Distribution and three-dimensional appearance of the interstitial cells of Cajal in the rat stomach and duodenum

Pharmacological evidence that GABA-induced relaxation of rat proximal duodenum longitudinal muscle depends on NKCC cotransporter activity and Ca2+ influx

γ-Aminobutyric acid (GABA) is the main inhibitory neurotransmitter in adult central nervous system (CNS) synapses, but it excites immature CNS neurons as well as neurons in the myenteric plexus. The present work aimed to determine whether GABA-induced nonadrenergic, noncholinergic (NANC) neuronal-mediated relaxation of the rat duodenum is dependent on the activity of Na⁺ K⁺ Cl^- cotransporters (NKCC) and requires calcium influx. In the presence of guanethidine (3 µmol/L), atropine (3 µmol/L), and indomethacin (1 µmol/L), relaxations induced by GABA (100 µmol/L), KCl (5-10 mmol/L) and electrical field stimulation (1-8 Hz, 2 ms, 60 V), but not those induced by bradykinin (10-100 nmol/L) were abolished by lidocaine (300 µmol/L). However, only GABA-induced relaxations were reduced in a concentration-dependent manner by the NKCC1/2 inhibitors bumetanide (0.1-1 µmol/L) and furosemide (1-10 µmol/L). GABA-induced NANC neuronal relaxation was abolished by bicuculline (30 µmol/L) and inhibited by N-nitroarginine methyl ester (l-NAME, 300 µmol/L). The ω-conotoxin GVIA (1 µmol/L), which acts exclusively on neuronal Ca_V2 channels, but not on smooth muscle voltage-gated Ca²⁺ Ca_V1 channels, and nonselective blockers of these channels (verapamil 100 nmol/L and ruthenium red 10 µmol/L), reduced GABA-induced relaxations. These results showed that the activation of GABA_A receptors induces NANC nitrergic neuronal relaxations in the rat duodenum, which depend on NKCC activity and Ca_V2 channel activation, suggesting that this phenomenon results from neuronal depolarization promoted by Cl^- efflux through GABA_A receptors, with subsequent Ca²⁺ influx and nitric oxide release.

Structural Relationships Between Interstitial Cells of Cajal and Smooth Muscle Cells/Nerve Fibers in the Gastric Muscularis Mucosae of Chinese Giant Salamander

Interstitial cells of Cajal (ICC) play an essential role in the motility of the gastrointestinal tract, and they have been identified in many laboratory animals and in humans. However, the information of ICC in lower animals is still very limited. In the present study, ICC were identified in the gastric muscularis mucosae of an amphibian—the Chinese giant salamander, by c-Kit immunohistochemistry and transmission electron microscopy. ICC showed c-Kit immunoreactivity and had spindle-shaped cell bodies and 1–2 long processes. ICC were located between smooth muscle cells (SMC) in gastric muscularis mucosae. Ultrastructurally, ICC appeared as polygon-, spindle-, and awl-shaped with long cytoplasmic prolongations between SMC. ICC had distinctive characteristics, such as nuclei with peripheral electron-dense heterochromatin, caveolae, and abundant intracytoplasmatic vacuoles, mitochondria, and rough endoplasmic reticula. Moreover, lamellar bodies and two types of condensed granules were observed in the cytoplasm of ICC. Notably, ICC establish close contacts with each other. Moreover, ICC establish gap junctions with SMC. In addition, ICC were frequently observed close to nerve fibers. In summary, the present study demonstrated the presence of ICC in the gastric muscularis mucosae of the Chinese giant salamander.

Role of enteric glial cells in intestinal function and intestinal diseases

Enteric glial cells, as a key component of the intestinal nervous system, not only have the function of nutrition and supporting intestinal neurons, but also participate in the regulation of various intestinal functions. Abnormal activation of enteric glial cells may also be one of the important pathogenic factors for inflammatory bowel disease, intestinal infection, intestinal obstruction, colon cancer, and other intestinal diseases. At present, the role of enteric glial cells in the occurrence and development of digestive system diseases remains to be elucidated. This paper reviews the research progress in this area.

Enteric glial cells and gastrointestinal motility

Enteric glial cells (EGCs) are an important part of the enteric nervous system and play an important role in maintaining gastrointestinal function. They can nourish and support gastrointestinal neurons, participate in the integration and regulation of neural activities in the gastrointestinal tract, mediate intestinal inflammation, and directly or indirectly regulate gastrointestinal motor function. Investigating the effect of EGCs on neurons and their role in intestinal inflammation caused by gastrointestinal movement disorders may help to reveal the mechanism underlying the impact of EGCs on gastrointestinal dynamics. In clinical practice, EGCs have the potential to be used as a therapeutic target for various gastrointestinal motor function disorders. This review will summarize current knowledge regarding the effect of EGCs on gastrointestinal motor function.

Two patterns of development of interstitial cells of Cajal in the human duodenum

At the end of the embryonic period of human development, c-kit immunoreactive (c-kit IR) cells identifiable as interstitial cells of Cajal (ICC) are present in the oesophagus and stomach wall. In the small and large bowel, c-kit-IR cells appear later (in the small bowel at 9 weeks, and in the colon at 10-12 weeks), also in the MP region. The object of this study was to determine the timing of appearance and distribution of c-kit IR cells in the human embryonic and foetal duodenum. I used immunohistochemistry to examine the embryonic and foetal duodenum for cells expressing CD117 (Kit), expressed by mature ICC and ICC progenitor cells and CD34 to identify presumed ICC progenitors. Enteric plexuses were examined by way of antineuron-specific enolase and the differentiation of smooth muscle cells was studied using antidesmin antibodies. At the end of the embryonic period of development, c-kit IR cells were solely present in the proximal duodenum in the form of a wide belt of densely packed cells around the inception of the myenteric plexus (MP) ganglia. In the distal duodenum, c-kit IR cells emerged at the beginning of the foetal period in the form of thin rows of pleomorphic cells at the level of the MP. From the beginning of the fourth month, the differences in the distribution of ICC in the different portions of the duodenum were established, and this relationship was still present in later developmental stages. In fact, in the proximal duodenum, ICC of the MP (ICC-MP), ICC of the circular muscle (ICC-CM) and ICC of the septa (ICC-SEP) were present, and in the distal duodenum ICC-MP and ICC-SEP only. In conclusion, in the humans there is a difference in the timing and patterns of development of ICC in the proximal duodenum compared to the distal duodenum.