An unusual colon atresia in a calf: at the junction of the distal loop and transverse colon. A brief overview

Congenital defects are those abnormalities present at birth. During embryogenesis, many anomalies can occur. The primitive gut tube lengthens quickly and rotates, allowing the gastrointestinal tract acquire its final position and orientation. Because the colon of large animals is complex, most changes occur in this segment. Thus, in ruminants, colon atresia is the most frequent malformation, affecting mainly ascending colon, at the level of the spiral loop. There are no previous references about a very atypical colon atresia at the junction of distal loop and transverse colon, such we have described in a 5-day-old calf, after a history of abdominal distention and absence of feces at birth, even with a patent anal opening. Atresia coli was detected at distal position of the typical colon atresia, at the junction of distal loop and transverse colon. In addition, the distal blind end was bent into a U-shape supported by the mesocolon. Besides the anatomical findings of this worthwhile atresia coli we discuss its possible etiology, in which local factors, such as a compromised blood supply during embryogenesis, are more consistent than genetic factors. Finding out the causes of atresia coli would help to reduce its incidence, lessen animal suffering and economic loss.     

Structural and functional differences in various divisions of the rabbit colon

Summary The rabbit colon displays a diversity of form and function along its proximo-distal axis. Morphologically, four regions can be discerned based on macroscopic and microscopic criteria: 1) the initial portion of the colon immediately distal to the cecum (P1), in which wart-like protrusions characterize the surface topography, is 10cm in length and endowed with three teniae. 2) The adjoining portion of the colon (P2) possesses one tenia, is about 20cm in length and also displays the wart-like protrusions in slightly less prominent form. 3) Fusus coli, a short segment approximately 4 cm in length, is free of teniae, but exhibits longitudinal folds on its inner aspect. Electron microscopically, it shows a paucity of microvilli in direct contrast to the two afore-mentioned regions. These three portions together constitute the proximal colon. 4) The fourth region of the colon, the distal colon, reaches a length of 80–100cm and shows no obvious second-order enlargements of its surface, displaying scanning electron microscopically ridges in looped configurations. Physiological parameters also showed differences depending on the region of the colon observed. Water content of the ingesta increases slightly during passage of the proximal colon, decreasing in the fusus coli and distal colon. Na concentration was highest in the area P1–P2, decreasing distally. K was low in area P2 and then rose toward the fusus, only to fall again distally. Nitrogen values decrease considerably during passage of P2 but only slightly distally. Transmural electrical potential differences also exhibit a characteristic, discontinuous gradient.     

Various aspects of organogenesis of the colon in Gallus domesticus: morphologic observation

The authors have investigated the morphological aspects of the wall components of the developing colon in the chick embryo (Gallus domesticus) from the 7th to th 15th day of incubation. Particular attention has been given to the lumen recanalization, phenomenon which occurs also in other animal species. The most significant results can be summarized as follows: 1) the lumen is recanalized at the 7th day only at the proximal part of the colon (Fig. 1, Tav. 1), while at the distal tract it is still completely filled by an epithelial plug (Fig. 2, Tav. 1). Therefore the recanalization of the lumen takes place cranio-caudad. 2) At the 8th day the process of recanalization of the lumen shows, in the distal part of the colon, well defined modalities. Radially oriented intraepithelial spaces within the epithelium filling the lumen join other semilunar intercellular spaces, which are placed near the central part of the occluded lumen (Fig. 3). By the junction of a couple of radially oriented spaces with one semilunar space, an U-shaped intercellular space derives, which delimits an incoming epithelial fold (Tav. 3). Such a phenomenon is continued also during the 9th and 10th day of incubation (Fig. 6, Tav. 2). 3) At the 11th day the colonic lumen is completely open and, in its distal part, the appearance of the primordial previllous ridges can be observed (Fig. 7). In the proximal tract the previllous ridges develop one day later (Fig. 8). 4) At the 13th day, in the distal part of the colon, the first appearance of crypts occurs (Fig. 10). So, while the process of recanalization of the lumen is cranio-caudad, the formation of previllous ridges and crypts proceeds caudo-cranially. 5) From the 11th day onwards the lamina propria is actively involved in the process of formation of the previllous ridges. Only at the 14th day, in the distal part of the colon anlage, the appearance of the muscularis mucosae is observed (Fig. 11). 6) The muscle layer and the subserous stratum do not show appreciable morphological changes in the course the considered period of incubation.     

