Neurons dissociated from rat myenteric plexus retain differentiated properties when grown in cell culture. II. Electrophysiological properties and responses to neurotransmitter candidates

Methods to Study the Myenteric Plexus of Rat Small Intestine

The close interaction between the enteric nervous system, microbiome, and brain in vertebrates is an emerging topic of recent studies. Different species such as rat, mouse, and human are currently being used for this purpose, among others. The transferability of protocols for tissue isolation and sample collection is not always straightforward. Thus, the present work presents a new protocol for isolation and sample collection of rat myenteric plexus cells for in vivo as well as in vitro studies. With the methods and chemicals described in detail, a wide variety of investigations can be performed with regard to normal physiological as well as pathological processes in the postnatal developing enteric nervous system. The fast and efficient preparation of the intestine as the first step is particularly important. We have developed and described a LIENS chamber to obtain optimal tissue quality during intestinal freezing. Cryosections of the flat, snap-frozen intestine can then be prepared for histological examination of the various wall layers of the intestine, e.g. by immunohistochemistry. In addition, these cryosections are suitable for the preparation of defined regions, as shown here using the ganglia of the mesenteric plexus. This specific tissue was obtained by laser microdissection, making the presented methodology also suitable for subsequent analyses that require high quality (specificity) of the samples. Furthermore, we present here a fully modernized protocol for the cultivation of myenteric neurons from the rat intestine, which is suitable for a variety of in vitro studies.

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.

Differential Ca(2+) signaling characteristics of inhibitory and excitatory myenteric motor neurons in culture

Physiological studies on functionally identified myenteric neurons are scarce because of technical limitations. We combined retrograde labeling, cell culturing, and fluorescent intracellular Ca(2+) concentration ([Ca(2+)](i)) signaling to study excitatory neurotransmitter responsiveness of myenteric motor neurons. 1, 1-Didodecyl-3,3,3',3'-tetramethyl indocarbocyanine (DiI) was used to label circular muscle motor neurons of the guinea pig ileum. DiI-labeled neurons were easily detectable in cultures prepared from these segments. The excitatory neurotransmitters (10(-5) M) acetylcholine, substance P, and serotonin induced a transient rise in [Ca(2+)](i) in subsets of DiI-labeled neurons (66.7, 56.5, and 84. 3%, respectively). DiI-labeled motor neurons were either inhibitory (23.8%) or excitatory (76.2%) as assessed by staining for nitric oxide synthase or choline acetyltransferase. Compared with excitatory motor neurons, significantly fewer inhibitory neurons in culture responded to acetylcholine (0 vs. 69%) and substance P (12.5 vs. 69.2%). We conclude that combining retrograde labeling and Ca(2+) imaging allows identification of differential receptor expression in functionally identified neurons in culture.

Investigation of the susceptibility of equine autonomic neuronal cell lines, clonally derived from the same paravertebral ganglion, to toxic plasma from equine dysautonomia (grass sickness) cases

In the autonomic nervous system (ANS) of equine grass sickness (GS) cases, some neurones show abnormal changes while neighbouring neurones are unaffected. To test whether noradrenergic neurones showed variable susceptibility to the GS toxin in culture, clonally-derived populations isolated from the same fetal thoracic sympathetic chain ganglion were challenged with plasma from GS cases previously shown to induce ANS damage when injected into normal horses. During the early stages of exposure to toxic plasma, cells within a clonal population showed variable susceptibility ranging from no obvious effect to characteristic patterns of pathology. However, after 3 days of exposure to toxic plasma all cells were killed. Dose response analysis on selected clonal populations showed no significant difference in TD(50) values.

