Paneth cells and their multiple functions

The small intestine mucosa is lined by specialized cells that form the crypt-villus axis, which expands its surface. Among the six intestinal epithelial cell types, the Paneth cell is located at the base of the crypt, and it contains numerous granules in its cytoplasm, composed of antimicrobial peptides, such as defensins and lysozyme, and growth factors, such as EGF, TGF-alpha, and Wnt ligands. Together, these elements act in the defense against microorganisms, regulation of intestinal microbiota, maintenance, and regulation of stem cell identity. Pathologies that target Paneth cells can disturb such defense activity, but they also affect the maintenance of stem cell niche. In that way, Crohn's disease, necrotizing enterocolitis, and graft-versus-host disease promote a reduction of Paneth cell population, and consequently of secretion of their products into the lumen of the crypts, making the affected organism predisposed to infections and dysbiosis. Additionally, the emergence of new intestinal cells is also decreased. This review aims to address the main characteristics of Paneth cells, highlighting their multiple functions and the importance of their preservation to ensure bowel homeostasis. This article is protected by copyright. All rights reserved.

Lifelong Adaptation of Gastric Cell Proliferation and Mucosa Structure to Early Weaning-Induced Effects

The gastric mucosa is disturbed when breastfeeding is interrupted, and such early weaning (EW) condition permanently affects the differentiation of zymogenic cells. The aim of the study was to evaluate the immediate and long-term effects of EW on gastric cell proliferation, considering the molecular markers for cell cycle, inflammation, and metaplasia. Overall, we investigated the lifelong adaptation of gastric growth. Wistar rats were divided into suckling-control (S) and EW groups, and gastric samples were collected at 18, 30, and 60 days for morphology, RNA, and protein isolation. Inflammation and metaplasia were not identified, but we observed that EW promptly increased Ki-67-proliferative index (PI) and mucosa thickness (18 days). From 18 to 30 days, PI increased in S rats, whereas it was stable in EW animals, and such developmental change in S made its PI higher than in EW. At 60 days, the PI decreased in S, making the indices similar between groups. Spatially, during development, proliferative cells spread along the gland, whereas, in adults, they concentrate at the isthmus-neck area. EW pushed dividing cells to this compartment (18 days), increased PI at the gland base (60 days), but it did not interfere in expression of cell cycle molecules. At 18 days, EW reduced Tgfβ2, Tgfβ3, and Tgfbr2 and TβRII and p27 levels, which might regulate the proliferative increase at this age. We demonstrated that gastric cell proliferation is immediately upregulated by EW, corroborating previous results, but for the first time, we showed that such increased PI is stable during growth and aging. We suggest that suckling and early weaning might use TGFβs and p27 to trigger different proliferative profiles during life course.

Breastfeeding importance and its therapeutic potential against SARS-CoV-2

During postnatal development, colostrum and breastmilk are sequentially the first sources of nutrition with protein components and bioactive molecules that confer protection and immunostimulatory function to the gut. Caseins, whey proteins, secretory immunoglobulin A (sIgA), mucins, tryptophan, and growth factors are among milk‐borne elements that are directly important in the control of mucosa development and protection. Consequently, breastfeeding is associated with the low incidence of gastrointestinal inflammation and with the decrease in respiratory diseases during postnatal period. The novel coronavirus (SARS‐CoV‐2) binds to angiotensin II‐converting enzyme (ACE2) on the cell membrane, allowing virus entrance, replication, and host commitment. ACE2 is expressed by different cell types, which include ciliated cells in the lungs and enterocytes in the intestine. Such cells are highly active in metabolism, as they internalize molecules to be processed and used by the organism. The disruption of ACE2 impairs leads to intestinal inflammation and decreased synthesis of serotonin, affecting motility. By reviewing the effects of SARS‐CoV‐2 in the gastrointestinal and respiratory tracts in infants, and gut responses to breastfeeding interruption, we suggest that it is important to maintain breastfeeding during SARS‐CoV‐2 infection, as it might be essential to protect newborns from gastrointestinal‐associated disorders and relieve disease symptoms.

Cancer cachexia induces morphological and inflammatory changes in the intestinal mucosa

BACKGROUND

Cachexia is a multifactorial and multiorgan syndrome associated with cancer and other chronic diseases and characterized by severe involuntary body weight loss, disrupted metabolism, inflammation, anorexia, fatigue, and diminished quality of life. This syndrome affects around 50% of patients with colon cancer and is directly responsible for the death of at least 20% of all cancer patients. Systemic inflammation has been recently proposed to underline most of cachexia-related symptoms. Nevertheless, the exact mechanisms leading to the initiation of systemic inflammation have not yet been unveiled, as patients bearing the same tumour and disease stage may or may not present cachexia. We hypothesize a role for gut barrier disruption, which may elicit persistent immune activation in the host. To address this hypothesis, we analysed the healthy colon tissue, adjacent to the tumour.

