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PubMed1998

Mastoid size and otitis media with effusion: question of correlation.

OBJECTIVES/HYPOTHESIS: To determine the incidence of otitis media (OME) with effusion on histologic examination in temporal bones with mastoid cavities reduced by the fenestration procedure for otosclerosis. STUDY DESIGN: Temporal bone histologic study. METHODS: Light-microscopic examination of serially sectioned temporal bones. RESULTS: The incidence of otitis media with effusion in temporal bones with prior fenestration operation was not any more frequent than the control group of temporal bones with surgically unaltered mastoid cavity. CONCLUSIONS: There is no increased incidence of otitis media with effusion in temporal bones with prior fenestration operation.

Aged↗
PubMed2004

Acoustic responses of vestibular afferents in a model of superior canal dehiscence.

HYPOTHESIS: Afferents innervating the superior semicircular canal are rendered especially sensitive to acoustic stimulation when there is a dehiscence of the superior canal. Other vestibular end organs are also more sensitive to acoustic stimulation. BACKGROUND: Dehiscence of the superior semicircular canal is associated with vertigo and nystagmus caused by loud sounds (Tullio phenomenon) or changes in middle ear or intracranial pressures. The mechanisms by which acoustic stimuli act on the vestibular end organs are unclear. The nystagmus caused by acoustic stimuli generally aligns with the affected superior canal. METHODS: Responses to acoustic stimuli in the superior vestibular nerves of anesthetized chinchillas were recorded before and after fenestration of the superior canal. RESULTS: Two acoustic response patterns were seen: rapid phase locking and slow tonic changes in firing rate. Phasic responses principally occurred in irregular afferents and tonic responses in regular afferents. Afferents from all of the vestibular end organs encountered could respond to acoustic stimuli, even before fenestration. However, fenestration lowered the thresholds for acoustic stimulation in superior canal afferents with phasic responses and increased the magnitude of tonic responses. CONCLUSIONS: Superior canal dehiscence may render the irregular afferents innervating the superior canal particularly sensitive to loud sounds. Rapid phase-locking responses may explain the short latency of nystagmus seen in patients with superior canal dehiscence syndrome. The mechanisms by which acoustic stimuli activate the vestibular end organs may differ from the damped endolymph motion associated with head acceleration.

Acoustic Stimulation↗
PubMedDate not supplied

Evidence for sound perception with the labyrinth.

A report is presented of experiments on guinea pigs and pigeons concerning behavioural and electrophysiological responses of the labyrinth to sound. In the guinea pigs the cochlea was destroyed on both sides by CO2 laser radiation and fenestration of the lateral semicircular canal was done. In the pigeons the cochlea was removed before fenestration. On account of the results obtained, fenestration of the lateral canal in patients with bilateral total cochlear loss can be considered as an alternative to monopolar cochlear implants.

Action Potentials↗
PubMed1991

[Selective resection of the lateral semicircular canal with hearing preservation--an animal experiment study].

The goal of our investigation was to develop a method for removing parts of the vestibular labyrinth by surgery without inducing a loss of auditory function. Three different surgical lesions were created in the lateral semicircular canal of the rabbit: (1) fenestration; (2) fibrin glue perfusion of the canal following fenestration; and (3) destruction of the semicircular canal by drilling after fenestration and fibrin glue perfusion. Brain-stem auditory potentials were recorded repeatedly up to 3 months after operation. They demonstrated preservation of hearing in all rabbits in the first group, in 78% of the second and 67% of the third group. In the last group a 20 dB deterioration of hearing was regularly noticed. Histological study revealed the utmost importance of the fibrin glue perfusion of the perilymph space of the semicircular canal inducing an interruption of the peri- and endolymph flow. A precise microsurgical technique was crucial for hearing preservation.

Animals↗
PubMed1997

Changes in vascular permeability and deciduoma formation during the peri-implantation period of the rat in response to exogenous gonadotropins.

