Ergastoplasmic paracrystalline inclusion bodies in the adipose gonadal envelope and fat body of the glow worm, Lampyris noctiluca (Insecta, Coleoptera)

The gonads of glow worm larvae are enveloped by adipose tissue which represents a specialized fat body. The adipose gonadal envelope, and also to a lesser extent the fat body cells, contain tubular paracrystalline inclusion bodies (PIBs). Cells of other tissues are devoid of such inclusions. The PIBs form in the cisternae of rough ER. In young larvae PIB formation is sparse, but at advanced larval stages PIBs often occur as bundles in stacks of ergastoplasm. Typically, a PIB within a cisterna consists of four to seven parallel tubules. The outer diameter of a tubule is ca 28.8 nm and the width of the tubule lumen ca 12.2 nm. The "wall" of a tubule contains globular protein subunits of ca 8.3 nm diameter; the subunits are arranged helically. Since the adipose gonadal envelope progresses through a cytological differentiation process during differentiation and maturation of the gonads, the increased number of PIBs may indicate enhanced metabolic activity of the tissue related to nutrition of the growing gonads.

Precalcaneal congenital fibrolipomatous hamartoma: a report of four cases

Four infants had soft, skin-colored nodules in the midline plantar region of the heels since birth. The lesions were asymptomatic, bilateral, and symmetric, and measured approximately 1 cm in diameter. Their size increased in proportion to the growth of the child. In three infants the lesions persisted at 1 year of age, while in the fourth they remained at age 12 years. The nodules were not associated with any other disease or abnormality. A review of the literature revealed only one Argentinean series comprising four cases, and two communications at international pediatric congresses by French and American authors who reported five and three cases, respectively. We describe four additional cases of precalcaneal congenital fibrolipomatous hamartoma and comment on their histopathologic and ultrastructural characteristics.

[Facial localized cosmetic filling by multiple injections of fat stored at -30 degrees C. Techniques, clinial follow-up of 99 patients and histological examination of 10 patients]

At the end of the 1980's and at the beginning of the 1990's, free fat autografts were abandoned because of the poor long-term results. Two theories supported by hystological studies (the host replacement theory or the cell survival theory) have now been proposed to explain survival of fat tissue. They demonstrate that, when harvested by a correct technique, fat tissue presents the ideal characteristics to be grafted, providing a good soft-tissue substitute with a minimum follow-up of four years up to 6 years. The authors present a multiple stage lipofilling technique in 99 cases of facial rejuvenation by means of lipolayering. Injections are performed every 20 days and fat is stored fat at -30 degrees C with good aesthetic results and minimal morbidity with clinical follow-up at 4 and 6 years. Histological examination of fat stored for 20 days and for 8 months was also performed in 10 patients. Microscopic and ultrastructural examination demonstrated that stored adipocytes retain their anatomical features and, when injected in multiple stages, are adequate to obtain good clinical results. Our histological study combined with the clinical outcomes, suggests the advantage of several stage injection of stored fat (-30 degrees C).

Cerebriform plantar hyperplasia: ultrastructural study of two cases

In the present work we report the histopathological features of the cerebriform plantar hyperplasia observed in two patients with a mild form of the Proteus syndrome. Light microscopy revealed increased fibro-adipose tissue and adnexal structures in the dermis. Ultrastructurally, densely packed collagen fibrils variable in diameter and configuration, described as composite fibrils and unraveled fibrils, as well as a few fragmented elastic fibrils presenting an altered ratio between the elastin and the microfibrillar components were the major features observed. We consider that these histopathological findings will contribute to further delineate cerebriform plantar hyperplasia and also to establish clues for the early diagnosis of the Proteus syndrome.

