Street scars: Suicide ideation and suicide attempt among street-involved adolescents and youth in southern Brazil.

OBJECTIVE: To measure the prevalence of suicidal ideation and attempts as well as suicide attempts' associated factors among street-involved youth in southern Brazil. PARTICIPANTS AND SETTING: Cross-sectional study was conducted with street-involved adolescents and children from Porto Alegre and Rio Grande, Brazil. METHODS: A respondent-driven sampling strategy was used to access this hard-to-reach population quickly and efficiently. Descriptive, bivariate, and multivariate analyses were conducted, with the latter being binary logistic regression. RESULTS: The prevalence of suicide attempts was 16.3%, while the frequency of suicidal ideation was 30.9%. Most participants were male, aged between 16 and 18 years, with no ties to school and family. Almost half of the sample had been in a street situation for five years or more, and two-thirds reported spending more than seven hours a day on the streets. Variables independently associated with suicide attempts were aged 19-21 years old, with reduced ties with school and family, having had an experience of sexual abuse, and lifetime use of crack. CONCLUSIONS: Public policies targeting the strengthening ties of street-involved children, adolescents, and youth with school and family might reduce their vulnerability to threats, such as sexual abuse and use of crack, and hence focus on decreasing suicide attempts.

Retrospective Analysis of Rechallenge with Ipilimumab in Patients with Metastatic Melanoma.

BACKGROUND: Checkpoint inhibitors are effective in the treatment of several types of cancer, either being used separately or in combination. Ipilimumab pioneered the treatment of metastatic melanoma, and nowadays, it has been used more frequently in combination with anti-PD-1. Since the development of anti-PD1 for melanoma, rechallenge with ipilimumab has not been considered, although its use was considered in early trials. CASES: In this study, we analyzed 22 patients with metastatic melanoma who had benefited from the first treatment with ipilimumab, but eventually had progressive disease. They received ipilimumab at the same dose as the first treatment. Most of the patients received the second course after six months or more from the first treatment with ipilimumab. The median progression-free survival (mPFS) of the treatment with ipilimumab was 8.9 months, and the median progression-free survival of the second course was 6.3 months. CONCLUSION: There are limited data on rechallenge with ipilimumab addressing progression-free survival (PFS). In our analysis, twenty-two patients treated with a second course of ipilimumab were analyzed and most of them had a significant benefit. Despite the current alternatives for salvage therapies, rechallenging with ipilimumab might be an alternative to be considered in patients who had initial benefit.

Spatial and temporal changes in cell proliferation in the chick jejunum during the folding of the ridges into zigzags.

Vilification in the chick gut involves the formation of longitudinal ridges, establishment of their zigzag pattern and emergence of individual villi. Although the morphological changes during vilification are well known in the chick gut, the pattern of cell proliferation during this process is poorly understood. The aim of the present study was to correlate spatial and temporal changes in cell proliferation to folding of the longitudinal ridges into zigzags. Embryos on the 13th pos-incubation day were injected with BrdU and sacrificed at 8 h intervals up to 64 h after injection. Spatial and temporal changes in cell proliferation were observed during the folding the longitudinal ridges into zigzags. Cell proliferation occurred throughout the epithelium of the folded ridges, was predominant in the epithelial cells at the sides of the zigzagging ridges, and finally appeared in the epithelial cells at the tips of the zigzag ridges. In conclusion, cell proliferation might be a requirement for the folding of the longitudinal ridges into zigzags.

Effects of loss of occlusal contact on the expression of matrix metalloproteinase-2, membrane type 1-MMP, tissue inhibitor of the MMP-2, eruption rate, organization and resistance of collagen fibers of the rat incisor periodontal ligament.