BACKGROUND: Permeability of thin-walled vessels of the endometrium could be a prerequisite for deciduoma formation. Exogenous gonadotropins alter endometrial morphology and inhibit vascular permeability on the day of implantation. The aim of this study was to investigate the effect of exogenous gonadotropins on vascular permeability in the peri-implantation period and relate this to deciduoma formation. METHODS: Female rats were hyperstimulated with follicle-stimulating hormone and human chorionic gonadotropin prior to mating. Control animals were not injected. Endometrial tissue was collected at 4.5, 5.5, and 6.5 days after mating. Tissue was processed for electron microscopy. RESULTS: The presence of thin-walled fenestrated vessels and decidualised stromal cells were found in all control groups. With the exception of one fenestration, which occurred in a vessel from one hyperstimulated animal on 5.5 days of pregnancy, no fenestrations were found in the vessels of hyperstimulated animals. Decidualisation of stromal cells did not occur in these animals. CONCLUSION: Hyperstimulation with exogenous gonadotropins inhibits vascular permeability and subsequent decidualisation. Implantation thus fails to occur.

Animals↗
PubMed2000

ACTH-regulated expression of vascular endothelial growth factor in the adult bovine adrenal cortex: a possible role in the maintenance of the microvasculature.

Endothelial cells lining vessels of endocrine tissues are fenestrated. Interactions with the local environment via either soluble factors or cell-cell interactions appear to govern this terminal endothelial differentiation. Adrenocorticotropin (ACTH) has previously been reported to modulate endothelial fenestration in the rat adrenal cortex. Since vascular endothelial growth factor (VEGF) has been characterized as a potent inducer of endothelial fenestration, we aimed to characterize the status of VEGF expression in the bovine adult adrenal cortex and asked whether ACTH may regulate VEGF expression. By immunohistochemical analysis, we observed VEGF expression in steroidogenic cells from both zona glomerulosa and zona fasciculata of the bovine adrenal cortex. Double-labeling experiments performed on isolated cells in primary culture revealed VEGF immunoreactivity, essentially colocalized with the Golgi apparatus. The expression of two predominant VEGF isoforms, VEGF(121) and VEGF(165), was observed by RT-PCR analysis. ACTH (10 nM) was found to rapidly (within 2-4 h) increase the abundance of these VEGF transcripts, as assessed by both RT-PCR and Northern blot analysis. In parallel, ACTH significantly induced VEGF secretion into the medium of fasciculata cells in primary culture. Thus, our data are consistent with the involvement of ACTH, through its regulation of VEGF expression, in the maintenance of the adult adrenal cortex endothelium.

Adrenal Cortex↗
PubMed1982

Fetal and neonatal rat intestinal capillaries: permeability to carbon, ferritin, hemoglobin, and myoglobin.

The function of the mural components involved in vascular exchange (pinocytotic vesicles, fenestrations, intercellular junctions, and the basal lamina) was assessed by intravascular injection of tracers (carbon, carbon plus histamine, ferritin, hemoglobin, and myoglobin) on separate gestational days in fetal and neonatal rat intestinal capillaries. The continuous capillaries present through day 17 of gestation were impermeable, even at junctions, to all the tracers within the maximum circulation time studied (3 minutes). Most of the luminal pinocytotic vesicles were labeled within 3 minutes with myoglobin (3.3-nm diameter) or hemoglobin (5.5-nm diameter), while only occasional vesicles contained ferritin (11-nm diameter) and none contained carbon (25-50nm diameter). Even though luminal pinocytotic vesicles contained the smaller tracers, no vesicular transport and discharge were ever seen. The fenestrated vessels present from day 18 of gestation allowed a rapid extravasation of ferritin and hemoglobin via diaphragmed fenestrations. At no time period did extravasation of carbon take place, nor did the carbon plus histamine solution induce vascular leakage. Once a tracer gained access to the extravascular space, the developing basal lamina did not seem to retard its movement.

Animals↗
PubMed1987

Tridimensional architecture of the Golgi apparatus and its components in mucous cells of Brunner's glands of the mouse.