Immunohistochemical and ultrastructural localization of leptin and leptin receptor in human white adipose tissue and differentiating human adipose cells in primary culture

Leptin is mainly produced in white adipose tissue and acts both at distant sites and locally at the tissue from which it originates. The cellular and subcellular localization of leptin and its receptor (Ob-receptor [Ob-R]) and their relationship to various stages of fat cell maturation have not been characterized as yet. Therefore, we analyzed leptin and Ob-R by using reverse transcriptase-polymerase chain reaction, immunohistochemistry, and ultrastructural immunogold labeling in human white adipose tissue and in human adipocyte cell cultures at early and late stages of differentiation. Both leptin and its receptor were present in mature unilocular fat cells. The thin cytoplasmic rim of the adipocytes exhibited the strongest expression of both leptin and Ob-R. At early stages of differentiating human adipocytes, leptin was mainly expressed in multilocular preadipocytes, whereas the Ob-R was found predominantly on fibroblast-like cells. Other cellular components of human white adipose tissue were characterized by anti-CD31 for endothelial cells, anti-CD68 for macrophages, and antibodies specifically labeling B-cells and T-cells. In addition to fat cells, endothelial cells were immunopositive for the full-length leptin receptor. On the ultrastructural level, leptin was mainly found attached to cellular membranes and in small alveolate vesicle-like structures in the cytoplasm of adipocytes. Leptin was also present on the cell membranes of endothelial cells and macrophages. We conclude that the expression of the Ob-R in human white adipose tissue is not restricted to adipocytes but is present in resident endothelial and immune cells. Ultrastructural localization studies revealed an association of leptin with cell membranes and small vesicles. The cellular and subcellular distribution of leptin and its receptor suggests an important autocrine and paracrine role for leptin in human adipose tissue.

Lipedematous alopecia: a clinicopathologic, histologic and ultrastructural study

Lipedematous alopecia is a rare condition of unknown etiology characterized by a thick, boggy scalp with varying degrees of hair loss that occurs in adult black females, with no clearly associated medical or physiologic conditions. The fundamental pathologic finding consists of an approximate doubling in scalp thickness resulting from expansion of the subcutaneous fat layer in the absence of adipose tissue hypertrophy or hyperplasia. Observations by light and electron microscopy detailed in this report suggest that this alteration principally manifests by localized edema with disruption and degeneration of adipose tissue. Some diminution in the number of follicles as well as focal bulb atrophy is noted. Aberrant mucin deposition such as that seen in myxedema or other cutaneous mucinoses is not a feature. The histologic findings bear some resemblance to those seen in lipedema of the legs, a relatively common but infrequently diagnosed condition. We present a case of lipedematous alopecia with emphasis on histologic and ultrastructural features. The etiology is unknown.

Delta9 desaturase activity in bovine subcutaneous adipose tissue of different fatty acid composition

Two experiments were conducted to investigate the relationship between delta9 desaturase (stearoyl-coenzyme A desaturase) activity and fatty acid composition in subcutaneous adipose tissue from cattle of different backgrounds. In Experiment 1, subcutaneous adipose tissue samples were taken from carcasses of pasture-fed cattle and feedlot cattle fed for 100, 200, or 300 d. Adipose tissue from pasture-fed cattle had significantly lower total saturated fatty acids and higher total unsaturated fatty acids than feedlot cattle. Desaturase activity correspondingly was 60-85% higher in pasture-fed cattle than in feedlot cattle. There was no difference in the fatty acid composition or desaturase activity among samples from the 100-, 200-, and 300-d feedlot cattle. In Experiment 2, adipose tissue samples were collected from carcasses of feedlot cattle fed for 180 d with either a standard feedlot ration (control group), or a ration containing rumen-protected cottonseed oil (CSO) for the last 70-80 d. Adipose tissue from the CSO-fed cattle was more saturated than that from the control group, having significantly more 18:0 and less 16:1 and 18:1. Correspondingly, adipose tissue from the CSO group had significantly lower desaturase activity. The elevated 18:2 in adipose tissue from the CSO group confirmed that unsaturated fatty acids (including cyclopropenoid fatty acids) were protected from biohydrogenation. Further studies are needed to determine whether the repression of desaturase activity results from direct inhibition by cyclopropenoic acids or by higher dietary contents of 18:2.