Synaptic transmission induces transient Ca2+ concentration changes in cultured myenteric neurones

The enteric nervous system controls most of the gastrointestinal functions. We applied confocal microscopy and the Ca2+ indicator Fluo-3 as an optical approach to study synaptic activation in cultures of myenteric neurones. The optical recording of [Ca2+]i (the intracellular Ca2+ concentration) was used to monitor activation, since [Ca2+]i is crucial in the coupling between neuronal excitation and the activation of several intracellular events. Extracellular fibre tract stimulation (2 s, 30 Hz) caused a transient [Ca2+]i rise in a subset of neurones (50%). These transients lasted for 5.2 s (n=36), with an average amplitude of 3.4 +/- 1.3 times the basal concentration. The removal of extracellular Ca2+ (n=15) or the application of 10-6 M tetrodotoxin (n=16) blocked this response. The N-type Ca2+-channel blocker omega-conotoxin (5 x 10 -7M) abolished the [Ca2+]i increase, while blockade of L-type and P/Q type Ca2+ channels had no effect. Single stimuli evoked a [Ca2+]i rise in the processes. omega-conotoxin-sensitive postsynaptic events required repetitive stimulation. Cholinergic blockade did not inhibit the [Ca2+]i rise in all neurones, suggesting that, besides acetylcholine, other neurotransmitters are involved. Optical imaging of [Ca2+]i can be used to study synaptic spread of activation in enteric neuronal circuits expressed in culture.

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.

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.

Myenteric ganglia from the adult guinea-pig small-intestine in tissue-culture

Myenteric ganglia dissociated from the small intestine of adult guinea-pigs survived in long-term culture (1-2 months) and progressed to structural organization resembling the myenteric plexus in situ. Developmental changes were similar to cultures derived from neonatal intestine. After one week, the neurons gathered into clusters on a glial cell carpet. Processes from the neurons branched and ramified over the glial substrate. As the cultures matured, the processes joined into tracts and the neurons and glia formed compact aggregates reminiscent of ganglia interconnected by fibre bundles. Injection of dye revealed characteristic Dogiel I and II neuronal morphology. Electrical recording identified electrical and synaptic behaviour comparable to intact myenteric plexus, longitudinal muscle preparations, except slow synaptic excitation was absent. Pharmacological responses to forskolin and 5-hydroxytryptamine were essentially the same as in freshly dissected preparations. Lucifer yellow injected into single glial cells spread to a broad population indicative of the dye coupling found among glia in the myenteric plexus in situ. The results suggest that adult myenteric ganglia in culture are a useful model for investigation of aspects of enteric neurobiology including: (a) formation of connections in microcircuits; (b) cellular neurophysiology of enteric neurons; (c) neuropharmacology; and (4) cell biology of neuronal-glial interactions in the myenteric plexus.

Substance P produces an inward current by suppressing voltage-dependent and -independent K+ currents in bullfrog primary afferent neurons

A whole-cell patch-clamp study was carried out to examine the effect of substance P (SP) on the excitability of neurons in bullfrog dorsal root ganglia (DRG). SP (3 nM to 1 microM) produced an inward current associated with decreased membrane conductance at voltage range between -10 and -130 mV. Neurokinin A (NKA) and neurokinin B (NKB) also produced the inward current in DRG cells; the rank order of agonist potency was NKA = SP much greater than NKB. An antagonist for SP receptors, [D-Arg1, D-Trp7,9, Leu11]SP, did not prevent the response to SP. SP (3 nM to 1 microM) suppressed the voltage-dependent non-inactivating K+ current, the M-current (IM) by reducing the maximum M-conductance. A voltage-independent background K+ current, IK(B), could be recorded at a hyperpolarizing voltage (< or = -60 mV) from DRG neurons. SP (3 nM to 1 microM) produced the inward current associated with decreased IK(B) at a holding potential more negative than -60 mV. The SP-induced inward current reversed its polarity at the equilibrium potential for K ions. Intracellular dialysis with Cs+ blocked the SP-induced responses. Depletion of intracellular ATP reduced SP-induced inward current. These results suggest that the SP-induced inward current was due to suppression of both the IM and IK(B) that are regulated by intracellular activity of ATP in bullfrog DRG neurons.