METHODS

Blood and rectosigmoid colon samples (20 cm distal to tumour margin) obtained during surgery, from cachectic (CC = 25) or weight stable (WSC = 20) colon cancer patients, who signed the informed consent form, were submitted to morphological (light microscopy), immunological (immunohistochemistry and flow cytometry), and molecular (quantification of inflammatory factors by Luminex® xMAP) analyses.

RESULTS

There was no statistical difference in gender and age between groups. The content of plasma interleukin 6 (IL-6) and IL-8 was augmented in cachectic patients relative to those with stable weight (P = 0.047 and P = 0.009, respectively). The number of lymphocytic aggregates/field in the gut mucosa was higher in CC than in WSC (P = 0.019), in addition to those of the lamina propria (LP) eosinophils (P < 0.001) and fibroblasts (P < 0.001). The area occupied by goblet cells in the colon mucosa was decreased in CC (P = 0.016). The M1M2 macrophages percentage was increased in the colon of CC, in relation to WSC (P = 0.042). Protein expression of IL-7, IL-13, and transforming growth factor beta 3 in the colon was significantly increased in CC, compared with WSC (P = 0.02, P = 0.048, and P = 0.048, respectively), and a trend towards a higher content of granulocyte-colony stimulating factor in CC was also observed (P = 0.061). The results suggest an increased recruitment of immune cells to the colonic mucosa in CC, as compared with WSC, in a fashion that resembles repair response following injury, with higher tissue content of IL-13 and transforming growth factor beta 3.

CONCLUSIONS

The changes in the intestinal mucosa cellularity, along with modified cytokine expression in cachexia, indicate that gut barrier alterations are associated with the syndrome.

Liraglutide modulates gut microbiota and reduces NAFLD in obese mice

Metabolic disorders such as insulin resistance and diabetes are associated with obesity and nonalcoholic fatty liver disease (NAFLD). The aggressive form of a fatty liver disease may progress to cirrhosis and hepatocellular carcinoma. Furthermore, recent studies demonstrated that there is a dysbiosis in the gut microbiota associated with early stages of metabolic disease. Therefore, the identification and repurposing of drugs already used to treat insulin resistance may be an excellent option for other disorders. We evaluated the effect of liraglutide on obesity, NAFLD and gut microbiota modulation in two different animal models of obesity: the ob/ob mice and the high-fat diet (HFD)-fed mice. Liraglutide treatment induced significant weight loss in both obesity models, showed improvements in glycemic parameters and reduced inflammatory cell infiltration in the cecum and the liver. In ob/ob mice, the liraglutide treatment was able to reduce the accumulation of liver fat by 78% and reversed steatosis in the HFD mice. The gut microbiota analysis showed that liraglutide changed the overall composition as well as the relative abundance of weight-relevant phylotypes such as a reduction of Proteobacteria and an increase of Akkermansia muciniphila in the treated HFD group. We show that liraglutide can lead to weight loss and gut microbiota modulations, and is associated with an improvement of NAFLD. Furthermore, by generating a profile of the intestinal microbiota, we compiled a list of potential bacterial targets that may modulate metabolism and induce a metabolic profile that is considered normal or clinically controlled.

Ghrelin and GHS-R in the rat gastric mucosa: Are they involved in regulation of growth during early weaning?

OBJECTIVES

Based on previous evidence showing that early weaning disturbs the ontogenesis of rat gastric glands, which are the major site of ghrelin synthesis, we investigated the distribution of ghrelin and its receptor (GHS-R) in the rat gastric epithelium during postnatal development and evaluated the effects of early weaning on their levels. Additionally, we studied the contribution of ghrelin to gastric growth during the abrupt nutrient transition.

METHODS

Wistar rats were submitted to early weaning at 15 d and suckling counterparts were taken as controls.

RESULTS

By running quantitative reverse transcription polymerase chain reaction, immunoblots, and immunohistochemistry, we detected a variation of ghrelin levels and an increase of expression and number of immunolabeled cells, 3 d after treatment (P < 0.05). Through confocal microscopy, we identified GHS-R in the neck region of the gland and did not observe changes in protein levels. Growth was evaluated after ghrelin antagonist ([D-Lys-3]-GHRP-6) administration, which reduced DNA synthesis index in early-weaned rats (P < 0.05) as determined by bromodeoxyuridine incorporation.

CONCLUSION

The present study demonstrated that ghrelin and GHS-R are distributed in gastric mucosa during the postnatal development, indicating that they can signal and function in epithelial cells. We concluded that early weaning increased ghrelin levels in the stomach, and it takes part of cell proliferation control that is essential for stomach growth. Therefore, among the many effects previously described for early weaning, this abrupt nutrient transition also changed ghrelin levels, which might represent an additional element in the complex mechanism that coordinates stomach development.

