Neurogenic and myogenic patterns of electrical activity in isolated intact mouse colon

Prebiotics counteract the morphological and functional changes secondary to chronic cisplatin exposition in the proximal colon of mice

Cisplatin is an antimitotic drug able to cause acute and chronic gastrointestinal side effects. Acute side effects are attributable to mucositis while chronic ones are due to neuropathy. Cisplatin has also antibiotic properties inducing dysbiosis which enhances the inflammatory response, worsening local damage. Thus, a treatment aimed at protecting the microbiota could prevent or reduce the toxicity of chemotherapy. Furthermore, since a healthy microbiota enhances the effects of some chemotherapeutic drugs, prebiotics could also improve this drug effectiveness. We investigated whether chronic cisplatin administration determined morphological and functional alterations in mouse proximal colon and whether a diet enriched in prebiotics had protective effects. The results showed that cisplatin caused lack of weight gain, increase in kaolin intake, decrease in stool production and mucus secretion. Prebiotics prevented increases in kaolin intake, changes in stool production and mucus secretion, but had no effect on the lack of weight gain. Moreover, cisplatin determined a reduction in amplitude of spontaneous muscular contractions and of Connexin (Cx)43 expression in the interstitial cells of Cajal, changes that were partially prevented by prebiotics. In conclusion, the present study shows that daily administration of prebiotics, likely protecting the microbiota, prevents most of the colonic cisplatin-induced alterations.

Advancing human gut microbiota research by considering gut transit time

Accumulating evidence indicates that gut transit time is a key factor in shaping the gut microbiota composition and activity, which are linked to human health. Both population-wide and small-scale studies have identified transit time as a top covariate contributing to the large interindividual variation in the faecal microbiota composition. Despite this, transit time is still rarely being considered in the field of the human gut microbiome. Here, we review the latest research describing how and why whole gut and segmental transit times vary substantially between and within individuals, and how variations in gut transit time impact the gut microbiota composition, diversity and metabolism. Furthermore, we discuss the mechanisms by which the gut microbiota may causally affect gut motility. We argue that by taking into account the interindividual and intraindividual differences in gut transit time, we can advance our understanding of diet-microbiota interactions and disease-related microbiome signatures, since these may often be confounded by transient or persistent alterations in transit time. Altogether, a better understanding of the complex, bidirectional interactions between the gut microbiota and transit time is required to better understand gut microbiome variations in health and disease.

Relationship Between Intestinal Slow-waves, Spike-bursts, and Motility, as Defined Through High-resolution Electrical and Video Mapping

Background/Aims

High-resolution extracellular mapping has improved our understanding of bioelectric slow-wave and spike-burst activity in the small intestine. The spatiotemporal correlation of electrophysiology and motility patterns is of critical interest to intestinal function but remains incompletely defined.

Methods

Intestinal jejunum segments from in vivo pigs and rabbits were exteriorized, and simultaneous high-resolution extracellular recordings and video recordings were performed. Contractions were quantified with strain fields, and the frequencies and velocities of motility patterns were calculated. The amplitudes, frequencies, and velocities of slow-wave propagation patterns and spike-bursts were quantified and visualized. In addition, the duration, size and energy of spike-burst patches were quantified.

Results

Slow-wave associated spike-bursts activated periodically at 10.8 ± 4.0 cycles per minute (cpm) in pigs and 10.2 ± 3.2 cpm in rabbits, while independent spike-bursts activated at a frequency of 3.2 ± 1.8 cpm. Independent spike-bursts had higher amplitude and longer duration than slow-wave associated spike-bursts (1.4 ± 0.8 mV vs 0.1 ± 0.1 mV, P < 0.001; 1.8 ± 1.4 seconds vs 0.8 ± 0.3 seconds, P < 0.001 in pigs). Spike-bursts that activated as longitudinal or circumferential patches were associated with contractions in the respective directions. Spontaneous peristaltic contractions were elicited by independent spike-bursts and travelled slower than slow-wave velocity (3.7 ± 0.5 mm/sec vs 10.1 ± 4.7 mm/sec, P = 0.007). Cyclic peristaltic contractions were driven by slow-wave associated spike-bursts and were coupled to slow-wave velocity and frequency in rabbit (14.2 ± 2.3 mm/sec vs 11.5 ± 4.6 mm/sec, P = 0.162; 11.0 ± 0.6 cpm vs 10.8 ± 0.6 cpm, P = 0.970).

