Morphology of the gills of larval and parasitic adult sea lamprey,Petromyzon marinus L.

The general morphology of the gills is similar in larval (ammocoetes) and parasitic adult sea lampreys, Petromyzon marinus, despite different methods of ventilation necessitated by their feeding habits. The gill lamellae are supported by randomly-distributed pillar cells which enclose blood spaces and collagen columns. The distribution of these cells in lampreys is different from that of higher fishes and it may be inefficient for respiratory exchange. The presence of cytoplasmic microfilaments suggests that these cells have the ability to reduce the lamellar blood spaces through contraction. Marginal channels at the tips of the lamellae are lined only by endothelial cells. The thickness of the water-blood pathway in lampreys falls within the range described for higher fishes, with the most efficient gas exchange likely occurring at the lamellar tips where only a single layer of epithelial cells is present. The abrupt increase in height of the epithelium near the lamellar bases in adults, compared to the gradual transition in height along the lamellae in ammocoetes, is perhaps reflective of higher oxygen requirements during the parasitic stage. The consistent appearance of wide, lateral intercellular spaces within the respiratory epithelium of lampreys indicates possible involvement of these spaces in transport. Mucous secretion appears to be an important function of the superficial platelet cells in ammocoetes. “Mitochondria-rich” and “mitochondria-poor” superficial cells are observed in both ammocoetes and adults, with the mitochondria-rich cells more prevalent toward the lamellar bases. The possibility that at least some of these cells may be involved in absorption is discussed. Mitochondria-rich cells in the interlamellar region are morphologically different in ammocoetes and adults but all possess an abundance of smooth endoplasmic reticulum and hence resemble “chloride cells” of higher fishes. The similarity of these cells in the parasitic adult lamprey to chloride cells of marine fishes may reflect the potential of the adult lamprey to osmoregulate in salt water. A scarcity of these cells in ammocoetes and their resemblance to chloride cells in freshwater fishes may reflect the restriction of larval lampreys to a freshwater habitat.     

A scanning electron microscopic study of secondary lamellae and chloride cells of rainbow trout (Salmo gairdneri)

Summary Scanning electron micrographs of gill tissue from rainbow trout fixed with 50% glutaraldehyde revealed the presence of microridges on surfaces of epithelial cells of the secondary lamellae. These microridges vary in length from 1 to 7 , with a mean height of 0.75 . Calculations show that they increase the total lamellar epithelial surface area approximately 2.5 fold. Mucus secreting cells are present on the body of the filament and on secondary lamellae. Chloride cells are located primarily in the interlamellae filamental epithelium and on the basal area of lamellae. Extensions of the chloride cell epithelium are microvillous in nature and their height is only slightly greater than that of the microridges of typical lamellar epithelial cells. A reduction in number or complete absence of microvilli on chloride cells appeared to be related to degenerative changes in these cells observed in transmission electron micrographs. Non secretory interlamellae filamental epithelial cells have microridges of very attenuated lengths.This research was supported by EPA Grant R-801034, USPHS Training Grant HL-05873, the Mich. Agr. Exp. Sta., Proj. 122 (Journal Article No. 5801), and OWRR Grant A-064. Acknowledgements: The authors wish to express their gratitude to Mrs. J. Mack and Mr. Wm. McAffe for their technical assistance with the electron microscopes.     

Fine structure of the gill epithelium of the terrestrial mudskipper, Periophthalmodon schlosseri