Intracellular calcium changes associated with cholinergic nicotinic receptor activation in cultured myenteric plexus neurones

Intracellular free calcium concentration ([Ca2+]i) was measured in cultured explants of myenteric plexus neurones by using the fluorescent calcium indicator Indol in combination with patch-clamp techniques. The basal [Ca2+]i was 94 nM and spontaneous oscillations in the internal free calcium concentration were recorded. These oscillations were associated with bursts of action potentials triggered by spontaneous nicotinic excitatory synaptic potentials. Under voltage clamp conditions, application of the selective nicotinic agonist m-hydroxyphenylpropyl-trimethylammonium iodide (10 microM) induced an inward current and increased the intracellular free calcium concentration. We conclude that cholinergic synaptic excitatory activity provide a regular calcium entry in myenteric neurone and suggest that the nicotinic channel might be significantly permeable to calcium.

Enteric glial cells are major contributors to formation of cyclic AMP in myenteric plexus cultures from adult guinea-pig small intestine

Cultures derived from ganglia isolated from the small intestine of adult guinea-pigs were used to determine relative contribution of neurons and glial cells to stimulation of cAMP formation by forskolin in myenteric ganglia. In untreated cultures (8-12 days), the ratio of glial cells to neurons was 5-fold higher than the ratio in intact myenteric plexus preparations. Treatment with cytosine arabinoside virtually eliminated the glia by the 12th day. Microelectrode recording of excitatory responses to forskolin in AH/Type 2 neurons confirmed the viability of cultured neurons in cytosine arabinoside. Forskolin elevated the cAMP content of cultures and cytosine arabinoside reduced this effect by 80-90%. This suggests that enteric glial cells are the major contributors to cAMP formation in the cultures and that glial cells contribute significantly to elevation of cAMP levels seen in intact myenteric ganglia.

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.

Excitatory and neurotoxic actions of platelet-activating factor on rat myenteric neurons in cell culture

At micromolar concentrations, PAF causes intense excitation and elevation of intracellular Ca in a subset of myenteric neurons. When applied for more than about 10 seconds, these concentrations of PAF kill a subset of myenteric neurons. The excitation and elevation of Ca levels are accompanied by increased membrane conductance and enhanced synaptic activity. The effects of brief applications are reversible, but responses to subsequent applications of PAF are substantially reduced. If such responses can be elicited in enteric neurons by the concentrations of PAF that are generated in vivo, they would account for the potent ability of PAF to evoke neurally-mediated secretory responses in GI tissues.

Fast and slow depolarizations produced by substance P and other tachykinins in sympathetic neurons of rat prevertebral ganglia

Using intracellular recording, we examined the effects of three mammalian tachykinins, substance P (SP), neurokinin A (NKA), and neurokinin B (NKB), on sympathetic neurons of isolated rat coeliac-superior mesenteric ganglia (C-SMG). The 3 tachykinins elicited two distinct depolarizing responses in ganglion cells: fast depolarization with time-to-peak of 1-2 sec and duration of 5-10 sec, and slow depolarization with time-to-peak of about 20 sec and duration of 120-140 sec. Both fast and slow responses persisted in a solution containing low Ca2+ and high Mg2+ or tetrodotoxin, which indicates that the tachykinins directly act on ganglion cells to produce fast and slow depolarizations. The two types of tachykinin-induced responses exhibited clearly distinguishable properties. The membrane conductance was increased during the fast response, but not significantly changed, slightly decreased or sometimes increased during the slow response. Within certain range of membrane potential, the amplitude of fast response increased upon membrane hyperpolarization and decreased upon depolarization of ganglion cells. In contrast, the amplitude of slow response associated with membrane conductance decrease was increased with membrane depolarization and decreased with hyperpolarization. The fast response was markedly suppressed in a Na(+)-deficient solution, a solution containing nominally zero Ca2+ (plus 0.1 mM EGTA in some cases), and in a solution containing Cd2+ or Mn2+, whereas the slow response was not affected in these solutions and was augmented in some cells in K(+)-free solution. Thus it seems that the increase in Ca(2+)-dependent cationic conductance underlies the fast response and that the slow response is produced at least in part by suppression of certain K+ channels. The fast response progressively decreased in amplitude upon repeated application of the peptides with short intervals, whereas the slow response was rather augmented by repeated application. Lowering the temperature markedly depressed the slow response, while the fast response remained almost unaffected. It is therefore likely that the fast and slow depolarizations are mediated by two different subtypes of tachykinin receptors or a single class of receptors linked with two different intracellular mechanisms. Measurement of tachykinins in several sympathetic ganglia by combined use of HPLC and radioimmunoassay revealed that the highest amount of SP occurs in the C-SMG where the content of SP (136.0 pmol/g protein) was higher than those of NKA (44.3) and NKB (18.7). SP thus appears to function as a major tachykinin in rat C-SMG.

