Morphological changes during ontogeny of the canine proximal colon

Development of the human tail bud and splanchnic mesenchyme

The purpose of this paper was to shed some light on anorectal development from a viewpoint of the tail bud and splanchnic mesenchyme for better understanding of the morphogenesis of the human anorectum. Human embryos ranging from Carnegie stage 11 to 23 (CS 11 to 23) were adopted in this study. Seventeen embryos preserved at the Congenital Anomaly Research Center of Kyoto University Graduate School of Medicine were histologically examined. The cloaca, extending caudally to the hindgut, was dramatically enlarged, particularly both its dorsal portion and membrane, that is, the cloacal membrane resulting from the development of the tailgut derived from the tail bud. The splanchnic mesenchyme surrounding the hindgut was spread out in the direction of the urorectal septum ventrally, suggesting that it participated in the formation of the septum. No fusion of the urorectal septum and the cloacal membrane was found. The splanchnic mesenchyme proliferated and developed into smooth muscle (circular and longitudinal) layers from cranial to caudal along the hindgut. The tail bud seems to cause both the adequate dilation of the dorsal cloaca and the elongation of the cloacal membrane; its dorsal portion in particular will be necessary for normal anorectal development. The splanchnic mesenchyme developed and descended toward the pectinate line and formed the internal sphincter muscle at the terminal bowel.

Interstitial cells of Cajal (ICC) and gastrointestinal stromal tumor (GIST): facts, speculations, and myths

Interstitial cells of Cajal (ICC) is a peculiar cell network composed of cells having processes described by the eminent Spanish neuroanatomist of the 19th century, S. Ramon y Cajal. ICC became a fascinating subject to many investigators and it is estimated that there are over 100 publications yearly on the subject related to ICC, in the last three years. Now it is widely accepted that ICC are pace maker cells of the gut and probable progenitor cells of gastrointestinal stromal tumors (GIST). Lately, interstitial Cajal-like cells (ICLC) are being found in various organs and their physiological role is still to be defined. We have reviewed the literature trying to evaluate the validity of the current concept and found that there are a few salient points to be considered. 1) There has been some important departure in defining the identity of ICC from the original criteria of Cajal. In particular, ICC with myoid feafures in intestinal smooth muscle layers (ICC-DPM) do not seem to fit to the original description of interstitial cell network by Cajal. We have also pointed out that the current reports assigning a pace maker role to ICC vastly depend on the scientific data on "ICC with myoid features", not on "fibroblast-like ICC", which are more abundant and easier to identify. 2) There seem to be an overwhelming amount of data proving the relationship between ICC and GIST. Both are known to express c-Kit and the ultrastructural characteristics seen in GIST roughly parallel those of ICC including minimal myoid differentiation seen in the majority of GIST, supporting the current concept that GIST are ICC tumors. 3) According to the original description of Cajal, ICC was not limited to the gut, suggesting an existence of ICC in other organs. The list of organs reported to contain ICC (currently identified by immunohistochemistry and electron microscopy) is ever growing and further studies are needed to define their identity and pathophysiologic role. 4). Recent data concerning gut development suggest that both c-Kit expressing ICC (fibroblasts-like as well as muscle-like) and gut muscle cells derive from the common progenitor cells of the embryonic gut unifying the histogenetic concept of all GIST with heterogeneous cytomorphologic features. In this review we attempted to incorporate recent information on interstitial Cajal-like cells (ICLC) found in other organs to broaden our understanding of ICC in general in terms of their ultrastructure, physiology, and neoplasia.

Development of the enteric nervous system, smooth muscle and interstitial cells of Cajal in the human gastrointestinal tract

The generation of functional neuromuscular activity within the pre-natal gastrointestinal tract requires the coordinated development of enteric neurons and glial cells, concentric layers of smooth muscle and interstitial cells of Cajal (ICC). We investigated the genesis of these different cell types in human embryonic and fetal gut material ranging from weeks 4-14. Neural crest cells (NCC), labelled with antibodies against the neurotrophin receptor p75NTR, entered the foregut at week 4, and migrated rostrocaudally to reach the terminal hindgut by week 7. Initially, these cells were loosely distributed throughout the gut mesenchyme but later coalesced to form ganglia along a rostrocaudal gradient of maturation; the myenteric plexus developed primarily in the foregut, then in the midgut, and finally in the hindgut. The submucosal plexus formed approximately 2-3 weeks after the myenteric plexus, arising from cells that migrated centripetally through the circular muscle layer from the myenteric region. Smooth muscle differentiation, as evidenced by the expression of alpha-smooth muscle actin, followed NCC colonization of the gut within a few weeks. Gut smooth muscle also matured in a rostrocaudal direction, with a large band of alpha-smooth muscle actin being present in the oesophagus at week 8 and in the hindgut by week 11. Circular muscle developed prior to longitudinal muscle in the intestine and colon. ICC emerged from the developing gut mesenchyme at week 9 to surround and closely appose the myenteric ganglia by week 11. By week 14, the intestine was invested with neural cells, longitudinal, circular and muscularis mucosae muscle layers, and an ICC network, giving the fetal gut a mature appearance.