In this paper, we describe the fine structure of the branchial epithelium of the amphibious, air-breathing mudskipper Periophthalmodon schlosseri, and relate the observed structure to functions in gas exchange, and to the elimination of sodium chloride and ammonia. Also, we describe the fine structure of the opercular epithelimicrom. The gill lamellar epithelium is thickened by the presence of large mitochondria-rich (MR) cells. These MR cells are further characterized by an extensive tubular system that is continuous with the basolateral plasma membrane and by a deep apical crypt often lined with microvilli. There are very few specialized MR accessory cells, which are associated with NaCl excretion in marine teleosts. Instead, MR cells are commonly isolated from each other laterally by flattened cells rich in intermediate filaments. These filament-rich (FR) cells are interconnected by desmosomes and have unusual canaliculi. These branchial FR cells are unique to P. schlosseri and may have a structural role. Electron-dense pavement cells rich in vesicles and large vacuous mitochondria compose the superficial layer of the epithelium. The unusual morphology of P. schlosseri's gill lamellae may be related to the animal's ability to effectively eliminate ammonia during air exposure. The inner opercular lining and parts of the leading edge of the filament have intraepithelial capillaries, which provide a more suitable gas exchange surface than the thickened lamellae with its restricted interlamellar water spaces. The arrangement of respiratory and ion exchange epithelia is opposite to that found in all other fish in which the lamellae typically function in gas exchange and the gill filament in ion regulation.     

The structure of the gill of the trout,Salmo gairdneri (Richardson)

Summary A light and electron microscopic study was made of the structure of the gill arch, filament and secondary lamella of Salmo gairdneri R. Blood pathways through the gill were traced from serial histological sections, and from the examination of ink perfused tissue and perspex casts formed following resin injection of the circulatory system.The epithelium covering the gill consists of unspecialized, dark, chloride and mucous cells. The distribution of specialized cells appears to be related to gill function. The basement membrane underlying the epithelium consists of three layers, the inner collagen layer being continuous with the connective tissue core of the gills.Blood supply to the secondary lamellar respiratory surface is via branchial, filament and secondary lamellar arteries. Blood spaces of the secondary lamellae are delimited by pillar cells containing what appears to be contractile material. The marginal channel of each lamella is bounded distally by cells of endothelial origin. A network of lymph spaces within the filaments connects with efferent branchial arteries. Nutritionary capillaries within the filaments connect with afferent branchial arteries. No shunts between afferent and efferent filament arteries were found.Data from this study and previous physiological and histopathological studies suggest a mechanism for the control of blood flow to suit the respiratory requirements of the fish. This mechanism involves a system of recruitment of additional respiratory units and changes in overall blood flow patterns.This work formed part of a thesis submitted for the degree of Doctor of Philosophy in 1971 and for which M. M. was in receipt of a studentship from the Natural Environmental Research Council. The authors are grateful for the support given by research grants from the M.R.C (P.T.) and the N.E.R.C. (M.M.), and to Prof. G. M. Hughes in whose department the work was carried out.     

Structure of the gills of Barbus sophor (Ham), a cyprinid with tertiary lamellae

A study of the structure of the gills using light and transmission electron microscopy showed that though the basic organisation of the filaments and secondary lamellae is very similar to that of other bony fishes, there was also a number of unusual features. Most of the blood channels of the secondary lamellae remain embedded in the tissue of the primary lamellae. The secondary lamellar surface is increased by the presence of irregular expansions which may be referred to as tertiary lamellae. The presence of an unusual structure on one side of many secondary lamellae was observed; this structure might possibly be due to the presence of a parasite. The possible functional significance of these observations is discussed and indicates the need for morphometric and experimental investigation of the respiration of this species.     

Scanning electron microscopy of the gills of a freshwater catfish,Rita Rita

Variations in the gross morphology and surface architecture of the gill filaments and secondary lamellae of a freshwater catfish (Rita rita) have been investigated using scanning electron microscopy. Heterogeneity of the gill has been correlated with the distribution of lamellar water-flow at different regions of a gill filament. Higher lamellar water flow (cc/pore/cmH₂O/sec) was estimated for the middle region of the filaments. The filaments are covered with epithelial cells whose surface is provided with well-developed microridges. The lamellae are generally covered with microvillous epithelial cells. The variations in surface architecture of the gill filaments and secondary lamellae have been correlated with their probable functions.     