Apical junction complex protein expression in the canine colon: differential expression of claudin-2 in the colonic mucosa in dogs with idiopathic colitis.

Canine idiopathic lymphocytic-plasmacytic colitis (LPC) is a well-recognized clinical and pathological entity in the dog, associated with altered immune cell populations and cytokine expression profiles. Clinical and experimental data indicate that alterations in the permeability of the intestinal epithelium contribute to the pathogenesis of a range of related conditions. The apical junction complex plays a significant role in regulating epithelial paracellular permeability, and we have characterized the distribution of a number of its component tight junction (ZO-1, occludin, claudin-2) and adherens junction (E-cadherin and beta-catenin) proteins in normal colon and colon from dogs with idiopathic LPC. ZO-1, occludin, E-cadherin, and beta-catenin exhibited a distribution in normal canine colon similar to that described previously in humans and rodents. In contrast to the situation in humans, claudin-2-specific labeling was observed in the normal canine colonic crypt epithelium, decreasing in intensity from the distal to the proximal crypt and becoming barely detectable at the luminal surface of the colon. There was little evidence for significant changes in ZO-1, occludin, E-cadherin, or beta-catenin expression in dogs affected by idiopathic LPC. However, claudin-2 expression markedly increased in the proximal crypt and luminal colonic epithelium in affected dogs, suggesting a role in the pathogenesis of canine LPC.     

Absorption of electrolytes and water by the jejunum and colon in milk-fed lambs

Net absorption of electrolytes (Na, Cl, K, Ca) and water from ligated loops was studied at various intestinal sites in milk-fed lambs. The unidirectional fluxes of Na across the intestinal mucosa were also investigated using 22Na. Net Na and water absorption in the mid-jejunum were about two-fold higher than in the proximal and distal jejunum and the colon descendens. With the exception of the proximal jejunum, Na and Cl absorption did not differ significantly. The unidirectional Na fluxes in both directions were much higher in the proximal and mid-jejunum than in the distal jejunum and colon descendens. K was also absorbed most efficiently from the mid-jejunum. In the colon descendens mean net K absorption was about zero. Ca absorption in the upper and mid-jejunum exceeded that of the distal jejunum and colon descendens, where the values were close to zero. The results show that in the whole jejunum of young milk-fed lambs net absorptive fluxes of Na, Cl, K, Ca and water occur, whereas the colon descendens appears to play a role only in Na, Cl and water absorption.     

Site-specific regulation of ion transport by prolactin in rat colon epithelium

The effect of prolactin (PRL) on ion transport across the rat colon epithelium was investigated using Ussing chamber technique. PRL (1 μg/ml) induced a sustained decrease in short-circuit current (I(sc)) in the distal colon with an EC(50) value of 100 ng/ml and increased I(sc) in the proximal colon with an EC(50) value of 49 ng/ml. In the distal colon, the PRL-induced decrease in I(sc) was not affected by Na(+) channel blocker amiloride or Cl(-) channel blockers, NPPB, DPC, or DIDS, added mucosally. However, the response was inhibited by mucosal application of K(+) channel blockers glibenclamide, quinidine, and chromanol 293B, whereas other K(+) channel blockers, Ba(2+), tetraethylammonium, clotrimazole, and apamin, failed to have effects. The PRL-induced decrease in I(sc) was also inhibited by Na(+)-K(+)-2Cl(-) transporter inhibitor bumetanide, Ba(2+), and chromanol 293B applied serosally. In the transverse and proximal colon, the PRL-induced increase in I(sc) was suppressed by DPC, glibenclamide, and bumetanide, but not by NPPB, DIDS, or amiloride. The PRL-induced changes in I(sc) in both distal and proximal colon were abolished by JAK2 inhibitor AG490, but not BAPTA-AM, the Ca(2+) chelating agent, or phosphatidylinositol 3-kinase inhibitor wortmannin. These results suggest a segment-specific effect of PRL in rat colon, by activation of K(+) secretion in the distal colon and activation of Cl(-) secretion in the transverse and proximal colon. Both PRL actions are mediated by JAK-STAT-dependent pathway, but not phosphatidylinositol 3-kinase pathway or Ca(2+) mobilization. These findings suggest a role of PRL in the regulation of electrolyte transport in mammalian colon.     

