Structure of the musculature of the chicken small intestine

Poultry nutrition

Nutrition is the most important environmental factor affecting development, health status, growth performance and profitability of poultry production. Feeds for poultry constitute up to 70–75% of total production costs. Poultry nutrition differs considerably from that of other livestock, which is determined by the specific anatomy of the gastrointestinal tract. Protein, energy, fat, fiber, minerals, vitamins, and water are of basic importance for poultry nutrition and their content in feeds must cover the requirement that differ depending on the bird’s age and species. In general, feed protein must be of good value including the content of essential amino acids. Among them lysine, methionine, cysteine, threonine and tryptophan are the limiting ones. The main ingredient of poultry feeds are cereal grains, i.e. wheat and maize, which predominantly constitute an energy source because their protein content is insufficient for birds. Because of that cereals cannot be the only feed for poultry and must be combined with protein sources such as soybean or rapeseed meal, legume seeds or protein concentrates. Despite birds’ requirement for nutrients and chemical composition of feeds are well known, nutrition must face many problems. One of the most important issues is to find alternatives to antibiotic growth promoters.

Characterization of Cecal Smooth Muscle Contraction in Laying Hens

The ceca play an important role in the physiology of the gastrointestinal tract in chickens. Nevertheless, there is a gap of knowledge regarding the functionality of the ceca in poultry, especially with respect to physiological cecal smooth muscle contraction. The aim of the current study is the ex vivo characterization of cecal smooth muscle contraction in laying hens. Muscle strips of circular cecal smooth muscle from eleven hens are prepared to investigate their contraction ex vivo. Contraction is detected using an isometric force transducer, determining its frequency, height and intensity. Spontaneous contraction of the chicken cecal smooth muscle and the influence of buffers (calcium-free buffer and potassium-enriched buffer) and drugs (carbachol, nitroprusside, isoprenaline and Verapamil) affecting smooth muscle contraction at different levels are characterized. A decrease in smooth muscle contraction is observed when a calcium-free buffer is used. Carbachol causes an increase in smooth muscle contraction, whereas atropine inhibits contraction. Nitroprusside, isoprenaline and Verapamil result in a depression of smooth muscle contraction. In conclusion, the present results confirm a similar contraction behavior of cecal smooth muscles in laying hens as shown previously in other species.

Morph-anatomic and histochemical study of ileum of goose (Alopochen egyptiacus) with special references to immune cells, mucous and serous goblet cells, telocytes, and dark and light smooth muscle fibers

The morphological characteristics of the ileum of 20 adult male Egyptian geese were determined using LM, SEM, and TEM. The mean length of the ileum in the male goose was approximately 158.71 mm, representing nearly 10.19% of the total length of the small intestine. The ileum is composed of four layers: mucosa, submucosa, muscular layer, and serosa. The mucosal layer comprises the epithelium, lamina propria, and muscularis mucosa. The mucosa forms finger-like villi and is invaginated at the bases, forming the crypts of Lieberkühn. The ileum is lined by simple columnar epithelium that contains absorptive dark and light enterocytes with two types of goblet cells (mucous and serous varieties) microfold like cells, dendritic reticulum cells, Paneth cells, and a closed type of enteroendocrine cells. The lamina propria has diffuse lymphoid tissue containing lymphocytes, macrophages, mast cells, plasma cells, and heterophils as well as telocytes. The muscularis mucosa comprises circular smooth muscle fibers extending into the core of the villi. The submucosa is a thin layer of elastic-rich connective tissue. The muscular level consists of four layers, with light and dark smooth muscle fibers. We described in detail the structure of all cellular components and histomorphometric measurements.