Conclusions

Motility patterns were dictated by patterns of spike-burst patches. When spike-bursts were coupled to slow-waves, periodic motility patterns were observed, while when spike-bursts were not coupled to slow-waves, spontaneous aperiodic motility patterns were captured.

British Society of Gastroenterology guidelines on the management of functional dyspepsia

Functional dyspepsia (FD) is a common disorder of gut-brain interaction, affecting approximately 7% of individuals in the community, with most patients managed in primary care. The last British Society of Gastroenterology (BSG) guideline for the management of dyspepsia was published in 1996. In the interim, substantial advances have been made in understanding the complex pathophysiology of FD, and there has been a considerable amount of new evidence published concerning its diagnosis and classification, with the advent of the Rome IV criteria, and management. The primary aim of this guideline, commissioned by the BSG, is to review and summarise the current evidence to inform and guide clinical practice, by providing a practical framework for evidence-based diagnosis and treatment of patients. The approach to investigating the patient presenting with dyspepsia is discussed, and efficacy of drugs in FD summarised based on evidence derived from a comprehensive search of the medical literature, which was used to inform an update of a series of pairwise and network meta-analyses. Specific recommendations have been made according to the Grading of Recommendations Assessment, Development and Evaluation system. These provide both the strength of the recommendations and the overall quality of evidence. Finally, in this guideline, we consider novel treatments that are in development, as well as highlighting areas of unmet need and priorities for future research.

Propulsive colonic contractions are mediated by inhibition-driven poststimulus responses that originate in interstitial cells of Cajal

The peristaltic reflex is a fundamental behavior of the gastrointestinal (GI) tract in which mucosal stimulation activates propulsive contractions. The reflex occurs by stimulation of intrinsic primary afferent neurons with cell bodies in the myenteric plexus and projections to the lamina propria, distribution of information by interneurons, and activation of muscle motor neurons. The current concept is that excitatory cholinergic motor neurons are activated proximal to and inhibitory neurons are activated distal to the stimulus site. We found that atropine reduced, but did not block, colonic migrating motor complexes (CMMCs) in mouse, monkey, and human colons, suggesting a mechanism other than one activated by cholinergic neurons is involved in the generation/propagation of CMMCs. CMMCs were activated after a period of nerve stimulation in colons of each species, suggesting that the propulsive contractions of CMMCs may be due to the poststimulus excitation that follows inhibitory neural responses. Blocking nitrergic neurotransmission inhibited poststimulus excitation in muscle strips and blocked CMMCs in intact colons. Our data demonstrate that poststimulus excitation is due to increased Ca2+ transients in colonic interstitial cells of Cajal (ICC) following cessation of nitrergic, cyclic guanosine monophosphate (cGMP)-dependent inhibitory responses. The increase in Ca2+ transients after nitrergic responses activates a Ca2+-activated Cl− conductance, encoded by Ano1, in ICC. Antagonists of ANO1 channels inhibit poststimulus depolarizations in colonic muscles and CMMCs in intact colons. The poststimulus excitatory responses in ICC are linked to cGMP-inhibited cyclic adenosine monophosphate (cAMP) phosphodiesterase 3a and cAMP-dependent effects. These data suggest alternative mechanisms for generation and propagation of CMMCs in the colon.

