of the vermiform appendix of the rabbit, using direct injection of Neoprene latex, electron microscopy and three-dimensional models. We observed that the vermiform appendix is made of absorbing lymphatic vessels distributed among the tubular glands of the tunica mucosa. Moreover, these absorbing lymphatic vessels continue through the straight vessels into a vast, basket-like lymphatic network, which envelopes the medium and basal portions of each single lymphoid follicle. In addition, the vessels of this network reach the submucosal network, whose vessels are peculiar in shape and size. The submucosal network, in turn, drains the lymph through the small caliber intramuscular vessels in the valved subserous precollector lymphatic vessels. We also highlighted the ultrastructural characteristics of the absorbing lymphatic vessels, which completely lack openings at the contacts between the adjacent endothelial cells, which were always joined by specialized junction complexes. Moreover, we reported the presence of intraendothelial channels which we affirm are dynamic morphologic entities, through which lymphocyte migration from the peri-interfollicular lymphoid tissue inside the absorbing lymphatic vessels takes place.

The lymphatic vessels and the so-called "lymphatic stomata" of the diaphragm: a morphologic ultrastructural and three-dimensional study

We studied the absorbing peripheral lymphatic vessel with the light microscope, the transmission electron microscope, the scanning electron microscope, and three-dimensional models of the diaphragm of several rodents and insectivores under normal and experimental conditions (lymphatic stasis and dehydration). To clarify the delicate and complex mechanism that permits drainage of the abdominal cavity contents into the lymphatic circulatory system, we introduced Polystyrene latex spherules, China ink, and Trypan blue into the abdominal cavities. After anatomical comparisons of the superficial and deep networks of absorbing peripheral lymphatic vessels at the tendinous and muscular portions of the diaphragm and after classification of lymphatic vessels into absorbing and conducting functions, we examined the stomata, which, owing to morphologic and topographic findings, we defined as stable structures. Furthermore, we observed that the stomata and submesothelial connective channel are fundamental elements that facilitate the flow of the corpuscular and liquid contents of the peritoneal cavity to the submesothelial absorbing lymphatic vessel wall. Also, we underlined that the genesis of the connective channel depends on the secondary cytoplasm extensions of two distinct adjacent endothelial cells, which, to facilitate the flow of the absorbed abdominal contents, completely coat this channel. Additionally, our observations illustrate that the secondary cytoplasm extensions do not engage in continuous relationships with the basal lamina of the mesothelium and with the margins of the stoma, and, hence, the hypothesis of "lymphatic stomata" as an expression of the anchoring of the borders of the open interendothelial junctions to the orifice margins of the stoma cannot be confirmed. Moreover, we describe the presence and formation of intraendothelial channels in the lymphatic endothelial wall. We affirm that this morphological entity is a dynamic unit, because its numerical density varies according to different physiological and experimental conditions to degrees of hydrostatic and colloidal osmotic pressure and, perhaps, also to the particular characteristics of the substances that the connective channel liberates into the endothelial wall of the lymphatic vessel. In conclusion, we affirm that the absorbing peripheral lymphatic vessels of the diaphragm, by way of intraendothelial channel formations, membrane diffusion, and the vesicular path of the endothelial cells, constitute the fundamental draining elements for the corpuscular and liquid contents of the abdominal cavity.

Three-dimensional and ultrastructural aspects of the lymphatic vascularization of the vermiform appendix