Atypical expression of mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase in subcutaneous adipose tissue of male rats

The mRNAs encoding mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase (mtHMG-CoA synthase), the rate limiting enzyme in ketone body production, are highly expressed in subcutaneous (SC) and, to a lesser extent, in peri-epididymal (PE) rat adipose tissues. This atypical mtHMG-CoA synthase gene expression is dependent on the age (from 9 weeks of age) and sex (higher in male than in female) of the rats. In contrast, the expression of mtHMG-CoA synthase in SC adipose deposit is independent of the nutritional state (fed versus starved) or of the thermic environment (24 degrees C versus 4 degrees C). The expression of mtHMG-CoA synthase is suppressed in SC fat pads of castrated male rats whereas treatment of castrated rats with testosterone restores a normal level of expression. Moreover, testosterone injection induces the expression mtHMG-CoA synthase in SC adipose tissue of age-matched females. The presence of the mtHMG-CoA synthase immunoreactive protein confers to mitochondria isolated from SC adipose deposits, the capacity to produce ketone bodies at a rate similar to that found in liver mitochondria (SC = 13.7 +/- 0.7, liver = 16.4 +/- 1.4 nmol/min/mg prot). mtHMG-CoA synthase is expressed in the stromal vascular fraction (SVF) whatever the adipose deposit considered. While acetyl-CoA carboxylase (ACC) is only expressed in mature adipocytes, the other lipogenic enzymes, fatty acid synthase (FAS) and citrate cleavage enzyme (CCE), are expressed both in SVF cells and mature adipocytes. The expression of lipogenic enzyme genes is markedly reduced in adipocytes but not in SVF cells isolated from 48-h starved male rats. When SVF is subfractionated, mtHMG-CoA synthase mRNAs are mainly recovered in two fractions containing poorly digested structures such as microcapillaries whereas the lowest expression is found in the pre-adipocyte fraction. Interestingly, FAS and CCE mRNAs co-segregate with mtHMG-CoA synthase mRNA. The possible physiological relevance of such atypical expression of mtHMG-CoA synthase is discussed.

Metabolism and morphology of brown adipose tissue from Brahman and Angus newborn calves

The objective of this study was to compare adipocyte morphology and lipogenesis between breed types (Angus vs Brahman) in brown adipose tissue (BAT) and white adipose tissue (WAT) from newborn calves. The Brahman calves (n = 7) were born during the fall season, whereas the Angus calves were born in fall (n = 6) or the following spring (n = 4). At parturition, Brahman cows were lighter than fall Angus cows, but were heavier than spring Angus cows (P < .05). Birth weights and perirenal BAT weights were greater in spring-born, but not in fall-born Angus calves, than in Brahman calves (P < .05). Fall-born Angus BAT contained 63% more (P < .05) adipocytes/100 mg tissue and contained a greater proportion (P < .05) of adipocytes with mean diameters of 40 to 50 microm, and fewer adipocytes with diameters of 60 microm or greater, than Brahman BAT. Brahman BAT contained two-to-three times as many beta-receptors as Angus BAT (P < .05), although the dissociation constant (Kd) was not different between breed types. Mitochondria in Brahman BAT were primarily spherical, whereas Angus BAT mitochondria were elongated, and mitochondrial cross-sectional area tended (P = .08) to be greater in Brahman BAT than in Angus BAT. The mitochondrial uncoupling protein (UCP) mRNA concentration (per 10(6) cells) was greater in Brahman BAT than in BAT from fall-born Angus calves. Lipogenesis from acetate was greater in Angus BAT than in Brahman BAT (P < .05), and glucose and palmitate contributed a greater proportion of carbon to lipogenesis in Brahman BAT than in Angus BAT. These differences in lipogenesis between breed types were not observed in s.c. WAT. The WAT from both breed types contained adipocytes with distinct brown adipocyte morphology, suggesting an involution of BAT to WAT in utero. We conclude that differences in UCP gene expression cannot cause the greater peak thermogenesis of Angus calves; however, differences between breed types in lipid metabolism and(or) mitochondrial morphology may contribute to this phenomenon.

