Comparative ultrastructure of the olfactory system in the East African root rat (Tachyoryctes splendens) and the naked mole rat (Heterocephalus glaber).

The ultrastructure of the olfactory system of most fossorial rodents remains largely unexplored. This study sought to investigate the functional structure of the olfactory mucosa and olfactory bulb of two species of fossorial rodents that have distinct behaviour and ecology, the East African root rat (RR) and the naked mole rat (NMR). Transmission electron microscopy and scanning electron microscopy were employed. The basic ultrastructural design of the olfactory system of the two species was largely comparable. In both species, the olfactory mucosa comprised an olfactory epithelium and an underlying lamina propria. The olfactory epithelium revealed olfactory knobs, cilia and microvilli apically and sustentancular cells, olfactory receptor neurons and basal cells in the upper, middle and basal zones, respectively. The lamina propria was constituted by Bowman's glands, olfactory nerve bundles and vasculature supported by loose connective tissue. Within the olfactory bulb, intracellular and extracellular structures including cell organelles, axons and dendrites were elucidated. Notable species differences were observed in the basal zone of the olfactory epithelium and on the luminal surface of the olfactory mucosa. The basal zone of the olfactory epithelium of the RR consisted of a single layer of flattened electron-dense horizontal basal cells while the NMR had juxtaposed electron-dense and electron-lucent heterogenous cells, an occurrence seen as being indicative of quiescent and highly proliferative states of the olfactory epithelia in the two species, respectively. The olfactory epithelial surface of the NMR comprised an elaborate cilia network that intertwined extensively forming loop-like structures whereas in the RR, the surface was rugged and consisted of finger-like processes and irregular masses. With gross and histological studies showing significant differences in the olfactory structures of the two species, these findings are a further manifestation that the olfactory system of the RR and the NMR have evolved differently to reflect their varied olfactory functional needs.

Functional Morphology of the Olfactory Mucosa and Olfactory Bulb in Fossorial Rodents: The East African Root Rat (Tachyoryctes splendens) and the Naked Mole Rat (Heterocephalus glaber).

Optimal functioning of the olfactory system is critical for survival of fossorial rodents in their subterranean lifestyle. This study examines the structure of the olfactory mucosa and olfactory bulb of two fossorial rodents exhibiting distinct social behaviors, the East African root rat and the naked mole rat. The social naked mole rat displayed simpler ethmoturbinates consisting of dorsomedial and broad discoid/flaplike parts that projected rostrally from the ethmoid bone. In the solitary root rat however, the ethmoturbinates were highly complex and exhibited elaborate branching which greatly increased the olfactory surface area. In addition, when correlated with the whole brain, the volume of the olfactory bulbs was greater in the root rat (4.24×10-2) than in the naked mole rat (3.92×10-2). Results of this study suggest that the olfactory system of the root rat is better specialized than that of the naked mole rat indicating a higher level of dependence on this system since it leads a solitary life. The naked mole rat to the contrary may have compensated for its relatively inferior olfactory system by living in groups in a social system. These findings demonstrate that structure of the olfactory system of fossorial mammals is dictated by both behavior and habitat.

Three-Dimensional Structure and Disposition of the Air Conducting and Gas Exchange Conduits of the Avian Lung: The Domestic Duck (Cairina moschata).

The anatomy of the domestic duck lung was studied macroscopically, by casting and by light, transmission, and scanning electron microscopy. The lung had four categories of secondary bronchi (SB), namely, the medioventral (MV, 4-5), laterodorsal (LD, 6-10), lateroventral (LV, 2-4), and posterior secondary bronchi (PO, 36-44). The neopulmonic parabronchi formed an intricate feltwork on the ventral third of the lung and inosculated those from the other SB. The lung parenchyma was organized into cylindrical parabronchi separated by thin septa containing blood vessels. Atria were shallow and well-fortified by epithelial ridges reinforced by smooth muscle bundles and gave rise to 2-6 elongate infundibulae. Air capillaries arose either directly from the atria or from infundibulae and were tubular or globular in shape with thin interconnecting branches. The newly described spatial disposition of the conducting air conduits closely resembles that of the chicken. This remarkable similarity between the categories, numbers, and 3D arrangement of the SB in the duck and chicken points to a convergence in function-oriented design. To illuminate airflow dynamics in the avian lung, precise directions of airflow in the various categories of SB and parabronchi need to be characterized.