Genotoxic and Histopathological Effects of Water Pollution on Two Fish Species, <Emphasis Type="Italic">Barbus capito pectoralis</Emphasis> and <Emphasis Type="Italic">Chondrostoma nasus</Emphasis> in the Büyük Menderes River,Turkey

The genotoxic and histopathological effects of water pollution were investigated on two fish species caught from the Buyuk Menderes River and from its tributary, the Cine Stream. The Buyuk Menderes basin is an important agricultural area in Turkey. The levels of copper, zinc, cadmium, cobalt, and lead were measured at the surface of the water and in gills, liver, and muscle tissue of Chondrostoma nasus and Barbus capito pectoralis. In some tissues, the concentrations of some of these metals exceeded acceptable levels for human consumption. Zinc was found to be the most abundant metal in water and tissues. Maximal metal accumulation was observed in the liver. To detect the genotoxic potential of contaminants, the formation of micronucleus in erythrocytes was used as indicator of chromosomal damage. The frequency of micronucleus formation did not show significant differences between locations and controls in B. capito pectoralis caught from three locations and C. nasus from two locations. The histological changes included significant decreases of the mean lengths of primary and secondary lamellae. In gills epithelia, we observed cellular proliferation that developed Because of secondary lamellae fusion, ballooning degenerations, or club deformation of secondary lamellae and cystic structures in secondary lamellae. In the liver, the changes included swollen and ruptured parenchymal cells, loss of cord structure, vacuoles filled with cellular debris, focal necrosis, and a significant increase in Kupffer cells.     

Gill lamellar pillar cell necrosis, a new birnavirus disease in Japanese eels.

Since the late 1980s, a birnaviral gill disease has been occurring in Japanese eels Anguilla japonica reared in warmwater ponds in western regions in Japan. Diseased eels mostly displayed marked formations of aneurysmal hematomas within gill lamellae and high mortalities. Histological examination revealed necrosis of pillar cells and subsequent aggregation of erythrocytes inside the lamellar capillaries, and proliferation of interlamellar epithelia onto the lamellae. Gastric gland cells were also necrotized. Electron microscopy revealed birnavirus infection in lamellar pillar cells. The causative birnavirus was isolated and cultured in fish cell lines and was found to be related to an infectious pancreatic necrosis virus (IPNV) Sp serotype by neutralization tests. The viral pathogenicity was confirmed by the results of histopathological examinations and infectivity experiments.     

Gill infection of Leporinus macrocephalus Garavello & Britski, 1988 (Osteichthyes: Anostomidae) by Henneguya leporinicola n. sp. (Myxozoa: Myxobolidae). Description, histopathology and treatment

Piau?us (Leporinus macrocephalus), were raised in 300 m2 ponds (density of 10 fish/m2) presenting asphyxia signals and daily mortality of 27 fishes. Specimens with 8-cm total body length, were collected for necropsy. Mucus of body surface and pieces of organs were collected and examined microscopically, in wet mounts, stained or in histological sections. The smears examination showed the presence of several spores in the secondary lamellae of the gill filaments, identified as Henneguya leporinicola n.sp (Myxozoa: Myxobolidae). Histopathological study showed epithelial hyperplasia and fulfilling of the spaces between the secondary lamellae, congestion and telangiectasia sinusoidal. It was also observed hyperplasia of the goblet cells and several cysts of parasite with 70.3 microns diameter. Such cysts were situated among the secondary lamellae, covered or not by the hyperplasic epithelium. With this diagnostic, three applications of formalin solution 10 ml/m3 were carried out. Fifteen days after that, fish were examined again to ascertain whether the treatment was efficient on disease caused by the protozoa. The tissue alterations present in the gills after the treatment were just a moderate sinusoidal congestion and a slight epithelial hyperplasia on the base of the secondary lamellae.     