The aim of the study is to reveal the three-dimensional distribution and ultrastructure of the peripheral absorbing lymphatic vessels of the vermiform appendix, since the gut-associated lymphoid tissue is necessary to the immune responses to the enteric antigens. Corrosion casts showed the beginning of the lymphatic vascularization at the tunica mucosa, which lacks intestinal villi, through a tight, delicate lymphatic network. This network drains the lymph by peculiar straight vessels, distributed in the mucosal beams that separate the adjacent follicle domes, in the fine network of the upper portion of the lymphatic basket, surrounding the lateral walls of the basal and medium portions of each lymphoid follicle. This network, which is made of large caliber vessels that are not dilated like sinuses, continues through small vessels into the large dome-like vessels of the submucosa, which in turn by way of the lymphatic vessels of the muscular tunica, drain into the subserous precollector valved lymphatic vessels that flow into the pre-lymph node collectors. We underlined that the particular fluidity of Neoprene latex and the direct injection method, when compared with other substances and injection methods, provided us with exceptionally clear and precise three-dimensional plastic images of the absorbing lymphatic vessels. Moreover, these images extraordinarily illustrated the preservation of the absorbing lymphatic spatial relationships with blood vessels. Ultrastructural features and three-dimensional models of ultrathin serial sections of the absorbing peripheral lymphatic vessels showed a continuous endothelial wall lacking basal lamina, as well as open junctions between adjacent cells. Moreover, we observed the presence of numerous lymphocytes, together with intense transendothelial migratory activity that occurs through intraendothelial channel formations, dynamic entities, at absorbing lymphatic vessels of the peri-interfollicular lymphoid tissue. Also, we saw that the germinal center, as well as the lymphoid follicle dome, lacked lymphatic absorbing vessels. In addition, many postcapillary high endothelial venules (HEV) were observed with lymphocyte migration into the extravasal compartment. Furthermore, we maintain that the absorbing peripheral lymphatic vessels (ALPA) of the tunica mucosa play an important role in liquid drainage. For the peri-interfollicular vessels, we hypothesize a potential migratory and a reserve capacity for lymphocytes, as well as a conduction activity for the muscular tunica and submucosa vessels.

Ultrastructure and immunocytochemistry of gustatory cells in man

Ultrastructural and immunocytochemical features of the taste buds of the vallate, foliate and fungiform papillae in young, adult and elderly men, revealed three types of sensorial cells: dark type I cells rich in free ribosomes and large dense granules, light type II cells with large amorphous areas of cytoplasmic matrix and light type III cells with a dense core immunoreactive for 5-HT. All sensorial cells send microvillous protrusions of the apical cytoplasm into the gustative canal and make contact with nerve endings. After comparative studies, we made several hypothetical propositions on the functional value of microvillous protrusions, as well as on the apical and basal dense core vesicles of the foliate and vallate papillae. Moreover, we think that sensorial cells are implicated in taste transduction and that subject age does not seem to play any role in taste perception.

Vallate, foliate and fungiform human papillae gustatory cells. An immunocytochemical and ultrastructural study

We studied the classifications, topographic distribution and cellular lines of taste bud components in vallate, foliate and fungiform papillae of young, mature and old men with light microscopy, SEM, and TEM. By identifying ultrastructural and immunocytochemical characteristics, three distinct sensorial cells were identified, along with a few basal cells: dark type I cells, light type II cells and light type III cells. These cells extend from the epithelial basal lamina to the gustatory canal, where their apical cytoplasm sends long microvillous expansions. Excluding those of the fungiform papillae-which never go beyond the lower third of the gustatory canal, and are always void of dense substance-the microvillous expansions continue to the external border of the taste pore. Dark type I cells are rich in free ribosomes, tubular RER and large dense granules. Light type II cells with scarce ribosomes and RER, do not have enough peculiar ultrastructural characteristics to be considered effector or phagocyte elements. Light type III cells are characterizes by dense core vesicles whose peculiar ultrastructural characteristics in the foliate and vallate papillae, should be considered a consequence of different functional phases. After comparative evaluation the authors hypothesized on the functional value of some ultrastructural aspects and on the dense core vesicles which are immunoreactive to 5-HT. They observed that all gustatory cells are involved in taste transduction based on behaviours caused by microvilli in the gustatory canal and gustatory cell relationships with nerve endings. Moreover the authors noted that age does not seem to influence taste perception.

