Histological findings in foetuses congenitally infected by cytomegalovirus

BackgroundCongenital cytomegalovirus (CMV) infection is a major cause of central nervous system damage leading to sensorineural hearing loss, mental retardation and cerebral palsy.ObjectivesIdentify the type of organ involvement and understand the histopathogenesis of damage in foetuses of women with a CMV-highly positive amniotic fluid.Study design34 foetuses with congenital CMV infection documented by prenatal diagnosis were studied. Three foetuses died in utero. The remaining pregnancies were electively terminated at 20–21 weeks gestation.ResultsFoetal organs positive for CMV antigens were: placenta (100%), pancreas (100%), lung (87%), kidney (87%), liver (71%), brain (55%) and heart (44%). Inflammatory infiltrate was almost always present in CMV-infected foetal organs and the severity of the inflammatory response was correlated with the organ damage. Brain damage with necrosis was observed in 33% (9/27) and a mild telencephalic leukoencephalopathy in 22% (6/27) of foetuses studied.ConclusionsFocal necrosis was observed very frequently in organs such as pancreases, livers, hearts and kidneys. However the damage in these organs is likely to be resolved by parenchymal regeneration. Brain damage, which seems to be the results of a combined effect of viral infection, inflammatory infiltration and hypoxia due to severe placentitis, is less likely to be resolved because of the low regeneration ability of this organ.     

Histological findings in the Paterson-Kelly syndrome

Forty-one specimens taken from lesions in the post-cricoid region of patients with the Paterson-Kelly syndrome have been examined. Most webs consist of normal oesophageal mucosa which may be associated with underlying muscle and nerve lesions. Strictures also show a chronic non-specific inflammation often with epithelial changes and sometimes squamous carcinoma. Other lesions observed clinically have also shown malignant change.     

实验性糖尿病大鼠海马星形胶质细胞形态和凋亡的研究

目的:研究糖尿病高血糖大鼠海马星形胶质细胞形态和凋亡改变。方法:采用链脲佐菌素(STZ)诱导Ⅰ型糖尿病SD大鼠模型,并以正常SD大鼠作对照。分别于1、2、4周和8周用组织学、免疫组织化学、免疫荧光和Western Blot等方法对比研究糖尿病高血糖对大鼠海马区星形胶质细胞形态和凋亡的作用。结果:与正常对照比较,大鼠糖尿病高血糖1~2周,脑组织结构基本正常,海马区固缩神经元偶见,4~8周固缩神经元数明显(P0.05),出现轻微脑水肿,星形胶质细胞胞体轻度肿胀;免疫荧光和免疫组织化学检测显示,糖尿病高血糖1~2周,星形胶质细胞胞体增大和突起增粗,4~8周时突起增粗变长,星形胶质细胞数量减少(P0.05);Western Blot结果表明,大鼠糖尿病高血糖4~8周时,脑组织胶质原纤维酸性蛋白(GFAP)含量明显升高(P0.05);免疫组化双标显示,糖尿病高血糖大鼠1~2周偶见cleavedcaspase-3阳性标记的星形胶质细胞(P0.05),4~8周海马区双标阳性细胞数明显增多(P0.01)。结论:大鼠糖尿病高血糖早期对星形胶质细胞可能有激活作用,而持续的糖尿病高血糖则可抑制海马区星形胶质细胞,并可能导致星形胶质细胞凋亡。     

Bone in-growth induced by biphasic calcium phosphate ceramic in femoral defect of dogs

Biphasic calcium phosphate (BCP) ceramics consisting of hydroxyapatite (HA) and tricalcium phosphate (TCP) has been used as a bone graft material during the last decade. In this paper, we report the bone in-growth induced by BCP ceramic in the experimentally created circular defects in the femur of dogs. This BCP ceramic consists of 55% hydroxyapatite (HA) and 45% b-tricalcium phosphate (TCP) prepared in situ by the microwave method. The defects were created as 4-mm holes on the lateral aspect of the femur of dogs and the holes were packed with the implant material. The defective sites were radiographed at a period of 4, 8, and 12 weeks postoperatively. The radiographical results showed that the process of ossification started after 4 weeks and the defect was completely filled with new woven bone after 12 weeks. Histological examination of the tissue showed the formation of osteoblast inducing the osteogenesis in the defect. The collageneous fibrous matrix and the complete Haversian system were observed after 12 weeks. The blood serum was collected postoperatively and biochemical assays for alkaline phosphatase activity were carried out. The measurement of alkaline phosphatase activity levels also correlated with the formation of osteoblast-like cells. This microwave-prepared BCP ceramic has proved to be a good biocompatible implant as well as osteoconductive and osteoinductive materials to fill bone defects.     

