Age, gender, height and weight in relation to joint cartilage thickness among school-aged children from ultrasonographic measurement.

BACKGROUND: Among school-age children, the decrease of cartilage thickness (Cth) with increasing age is well known. However, the influence of body mass index (BMI), height or weight on Cth has not been revealed. Here in, we aim to establish an age- and gender-specific Cth standard reference among Asians and investigate the possible prestige of BMI, height and weight. METHODS: A cross-sectional study was performed in healthy Asian children. Bilateral knees, ankles, wrists, second metacarpophalangeals (MCPs) and proximal interphalangeals (PIPs) were measured using ultrasound. The children's height, weight and BMI were also recorded for later adjustment. RESULTS: A total of 200 school age Asian children (including 86 girls and 114 boys, aged between 5 to 13 years-old) were investigated. Cth differences were observed in the knees, ankles, wrists, MCPs and PIPs between sexes (p < 0.05), with girls having thinner cartilage thickness. While Cth decreases with increasing age (p < 0.0001, 0.039, 0.001, 0.023, 0.091 in girls' knees, ankles, wrists, MCPs and PIPs and p = 0.002, 0.001, < 0.0001, 0.001, 0.045 in boys', respectively). Our data showed that weight, height and BMI are not the main factors contributing to Cth. A formula to calculate gender-specific cartilage thickness for Asian school age children is suggested. There was no difference in Cth after adjusting for height or weight between Asian or Caucasian group. CONCLUSIONS: A formula to calculate gender-specific cartilage thickness for Asian school age children is suggested. Height, weight and BMI were not the major contributor for Cth among school age children.

Interplay between genetics and epigenetics in osteoarthritis.

Research into the molecular genetics of osteoarthritis (OA) has been substantially bolstered in the past few years by the implementation of powerful genome-wide scans that have revealed a large number of novel risk loci associated with the disease. This refreshing wave of discovery has occurred concurrently with epigenetic studies of joint tissues that have examined DNA methylation, histone modifications and regulatory RNAs. These epigenetic analyses have involved investigations of joint development, homeostasis and disease and have used both human samples and animal models. What has become apparent from a comparison of these two complementary approaches is that many OA genetic risk signals interact with, map to or correlate with epigenetic mediators. This discovery implies that epigenetic mechanisms, and their effect on gene expression, are a major conduit through which OA genetic risk polymorphisms exert their functional effects. This observation is particularly exciting as it provides mechanistic insight into OA susceptibility. Furthermore, this knowledge reveals avenues for attenuating the negative effect of risk-conferring alleles by exposing the epigenome as an exploitable target for therapeutic intervention in OA.

Radiographic study of the development of the pelvis and hip and the femorotibial joints in domestic cats.

OBJECTIVES: The aims of the present study were to monitor, by radiographic examination, the skeletal development of the pelvis and the femorotibial joints of the domestic cat from the first week of life until the closing of the growth plates. METHODS: Radiographic examinations were collected from 15 domestic cats at weekly intervals during the first month and every 2 weeks from the second to the fourth month of age. After that, examinations were performed monthly until the age of 18 months. RESULTS: The ischiopubic growth plate closed at 2 months of age, followed by the fusion of the iliopubic, ilioischial, proximal femoral, greater trochanter and proximal fibular growth plates. The distal femur and proximal tibial growth plates were the last to close, with fusion occurring at 18 months. The mean time to closure of the iliopubic, ilioischial and distal femoral growth plates was shorter in females. The ossification centers first appeared, in ascending order, beginning with the lesser trochanter, followed by the greater trochanter, proximal fibular epiphysis, tibial tuberosity, patella, ischial tuberosity and lateral sesamoid of the popliteus muscle. CONCLUSIONS AND RELEVANCE: The complete closure of the growth plates of domestic cats occurs at approximately 18 months of age. Skeletal maturation at approximately 18 months of age is an important parameter to be considered in radiographic evaluation of certain skeletal changes, evolution of fractures and nutritional imbalance.

Computational model of a synovial joint morphogenesis.