The three-dimensional structure of the Golgi apparatus and its components has been analyzed in thin and thick sections of mucous cells of mouse Brunner's glands by using low- and high-voltage electron microscopes and a stereoscopic approach. In thick sections of glands impregnated with osmium or treated to detect nicotinamide adenine dinucleotide phosphatase (NADPase) or thiamine pyrophosphatase (TPPase) activity, the Golgi apparatus appeared, at low magnification, as a continuous network located in the supranuclear region. At higher magnifications and in thin sections of tissue postfixed with reduced osmium and stained with lead citrate or treated to demonstrate phosphatase activity, the following components were observed: on the cis-face of the Golgi stacks, an osmiophilic tubular network referred to as the cis-element; a cis-saccular-compartment composed of a distended porous saccule slightly reactive for NADPase and three or four underlying NADPase-positive, flattened, poorly fenestrated saccules; a trans-saccular-compartment consisting of four to six TPPase-positive saccules or sacculo-tubular elements, prosecretory granules, and "peeling off" trans-tubular networks. The saccules of the cis-compartment were often perforated by large pores in register. The cavities thus formed in the stacks were called wells and were pan-shaped with a mouth directed toward the cis-face of the stacks and a bottom closed by TPPase-positive saccules. The wells always contained 80-nm vesicles. The saccules of the trans-compartment were involved in the formation of secretory granules according to the following proposed sequence of transformation. The secretion product appeared initially as a granular material evenly distributed throughout a slightly distended, poorly fenestrated saccule. These saccules appeared to transform into fenestrated elements with irregular pores and with parts of them taking on the appearance of a tubular network; they were thus referred to as sacculotubular elements. The secretory material initially distributed throughout these elements accumulated in nodular dilatations randomly distributed along the tubular portions of the elements. The dilatations, considered as prosecretory granules, increased in size as they drained the secretory material from the rest of the sacculotubular elements. Such prosecretory granules, large and irregular in shape, "peeled off" from the stacks of saccules with residual saccular or tubular structures still attached to them, some of the latter forming trans-tubular networks. The prosecretory granules detached from such membranous residues, condensed, and finally transformed into spherical secretion granules.

Animals↗
PubMed1995

Distribution of epithelioid cells in the wall of the chicken aorta and their functional role as chemoreceptors.

BACKGROUND: The ultrastructural characteristics of epithelioid cells in the wall of the chicken aorta have been studied by several investigators. Their characteristics were homologous to those of carotid body type I cells and are considered to be one of the peripheral chemoreceptors. However, there are few descriptions about their location, distribution, and how they react to chemical signals, nor have there been many reports about the localization of bioactive substances in the epithelioid cells. Therefore we designed this investigation to address these problems. METHODS: Wholemount immunohistochemistry using antiserotonin antiserum, scanning (SEM), and transmission (TEM) electron microscopy were used to observe the epithelioid cells and the lumen of the chicken aorta. The localizations of bioactive substances in the epithelioid cells were immunohistochemically investigated using 11 antisera. RESULTS: Epithelioid cells were dispersed in the wall of the aorta, forming a band approximately 1 mm in width, located 10 mm proximal to the confluence of the right and left ligamenta arteriosa. Serotonin, chromogranin, and neuron specific enolase immunoreactivities were detected in the epithelioid cells. SEM observations clearly demonstrated intraendothelial fenestrations, 1-3 microns in diameter, on the endothelial surface of the region of the band of epithelioid cells. TEM observations revealed that these fenestrations corresponded to endothelial gaps, directly beneath which epithelioid cells were sometimes located. CONCLUSIONS: The epithelioid cells are in direct access to the aortic lumen through endothelial fenestrations. Thus they may be able to perceive chemical signals from arterial blood directly.

Animals↗
PubMed1987

Topography and morphometry of capillaries in the rat subfornical organ.

A comprehensive stereological analysis was performed to define capillary dimensions in individual subregions of the subfornical organ in Long-Evans, homozygous Brattleboro, and Sprague-Dawley rats. Capillary density, volume fraction, length, surface area, and diameter were assessed in four regions in the sagittal plane (rostral, "transitional," central, and caudal) and two zones in the coronal plane (dorsal and ventromedial). The ventromedial zones in the central and caudal regions correspond to areas of dense perikarya and neuropil containing neural afferent inputs to the subfornical organ (e.g., putative fiber terminals for angiotensin II), whereas the dorsal zones of these regions are apparently the predominant sites of perikarya having efferent projections directed outside of the organ. The morphometric analysis revealed heterogeneous capillary density across subregions of the subfornical organ (range of 132 to 931 capillaries/mm2 in the three rat groups). Capillaries in the ventromedial zones of the central and caudal regions had significantly greater density, volume fraction, and surface area, but smaller diameters, than those in the adjacent dorsal zones and more rostral regions. Across all subregions within the dorsal zone, there was generally a consistent morphometric pattern in the three rat groups. No differences in capillary dimensions in any part of the subfornical organ were found between the Long-Evans and Brattleboro rats. A qualitative electron microscopic investigation of endothelial cells in each subregion of the subfornical organ in Long-Evans rats revealed at least three types of capillary oriented according to region: in the rostral region were capillaries having no endothelial fenestrations or pericapillary spaces, and few vesicles, in the "transitional" region between the rostral and central regions, capillaries having no endothelial fenestrations, substantial numbers of vesicles, and narrow but perceptible pericapillary spaces were found, and in the central and caudal regions, capillaries having abundant endothelial fenestrations and vesicles, expansive pericapillary labyrinths, and relatively thin walls were present. These findings from light microscopic morphometry and electron microscopy in rats indicate a heterogeneity of capillary organization that shows topographical correspondence to the cytology and putative functions of the subfornical organ.