BACKGROUND AND OBJECTIVE: This study investigated the effect of occlusal contact loss (induced by tooth shortening), on matrix metalloproteinase (MMP)-2, membrane type 1-MMP (MT1-MMP) and tissue inhibitor of the MMP-2 (TIMP-2) expressions in the periodontal ligament of the rat incisor, as well as eruption rate, resistance and collagen organization. MATERIAL AND METHODS: Male Wistar rats were distributed into a control group, denominated normofunctional group, whose lower teeth underwent a normal eruption process; and a hypofunctional group, whose lower left incisor teeth were shortened every 2 days during 14 days. Parameters were evaluated on the first, seventh and 14th days and the eruption rate was determined according to the size of the incisor during the eruption process. MMP-2 activity was determined by zymography and the expressions of the MT1-MMP and TIMP-2 proteins were quantitated by western blot. Collagen protein organization, as indicated by the birefringence of the periodontal ligament, was analyzed under polarized light and the periodontal ligament's resistance was determined from the load necessary to inject the incisor into its alveolar space, before extraction. RESULTS: Loss of occlusal contact, in rats submitted to hypofunctional eruption, increased MMP-2 activity and eruption rate, but decreased MT1-MMP and TIMP-2 expression and disrupted collagen organization in the periodontal ligament, consequently reducing periodontal ligament resistance. CONCLUSION: We conclude that, after incisor eruption, occlusal contact may be an important factor for regulating the remodeling and the physiological resistance of the periodontal ligament against the continuous eruption process observed in rat incisors.

Effect of HAp and ß-TCP incorporation on the tribological response of Ti6Al4V biocomposites for implant parts.

Titanium and its alloys have been widely used in many engineering areas due to their properties. Despite having a high implant-tissue osseointegration time, Ti6Al4V has been extensively used in prosthesis and articular implants. To promote a faster bone ingrowth and consequently reduce the implant fixation time, the addition of a bioactive phase to form a biocomposite seems to be an excellent solution. Because of their bioactivity and similarity in composition with the human bone, HAp and ß-TCP are two of the most widely used calcium phosphates in biomedical applications. To guarantee a strong adhesion of the previous bioactive materials in the implants surface, samples of Ti6Al4V, Ti6Al4V+HAp (10 vol %) and Ti6Al4V+ß-TCP (10 vol %) TCP were processed by the hot pressing technique. Tribological tests against Al2 O3, lubricated in PBS at 37°C were carried out on a ball-on-flat reciprocating sliding geometry. Loads in the range of 3 N to 30 N were applied and their effect on the friction behavior and wear resistance of the tested materials was evaluated. Values of the coefficient of friction as well as the wear rate tend to increase with the addition of a bioactive phase to the Ti alloy. Micrographs of the worn surfaces showed that abrasion and plastic deformation are the prevailing wear mechanisms in the studied tribosystems. For biocomposites, particularly in the case of Ti6Al4V+HAp, pull-out of bioactive particle clusters has a determinant role on the tribological response, increasing both the friction coefficient and the specific wear rate. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1010-1016, 2018.

Bioactive materials driven primary stability on titanium biocomposites.

The Ti6Al4V alloy constitutes an alternative choice to the most common metal-polymer solutions for total hip arthroplasty (THA) due to good biocompatibility, optimal mechanical properties and high load bearing capacity. However, as Ti6Al4V is not bioactive in its conventional form, hydroxyapatite (HAp) and tricalcium phosphate (TCP) have been widely used as coatings of metal prostheses due to their osteogenic properties and ability to form strong bonds with bone tissue. A promising approach consists in creating a bioactive surface metal matrix composite Ti6Al4V+ß-TCP or Ti6Al4V+HAp, obtained by hot pressing (HP) of powders. In this work, the tribological performance of Ti6Al4V+ß-TCP and Ti6Al4V+HAp composites is studied to evaluate the frictional response and surface damage representative of prosthesis implantation, key factors in bone fixation. Biocomposites with 10vol% ß-TCP and 10vol% Hap, as well as base titanium alloy, were prepared by HP with two surface finishing conditions - polished (Ra=0.3-0.5µm) and sandblasted (Ra=2.1-2.5µm) - for tribological testing against bovine cortical bone tissue. The static friction increases with surface roughness (from 0.20 to 0.60), whereas the kinetic regime follows an inverse trend for the biocomposites. In contrast with current knowledge, this study shows that an implant design solution based on Ti6Al4V+ß-TCP or Ti6Al4V+HAp biocomposites with polished surfaces results in an improved primary stability of implants, when compared to traditional rough surfaces. Moreover, it is also expected that the secondary stability will improve due to the adhesion between bone and HAp/ß-TCP, increasing the overall stability of the implant.

Tribological behavior of Ti6Al4V cellular structures produced by Selective Laser Melting.