Modification of Neurogenic Colonic Motor Behaviours by Chemogenetic Ablation of Calretinin Neurons

How the enteric nervous system determines the pacing and propagation direction of neurogenic contractions along the colon remains largely unknown. We used a chemogenetic strategy to ablate enteric neurons expressing calretinin (CAL). Mice expressing human diphtheria toxin receptor (DTR) in CAL neurons were generated by crossing CAL-ires-Cre mice with Cre-dependent ROSA26-DTR mice. Immunohistochemical analysis revealed treatment with diphtheria toxin incurred a 42% reduction in counts of Hu-expressing colonic myenteric neurons (P = 0.036), and 57% loss of CAL neurons (comprising ∼25% of all Hu neurons; P = 0.004) compared to control. As proportions of Hu-expressing neurons, CAL neurons that contained nitric oxide synthase (NOS) were relatively spared (control: 15 ± 2%, CAL-DTR: 13 ± 1%; P = 0.145), while calretinin neurons lacking NOS were significantly reduced (control: 26 ± 2%, CAL-DTR: 18 ± 5%; P = 0.010). Colonic length and pellet sizes were significantly reduced without overt inflammation or changes in ganglionic density. Interestingly, colonic motor complexes (CMCs) persisted with increased frequency (mid-colon interval 111 ± 19 vs. 189 ± 24 s, CAL-DTR vs. control, respectively, P < 0.001), decreased contraction size (mid-colon AUC 26 ± 24 vs. 59 ± 13 gram/seconds, CAL-DTR vs. control, respectively, P < 0.001), and lacked preferential anterograde migration (P < 0.001). The functional effects of modest calretinin neuron ablation, particularly increased neurogenic motor activity frequencies, differ from models that incur general enteric neuron loss, and suggest calretinin neurons may contribute to pacing, force, and polarity of CMCs in the large bowel.

Vulnerability to acid reflux of the airway epithelium in severe asthma

BACKGROUND

Severe asthma is associated with multiple co-morbidities, including gastro-oesophageal reflux disease (GORD) which can contribute to exacerbation frequency and poor quality of life. Since epithelial dysfunction is an important feature in asthma, we hypothesised that in severe asthma the bronchial epithelium is more susceptible to the effects of acid reflux.

METHODS

We developed an in vitro model of GORD using differentiated bronchial epithelial cells (BECs) from normal or severe asthmatic donors exposed to a combination of pepsin, acid pH, and bile acids using a multiple challenge protocol (MCP-PAB). We also analysed bronchial biopsies and undertook RNA-sequencing of bronchial brushings from controls and severe asthmatics without or with GORD.

RESULTS

Exposure of BECs to the MCP-PAB caused structural disruption, increased permeability, IL-33 expression, inflammatory mediator release and changes in gene expression for multiple biological processes. Cultures from severe asthmatics were significantly more affected than those from healthy donors. Analysis of bronchial biopsies confirmed increased IL-33 expression in severe asthmatics with GORD. RNA-sequencing of bronchial brushings from this group identified 15 of the top 37 dysregulated genes found in MCP-PAB treated BECs, including genes involved in oxidative stress responses.

CONCLUSIONS

By affecting epithelial permeability, GORD may increase exposure of the airway submucosa to allergens and pathogens, resulting in increased risk of inflammation and exacerbations.

CLINICAL IMPLICATION

These results suggest the need for research into alternative therapeutic management of GORD in severe asthma.

Downregulation of ICCs and PDGFRα+ cells on colonic dysmotility in hirschsprung disease

BACKGROUND

To investigate the effect of the distribution and expression of interstitial cells of Cajal (ICCs) and platelet-derived growth factor receptor-α positive (PDGFRα+) cells in different colon segments on colonic motility in children with Hirschsprung disease (HSCR).