Suppression of experimental allergic encephalomyelitis by a synthetic polypeptide

Three random basic copolymers of amino acids were tested for their effect on experimental allergic encephalomyelitis (EAE). One of these copolymers denoted as Cop 1, composed of alanine, glutamic acid, lysine and tyrosine, with a molecular weight of 23 000, showed a marked suppressive effect on the disease. The intravenous administration of Cop 1 in physiological saline, as late as 5 days following the challenge with the disease-inducing dose of the basic encephalitogenic protein, reduced the clinical incidence of EAE from 64% in the control group to 22%; the histological lesions were also decreased both in prevalence and in severity. The suppressive effect on the disease attained by the synthetic copolymer is of the same order of magnitude as that previously reported for the basic encephalitogen. The effect of the copolymers appears to be specific, since neither an acidic amino acid copolymer, nor unrelated basic proteins, had any protective action. On the other hand, a second batch of Cop 1 showed activity identical to that of the first batch. The potential applicability of this non-encephalitogenic and non-immunosuppressive material is discussed.     

Assessment of the effect of a biphasic ceramic on bone response in a rat calvarial defect model

Calcium phosphate ceramics are being extensively used for orthopedic, periodontal, and dental applications. This study aimed to assess the effect of a biphasic ceramic such as Ceraform on the osteogenesis in a rat calvarial defect model. 20 Wistar rats were enrolled in the study. Two symmetrical, circular, and 5-mm-wide full thickness defects were created in the parietal bones of each animal. The left defect was left empty as a control and the right defect was filled with the particular implant material. Animals were divided into two groups, and 10 animals were sacrificed at month 3 and the rest were sacrificed at month 6. The calvarial specimens were harvested for histological examinations. Defect area samples were stained with hematoxylin-eosin and Masson Thrichrom. A semiquantitative method was used to quantify the bone regeneration. The defects were mostly filled with fibrous connective tissue (3-6 months) in the control site. A loose, fibrovascular tissue was observed at the side of ceraform implantation at month 3. By 6 month, a dense collagenous tissue was observed at the same area. Multinuclear giant cells (MNGC) were detected around the implant bed at month 3 and month 6. No necrosis, tumorigenesis, or infection was observed at the implantation site at any time. There was no statistically meaningful difference regarding bone regeneration between the two defects at each observation period (p>0.05). This study showed that Ceraform is biocompatible. However, this study indicates that biphasic ceramic do not offer any advantage over hydroxyapatite ceramics. It was also revealed that it had no effects on bone regeneration and that it seemed to be a space maintainer.     

Bovine serum albumin (BSA) nephritis in rats II. Histological findings and complement activation by immune complex in SHR rats

We introduced a mesangiopathic form of glomerulonephritis in spontaneously hypertensive (SHR) rats. Bovine serum albumin (BSA) was given i.v. to primed rats for 3 weeks and they were unilaterally nephrectomized (Nx). Then, they received rabbit anti-BSA- (Group A) or normal serum (Group B) for seven days, and half the rats were killed to obtain another kidney (Ex-1). The remainder were killed two weeks later and their kidneys were examined (Ex-2). In Nx kidneys, the glomerular lesions were characterized by leucocyte accumulation in the capillary lumina and by deposition of rat IgG, rat C3 and BSA both in the mesangial area and along the capillary walls. Glomeruli of Ex-1 kidneys manifested varying degrees of hypercellularity in the mesangium; a few leucocyte accumulations in the capillary lumina were noted and the immune deposits had decreased in the mesangium but not on the capillary walls. In Ex-2 kidneys, mesangial hypercellularity was conspicuous. There were no remarkable histological differences between Group A and B rats; in Ex-1 and Ex-2 kidneys of Group A, rabbit IgG was closely associated with rat IgG or C3. Serological evaluation revealed that the amount of circulating rat anti-BSA antibody was relatively small and that C3 was consumed by newly formed circulating immune complexes during BSA administration. Polymorphonuclear leucocyte (PMN) binding assay revealed that complement fixation to the immune deposits occurred in vitro and that this activity was highest in tissue from Nx kidneys.     