Anti-proliferative activities of centella asiatica extracts on human respiratory epithelial cells in vitro / Actividades antiproliferativas del extracto de centella asiatica sobre células epiteliales respiratorias humanas in vitro

Centella asiatica or "pegaga" is well known for its ability in promoting wound healing. This study focused on the effect of Centella asiatica on the proliferation of human respiratory epithelial (RE) cells. RE cells were cultured using co-culture techniques until first passage (P1). Viability cell test by tryphan blue dye exclusion assay showed that there was high percentage of cell viability at both P0 (74 percent) and P1 (91.61 percent). Triplicate MTT assays were carried out with different concentrations of C. asiatica from 15.6 ppm, 31.3 ppm, 62.5 ppm, 125 ppm, 250 ppm, 500 ppm, 1000 ppm, until 2000 ppm. The higher the concentration of C. asiatica, the more inhibitory effect was seen. C. asiatica aqueous extract at concentration 1000 ppm and 2000 ppm demonstrated a significant (p<0.05) inhibitory effect on human RE cells proliferation on day 4 and day 7 after treatment. This provides potential use of C. asiatica extract for the treatment of conditions with respiratory epithelial cells overgrowth.

La Centella asiatica o "pegaga" es conocida por su capacidad para promover la cicatrización de heridas. Este estudio se centró en el efecto de la Centella asiatica sobre la proliferación de las células del epitelio respiratorio (ER) humano. Las células del ER se cultivaron usando técnicas de co-cultivo hasta el primer paso (P1). La prueba la viabilidad celular mediante el ensayo de exclusión del colorante azul de tripano demostró un alto porcentaje de viabilidad celular tanto en P0 (74 por ciento) y P1 (91,61 por ciento). Ensayos de MTT por triplicado se llevaron a cabo con diferentes concentraciones de C. asiatica, desde 15,6 ppm, 31,3 ppm, 62,5 ppm, 125 ppm, 250 ppm, 500 ppm, 1000 ppm, hasta 2000 ppm. Con una mayor concentración de C. asiatica, se observó un mayor efecto inhibitorio. El extracto acuoso de C. asiatica a una concentración de 1000 ppm y 2000 ppm demostró un efecto inhibidor significativo (p<0,05) sobre la proliferación de células del ER humano los días 4 y 7 posterior al tratamiento. Esto proporciona el uso potencial del extracto de C. asiatica para el tratamiento de condiciones con crecimiento excesivo células epiteliales respiratorias.

Morphological evaluation of spermatogenesis in Lake Magadi tilapia (Alcolapia grahami): a fish living on the edge.

Spermatogenesis in Lake Magadi tilapia (Alcolapia grahami), a cichlid fish endemic to the highly alkaline and saline Lake Magadi in Kenya, was evaluated using light and transmission electron microscopy. Spermatogenesis, typified by its three major phases (spermatocytogenesis, meiosis and spermiogenesis), was demonstrated by the presence of maturational spermatogenic cells namely spermatogonia, spermatocytes, spermatids and spermatozoa. Primary spermatogonia, the largest of all the germ cells, underwent a series of mitotic divisions producing primary spermatocytes, which then entered two consecutive meiotic divisions to produce secondary spermatocytes and spermatids. Spermatids, in turn, passed through three structurally distinct developmental stages typical of type-I spermiogenesis to yield typical primitive anacrosomal spermatozoa of the externally fertilizing type (aquasperm). The spermatozoon of this fish exhibited a spheroidal head with the nucleus containing highly electron-dense chromatin globules, a midpiece containing ten ovoid mitochondria arranged in two rows and a flagellum formed by the typical 9 + 2 microtubule axoneme. In addition, the midpiece, with no cytoplasmic sheath, appeared to end blindly distally in a lobe-like pattern around the flagellum; a feature that was unique and considered adaptive for the spermatozoon of this species to the harsh external environment. These observations show that the testis of A. grahami often undergoes active spermatogenesis despite the harsh environmental conditions to which it is exposed on a daily basis within the lake. Further, the spermiogenic features and spermatozoal ultrastructure appear to be characteristic of Cichlidae and, therefore, may be of phylogenetic significance.