Animals↗
PubMed2002

Morphological and cytochemical aspects of capillary permeability.

Transport of plasma soluble constituents across the capillary wall is of primordial importance in cardiovascular physiology. While physiological experiments have concluded with the existence of two sets of pores, a large one responsible for the transport of proteins and a small one designed for the diffusion of small solutes, the morphological counterparts have yet to get general agreement. In this review, we present the different proposed paths within and between the endothelial cells that do allow passage of plasma constituents and may respond to the definitions established by physiological means. The vesicular system existing in endothelial cells has been the first transendothelial path to be proposed. Several data have demonstrated the involvement of this system in transport, although others have systematically brought controversy. One alternative to the vesicles has been the demonstration of membrane-bound tubules creating, in certain cases, transendothelial channels that would allow diffusion of plasma proteins and other constituents across the capillary wall. Access to this tubulo-vesicular system could be restrained by the stomatal diaphragm and facilitated by specific membrane receptors. Further, we have demonstrated for the first time with morpho-cytochemical tools, that the intercellular clefts are the site of diffusion for small molecules such as peptides having a molecular weight inferior to 3,000. For the fenestrated capillary bed, we have shown that fenestrae are the site through which plasma constituents cross the capillary wall. However, and in spite of the existence of these large open pores, the endothelial cells still display the tubulo-vesicular system involved in transport of large molecules and their intercellular clefts are also the site of diffusion of small molecules. Making consensus on the existence of an intracellular tubulo-vesicular system in non-fenestrated capillaries, responsible for the transport of large molecules by the endothelial cells, and understanding the rational for the fenestrated capillary to have three paths for transport--the fenestrae, the tubulo-vesicular system, and the inter-endothelial clefts--require further investigation.

Animals↗
PubMed1996

Chemical induction of fenestrae in vessels of the blood-brain barrier.

The endothelium responsible for the blood-brain barrier to hydrophilic solutes has been converted here, by chemical means, to the fenestrated, permeable type of vessel (FV). During development, some brain vessels are reported to be transiently fenestrated. Endothelial fenestrae of adrenal glands are known to be reinduced in vitro by retinoic acid (RA) or phorbol myristate acetate (PMA). Could fenestrae be likewise reinduced in brain barrier vessels? When RA or PMA were infused continuously by an osmotic pump for 28 days into the cerebral cortex of rats, some brain vessels in the lesion cavity created by the reagents were FV. There were no FV in adjacent brain. When 100 microM RA was infused, about 20% of vessels in the cyst were FV, as were about 29% after infusion of 150 ng/ml PMA. Fenestra development depended on concentration and time. Reversibility of fenestra formation was complete at 1-2 months after delivery of RA or PMA had ceased. It is proposed that the RA and PMA effect is mediated by the plasminogen activator urokinase, in as much as both RA and PMA stimulate its production. This notion is supported by preliminary experiments in which urokinase infusion into brain also produced fenestrae. It is further suggested that the reversible induction of fenestrae in the mature brain by RA, PMA, and, perhaps, a variety of other conversion factors may be confined to a subset of brain barrier vessels that must be regenerating and of the kind that were temporarily fenestrated during fetal life.

Animals↗
PubMed1994

Viscous and osmotically mediated changes in fluid movement across synovium in response to intraarticular albumin.