Season related ultrastructural features of the parotid, submandibular and von Ebner's glands in hibernating bats

The parotid, submandibular and the von Ebner's salivary glands of hibernating insectivorous bats (Pipistrellus pipistrellus, Rhinolophus f. e. and Eptesicus serotinus) were studied by transmission electron microscopy and by histochemical methods during various seasons of the year. We report the seasonal ultrastructural changes that occur in the cytoplasmic organelles and the secretory granules of the serous and mucous cells and in the intercalated and striated ducts of the major glands. It previously has been hypothesized that the heterogeneity of the inclusions in the serous granules is closely related to the varying seasonal levels of proteinaceous and glycidic constituents. Lymphatic vessels are present only in the perivascular and periductal connective tissue. Morphofunctional and comparative studies seem to confirm a relationship between secretory activity and nutritional status as well as a likely involvement of the intercalated and striated ducts in determining the composition of the saliva.

[Structure and immunohistochemistry of the hypophysis of Alosa fallax nilotica during the reproductive migratory cycle]

The Pituitary of the Alosa fallax nilotica consists of a pars distalis, a pars intermedia and a pars nervosa. The pars distalis is divided into rostral and proximal. The pars nervosa extends also into proximal pars distalis. The rostral pars distalis, on the contrary in primitive Teleostei, has organized into cellular cords defining cavities or intercommunicating follicles. These latter finish into the oral adenohypophysial duct, which don't open in pharyngeal cavity. The cords contain three cell types: the columnar cells LTH, TSH cells and basal cells not yet functionally determined. The cord cells are separated from follicle cavity by an one layer of flat degranulated cells. The LTH cell, the chief cell type, together the TSH and basal cells shows evident cytologic differences in organelles of synthesis and secretion during the various stages of the reproductive migration. Besides globular and baton-shape projections are underlined in the apical cytoplasm of LTH cells. These structure, extending into follicle cavity, seem to dispatch sensory function probably. The proximal pars distalis consists of compact cords of gonadotropic cells (particularly active during the stage of migration from rivers to the sea) with inserted orangiophilic cells (probably STH) and phloxine cells: these latter cells are chiefly arranged at the periphery and immunocytochemical positive for the antibodies against ACTH. The pars intermedia contains cord of ACTH cells, particularly manifest during the periods of transit from sea water to fresh water and on the contrary, they are characterized by positive-ACTH dense granules. On the ground of ultrastructural aspects of vesicles, the pars nervosa shows three types of nervous fibers which correlate with neurosecretory hypothalamus and catecholaminergic dopaminergic fibers. The Authors think of underlining particularly that the all cells of rostral pars distalis and chiefly the LTH cells are involved significantly in the regulation of reproduction and hydro-mineral metabolic equilibrium.

Comparative anatomical and ultrastructural features of the sensory papillae in the tongue of hibernating bats

The papillae of the tongue dorsal surface of the insectivorous, hibernating bats (Vespertilionidae and Rhinolophidae), whose function is mainly sensorial, consist of two circumvallate papillae, two foliate papillae, located at the side edges at the glossopalatine arch, and numerous fungiform papillae. The circumvallate and foliate papillae are characterized not only by their position, but also by presence of several taste buds which open through the external orifice of the gustatory canal into the cavity of the vallum, or furrow, which divides the two folds of the lingual mucosa. The fungiform papillae (extremely numerous on the whole dorsal surface) are characterized by an unusual arrangement (along 3 oblique lines on the anterior two-thirds and predominantly on the middle line of the tongue body) and by the presence of only one to three taste buds which open on the heavily keratinized dorsal epithelial surface. The taste buds are made up of sensory cells with a light or dark matrix; their apical cytoplasmic expansions are not found beyond the middle part of the gustatory canal, in contrast with the circumvallate and foliate papillae which protrude from the orifice of the gustatory pore. Comparisons with the papillae of other types of bats and Insectivora and evaluations of the morphological characteristics and their functional values (unusual areas of distribution of the papillae, apical cytoplasmic expansions and behaviour of microfolds observed under SEM) have been made in different environmental conditions and nutritional habits, with attention to the mechanical events in the course of feeding.