Lipoprotein lipase and the disposition of dietary fatty acids

Lipoprotein lipase (EC 3.1.1.34; LPL) is a key enzyme regulating the disposal of lipid fuels in the body. It is expressed in a number of peripheral tissues including adipose tissue, skeletal and cardiac muscle and mammary gland. Its role is to hydrolyse triacylglycerol (TG) circulating in the TG-rich lipoprotein particles in order to deliver fatty acids to the tissue. It appears to act preferentially on chylomicron-TG, and therefore may play a particularly important role in regulating the disposition of dietary fatty acids. LPL activity is regulated according to nutritional state in a tissue-specific manner according to the needs of the tissue for fatty acids. For instance, it is highly active in lactating mammary gland; in white adipose tissue it is activated in the fed state and suppressed during fasting, whereas the reverse is true in muscle. Such observations have led to the view of LPL as a metabolic gatekeeper, especially for dietary fatty acids. However, closer inspection of its action in white adipose tissue reveals that this picture is only partially true. Normal fat deposition in adipose tissue can occur in the complete absence of LPL, and conversely, if LPL activity is increased by pharmacological means, increased fat storage does not necessarily follow. LPL appears to act as one member of a series of metabolic steps which are regulated in a highly coordinated manner. In white adipose tissue, it is clear that there is a major locus of control of fatty acid disposition downstream from LPL. This involves regulation of the pathway of fatty acid uptake and esterification, and appears to be regulated by a number of factors including insulin, acylation-stimulating protein and possibly leptin.

Snareing GLUT4 at the plasma membrane in muscle and fat

Explosive advances in the understanding of vesicle trafficking between intracellular compartments have occurred in recent years. These investigations inspired an attractive model for intracellular membrane transport, referred as the SNARE hypothesis. These advances have been profitably applied to one system in muscle and fat; the regulation of intracellular trafficking of the insulin-regulatable facilitative glucose transporter (GLUT4). Investigations in insulin-sensitive cell types revealed a remarkable conservation in the mechanism of vesicular transport between synaptic vesicles in the presynaptic nerve terminal and GLUT4-containing vesicles in muscle and fat. On the other hand, unique players in insulin-regulatable GLUT4 movement have also been clarified during this process. Thus, unveiling the molecular mechanisms regulating insulin-stimulated GLUT4 trafficking will significantly contribute to our understanding of whole body glucose homeostasis as well as the cell biology of protein trafficking, membrane dynamics, and organelle biogenesis.

Expression of putative fatty acid transporter genes are regulated by peroxisome proliferator-activated receptor alpha and gamma activators in a tissue- and inducer-specific manner

Regulation of gene expression of three putative long-chain fatty acid transport proteins, fatty acid translocase (FAT), mitochondrial aspartate aminotransferase (mAspAT), and fatty acid transport protein (FATP), by drugs that activate peroxisome proliferator-activated receptor (PPAR) alpha and gamma were studied using normal and obese mice and rat hepatoma cells. FAT mRNA was induced in liver and intestine of normal mice and in hepatoma cells to various extents only by PPARalpha-activating drugs. FATP mRNA was similarly induced in liver, but to a lesser extent in intestine. The induction time course in the liver was slower for FAT and FATP mRNA than that of an mRNA encoding a peroxisomal enzyme. An obligatory role of PPARalpha in hepatic FAT and FATP induction was demonstrated, since an increase in these mRNAs was not observed in PPARalpha-null mice. Levels of mAspAT mRNA were higher in liver and intestine of mice treated with peroxisome proliferators, while levels in hepatoma cells were similar regardless of treatment. In white adipose tissue of KKAy obese mice, thiazolidinedione PPARgamma activators (pioglitazone and troglitazone) induced FAT and FATP more efficiently than the PPARalpha activator, clofibrate. This effect was absent in brown adipose tissue. Under the same conditions, levels of mAspAT mRNA did not change significantly in these tissues. In conclusion, tissue-specific expression of FAT and FATP genes involves both PPARalpha and -gamma. Our data suggest that among the three putative long-chain fatty acid transporters, FAT and FATP appear to have physiological roles. Thus, peroxisome proliferators not only influence the metabolism of intracellular fatty acids but also cellular uptake, which is likely to be an important regulatory step in lipid homeostasis.

