Growth of enteric neurones from isolated myenteric ganglia in dissociated cell culture

A novel method for culturing enteric neurons generates neurospheres containing functional myenteric neuronal subtypes

BACKGROUND

The enteric nervous system (ENS) is comprised of neurons, glia, and neural progenitor cells that regulate essential gastrointestinal functions. Advances in high-efficiency enteric neuron culture would facilitate discoveries surrounding ENS regulatory processes, pathophysiology, and therapeutics.

NEW METHOD

Development of a simple, robust, one-step method to culture murine enteric neurospheres in a 3D matrix that supports neural growth and differentiation.

RESULTS

Myenteric plexus cells isolated from the entire length of adult murine small intestine formed ≥3000 neurospheres within 7 days. Matrigel-embedded neurospheres exhibited abundant neural stem and progenitor cells expressing Sox2, Sox10 and Msi1 by day 4. By day 5, neural progenitor cell marker Nestin appeared in the periphery of neurospheres prior to differentiation. Neurospheres produced extensive neurons and neurites, confirmed by Tubulin beta III, PGP9.5, HuD/C, and NeuN immunofluorescence, including neural subtypes Calretinin, ChAT, and nNOS following 8 days of differentiation. Individual neurons within and external to neurospheres generated depolarization induced action potentials which were inhibited in the presence of sodium channel blocker, Tetrodotoxin. Differentiated neurospheres also contained a limited number of glia and endothelial cells.

COMPARISON WITH EXISTING METHODS

This novel one-step neurosphere growth and differentiation culture system, in 3D format (in the presence of GDNF, EGF, and FGF2), allows for ∼2-fold increase in neurosphere count in the derivation of enteric neurons with measurable action potentials.

CONCLUSION

Our method describes a novel, robust 3D culture of electrophysiologically active enteric neurons from adult myenteric neural stem and progenitor cells.

A functional network of highly pure enteric neurons in a dish

The enteric nervous system (ENS) is the intrinsic nervous system that innervates the entire digestive tract and regulates major digestive functions. Recent evidence has shown that functions of the ENS critically rely on enteric neuronal connectivity; however, experimental models to decipher the underlying mechanisms are limited. Compared to the central nervous system, for which pure neuronal cultures have been developed for decades and are recognized as a reference in the field of neuroscience, an equivalent model for enteric neurons is lacking. In this study, we developed a novel model of highly pure rat embryonic enteric neurons with dense and functional synaptic networks. The methodology is simple and relatively fast. We characterized enteric neurons using immunohistochemical, morphological, and electrophysiological approaches. In particular, we demonstrated the applicability of this culture model to multi-electrode array technology as a new approach for monitoring enteric neuronal network activity. This in vitro model of highly pure enteric neurons represents a valuable new tool for better understanding the mechanisms involved in the establishment and maintenance of enteric neuron synaptic connectivity and functional networks.

Mouse Enteric Neuronal Cell Culture

In the enteric nervous system, there exist a huge number of local intrinsic neurons, which control the gastrointestinal functions. Culture of enteric neurons provides a good model system for physiological, electrophysiological, and pharmacological studies. Here, we describe two methods to obtain sufficient enteric neurons from mouse myenteric plexuses by directly culturing primary neurons or inducing neuronal differentiation of enteric neural stem/progenitor cells.

Mouse enteric neuronal cell culture

In the enteric nervous system, there exist a lot of local intrinsic neurons which control the gastrointestinal functions. Culture of enteric neurons provides a good model system for physiological, electrophysiological, and pharmacological studies. Here, we describe two methods to obtain sufficient enteric neurons from mouse myenteric plexuses by directly culturing primary neurons or inducing neuronal differentiation of enteric neural stem/progenitor cells.

Tissue culture of the enteric nervous system from equine ileum

Ileal samples were harvested fresh from euthanized adult horses. The tissues were microdissected to prepare wholemount preparations for immunohistochemistry and for either explant or dissociated culture systems of the enteric nervous system. Explant culture systems were established using whole-mounts of either the submucous plexus or the muscularis externa (including the myenteric plexus). Dissociated cell cultures could only be obtained from the submucous plexus. Culture systems were maintained for up to 5 days. Immunoreactivity for a neuronal marker (Pan-N) and for glial cell markers (GFAP and S100) indicated the presence of both neurons and enteric glia in the tissue culture preparations. This is the first report of equine enteric neurons being grown in tissue culture Further refinements to the techniques will be required before this in vitro model can be used for quantitative analysis.