Smooth muscle: a stiff sculptor of epithelial shapes

Smooth muscle is increasingly recognized as a key mechanical sculptor of epithelia during embryonic development. Smooth muscle is a mesenchymal tissue that surrounds the epithelia of organs including the gut, blood vessels, lungs, bladder, ureter, uterus, oviduct and epididymis. Smooth muscle is stiffer than its adjacent epithelium and often serves its morphogenetic function by physically constraining the growth of a proliferating epithelial layer. This constraint leads to mechanical instabilities and epithelial morphogenesis through buckling. Smooth muscle stiffness alone, without smooth muscle cell shortening, seems to be sufficient to drive epithelial morphogenesis. Fully understanding the development of organs that use smooth muscle stiffness as a driver of morphogenesis requires investigating how smooth muscle develops, a key aspect of which is distinguishing smooth muscle-like tissues from one another in vivo and in culture. This necessitates a comprehensive appreciation of the genetic, anatomical and functional markers that are used to distinguish the different subtypes of smooth muscle (for example, vascular versus visceral) from similar cell types (including myofibroblasts and myoepithelial cells). Here, we review how smooth muscle acts as a mechanical driver of morphogenesis and discuss ways of identifying smooth muscle, which is critical for understanding these morphogenetic events.This article is part of the Theo Murphy meeting issue 'Mechanics of Development'.

Transcriptome of the inner circular smooth muscle of the developing mouse intestine: Evidence for regulation of visceral smooth muscle genes by the hedgehog target gene, cJun

BACKGROUND

Digestion is facilitated by coordinated contractions of the intestinal muscularis externa, a bilayered smooth muscle structure that is composed of inner circular muscles (ICM) and outer longitudinal muscles (OLM). We performed transcriptome analysis of intestinal mesenchyme tissue at E14.5, when the ICM, but not the OLM, is present, to investigate the transcriptional program of the ICM.

RESULTS

We identified 3967 genes enriched in E14.5 intestinal mesenchyme. The gene expression profiles were clustered and annotated to known muscle genes, identifying a muscle-enriched subcluster. Using publically available in situ data, 127 genes were verified as expressed in ICM. Examination of the promoter and regulatory regions for these co-expressed genes revealed enrichment for cJUN transcription factor binding sites, and cJUN protein was enriched in ICM. cJUN ChIP-seq, performed at E14.5, revealed that cJUN regulatory regions contain characteristics of muscle enhancers. Finally, we show that cJun is a target of Hedgehog (Hh), a signaling pathway known to be important in smooth muscle development, and identify a cJun genomic enhancer that is responsive to Hh.

CONCLUSIONS

This work provides the first transcriptional catalog for the developing ICM and suggests that cJun regulates gene expression in the ICM downstream of Hh signaling. Developmental Dynamics 245:614-626, 2016. © 2016 Wiley Periodicals, Inc.

Comprehensive timeline of mesodermal development in the quail small intestine

BACKGROUND

To generate the mature intestine, splanchnic mesoderm diversifies into six different tissue layers each with multiple cell types through concurrent and complex morphogenetic events. Hindering the progress of research in the field is the lack of a detailed description of the fundamental morphological changes that constitute development of the intestinal mesoderm.

RESULTS

We used immunofluorescence and morphometric analyses of wild-type and Tg(tie1:H2B-eYFP) quail embryos to establish a comprehensive timeline of mesodermal development in the avian intestine. The following landmark features were analyzed from appearance of the intestinal primordium through generation of the definitive structure: radial compartment formation, basement membrane dynamics, mesothelial differentiation, mesenchymal expansion and growth patterns, smooth muscle differentiation, and maturation of the vasculature. In this way, structural relationships between mesodermal components were identified over time.

CONCLUSIONS

This integrated analysis presents a roadmap for investigators and clinicians to evaluate diverse experimental data obtained at individual stages of intestinal development within the longitudinal context of intestinal morphogenesis.