Additive manufacturing (AM) technologies enable the fabrication of innovative structures with complex geometries not easily manufactured by traditional processes. Regarding metallic cellular structures with tailored/customized mechanical and wear performance aiming to biomedical applications, Selective Laser Melting (SLM) is a remarkable solution for their production. Focusing on prosthesis and implants, in addition to a suitable Young's modulus it is important to assess the friction response and wear resistance of these cellular structures in a natural environment. In this sense, five cellular Ti6Al4V structures with different open-cell sizes (100-500µm) were designed and produced by SLM. These structures were tribologicaly tested against alumina using a reciprocating sliding ball-on-plate tribometer. Samples were submerged in Phosphate Buffered Saline (PBS) fluid at 37°C, in order to mimic in some extent the human body environment. The results showed that friction and wear performance of Ti6Al4V cellular structures is influenced by the structure open-cell size. The higher wear resistance was obtained for structures with 100µm designed open-cell size due to the higher apparent area of contact to support tribological loading.

Doxycycline reduces the expression and activity of matrix metalloproteinase-2 in the periodontal ligament of the rat incisor without altering the eruption process.

BACKGROUND AND OBJECTIVE: Doxycycline is an antibiotic agent that inhibits the activity of matrix metalloproteinases (MMPs) present in the extracellular matrix. In this study, the rat incisor was submitted to a hypofunctional condition, and the effects of doxycycline (80 mg/kg/d) on the expression and activity of MMP-2, as well as on eruption rate, were determined in the odontogenic region and in the periodontal ligament for 14 d. MATERIAL AND METHODS: Rats were distributed into four groups: normofunctional (NF); doxycyline normofunctional (DNF); hypofunctional (HP); and doxycyline hypofunctional (DHP). The left lower incisors of 10 rats were shortened every 2 d, using a high-rotation drill, to produce the HP and DHP groups, after starting doxycycline treatment (80 mg/kg) by gavage. Eruption was measured using a millimeter ocular, from the gingival margin to the top of the tooth in the HP and DHP groups, and also by a mark made in the tooth previously, in the NF and DNF groups. The hemimandibles were removed and the teeth were extracted to collect the periodontal and odontogenic tissues for immunohistochemical analyses and zymography. RESULTS: The eruption rates were higher in the HP and the DHP groups than in the NF and DNF groups, respectively (p < 0.05). In the odontogenic region, neither of the treatments changed the expression and activity of MMP-2. In the HP group, the shortening treatment decreased the expression, but not the activity, of MMP-2, while doxycycline was able to inhibit the increase of expression and activity of MMP-2. CONCLUSION: We conclude that the inhibition of MMP-2 by doxycycline, during incisor shortening, was not enough to alter the eruption rate, which suggests that MMP-2 may have an important role in the turnover of extracellular matrix of the periodontal ligament during the tooth-eruption process.

MT1-MMP and its potential role in the vertebrate intestinal morphogenesis.

Membrane type 1-matrix metalloproteinase (MT1-MMP) is involved in numerous biological processes, including morphogenesis. However, the role of MT1-MMP in the development of the vertebrate intestine is poorly understood. This study aimed to evaluate the expression of MT1-MMP in the intestine of rats and chickens along the embryonic and postnatal periods using immunohistochemistry. Results revealed a remarkable spatiotemporal correlation between MT1-MMP expression and intestinal villi morphogenesis in both vertebrates. However, the villi morphogenesis process was found to be different in chickens to that of rats. Moreover, extensive MT1-MMP labeling was observed in the entire villus epithelium from birth until the complete maturation of the small intestinal mucosa in both vertebrates. From these results, we suggest that MT1-MMP contributes to intestinal development, particularly to villi morphogenesis, in both vertebrates. However, further studies are necessary to confirm the role of MT1-MMP in this cellular process. In addition, we performed validation of the primary antibody against human MT1-MMP for adult chickens.

Effects of Physical Exercise on the Intestinal Mucosa of Rats Submitted to a Hypothalamic Obesity Condition.