Myoblast-acellular skeletal muscle matrix constructs guarantee a long-term repair of experimental full-thickness abdominal wall defects

To obtain a valuable treatment of congenital muscle defect, cell-matrix constructs composed of satellite cell-derived myoblasts (XY karyotype) seeded on muscle acellular matrices were used to repair a previously created full-thickness defect of abdominal wall of 18 1-month-old female Lewis rats. Acellular abdominal matrices, obtained by a detergent-enzymatic method, were positive for both basic fibroblast growth factor and transforming growth factor-beta, and were able to support in vitro cell adhesion. All animals survived the surgery, without signs of infection or implant rejection, and were humanely killed at 1, 3, or 9 months after surgery. The implants appeared well preserved, were integrated in the host tissue, and maintained their original dimension and thickness until 9 months. Vesicular acetylcholine transporter was expressed on the surface of muscle fibers from 1 month postsurgery. Finally, implanted male myoblasts were present inside the patches until 9 months, as demonstrated by the expression of SrY mRNA and by the presence of Y chromosome probe signal. These results allow us to conclude that cell-matrix constructs could represent a promising approach to the repair of muscle defects, because they are repopulated in vivo by skeletal muscle cells and nervous elements and maintain their structural integrity over the long term.     

Histopathologycal findings in the ovaries and uterus of albino female rats promoted by co-administration of synthetic steroids and nicotine

The use of anabolic androgenic steroids is often associated with the use of other substances, licit or not, such as nicotine present in the tobacco. The present study investigated for the first time the effects of co-administration of synthetic steroids and nicotine on the ovarian and uterine tissue and fertility of adult female rats. Animals were submitted to treatment groups (n = 16/group): nandrolone decanoate (ND; 7.5 mg/kg BW/week); testosterone mixture (T; 7.5 mg/kg BW/week); nicotine (N; 2.0 mg/kg BW/day), and co-administration of ND/N, T/N and ND/T/N. The control group received saline solution daily. The injections were administered subcutaneously for 30 consecutive days. Results demonstrated that all androgenized rats exhibited estral acyclicity and there was suppression of reproductive capacity due to notable ovarian and uterine histological changes. Treatments promoted decrease (p < 0.05) in the ovarian weight. Uterine weight increased (p < 0.05) in the T and T/N groups, in comparison to control group. ND or T co-administered or not to nicotine promoted intense follicular degeneration, with formation of cysts in the ovaries. High levels of circulating androgens in the ND/T/N group induced the presence of ovarian sex cord-stromal tumors of Sertoli cell pattern. Androgenized females presented endometrial changes characterized by papilliferous or pleated luminal epithelium, oedematous and hemorrhagic stroma and presence of gland cysts. In conclusion, the co-administration of three drugs promoted atypical morphological pattern on the ovaries and uterus of female rats.     

Pathological findings in rats with experimental allergic encephalomyelitis

The aim of this study was to establish an animal model of experimental allergic encephalomyelitis (EAE) and examine the basic pathological changes, as well as expression and distribution of MMP‐2 and MMP‐9, in Wistar rats. Tissue sections were processed for HE staining, Weil myelin staining, and modified Bielschowsky staining. Expression and distribution of glial fibrillary acidic protein (GFAP), matrix metalloproteinase‐2 (MMP‐2) and matrix metalloproteinase‐9 (MMP‐9) were detected with immunohistochemistry. We divided the EAE into five types, depending on pathological characteristics and clinical manifestations: acute EAE, relapsing‐remitting EAE, progressive EAE, benign EAE, and asymptomatic EAE. Rats with acute EAE suffered from quick, severe attacks with widespread inflammatory cells and axonal loss. No demyelination or astrocytic hyperplasia was found around the lesions. Rats with relapsing‐remitting EAE broke down twice, with many perivascular cuffs and demyelinating plaques in lesions; hyperplastic and hypertrophic astrocytes characterized old lesions and axonal loss was evident. Rats suffering from progressive EAE exhibited continuous aggravation without improvement, accompanied by perivascular cuffs, demyelination, increased gliocytes and axonal damage. Rats with benign EAE recovered to a normal state with obviously decreased inflammatory cells and almost entirely unaffected myelin and axons. Rats with asymptomatic EAE also had various pathological changes that were not coincident with their clinical manifestations. Elevated expression of MMP‐2 and MMP‐9 was concordant in different types of EAE, but the extent differed in each type of EAE. MMP‐2 and MMP‐9 can be expressed in the form of vascular endothelial cells, meninges, or accumulated inflammatory cells. Multiple clinical courses of disease were demonstrated in Wistar rat EAE, with attributes similar to multiple sclerosis (MS) in clinical and pathological characteristics. Elevated expression of MMP‐2 and MMP‐9 may play a role in some aspects of pathological changes in EAE, for example, destroying the blood‐brain barrier, degrading the myelin sheath, and damaging axons.     