The passage of macrophage and lymphocytes from the interstitium across the lymphatic endothelium of rat lacteals

The passage of cells across the lymphatic endothelium of rat lacteals in both normal and non-pathological experimental conditions (fasting, lymphatic, stasis) was studied by means of serial thin sections and three-dimensional models. Two different pathways of transendothelial migration were observed: (1) macrophages enter the lymphatic lumen via the cytoplasm of endothelial cells, without involvement of intercellular junctions, whereas (2) lymphocytes migrate through "intraendothelial channels", dynamic structures organized by the lymphatic endothelium under physiological conditions.

The migration of lymphocytes and polymorphonuclear leukocytes across the endothelial wall of the absorbing peripheral lymphatic vessel

We studied the process of transendothelial migration of lymphocytes and polymorphonuclear leukocytes in the absorbing peripheral lymphatic vessels of small intestine and urinary bladder, under normal conditions, lymphatic stasis and prolonged fast. By ultrathin serial sections and three-dimensional models we found that lymphocytes and leukocytes share a common migration pathway from the interstitium into the lumen of the lymphatic vessel, namely 'the intraendothelial channel'. The migratory process of these cells occurs in several steps: approach to the endothelial wall, entry and run along the channel and finally coming out into lymphatic lumen. Our findings are compared with those concerning lymphatics in pathological conditions and blood vessels. Further considerations concern the possible mechanisms underlying this kind of transendothelial migration.

Seasonal changes of parafollicular and follicular cells of the dormouse thyroid (Myoxus glis): an ultrastructural and immunocytochemical study

The follicular epithelium of dormouse thyroid consists of two distinct cellular types, follicular and parafollicular cells. Parafollicular cells can be easily identified by their high cytoplasmic dye-affinity for phloxine, round to ovoid shape, basal arrangement and lack of contact with follicular colloid. The wide cytoplasmic matrix is clear and contains many secretory granules of variable electron density whose contents histochemically appears to be proteic with a lean glucidic component. Furthermore immunocytochemical reactions with antibodies against calcitonin and somatostatin showed that both hormones are co-stored in the secretory granules of all parafollicular cells. Both follicular and parafollicular cells show seasonal morphological variations in their secretory activity. Follicular cell activity is high in summer, reaches a peak in late fall or prehibernation and progressively slows down throughout hibernation. Parafollicular cells exhibit a fair synthetic activity in summer, in fall, and in the animals captured during winter hibernating sleep and killed after 12 days stay in laboratory. In winter sleep, granules with interrupted membrane and cottony contents are prevalent and the ultrastructural aspects suggest an intense discharge of secretion. The results are compared with those from other hibernating mammalians and discussed in the light of blood calcium values and seasonal balances of other metabolisms.

Macrophage migration through the endothelium in the absorbing peripheral lymphatic vessel of the small intestine

TEM and three-dimensional models of the absorbing peripheral lymphatic vessel (ALPA) of the small intestine demonstrate that macrophages migrate from the interstitium into the lumen through the endothelial cell (transcellular pathway). Macrophages cross through a 'migration pore' which arises by an 'erosive process' in the cytoplasmic expansion of the endothelial cell. The pore is completely independent of the intercellular junction which is always sealed by junctional complexes. Furthermore several sites of contact between macrophage and endothelial cell membranes stress a possible functional role played by cellular interactions. Transcellular migration processes under normal conditions are compared with pathological or experimental ones.

Fine structure of bat deep posterior lingual glands (von Ebner's)