Dimensions and histologic characteristics of the small intestine of dogs during postnatal development

OBJECTIVE

To quantify dimensions of the small intestine of dogs and describe changes in histologic characteristics of the mucosa during postnatal development.

SAMPLE POPULATION

Gastrointestinal tract tissues obtained from 110 Beagles (15 adult females and 95 puppies of both sexes).

PROCEDURE

Several variables (length, total weight, mucosal weight, and nominal surface area) of the small intestine were measured in puppies at birth but before suckling; 1 day after birth and subsequent suckling, 21, 42, and 63 days after birth, and in the adult dams of the puppies. Tissue structure was examined and quantified at each time point by use of routine histologic examination and ocular micrometry of formalin-fixed specimens stained with H&E.

RESULTS

Small intestinal dimensions increased throughout development with the greatest proportional changes during the first day after birth and onset of suckling. Villus height decreased during suckling but had consistent values from 42 days after birth to maturity, whereas crypt depth increased from birth to maturity. Vacuolated enterocytes were evident from birth to 21 days but not thereafter.

CONCLUSIONS AND CLINICAL RELEVANCE

Increases in intestinal dimensions provide growing dogs with a greater capacity for digestion and absorption. Changes in mucosal architecture and cell populations coincided with shifts in dietary inputs. These findings may assist in the diagnosis of small intestinal diseases and nutritional responses during growth and development of dogs.

Development of visceral smooth muscle

The development of the smooth musculature of viscera has attracted the interest of only relatively few investigators, and thus the field appears somewhat underexplored. The major emphasis on histochemical evidence--at the expense of ultrastructural and functional studies--may have limited the progress in this area. Mature tissue is formed through the differentiation of precursors into muscle cells and through the organization of these cells into a complex tissue where distribution and orientation of muscle cells, deployment of abundant extracellular materials and addition of other cellular elements (interstitial cells, fibroblasts, nerves, blood vessels) are characteristic and specific features. The precursor cells are found at sites where a muscle develops, and they derive predominantly from the mesoderm, but also from the neuroectoderm and from the endoderm. The process starts at different times in different organs. The earliest stages of differentiation are characterized by the precursor cells aggregating and becoming elongated; their longitudinal axis lies in a position similar to the one they will have in the mature muscle. Both the cytological and the histochemical differentiation follow distinct patterns in various muscles, with characteristic temporal sequences in the appearance of key features. This process must impart distinct functional properties to a muscle cell at each stage of its development. However, the chronological correspondence between ultrastructural and histochemical development is poorly understood. Histochemical studies have detected gradients of maturation of the muscle cells, for example, across the thickness of the gizzard musculature and along the length of the small intestine; ultrastructural studies have not yet confirmed the existence of these gradients. Muscle growth is accounted for by muscle cell enlargement (without nucleus duplication) and an increase in muscle cell number by mitosis of pre-existing differentiated muscle cells. De-differentiation and division of muscle cells, migration of muscle cells and late development of muscle cell precursors have all also been considered as possible mechanisms for muscle growth. Several authors have described the presence of precursor cells within developing smooth muscles, and they have described late differentiation of some muscle cells or waves of differentiation that would give rise to phenotypic heterogeneity of the mature muscle cell population. In contrast, other studies, mainly by electron microscopy, have suggested that, within large visceral muscles, the muscle cells differentiate synchronously. There are interesting data on the influence of adjacent tissues on the development of a smooth muscle, but the interplay of these and other factors has not been fully investigated. Smooth muscles contract from early in their development, hence mechanical factors are likely to influence development: on the one hand, passive stresses imposed on the muscle by other tissues, such as adjacent muscles or the contents of the viscera and, on the other hand, active forces generated by the muscle itself. The very attraction of visceral smooth muscles in the study of cellular morphogenesis--an attraction that has not yet been highlighted or exploited in scientific studies, either descriptively or experimentally--is that, onto a single type of cell, a large range of factors interact, such as the genetic expression, chemical influences (from other muscles, endocrine glands, nerves, other intramuscular cells) and mechanical factors.

Arginine supplementation prevents necrotizing enterocolitis in the premature infant

OBJECTIVES

To determine whether supplementation with L -arginine reduces the incidence of all stages of necrotizing enterocolitis (NEC) in premature infants with birth weight < or =1250 g and gestational age < or =32 weeks.