Gene delivery to rat enteric neurons using herpes simplex virus-based vectors

Neurons of the enteric (gut) nervous system can be cultured in vitro and readily survive transplantation into the brain making close connections with host neurons. As such, they could potentially be used to deliver therapeutic gene products to the brain after transduction with appropriate genes in culture. Here the authors report the first example of gene delivery to such cultured neurons using herpes simplex virus based vectors. They show that viruses lacking the immediate early gene encoding ICP27 (which are unable to replicate lytically) can efficiently deliver a marker gene to enteric neurons without producing extensive cellular damage. In contrast, viruses lacking only the viral neurovirulence factor encoded by ICP34.5 are inefficient in gene delivery, and produce extensive cellular damage, although they cannot replicate lytically in enteric neurons. A virus lacking both ICP27 and ICP34.5, however, produces less cellular damage than one lacking only ICP27, and is as efficient in gene transfer, whereas inactivation of VMW65 reduces toxicity further. The identification of this virus as a safe and efficient gene delivery vector for enteric neurons paves the way for the eventual delivery of therapeutic genes and subsequent transplantation of engineered neurons into the CNS.

Non-adrenergic non-cholinergic (NANC) transmission to smooth muscle: 35 years on

In 1963, two substances were thought to mediate all transmission between neurons, as well as between nerve and muscle in the peripheral nervous system, namely acetylcholine and noradrenaline. This paradigm primarily was due to the research of Dale, Loewi and von Euler in the first half of the century [Dale, 1937 (Transmission of nervous effects by acetylcholine, Harvey Lect. 32, pp. 229-245)]. However, in 1963, a series of experiments were carried out using recently introduced electrophysiological techniques, which showed unequivocally for the first time that the classical paradigm was not correct. Both inhibitory and excitatory junctions between nerves and smooth muscle cells were shown to exist in which transmission was mediated by non-adrenergic, non-cholinergic (NANC) transmitters. In the succeeding 35 years, identification of these NANC transmitters has been a major task of neuropharmacology, with nitric oxide, neuropeptides, and purines being isolated. This review presents an historical account of the developments this century of the classical paradigm, of how it was displaced, and of the progress made in identifying the neuromuscular transmitters of the autonomic nervous system.

A new method for the isolation of myenteric plexus from the newborn rat gastrointestinal tract

The myenteric plexus is not only essential for gastrointestinal functions, but it is also a very interesting model for the study of neuronal circuits and neuron-glial interrelationships and may be a valuable source of donor tissue, for grafting into different regions of the central nervous system. For both grafting and culture procedures it is a great advantage to obtain the maximum amount of tissue. To date, most studies have isolated the myenteric plexus by manual microdissection after collagenase digestion. Using this method, it has only been possible to obtain relatively small amounts of the myenteric plexus, mostly from the cecum and proximal colon of the guinea-pig or rat. We present here a new method, which enables much greater quantities of the plexus from the small intestine and colon to be obtained. The myenteric plexus of the entire small intestine can be isolated by a combination of enzymatic digestion and mechanical agitation. The method works from birth up to 3 week old pups, and with some modifications tissue from older or even adult animals can also be processed. Another advantage over the microdissection method is that the myenteric plexuses of the different parts of the intestine can be cultured and studied separately.

Immunohistochemical and electrophysiological characterization of submucous neurons from the guinea-pig small intestine in organ culture