Fluid exchange in synovial joints involves both interstitial and transcapillary flow. Here the influence of intraarticular albumin, a normal component of intraarticular fluid, on net transsynovial flow was explored by infusing albumin solutions into the synovial cavity of rabbit knees and recording net flow across the synovial lining. The latter is a discontinuous cell layer possessing matrix-filled intercellular spaces and fenestrated capillaries. Albumin solutions (10-250 g.liter-1) of known oncotic pressure and viscosity were infused at a constant pressure between 3 and 18 cm H2O, either in vivo or post mortem. The rate of absorption (outflow) of Krebs solution from the cavity at the same pressure was measured as the control. Albumin reduced the net rate of absorption of fluid from the joint cavity (Qs). The reduction in Qs in vivo, expressed as a fraction of control, was greater than the fractional reduction in the fluidity of the albumin solution (i.e., 1/relative viscosity). At high albumin concentrations in vivo, the net flow reversed direction and became a net filtration into the joint cavity. The change in Qs per unit change in intraarticular oncotic pressure was then 29.7 x 10(-3) microliters.min-1.cm H2O-1. Even when there was continuous net outflow across the lining, however, as at lower albumin concentrations or higher joint pressures, the intraarticular albumin became diluted compared with the infusate. When synovial blood flow was stopped by killing the animal, albumin had less effect on net transsynovial outflow than that in vivo. Outflow was still reduced by albumin but the fractional reduction was now less than the fractional reduction in bulk fluidity. Also, intraarticular dilution was less marked postmortem than in vivo. The observations were compatible with the view that the net transsynovial flow in vivo comprised two opposing flows, namely, capillary (fenestral) filtration into the joint cavity and interstitial flow from cavity to subsynovium. These two flows were affected oppositely by albumin: filtration was enhanced by the oncotic pressure of albumin in the pericapillary interstitium, whereas interstitial flow was reduced by the effect of albumin on fluidity. The results also raised the issues of whether fenestral filtration reduces nearby interstitial albumin concentration and how interstitial and bulk-phase fluidities are related.

Albumins↗
PubMed1997

Electron microscopic demonstrations of filamentous molecular sieve plugs in capillary fenestrae.

The permeability of capillaries is usually explained with reference to "small pores," permeable to water and small solutes, and "large pores," permeable to proteins. Fenestrated capillaries are far more permeable to water and small solutes than nonfenestrated capillaries; moreover, the permeability is highest in the capillaries with the most fenestrae. This suggests that the small pores reside in the fenestral diaphragms; however, no such pores have been illustrated using electron microscopy. In an attempt to clarify this controversy, fenestrated capillaries in the small intestine, stomach, and kidney of the rat were reinvestigated by electron microscopy. A new method of vascular perfusion-fixation was employed, which included the use of glutaraldehyde dissolved in an oxygen-carrying blood substitute (fluorocarbon) and delivered by a peristaltic pump controlled by pressure feedback. The investigation disclosed a prominent endocapillary surface coat, about 50-100 nm thick, and the existence of bush-like filamentous sieve plugs in the fenestrae. Each filamentous plug was composed of 20-40 filaments, each filament measuring 300-400 nm in length and 5-10 nm in thickness. The filamentous plugs have tentatively been named fascinae fenestrae, because they resemble fascines and may also function as such.

Actin Cytoskeleton↗
PubMed1985

Lamellar to tubular conformational changes in the endoplasmic reticulum of the retinal pigment epithelium of the newt, Notophthalmus viridescens.

The retinal pigment epithelium (RPE) of the newt (Notophthalmus viridescens) was examined ultrastructurally under both in-vivo and in-vitro conditions. Five distinct conformations of smooth endoplasmic reticulum (SER), two lamellar and three tubular, were observed. The two lamellar conformations included myeloid bodies, which have previously been described (Yorke and Dickson 1984), and fenestrated SER. The latter appeared as layers of flattened or curved cisternae which were penetrated by fenestrations. Fenestrated SER became indistinguishable from the highly branched and convoluted random-tubular SER through the formation of an intermediate configuration ("tubular sheets"). The remaining tubular SER conformations appeared to arise from random-tubular SER through a progressive reduction in branching and a straightening of individual tubules. Fascicular SER was represented by the hexagonal organization of straight, unbranched tubules into bundles (fascicles). Spiral SER consisted of a similar hexagonal arrangement, but the unbranched tubules spiralled about one another. Neighbouring tubules in areas of spiral SER were also joined together by pairs of electron-dense bars. Although lamellar (especially myeloid bodies) and random-tubular configurations of the SER were common features in vivo, fascicular and spiral SER were primarily conformations encountered in vitro. Conditions favouring bilayer lipid phases also appear to facilitate the formation of both myeloid bodies and fascicular SER. These conditions included increased duration of incubation, low (less than 20 degrees C) incubation temperatures, and Ca2+-free incubations with EGTA. Random-tubular SEB was most prevalent in media supplemented with fetal calf serum and also after warmer (30 degrees C) incubation temperatures.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Ultrastructure of the endometrial blood vessels during implantation of the rat blastocyst.