MAPKs and signal transduction in the control of gastrointestinal epithelial cell proliferation and differentiation

Mitogen-activated protein kinase (MAPK) pathways are activated by several stimuli and transduce the signal inside cells, generating diverse responses including cell proliferation, differentiation, migration and apoptosis. Each MAPK cascade comprises a series of molecules, and regulation takes place at different levels. They communicate with each other and with additional pathways, creating a signaling network that is important for cell fate determination. In this review, we focus on ERK, JNK, p38 and ERK5, the major MAPKs, and their interactions with PI3K-Akt, TGFβ/Smad and Wnt/β-catenin pathways. More importantly, we describe how MAPKs regulate cell proliferation and differentiation in the rapidly renewing epithelia that lines the gastrointestinal tract and, finally, we highlight the recent findings on nutritional aspects that affect MAPK transduction cascades.

EGFR is involved in control of gastric cell proliferation through activation of MAPK and Src signalling pathways in early-weaned rats

OBJECTIVES

Early weaning (EW) increases proliferation of the gastric epithelium in parallel with higher expression of transforming growth factor alpha and its receptor epidermal growth factor receptor (EGFR). The primary objective of the present study was to examine involvement of EGFR signalling in regulating mucosal cell proliferation during the early weaning period.

MATERIALS AND METHODS

Fifteen-day-old rats were split into two groups: suckling (control) and EW, in which pups were separated from the dam. Animals were killed daily until the 18th day, 3 days after onset of treatment. To investigate the role of EGFR in proliferation control, EW pups were injected with AG1478, an EGFR inhibitor; signalling molecules, proliferative indices and cell cycle-related proteins were evaluated.

RESULTS

EW increased ERK1/2 and Src phosphorylation at 17 days, but p-Akt levels were unchanged. Moreover, at 17 days, AG1478 administration impaired ERK phosphorylation, whereas p-Src and p-Akt were not altered. AG1478 treatment reduced mitotic and DNA synthesis indices, which were determined on HE-stained and BrdU-labelled sections. Finally, AG1478 injection decreased p21 levels in the gastric mucosa at 17 days, while no changes were detected in p27, cyclin E, CDK2, cyclin D1 and CDK4 concentrations.

CONCLUSIONS

EGFR is part of the mechanism that regulates cell proliferation in rat gastric mucosa during early weaning. We suggest that such responses might depend on activation of MAPK and/or Src signalling pathways and regulation of p21 levels.

Fasting differentially regulates plasma corticosterone-binding globulin, glucocorticoid receptor, and cell cycle in the gastric mucosa of pups and adult rats

The nutritional status influences gastric growth, and interestingly, whereas cell proliferation is stimulated by fasting in suckling rats, it is inhibited in adult animals. Corticosterone takes part in the mechanisms that govern development, and its effects are regulated in particular by corticosterone-binding globulin (CBG) and glucocorticoid receptor (GR). To investigate whether corticosterone activity responds to fasting and how possible changes might control gastric epithelial cell cycle, we evaluated different parameters during the progression of fasting in 18- and 40-day-old rats. Food restriction induced higher corticosterone plasma concentration at both ages, but only in pups did CBG binding increase after short- and long-term treatments. Fasting also increased gastric GR at transcriptional and protein levels, but the effect was more pronounced in 40-day-old animals. Moreover, in pups, GR was observed in the cytoplasm, whereas, in adults, it accumulated in the nucleus after the onset of fasting. Heat shock protein (HSP) 70 and HSP 90 were differentially regulated and might contribute to the stability of GR and to the high cytoplasmic levels in pups and elevated shuttling in adult rats. As for gastric epithelial cell cycle, whereas cyclin D1 and p21 increased during fasting in pups, in adults, cyclin E slowly decreased, concomitant with higher p27. In summary, we demonstrated that corticosterone function is differentially regulated by fasting in 18- and 40-day-old rats, and such variation might attenuate any possible suppressive effects during postnatal development. We suggest that this mechanism could ultimately increase cell proliferation and allow regular gastric growth during adverse nutritional conditions.

Opposite effects of fasting on TGF-beta3 and TbetaRI distribution in the gastric mucosa of suckling and early weanling rats

OBJECTIVE

Our aim was to evaluate the effects of a dietary regimen (suckling or early weaning) and feeding status (fed or fasted) on the distribution of transforming growth factor-beta3 (TGF-beta3) and TGF receptor-I (TbetaRI) in the gastric epithelium of pups.

METHODS

Wistar rats were used. At 15 d, half of the pups were separated from dams and fed with hydrated powered chow. On day 17, suckling and early weanling rats were subjected to fasting (17h). Four different conditions were established: suckling fed and fasted and early weanling fed and fasted. At 18 d stomachs were collected under anesthesia and were fixed in 4% formaldehyde for immunohistochemistry. The number of immunostained epithelial cells per microscopic field was determined for TGF-beta3 and TbetaRI in longitudinal sections from the gastric mucosa.