Immunohistochemical and electrophysiological properties of submucous neurons were investigated in organ cultures of the guinea-pig small intestine. Preparations of submucosa, with or without the myenteric plexus attached, were maintained in vitro for 3 to 5 days. Immunohistochemical labelling for peptides revealed that the cultured submucous plexus remained substantially intact and the immunoreactivity of cell bodies was well preserved. Substantial sprouting of nerve fibers immunoreactive for vasoactive intestinal peptide (VIP) or neuropeptide Y (NPY) was evident in submucous ganglia after 5 days in organ culture. Nerve fibers immunoreactive for substance P. somatostatin, 5-hydroxytryptamine or tyrosine hydroxylase were substantially depleted in submucous ganglia or perivascular nerves at 3 days and had virtually disappeared after 5 days in cultures of isolated submucosa. During intracellular recording from submucous neurons, action potentials were initiated by depolarizing current pulses in all neurons cultured with or without the myenteric plexus and muscle layers. Electrical stimulation of internodal strands evoked fast excitatory synaptic potentials (fast EPSPs) in nearly all neurons whether or not the myenteric plexus was present during the culture period up to 5 days. The removal of myenteric plexus and extrinsic nerves did not abolish fast EPSPs from submucous neurons, suggesting that some fast EPSPs may originate from neurons in the submucous plexus, although the possibility that new synapses formed by sprouting, or surviving axons severed from myenteric or sympathetic ganglia may have been functional, cannot be entirely excluded. This work demonstrates that the immunohistochemical and electrophysiological characteristics of submucous neurons are largely maintained in organ cultures of the submucosa.

Disturbed intestinal movement, bile reflux to the stomach, and deficiency of c-kit-expressing cells in Ws/Ws mutant rats

BACKGROUND & AIMS

Interstitial cells of Cajal (ICCs) are believed to initiate the basic contractile activity of the gastrointestinal tract. Because ICCs in the intestine of mice express c-kit receptor tyrosine kinase and because rats are more commonly used than mice for pathophysiological investigations of the gastrointestinal tract, the number of the c-kit messenger RNA-expressing cells was compared with gastrointestinal movement in rats.

METHODS

The c-kit messenger RNA-expressing cells were detected by in situ hybridization. The autonomous contraction of excised segments of the ileum was recorded. The function of the pyloric sphincter was evaluated by measuring the content of bile acids in the stomach.

RESULTS

The c-kit messenger RNA-expressing cells were not detectable in the stomach of Ws/Ws mutant rats with a small deletion at the tyrosine kinase domain of c-kit, and the number of c-kit messenger RNA-expressing cells decreased to 7% that of normal control rats in the ileum of Ws/Ws rats. The contractile activity of the ileum was apparently impaired, and the content of bile acids in the stomach was significantly increased in Ws/Ws rats.

CONCLUSIONS

The abnormalities in the ileal movement and pyloric sphincter function in Ws/Ws rats were attributable to the deficiency of c-kit messenger RNA-expressing cells.

Ultrastructural studies of the myenteric plexus and smooth muscle in organotypic cultures of the guinea-pig small intestine

External muscle and myenteric plexus from the small intestine of adult guinea-pigs were maintained in vitro for 3 or 6 days. Myenteric neurons and smooth muscle cells from such organotypic cultures were examined at the electron-microscopic level. An intact basal lamina was found around the myenteric ganglia and internodal strands. Neuronal membranes, nuclei and subcellular organelles appeared to be well preserved in cultured tissues and ribosomes were abundant. Dogiel type-II neurons were distinguishable by their elongated electron-dense mitochondria, numerous lysosomes and high densities of ribosomes. Vesiculated nerve profiles contained combinations of differently shaped vesicles. Synaptic membrane specializations were found between vesiculated nerve profiles and nerve processes and cell bodies. The majority of nerve fibres were well preserved in the myenteric ganglia, in internodal strands and in bundles running between circular muscle cells. No detectable changes were found in the ultrastructure of the somata and processes of glial cells. Longitudinal and circular muscle cells from cultured tissue had clearly defined membranes with some close associations with neighbouring muscle cells. Caveolae occurred in rows that ran parallel to the long axis of the muscle cells. These results indicate that the ultrastructural features of enteric neurons and smooth muscle of the guinea-pig small intestine are well preserved in organotypic culture.

Neurons and glial cells of the enteric nervous system: studies in tissue culture

The enteric nervous system (ENS) has been recognized as the main component in regulating the function of the digestive tract and as a model for studying neuronal physiology and pharmacology. Most of the present knowledge on the ENS was derived from in vitro studies on freshly isolated plexuses. In 1978 the first study on cultured myenteric neurons was published and since then there has been a growing interest in this method. Several different culture preparations have been introduced, including the recent development of cultures from adult guinea-pigs and humans. This review summarizes the findings which have been made using cultured enteric neurons and glia. The main topics that are described are the role of the extracellular matrix and of hormones on neuronal growth, neuron-glia interactions, release of neuropeptides and their actions on neurons and co-transmission between neurons.