The small intestine plays a role in obesity as well as in satiation. However, the effect of physical exercise on the morphology and function of the small intestine during obesity has not been reported to date. This study aimed to evaluate the effects of physical exercise on morphological aspects of the rat small intestine during hypothalamic monosodium glutamate (MSG)-induced obesity. The rats were divided into four groups: Sedentary (S), Monosodium Glutamate (MSG), Exercised (E), and Exercised Monosodium Glutamate (EMSG). The MSG and EMSG groups received a daily injection of monosodium glutamate (4 g/kg) during the 5 first days after birth. The S and E groups were considered as control groups and received injections of saline. At weaning, at 21 days after birth, the EMSG and E groups were submitted to swimming practice 3 times a week until the 90th day, when all groups were sacrificed and the parameters studied recorded. Exercise significantly reduced fat deposits and the Lee Index in MSG-treated animals, and also reduced the thickness of the intestinal wall, the number of goblet cells and intestinal alkaline phosphatase activity. However, physical activity alone increased the thickness and height of villi, and the depth of the crypts. In conclusion, regular physical exercise may alter the morphology or/and functions of the small intestine, reducing the prejudicial effects of hypothalamic obesity. Anat Rec, 299:1389-1396, 2016. © 2016 Wiley Periodicals, Inc.

Transthyretin provides trophic support via megalin by promoting neurite outgrowth and neuroprotection in cerebral ischemia.

Transthyretin (TTR) is a protein whose function has been associated to binding and distribution of thyroid hormones in the body and brain. However, little is known regarding the downstream signaling pathways triggered by wild-type TTR in the CNS either in neuroprotection of cerebral ischemia or in physiological conditions. In this study, we investigated how TTR affects hippocampal neurons in physiologic/pathologic conditions. Recombinant TTR significantly boosted neurite outgrowth in mice hippocampal neurons, both in number and length, independently of its ligands. This TTR neuritogenic activity is mediated by the megalin receptor and is lost in megalin-deficient neurons. We also found that TTR activates the mitogen-activated protein kinase (MAPK) pathways (ERK1/2) and Akt through Src, leading to the phosphorylation of transcription factor CREB. In addition, TTR promoted a transient rise in intracellular calcium through NMDA receptors, in a Src/megalin-dependent manner. Moreover, under excitotoxic conditions, TTR stimulation rescued cell death and neurite loss in TTR KO hippocampal neurons, which are more sensitive to excitotoxic degeneration than WT neurons, in a megalin-dependent manner. CREB was also activated by TTR under excitotoxic conditions, contributing to changes in the balance between Bcl2 protein family members, toward anti-apoptotic proteins (Bcl2/BclXL versus Bax). Finally, we clarify that TTR KO mice subjected to pMCAO have larger infarcts than WT mice, because of TTR and megalin neuronal downregulation. Our results indicate that TTR might be regarded as a neurotrophic factor, because it stimulates neurite outgrowth under physiological conditions, and promotes neuroprotection in ischemic conditions.

Comparison between PEEK and Ti6Al4V concerning micro-scale abrasion wear on dental applications.

In the oral cavity, abrasive wear is predictable at exposed tooth or restorative surfaces, during mastication and tooth brushing. Also, wear can occur at contacting surfaces between the Ti-based prosthetic structures and implants in presence of abrasive compounds from food or toothpaste. Thus, the aim of this work was to compare the abrasive wear resistance of PEEK and Ti6Al4V on three-body abrasion related to different hydrated silica content and loads. Surfaces of Ti6Al4V or PEEK cylinders (8mm diameter and 4mm height) were wet ground on SiC papers and then polished with 1µm diamond paste. After that, surfaces were ultrasonically cleaned in propyl alcohol for 15min and then in distilled water for 10min. Micro-scale abrasion tests were performed at 60rpm and on different normal loads (0.4, 0.8 or 1.2N) after 600 ball revolutions using suspensions with different weight contents of hydrated silica. After abrasive tests, wear scars on flat samples were measured to quantify the wear volume and characterized by scanning electron microscope (SEM) to identify the dominant wear mechanisms. Results showed a higher volume loss rate on PEEK than that recorded on Ti6Al4V,, when subjected to three-body abrasion tests involving hydrated silica suspensions. An increase in volume loss was noted on both tested materials when the abrasive content or load was increased. PEEK was characterized by less wear resistance than that on Ti6Al4V after micro-scale abrasion wear in contact with hydrated silica particles, as commonly found in toothpastes.

Bone sialoprotein, matrix metalloproteinases and type I collagen expression after sealing infected caries dentin in primary teeth.