Joints enable the relative movement between the connected bones. The shape of the joint is important for the joint movements since they facilitate and smooth the relative displacement of the joint's parts. The process of how the joints obtain their final shape is yet not well understood. Former models have been developed in order to understand the joint morphogenesis leaning only on the mechanical environment; however, the obtained final anatomical shape does not match entirely with a realistic geometry. In this study, a computational model was developed with the aim of explaining how the morphogenesis of joints and shaping of ossification structures are achieved. For this model, both the mechanical and biochemical environments were considered. It was assumed that cartilage growth was controlled by cyclic hydrostatic stress and inhibited by octahedral shear stress. In addition, molecules such as PTHrP and Wnt promote chondrocyte proliferation and therefore cartilage growth. Moreover, the appearance of the primary and secondary ossification centers was also modeled, for which the osteogenic index and PTHrP-Ihh concentrations were taken into account. The obtained results from this model show a coherent final shape of an interphalangeal joint, which suggest that the mechanical and biochemical environments are crucial for the joint morphogenesis process.

Anatomy and Ontogeny of the Mandibular Symphysis in Alligator mississippiensis.

Crocodylians evolved some of the most characteristic skulls of the animal kingdom with specializations for semiaquatic and ambush lifestyles, resulting in a feeding apparatus capable of tolerating high biomechanical loads and bite forces and a head with a derived sense of trigeminal-nerve-mediated touch. The mandibular symphysis accommodates these specializations being both at the end of a biomechanical lever and an antenna for sensation. Little is known about the anatomy of the crocodylian mandibular symphysis, hampering our understanding of form, function, and evolution of the joint in extant and extinct lineages. We explore mandibular symphysis anatomy of an ontogenetic series of Alligator mississippiensis using imaging, histology, and whole mount methods. Complex sutural ligaments emanating about a midline-fused Meckel's cartilage bridge the symphysis. These tissues organize during days 37-42 of in ovo development. However, interdigitations do not manifest until after hatching. These soft tissues leave a hub and spoke-like bony morphology of the symphyseal plate, which never fuses. Interdigitation morphology varies within the symphysis suggesting differential loading about the joint. Neurovascular canals extend throughout the mandibles to alveoli, integument, and bone adjacent to the symphysis. These features suggest the Alligator mandibular symphysis offers compliance in an otherwise rigid skull. We hypothesize a fused Meckel's cartilage offers stiffness in hatchling mandibles prior to the development of organized sutural ligaments and mineralized bone while offering a scaffold for somatic growth. The porosity of the dentaries due to neurovascular tissues likely allows transmission of sensory and proprioceptive information from the surroundings and the loaded symphysis. Anat Rec, 302:1696-1708, 2019. © 2019 American Association for Anatomy.

Histological Development of the Fused Mandibular Symphysis in the Pig.

The development of the mandibular symphysis in late fetal and postnatal pigs, Sus scrofa dom. (n = 17), was studied as a model for the early fusing symphysis of anthropoid primates, including humans. The suture-like ligaments occurring in species that retain a mobile symphysis are not present in the pig. Instead, cartilage is the predominant tissue in the mandibular symphysis prior to fusion. In late fetuses the rostrum of the fused Meckel's cartilages forms a minor posterior component of the symphysis whereas the major component is secondary cartilage, developing bilaterally and joined at the midline with mesenchyme. This remnant of Meckel's cartilage likely fuses with the flanking secondary cartilage. The overall composition of pig symphyseal histology in fetal and infant animals varies regionally and individually. Regions where the paired secondary cartilages abut in the midline resemble double growth plates. Chondrogenic growth in width of the symphysis is likely important in early stages, and central proliferation of mesenchyme is the probable source of new chondrocytes. Laterally, the chondrocytes hypertrophy near the bone fronts and are replaced by alveolar bone. Complete synostosis except for a small cartilage remnant had occurred in one 8-week-old postnatal specimen and all older specimens. Surprisingly, however, the initial phase of symphyseal fusion, observed in a 5-week-old postnatal specimen, involved intramembranous ossification of midline mesenchyme rather than endochondral ossification. Subsequently, fusion progresses rapidly at the anterior and labial aspects of the symphysis, leaving only a small postero-lingual cartilage pad that persists for at least several months. Anat Rec, 302:1372-1388, 2019. © 2018 Wiley Periodicals, Inc.

A regulatory pathway involving retinoic acid and calcineurin demarcates and maintains joint cells and osteoblasts in regenerating fin.