Substance P mediates synaptic transmission between rat myenteric neurones in cell culture

1. Whole-cell patch-clamp recordings were made from pairs of neurones in cell cultures of rat myenteric neurones. In some pairs, action potentials evoked in the first neurone evoked a slow excitatory postsynaptic potential (EPSP) in the second neurone. 2. Action potentials at a frequency of at least 5 Hz were required to evoked slow EPSPs. In one group of cells, the slow EPSP followed a series of nicotinic fast EPSPs; in another group, fast EPSPs did not precede the slow EPSP. 3. The slow EPSPs were 2-16 mV in amplitude and were accompanied by decreased resting potassium conductance. 4. Most (17/28) neurones in which action potentials evoked only slow EPSPs in a follower cell contained substance P (SP)-like immunoreactivity; they were not immunoreactive for 5-hydroxytryptamine (0/15) or vasoactive intestinal peptide (0/22). 5. Postsynaptic responses to SP, neurokinin A and a synthetic tachykinin [( pGlu6, Pro9]SP6-11) mimicked the slow EPSPs. The non-tachykinin peptide vasoactive intestinal polypeptide (VIP), which was not found in neurones that evoked only slow EPSPs, also mimicked the slow EPSPs. Responsiveness to SP decreased significantly during slow EPSPs. 6. Desensitization to either SP or VIP reduced or prevented the slow EPSPs and also responses to each other. Two proposed antagonists of SP receptors, [D-Arg1, D-Pro2,D-Trp7,9,Leu11]substance P and [D-Arg1,D-Trp7,9,Leu11]substance P, did not affect the slow EPSPs significantly. 7. Antisera against SP reversibly blocked or reduced slow EPSPs evoked by eight of thirteen presynaptic neurones that evoked slow EPSPs without evoking fast EPSPs. All eight of the presynaptic neurones that evoked anti-SP-sensitive slow EPSPs contained SP-like immunoreactivity. None of the presynaptic neurones that evoked anti-SP-insensitive slow EPSPs contained detectable SP-like immunoreactivity. Normal sera and anti-VIP antisera did not alter the slow EPSPs detectably. 8. It is concluded that subsets of myenteric neurones release an SP-like transmitter to evoke slow EPSPs. These neurones appear to lack a 'classical' neurotransmitter that evokes fast EPSPs.

Tachykinins produce fast and slow depolarizations in sympathetic neurons of rat coeliac-superior mesenteric ganglia

The actions of mammalian tachykinins on neurons of rat coeliac-superior mesenteric ganglia (C-SMG) were examined using intracellular recording in isolated preparations. Application of substance P, neurokinin A and neurokinin B produced fast and slow depolarizations in the ganglion cells. The two responses were clearly distinguishable in their electrophysiological characteristics. The results suggest that different receptor mechanisms are involved in fast and slow depolarizing actions of tachykinins in rat C-SMG cells.

The use of cell and tissue culture techniques in the study of regulatory peptides

Cell and tissue culture preparations have a number of general advantages for the study of biological processes: cells are more accessible for study, diffusion delays and barriers to applied substances are minimised, the humoral and cellular components of the culture environment can be controlled and progressive changes in intracellular and intercellular events can be directly monitored. These significant advantages mean that culture preparations can provide unique opportunities for investigation of the properties and functions of regulatory peptides. Culture preparations also have disadvantages and not all cultures are suitable for use in all types of experiments; therefore, the choice of preparation must be made accordingly. Here we describe different types of culture preparation and give examples where cultures have been used to examine peptide synthesis, storage, secretion and receptor localisation, as well as the short-term and trophic actions of regulatory peptides.