METHODS

Smooth muscles of the narrow and dilated segments of the colon were obtained from 16 pediatric patients with HSCR. The proximal margin was set as the control section. The mRNA and protein expressions of c-Kit, PDGFRα, ANO1, and SK3 channels were examined. Circular smooth muscle strips of the colon were prepared for performing electrophysiology experiments using electric field stimulation (EFS) and intervention from different drugs (TTX, NPPB, Apamin, L-NAME, and CyPPA).

RESULTS

The mRNA and protein expressions of c-Kit, ANO1, PDGFRα, and SK3 were much lower in the narrow segment than those in the dilated and proximal segments of the colon. The narrow segment showed a considerably spontaneous contraction of the muscle strip. After the EFS, the relaxation response decreased from the proximal to the narrow segment, whereas the contraction response increased. TTX blocking did not cause any significant changes in the narrow segment. In contrast, when NPPB, Apamin, L-NAME, and CyPPA were used to intervene in the muscle strips, the proximal segment showed a more sensitive inhibitory or excitatory response than the narrow segment.

CONCLUSIONS

Downregulation of the ICCs and PDGFRα+ cells from the proximal to narrow segment may be responsible for the dysmotility of the colon in pediatric HSCR.

Activation of ENS Circuits in Mouse Colon: Coordination in the Mouse Colonic Motor Complex as a Robust, Distributed Control System

The characteristic motor patterns of the colon are coordinated by the enteric nervous system (ENS) and involve enterochromaffin (EC) cells, enteric glia, smooth muscle fibers, and interstitial cells. While the fundamental control mechanisms of colonic motor patterns are understood, greater complexity in the circuitry underlying motor patterns has been revealed by recent advances in the field. We review these recent advances and new findings from our laboratories that provide insights into how the ENS coordinates motor patterns in the isolated mouse colon. We contextualize these observations by describing the neuromuscular system underling the colonic motor complex (CMC) as a robust, distributed control system. Framing the colonic motor complex as a control system reveals a new perspective on the coordinated motor patterns in the colon. We test the control system by applying electrical stimulation in the isolated mouse colon to disrupt the coordination and propagation of the colonic motor complex.

Enteric Control of the Sympathetic Nervous System

The autonomic nervous system that regulates the gut is divided into sympathetic (SNS), parasympathetic (PNS), and enteric nervous systems (ENS). They inhibit, permit, and coordinate gastrointestinal motility, respectively. A fourth pathway, "extrinsic sensory neurons," connect gut to the central nervous system, mediating sensation. The ENS resides within the gut wall and its activities are critical for life; ENS failure to populate the gut in development is lethal without intervention."Viscerofugal neurons" are a distinctive class of enteric neurons, being the only type that escapes the gut wall. They form a unique circuit: their axons project out of the gut wall and activate sympathetic neurons, which then project back to the gut, and inhibit gut movements.For 80 years viscerofugal/sympathetic circuits were thought to have a restricted role, mediating simple sensory-motor reflexes. New data shows viscerofugal and sympathetic neurons behaving unexpectedly, compelling a re-evaluation of these circuits: both viscerofugal and sympathetic neurons transmit higher order, synchronized firing patterns that originate within the ENS. This identifies them as driving long-range motility control between different gut regions.There is need for gut motor control over distances beyond the range of ENS circuits, yet no mechanism has been identified to date. The entero-sympathetic circuits are ideally suited to meet this need. Here we provide an overview of the structure and functions of these peripheral sympathetic circuits, including new data showing the firing patterns generated by enteric networks can transmit through sympathetic neurons.

Evidence for tetrodotoxin-resistant spontaneous myogenic contractions of mouse isolated stomach that are dependent on acetylcholine

Background and Purpose

Gastric pacemaker cells, interstitial cells of Cajal (ICC), are believed to initiate myogenic (non‐neuronal) contractions. These become damaged in gastroparesis, associated with dysrhythmic electrical activity and nausea. We utilised mouse isolated stomach to model myogenic contractions and investigate their origin and actions of interstitial cells of Cajal modulators.

