Comparative evaluation of the muscular coat of the esophagus from fish and mammals

Light optic analysis revealed that morphological parameters of fish and mammals oesophageal parameters are conditioned functionally. Combination of respiratory and transport functions in anterior portion of digestive systems in fish determines insignificant length of the esophagus and developed muscular coat which excludes disorders of gas exchange. Heterodonteal dentition, pulmonary type of respiration and long esophagus of mammals provide factors that unable to prevent gas exchange. Electron microscopic study of oesophageal fibres of these animals demonstrated that they are alike in their structure with skeletal muscular fibres.     

A comparative electron microscope study on the fine structure of the muscular coat in the common bile duct

Little is known about the architecture of common bile duct, especially smooth muscle, except for Oddi's sphincter. The purpose of this study is to reveal the ultrastructural architecture of the upper part of the common bile duct from the viewpoint of comparative anatomy. Animals used in this study were the hamster, rat, dog, monkey and rabbit, and the results obtained were as follows. There were considerable differences in the structural appearance and distribution of smooth muscle cells in the upper part of the common bile duct among the animals examined. In the rat, a small number of smooth muscle cells were sparsely distributed in the subepithelial connective tissue of the duct. In the dog, smooth muscle cells showed a star-shaped appearance with many cytoplasmic processes, by which networks were formed. In the monkey, smooth muscle cells with fibroblast-like appearance were circularly distributed. In the monkey and rabbit, muscular coats consisting of typical smooth muscle cells were observed in the outermost layer of the duct. The muscular coat in the monkey was arranged longitudinally, and in the rabbit circularly. The muscular coat in the rabbit was thicker than that in the monkey. In the hamster, however, the duct wall was devoid of smooth muscle cells. The present study suggests that the occurrence of smooth muscular coat is not essential for transport of the bile.     

Innervation of intestinal arteries by axons with immunoreactivity for the vesicular acetylcholine transporter (VAChT)

The presence of a cholinergic innervation of arterioles within the gut wall is suggested by pharmacological studies of nerve mediated vasodilatation, but attempts to identify nerve cells that give rise to cholinergic vasodilator fibres have yielded discrepant results. In the present work, antibodies to the vesicular acetylcholine transporter protein (VAChT) were used to investigate the relationships of immunoreactive nerve fibres to submucosal arterioles. Comparison was made with cerebral arteries, which are known to be cholinergically innervated. Double labelling immunohistochemical techniques revealed separate VAChT and tyrosine hydroxylase (TH) immunoreactive (IR) fibres innervating all sizes of arteries of the submucosa of the stomach, ileum, proximal colon, distal colon and rectum as well as the cerebral arteries. Arterioles of all digestive tract regions had greater densities of TH-IR innervation than VAChT-IR innervation. In the ileum, double labelling for VAChT-IR and VIP-IR or calretinin-IR showed more VAChT-IR than either VIP-IR or calretinin-IR fibres. Calretinin-IR and VAChT-IR were colocalised in a majority of calretinin-IR axons, but VIP-IR and VAChT-IR were not colocalised. All calretinin-IR nerve cells in submucous ganglia were immunoreactive for choline acetyltransferase, but only 1–2% of VIP-IR nerve cells were immunoreactive. Extrinsic denervation of the ileum did not alter the distribution of VAChT-IR fibres, but it eliminated TH-IR fibres. Removal of myenteric ganglia (myectomy) did not alter the distribution of fibres with VAChT or TH-IR. This work thus provides evidence for cholinergic innervation of intrinsic arterioles throughout the digestive tract and indicates that the fibres in the small intestine originate from submucosal nerve cells.     

Structural changes in the stomach muscular coat as basis for heterochronia in human early postnatal ontogenesis

The structure of muscular tunic of human stomach since birth up to the age of 3 months in cadavers of 15 infants was studied using light microscopy. Wideness of groups of smooth myocytes and of stromal gaps between them was measured in cardial and pyloric regions. Stomach regions were compared according to the results of measuring using parametric statistics. Periods of rapid (0-2 months) and slow (2-3 months) structural changes of muscular tunic were found out. It was exposed that decrease of wideness of the groups of myocytes and of the stromal gaps accompanied increase of transverse size of the organ. Outstripping development of nonstriated musculature determined rapid growth of stomach region, outstripping changes of stroma determined delayed growth of the region.     