A model for ultrasonic scattering in cancellous bone based on velocity fluctuations in a binary mixture

A scattering model based on velocity fluctuations in a binary mixture (marrow fat and cortical matrix) was used to estimate the ultrasonic attenuation in cancellous bone as a function of volume fraction. The calculation of velocity fluctuations alone seems to be suitable for the qualitative estimation of attenuation. The predicted values of the attenuation were of the same order of magnitude as experimentally determined values from the literature. This agreement was achieved with only a small number of variables (the velocities of the two components and the scatterer size) in the model, representing a major advantage compared with other theories. Hence the suggested approach appears to be a good starting point for further theoretical investigations using scattering theories. However, this has to be accompanied by accurate ultrasonic and microstructural measurements.

Cerium ions in the histochemical demonstration of second-messenger enzymes

Second-messenger systems are involved in the regulation of numerous cellular processes. Adenylate cyclase (AC) and guanylate cyclase (GC) enzymes are in key positions in the regulation of these systems. The cerium method has been successfully applied to demonstrate amine- and neuropeptide-stimulated AC in rat nervous and adipose tissues and human sweat glands at the electron microscopic level. AC was also localized in cultured neurons. Nitric oxide compounds stimulated GC were demonstrated in rat hippocampal areas. Enzyme reactions were located in neurons pre- and postsynaptically in synapses; in addition, GC activity was seen intraneuronally and in glial cells. Adipocytes and eccrine glandular cells exhibited reaction products in their plasmalemmas. Optimal histochemical conditions are described, combined with control experiments. Some handicaps, related to the sensitivity of the enzymes to the fixatives, penetration problems of cerium salts, and especially the specificity of the method in phosphatase enzyme histochemistry in general are discussed.

Desensitization of beta3-adrenergic receptor-stimulated adenylyl cyclase activity and lipolysis in rats

The beta3-adrenergic receptor is an integral membrane protein consisting of seven transmembrane domains. Unlike the beta1 and beta2 receptors, this subtype lacks the consensus phosphorylation sites required for desensitization by serine kinases. Using the rodent specific beta3 agonist BRL 35135, our initial data indicated that beta3 receptor-mediated glycerol levels progressively decreased following daily oral doses of 5 mg/kg. Therefore, we initiated studies designed to delineate the possible mechanism(s) for this decreased response. Within 3 hours following a single oral dose of BRL 35135, serum glycerol levels and UCP (uncoupling protein) RNA levels were significantly increased whereas beta3 RNA levels were significantly decreased. Rats were dosed daily for 5 days with either vehicle or BRL 35135 (5 mg/kg, p.o.) and blood samples were collected for glycerol analysis. Adipose tissue was excised for lipolysis and adenyl cyclase measurements. In addition, UCP and beta3 receptor RNA levels were assessed. No effect on adipocyte BRL 37344-stimulated adenylyl cyclase activity was observed 3 hours following the initial dose of BRL 35135. Although a slight decrease (approximately 25%) in adenylyl cyclase activity could be observed 24 hours following the initial dose, it wasn't until day 4 of dosing that a significant decrease (50%) was observed. In contrast, beta3- stimulated lipolysis in adipocytes from BRL 35135-treated rats was decreased 85% within 24 hours and this decrease persisted through four days of treatment. These data indicate that the lipolytic response to beta3 receptor activation is decreased after only a single oral dose of BRL 35135, whereas receptor-mediated adenylyl cyclase activation, although initially unaffected, also desensitizes by day four of treatment.

