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

GDNF rescues hyperglycemia-induced diabetic enteric neuropathy through activation of the PI3K/Akt pathway

Diabetes can result in loss of enteric neurons and subsequent gastrointestinal complications. The mechanism of enteric neuronal loss in diabetes is not known. We examined the effects of hyperglycemia on enteric neuronal survival and the effects of glial cell line-derived neurotrophic factor (GDNF) on modulating this survival. Exposure of primary enteric neurons to 20 mM glucose (hyperglycemia) for 24 hours resulted in a significant increase in apoptosis compared with 5 mM glucose (normoglycemia). Exposure to 20 mM glucose resulted in decreased Akt phosphorylation and enhanced nuclear translocation of forkhead box O3a (FOXO3a). Treatment of enteric neurons with GDNF ameliorated these changes. In streptozotocin-induced diabetic mice, there was evidence of myenteric neuronal apoptosis and reduced Akt phosphorylation. Diabetic mice had loss of NADPH diaphorase-stained myenteric neurons, delayed gastric emptying, and increased intestinal transit time. The pathophysiological effects of hyperglycemia (apoptosis, reduced Akt phosphorylation, loss of inhibitory neurons, motility changes) were reversed in diabetic glial fibrillary acidic protein-GDNF (GFAP-GDNF) Tg mice. In conclusion, we demonstrate that hyperglycemia induces neuronal loss through a reduction in Akt-mediated survival signaling and that these effects are reversed by GDNF. GDNF may be a potential therapeutic target for the gastrointestinal motility disorders related to diabetes.

Nicotinic synapses formed between chick ciliary ganglion neurons in culture resemble those present on the neurons in vivo

We studied nicotinic synapses between chick ciliary ganglion neurons in culture to learn more about factors influencing their formation and receptor subtype dependence. After 4--8 days in culture, nearly all neurons displayed spontaneous excitatory postsynaptic currents (sEPSCs), which occurred at about 1 Hz. Neurons treated with tetrodotoxin displayed miniature EPSCs (mEPSCs), but these occurred at low frequency (0.1 Hz), indicating that most sEPSCs are actually impulse driven. The sEPSCs could be classified by decay kinetics as fast, slow, or biexponential and, reminiscent of the situation in vivo, were mediated by two major nicotinic acetylcholine receptor (AChR) subtypes. Fast sEPSCs were blocked by alpha-bungarotoxin (alpha Bgt), indicating dependence on alpha Bgt-AChRs, most of which are alpha 7 subunit homopentamers. Slow sEPSCs were unaffected by alpha Bgt, and were blocked instead by the alpha 3/beta 2-selective alpha-conotoxin-MII (alpha CTx-MII), indicating dependence on alpha 3*-AChRs, which lack alpha 7 and contain alpha 3 subunits. Biexponential sEPSCs were mediated by both alpha Bgt- and alpha 3*-AChRs because they had fast and slow components qualitatively similar to those comprising simple events, and these were reduced by alpha Bgt and blocked by alpha CTx-MII, respectively. Fluorescence labeling experiments revealed both alpha Bgt- and alpha 3*-AChR clusters on neuron somata and neurites. Colabeling with antisynaptic vesicle protein antibody suggested that some alpha 3*-AChR clusters, and a few alpha Bgt-AChR clusters are associated with synaptic sites, as is the case in vivo. These findings demonstrate the utility of ciliary ganglion neuron cultures for studying the regulation of nicotinic synapses, and suggest that mixed AChR subtype synapses characteristic of the neurons in vivo can form in the absence of normal inputs or targets.

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.

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.

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.

Simultaneous intracellular recordings from enteric neurons reveal that myenteric AH neurons transmit via slow excitatory postsynaptic potentials

Simultaneous intracellular electrical recordings were made from pairs of neurons separated circumferentially by 100-200 microns of the myenteric plexus of the guinea-pig ileum in vitro. The recording electrodes were filled with the dye neurobiotin which was injected into impaled nerve cells, and later revealed histochemically. Intracellular current pulses were used to evoke action potentials via the recording electrode in one type of myenteric neuron, in most cases an AH neuron, while a second electrode was used to record from a simultaneously impaled S neuron or AH neuron. AH neurons are thought to be primary sensory neurons, whereas S neurons are interneurons and motor neurons. Ninety pairs of neurons were adequately tested for interaction. From these, 17 S neurons and three AH neurons that responded to AH neuron stimulation were detected. In each case, the response was a slow depolarization that was seen only in response to a train of stimuli at 10 Hz. The slow depolarizations were enhanced by passing depolarizing current and diminished by hyperpolarization. Responses were also diminished by lowering external Ca.2+ and elevating Mg2+. In all cases in which intracellular recording indicated communication between neurons, morphological evidence of connection was seen. In no case was there communication without connection, but in four instances, morphological connections appeared to exist, although no physiological evidence of communication was obtained.

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.

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.

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.

Neural regulation of acetylcholine sensitivity in embryonic sympathetic neurons

The development of transmitter sensitivity is an important component of synaptic differentiation. Despite a wealth of information about the appearance of acetylcholine (AcCho) sensitivity at the neuromuscular junction, the onset and regulation of this critical aspect of synaptogenesis has not previously been examined for synapse formation between neurons. To determine whether there is a role of presynaptic input in the induction of AcCho sensitivity at interneuronal synapses, AcCho-induced currents were measured in embryonic sympathetic neurons before and after synapse formation in vitro. The total AcCho sensitivity of postsynaptic neurons was increased nearly 10-fold after innervation. The effects of innervation are mimicked by medium conditioned by preganglionic neurons, suggesting that presynaptic neurons regulate postsynaptic AcCho sensitivity by release of a soluble factor. These observations provide evidence that presynaptic input regulates neuronal sensitivity to an identified synaptic transmitter.

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. 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.

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

We have used intracellular recordings to study the electrophysiological and pharmacological properties of neurons that have been grown in cell cultures after having been dissociated from the myenteric plexus of the small intestine of newborn rats. Studies of action potential mechanisms revealed that all of the neurons could generate Na+-dependent action potentials in the presence of Ca2+-channel blockers and that about 70% could generate Ca2+-dependent action potentials when Na+ channels were blocked with tetrodotoxin. No neurons generated long afterhyperpolarizations after single action potentials but about 50% of neurons did so following trains of action potentials. Over 95% of the neurons tested accommodated rapidly to sustained depolarization. The effects of several enteric neurotransmitter candidates were studied by superfusing or pressure-ejecting test solutions while recording neuronal responses. All of the cultured neurons tested had nicotinic responses to acetylcholine. Subsets of neurons responded to muscarinic cholinergic agonists (slow depolarization and increased excitability), serotonin (fast depolarization or slow depolarization and increased excitability), gamma-aminobutyrate (fast depolarization), substance P (slow depolarization, biphasic fast and slow depolarization or increased excitability without a change in membrane potential), vasoactive intestinal peptide (slow depolarization and increased excitability), or [Met]enkephalin (slow hyperpolarization and/or decreased action potential duration). We conclude that myenteric neurons grown in cell culture retain many of the physiological and pharmacological properties that they have in situ. Such cultures will permit detailed biophysical and pharmacological studies of the mechanisms of action of enteric neurotransmitter candidates.