Anticancer drug vinblastine sulphate induces transient morphological changes on the olfactory mucosa of the rabbit.

Vinblastine sulphate (VBS) is an anticancer drug that acts by disrupting microtubule dynamics of highly mitotic tissue cells. The consequences of VBS on the olfactory mucosa (OM), a tissue with high mitotic numbers, are not clearly understood. We used qualitative and quantitative methods to determine the structural changes that may be produced on the rabbit OM by VBS. Following a single dose (0.31 mg/kg) of this drug, the structure of the mucosa was greatly altered on the first 3-5 days. The alteration was characterized by disarrangement of the normal layering of nuclei of the epithelia, degeneration of axonal bundles, occurrence of blood vessels within the bundles, localized death of cells of Bowman's glands and glandular degeneration. Surprisingly on or after day 7 and progressively to day 15 post-exposure, the OM was observed to regenerate and acquire normal morphology, and the vessels disappeared from the bundles. Relative to control values, bundle diameters, olfactory cell densities and cilia numbers decreased to as low as 53.1, 75.2 and 71.4%, respectively, on day 5. Volume density for the bundles, which was 28.6% in controls, decreased to a lowest value of 16.8% on day 5. In contrast, the volume density for the blood vessels was significantly lower in controls (19.9%) than in treated animals at day 2 (25.8%), day 3 (34.3%) and day 5 (31.5%). These findings suggest that the changes induced on the rabbit OM by VBS are transient and that regenerative recovery leads to the restoration of the normal structure of the mucosa.

Pre-hatch lung development in the ostrich.

We studied development of the ostrich lung using light microscopy as well as electron microscopy techniques. At E24, the lung comprised a few epithelial tubes, interspersed with abundant mesenchyme with scattered profiles of incipient blood vessels. Between E24 and E39, the epithelial thickness was reduced by 90% from 13.5 ± 0.41 µm to 1.33 ± 0.014 µm (mean ± SD, respectively). Atria were evident at E32, and by E35, the first portions of the blood-gas barrier (BGB) measuring 3.41 ± 1.12 µm were encountered. Gas exchange tissue was well formed by E39 with atria, infundibulae, air capillaries and a mature blood-gas barrier (BGB). BGB formation proceeded through the complex processes of secarecytosis and peremerecytosis, which entailed decapitation of epithelial cells by cutting or pinching off respectively and by E39, the BGB was thin at 2.21 ± 1.21 µm. Vascular remodeling by intussusceptive angiogenesis was a late stage process mediated by intraluminal pillars in the pulmonary vasculature.

Comparative Quantitative and Qualitative Attributes of the Surface Respiratory Macrophages in the Domestic Duck and the Rabbit / Atributos Cualitativos, Cuantitativos y Comparativos de los Macrófagos de la Superficie Respiratoria en el Pato Doméstico y el Conejo