During zebrafish fin regeneration, blastema cells lining the epidermis differentiate into osteoblasts and joint cells to reconstruct the segmented bony rays. We show that osteoblasts and joint cells originate from a common cell lineage, but are committed to different cell fates. Pre-osteoblasts expressing runx2a/b commit to the osteoblast lineage upon expressing sp7, whereas the strong upregulation of hoxa13a correlates with a commitment to a joint cell type. In the distal regenerate, hoxa13a, evx1 and pthlha are sequentially upregulated at regular intervals to define the newly identified presumptive joint cells. Presumptive joint cells mature into joint-forming cells, a distinct cell cluster that maintains the expression of these factors. Analysis of evx1 null mutants reveals that evx1 is acting upstream of pthlha and downstream of or in parallel with hoxa13a Calcineurin activity, potentially through the inhibition of retinoic acid signaling, regulates evx1, pthlha and hoxa13a expression during joint formation. Furthermore, retinoic acid treatment induces osteoblast differentiation in mature joint cells, leading to ectopic bone deposition in joint regions. Overall, our data reveal a novel regulatory pathway essential for joint formation in the regenerating fin.

A computational model for the joint onset and development.

Joints connect the skeletal components and enable movement. The appearance and development of articulations is due to different genetic, biochemical, and mechanical factors. In the embryonic stage, controlled biochemical processes are critical for organized growth. We developed a computational model, which predicts the appearance, location, and development of joints in the embryonic stage. Biochemical events are modeled with reaction diffusion equations with generic molecules representing molecules that 1) determine the site where the articulation will appear, 2) promote proliferation, and matrix synthesis, and 3) define articular cartilage. Our model accounts for cell differentiation from mesenchymal cells to pre-cartilaginous cells, then cartilaginous cells, and lastly articular cartilage. These reaction-diffusion equations were solved using the finite elements method. From a mesenchymal 'bud' of a phalanx, the model predicts growth, joint cleavage, joint morphology, and articular cartilage formation. Our prediction of the gene expression during development agrees with molecular expression profiles of joint development reported in literature. Our computational model suggests that initial rudiment dimensions affect diffusion profiles result in Turing patterns that dictate sites of cleavage thereby determining the number of joints in a rudiment.

The Role of Bmp2 in the Maturation and Maintenance of the Murine Knee Joint.

Bone morphogenetic proteins (BMPs) are key regulators of skeletal development, growth, and repair. Although BMP signaling is required for synovial joint formation and is also involved in preserving joint function after birth, the role of specific BMP ligands in adult joint homeostasis remains unclear. The purpose of this study was to define the role of Bmp2 in the morphogenesis and maintenance of the knee joint. To do this, we first created Bmp2-LacZ and Gdf5-LacZ knock-in mice and compared their expression patterns in the developing and postnatal murine knee joint. We then generated a knockout mouse model using the Gdf5-cre transgene to specifically delete Bmp2 within synovial joint-forming cells. Joint formation, maturation, and homeostasis were analyzed using histology, immunohistochemistry, qRT-PCR, and atomic force microscopy (AFM)-based nanoindentation to assess the cellular, molecular, and biomechanical changes in meniscus and articular cartilage. Bmp2 is expressed in the articular cartilage and meniscus of the embryonic and adult mouse knee in a pattern distinct from Gdf5. The knee joints of the Bmp2 knockout mice form normally but fail to mature properly. In the absence of Bmp2, the extracellular matrix and shape of the meniscus are altered, resulting in functional deficits in the meniscus and articular cartilage that lead to a progressive osteoarthritis (OA) like knee pathology as the animals age. These findings demonstrate that BMP activity provided by Bmp2 is required for the maturation and maintenance of the murine knee joint and reveal a unique role for Bmp2 that is distinct from Gdf5 in knee joint biology. © 2018 American Society for Bone and Mineral Research.

Development of reaching during mid-childhood from a Developmental Systems perspective.

Inspired by the Developmental Systems perspective, we studied the development of reaching during mid-childhood (5-10 years of age) not just at the performance level (i.e., endpoint movements), as commonly done in earlier studies, but also at the joint angle level. Because the endpoint position (i.e., the tip of the index finger) at the reaching target can be achieved with multiple joint angle combinations, we partitioned variability in joint angles over trials into variability that does not (goal-equivalent variability, GEV) and that does (non-goal-equivalent variability, NGEV) influence the endpoint position, using the Uncontrolled Manifold method. Quantifying this structure in joint angle variability allowed us to examine whether and how spatial variability of the endpoint at the reaching target is related to variability in joint angles and how this changes over development. 6-, 8- and 10-year-old children and young adults performed reaching movements to a target with the index finger. Polynomial trend analysis revealed a linear and a quadratic decreasing trend for the variable error. Linear decreasing and cubic trends were found for joint angle standard deviations at movement end. GEV and NGEV decreased gradually with age, but interestingly, the decrease of GEV was steeper than the decrease of NGEV, showing that the different parts of the joint angle variability changed differently over age. We interpreted these changes in the structure of variability as indicating changes over age in exploration for synergies (a family of task solutions), a concept that links the performance level with the joint angle level. Our results suggest changes in the search for synergies during mid-childhood development.