First observations of histopathological effects of 2,4,6-trinitrotoluene (TNT) in gills of European eel <Emphasis Type="Italic">Anguilla anguilla</Emphasis> (Linnaeus, 1758)

The aim of the present study was to investigate the effects on gill morphology of the explosive 2,4,6-trinitrotoluene (TNT) in a model fish, the European eel, Anguilla anguilla (Linnaeus, 1758) to assess potential detrimental effects in marine fish due to its presence in dumping areas. Juvenile specimens of A. anguilla were exposed in vivo for 6 and 24 h to 0.5, 1 and 2.5 mg/l nominal concentrations of TNT using dimethyl sulfoxide (0.1‰) as solvent carrier. Histological analysis of gills indicated that TNT induced several structural lesions. After 6h of exposure at 0.5 and 1 mg/l TNT, oedema of some secondary lamellae was evident: this change at the highest dose of 2.5 mg/l led to epithelial lifting and detachment from the endothelium and rupture of the branchial membrane and vascular congestion. After 24 h at 0.5 mg/l, increased oedema in secondary lamellae, extensive epithelial detachment and vascular congestion and dilation of lamellar capillaries and pooling of blood at 1 mg/l were observed. At 2.5 mg/l, epithelial hyperplasia, fusion of adjacent lamellae, obliteration of interlamellar spaces by means of tight junctions were also observed. Moreover, chloride cells proliferated along secondary lamellae, and mucus hypersecretion was evident. The overall results clearly indicate that gills are sensitive targets of TNT.     

Histopathological alterations and induction of cytochrome P-450 1A in the liver and gills of the gilthead seabream (Sparus aurata) exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

The toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been demonstrated in the seabream Sparus aurata specimens. Liver presented hepatocytic alterations, with an increase of lipid droplets and glycogen granules. Ultrastructural modifications of hepatocytes included RER fractionation, glycogen augmentation, as well as a rise in the number of lipid droplets, vacuoles and secondary lysosomes. In the gills, secondary lamellar epithelium showed hyperplasia, hypertrophy and lamellar fusion on the edge of the filaments. At the end of the exposure period (1 pg1(-1) TCDD for 20 days), some organelles in epithelial cells of the secondary lamellae and the tubular system of the chloride cells appeared altered. In the liver of TCDD-exposed specimens, immunoreactive cytochrome P-450 1A was concentrated close to the cytoplasmic and nuclear membranes, and positive granules were also evident throughout cytoplasm of the hepatocytes. Significant cytochrome P-450 staining was especially evident in endothelium of the hepatic vascular system. At the beginning of the exposure (1 pg 1(-1) TCDD, for 5 and 10 days), cytochrome P-450 immunostaining was observed in the cytoplasm of scarce hepatic cells and after 20 days of treatment, specific immunostained cytoplasmic granules were detected in most hepatocytes. In gills of TCDD-treated specimens, pillar-endothelial cells showed a cytochrome P-450 1A immunostaining concentrated close to the base of gill filaments and dispersed through the gill lamellae. There was also significant cytochrome staining of the endothelium of the branchial vascular system. However, no cytochrome immunoreactivity was observed in epithelial-respiratory cells.     

Chloride cell responses to ion challenge in two tropical freshwater fish,the erythrinids Hoplias malabaricus and Hoplerythrinus unitaeniatus

Chloride cell (CC) responses to ion challenge and plasma ion concentration were evaluated in two ecologically distinct erythrinids, Hoplias malabaricus, an exclusively water-breathing species, and Hoplerythrinus unitaeniatus, a facultative air-breathing fish, at one, two, seven, and 15 days of exposure to deionized water and to ion-rich water. H. malabaricus displayed high CC proliferation on filament and lamellar epithelium during exposure to deionized water and significant CC proliferation in the filament epithelium on the first day of exposure to water rich in NaCl and Ca2+ and in the lamellar epithelium on the first, second, and seventh day of exposure to such water. CC proliferation in H. unitaeniatus occurred only in the lamellar epithelium of fish exposed to deionized water. CC proliferation on both species was not accompanied by significant increase of CC density in contact with the external medium. The increase in the CC fractional area (CCFA) resulted from the increase of individual CC apical surface area on the first and second days of exposure to deionized water in H. malabaricus and only on the first day in H. unitaeniatus. Plasma ions in both erythrinid species showed transitory changes and, on the fifteenth day of exposure to the two types of experimental water, the plasma ion concentration was similar to the control fish. The CC responses of these erythrinid fish showed that CC proliferation depends on previous CC density in the gill and is not related solely to exposure to ion-poor water. Furthermore, CC proliferation in gill epithelium did not always involve an increase of CC density in contact with the external medium.     