STUDY DESIGN

In a randomized, double-blind, placebo-controlled study, 152 premature infants were prospectively, randomly assigned to receive either supplemental L -arginine (1.5 mmol/kg per day; n =75 [group A]) or placebo (control group; n = 77 [group B]) with oral feeds/parenteral nutrition during the first 28 days of life. Nutrient intake, plasma ammonia, arginine, and amino acid concentrations were measured in all infants at days 3, 14, and 28 and at the time of diagnosis of NEC.

RESULTS

NEC developed in 5 infants in group A compared with 21 infants in group B (P <.001). Arginine intake and plasma arginine concentrations were similar in both groups at study entry and (as expected) increased in group A at days 14 and 28. Plasma arginine concentrations were lower in both groups at time of diagnosis of NEC. No significant differences in maternal and neonatal demographics, nutrient intake, plasma ammonia and total and essential amino acid concentrations were present between the two groups.

CONCLUSIONS

Arginine supplementation (1.5 mmol/kg per day) in premature infants reduces the incidence of all stages of NEC.

A gross and microscopical morphometric evaluation of feline large intestinal anatomy

The objective of this study was to examine measurable parameters that could be used to describe the gross and microscopical anatomy of the feline colon, which has not been previously characterized. Post-mortem data were collected from 35 specific pathogen-free cats. Gross morphometric data (total colonic length, wet weight, number of lymphoid aggregates) were collected together with microscopical measurement of crypt depth and numbers, intra-epithelial lymphocyte numbers and the number of proliferating cell nuclear antigen (PCNA)-positive cells and their relative position within the crypt. Colonic length as a percentage of intestinal length was remarkably constant (20.9+/-2.0%). Crypt depth, however, showed considerable inter-cat variation (149-688 microm); the crypts became deeper with distance from the anus. Cellular proliferation was predominantly in the lower part of the crypt, and the numbers of PCNA-positive cells increased with distance from the anus. The number of lymphoid aggregates varied with distance from the anorectum and appeared to reflect the bacterial load. Intra-epithelial lymphocytes were relatively sparse (3.9+/-2.7/100 epithelial cells); they showed considerable inter-cat variation but did not vary with distance from the anus. These data suggest that to improve the interpretation of morphometric parameters by reducing inter-cat variation, samples should be taken at a consistent distance from the anus, broad reference ranges having now been established.

Guide to the identification of interstitial cells of Cajal

The interstitial cell of Cajal, abbreviated ICC, is a specific cell type with a characteristic distribution in the smooth muscle wall throughout the alimentary tract in humans and laboratory mammals. The number of publications relating to ICC is rapidly increasing and demonstrate a rich variation in the structure and organization of these cells. This variation is species-, region-, and location-dependent. We have chosen to define a "reference ICC," basically the ICC in the murine small intestine, as a platform for discussion of variability. The growing field of ICC markers for light and electron microscopy is reviewed. Although there is a rapidly increasing number of approaches applicable to bright field and fluorescence microscopy, the location of markers by electron microscopy still suffers from inadequate preservation of ultrastructural detail. Finally, we summarize evidence related to ICC ultrastructure under conditions differing from those of the normal, adult individual (during differentiation, in pathological conditions, transplants, mutants, and in cell culture).

Morphological changes of the myenteric plexus during early postnatal development of the rat

The enteric nervous system needs to adapt itself constantly to the postnatal changes of the developing gut. The aim of this study was to examine the morphological changes between the distal and proximal segments of the gastrointestinal (GI) tract during the first two postnatal weeks. Myenteric plexus from the duodenum, proximal and distal colon of 1-, 7- and 14-day-old rat pups was dissected and examined under the scanning electron microscope. Wholemounts from the same regions and postnatal stages were stained with cuprolinic blue. Neuronal numbers per ganglionic area were counted and neuronal sizes were measured. Furthermore, segments of the above-mentioned areas were embedded in resin and semithin sections were cut. The thickness of the circular and longitudinal muscle layers was measured. The morphology of the myenteric plexus depends on localization as well as on the age of the animal. While in younger animals the myenteric plexus is usually densely packed, the network expands with increasing age. Similarly, the thickness of the circular and the longitudinal muscle layers increases. Nerve cell numbers per ganglionic area increase from duodenum to distal colon and decrease from the 1-day (P1) to the 14-day-old (P14) animal. The longest diameters and the area of the nerve cells decrease from duodenum to distal colon and increase with age of the animal. The intensity of the cuprolinic blue staining varies also according to age and segment of the gut. During the first two postnatal weeks the three-dimensional architecture of the myenteric plexus as well as the size and densities of the enteric neurons change according to the increasing gut length and the thickness of the muscle layer. The differences between duodenum and colon might reflect the different physiological properties of the proximal and distal gut as well as a varying grade of maturity, which is also supported by a variation in the cuprolinic blue staining intensity.