Repair of osteochondral defects with biphasic cartilage-calcium polyphosphate constructs in a sheep model

There has been interest in developing novel biological treatments to repair focal cartilage defects. We have developed a method of forming biphasic constructs ("osteochondral"-type plug) in vitro consisting of cartilaginous tissue, formed on and anchored to the intended articulation surface of a porous ceramic substrate. The purpose of this study was to evaluate the biochemical and biomechanical properties and morphology of in vitro-formed biphasic constructs 3 and 9 months after implantation into 4mm diameter full thickness osteochondral defects in the trochlear groove of sheep stifles. The implants withstood loading in vivo up to 9 months with evidence of fusion to adjacent native cartilage and fixation by bone ingrowth into the ceramic substrate. The cartilage layer was eroded from those implants that were proud to the joint surface. Control implants (ceramic only) had fibrous tissue on the articulating surface after implantation for 3-4 months. Neither the cellularity nor proteoglycan content of the implanted cartilage, when it remained, changed significantly between 3 and 9 months and the collagen content increased slightly. The elastic equilibrium modulus of the cartilage improved with time with the greatest improvement (10-fold) occurring early during the first 3-4 months after implantation. This study suggests that biphasic constructs may be suitable to repair joint defects as the implants were maintained up to 9 months in sheep. Importantly the mechanical properties of the implanted cartilage improved significantly after implantation suggesting that cartilage can mature in vivo after implantation. The results indicate that further study of this treatment approach is warranted to attempt to overcome the technical surgical difficulties identified in this study.     

Bovine serum albumin (BSA) nephritis in rats II. Histological findings and complement activation by immune complex in SHR rats.

We introduced a mesangiopathic form of glomerulonephritis in spontaneously hypertensive (SHR) rats. Bovine serum albumin (BSA) was given i.v. to primed rats for 3 weeks and they were unilaterally nephrectomized (Nx). Then, they received rabbit anti-BSA- (Group A) or normal serum (Group B) for seven days, and half the rats were killed to obtain another kidney (Ex-1). The remainder were killed two weeks later and their kidneys were examined (Ex-2). In Nx kidneys, the glomerular lesions were characterized by leucocyte accumulation in the capillary lumina and by deposition of rat IgG, rat C3 and BSA both in the mesangial area and along the capillary walls. Glomeruli of Ex-1 kidneys manifested varying degrees of hypercellularity in the mesangium; a few leucocyte accumulations in the capillary lumina were noted and the immune deposits had decreased in the mesangium but not on the capillary walls. In Ex-2 kidneys, mesangial hypercellularity was conspicuous. There were no remarkable histological differences between Group A and B rats; in Ex-1 and Ex-2 kidneys of Group A, rabbit IgG was closely associated with rat IgG or C3. Serological evaluation revealed that the amount of circulating rat anti-BSA antibody was relatively small and that C3 was consumed by newly formed circulating immune complexes during BSA administration. Polymorphonuclear leucocyte (PMN) binding assay revealed that complement fixation to the immune deposits occurred in vitro and that this activity was highest in tissue from Nx kidneys.     

Loss of long-term potentiation in the hippocampus after experimental subarachnoid hemorrhage in rats