RESULTS

We found that during suckling, fasting reduced the number of immunolabeled cells per field of both molecules when compared with the fed group (P<0.05), whereas in early weaning, food restriction increased TGF-beta3 and TbetaRI distributions (P<0.05). We also observed that TGF-beta3 and TbetaRI were more concentrated in parietal cells in the upper gland in suckling pups, whereas after early weaning these were displaced to parietal and chief cells at the bottom of the gland.

CONCLUSION

Suckling and early weaning directly influence TGF-beta3 and TbetaRI distributions in the gastric epithelium in response to fasting, such that early weaning anticipates the effects observed in adult rats. Furthermore, the differential concentrations of TGF-beta3 and TbetaRI indicate that they might be important for cell proliferation events in growth control.

In vivo effects of TGFbeta1 on the growth of gastric epithelium in suckling rats

As the content of Transforming Growth Factor-beta (TGFbeta) wanes in the milk of lactating rat, an increase in TGFbeta is observed in the gastric epithelia concomitant with differentiation of the glands upon weaning. Whereas TGFbeta has been shown to inhibit the proliferation of gastrointestinal cells in vitro, its functional significance and mechanisms of action have not been studied in vivo. Therefore, we administered TGFbeta1 (1 ng/g body wt.) to 14-day-old rats in which the gastric epithelium was induced to proliferate by fasting, and determined the involvement of signaling through Smads and the impact on epithelial cell proliferation and apoptosis. After the gavage, we observed the progressive increase of active TGFbeta1 while TbetaRII-receptor remained constant in the gastric mucosa. By immunohistochemistry, we showed Smad2/3 increase at 60 min (p<0.05) and Smad2 phosphorylation/activation and translocation to the nucleus most prominently between 0 and 30 min after treatment (p<0.05). Importantly, TGFbeta1 inhibited cell proliferation (p<0.05), which was estimated by BrDU pulse-labeling 12 h after gavage. Lower proliferation was reflected by increased p27(kip1) at 2 h (p<0.05). Also, TGFbeta1 increased apoptosis as measured by M30 labeling at 60 and 180 min (p<0.001), and by morphological features at 12 h (p<0.05). In addition, we observed higher levels of activated caspase 3 (17 kDa) from 0 to 30 min. Altogether, these data indicate a direct effect of TGFbeta1 signaling through Smads on both inhibiting proliferation, through alteration of cycle proteins, and inducing apoptosis of gastric epithelial cells in vivo. Further, the studies suggest a potential role for both milk and tissue-expressed TGFbeta1 in gastric growth during postnatal development.

Chronic hyperglycaemia increases TGFβ2 signaling and the expression of extracellular matrix proteins in the rat parotid gland

The majority of the oral manifestations of diabetes mellitus are secondary to a reduced salivary flow, whose causes are still poorly understood. In the kidney, diabetes complications involve increased Transforming Growth Factor beta (TGFbeta) production and the thickening of basement membrane in small vessels. By using immunohistochemistry and western blotting, we studied the expression and signaling of TGFbeta and the distribution of extracellular matrix (ECM) proteins: laminin, fibronectin, collagens III, IV and V in the parotid gland of control and diabetic rats, 30 and 60 days after streptozotocin injection (D30 and D60). At D30, there was an important increase of laminin whereas fibronectin and collagen V were moderately augmented. At D60, an additional increase of all ECM proteins was observed. TGFbeta1 expression was not affected at any time. In contrast, TGFbeta2 levels were significantly higher at D30, concomitant with increased TGFbeta receptor II (TbetaRII), phosphorylated Smads 2 and 3 (pSmads 2-3) and Latent TGFbeta Binding Protein 1 (LTBP1). At D60, TGFbeta2 and TbetaRII were still increased, whereas phosphorylation of Smads was markedly decreased, and LTBP1 returned to control levels. In the control groups, TGFbeta2 labeling was localized preferentially in ductal cells, whereas at D30 and D60 the staining was also observed in acinar cells. The same pattern of distribution was observed for pSmads 2-3 at D30, especially in nuclei. At D60, labeling was weak and dispersed throughout the cytoplasm. These data suggest that hyperglycaemia increases the deposition of ECM proteins in the rat parotid gland, possibly through augmentation of TGFbeta2 expression and signaling.