Distribution and colocalization of NADPH-diaphorase activity, nitric oxide synthase immunoreactivity, and VIP immunoreactivity in the newly hatched chicken gut

BACKGROUND

The distribution and colocalization of nitric oxide synthase and NADPH-diaphorase have been investigated quite extensively in the mammalian gut; however, no such study has been undertaken in the avian gut. In the present report, we have therefore studied the distribution and coexpression of nitric oxide synthase (NOS), NADPH-diaphorase, and vasoactive intestinal polypeptide (VIP) in enteric neurons of the newly hatched chicken gut.

METHODS

Immunohistochemical methods were used to detect NOS immunoreactivity (NOS-IR) and VIP immunoreactivity (VIP-IR). NADPH-diaphorase activity was detected using a histochemical technique.

RESULTS

Neurons expressing NADPH-diaphorase activity, NOS-IR, and VIP-IR were detected in both the myenteric and submucous plexus of all regions of the gastrointestinal tract examined. All NADPH-diaphorase positive neurons were also NOS-IR and all NOS-IR neurons were NADPH-diaphorase positive, in both plexuses, indicating that NADPH-diaphorase can be used as a marker for NOS containing neurons in the chicken gut. The majority of VIP-IR neurons also expressed NADPH-diaphorase activity. Only few neurons that expressed NADPH-diaphorase activity did not express VIP-IR. The proportion of VIP immunopositive neurons that were NADPH-diaphorase negative increased anally and these neurons were more prominent in the submucous than the myenteric plexus ganglia. NADPH-diaphorase positive, NOS-IR, and VIP-IR nerve fibres were detected in the circular muscle, but very few, if any, were present in the longitudinal muscle. VIP-IR, but not NOS-IR or NADPH-diaphorase activity, was detected in mucosal fibres, in contrast to the situation in the mammalian gut.

CONCLUSIONS

These results indicate that in birds, as in mammals, nitric oxide may play a role in the neural control of the gut musculature, but that it is unlikely to be involved in the nervous control of mucosal activity.

Spatial and functional relationship between myocytes and fibroblasts in the rabbit sinoatrial node

In an attempt to understand better the directional differences in conduction velocity in the rabbit sinoatrial node, a possible conductive role of the abundant connective tissue surrounding the myocytes has been investigated. In particular, starting from the finding of communicating junctions between heart muscle cells and fibroblasts in tissue culture, heterologous gap junctions were searched for in thin sections of the rabbit sinoatrial node. Within and at the edge of nodal cell clusters, fibroblasts often show thin sheet-like extensions parallel to the surface of myocytes. In contrast to the intimately contacting myocytes, fibroblast extensions are kept separated from the myocytes by the basement membrane of the latter. Besides some rare undefined membrane appositions a single tiny gap junction-like structure was found between a fibroblast and a myocyte in a tissue area in which the calculated number of gap junctions between myocytes amounts from 1.10(4) to 3.10(4). Yet, fibroblasts are linked together regularly by small gap junctions containing a wider gap than the junctions between the myocytes (1.4 +/- 0.4 nm vs. 1.0 +/- 0.4 nm, resp., P less than 0.05). As an alternative to direct electrical coupling, the possibility of interaction between fibroblasts and nodal cells by capacitive coupling has been considered. Model calculations based on the reconstruction of some fibroblast extensions parallel to nodal cells show that the current which can be transmitted from discharging nodal cells to fibroblasts is negligible. It is concluded that fibroblasts do not participate in the impulse conduction within the sinoatrial node. The origin of the directional differences in conduction velocity in the sinoatrial node must be found in the spatial arrangement of the myocytes and the distribution of the gap junctions between these cells only.

Use of rhodamine 123 to label and lesion interstitial cells of Cajal in canine colonic circular muscle

The role of interstitial cells of Cajal (ICC) is difficult to determine because these cells are not easily identified by light microscopy, and there are no compounds available to specifically lesion ICC. Ultrastructural studies have shown an abundance of mitochondria in ICC. Therefore, we have used rhodamine 123, a fluorescent dye that is specifically accumulated by mitochondria, to identify ICC in canine proximal colon. This technique provided good discrimination between ICC and smooth muscle cells, but enteric neurons were labeled with rhodamine 123. This compound has cytotoxic properties in some cells. Therefore, we treated intact muscle strips with rhodamine 123 while recording intracellular electrical activity from circular muscle cells. Uptake of rhodamine 123 by ICC was associated with an alteration in electrical rhythmicity. These data suggest that rhodamine 123 may be a useful tool for visualizing and perhaps chemically lesioning ICC.