We studied the morphology and ultrastructure of the bat (Pipistrellus k.k. and Rhinolophus f.e.) deep posterior lingual glands (Ebner's glands) during hibernation, summer and after stimulation with pilocarpine. Ebner's glands are formed by serous tubulo-alveolar adenomeres and by an excretory system organized in intercalated ducts, long excretory ducts and a main excretory duct. The latter opens in the vallum which surrounds the circumvallate papillae and in the groove of the foliate papillae. The secretory cells, which lack basal folds, show abundant and dense granules (PAS+, Alcian blue -), microvilli (scarce during hibernation), a Golgi apparatus (well developed during summer and after stimulation with pilocarpine), a large nucleus and RER cisternae stacked at the basal pole. Centrioles, lipid droplets, heterogeneous bodies (in content and density, probably lipofuscin bodies), lysosomal multivesicular bodies and large, dense granules with a microcrystalline structure were also encountered. The lateral membranes of adjacent cells are joined by desmosomes; their interdigitations are neither numerous nor prominent during summer. Microfilaments, often gathered in small bundles, lie in the lateral, peripheral cytoplasm without any relation with desmosomes. In summer and particularly after stimulation with pilocarpine, the apical pole of the secretory cells is characterized by many long microvilli, pedunculated hyaloplasmic protrusions and secretory granules. During hibernation the lumen is filled with secretory material. Myoepithelial cells are arranged among secretory cells or between them and the basal lamina. The short intercalated ducts show similarities with the analogous ducts of the parotid gland. Striated ducts are absent. Excretory ducts are endowed with: a) an inner layer of cuboidal cells characterized by poorly developed cytoplasmic organelles, rare dense granules and a few small microvilli; b) an outer layer of basal cells lying on the basal lamina. Myoepithelial cells are absent. The main excretory duct is lined by a stratified epithelium with an inner layer of conical-pyramidal cells surrounded by two-three rows of basal cells. The conical-pyramidal cells show poorly developed organelles, an apical border with small short microvilli and a prominent terminal web.

Fine structure of the excretory system of the deep posterior (Ebner's) salivary glands of the human tongue

Human deep posterior lingual glands (von Ebner's glands) are located beneath the circumvallate papillae. They are formed by tubuloalveolar adenomeres, intercalated ducts and excretory ducts coming together in the main excretory duct. The tubuloalveolar cells, pyramid-shaped, show large and dense secretory granules (clear cored) throughout the cytoplasm, rare basal folds and packed cisternae of rough endoplasmic reticulum (RER) at the basal pole. The columnar cells of the intercalated ducts are arranged in a monolayer. They are characterized by dense, clear-core secretory granules (mostly in the apical cytoplasm), a basal nucleus, well-developed RER and Golgi apparatus, and thin filaments distributed in supra- and perinuclear cytoplasm. Striated ducts are absent. Excretory ducts, coming together in the main duct, are lined by a bistratified epithelium. The inner layer consists of columnar cells showing bundles of tonofilaments with scarce secretory activity. The outer layer is composed of basal cells lying on the basal lamina. The main excretory duct, which opens at the bottom of the vallum, shows a stratified epithelium. The outer side is composed of 2-3 layers of malpighian cells lying on the basal lamina. The inner side consists of a single layer of cuboidal-columnar cells with dense apical granules and well-developed organelles synthesizing and condensing secretions. These cells interpolate with goblet cells, rare mitochondria-rich cells, ciliated cells and numerous small globous cells showing a clear matrix and lacking secretory granules. The cilia show a 9 + 2 microtubular structure with basal bodies provided with striated rootlets. Myoepithelial cells surround with their processes the basal portions of the secretory cells and the intercalated ducts. The conclusions concern some comparative aspects and some hypothesis on the functional role of goblet cells, ciliated cells and epithelial cells lining the different ducts, also in relation to the final secretory product.

Topography and ultrastructure of kidney lymphatics in some hibernating bats

The kidney lymphatic system of some bats consists of intraparenchymal (interlobar, arcuate, and interlobular) and extraparenchymal vessels (capsular and prehilar connective). These vessels drain lymph via precollecting and prenodal collecting lymphatics into a hilar lymph node. There are no lymphatics in the renal medulla. The lymphatic vasculature (precollecting vessels excluded) is characterized by an endothelial wall lacking basal lamina and fenestrations. The endothelial cells, mostly rectangular in shape, are joined together by overlapping, end-to-end, and complex interdigitating junctions. Cytoplasmic expansions profile and thickness, intercellular junctions and particularly the different categories of uncoated vesicles (free or opened on luminal or abluminal surface) show qualitative and quantitative seasonal variations. Luminal and abluminal cytoplasmic processes appear (when analyzed in tridimensional reconstructions) as "intraendothelial channels." The increased number of these structures during summer characterizes them as dynamic elements and supports the concept of an active role played by them in transendothelial transport. Nevertheless, the main functional role is still ascribed (in addition to membrane transport mechanisms) to the vesicular system, also defined as the "vesicular route." We did not find any open intercellular junctions.