Differential distribution of transforming growth factor beta and receptors in the hyper or hypoproliferative gastric mucosa of developing and adult rats

Transforming growth factor beta (TGFbeta) isoforms are known for their antiproliferative effect on epithelial cells in vitro, but the role of each isoform in vivo is poorly understood, mainly when non-pathological conditions are considered. We correlated the presence and distribution of isoforms and receptors to physiological changes in gastric cell proliferation in developing and adult rats. We used fasting to induce either the hyper (14-day-old pups) or hypoproliferation (60-day-old rats) of the gastric epithelium. In 14-d-old pups fasting reduced only TGFbeta3 labelling in the gland. Conversely, in 60-d-old rats there was an increase of TGFbeta1 and TGFbeta3 immunolabelled cells. Receptors were detected at both ages. Therefore, the changes induced by fasting in the constitutive TGFbeta expression can be correlated to the differential epithelial proliferation in the stomach of developing and adult rats. These results suggest that one of the functional roles of TGFbeta in vivo is to locally regulate cell proliferation.

Myenteric denervation differentially reduces enteroendocrine serotonin cell population in rats during postnatal development

The enteric nervous and enteroendocrine systems regulate different processes in the small intestine. Ablation of myenteric plexus with benzalkonium chloride (BAC) stimulates epithelial cell proliferation, whereas endocrine serotonin cells may inhibit the process. To evaluate the connection between the systems and the influence of myenteric plexus on serotoninergic cells in rats during postnatal development, the ileal plexus was partially removed with BAC. Rats were treated at 13 or 21 days and sacrificed after 15 days. The cell bodies of myenteric neurons were stained by beta NADH-diaphorase to detect the extension of denervation. The number of enteroendocrine cells in the ileum was estimated in crypts and villi in paraffin sections immunostained for serotonin. The number of neurons was reduced by 27.6 and 45% in rats treated on the 13th and 21st days, respectively. We tried to establish a correlation of denervation and the serotonin population according to the age of treatment. We observed a reduction of immunolabelled cells in the crypts of rats treated at 13 days, whereas this effect was seen in the villi of rats denervated at 21 days. These results suggest that the enteric nervous system might control the enteroendocrine cell population and this complex mechanism could be correlated to changes in cell proliferation.

Corticosteroids induce the differential expression of TGFbeta isoforms, receptors and signaling in the gastric mucosa of suckling rats

Glucocorticoids inhibit the cell proliferation in the gastric epithelium, and induce differentiation, migration and death. The mechanism by which these effects are triggered and controlled is still discussed and can involve the transcription and activation of transforming growth factor beta (TGFbeta). The present study was conducted to evaluate the effect of hydrocortisone short-term treatment on tissue level and distribution of TGFbeta isoforms, receptors and signaling through Smad2/3. To achieve that, 18-day-old rats were injected with hydrocortisone (50 mg/Kg b.wt.) for 0, 1 and 3 h. The stomachs were collected and processed for immunohistochemistry and western blotting. We observed that the treatment for 3 h increased the number of labeled epithelial cells for TGFbeta1 (p < 0.05), decreased the distribution of TGFbeta2 (p < 0.05) and did not alter TGFbeta3, TbetaRI and TbetaRII status. The levels of TGFbeta1 and receptors were checked by western blotting and results corroborate the immunodetection. We also found that phosphorylation of Smad2/3 into Smad2P increased after 3 h (p < 0.05), indicating that the high level TGFbeta1 was active on the cells. We suggest that glucocorticoids differentially regulate the expression of TGFbeta isoforms, receptors and signaling, and so TGFbeta1 might be involved in the inhibitory pathway triggered by the hormone.

Intestinal damage in strongyloidiasis: the imbalance between cell death and proliferation

Strongyloidiasis is an endemic tropical parasitosis caused by Strongyloides stercoralis that also affects immigrants in nontropical countries. The nematode colonizes the duodenum and upper jejunum, inducing mucosal alterations. Because integrity is essential for a functional barrier, we aimed to study apoptosis and proliferation in the small bowel epithelium infected with S. stercoralis. We evaluated 23 patients and 17 controls. Apoptotic cells were detected by TUNEL and M30 immunolabelling, whereas proliferation was scored by Ki67 immunostaining and mitotic counting. Infection increased apoptotic indices in duodenum and jejunum (P < 0.001). Conversely, it decreased cell proliferation in both segments (P < 0.001). Our results showed that intestinal strongyloidiasis promotes an imbalance between cell death and proliferation. This is the first evidence of disruption of the epithelial kinetics with S. stercoralis infection, though the mechanisms remain unclear. Furthermore, our results support the idea that strongyloidiasis disturbs the mucosal integrity and can compromise the intestinal barrier.