The roof plate regulates cerebellar cell-type specification and proliferation

During embryogenesis, the isthmic organizer, a well-described signaling center at the junction of the mid-hindbrain, establishes the cerebellar territory along the anterior/posterior axis of the neural tube. Mechanisms specifying distinct populations within the early cerebellar anlage are less defined. Using a newly developed gene expression map of the early cerebellar anlage, we demonstrate that secreted signals from the rhombomere 1 roof plate are both necessary and sufficient for specification of the adjacent cerebellar rhombic lip and its derivative fates. Surprisingly, we show that the roof plate is not absolutely required for initial specification of more distal cerebellar cell fates, but rather regulates progenitor proliferation and cell position within the cerebellar anlage. Thus, in addition to the isthmus, the roof plate represents an important signaling center controlling multiple aspects of cerebellar patterning.     

A mutation in the 530 loop of Escherichia coli 16S ribosomal RNA causes resistance to streptomycin.

Oligonucleotide-directed mutagenesis was used to introduce an A to C transversion at position 523 in the 16S ribosomal RNA gene of Escherichia coli rrnB operon cloned in plasmid pKK3535. E. coli cells transformed with the mutated plasmid were resistant to streptomycin. The mutated ribosomes isolated from these cells were not stimulated by streptomycin to misread the message in a poly(U)-directed assay. They were also restrictive to the stimulation of misreading by other error-promoting related aminoglycoside antibiotics such as neomycin, kanamycin or gentamicin, which do not compete for the streptomycin binding site. The 530 loop where the mutation in the 16S rRNA is located has been mapped at the external surface of the 30S subunit, and is therefore distal from the streptomycin binding site at the subunit interface. Our results support the conclusion that the mutation at position 523 in the 16S rRNA does not interfere with the binding of streptomycin, but prevents the drug from inducing conformational changes in the 530 loop which account for its miscoding effect. Since this effect primarily results from a perturbation of the translational proofreading control, our results also provide evidence that the 530 loop of the 16S rRNA is involved in this accuracy control.     

Cholinesterase histochemistry of the rabbit distal colon

Summary The distribution of cholinesterase in the rabbit distal colon has been studied using histochemical methods. Non-specific cholinesterase predominates in muscle tissue, the longitudinal layer of the muscularis externa staining slightly more strongly than the circular layer. The muscularis mucosae stains the most intensely but its non-specific cholinesterase is markedly inactivated by 20 hr fixation in formaldehyde. Specific cholinesterase is present in ganglion cells in the myenteric and submucous plexuses, and these cells vary in staining intensity. Nerve fibres which stain for specific cholinesterase are present in the nerve plexuses and in the muscle layers. It is concluded that there are cholinergic nervous elements in the myenteric and submucous plexuses and in the muscle layers of the rabbit distal colon.M. R. C. Junior Research Fellow.     

Changes of contractile activity of the colon under psychogenic stress before and after blockade of M- and N-cholinergic and beta-adrenoceptors

In experiments on conscious rabbits, myoelectric activity (contractile activity index) was recorded in 2 sites of proximal and in 2 sites of distal part of the colon under psychogenic stress induced by firm fastening of the animal to a frame in supine position. Stressor impact caused decrease of the contractile activity in proximal and distal parts of the colon, due to "alpha-adrenergic" (in initial stage of stress reaction) and "nonadrenergic noncholinergic" inhibition. Stress-induced increase of the contractile activity of the colon was limited to the initial segment of its distal part, and was due to centrogenic stimulation of the preganglionic neurons of the parasympathetic nervous system and effector cholinergic neurons of the enteric nervous system.     