Effect of the addition of glycosaminoglycans on bone and cartilaginous development of broiler chickens.

Locomotion issues in broiler production may decrease performance (carcass yield and traits) and lead to high financial losses. This study evaluates the addition of glucosaminoglycans in broiler diets to minimize the lack of proper bone development and joint weakening. The experiment was conducted using 2,160 broilers randomly distributed in a factorial pattern (3 × 3) using 3 levels of glucosamine sulfate (0, 0.12, and 0.24%) and 3 levels of chondroitin sulfate addition (0, 0.08, and 0.16%). Eight repetitions were used for each treatment, distributed in 72 pens with 30 broilers each. There was a quadratic effect on feed conversion for broilers from 1 to 42 d old (P = 0.0123) for the addition of chondroitin, and better feed conversion was obtained by adding 0.08% of chondroitin. The relative tibia weight, the width of the proximal epiphysis and diaphysis presented a linear increased effect in broilers at 42 d old. An interaction was found between the amount of chondroitin × glucosamine and the number of chondrocytes in the proximal cartilage of the tibia (P = 0.0072). There was a quadratic effect of glucosamine levels (P = 0.0107) in the birds that had received the 0.16% addition of chondroitin, and the presence of 0.18% glucosamine increased the number chondrocytes in the cartilage of broilers. These results provide the first evidence that broilers may benefit from increased dietary chondroitin sulfate. These results indicate that the addition of glucosamine and chondroitin sulfates in broiler feed rations might alleviate leg conditions and decrease financial losses in the broiler industry.

Age-related modulation of angiogenesis-regulating factors in the swine meniscus.

An in-depth knowledge of the native meniscus morphology and biomechanics in its different areas is essential to develop an engineered tissue. Meniscus is characterized by a great regional variation in extracellular matrix components and in vascularization. Then, the aim of this work was to characterize the expression of factors involved in angiogenesis in different areas during meniscus maturation in pigs. The menisci were removed from the knee joints of neonatal, young and adult pigs, and they were divided into the inner, intermediate and outer areas. Vascular characterization and meniscal maturation were evaluated by immunohistochemistry and Western blot analysis. In particular, expression of the angiogenic factor Vascular Endothelial Growth Factor (VEGF) and the anti-angiogenic marker Endostatin (ENDO) was analysed, as well as the vascular endothelial cadherin (Ve-CAD). In addition, expression of Collagen II (COLL II) and SOX9 was examined, as markers of the fibro-cartilaginous differentiation. Expression of VEGF and Ve-CAD had a similar pattern in all animals, with a significant increase from the inner to the outer part of the meniscus. Pooling the zones, expression of both proteins was significantly higher in the neonatal meniscus than in young and adult menisci. Conversely, the young meniscus revealed a significantly higher expression of ENDO compared to the neonatal and adult ones. Analysis of tissue maturation markers showed an increase in COLL II and a decrease in SOX9 expression with age. These preliminary data highlight some of the changes that occur in the swine meniscus during growth, in particular the ensemble of regulatory factors involved in angiogenesis.

A point mutation in Fgf9 impedes joint interzone formation leading to multiple synostoses syndrome.

Human multiple synostoses syndrome (SYNS) is an autosomal dominant disorder characterized by multiple joint fusions. We previously identified a point mutation (S99N) in FGF9 that causes human SYNS3. However, the physiological function of FGF9 during joint development and comprehensive molecular portraits of SYNS3 remain elusive. Here, we report that mice harboring the S99N mutation in Fgf9 develop the curly tail phenotype and partially or fully fused caudal vertebrae and limb joints, which mimic the major phenotypes of SYNS3 patients. Further study reveals that the S99N mutation in Fgf9 disrupts joint interzone formation by affecting the chondrogenic differentiation of mesenchymal cells at the early stage of joint development. Consistently, the limb bud micromass culture (LBMMC) assay shows that Fgf9 inhibits mesenchymal cell differentiation into chondrocytes by downregulating the expression of Sox6 and Sox9. However, the mutant protein does not exhibit the same inhibitory effect. We also show that Fgf9 is required for normal expression of Gdf5 in the prospective elbow and knee joints through its activation of Gdf5 promoter activity. Signal transduction assays indicate that the S99N mutation diminishes FGF signaling in developmental limb joints. Finally, we demonstrate that the conformational change in FGF9 resulting from the S99N mutation disrupts FGF9/FGFR/heparin interaction, which impedes FGF signaling in developmental joints. Taken together, we conclude that the S99N mutation in Fgf9 causes SYNS3 via the disturbance of joint interzone formation. These results further implicate the crucial role of Fgf9 during embryonic joint development.

