Morphological and Immunohistochemical Characterization of Human Intrinsic Gastric Neurons

The Eph/ephrin system symphony of gut inflammation

The extent of gut inflammation depends largely on the gut barrier's integrity and enteric neuroimmune interactions. However, the factors and molecular mechanisms that regulate inflammation-related changes in the enteric nervous system (ENS) remain largely unexplored. Eph/ephrin signaling is critical for inflammatory response, neuronal activation, and synaptic plasticity in the brain, but its presence and function in the ENS have been largely unknown to date. This review discusses the critical role of Eph/ephrin in regulating gut homeostasis, inflammation, neuroimmune interactions, and pain pathways. Targeting the Eph/ephrin system offers innovative treatments for gut inflammation disorders, offering hope for enhanced patient prognosis, pain management, and overall quality of life.

Topographical distribution and morphology of SP-IR axons in the antrum, pylorus, and duodenum of mice

Substance-P (SP) is a commonly used marker of nociceptive afferent axons, and it plays an important role in a variety of physiological functions including the regulation of motility, gut secretion, and vascular flow. Previously, we found that SP-immunoreactive (SP-IR) axons densely innervated the pyloric antrum of the flat-mount of the mouse whole stomach muscular layer. However, the regional distribution and morphology of SP-IR axons in the submucosa and mucosa were not well documented. In this study, the mouse antrum-pylorus-duodenum (APD) were transversely and longitudinally sectioned. A Zeiss M2 imager was used to scan the serial sections of each APD (each section montage consisted of 50-100 all-in-focus maximal projection images). To determine the detailed structures of SP-IR axons and terminals, we used the confocal microscope to scan the regions of interest. We found that 1) SP-IR axons innervated the muscular, submucosal, and mucosal layers. 2) In the muscular layer, SP-IR varicose axons densely innervated the muscles and formed varicose terminals which encircled myenteric neurons. 3) In the submucosa, SP-IR axons innervated blood vessels and submucosal ganglia and formed a network in Brunner's glands. 4) In the mucosa, SP-IR axons innervated the muscularis mucosae. Some SP-IR axons entered the lamina propria. 5) The muscular layer of the antrum and duodenum showed a higher SP-IR axon density than the pyloric sphincter. 6) SP-IR axons were from extrinsic and intrinsic origins. This work provided a comprehensive view of the distribution and morphology of SP-IR axons in the APD at single cell/axon/varicosity scale. This data will be used to create a 3D scaffold of the SP-IR axon innervation of the APD.

Annotated translation of Georg Meissner's first description of the submucosal plexus

BACKGROUND

The discovery and detailed descriptions of the enteric nervous system dates back only ˂200 years. The 19th century was a golden age of histological, morphological, and physiological breakthroughs propelled by technological advances in microscopy, electricity, and scientific methodology. As a matter of fact, German-speaking scientists were highly successful during this period as can still be appreciated by the sheer number of German eponyms in anatomy. Therefore, the main language in scientific literature of this field was German at the time, thus, limiting the accessibility to the publications and scientific discussions from back then for the broader English-speaking scientific community today.

PURPOSE

Here, an annotated translation of Meissner's first description of the submucosal plexus is provided along with a short biography of Georg Meissner and a review of the scientific literature and controversy surrounding his discovery.

Intrinsic innervation of the ovary and its variations in the rat senescence process

Ovarian functions decrease with perimenopause. The ovary has extrinsic innervation, but the neural influence on ovarian functions and dysfunction is not well-studied. The present study aimed to biochemically and morphometrically characterize the intrinsic neurons in ovaries from young adult, middle-aged, and senescent Long Evans CII-ZV rats (3, 12, and 15 months old, respectively). Ovaries were extracted from four rats of each age group (n = 12 total), cryopreserved, and processed for immunofluorescence studies with the primary NeuN/β-tubulin and NeuN/tyrosine hydroxylase (TH) antibodies. The soma area and number of intrinsic neurons in the ovarian stroma, surrounding follicles, corpus luteum, or cyst were evaluated. The intrinsic neurons were grouped in cluster-like shapes in ovarian structures. In senescent rats, the intrinsic neurons were mainly localized in the ovarian stroma and around the cysts. The number of neurons was lower in senescent rats than in young adult rats (p < 0.05), but the soma size was larger than in young adult rats. Immunoreactivity to TH indicated the presence of noradrenergic neurons in the ovary with the same characteristics as NeuN/β-tubulin, which indicates that they are part of the same neuronal group. Taken together, the findings indicate that the intrinsic neurons may be related to the loss of ovarian functions associated with aging.