Interstitial cells of Cajal as precursors of gastrointestinal stromal tumors

Interstitial cells of Cajal (ICC) are implicated in the regulation of gut peristalsis and are immunostained by antibodies against Kit (CD117), a tyrosine kinase receptor. Most gastrointestinal mesenchymal tumors (GIMTs) are of uncertain histogenesis, although many are CD34-positive. CD34 was found to colocalize with vimentin (Vim) and the Kit-positive networks of cells within and around neural plexi, indicating that ICC can be Vim- and CD34-positive. ICCs appear to be the only Kit+CD34+Vim+ cell in the gut. Formalin-fixed, paraffin-embedded tissues from 43 GIMTs were immunostained for Kit, CD34, Vim, PGP 9.5 (PGP, a neural marker), muscle-specific actin (MSA), and other markers including desmin (Des). Eight tumors were myoid (MSA+Des+Vim-Kit-CD34-), and one was a schwannoma (PGP+S100+Vim+Kit-CD34-), but 34 tumors were of uncertain histogenesis (gastrointestinal stromal tumors, GIST), exhibiting neither a complete myoid nor a schwannian immunophenotype. All 34 were Vim+, and 33/34 were either Kit (n = 30) or CD34 (n = 23) immunoreactive. Of these 34 GIST, 24 were negative for all myoid and neural markers, 6 were PGP+S100-, and 4 were MSA+Des-. The Kit+CD34+Vim+ immunophenotype of GIST suggests that they originate from, or have differentiated into, ICC-like cells; the term ICC tumor (ICCT) is suggested. Kit is a more sensitive marker than CD34 for ICCT, but both are required in tumor identification. All clinically malignant GISTs were pathologically malignant (size, mitoses) but also showed loss of either CD34 or Kit. "Blind" examination of electron micrographs in 10 tumors showed them to be heterogeneous. Some had features seen in normal ICC, but cells could not be positively identified as being adult ICC. GIMT may therefore be classifiable into those with pure myoid, schwannian (or neural) differentiation, but the majority are of ICC origin or show ICC differentiation immunophenotypically (ICCT).

Bi-phasic allometric growth of the small intestine, cecum and the proximal, middle, and distal colon of rats (Rattus norvegicus Berkenhout, 1764) before and after weaning

We studied whether the growth of the intestinal tract changes at weaning. We weighted fresh tissue and measured segment length of the small intestine, cecum and proximal, middle, and distal colon of 45 male and 51 female F344/Yit rats (Rattus norvegicus Berkenhout, 1764) of 0 to 428 days old. We performed correlation analysis among tissue weight, segment length and empty body weight after logarithmic transformation of the data. The growth of the small and large intestine was biphasic. Intestinal growth exceeded body growth during the suckling period and slowed down suddenly after weaning. Sexual differences existed in intestinal growth, although much smaller than the difference before and after weaning. These results appear to suggest that the size of intestinal tract of the rat does not adapt to nutritional changes at weaning, but prepare for weaning beforehand.

Nitroglycerin attenuates the bowel damage of necrotizing enterocolitis in a rabbit model

Endogenous enteric nitric oxide has multiple functions. Enteric nitric oxide may be diminished in the premature infant and may therefore predispose the immature intestine to injury. The aim of this study was to determine if the infusion of a nitric oxide donor (nitroglycerin) would attenuate intestinal damage in a rabbit model of necrotizing enterocolitis. Transmural injection of rabbit intestinal loops with an acidified solution of casein and calcium gluconate simulates certain aspects of necrotizing enterocolitis. After injection of acidified casein solution into rabbit intestinal loops, twelve rabbits were randomly divided into two groups: six received maintenance fluids only and six received maintenance fluids and a nitroglycerin infusion adjusted to maintain mean arterial pressure 10 mm Hg below baseline (range, 2 to 12 micrograms/kg/min). After 3 hours, the rabbits were killed, and the intestinal tissue graded histologically. Intestinal damage in the nitroglycerin-treated rabbits was significantly less than that of untreated controls (mean histological grade of 0.39 v 1.48, P < .001). In this rabbit model of necrotizing enterocolitis, infusion of the nitric oxide donor nitroglycerin significantly attenuates intestinal damage. We speculate that enteric nitric oxide deficiency, as may exist in the preterm infant, predisposes the intestine to necrotizing enterocolitis.