Neonate antigen presenting cells within murine intestinal muscular layer

The intestinal mucosa is exposed to a vast antigenic contact. Several antigen presenting cell (APCs) have been described within the gut associated lymphoid tissue (GALT) (Peyer's patches, lamina propria, mesenteric lymph nodes, muscular layer); however, this has been done almost exclusively in adult organisms. As there is no characterization of intestinal muscular layer's APCs during early neonate development we adapted the conventional technique used in adults, to the neonate intestine. We obtained the intestinal muscular layer from early neonates (days 0-3 upon birth) and from young mice (2 and 3 weeks after birth). A planar network of CD45(+), MHC-II(+), DEC-205(+) cells with irregular, some with prominent dendritic morphology was found at birth under basal physiological conditions, whereas Langerin(+) DCs appeared after two weeks. The variations seen in CD45(+), MHC-II(+) and DEC-205(+) cells along the early neonatal development, could be related to the new challenges by intestinal antigen exposure from the newborn diet (breast milk, solid food), and to important environmental changes (start walking, exploring the surroundings, etc). Our study reveals the presence of APCs in intestinal muscular layer at birth, and their subsequent changes in physiological, non-induced conditions, contributing basic information about these cells in the neonate intestinal immune system.     

Cytodifferentiation of the interstitial cells of Cajal related to the myenteric plexus of mouse intestinal muscle coat

Summary The cytodifferentiation of the interstitial cells of Cajal (Type I) related to the myenteric plexus of the mouse intestinal muscle coat was studied in foetuses at term, neonates not yet fed, suckling animals, weaning animals and adult animals. In foetuses at term, interstitial cells of Cajal and their precursor cells are not identifiable. In neonates not yet fed, presumed precursor cells of the interstitial cells of Cajal, i.e. ICC-blasts, can be identified as cells surrounding the developing myenteric plexus and interposed between the circular and longitudinal muscle layers. These ICC-blasts are poorly differentiated but, like the adult interstitial cells, are always related to nerve endings and possess large and numerous mitochondria. In suckling animals these cells gradually develop, and are fully differentiated only after the end of the weaning period.     

Innervation of the cerebral vasculature

With the development of specific antibodies to vasoactive peptides and application of immunohistochemistry and radioimmunoassay methods, knowledge of vascular innervation has grown rapidly. In the cerebral circulation, four possible neurotransmitters are present: norepinephrine, acetylcholine, vasoactive intestinal peptide (VIP), and substance P. There is a dense adrenergic innervation of cerebral arteries, but contractile responses to nerve stimulation or circulating catecholamines are relatively small both in vitro and in vivo. Recent studies using radioligand binding techniques indicate a lack of specific³H-prazosin binding in cerebral arteries, in contrast to other vascular beds. Thus a lack of α₁-adrenergic receptors in cerebral arteries may account for weak responsiveness to sympathetic stimulation. Both VIP and acetylcholine may be vasodilator neurotransmitters, but blockade of cholinergic responses does not alter neurogenic vasodilation. The lack of specific VIP antagonists hampers efferots to explore this system more fully. Substance P-containing nerves are affected by capsaicin, supporting the hypothesis that these are primary sensory afferents, perhaps mediating pain. Future work in this area may focus on defining the pathways of these nerves and exploring the role of co-transmitters and possible interactions between nerves. With this basic information, experiments can be designed to elucidate more clearly the functional roles these nerves play. Established Investigator of the American Heart Association with funds contributed in part by the Arizona Affiliate.     