Complex regulation of mucosal pentraxin (Mptx) revealed by discrete micro-anatomical locations in colon

Recently a mucosal pentraxin, Mptx, regulated by heme and calcium was reported in rat gut mucosal scrapings using microarray strategies. Considering the heterogeneity of gut mucosa scrapings and the widespread use of the rat as a model to study colon pathologies this study was undertaken to generate detailed mapping of micro-anatomical locations of Mptx and gain further insight into potential functions of this mucosal pentraxin in rat colon. Differential regulation was also examined in colon from different rat strains and rat models of oxidative stress and in pre-cancerous colon tissue. Different regional patterns of expression and discrete localisation in epithelial cells within transverse and distal colon crypts and an absence of expression in proximal colon were confirmed by regional PCR analysis and in situ hybridisation studies of colon. This study demonstrates that consideration of regional differences in Mptx gene expression and micro-anatomical location is necessary in the interpretation and deciphering of its regulation in colon.     

T-loop assembly in vitro involves binding of TRF2 near the 3' telomeric overhang

Mammalian telomeres contain a duplex TTAGGG-repeat tract terminating in a 3' single-stranded overhang. TRF2 protein has been implicated in remodeling telomeres into duplex lariats, termed t-loops, in vitro and t-loops have been isolated from cells in vivo. To examine the features of the telomeric DNA essential for TRF2-promoted looping, model templates containing a 500 bp double-stranded TTAGGG tract and ending in different single-stranded overhangs were constructed. As assayed by electron microscopy, looped molecules containing most of the telomeric tract are observed with TRF2 at the loop junction. A TTAGGG-3' overhang of at least six nucleotides is required for loop formation. Termini with 5' overhangs, blunt ends or 3' termini with non-telomeric sequences at the junction are deficient in loop formation. Addition of non-telomeric sequences to the distal portion of a 3' overhang beginning with TTAGGG repeats only modestly diminishes looping. TRF2 preferentially localizes to the junction between the duplex repeats and the single-stranded overhang. Based on these findings we suggest a model for the mechanism by which TRF2 remodels telomeres into t-loops.     

Protein folding kinetics beyond the phi value: using multiple amino acid substitutions to investigate the structure of the SH3 domain folding transition state

The SH3 domain folding transition state structure contains two well-ordered turn regions, known as the diverging turn and the distal loop. In the Src SH3 domain transition state, these regions are stabilized by a hydrogen bond between Glu30 in the diverging turn and Ser47 in the distal loop. We have examined the effects on folding kinetics of amino acid substitutions at the homologous positions (Glu24 and Ser41) in the Fyn SH3 domain. In contrast to most other folding kinetics studies which have focused primarily on non-disruptive substitutions with Ala or Gly, here we have examined the effects of substitutions with diverse amino acid residues. Using this approach, we demonstrate that the transition state structure is generally tolerant to amino acid substitutions. We also uncover a unique role for Ser at position 41 in facilitating folding of the distal loop, which can only be replicated by Asp at the same position. Both these residues appear to accelerate folding through the formation of short-range side-chain to backbone hydrogen bonds. The folding of the diverging turn region is shown to be driven primarily by local interactions. The diverging turn and distal loop regions are found to interact in the transition state structure, but only in the context of particular mutant backgrounds. This work demonstrates that studying the effects of a variety of amino acid substitutions on protein folding kinetics can provide unique insights into folding mechanisms which cannot be obtained by standard Phi value analysis.     