Immunocytochemical localization of piscidin in mast cells of infected seabass gill

Annual losses of ～5–10% of the juvenile stock of European seabass, Dicentrarchus labrax (L.) in the northern coast of the Adriatic Sea has been attributed to heavy infections of the gill monogenean Diplectanum aequans. Immunocytochemical, light and ultrastructural studies were carried out on seabass naturally parasitized with this monogenean. The site of the worm's attachment was marked by the common presence of haemorrhages and white mucoid exudate. In histological sections, infected gills showed hyperplasia, as well as proliferation of mucous cells and rodlet cells. Disruption and fusion of the secondary lamellae were common in all infected seabass, with several specimens also showing marked inflammation and erosion of the primary and secondary lamellar epithelium. Immunostaining of primary and secondary gill filaments with an antibody against the antimicrobial peptide piscidin 3 (anti-piscidin 3 antibody, anti-HAGR) revealed a subpopulation of mast cells that were positive. Mast cells were both within and outside the blood vessels of the primary and secondary lamellae, and often made intimate contact with vascular endothelial cells. Mast cells were irregular in shape with a cytoplasm filled by numerous electron-dense, membrane-bound granules. Our data provide evidence showing the presence of piscidin 3 in the cytoplasmic granules of an important group of fish inflammatory cells, the mast cells resident in seabass gill tissue. There was no significant difference in the number of HAGR-positive mast cells between infected and uninfected fish (ANOVA, p > 0.05). However, mast cells in parasitized gills usually showed much stronger immunostaining intensity compared to those in unparasitized gills. These data are the first to document a response of piscidins or any other antimicrobial peptide of fish to parasite infection and suggest that mast cells may play a role in certain inflammatory responses without a detectable increase in their numbers.     

The source of lamellar mitochondria-rich cells in the air-breathing fish, Trichogaster leeri

Pavement cells and the mitochondria-rich cells (MRCs) are two of the main types of cells in fish gill epithelia. The pavement cells are generally responsible for gas exchange and MRCs for ion regulation. MRCs are found especially in the trailing edge and the interlamellar region of gill filament. In some species, MRCs are also observed in the gill lamellae. A previous study reported the likelihood of having lamellar MRCs in air-breathing fishes. Nevertheless, the source of lamellar MRCs is unclear. We used the air-breathing fish, Trichogaster leeri, to investigate the source of proliferated cells on the lamellae when 5-bromo-2-deoxyuridine (BrdU) was injected at different times before fish were sampled from deionized water. There were two major findings in this study. First, undifferentiated cells were found in the lamellae, as well as in the filaments. And, within 12-24 hr, a proliferated cell, identified as BrdU cell, could differentiate to an MRC in the gill lamellae. Second, the filaments and the lamellae in T. leeri responded to ionic stress differently but the proportion of the proliferated MRCs to the BrdU cells remained constant. Our results suggested that the lamellar MRCs were mainly differentiated from the cells that proliferated earlier from the lamellae.     