In mammals, surface respiratory macrophages (SM) are known to play a foremost role in protecting the respiratory system by providing first line of defense through engulfing pathogens and particulate matter respired with air. It has been reported that the pulmonary cellular defense system of domestic birds is inadequate. In particular, low number of SM and even lack of the cells in a healthy avian respiratory system have been associated with susceptibility of domestic birds to respiratory diseases. In an endeavor to resolve the existing controversy, the quantitative and qualitative attributes of the surface respiratory macrophages of the domestic duck and of the domestic rabbit were compared under similar experimental conditions. Quantitatively, the rabbit SM were on average approximately fourteen times more than the duck SM. The SM were found to have comparable diameters measuring about 12 µm in the duck and 13 µm in the rabbit. Similarly, the duck and the rabbit SM were structurally similar. Typically, they were round granular cells possessing filopodial extensions and variable electron dense bodies in the cytoplasm. The phagocytic capacity measured using polystyrene particles revealed that the duck SM had a higher phagocytic capacity than the rabbit SM. The volume density of the engulfed polystyrene particles, i.e. the volume of the particles per unit volume of the cell was estimated at 20 percent in the duck and 9 percent in the rabbit. These results suggest that the comparatively low numbers of SM in domestic birds may contribute to susceptibility of the birds to diseases. However, given the high phagocytic capacity of the avian SM, susceptibility of the domestic birds may not be due to dearth of the SM alone but some other factor (s) such as persistent exposure of the birds to particulate matter which is known to reduce robustness of the SM may be involved.

En los mamíferos, los macrófagos de la superficie respiratoria (SM) son conocidos por jugar el papel más importante en la protección del sistema respiratorio, proporcionando la primera línea de defensa en contra de agentes patógenos y envolviendo las partículas de aire respirado. Se ha informado que el sistema de defensa celular pulmonar de las aves domésticas es insuficiente. En particular, el bajo número de SM, e incluso las células del sistema respiratorio de las aves domésticas, en un ambiente sano, se ha asociado con susceptibilidad a enfermedades respiratorias. En un esfuerzo para resolver la controversia existente, los atributos cuantitativos y cualitativos de los macrófagos de la superficie respiratoria del pato doméstico y el conejo doméstico fueron comparados en las mismas condiciones experimentales. Cuantitativamente, los SM del conejo fueron en promedio aproximadamente catorce veces más que los SM en el pato. Los SM se encontraron con un diámetro comparable, al medir alrededor de 12 micras en el pato y 13 micras en el conejo. Del mismo modo, en el pato y el conejo los SM eran estructuralmente similares. Por lo general, correspondieron a células granulares con extensiones filopodiales y organismos electrodensos variables en el citoplasma. La capacidad fagocítica medida utilizando partículas de poliestireno reveló que los SM del pato tenían una mayor capacidad fagocítica que el conejo. La densidad de volumen de las partículas de poliestireno envueltas, es decir, el volumen de las partículas por unidad de volumen se estimó en 20 por ciento en el pato y 9 por ciento en el conejo. Estos resultados sugieren que el número comparativamente bajo de los SM en las aves domésticas puede contribuir a su susceptibilidad a enfermedades. Sin embargo, dada la alta capacidad fagocítica de los SM aviares, la susceptibilidad de las aves domésticas no puede deberse solamente a la escasez de SM, sino a algunos otros factores pueden estar involucrados, como la exposición persistente de las aves a partículas, las cuales se sabe reducen la robustez de los SM.

The pulmonary blood-gas barrier in the avian embryo: inauguration, development and refinement.

In vertebrates, efficient gas exchange depends primarily on establishment of a thin blood-gas barrier (BGB). The primordial air conduits of the developing avian lung are lined with a cuboidal epithelium that is ultimately converted to a squamous one that participates in the formation of the BGB. In the early stages, cells form intraluminal protrusions (aposomes) then transcellular double membranes separating the aposome from the basal part of the cell establish, unzip and sever the aposome from the cell. Additionally, better endowed cells squeeze out adjacent cells or such cells constrict spontaneously thus extruding the squeezed out aposome. Formation of vesicles or vacuoles below the aposome and fusion of such cavities with their neighboring cognates results in severing of the aposome. Augmentation of cavities and their subsequent fusion with the apical plasma membranes results in formation of numerous microfolds separating concavities on the apical part of the cell. Abscission of such microfolds results in a smooth squamous epithelium just before hatching.

Parabronchial angioarchitecture in developing and adult chickens.