Effects of tetrodotoxin and ion replacements on the short-circuit current induced by Escherichia coli enterotoxin STa across the colon of the gerbil (Gerbillu cheesmani) in different dietary states

The effects of mucosally added Escherichia coli heat stable enterotoxin (STa, 30 ng mL(-1)) on the basal short-circuit current (Isc in microA cm(-2)) across stripped and unstripped sheets of proximal, mid and distal colon were investigated. Samples were taken from fed, starved (4 days, water ad lib) and undernourished (50% of control food intake for 21 days) gerbils (Gerbillus cheesmani). The effect of neurotoxin tetrodotoxin (TTX 10 microM) and the effect of replacing chloride by gluconate or the effect of removing bicarbonate from bathing buffer on the maximum increase in Isc induced by E. coli heat stable enterotoxin STa were also investigated. The results showed that there is a segmental difference both in the basal and STa-induced Isc. Also, STa is more effective in the proximal than distal colon in the three feeding conditions. Undernourishment raised the STa-induced Isc in the three regions of the colon. In fed and starved gerbils part of STa-induced Isc in the proximal colon was chloride-dependent, while the other was bicarbonate-dependent; in the mid colon, the STa-induced Isc was bicarbonate-dependent only. In the three regions of the colon taken from undernourished gerbil, the STa-induced Isc was both chloride-and bicarbonate-dependent. The increase in STa-induced Isc as a results of undernourishment in proximal and mid colon was chloride-dependent, while in the distal colon, it was both chloride- and bicarbonate-dependent.     

Stretch-activated neuronal pathways to longitudinal and circular muscle in guinea pig distal colon

The role of the longitudinal muscle (LM) layer during the peristaltic reflex in the small and large intestine is unclear. In this study, we have made double and quadruple simultaneous intracellular recordings from LM and circular muscle (CM) cells of guinea pig distal colon to correlate the electrical activities in the two different muscle layers during circumferential stretch. Simultaneous recordings from LM and CM cells (<200 microm apart) at the oral region of the colon showed that excitatory junction potentials (EJPs) discharged synchronously in both muscle layers for periods of up to 6 h. Similarly, at the anal region of the colon, inhibitory junction potentials (IJPs) discharged synchronously in the two muscle layers. Quadruple recordings from LM and CM orally at the same time as from the LM and CM anally revealed that IJPs occurred synchronously in the LM and CM anally at the same time as EJPs in LM and CM located 20 mm orally. Oral EJPs and anal IJPs were linearly related in amplitude between the two muscle layers. Spatiotemporal maps generated from simultaneous video imaging of the movements of the colon, combined with intracellular recordings, revealed that some LM contractions orally could be correlated in time with IJPs in CM cells anally. N(omega)-nitro-L-arginine (L-NA; 100 microM) abolished the IJP in LM, whereas a prominent L-NA-resistant "fast" IJP was always observed in CM. In summary, in stretched preparations, synchronized EJPs in both LM and CM orally are generated by synchronized firing of many ascending interneurons, which simultaneously activate excitatory motor neurons to both muscle layers. Similarly, synchronized IJPs in both LM and CM anally are generated by synchronized firing of many descending interneurons, which simultaneously activate inhibitory motor neurons to both muscle layers. This synchronized motor activity ensures that both muscles around the entire circumference are excited orally at the same time as inhibited anally, thus producing net aboral propulsion.     

Evaluation of breed as a risk factor for atresia coli in cattle

Systematic review of published cases and a hospital-based case-control study were completed to evaluate breed as a risk factor for atresia coli in cattle. Systematic review of 37 published studies indicated that atresia coli has been diagnosed in 10 cattle breeds and 12 countries, with the marked preponderance of cases occurring in Holstein-Friesian calves (485/514 cases, 94%). Epidemiologic analysis based on 28,373 cattle < 2 mo of age admitted to North American veterinary schools between 1964 and 1993 identified 291 cases of atresia coli in 13 breeds, with the marked preponderance of cases occurring in Holstein-Friesian calves (228/291, 78%). Holstein-Friesian cattle were at significantly greater risk for the condition than all other dairy cattle breeds (crude odds ratio 4.55, P < 0.0001) and all other cattle breeds (crude odds ratio 7.12, P < 0.0001), whereas there was no difference in the odds ratio between dairy cattle (not Holstein-Friesian) and beef cattle (crude odds ratio 1.68, P = 0.11). Atresia coli probably occurs secondary to vascular insufficiency of the developing colon. Holstein-Friesian cattle may be genetically predisposed to atresia coli, possibly because their developing colon grows at a faster rate and/or to a greater extent than that in other cattle breeds. Early or vigorous palpation per rectum of the amniotic vesicle appears to increase the risk of atresia coli in a genetically predisposed fetus, probably through palpation-induced damage to the developing colonic vasculature.     