Lack of insulin receptors affects the formation of white adipose tissue in mice. A morphometric and ultrastructural analysis

Lack of insulin receptors in mice is associated with near-normal intrauterine growth, unlike patients with leprechaunism, in whom growth deficiency is a prominent clinical feature. Genetic crosses of insulin receptor- and insulin-like growth-factor-1 (IGF-1) receptor-deficient mice indicate, however, that insulin receptors play an important role in late gestational growth, and that absence of growth retardation in insulin receptor-deficient (IR-/-) mice may be due to a compensatory increase in IGF-1 receptor levels. In human fetuses, insulin has a paramount role in the generation and maintenance of adipose tissue, as demonstrated by changes associated with genetic and maternally caused fetal hyperinsulinaemia. In the present study, we have investigated whether genetic ablation of insulin receptors affects differentiation and trophism of white adipose tissue, the main target organ for the growth-promoting actions of fetal insulin. Histological, immunohistochemical, and ultrastructural analyses of white dermal adipose tissue were performed in newborn IR-/- mice, as well as normal (IR +/+ ) and heterozygous controls (IR+/-). Stereological measurements revealed a marked decrease of the adipose area in IR-/- mice compared to IR+/+ and IR+/- mice. Fat cell depletion resulted mainly from a reduction of adipocyte volume ( approximately 90 %), with a small decrease of adipocyte number. Electron microscopy analysis detected all stages of differentiation of the adipocyte precursor in IR-/- mice, suggesting that lack of insulin receptors is not associated with selective impairment of the adipocyte differentiation process. These data are consistent with a bi-modal action of fetal insulin receptors, one to mediate embryonic growth in response to IGF-2, and one to mediate adipose cell formation in response to insulin.

Morphological effects of wortmannin on the endosomal system and GLUT4-containing compartments in rat adipose cells

Studies using functional and pharmacological approaches have implicated PI 3-kinase as a key intermediate in the glucose transport and GLUT4 translocation responses to insulin. Confocal microscopy was used to investigate the effects of the PI 3-kinase inhibitor wortmannin in isolated rat adipose cells. Independent of insulin, wortmannin induces the appearance of phase-lucent vacuoles containing the endosomal markers TfR, Rab4, M6PR, and cellubrevin. When added before or with insulin, wortmannin blocks insulin-stimulated GLUT4 translocation, but does not influence the basal VAMP2-containing GLUT4 compartment. These results substantiate the concept of a specialized basal GLUT4 compartment mostly distinct from that of the recycling receptors. However, when added after insulin, wortmannin induces a rapid redistribution of GLUT4 from the cell surface into those endosomal-derived vacuoles where the GLUT4 co-localize with TfR, Rab4, cellubrevin, and VAMP2, but not with clathrin, M6PR, Golgi complex markers TGN38-mannosidase II and gamma-adaptin, and lysosomal marker lgp-120. Therefore, wortmannin also disrupts insulin-stimulated GLUT4 traffic in the recycling endosomal pathway, at a step distal to the sorting of recycling proteins from late endosomal and TGN markers; wortmannin does not appear to affect internalization from the plasma membrane, and delivery from early to late endosomes or from late endosomes to the TGN. In combination with previous kinetic biochemical studies, these results suggest that: (i) insulin stimulates the exocytosis of GLUT4 through a direct pathway from a specialized basal compartment to the plasma membrane, (ii) during endocytosis in the presence of insulin, GLUT4 is sorted out of the TfR compartment into a separate recycling pathway back to the plasma membrane, and (iii) both of these pathways involve wortmannin sensitive enzymes.