The avian lung has a highly sophisticated morphology with a complex vascular system. Extant data regarding avian pulmonary angioarchitecture are few and contradictory. We used corrosion casting techniques, light microscopy, as well as scanning and transmission electron microscopy to study the development, topography, and distribution of the parabronchial vasculature in the chicken lung. The arterial system was divisible into three hierarchical generations, all formed external to the parabronchial capillary meshwork. These included the interparabronchial arteries (A1) that ran parallel to the long axes of parabronchi and gave rise to orthogonal parabronchial arteries (A2) that formed arterioles (A3). The arterioles formed capillaries that participated in the formation of the parabronchial mantle. The venous system comprised six hierarchical generations originating from the luminal aspect of the parabronchi, where capillaries converged to form occasional tiny infundibular venules (V6) around infundibulae, or septal venules (V5) between conterminous atria. The confluence of the latter venules formed atrial veins (V4), which gave rise to intraparabronchial veins (V3) that traversed the capillary meshwork to join the interparabronchial veins (V1) directly or via parabronchial veins (V2). The primitive networks inaugurated through sprouting, migration, and fusion of vessels and the basic vascular pattern was already established by the 20th embryonic day, with the arterial system preceding the venous system. Segregation and remodeling of the fine vascular entities occurred through intussusceptive angiogenesis, a process that probably progressed well into the posthatch period. Apposition of endothelial cells to the attenuating epithelial cells of the air capillaries resulted in establishment of the thin blood-gas barrier. Fusion of blood capillaries proceeded through apposition of the anastomosing sprouts, with subsequent thinning of the abutting boundaries and ultimate communication of the lumens. Orthogonal reorientation of the blood capillaries at the air capillary level resulted in a cross-current system at the gas exchange interface.

Development and spatial organization of the air conduits in the lung of the domestic fowl, Gallus gallus variant domesticus.

We employed macroscopic and ultrastructural techniques as well as intratracheal casting methods to investigate the pattern of development, categories, and arrangement of the air conduits in the chicken lung. The secondary bronchi included four medioventral (MVSB), 7-10 laterodorsal (LDSB), 1-3 lateroventral (LVSB), several sacobronchi, and 20-60 posterior secondary bronchi (POSB). The latter category has not been described before and is best discerned from the internal aspect of the mesobronchus. The secondary bronchi emerged directly from the mesobronchus, except for the sacobronchi, which sprouted from the air sacs. Parabronchi from the first MVSB coursed craniodorsally and inosculated their cognates from the first two LDSB. The parabronchi from the rest of the LDSB curved dorsomedially to join those from the rest of the MVSB at the dorsal border. Sprouting, migration, and anastomoses of the paleopulmonic parabronchi resulted in two groups of these air conduits; a cranial group oriented rostrocaudally and a dorsal group oriented dorsoventrally. The neopulmonic parabronchial network formed through profuse branching and anastomoses and occupied the ventrocaudal quarter of the lung. There were no differences in the number of secondary bronchi between the left and right lungs. Notably, a combination of several visualization techniques is requisite to adequately identify and enumerate all the categories of secondary bronchi present. The 3D arrangement of the air conduits ensures a sophisticated system, suitable for efficient gas exchange. Microsc. Res. Tech., 2008. (c) 2008 Wiley-Liss, Inc.

Functional respiratory morphology in the newborn quokka wallaby (Setonix brachyurus).