The objective of this in vivo study was to compare the expression of matrix metalloproteinases (MMP-2, MMP-8, MMP-9), type I collagen and bone sialoprotein (BSP) in infected dentin of primary teeth at baseline and after cavity sealing with glass ionomer cement. Dentin samples from 45 primary molars with deep and active carious lesions were collected before (baseline sample) and after cavity sealing (60-day sample). The samples were fixed, demineralized and processed for immunohistochemistry assays. Monoclonal antibodies were used for the localization of the cited antigens with an avidin-biotin method. Digital images of the sections were captured and analyzed with ImageJ software. The mean intensity of RGB channels in the images was obtained and compared using Student's t test (α = 0.05). The expression of the MMPs, type I collagen and BSP increased after sealing, but statistical differences were observed only for MMP-8, type I collagen and BSP. MMP-2 and MMP-9 were more concentrated around dentin tubules; MMP-8 and collagen showed strong expression throughout the organic matrix; BSP exhibited strong expression both in the matrix and around dentin tubules. The increased expression of the enzymes investigated 60 days after cavity sealing suggests that they are not related with disease progression but with the healing process of dentin.

Relationship between cell proliferation and eruption rate in the rat incisor.

The aim of this study was to further define the relationship between cell proliferation and the rate of tooth eruption in the rat incisor. Vinblastine is a drug that blocks cellular mitosis and was used to inhibit cell proliferation in the odontogenic region of rat incisors that were submitted to a shortening treatment or to higher masticatory forces. Male Wistar rats were divided into five groups: normofunctional (control group for incisor eruption), hypofunctional (incisor submitted to eruption acceleration), hyperfunctional (incisors under higher masticatory forces), hypofunctional with vinblastine and hyperfunctional with vinblastine. In incisors submitted to shortening procedures, a significant decrease in the eruption rate and cell proliferation was observed two days after vinblastine injection, suggesting that incisor eruption is dependent on cell proliferation.

Development of Plasmodium falciparum protease inhibitors in the past decade (2002-2012).

New drug targets for the development of antimalarial drugs have emerged after the unveiling of the Plasmodium falciparum genome in 2002. Potential antimalarial drug targets can be broadly classified into three categories according to their function in the parasite's life cycle: (i) biosynthesis, (ii) membrane transport and signaling, and (iii) hemoglobin catabolism. The latter plays a key role, as inhibition of hemoglobin degradation impairs maturation of bloodstage malaria parasites, ultimately leading to remission or even cure of the most severe stage of the infection. Intraerythrocytic Plasmodia parasites have limited capacity to biosynthesize amino acids which are vital for their growth. Therefore, the parasites obtain those essential amino acids via degradation of host cell hemoglobin, making this a crucial process for parasite survival. Several plasmodial proteases are involved in hemoglobin catabolism, among which plasmepsins and falcipains are well-known examples. Hence, development of P. falciparum protease inhibitors is a promising approach to antimalarial chemotherapy, as highlighted by the present review which is focused on the Medicinal Chemistry research effort recorded in the past decade in this particular field.

Spatiotemporal resolution of BDNF neuroprotection against glutamate excitotoxicity in cultured hippocampal neurons.

Brain-derived neurotrophic factor (BDNF) protects hippocampal neurons from glutamate excitotoxicity as determined by analysis of chromatin condensation, through activation of extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-kinase (PI3-K) signaling pathways. However, it is still unknown whether BDNF also prevents the degeneration of axons and dendrites, and the functional demise of synapses, which would be required to preserve neuronal activity. Herein, we have studied the time-dependent changes in several neurobiological markers, and the regulation of proteolytic mechanisms in cultured rat hippocampal neurons, through quantitative western blot and immunocytochemistry. Calpain activation peaked immediately after the neurodegenerative input, followed by a transient increase in ubiquitin-conjugated proteins and increased abundance of cleaved-caspase-3. Proteasome and calpain inhibition did not reproduce the protective effect of BDNF and caspase inhibition in preventing chromatin condensation. However, proteasome and calpain inhibition did protect the neuronal markers for dendrites (MAP-2), axons (Neurofilament-H) and the vesicular glutamate transporters (VGLUT1-2), whereas caspase inhibition was unable to mimic the protective effect of BDNF on neurites and synaptic markers. BDNF partially prevented the downregulation of synaptic activity measured by the KCl-evoked glutamate release using a Förster (Fluorescence) resonance energy transfer (FRET) glutamate nanosensor. These results translate a time-dependent activation of proteases and spatial segregation of these mechanisms, where calpain activation is followed by proteasome deregulation, from neuronal processes to the soma, and finally by caspase activation in the cell body. Moreover, PI3-K and PLCγ small molecule inhibitors significantly blocked the protective action of BDNF, suggesting an activity-dependent mechanism of neuroprotection. Ultimately, we hypothesize that neuronal repair after a degenerative insult is initiated at the synaptic level.