Conditioned medium alters electrophysiological and transmitter-related properties expressed by rat enteric neurons in cell culture

We have previously shown that rat enteric neurons display many of their in vivo phenotypes when they are dissociated and grown in long-term cell culture. To assess the degree of plasticity of these phenotypes we have examined the effect of medium conditioned by rat heart cells because this treatment strongly affects transmitter properties in rat sympathetic neurons in culture. Growth of enteric neurons for 3-4 weeks in conditioned medium caused several changes that are similar to previously described effects of conditioned medium on other neuronal cell types in culture. When compared to cultures grown in control medium, cultures grown in conditioned medium: (i) contained three times as many large (greater than 25 micron) neurons; (ii) synthesized and stored 3-4 times as much acetylcholine; (iii) contained 4-5 times as many neurons with detectable 5-hydroxytryptamine immunoreactivity; and (iv) contained 10 times as many neurons that fired repetitively during sustained depolarization. Several other changes, which have not been reported in other systems, were also observed. Conditioned medium cultures: (i) contained many fewer neuronal processes with immunohistochemically detectable vasoactive intestinal polypeptide, substance P, somatostatin, and [Met]enkephalin; (ii) contained 70% fewer neuronal cell bodies with vasoactive intestinal polypeptide-like immunoreactivity; and (iii) contained four times as many neurons that had muscarinic responses to acetylcholine. None of the changes in properties described above uniformly affected all enteric neurons, even after 6 weeks of growth in conditioned medium. We conclude that the heterogeneity of enteric neuron phenotypes is established prior to birth and limits the capacity of certain subsets of neurons to respond to exogenous factors in the environment. Nevertheless, the phenotypes of other subsets of neurons displayed considerable plasticity when exposed to conditioned medium.

Establishment and properties of separate cultures of enteric neurons and enteric glia

In this paper methods are described for the preparation of two types of culture derived from myenteric explants: (a) highly enriched neuronal cell cultures, and (b) purified glial cells (greater than 98%). Both procedures combine the technique of antibody complement-mediated cytolysis with the use of an antimitotic agent. Immunohistochemical methods were used to compare the purified cells to their counterparts in mixed cultures (see accompanying paper). Antibodies to the glycoprotein Thy-1 and the monoclonal antibody A2B5 which recognizes gangliosides, labelled the cell surface of all enteric neurons in enriched cultures while subpopulations of the neurons expressed the Leu 7 carbohydrate epitope, the neurotransmitter 5-hydroxytryptamine and the neuropeptides substance P, methionine-enkephalin and vasoactive intestinal polypeptide. Autoradiographic experiments show that a subpopulation of enriched neurons exhibit high-affinity uptake sites for gamma-[3H]aminobutyric acid (GABA). All purified enteric glia continue to express the calcium binding protein S100, the basement membrane glycoprotein laminin and the antigens recognized by the A2B5 antibody, and subpopulations of glia are labelled by the monoclonal antibodies LB1 which binds to GD3 gangliosides, and Leu 7. Thus enteric neurons and glia can survive independently of each other and express molecular properties which are present in cultures normally containing both cell types.