A morphological and morphometric study of the lung of the newborn quokka wallaby (Setonix brachyurus) was undertaken to assess its morphofunctional status at birth. Additionally, skin structure and morphometry were investigated to assess the possibility of cutaneous gas exchange. The lung was at canalicular stage and comprised a few conducting airways and a parenchyma of thick-walled tubules lined by stretches of cuboidal pneumocytes alternating with squamous epithelium, with occasional portions of thin blood-gas barrier. The tubules were separated by abundant intertubular mesenchyme, aggregations of developing capillaries and mesenchymal cells. Conversion of the cuboidal pneumocytes to type I cells occurred through cell broadening and lamellar body extrusion. Superfluous cuboidal cells were lost through apoptosis and subsequent clearance by alveolar macrophages. The establishment of the thin blood-gas barrier was established through apposition of the incipient capillaries to the formative thin squamous epithelium. The absolute volume of the lung was 0.02 +/- 0.001 cm(3) with an air space surface area of 4.85 +/- 0.43 cm(2). Differentiated type I pneumocytes covered 78% of the tubular surface, the rest 22% going to long stretches of type II cells, their precursors or low cuboidal transitory cells with sparse lamellar bodies. The body weight-related diffusion capacity was 2.52 +/- 0.56 mL O(2) min(-1) kg(-1). The epidermis was poorly developed, and measured 29.97 +/- 4.88 microm in thickness, 13% of which was taken by a thin layer of stratum corneum, measuring 4.87 +/- 0.98 microm thick. Superficial capillaries were closely associated with the epidermis, showing the possibility that the skin also participated in some gaseous exchange. Qualitatively, the neonate quokka lung had the basic constituents for gas exchange but was quantitatively inadequate, implying the significance of percutaneous gas exchange.

Microvascular endowment in the developing chicken embryo lung.

In the current study, the contribution of the major angiogenic mechanisms, sprouting and intussusception, to vascular development in the avian lung has been demonstrated. Sprouting guides the emerging vessels to form the primordial vascular plexus, which successively surrounds and encloses the parabronchi. Intussusceptive angiogenesis has an upsurge from embryonic day 15 (E15) and contributes to the remarkably rapid expansion of the capillary plexus. Increased blood flow stimulates formation of pillars (the archetype of intussusception) in rows, their subsequent fusion and concomitant delineation of slender, solitary vascular entities from the disorganized meshwork, thus crafting the organ-specific angioarchitecture. Morphometric investigations revealed that sprouting is preponderant in the early period of development with a peak at E15 but is subsequently supplanted by intussusceptive angiogenesis by the time of hatching. Quantitative RT-PCR revealed that moderate levels of basic FGF (bFGF) and VEGF-A were maintained during the sprouting phase while PDGF-B remained minimal. All three factors were elevated during the intussusceptive phase. Immunohistoreactivity for VEGF was mainly in the epithelial cells, whereas bFGF was confined to the stromal compartment. Temporospatial interplay between sprouting and intussusceptive angiogenesis fabricates a unique vascular angioarchitecture that contributes to the establishment of a highly efficient gas exchange system characteristic of the avian lung.

Epithelial transformations in the establishment of the blood-gas barrier in the developing chick embryo lung.

The tall epithelium of the developing chick embryo lung is converted to a squamous one, which participates in formation of the thin blood-gas barrier. We show that this conversion occurred through processes resembling exocrine secretion. Initially, cells formed intraluminal protrusions (aposomes), and then transcellular double membranes were established. Gaps between the membranes opened, thus, severing the aposome from the cell. Alternatively, aposomes were squeezed out by adjacent cells or were spontaneously constricted and extruded. As a third mechanism, formation and fusion of severed vesicles or vacuoles below the aposome and their fusion with the apicolateral plasma membrane resulted in severing of the aposome. The atria started to form by progressive epithelial attenuation and subsequent invasion of the surrounding mesenchyme at regions delineated by subepithelial alpha-smooth muscle actin-positive cells. Further epithelial attenuation was achieved by vacuolation; rupture of such vacuoles with resultant numerous microfolds and microvilli, which were abscised to accomplish a smooth squamous epithelium just before hatching.

Morphometry and allometry of the postnatal marsupial lung development: an ultrastructural study.

An utrastructural morphometric study of the postnatally remodelling lungs of the quokka wallaby (Setonix brachyurus) was undertaken. Allometric scaling of the volumes of the parenchymal components against body mass was performed. Most parameters showed a positive correlation with body mass in all the developmental stages, except the volume of type II pneumocytes during the alveolar stage. The interstitial tissue and type II cell volumes increased slightly faster than body mass in the saccular stage, their growth rates declining in the alveolar stage. Conversely, type I pneumocyte volumes increased markedly in both the saccular and alveolar stages. Both capillary and endothelial volumes as well as the capillary and airspace surface areas showed highest rates of increase during the alveolar stage, at which time the rate was notably higher than that of the body mass. The pulmonary diffusion capacity increased gradually, the rate being highest in the alveolar stage and the adult values attained were comparable to those of eutherians.