Mast cell responses to Ergasilus (Copepoda), a gill ectoparasite of sea bream

Immunocytochemical, light microscopy and ultrastructural studies were conducted on gill of sea bream, Sparus aurata L., naturally parasitized with the important parasitic copepod Ergasilus sp. to assess pathology and cellular responses. Thirty-seven S. aurata were examined from a fish farm; 26 (70%) were parasitized, with infection intensity ranging from 3 to 55 parasites per fish. Hosts were divided into two groups, lightly infected fish (<15 parasites per fish) and heavily infected fish (>15 parasites per fish). In histological sections, the copepod encircled gill lamellae with its second antennae, compressed the epithelium, provoked hyperplasia and hemorrhage, occluded arteries and often caused lamellar disruption. Fusion of the secondary lamellae due to epithelial hyperplasia was common in all infected fish; heavily infected fish showed more intense branchial inflammation. In both healthy and infected fish, mast cells (MCs) were free within the connective tissue inside and outside the blood vessels of the primary lamellae and made close contact with vascular endothelial cells, mucous cells and rodlet cells (RCs). MCs were irregular in shape with a cytoplasm filled by numerous electron-dense, membrane-bound granules. Immunostaining of primary and secondary gill filaments with an antibody against the antimicrobial peptide (AMP) piscidin 3 (anti-piscidin 3 antibody, anti-HAGR) revealed a subpopulation of MCs that were positive. These MCs were more abundant in gills of heavily infected fish than in either lightly infected or uninfected fish (ANOVA, P<0.05). Our report documents the response of gill to ectoparasite infection and provides further evidence that mast cells and their AMPs may play a role in responding to branchial ectoparasite infections.     

Fine structure of the branchial epithelium in the teleost Oreochromis niloticus

We have studied the gill epithelium of Oreochromis niloticus using transmission electron microscopy with the particular interested relationship between cell morphology and osmotic, immunoregulatory, or other non‐regulatory functions of the gill. Pavement cells covered the filament epithelium and lamellae of gills, with filament pavement cells showing distinct features from lamellar pavement cells. The superficial layer of the filament epithelium was formed by osmoregulatory elements, the columnar mitochondria‐rich, mucous and support cells, as well as by their precursors. Light mitochondria‐rich cells were located next to lamellae. They exhibited an apical crypt with microvilli and horizontal small dense rod‐like vesicles, sealed by tight junctions to pavement cells. Dark mitochondria‐rich cells had long dense rod‐like vesicles and a small apical opening sealed by tight junctions to pavement cells. The deep layer of the filament epithelium was formed by a network of undifferentiated cells, containing neuroepithelial and myoepithelial cells, macrophage and eosinophil‐like cells and their precursors, as well as precursors of mucous cells. The lateral‐basal surface was coated by myoepithelial cells and a basal lamina. The lamellar blood lacunae was lined by pillar cells and surrounded by a basal lamina and pericytes. The data presented here support the existence of two distinct types of pavement cells, mitochondria‐rich cells, and mitochondria‐rich cells precursors, a structural role for support cells, a common origin for pavement cells and support cells, a paracrine function for neuroepithelial cells in the superficial layer, and the control of the lamellar capillary base by endocrine and contractile cells. Data further suggest that the filament superficial layer is involved in gill osmoregulation, that may interact, through pale mitochondria‐rich cells, with the deep layer and lamellae, whereas the deep layer, through immune and neuroendocrine systems, acts in the regeneration and defense of the tissue. J. Morphol. 2010. © 2010 Wiley‐Liss, Inc.     

Bacteria in ovarioles of females from maleless families of ladybird beetles Adalia bipunctata L. (Coleoptera: Coccinellidae) naturally infected with Rickettsia,Wolbachia, and Spiroplasma

Ovarioles were found to be infected with Spiroplasma, Wolbachia, and Rickettsia in Adalia bipunctata females with maleless progeny in different natural populations. Ooplasm was infected with few Wolbachia bacteria. In ooplasm infected by Rickettsia, bacteria were present in small foci. Spiroplasmas were found encapsulated into ooplasm from the wider intercellular spaces between epithelial and oocyte cells. The cytoplasm of follicular epithelia infected with Rickettsia was heavily destroyed, but the nucleus was intact and free from bacteria. The essential feature of follicular epithelium cells from Spiroplasma and Wolbachia infected A. bipunctata females was inclusions of three types: crystalline, filaments, and concentric myelin-like lamellae. Observations of smears prepared from ovaries of A. bipunctata from natural populations revealed a low concentration of bacteria within a microscopy field (less 10 bacteria) in more than 90% of specimens, and only a few ovaries were heavily infected. Two different ways of bacterial invasion of the oocyte are suggested: Spiroplasma-like, through the intercellular spaces in the epithelium and Rickettsia-like, through the cytoplasm of follicular epithelium cells. Bacteria were not found in germarium zones and we suggest that each follicle is infected from haemolymph.     