Intracellular recordings from cells in the myenteric plexus of the rat duodenum

Intracellular recordings were made in vitro from neurons in the myenteric plexus of freshly dissected preparations of the duodenum of the rat. Nearly one-quarter of neurons (18 out of 77) had long after-hyperpolarizations following their action potentials. Over 60% of neurons (20 out of 32) which were tested exhaustively by focal stimulation at seven points around the recording site were seen to receive fast excitatory synaptic inputs. These were of very short duration (10-30 ms) and were reversibly blocked by the nicotinic antagonist hexamethonium. Only four out of 18 after-hyperpolarization cells (22%) had visible fast synaptic inputs. Seven out of 32 neurons tested received slow excitatory synaptic inputs lasting up to 60 s that were associated with a decrease in conductance and an increase in excitability. No evidence for muscarinic synaptic potentials was seen; only four cells out of 30 with fast excitatory postsynaptic potentials had slow excitatory synaptic potentials visible after a single-shot stimulus; in none of these were the slow excitatory postsynaptic potentials blocked by atropine (up to 1 x 10(-5) M). No inhibitory postsynaptic potentials were recorded in any of the 77 neurons recorded in this study. The effects of five neurotransmitter candidates (acetylcholine, GABA noradrenaline, 5-hydroxytryptamine and substance P) applied by pressure microejection were studied. It is concluded that most of the neurophysiological features reported in the extensively studied guinea-pig small bowel myenteric plexus are present in the rat duodenum. However, the apparent lack of muscarinic synaptic potentials and inhibitory synaptic potentials suggests that there may be some differences between the two species. Our recordings also differ slightly from recently reported studies of rat myenteric neurons grown in cell culture.

Neuropeptides mark functionally distinguishable cholinergic enteric neurons

Subpopulations of physiologically identified cholinergic enteric neurons in cell culture contain somatostatin (SOM)- or vasoactive intestinal peptide (VIP)- like immunoreactivity (LIR). These subpopulations differ in their synaptic effects on other neurons: cholinergic neurons that contain SOM-LIR cause fast nicotinic excitatory postsynaptic potentials (EPSPs) that have significantly larger amplitudes than do EPSPs caused by cholinergic neurons that lack SOM-LIR. Cholinergic neurons containing VIP-LIR cause slow non-cholinergic depolarizations in addition to fast nicotinic EPSPs. These findings are the first correlation between neuropeptide content and functional differences in the synaptic effects of subpopulations of cholinergic enteric neurons.

Intracellular recordings from myenteric neurones in the human colon

1. Intracellular recordings were made from cells in the myenteric plexus of the human colon in freshly dissected tissue obtained from patients undergoing surgery for the removal of carcinomas or diverticular bowel. 2. Twenty-seven cells from ten preparations were classified as neurones and had overshooting action potentials, an average resting potential of -54 +/- 9 mV, an average input impedance of 1.05 +/- 0.59 x 10(8) omega and a variety of synaptic inputs. 3. Twenty-three (out of twenty-five neurones tested) received nicotinic fast excitatory synaptic inputs (fast e.p.s.p.s) that were blocked reversibly by hexamethonium and mimicked by acetylcholine. These nerve cells bore a close resemblance to S cells that have been characterized in the guinea-pig small-bowel myenteric plexus. 4. One cell had a long after-hyperpolarization following its impulses and was similar to AH cells in the guinea-pig small bowel. 5. Three neurones received inhibitory synaptic inputs, up to 15 mV in amplitude, lasting up to 10 s, associated with a decrease in input impedance and with a reversal potential between -80 and -90 mV. 6. Slow excitatory synaptic potentials were only detected in the single AH cell. The slow e.p.s.p. was associated with a depolarization of up to 12 mV, an increase in excitability and an increase in the input impedance of the neurone. 7. The proportion of S and AH cells differ considerably from that reported in the guinea-pig small-bowel preparation. Possible causes of the differences are discussed.

Urinary bladder intramural neurones: an electrophysiological study utilizing a tissue culture preparation

An enzymic dispersion technique was used to free the intramural ganglia from their usual close association with the other components of the urinary bladder wall. The isolated ganglia obtained were viable and could be kept in culture for several weeks. The development of the cultures was monitored by phase-contrast microscopy and their electrophysiological properties were investigated using intracellular recording techniques. Neurones could be visually identified after 2-3 days in culture; cell groups contained from 2-50 neurones. Three types of spontaneous activity were seen: small changes in membrane potential and action potentials, and slow oscillatory conductance changes. These events were not blocked by hexamethonium but were abolished by hyperpolarizing current. Most neurones spiked without adaptation to direct stimulation; in a few cells the train of spikes was damped out. No neurones generated long afterhyperpolarizations. Indirect stimulation produced responses in the ganglia which are consistent with synaptic activity. Summation of inputs was demonstrated. These results provide evidence for local intraganglionic circuits since the ganglia or neurone groups are unequivocally extrinsically denervated. It was concluded that the intramural ganglia have the capacity to integrate preganglionic input and the question of whether or not they might mediate reflex activity is raised.