Alternative model to human skin organ culture: A preliminary study with Leibovitz L15 medium

Organ culture has been used to maintain the three-dimensional structure of the skin and the interaction between melanocytes and keratinocytes, which is essential for melanin production. In the current study we aimed to evaluate the general morphology, viability, and distribution of human melanocytes in a system that uses Leibovitz L15 medium at room temperature. By comparison with human skin explants maintained in Dulbecco's minimum Eagle's medium at 37 degrees C, we found that the skin was better preserved with Leibovitz L15 after 7 days in culture. The addition of 10% fetal bovine serum to this medium did not promote any change. Dividing cells labeled with Ki-67 were visualized at the basal and suprabasal epidermal layers. Retinoic acid was tested at 1 microg/mL and we recorded a reduction of the corneal layer after 48 hours and a complete detachment of the epidermis after 7 days, probably due to a toxic effect in the medium. Melanin and melanocytes were detected by ammoniacal silver and Dopa stainings under light microscopy. We observed that cells were viable throughout the culture period and melanin was distributed in melanocytes and keratinocytes. In conclusion, we suggest that the use of Leibovitz L15 medium at room temperature can be a viable alternative to the normal organ culture of human skin, which is an important system to study the activity and reaction of melanocytes to dermatological products and cosmetics.

Ileal VIP submucous neurons: confocal study of the area enlargement induced by myenteric denervation in weanling rats

Vasoactive Intestinal Peptide (VIP) neurons are maturing during suckling and weaning periods and the neuropeptide VIP is thought to be neurotrophic during ontogenesis. We have previously demonstrated that suckling rats with myenteric ablation have significantly higher mitotic index and an increase on villus height and crypt depth 15 days after treatment. In the current study, we measured the area of VIP neurons of submucous plexus in the ileum of weanling rats, in which myenteric neurons were ablated by serosal application of benzalkonium chloride (BAC). The area of VIP immunoreactive cell bodies, reconstructed under confocal microscope, was significantly increased in response to denervation. This result suggests that the myenteric plexus may have an inhibitory role over submucous plexus in the normal intestine. The enhanced production of VIP may be correlated with the increased epithelial proliferation induced by denervation in a critical period of life, from suckling to weaning time.

Serotonin in the nervous system of the head region of the land planarian Bipalium kewense

The presence and distribution of serotonin (5-hydroxytryptamine, or 5-HT) in the head region of the land planarian Bipalium kewense has been investigated by an indirect immunofluorescence technique combined with confocal scanning laser microscopy (CSLM), and also by immunogold labeling at ultrastructural level. Serotonin immunoreactivity (IR) was restricted to elements of the nervous system, such as the cerebral ganglion, and the peripheral nerve net. Most of 5-HT-immunoreactive neurons are at the periphery of the brain; they were identified as unipolar, bipolar, and multipolar neurons. The ultrastructural results using immunogold labeling confirm the location of 5-HT within electron-dense vesicles (50-120 nm in diameter), clustered both in the cell bodies and in their processes. The intense 5-HT-IR herein demonstrated for B. kewense adds new data to the poorly studied nervous system of land planarians.

Ontogenic expression of TGFbeta 1, 2, and 3 and its receptors in the rat gastric mucosa

The stomach of the rat undergoes extensive changes during the formation and maturation of gastric glands. The presence of transforming growth factor beta (TGFbeta) in rat milk and in the gastrointestinal tract of pups may suggest its role in this process. The current study evaluated the in vivo dynamic expression and distribution of TGFbeta1, beta2, beta3 and their receptors TbetaRI and TbetaRII in the gastric epithelium of 20-day fetal rats and 1-, 14-, 21-, and 30-day-old pups. Immunohistochemistry was used to detect the proteins, and staining was classified according to intensity and cell type. The results showed that the gastric epithelium expresses TGFbeta isoforms and receptors throughout development. We found that immunoreactivity paralleled the appearance of differentiated cells, such that surface mucous cells were the first to be immunostained and chief cells were the last. The intensity of reactions followed this same pattern, showing that the expression of TGFbeta isoforms spread along the gland with growth. Of interest, the highest apparent activity of TGFbeta was observed from 21 days onward, a period that is concomitant with weaning and maturation of most gastric cell types. In addition, surface mucous cells were strongly labeled at the basal cytoplasm at 14 days, suggesting an interaction with the connective tissue. In conclusion, the dynamic expression of TGFbeta1, beta2, beta3, and TbetaRI and TbetaRII through stomach development suggests significant paracrine and autocrine roles for this growth factor. We propose that temporal and spatial differences may be regulated by dietary changes, which in turn control cell proliferation and differentiation in the gastric epithelium.

Localization of luteinizing-hormone releasing hormone binding sites in the gastric mucosa of suckling rats

Luteinizing-hormone releasing hormone (LHRH) is a hypothalamic and milk-borne hormone that inhibits the cell proliferation of gastric epithelium in developing rats, although the mechanism of such action is unknown. We investigated the presence of binding sites for LHRH in the stomach of suckling rats after the injection of the hormone. Immunofluorescence at the confocal microscopy level revealed that LHRH binds to gastric cells, being particularly abundant over the gland. Different fluorescent lectins were used to identify gastric cell types and determine which were labeled by the hormone. Colocalization studies in these double-labeling experiments showed that LHRH staining colocalizes with parietal cells, suggesting the presence of binding sites in these cells. The three-dimensional (3-D) reconstruction of isolated parietal cells revealed the localization of the signal, which appears to be in the membrane of the canalicular region. These results suggest that there are binding sites for LHRH in the gastric epithelium, specifically in parietal cells, and they might play a role in the control of cell proliferation during suckling.