Intrinsic reflexes underlying peristalsis in the small intestine of the domestic fowl

Peristalsis in the chicken small intestine was studied using either a modified Trendelenburg method or a technique in which changes in circular muscle activity were recorded in response to application of a localized radial distension. A localized radial distension had no effect on either the resting tension or the spontaneous activity of the circular muscle on the oral side of distension. On the aboral side of the distension a transient contraction was recorded in the ileum and jejunum after a mean delay of 2.74 s at 37 degrees C. In about a third of the preparations a tonic contraction was also present which persisted for as long as distension was maintained. The transient contraction was blocked by hyoscine (0.6-2.3 microM) and hexamethonium (275 microM); whereas the tonic contraction persisted in the presence of hyoscine. Both types of contraction were blocked by tetrodotoxin (0.31 microM). No such responses were recorded in the duodenum. The descending excitatory reflex responses were followed in all preparations by a fall in the amplitude and frequency of spontaneous contractions and in a few preparations by a concomitant fall in the tone of the circular muscle lasting for up to 3 min. This inhibitory component of the descending reflex was not blocked by guanethidine (3-10 microM). The transient contraction, which originated most frequently at the site of distension, always propagated aborally at a mean speed of 14.2 mm s-1. Surgical interruption of the longitudinal muscle and myenteric plexus effectively blocked the transmission of the excitatory and inhibitory components of the descending reflex past the site of the lesion. In the modified Trendelenburg apparatus raising the intraluminal pressure elicited peristalsis in the isolated ileum. Peristaltic contractions never started at the most oral end of the preparation but appeared instead at any other point on the ileum. This resulted in several contractions contributing to each emptying cycle. Peristalsis was blocked by tetrodotoxin (0.31 microM). These results are discussed in the terms of the organization of the descending reflex. It is suggested that within the enteric nervous system of the ileum and jejunum of the chicken, there are cholinergic and non-cholinergic excitatory neurones and non-adrenergic inhibitory neurones. The results of this study demonstrate that neurogenic peristalsis in the avian small intestine does not conform to the 'law of the intestine' as originally postulated by Bayliss & Starling (1899).

Chicken gizzard. The muscle, the tendon and their attachment

The fine structure and the organization of muscle and connective tissue in the middle portion of the chicken gizzard (muscular stomach) has been studied by light and electron microscopy. The musculature is divided into long, well-defined bundles arranged circularly and concentrically and extending between the two tendons (tendinous aponeurosis). The muscle bundles are inserted onto the inner surface of the tendon at an angle of about 45 degrees. In addition to muscle cells (which are ultrastructurally similar to those of the small intestine) the musculature contains fibroblasts and interstitial cells and a small number of nerve bundles and capillaries. The gizzard tendons are very compact, made of parallel fascicles of collagen fibrils with interposed stellate tendon cells; ultrastructurally they are very similar to the tendon of skeletal muscles of this and other species. Their collagen fibrils range in size from 30 to 160 nm. The muscle cells that approach the tendon develop longitudinal invaginations of the cell membrane and then break into finger-like terminal processes heavily encrusted with dense bands. The membrane of the invaginations and the terminal processes are surrounded by a basal lamina material which embeds a conspicuous web of small collagen fibrils. The boundary between tendon and muscle is sharp, without interpenetration of the two tissues. A novel type of cell is found at the interface of muscle and tendon (junctional cells), filled with intermediate filaments and some rough endoplasmic reticulum and displaying a trace of a basal lamina.