The ultrastructure of the blood vessels of the endometrium was analysed during implantation of the blastocyst in rats, at the time of appearance of the Pontamine Blue Reaction. Vessels from implantation sites and from interimplantation sites were compared. In vessels from implantation sites the endothelial cells showed fenestrations covered by diaphragms. In addition, small interruptions (gaps) between the endothelial cells were observed. These features were present in vessels larger than 5 micrometers in diameter and more than 100 micrometers away from the uterine epithelium, both in the mesometrial and antimesometrial wall of the endometrium. Vessels from interimplantation sites displayed neither fenestrations nor interruptions. The endothelial cells of the implantation sites displayed morphological signs of metabolic activation. These consisted of increased numbers of polyribosomes, well developed Golgi complexes and prominent nucleoli. The fenestrations and gaps in the vessel wall were interpreted as constituting the morphological basis for the increase in vascular permeability and the consequent edema which characterize the Pontamine Blue Reaction.

Animals↗
PubMed1987

Segmental variations in the organization of the endoplasmic reticulum of the rat nephron. A stereomicroscopic study.

The spatial organization of endoplasmic reticulum (ER) was examined in all segments of rat nephron. Tissues were fixed with glutaraldehyde, impregnated "en bloc" with osmium tetroxide, prepared for and examined by standard (80-100 kV) and high voltage (1 mEV) transmission electron microscopy. In all proximal tubule cells, ER forms a continuous and extensive network of canaliculi and abundant fenestrated saccules which surround mitochondria and cytoplasmic bodies; the cage-like structure of the fenestrated saccules was most evident around the spherical mitochondria of the S3 segment. In the cells of the distal straight and convoluted tubules, the network consists mostly of canaliculi with rare non-fenestrated saccules. The ER network of canaliculi is particularly rich in intercalated cells, in contrast with its rudimentary appearance in the adjacent principal cells of the collecting tubule. In fact, in these cells there are few isolated ER cisternae and they are rarely impregnated. The nuclear envelope is well impregnated in most cells throughout the various segments. Segmental variations in ER organization and its relative abundance are most likely related to the well, established functional heterogeneity of the nephron segments. Moreover, the extensive and unique organization among mitochondria, ER and the basolateral membrane suggests that these three organelles function as a unit which is related to active electrolyte transport. In addition, because of its transepithelial organization, ER may well constitute a transcellular pathway for molecules.

Animals↗
PubMed1988

Ultrastructure of the kidney of a South American caecilian, Typhlonectes compressicaudus (Amphibia, Gymnophiona). I. Renal corpuscle, neck segment, proximal tubule and intermediate segment.

The ultrastructure of the renal corpuscle, the neck segment, the proximal tubule and the intermediate segment of the kidney of a South American caecilian, Typhlonectes compressicaudus (Amphibia, Gymnophiona) was examined by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM) and freeze-fracture technique. The glomerular filter apparatus consists of the podocyte epithelium, a distinct basement membrane, a subendothelial space and the capillary endothelium. Emanating from the podocyte cell body, several long primary processes encircle neighboring capillaries. The short slender foot processes originating from the primary processes interdigitate with those from other primary processes, thereby forming the meandering filtration slit. Thick bundles of microfilaments are found in the primary processes, but absent in the foot processes. The basement membrane consists of a lamina rara externa and a rather thin lamina densa (50 nm thickness). The wide subendothelial space contains abundant microfibrils, a few collagen fibrils and many thin processes of mesangial cells. The endothelium is flat and fenestrated (compared to mammals displaying relatively few fenestrations); some of the fenestrations are bridged by a diaphragm. The glomerular mesangium is made up of the mesangial cells and a prominent mesangial matrix containing microfibrils and collagen fibrils. The cells of the neck and intermediate segments display numerous cilia with their microtubules arranged in the typical 9 + 2 pattern. The basal bodies of the cilia are attached to thick filaments with a clear crossbanding pattern of 65 nm periodicity. The proximal tubule is composed of cells typical for this segment (PT cells) and light cells lacking a brush border (bald-headed cells). The PT cells measure 10-25 micron in height and 15-30 micron in width and do not interdigitate at their lateral borders with each other. Their basolateral cell membrane is amplified by many folds projecting into lateral intercellular spaces and into basal recesses. The brush border is scarce and composed of loosely arranged short microvilli.

Amphibians↗