Morphometry and allometry of the postnatal lung development in the quokka wallaby (Setonix brachyurus): a light microscopic study.

The postnatally developing lungs of the quokka wallaby, Setonix brachyurus, were investigated macroscopically and by light microscopic morphometry. Lung, parenchymal and non-parenchymal volumes as well as the components of the latter two were analysed by regression analysis. The lungs comprised a single undivided left lung and a right lung with an adherent accessory lobe. Septal tissue growth was most remarkable in the canalicular and saccular stages. Between mid-canalicular stage and the saccular stage, the lung volume increased 2-fold, mainly due to airspace expansion, coupled with septal tissue thinning. The non-parenchymal vascular volume increase accelerated in the successive developmental stages while the airway and connective tissue volumes progressed in a decreasing order, being highest in the canalicular and saccular stages and lowest in the alveolar stage. Growth and remodelling of the alveolar septa occurred simultaneously with airspace subdivision. Airspace expansion accelerated during the stage of microvascular maturation, when most other parameters showed the least rate of increase.

Gut morphology and morphometry in the epauletted Wahlberg's fruit bat (Epomophorus wahlbergi, Sundevall, 1846).

The morphological adaptations of the fruit bat small intestine to which the high functional efficiency could be related and the possible landmarks delineating the various parts of the gut were examined. The stomach was the carnivorous type with large rugae spanning the entire luminal aspect down to the pyloric sphincter, which was reflected internally as a prominent fold. Externally, the intestine was a continuous tube uninterrupted by any structures. The cranial fifth of the small gut had long, branching and anastomosing villi, which caudally turned to finger-like discrete structures that became rather short and stumpy and diminished at the beginning of the colon. The colon had longitudinal folds that were macroscopically discernible from the mucosal aspect of the opened intestine and that continued into the rectum. The small gut formed 94% of the whole intestinal length, the colon and the rectum taking 4 and 2%, respectively. Ultrastructurally, the enterocyte showed a prominent brush border and the lateral membranes were modified into numerous tortuous interdigitating processes. Adjacent enterocytes were joined by these processes through desmosomes. The processes also participated in pinocytotic fluid uptake from the intercellular spaces with resultant numerous intracellular vacuoles of varied sizes. Solutes absorbed into the cells were probably first passed into the intercellular compartment to create a concentration gradient thus enhancing further absorption into the cell. We conclude that the uniquely elaborate ultrastructure of the enteric epithelium coupled with the vast microvillous surface areas reported elsewhere are partly responsible for the very high absorption rates reported in the fruit bat small intestine.

Morphological analysis of the postnatally developing marsupial lung: The quokka wallaby.

We investigated the events that take place during the postnatal morphogenesis of the lung of the quokka wallaby, Setonix brachyurus, using the light microscope and both the scanning and transmission electron microscopes. The lung of term, newborn babies (joeys) at 3-days of postnatal life was at late canalicular stage and comprised large airways and tubules separated by thick mesenchymal interstitium. The tubules were lined by a low cuboidal epithelium but had few portions with true gas exchange barrier where capillaries came into close contact with squamous type of epithelium. By the fifth day postpartum, the lung entered the early saccular stage characterised by large air sacs, thinner septa, a better developed double capillary system and conversion of the cuboidal epithelium into a squamous one of type I cells interrupted by groups of cuboidal type II cells with lamellar bodies. Transitory respiratory bronchioles were recognisable toward the end of this stage. Formation of secondary septa started by Day 15, dividing the saccules into several generations of smaller air spaces. There were alternating and concurrent periods of tissue proliferation and air space expansion, followed by septal thinning. Alveolization started from about 125 days postpartum when the first burst of small sized air spaces bounded by septa with a single capillary layer were encountered. By Day 180 the process of alveolization was completed with only occasional septa showing a double capillary system and by Day 210 postnatally, the lung resembled that of an adult. For the first time in a mammal, the canalicular stage was encountered postnatally during lung development.