Streptozotocin-induced diabetes duration is important to determine changes in the number and basophily of myenteric neurons

The aim of present study was to evaluate the number and basophily of cell bodies of myenteric neurons in the ileum of rats with diabetes mellitus induced by streptozotocin. Four groups of rats were used: diabetes was induced in two (D) whereas the other two worked as controls (N). Animals were sacrificed six (6N, 6D) or nineteen (19N, 19D) weeks after diabetes induction. A segment of the terminal portion of the ileum of each rat was obtained and stained with Giemsa's solution, for whole-mount preparation studies. Forty fields were analyzed in each animal, and the number and basophily intensity of cell bodies were recorded. After counting, the following mean numbers of neurons/mm2 were obtained: 6N=593.1 +/- 95.75, 6D=639.1 +/- 130.8, 19N=580.1 +/- 175.6 and 19D=402.0 +/- 144.8. The analysis of basophily shown that highest frequency of neurons with weak/intermediary basophily was verified in 6D group (55.3%), whereas the groups 6N, 19N e 19D presented 38%, 36% e 40% respectively. The statistical analysis showed that a long period is necessary to decrease the number of neurons/mm2 in the rat ileum after diabetes induction, and that there was a reduction in basophily intensity in diabetic rats after 6 weeks of treatment, and such cells do not recover after a longer period (19 weeks).

Cell proliferation and death in the gastric epithelium of developing rats after glucocorticoid treatments

Glucocorticoids take part in the intense morphofunctional modifications that occur in the gastric mucosa during fetal and postnatal development. Two studies were designed to evaluate corticoids role in gastric cell proliferation and apoptosis in developing rats: in vivo, using suckling animals; in vitro, using gastric explants obtained from 20-day fetuses. These explants were cultured in DMEM/F12 medium treated or not with 50 ng/ml of corticosterone; after 22 hr, vincristine was added to the medium for 2 hr to block mitosis. The metaphasic index decreased significantly after the 24-hr treatment (controls: 1.52 +/- 0.53; treated: 0.40 +/- 0.21) and apoptotic cells were visualized under light and electron microscopy. Fifteen-day-old rats were treated with hydrocortisone (25 mg/Kg) for 3 days, and injected with BrDU (100 mg/Kg) 1 hr before sacrifice on the 18th day. BrDu-labeled and non-labeled cells were counted to determine the labeling index of epithelial cells. As apoptotic cells are rapidly eliminated, other animals were treated for only 2-3 hr. Sections were investigated for the presence of apoptotic cells, using morphological criteria and TUNEL labeling. Hydrocortisone significantly reduced the labeling index (controls: 15.6 +/- 1.6 vs. treated: 11.7 +/- 1.1), besides altering the body weight gain. Hydrocortisone treatment doubled the number of apoptotic cells after 2 hr, and quadruplicated it after 3 hr. The results demonstrated that glucocorticoids inhibit cell proliferation in the gastric epithelium of fetuses and suckling rats and increase apoptotic rates, suggesting the exit from cell cycle.

Early weaning and prolonged nursing induce changes in cell proliferation in the gastric epithelium of developing rats

Food deprivation stimulates cell proliferation in the gastric epithelium of suckling, but not weanling rats. This study was designed to investigate the role of diet on proliferation in developing animals, using early weaning and prolonged nursing models. Rat pups were subjected to these dietary conditions at d 15 and were killed 3 or 7 d afterwards. One day before killing, half of pups were deprived of food. Body weights were recorded. After mitosis blockade, the histologic sections of the stomach were used for the evaluation of cell proliferation and methapasic cell distribution along the gland, and for the measurement of mucosa thickness. Body weight was impaired at 18 d by early weaning and at 22 d by prolonged nursing. Food restriction promoted a 10-15% weight loss regardless of dietary conditions. At 18 d, food deprivation inhibited cell division (P: < 0.01) and reduced the thickness of the mucosa (P: < 0.05) in rats that were weaned early. At 22 d, only the thickness of the mucosa was different between the groups that were subjected to early weaning and prolonged nursing (P: < 0.05), regardless of feeding state. The frequency of dividing cells along the gland was affected by early weaning in 18- and 22-d-old rats. These results suggest the following: 1) food deprivation effects are dependent on dietary condition at 18 d because different proliferative responses were achieved after early weaning and prolonged nursing; 2) the lack of changes after dietary manipulation in 22-d-old rats indicates a nonresponsive period during postnatal development. We conclude that milk is a modulatory factor for cell proliferation in the gastric mucosa of rats.