Innervation of the extrahepatic biliary tract

The extrahepatic biliary tract is innervated by dense networks of extrinsic and intrinsic nerves that regulates smooth muscle tone and epithelial cell function of extrahepatic biliary tree. Although these ganglia are derived from the same set of precursor neural crest cells that colonize the gut, they exhibit structural, neurochemical, and physiological characteristics that are distinct from the neurons of the enteric nervous system. Gallbladder neurons are relatively inexcitable, and their output is driven by vagal inputs and modulated by hormones, peptides released from sensory fibers, and inflammatory mediators. Gallbladder neurons are cholinergic and they can express a number of other neural active compounds, including substance P, galanin, nitric oxide, and vasoactive intestinal peptide. Sphincter of Oddi (SO) ganglia, which are connected to ganglia of the duodenum, appear to be comprised of distinct populations of excitatory and inhibitory neurons, based on their expression of choline acetyltransferase and substance P or nitric oxide synthase, respectively. While SO neurons likely receive vagal input and their activity is modulated by release of neuropeptides from sensory fibers, a significant source of excitatory synaptic input to these cells arise from the duodenum. This duodenum-SO circuit is likely to play an important role in the coordination of SO tone with gallbladder motility in the process of gallbladder emptying. Now that we have gained a relatively thorough understanding of the innervation of the biliary tree under healthy conditions, the way is paved for future studies of altered neural function in biliary disease.     

Innervation of the rabbit cardiac ventricles

The rabbit is widely used in experimental cardiac physiology, but the neuroanatomy of the rabbit heart remains insufficiently examined. This study aimed to ascertain the architecture of the intrinsic nerve plexus in the walls and septum of rabbit cardiac ventricles. In 51 rabbit hearts, a combined approach involving: (i) histochemical acetylcholinesterase staining of intrinsic neural structures in total cardiac ventricles; (ii) immunofluorescent labelling of intrinsic nerves, nerve fibres (NFs) and neuronal somata (NS); and (iii) transmission electron microscopy of intrinsic ventricular nerves and NFs was used. Mediastinal nerves access the ventral and lateral surfaces of both ventricles at a restricted site between the root of the ascending aorta and the pulmonary trunk. The dorsal surface of both ventricles is supplied by several epicardial nerves extending from the left dorsal ganglionated nerve subplexus on the dorsal left atrium. Ventral accessing nerves are thicker and more numerous than dorsal nerves. Intrinsic ventricular NS are rare on the conus arteriosus and the root of the pulmonary trunk. The number of ventricular NS ranged from 11 to 220 per heart. Four chemical phenotypes of NS within ventricular ganglia were identified, i.e. ganglionic cells positive for choline acetyltransferase (ChAT), neuronal nitric oxide synthase (nNOS), and biphenotypic, i.e. positive for both ChAT/nNOS and for ChAT/tyrosine hydroxylase. Clusters of small intensely fluorescent cells are distributed within or close to ganglia on the root of the pulmonary trunk, but not on the conus arteriosus. The largest and most numerous intrinsic nerves proceed within the epicardium. Scarce nerves were found near myocardial blood vessels, but the myocardium contained only a scarce meshwork of NFs. In the endocardium, large numbers of thin nerves and NFs proceed along the bundle of His and both its branches up to the apex of the ventricles. The endocardial meshwork of fine NFs was approximately eight times denser than the myocardial meshwork. Adrenergic NFs predominate considerably in all layers of the ventricular walls and septum, whereas NFs of other neurochemical phenotypes were in the minority and their amount differed between the epicardium, myocardium and endocardium. The densities of NFs positive for nNOS and ChAT were similar in the epicardium and endocardium, but NFs positive for nNOS in the myocardium were eight times more abundant than NFs positive for ChAT. Potentially sensory NFs positive for both calcitonin gene‐related peptide and substance P were sparse in the myocardial layer, but numerous in epicardial nerves and particularly abundant within the endocardium. Electron microscopic observations demonstrate that intrinsic ventricular nerves have a distinctive morphology, which may be attributed to remodelling of the peripheral nerves after their access into the ventricular wall. In conclusion, the rabbit ventricles display complex structural organization of intrinsic ventricular nerves, NFs and ganglionic cells. The results provide a basic anatomical background for further functional analysis of the intrinsic nervous system in the cardiac ventricles.