A stereological comparison of villous and microvillous surfaces in small intestines of frugivorous and entomophagous bats: species, inter-individual and craniocaudal differences.

The extents of functional surfaces (villi, microvilli) have been estimated at different longitudinal sites, and in the entire small intestine, for three species of bats belonging to two feeding groups: insect- and fruit-eaters. In all species, surface areas and other structural quantities tended to be greatest at more cranial sites and to decline caudally. The entomophagous bat (Miniopterus inflatus) had a mean body mass (coefficient of variation) of 8.9 g (5%) and a mean intestinal length of 20 cm (6%). The surface area of the basic intestinal tube (primary mucosa) was 9.1 cm2 (10%) but this was amplified to 48 cm2 (13%) by villi and to 0.13 m2 (20%) by microvilli. The total number of microvilli per intestine was 4 x 10(11) (20%). The average microvillus had a diameter of 8 nm (10%), a length of 1.1 microns (22%) and a membrane surface area of 0.32 micron 2 (31%). In two species of fruit bats (Epomophorus wahlbergi and Lisonycteris angolensis), body masses were greater and intestines longer, the values being 76.0 g (18%) and 76.9 g (4%), and 73 cm (16%) and 72 cm (7%), respectively. Surface areas were also greater, amounting to 76 cm2 (26%) and 45 cm2 (8%) for the primary mucosa, 547 cm2 (29%) and 314 cm2 (16%) for villi and 2.7 m2 (23%) and 1.5 m2 (18%) for microvilli. An increase in the number of microvilli, 33 x 10(11) (19%) and 15 x 10(11) (24%) per intestine, contributed to the more extensive surface area but there were concomitant changes in the dimensions of microvilli. Mean diameters were 94 nm (8%) and 111 nm (4%), and mean lengths were 2.8 microns (12%) and 2.9 microns (10%), respectively. Thus, an increase in the surface area of the average microvillus to 0.83 micron 2 (12%) and 1.02 microns 2 (11%) also contributed to the greater total surface area of microvilli. The lifestyle-related differences in total microvillous surface areas persisted when structural quantities were normalised for the differences in body masses. The values for total microvillous surface area were 148 cm2g-1 (20%) in the entomophagous bat, 355 cm2g-1 (20%) in E. wahlbergi and 192 cm2g-1 (17%) in L. angolensis. This was true despite the fact that the insecteater possessed a greater length of intestine per unit of body mass: 22 mm g-1 (8%) versus 9-10 mm g-1 (9-10%) for the fruit-eaters.

The morphology of the intestine of the entomophagous longfingered bat, Miniopterus inflatus: mucosal topography and possible landmarks.

The intestinal tract of the longfingered bat, Miniopterus inflatus, was studied macroscopically, with the light microscope and the scanning electron microscope. The intestine comprised a small mass of coiled loops contained in a rather small abdominal cavity. Macroscopically, the stomach was of the simple type and the intestine was a short convoluted tube whose diameter decreased craniocaudally. A caecum, an appendix and a colon were absent and the only portion of the large intestine observed was a short rectum grossly identifiable only on the account of its greater diameter. Microscopically, a small initial part of the intestine bordering the pylorus was characterized by numerous pits of variable sizes and shapes. This segment preceeded the ridge-like, transversely oriented villi that occupied the rest of the foregut. These villi were tallest in the proximal parts of the foregut and decreased in height caudally, ceasing completely at the junction between the small intestine and the rectum. Goblet cells were few in the cranial part of the intestine and increased caudally, reaching a maximum in the rectum. Intestinal glands were abundant in the region between the villi but Brunner's glands were absent in the submucosa. Generally the intestine of Miniopterus resembles that of the other bats which have been studied but showed structural details suggestive of an increased digestive and absorptive efficiency.