Survivors of aneurysmal subarachnoid hemorrhage (SAH) often suffer from cognitive impairment such as memory loss. However, the underlying mechanisms of these impairments are not known. Long-term potentiation (LTP) of synapses in the hippocampus is generally regarded as a molecular substrate of memory. The purpose of this study was to examine the effect of SAH on LTP in the hippocampal Schaffer collateral (CA3–CA1) pathway in a rat model of SAH. We found SAH caused significant vasospasm of the middle cerebral artery (MCA) compared to saline injected or sham controls (P<0.001). Basic neurotransmission quantified as excitatory post synaptic and spike response from animals with SAH were significantly decreased as compared to naive controls (P<0.05). However, sham operated and saline injected controls showed similar amplitude as naive controls. This suggests that reduction in basic neurotransmission is due to blood in the subarachnoid space. Similarly, analysis of LTP demonstrated that naive, sham and saline controls have a 92±16%, 69±27% and 71±14% increase over the baseline in the average spike amplitude following high frequency stimulation (HFS), respectively. This indicates the presence of LTP (P<0.05). In contrast, the spike amplitude in animals of SAH returned to baseline level within 60 min post HFS indicating the absence of LTP. We conclude that SAH caused vasospasm of the MCA that was associated with disrupted basic neurotransmission and plasticity at CA3–CA1 synapses. These changes might be accountable for the memory loss in humans with SAH.     

胰岛素干预对糖尿病大鼠骨折愈合及骨痂内细胞因子的影响

BACKGROUND: Fracture healing in diabetic patients is usually unsatisfactory because of hormones and metabolic disorder, and an eventual multiple organ dysfunction resulting from high blood glucose. OBJECTIVE: To dynamically observe the changes of cytokines during the fracture healing process in diabetic rats before and after insulin treatment. METHODS:A total of 120 Sprague-Dawley rats were included in this study. Of them, 90 rats intravenously injected with 5% tetraoxypyrimidine to induce rat models of diabetes were randomized into insulin treatment and diabetes groups, respectively. The remaining 30 rats were intravenously injected with equal volume of saline and selected as control group. The next day, blood glucose was determined. Healing at 1, 4, and 8 weeks after fracture were observed by the X-ray film. Biomechanical strength of the injured right tibia was measured at 4, 6, and 8 weeks after modeling. Cytokines in the osteotylus were determined by immunohistochemical staining and in situ hybridization technique. RESULTS AND CONCLUSION: The X-ray films showed that the speed of fracture healing in the diabetes group was slower than insulin treatment and control groups. Biomechanical strength of the osteotylus in the diabetes group was significantly decreased compared with the insulin treatment and control groups. However, there were no significant differences in above-mentioned parameters between the control and insulin treatment groups. Bone morphogenetic protein 2, basic fibroblast growth factor, transforming growth factor-beta, and vascular endothelial growth factor were widely expressed in the osteotylus and their expressions in diabetes group were significantly lower and slower than those in the control and insulin treatment groups. There was no statistical difference between control and insulin treatment groups. These results indicate that osteotylus formation speed, biomechanical strength, and growth factor expressions at the fracture site in diabetes rats were decreased compared with normal rats. Insulin treatment can enhance cytokine levels at the fracture site, thereby promoting the osteoblast proliferation and fracture healing. 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

The modulation of gene expression in osteoblasts by thrombin coated on biphasic calcium phosphate ceramic

For many years, fibrin sealants were associated with bone substitutes to promote bone healing. However, the osteoblastic response to fibrin sealant components remains poorly documented. In this study, MC3T3-E1 osteoblastic cells were cultured on biphasic calcium phosphate ceramic (MBCP) coated with Tissucol components (thrombin and fibrinogen). Analysis of osteoblastic differentiation markers by RT-PCR revealed that MBCP coated with Tissucol stimulated mRNA levels for osteocalcin and alkaline phosphatase (ALP). Of all the components of Tissucol, thrombin has been reported to affect osteoblastic behavior. Our results demonstrated that low thrombin concentrations (0.5-5 U/ml) stimulated mRNA levels for ALP, whereas high thrombin concentrations (50-100 U/ml) decreased mRNA levels for ALP and PTH/PTHrP receptor and also increased mRNA level for the osteoclastogenesis inhibitor OPG. As thrombin stimulated angiogenesis, we then wondered whether thrombin could influence the expression of angiogenic factors. Low thrombin concentrations were shown to up-regulate mRNA levels for VEGF-B and VEGF-R1, suggesting an autocrine/paracrine role for VEGF-B. Higher thrombin concentrations also up-regulated mRNA for VEGF-A and neuropilin-1. In conclusion, the association of MBCP with thrombin and fibrinogen appears to be a convenient scaffold for bone cell differentiation. Thrombin could also acts at the cellular level by increasing the angiogenic potential of osteoblasts as well as their responsiveness to thrombin and VEGF.     