Ultrastructural and seasonal aspects of the kidney lymphatic system of hibernating animals

The kidney lymphatic system of bat, dormouse and marmot consists of intraparenchymal (interlobar, arcuate, interlobular) and extraparenchymal (capsular) vessels sharing common ultrastructural aspects. We did not observe medullary lymphatics. The qualitative and quantitative seasonal changes in the ultrastructure of the lymphatic endothelium represent not only a species-linked feature but also (and mainly) an evident seasonal fluctuation in lymph formation. Furthermore, these ultrastructural changes emphasize the important role played by the different mechanisms involved in the translymphatic movement of proteins and interstitial fluid with particular regard to the 'vesicular route' and intraendothelial channels.

[Ultrastructure of the lymphatic vessels of the urinary bladder]

The fine structure and morphological aspects of superficial and deep lymphatic vessels of Chiroptera' bladder (Vesperugo savi and Rinolophus f.e.) have been studied, under seasonal, physiological conditions of different lymphatic flux (winter lethargic state and summertime). The endothelial walls of subepithelial, intramuscular and subserosal-peritoneal, lymphatic networks show an uninterrupted course together with both simple and complex intercellular contacts, constantly jointed by specialized junctional complexes, such as zonulae adhaerentes and occludentes. The abluminal surface is often almost entirely encircled by a thick layer of fibrillary connective tissue. Seasonal cytological modifications of possible importance and morphological aspects typical of the each individual network have not been detected in the lymphatic endothelium. On the other hand the abundance distribution of clear intracytoplasmic vesicles and the frequent occurrence of micropinocytotic vesicles in the luminal and abluminal membrane surface have been shown. Canalicular structures have also been demonstrated, even if quantitatively less numerous with respect to those seen in the chiliferous vessels of the same species of Chiroptera. The Authors believe that most of the transendothelial transport in the above mentioned lymphatic vessels occur through the micropinocytotic vesicles and also through the intra-endothelial channels made up by the vessel wall, without any intervention of intercellular contacts or specialized junctions. The possible role of substances within the interstitium in inducing the appearance of canaliculi in the endothelial wall is discussed.

Ultrastructure of small intestine submucosal and serosal-muscular lymphatic vessels

Lymphatic vessels of small intestine submucosal and serosal-muscular layers in mice and bats have been studied by electron microscopy and tridimensional reconstruction of thin serial sections. Lymphatic endothelium has a continuous appearance, it lacks fenestrations and pores and it is encircled by a thick connective tissue layer. The endothelial wall shows intraendothelial channels, quite similar to those previously described in the lacteal vessels. The author believes that the above mentioned intraendothelial channels, together with pinocytotic vesicles, play a fundamental role in the transendothelial transport of fluids, proteins and macromolecules. Moreover, intercellular specialized junctional complexes do not appear to take any part in this process.

Transendothelial transport of lipids in the absorbing lymphatic vessel

Intraendothelial channels have been shown in the lacteal vessels under normal conditions and during experimentally induced stasis, using ultrastructural and tridimensional reconstruction methods. Through the channels of the lymphatic endothelial wall, free lipid drainage from the interstitium into lymph was detected, although the intercellular junctions did not appear to be modified.

The ultrastructural basis of lipid transport in the absorbing lymphatic vessel

Absorbing lymphatic vessels of intestinal villi were studied by electron microscopy tridimensional reconstruction in order to follow the passage of lipid from the interstitium into the capillary lumen. The duodenum and ileum of kittens after milk feeding, fasting and lymphatic stasis were investigated. Lipids reach the lymphatic system by intraendothelial 8-14 micrometers long channels, which are directed from the apical to the basal portion of the lacteals. Endothelial junctions were always intact, indicating that these complexes were not involved in the transport of large size molecules.