Medial meniscus replacement by a fat pad autograft. An experimental study in sheep

The medial meniscus in 15 sheep was replaced by a pediculated infrapatellar fat pad graft and resulted in the development of a macroscopically meniscus-like structure within 6 months. Five additional sheep with a meniscectomy were controls. Degenerative changes in the fat pad autograft were visible after one year. Osteoarthritis of the weightbearing medial compartment was detected after 6 months. A temporary protective effect on the cartilage could be attributed to the autograft, but the long term results indicated that this was not permanent. Fat is not suitable as a meniscal substitute.

Composite morphology of the bone and associated support-tissue interfaces to osseointegrated dental implants: TEM and HVEM analyses

Correlated transmission electron and high-voltage electron microscopic analyses examined the undecalcified bone and associated support tissues of 60 endosseous titanium blade and titanium and ceramic root-form implants in dogs. The implants supported fixed partial dentures for up to 2 years. Data obtained from this investigation suggest that a range of tissues, both mineralized and unmineralized, support osseointegrated dental implants. This study examined the tissues apposing not just isolated aspects of the implant surface, but the entire length of the implant, and found that mineralized and unmineralized tissues existed concurrently. Much of the implant surface was apposed by mandibular bone, and both root-form and blade implants osseointegrated. The densely mineralized collagen fibril matrix was often separated from the implant by only a 20-nm to 50-nm electron-dense, ruthenium-positive deposit. High-voltage electron microscope stereology demonstrated that cellular processes extended directly to the implant from underlying osteocytes. In the same implants, areas containing an unmineralized collagen matrix interposed between the bone and implant surface were observed. In this region osteoblasts interacted with this matrix, and Howship's lacunae, containing vascular elements and osteoclasts, were also observed. The remodeling activities appear to be a homeostasis of catabolic activity (osteoclasts) and metabolic activity (osteoblasts). The apex of the implant was often apposed by a fibrofatty stroma. The support tissue response appears to be the result of the interrelations of osteoblasts, osteocytes, and osteoclasts in association with vascular elements. Therefore, the support tissue response to osseointegrated implants is a dynamic activity that involves the healthy interaction of these cells and tissues along the entire length of the implant.

Myxoid tissue: its morphology, histochemistry, and relationship with other supporting tissues

Myxoid tissue was studied in the supporting organ of the cat epiglottis ("epiglottic cartilage"). Under the light microscope, myxoid tissue was characterized by stellate cells placed into an avascular acidic extracellular matrix. This extracellular matrix was alcianophilic at pH = 2.5, reacting with the colloidal iron stain, and staining metachromatically with toluidine blue O at pH = 5.0. Treatment of sections with testicular hyaluronidase abolished these reactions. In addition, staining persisted after methylation/saponification pretreatment, indicating hyaluronic acid as the main acidic component of myxoid extracellular matrix. Under the electron microscope, myxoid extracellular matrix formed flocculent electron dense precipitates. Stellate myxoid cells were characterized by bundles of intermediate (8 nm) cytoplasmic filaments. Myxoid cells were devoid of a basal lamina, contained a few small lipid droplets, and stored some glycogen. Bundles of collagen fibrils, 80-120 nm in diameter, were seen in myxoid areas. Myxoid cells reacted to S-100 protein, glial fibrillary acidic protein, and neuron specific enolase. Moreover, in adult animals, myxoid cells stained for neurofilament protein 200. All these markers were also present in chondrocytes of elastic and fibrous cartilage, indicating a close relationship between myxoid cells and chondrocytes. This was supported by the observation of continuous transitional forms of myxoid tissue into elastic or fibrous cartilage. In 8-week-old kittens, the supporting organ of the epiglottis was found mainly to consist of myxoid tissue with only a few interspersed islets of chondrocytes. It is therefore concluded that myxoid tissue can serve as a precursor of cartilage.