Neurons dissociated from rat myenteric plexus retain differentiated properties when grown in cell culture. III. Synaptic interactions and modulatory effects of neurotransmitter candidates

We have used intracellular recordings to study synaptic interactions between myenteric neurons grown in dissociated cell culture. Intracellular stimulation of individual myenteric neurons caused several types of synaptic effects in nearby neurons: fast excitatory synaptic potentials mediated by nicotinic acetylcholine receptors; slow, non-cholinergic synaptic potentials; dual transmission having both fast cholinergic and slow non-cholinergic components and inhibition of spontaneously occurring fast nicotinic synaptic potentials. Fast nicotinic synaptic potentials were elicited by about 40% of neurons tested and often occurred spontaneously. The fast synaptic potentials were similar to those that have been studied in other autonomic neurons with respect to their estimated reversal potential and their sensitivity to cholinergic antagonists. The amplitudes of the fast synaptic potentials declined if evoked at frequencies greater than 0.5 Hz. Potentiation of the fast synaptic potentials was observed following high-frequency stimulation of presynaptic neurons. Several transmitter candidates modulated fast cholinergic transmission. Substance P and vasoactive intestinal peptide promoted nicotinic transmission by causing increased amplitudes of evoked and spontaneous fast synaptic potentials and an increased frequency of spontaneous synaptic potentials. gamma-Aminobutyrate and [Met]enkephalin both caused decreased amplitudes and frequency of nicotinic synaptic potentials. Serotonin depressed synaptic potentials in some neurons while enhancing them or having no effect in others. Slow, non-cholinergic, synaptic potentials were elicited by about 10% of neurons tested. These synaptic effects lasted 15-300s, caused depolarizations of 3-15 mv and were accompanied by increased neuronal input resistance. The transmitter(s) causing these slow synaptic potentials has not yet been identified.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurons dissociated from rat myenteric plexus retain differentiated properties when grown in cell culture. I. Morphological properties and immunocytochemical localization of transmitter candidates

We have developed procedures for dissociating neurons from the myenteric plexus of the small intestine of newborn rats and for growing those neurons in cell cultures for up to 3 months. Neurons in these cultures retain many of the differentiated properties of myenteric neurons in vivo. This is the first of a series of 3 papers describing those properties. In this paper, we describe the morphology of cultured neurons that we have observed with light and electron microscopy; we also describe the patterns of straining observed when immunocytochemical techniques were used to localize neurotransmitter candidates in the cultured neurons. Intracellular injections of a fluorescent dye, Lucifer yellow, revealed that many of the cultured neurons had morphologies similar to those of myenteric neurons in vivo. When thin sections of cultures were viewed in an electron microscope, many neurons were observed to have numerous small (40-60 nm), clear synaptic vesicles and/or large (80-150 nm), opaque-cored (p-type) vesicles. Synaptic profiles were most often observed on neuronal somata. Neurons containing immunoreactive serotonin, substance P, somatostatin, enkephalin, bombesin and gastrin/cholecystokinin were observed in about the same proportions as they occur in the intact myenteric plexus. Neurons containing immunoreactive vasoactive intestinal polypeptide were found in higher numbers than reported in vivo. Neurons containing immunoreactive neurotensin, secretin and glutamate decarboxylase were not observed. An antiserum directed against choline acetyltransferase stained 40-50% of the neurons. We conclude that myenteric neurons continue to express much of their normal differentiated properties even when they are removed from the gut, dissociated into a suspension of single cells and grown in culture. Such cultures will be useful for correlating the morphological, biophysical, pharmacological and synaptic properties of individual myenteric neurons and for testing the ability of altered environmental conditions to change those properties.