Ketogenesis from butyrate and acetate by the caecum and the colon of rabbits

1. When studied in vitro, tissue from the caecum and the proximal colon of rabbits converted butyrate into ketone bodies. The conversion was similar to that observed with liver slices. The ketogenic activity was associated with the mucosa rather than the muscle of the gut wall and, in the colon, diminished as the distance from the caecal-colonic junction increased. 2. Tissue from the wall of the ileum, caecum, proximal colon and distal colon was also shown to metabolize [1-(14)C]butyrate to carbon dioxide. 3. Enzyme assays showed that in both liver tissue and caecal mucosa the activity of hydroxymethylglutaryl-CoA synthase was more than ten times that of acetoacetyl-CoA deacylase. Labelling experiments in vitro gave confirmation of the hydroxymethylglutaryl-CoA pathway. 4. The significance of the conversion of butyrate into ketone bodies is discussed.     

Glucose absorption by the interposed colon segment after intestinal resection.

One of the proposed surgical treatments of Short Bowel Syndrome is the interposition of a distal colon segment between two portions of the remnant small intestine. This method proved to reverse the nutritional disorders caused by this morbid entity. Surgical technique consisted in an 80% small bowel resection and the interposition of a 3 cm segment of distal colon between the remaining jejunum and ileum. After 70 days, the animals were reoperated and the interposed and the distal colon were isolated and tied. By using the method of rapid and successive absorptions of a glucose solution through the intestinal lumen, the relations between the absorption curves of the interposed and the normal colon could be drawn. Results show that the interposed colon segment absorbs more glucose (mean = 1.43 +/- 1.16 mg/dl) than the distal colon (mean = 0.37 +/- 0.29 mg/dl) and that its absorption pattern is similar to the small bowel rather than the colon. These results allow the use of this method for further studies in which the interposed colon adaptation is studied with other nutrients and/or under specific conditions.     

Oxidatively damaged DNA and its repair in colon carcinogenesis

Inflammation, high fat, high red meat and low fiber consumption have for long been known as the most important etiological factors of sporadic colorectal cancers (CRC). Colon cancer originates from neoplastic transformation in a single layer of epithelial cells occupying colonic crypts, in which migration and apoptosis program becomes disrupted. This results in the formation of polyps and metastatic cancers. Mutational program in sporadic cancers involves APC gene, in which mutations occur most abundantly in the early phase of the process. This is followed by mutations in RAS, TP53, and other genes. Progression of carcinogenic process in the colon is accompanied by augmentation of the oxidative stress, which manifests in the increased level of oxidatively damaged DNA both in the colon epithelium, and in blood leukocytes and urine, already at the earliest stages of disease development. Defence mechanisms are deregulated in CRC patients: (i) antioxidative vitamins level in blood plasma declines with the development of disease; (ii) mRNA level of base excision repair enzymes in blood leukocytes of CRC patients is significantly increased; however, excision rate is regulated separately, being increased for 8-oxoGua, while decreased for lipid peroxidation derived ethenoadducts, ?Ade and ?Cyt; (iii) excision rate of ?Ade and ?Cyt in colon tumors is significantly increased in comparison to asymptomatic colon margin, and ethenoadducts level is decreased. This review highlights mechanisms underlying such deregulation, which is the driving force to colon carcinogenesis.