Evaluation of the osteogenesis and biodegradation of porous biphasic ceramic in the human spine

The histological reports on porous biphasic calcium phosphate ceramic (PBC) in human spine are limited. The osteogenesis and biodegradation of PBC are insufficiently known in human. In present study, the undecalcified histological study was carried out on 20 samples retrieved from posterior spinal fusion in order to reveal the osteogenesis and biodegradation of the PBC in human spine. The quantitative study was performed in 14 samples with sufficient size. Newly formed bone was found in all the samples. More new bone was formed in those samples closely in contact with autogenous bone. The PBC degradation particles were present both in the macrophages and around the tissue. However, those phenomena were highly variable among the samples. New bone formation increased with time and decreased with age. The PBC degradation decreased with age, but it did not differ greatly with time. New bone formation was higher and the residual material was lower in the fusion group than that in non-fusion group. The PBC is a kind of osteoconductive material and do not transform into new bone after a relatively long time. The PBC should be well mixed with the autogenous bone in order to achieve high new bone colonization. The PBC degradation particles and related active phagocytotic activity have been noted.     

Histological examination of experimental arthritis induced by gonococcal peptidoglycan

The course of hindpaw arthropathy induced by single intradermal tail injections of sonicated, extensively-o-acetylated peptidoglycan (S-o-PG) from Neisseria gonorrhoeae was studied in male Lewis rats. Following a latent period of approximately 2 weeks, the hindpaw skin became inflamed and the ankles and hindfeet became swollen. Swelling was greatest at 32 days after injection, and decreased somewhat by day 40 to a level which remained well above normal. An aggressive, acute arthritis accompanied the swelling through day 24. The main features of the arthritis included the infiltration of periarticular tissues by many neutrophils, pannus formation, and the erosion of cartilage and subchondral bone. By day 32 the process had progressed and chronic inflammatory changes were becoming superimposed upon the acute changes. By day 40, chronic inflammatory changes predominated and fibrous ankylosis were established. In addition to the arthritis, deposition and absorption of bone occurred on surfaces unrelated to joints (e.g., the tibial shaft and plantar surface of the calcaneum), while tendons about the ankle developed adhesions following a severe tenosynovitis. This study supports the notion that cell-wall components may trigger severe arthropathy even in the absence of viable intraarticular gonococci.     

Effects of experimental hypercapnia on hippocampal long-term potentiation in anesthetized rats

Neuronal voltage-dependent P/Q Ca2+ channels are genetically abnormal in many cases of familial hemiplegic migraine and possibly associated with the more common forms of migraine with and without aura. Besides the brain, these channels are found in motor nerve endings where they control stimulation-induced acetylcholine release. Using single fiber EMG recordings we were able to demonstrate subclinical abnormalities of neuromuscular transmission in a subgroup of patients suffering from migraine with aura. This could be related to genetic abnormalities of P/Q Ca2+ channels in certain patients suffering from migraine with aura, which needs to be explored by proper genetic analyses.     

The influence of age on the wound healing of experimental myocardial infarction in rats.

In 6-weeks-old, 5-months-old and 21-months-old rats myocardial infarction was induced by coronary artery ligature. After performing the ligature the animals were administered 3H-thymidine, 3H-proline or 35S-sulphate at different times. The following parameters were determined: number of DNA- and tropocollagen-synthesizing connective tissue cells at the infarction border and at the infarction site; mean silver grain density above the nuclei or cells; duration of a cycle; number of mitoses, and incorporation of radioactive sulphate at the infarction site. In addition, the labelling and mitotic indices as well as the percentage of the standard deviation from the mean values were estimated. The following results were obtained: 1. The rate of granulation tissue formation in the necrotic zone is determined by the mitotic activity of the cells. With advancing age the cell cycles are being prolonged which results in retardation of wound healing. 2. The disturbed DNA-replication in old age is not associated with a time shift in the occurrence of the mitotic and labelling peaks. 3. With advancing age the number of fibroblasts synthesizing collagen precursors decreases. There exists no age-dependence of the 3H-proline incorporation rate, of the intracellular transport, of the synthesis of collagen precursor and of the release of labelled tropocollagen. In all age-groups under study these processes last approximately 4 hours. 4. Collagen fibre formation is accompanied by an increased synthesis of acid mucopolysaccharides. In infarction callosities the content of acid mucopolysaccharides mostly is constant. 5. The proliferating endothelial cells have a pronounced metabolic activity and a markedly short generation time.