Development of Loxosceles intermedia Mello-Leitão (1934) (Araneae, Sicariidae) genital tract.

We examined the post-embryonic development of the male and female genital apparatus of the brown spider, Loxosceles intermedia. The development of the genital apparatus for both sexes begins with the appearance of inner structures. In the male genital apparatus, formation of the testes occurs first, followed by differentiation of the duct, ampulla and vas deferens, and finally the formation of the genital opening and differentiation of the copulatory organ (secondary sexual characteristic). Similarly, the development of the female genital apparatus begins with the formation of the ovaries, followed by the appearance of oocytes in vitellogenesis, then the development of oviducts and uterus internus and, finally, the spermatheca. These data may be very important in further comparative studies on the development of the reproductive system of spiders.

Falcipains, Plasmodium falciparum cysteine proteases as key drug targets against malaria.

There is a high demand for new drugs against malaria, which takes millions of lives annually. The abuse of classical antimalarials from the late 1940's to the early 1980's has bred resistant parasites, which led to the use of more potent drugs that ended up by refueling the resistance cycle. An example is chloroquine, once highly effective but now virtually useless against malaria. Structure-based rational drug design relies on high-resolution target structures to allow for screening of selective ligands/inhibitors. For the past two decades, and especially after the unveiling of the Plasmodium falciparum genome in 2002, enzymes of this lethal malaria parasite species have been increasingly attracting the attention of Medicinal Chemists worldwide as promising drug targets. There is particular emphasis on proteases having key roles on the degradation of host's hemoglobin within the food vacuole of blood-stage parasites, as these depend on such process for their survival. Among such enzymes, Plasmepsins (aspartic proteases) and, especially, Falcipains (cysteine proteases) are highly promising antimalarial drug targets. The present review will focus on the computational approaches made so far towards the unraveling of the structure, function and inhibition of Falcipains that, by virtue of their quite specific features, are excellent targets for highly selective inhibitors.

Immunolocalization of CSF-1, RANKL and OPG in the enamel-related periodontium of the rat incisor and their implications for alveolar bone remodeling.

The enamel-related periodontium (ERP) in rat incisors is related to bone resorption. In these teeth the face of the socket related to the enamel is continuously removed at the inner side and newly formed at the outer side. CSF-1, RANKL and OPG are regulatory molecules essential for osteoclastogenesis. To verify the effects of impeded eruption on bone remodeling, the tooth eruption was prevented by immobilization of lower rat incisor and CSF-1, RANKL and OPG distribution in the ERP was analyzed after 18 days of immobilization and in normal eruption. The region of the alveolar crest of the rat incisor was used. Immunohistochemistry and tartrate-resistant acid phosphatase (TRAP) were performed. The immunostaining of the dental follicle was quantified using Leica QWin software. Positive-TRAP osteoclasts were counted, and both groups were compared. In the normal incisor, the number of osteoclasts was significantly greater than in the immobilized tooth. In the dental follicle, there was no significant difference in the immunostaining intensity for CSF-1 and OPG between the groups (p > 0.05), but for RANKL the immobilized incisor group showed immunostaining intensity smaller than the normal incisor group (p < 0.01). These findings suggest that changes in the ERP, in the immobilized incisor, modify the RANKL/OPG ratio, in the presence of CSF-1, altering the metabolism of cells that participate in the bone remodeling.

Circadian variation of the cell proliferation in the jejunal epithelium of rats at weaning phase.

Circadian variation in cell proliferation of the jejunal epithelium of 18-day-old rats was studied using the 2-h arrested metaphase score and crypt isolation method. A continuous decrease in the arrested metaphases occurred from 07.00 h to 13.00 h. From 17.00 h arrested metaphase values increased and were maintained at the higher level during the dark period as showed by Cosinor analyses (P < 0.05). These results indicate that in the young rat there is already a circadian variation in jejunal epithelial cell proliferation as early as 18 days. We can even suggest that the presence of a circadian rhythm at weaning contributes to the steady state of cell proliferation in the intestinal epithelium observed in adult life.