Signaling networks in joint development.

Here we review studies identifying regulatory networks responsible for synovial, cartilaginous, and fibrous joint development. Synovial joints, characterized by the fluid-filled synovial space between the bones, are found in high-mobility regions and are the most common type of joint. Cartilaginous joints such as the intervertebral disc unite adjacent bones through either a hyaline cartilage or a fibrocartilage intermediate. Fibrous joints, which include the cranial sutures, form a direct union between bones through fibrous connective tissue. We describe how the distinct morphologic and histogenic characteristics of these joint classes are established during embryonic development. Collectively, these studies reveal that despite the heterogeneity of joint strength and mobility, joint development throughout the skeleton utilizes common signaling networks via long-range morphogen gradients and direct cell-cell contact. This suggests that different joint types represent specialized variants of homologous developmental modules. Identifying the unifying aspects of the signaling networks between joint classes allows a more complete understanding of the signaling code for joint formation, which is critical to improving strategies for joint regeneration and repair. Developmental Dynamics 246:262-274, 2017. © 2016 Wiley Periodicals, Inc.

Heads, Shoulders, Elbows, Knees, and Toes: Modular Gdf5 Enhancers Control Different Joints in the Vertebrate Skeleton.

Synovial joints are crucial for support and locomotion in vertebrates, and are the frequent site of serious skeletal defects and degenerative diseases in humans. Growth and differentiation factor 5 (Gdf5) is one of the earliest markers of joint formation, is required for normal joint development in both mice and humans, and has been genetically linked to risk of common osteoarthritis in Eurasian populations. Here, we systematically survey the mouse Gdf5 gene for regulatory elements controlling expression in synovial joints. We identify separate regions of the locus that control expression in axial tissues, in proximal versus distal joints in the limbs, and in remarkably specific sub-sets of composite joints like the elbow. Predicted transcription factor binding sites within Gdf5 regulatory enhancers are required for expression in particular joints. The multiple enhancers that control Gdf5 expression in different joints are distributed over a hundred kilobases of DNA, including regions both upstream and downstream of Gdf5 coding exons. Functional rescue tests in mice confirm that the large flanking regions are required to restore normal joint formation and patterning. Orthologs of these enhancers are located throughout the large genomic region previously associated with common osteoarthritis risk in humans. The large array of modular enhancers for Gdf5 provide a new foundation for studying the spatial specificity of joint patterning in vertebrates, as well as new candidates for regulatory regions that may also influence osteoarthritis risk in human populations.

Insulin-Like Growth Factor I Does Not Drive New Bone Formation in Experimental Arthritis.

INTRODUCTION: Insulin like growth factor (IGF)-I can act on a variety of cells involved in cartilage and bone repair, yet IGF-I has not been studied extensively in the context of inflammatory arthritis. The objective of this study was to investigate whether IGF-I overexpression in the osteoblast lineage could lead to increased reparative or pathological bone formation in rheumatoid arthritis and/or spondyloarthritis respectively. METHODS: Mice overexpressing IGF-I in the osteoblast lineage (Ob-IGF-I+/-) line 324-7 were studied during collagen induced arthritis and in the DBA/1 aging model for ankylosing enthesitis. Mice were scored clinically and peripheral joints were analysed histologically for the presence of hypertrophic chondrocytes and osteocalcin positive osteoblasts. RESULTS: 90-100% of the mice developed CIA with no differences between the Ob-IGF-I+/- and non-transgenic littermates. Histological analysis revealed similar levels of hypertrophic chondrocytes and osteocalcin positive osteoblasts in the ankle joints. In the DBA/1 aging model for ankylosing enthesitis 60% of the mice in both groups had a clinical score 1<. Severity was similar between both groups. Histological analysis revealed the presence of hypertrophic chondrocytes and osteocalcin positive osteoblasts in the toes in equal levels. CONCLUSION: Overexpression of IGF-I in the osteoblast lineage does not contribute to an increase in repair of erosions or syndesmophyte formation in mouse models for destructive and remodeling arthritis.