Fine structure of the gills of some Indian air-breathing fishes

A detailed account is given of the structure of the gills of Clarias batrachus, Heteropneustes (= Saccobranchus) fossilis, Channa punctata, Monopterus (= Amphipnous) cuchia and Boleophthalmus boddaerti, based upon light and electron microscopy. In all five species the basic organization into primary and secondary lamellae is apparent but the latter are very much more modified in Monopterus. Three main layers separate the water and blood on the surface of the secondary lamellae. The outer epithelium is usually two layered but may be multilayered close to the origin of the secondary lamellae from the gill filament. The basement membrane is relatively thin and a middle dense layer containing collagen fibrils separates two clear layers. The pillar cells, so characteristic of secondary lamellae, are present in all except Monopterus and flanges from these cells surround the blood channels with the exception of the marginal channels. The latter are lined by endothelial cells which line all the blood channels of Monopterus. The overall thickness of the three layers comprising the water/blood barrier ranges from 1.5 to 13 microns. A number of modifications to this basic organization can be related to the degree of dependence of the different species on air-breathing. Boleophthalmus is the only species commonly found in brackish water and its secondary lamellae have well developed lymphoid spaces between two layers of the epithelium. Special densely-stained regions of the pillar cell flanges were also present in this fish and may have a supporting function.     

Retention of lipolytic products in chylomicrons incubated with lipoprotein lipase: electron microscope study.

Early effects of lipolysis on the structure of chylomicrons in vitro were studied in rat chylomicrons incubated with purified bovine mild lipoprotein lipase at pH 8.1. The amount of the albumin added to the incubation medium was limited so that free fatty acids (FFA) and partial glycerides formed during lipolysis would accumulate in the chylomicrons. The structures visualized in lipolyzed chylomicrons was found to be affected by pH during preparation of specimens for microscopy, whether fixed with OsO4 and sectioned, or stained with sodium phosphotungstate and examined as whole mounts. Circular aqueous spaces were present in the triglyceride core of lipolyzed chylomicrons processed at pH 8.1 and 7.4. Sometimes the spaces contained aggregates of osmiophilic material and whorls of bilayered lamellae. The spaces were replaced by lamellar structures having a periodicity of 40 A, in chylomicrons processed at pH 5.5, and the spaces and lamellae were both absent at pH 3.0. The findings indicate that these spaces were lined by a lipid monolayer which formed bilayered lamellae under certain conditions. It is concluded that the monolayer lining the aqueous spaces is an inward extension of the chylomicron surface film produced by the accumulation and movement of lipolytic products, FFA and partial glycerides, in the interfacial plane between core triglyceride and water.     

Ultrastructural study of the early development and localization of Loma salmonae in the gills of experimentally infected rainbow trout

The early ultrastructural stages of Loma salmonae were studied in the gills of experimentally infected rainbow trout. No parasitic stages were identified during the first 2 wk of the infection. By week 3 postexposure (PE), uninucleate and binucleate meronts were recognized within host cells (no xenomas) associated with the capillary channels of secondary lamellae and lamellar arteries. An inflammatory reaction was absent. In secondary lamellae, infected cells were isolated from the capillary lumen, and some were recognized as pillar cells. In lamellar arteries, infected cells were localized beneath the endothelium and not in the lumen. Inflammatory reaction and destruction of parasites inside blood cells in the lumen of secondary lamellae were observed by week 4 PE. Three hypotheses, i.e., isolation, internalization, and evasion, are proposed to explain the localization of the infected cells in the gills. It is concluded that meronts are the earliest parasitic stage observed by week 3 PE, pillar cells are secondarily infected by phagocytosis of infected cells in the blood, endothelial cells of gills are not infected, and inflammatory response to the parasite starts by week 4 PE.