LHRH antagonist inhibits gastric cell proliferation in suckling rats

The cell proliferation of the gastric epithelium is stimulated by food deprivation in suckling rats, and LHRH inhibits this process as it does in other hyperproliferating tissues. However, as LHRH antagonist is also being used as a potent antiproliferative agent for tumors, this study aims to investigate whether it plays any role on the cell proliferation of the gastric epithelium. Seventeen-day-old rats were fasted for 20 h and treated with LHRH antagonist, LHRH, or both during this period. The following morning, animals were injected with BrDU to label proliferating cells, and were sacrificed 1 h later. Paraffin sections of the gastric mucosa were processed for immunohistochemistry and BrDU labeled and non-labeled epithelial cells were counted to determine the labeling index (LI). None of the hormone treatments changed body weight or the morphology of the stomach. Apoptotic cells were observed in the gastric gland in treated rats. The LI were inhibited by the antagonist, LHRH or both, showing that the LHRH antagonist plays an inhibitory role on the hyperproliferating gastric epithelium. These results suggest that both LHRH agonist and antagonist can influence the proliferative activity in suckling rats, though the mode of action remains to be determined.

Corticosterone treatment inhibits cell proliferation in the gastric epithelium of suckling rats

During the 3rd postnatal week, the rat gastrointestinal tract undergoes major changes which depend on the different factors such as dietary transition and hormones. Glucocorticoids are closely involved in these processes, yet a clear proliferative response to these agents in the gastric epithelium has not yet been established. The aim of this study was to determine the effect of corticosterone on cell proliferation in the gastric mucosa of suckling rats. We also measured plasma corticosterone concentration in fed and fasted suckling (18-day-old) and weaning rats (22-day-old) observing that fasting increased the levels in animals of both ages (P < 0.05). Cell kinetic parameters, i.e., metaphase index, cell production rate, and potential doubling time, were obtained by vincristine blockade in control and corticosterone-treated 18-day-old pups. The metaphase index was strongly inhibited by corticosterone (P < 0.001), as was the cell production rate (P < 0.05), indicating a high potential doubling time in treated rats. Mucosal and glandular thickness were also measured, but no differences between treated and untreated animals were found. The results suggest that corticosterone treatment has an inhibitory effect on cell proliferation in the gastric mucosa in suckling rats, and that the high endogenous levels observed during fasting do not affect the proliferative activity.

LHRH and somatostatin effects on the cell proliferation of the gastric epithelium of suckling and weaning rats

The aim of this study was to investigate the effects of LHRH and somatostatin on the cell proliferation of the gastric epithelium of suckling and weaning rats after fasting treatment. Previous studies on the cell proliferation of the gastric epithelium have shown that fasting stimulates this process in suckling, but not in weaning and adult rats. As milk is the most important source of nutrients and hormones during the suckling phase, and luteinizing hormone-releasing hormone (LHRH) and somatostatin are found in milk, their possible inhibitory roles on the gastric epithelium were investigated. Metaphasic index was achieved by vincristine blockade in 18- and 22-day-old treated and non-treated rats. The results showed that at 18 days, both hormones inhibited the enhanced proliferation activity due to fasting treatment, while at 22 days, no effect was detected. Therefore, LHRH and somatostatin were considered to have inhibitory roles on the cell proliferation of the gastric epithelium in suckling rats only.

Fasting enhances cell proliferation of gastric epithelium during the suckling period in rats

The effect of fasting on cell proliferation was studied during the postnatal development of the maturing stomach. Metaphase indices were obtained after counting mitotic cells blocked by vincristine. The indices were examined at different times of day (10:00 a.m. and 6:00 p.m.) in 16 Wistar rats for each age (10, 18, 22 and 30 days) with different dietary patterns: only milk; weaning with milk and chow; recently weaned, with only chow, and fully weaned, respectively. Metaphase indices (mean +/- SEM) for both periods taken together for 10 and 18-day old animals were significantly higher in fasted (2.25 +/- 0.22% and 2.49 +/- 0.28%, respectively) than in control fed animals (1.67 +/- 0.09% and 1.84 +/- 0.05%, respectively), even if not significantly different for one period alone (18 h). No significant difference in indices was observed for 22-day old rats (fasted = 1.65 +/- 0.28%). The metaphase index of 30-day old rats was significantly higher in fed (1.02 +/- 0.16%) than in fasted animals (0.20 +/- 0.03%). We conclude that fasting enhances cell proliferation in stomach epithelium during the milk intake period, in contrast to the inhibitory effect observed in adult animals. The weaning period marks a transition to the opposite effect of fasting, i.e., a decrease in cell proliferation in 30-day old animals.