Molecular and cellular mechanisms involved in leg joint morphogenesis.

In summary, the patterning of the presumptive leg depends on gradients of Dpp and Wg morphogens, which lead to the establishment of the proximo-distal axis marked by the expression of Hth, Dac and Dll in broad domains along the leg. Then, EGFR signaling specifies the tarsal region by regulating the expression of tarsal gap genes in different tarsal segments. This patterning is closely linked to the formation of rings of Notch activation in the distal part of each leg segment. These rings of Notch activation are further regulated by different mechanisms: (1) the maintenance of a sharp border of Dl expression, (2) the inhibition of N activation in cells located proximally to the ligands, thus restricting N activity specifically to the distal part of cells. This localised activation of Notch induces the expression of Dysfusion which controls the expression of both pro-apoptotic genes and RhoGTPase regulators. Finally, apoptotic cells appear within the pro-apoptotic domain, and while dying, generate a transient pulling force. This force constitutes a mechanical signal that propagates to the rest of the tissue and triggers cytoskeleton reorganisation specifically in the presumptive fold, where RhoGTPase regulators are expressed. Altogether, this complex array of patterning and signaling leads to precise cellular mapping of the developing leg to correctly position local cell shape modifications, inducing tissue folding.

Adaptation of multijoint coordination during standing balance in healthy young and healthy old individuals.

Standing balance requires multijoint coordination between the ankles and hips. We investigated how humans adapt their multijoint coordination to adjust to various conditions and whether the adaptation differed between healthy young participants and healthy elderly. Balance was disturbed by push/pull rods, applying two continuous and independent force disturbances at the level of the hip and between the shoulder blades. In addition, external force fields were applied, represented by an external stiffness at the hip, either stabilizing or destabilizing the participants' balance. Multivariate closed-loop system-identification techniques were used to describe the neuromuscular control mechanisms by quantifying the corrective joint torques as a response to body sway, represented by frequency response functions (FRFs). Model fits on the FRFs resulted in an estimation of time delays, intrinsic stiffness, reflexive stiffness, and reflexive damping of both the ankle and hip joint. The elderly generated similar corrective joint torques but had reduced body sway compared with the young participants, corresponding to the increased FRF magnitude with age. When a stabilizing or destabilizing external force field was applied at the hip, both young and elderly participants adapted their multijoint coordination by lowering or respectively increasing their neuromuscular control actions around the ankles, expressed in a change of FRF magnitude. However, the elderly adapted less compared with the young participants. Model fits on the FRFs showed that elderly had higher intrinsic and reflexive stiffness of the ankle, together with higher time delays of the hip. Furthermore, the elderly adapted their reflexive stiffness around the ankle joint less compared with young participants. These results imply that elderly were stiffer and were less able to adapt to external force fields.

Safety study of Ciprofloxacin in newborn mice.

Ciprofloxacin, a broad-spectrum antimicrobial agent belonging to the fluoroquinolone family, is prescribed off-label in infants less than one year of age. Ciprofloxacin is included in the European Medicines Agency priority list of off-patent medicinal products requiring evaluation in neonates. This evaluation is undergoing within the TINN (Treat Infections in Neonates) FP7 EU project. As part of the TINN project, the present preclinical study was designed to assess the potential adverse effects of Ciprofloxacin on neurodevelopment, liver and joints in mice. Newborn mice received subcutaneous Ciprofloxacin at 10, 30 and 100 mg/kg/day from 2 to 12 postnatal days. Peak plasma levels of Ciprofloxacin were in the range of levels measured in human neonates. We examined vital functions in vivo, including cardiorespiratory parameters and temperature, psychomotor development, exploratory behavior, arthro-, nephro- and hepato-toxic effects. We found no effect of Ciprofloxacin at 10 and 30 mg/kg/day. In contrast, administration at 100 mg/kg/day delayed weight gain, impaired cardiorespiratory and psychomotor development, caused inflammatory infiltrates in the connective tissues surrounding the knee joint, and moderately increased extramedullary hematopoiesis. The present study pleads for careful watching of cardiorespiratory and motor development in neonates treated with Ciprofloxacin, in addition to the standard surveillance of arthrotoxicity.