Morphologies, dimensions and targets of gastric nitric oxide synthase neurons

We investigated the distributions and targets of nitrergic neurons in the rat stomach, using neuronal nitric oxide synthase (NOS) immunohistochemistry and nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase histochemistry. Nitrergic neurons comprised similar proportions of myenteric neurons, about 30%, in all gastric regions. Small numbers of nitrergic neurons occurred in submucosal ganglia. In total, there were ~ 125,000 neuronal nitric oxide synthase (nNOS) neurons in the stomach. The myenteric cell bodies had single axons, type I morphology and a wide range of sizes. Five targets were identified, the longitudinal, circular and oblique layers of the external muscle, the muscularis mucosae and arteries within the gastric wall. The circular and oblique muscle layers had nitrergic fibres throughout their thickness, while the longitudinal muscle was innervated at its inner surface by fibres of the tertiary plexus, a component of the myenteric plexus. There was a very dense innervation of the pyloric sphincter, adjacent to the duodenum. The muscle strands that run between mucosal glands rarely had closely associated nNOS nerve fibres. Both nNOS immunohistochemistry and NADPH histochemistry showed that nitrergic terminals did not provide baskets of terminals around myenteric neurons. Thus, the nitrergic neuron populations in the stomach supply the muscle layers and intramural arteries, but, unlike in the intestine, gastric interneurons do not express nNOS. The large numbers of nNOS neurons and the density of innervation of the circular muscle and pyloric sphincter suggest that there is a finely graded control of motor function in the stomach by the recruitment of different numbers of inhibitory motor neurons.

Effects of a P2X7 receptor antagonist on myenteric neurons in the distal colon of an experimental rat model of ulcerative colitis

Inflammatory bowel diseases (IBDs) are chronic diseases of the gastrointestinal tract that include ulcerative colitis and Crohn's disease and affect enteric neurons. Research has shown that Brilliant Blue G (BBG), a P2X7 receptor antagonist, restores enteric neurons following ischemia and reperfusion. This study aimed to evaluate the effect of BBG on myenteric neurons of the distal colon in an experimental rat model of ulcerative colitis. Colitis was induced by injection of 2,4,6-trinitrobenzene sulfonic acid (TNBS) into the large intestine. BBG was administered 1 h after colitis induction and for five consecutive days thereafter. Distal colons were collected 24 h or 7 days after TNBS injection. The animals were divided into 24-h and 7-day sham (vehicle injection rather than colitis induction), 24-h colitis, 24-h BBG, 7-day colitis and 7-day BBG groups. The disease activity index (DAI), neuronal density and profile of neuronal nitric oxide synthase (nNOS)-, choline acetyltransferase (ChAT)- and P2X7 receptor-immunoreactive enteric neurons were analyzed, and histological analysis was performed. The results showed recovery of the DAI and histological tissue integrity in the BBG groups compared to those in the colitis groups. In addition, the numbers of neurons positive for nNOS, ChAT and the P2X7 receptor per area were decreased in the colitis groups, and these measures were recovered in the BBG groups. Neuronal size was increased in the colitis groups and restored in the BBG groups. In conclusion, BBG is effective in improving experimental ulcerative colitis, and the P2X7 receptor may be a therapeutic target.

Classification of human enteric neurons

Major advances in our understanding of the functional heterogeneity of enteric neurons are driven by the application of newly developed, innovative methods. In contrast to this progress, both animal and human enteric neurons are usually divided into only two morphological subpopulations, “Dogiel type II” neurons (with several long processes) and “Dogiel type I” neurons (with several short processes). This implies no more than the distinction of intrinsic primary afferent from all other enteric neurons. The well-known chemical and functional diversity of enteric neurons is not reflected by this restrictive dichotomy of morphological data. Recent structural investigations of human enteric neurons were performed by different groups which mainly used two methodical approaches, namely detecting the architecture of their processes and target-specific tracing of their axonal courses. Both methods were combined with multiple immunohistochemistry in order to decipher neurochemical codes. This review integrates these morphological and immunohistological data and presents a classification of human enteric neurons which we believe is not yet complete but provides an essential foundation for the further development of human gastrointestinal neuropathology.

The identification of neuronal control pathways supplying effector tissues in the stomach

The stomach acts as a buffer between the ingestion of food and its processing in the small intestine. It signals to the brain to modulate food intake and it in turn regulates the passage of a nutrient-rich fluid, containing partly digested food, into the duodenum. These processes need to be finely controlled, for example to restrict reflux into the esophagus and to transfer digesta to the duodenum at an appropriate rate. Thus, the efferent pathways that control gastric volume, gastric peristalsis and digestive juice production are critically important. We review these pathways with an emphasis on the identities of the final motor neurons and comparisons between species. The major types of motor neurons arising from gastric enteric ganglia are as follows: immunohistochemically distinguishable excitatory and inhibitory muscle motor neurons; four neuron types innervating mucosal effectors (parietal cells, chief cells, gastrin cells and somatostatin cells); and vasodilator neurons. Sympathetic efferent neurons innervate intramural arteries, myenteric ganglia and gastric muscle. Vagal efferent neurons with cell bodies in the brain stem do not directly innervate gastric effector tissues; they are pre-enteric neurons that innervate each type of gastric enteric motor neuron. The principal transmitters and co-transmitters of gastric motor neurons, as well as key immunohistochemical markers, are the same in rat, pig, human and other species.