Experimental Approach

Intraluminal pressure was recorded following distension with a physiological volume; tone, contraction amplitude and frequency were quantified. Compounds were bath applied.

Key Results

The stomach exhibited regular large amplitude contractions (median amplitude 9.0 [4.7–14.8] cmH₂O, frequency 2.9 [2.5–3.4] c.p.m; n = 20), appearing to progress aborally. Tetrodotoxin (TTX, 10⁻⁶ M) had no effect on tone, frequency or amplitude but blocked responses to nerve stimulation. ω‐conotoxin GVIA (10⁻⁷ M) ± TTX was without effect on baseline motility. In the presence of TTX, (1) atropine (10⁻¹⁰–10⁻⁶ M) reduced contraction amplitude and frequency in a concentration‐related manner (pIC₅₀ 7.5 ± 0.3 M for amplitude), (2) CaCC channel (previously ANO1) inhibitors MONNA and CaCCinh‐A01 reduced contraction amplitude (significant at 10⁻⁵, 10⁻⁴ M respectively) and frequency (significant at 10⁻⁵ M), and (3), neostigmine (10⁻⁵ M) evoked a large, variable, increase in contraction amplitude, reduced by atropine (10⁻⁸–10⁻⁶ M) but unaffected (exploratory study) by the H1 receptor antagonist mepyramine (10⁻⁶ M).

Conclusions and Implications

The distended mouse stomach exhibited myogenic contractions, resistant to blockade of neural activity by TTX. In the presence of TTX, these contractions were prevented or reduced by compounds blocking interstitial cells of Cajal activity or by atropine and enhanced by neostigmine (antagonised by atropine), suggesting involvement of non‐neuronal ACh in their regulation.

Identification of a novel distension-evoked motility pattern in the mouse uterus

The dynamic changes in uterine contractility in response to distension are incompletely understood. Rhythmic, propagating contractions of nonpregnant uterine smooth muscle occur in the absence of nerve activity (i.e., myogenic), events that decline during pregnancy and reemerge at parturition. We therefore sought to determine how myogenic contractions of the nonpregnant uterus are affected by distension, which might provide mechanistic clues underlying distension-associated uterine conditions such as preterm birth. Uteri isolated from nulliparous adult female mice in proestrus were video imaged to generate spatiotemporal maps, and myoelectrical activity simultaneously recorded using extracellular suction electrodes. Motility patterns were examined under basal conditions and following ramped intraluminal distension with fluid to 5 and 10 cmH₂O. Intraluminal distension caused pressure-dependent changes in the frequency, amplitude, propagation speed, and directionality of uterine contractions, which reversed upon pressure release. Altered burst durations of underlying smooth muscle myoelectric events were concurrently observed, although action potential spike intervals were unchanged. Voltage-gated sodium channel blockade [tetrodotoxin (TTX); 0.6 µM] attenuated both the amplitude of contractions and burst duration of action potentials, whereas all activity was abolished by L-type calcium channel blockade (nifedipine; 1 µM). These data suggest that myogenic motility patterns of the nonpregnant mouse uterus are sensitive to changes in intraluminal pressure and, at high pressures, may be modulated by voltage-gated sodium channel activity. Future studies may investigate whether similar distension-evoked changes occur in the pregnant uterus and the possible pathophysiological role of such activity in the development of preterm birth.

Characterization of alternating neurogenic motor patterns in mouse colon

BACKGROUND

Colonic motor complexes (CMCs) have been widely recorded in the large intestine of vertebrates. We have investigated whether in the smooth muscle, a single unified pattern of electrical activity, or different patterns of electrical activity give rise to the different neurogenic patterns of motility underlying CMCs in vitro.

METHODS

To study differences of the CMCs between proximal and distal colon, we used a novel combination of techniques to simultaneously record muscle diameter and force at multiple sites along the whole mouse colon ex vivo. In addition, electrical activity of smooth muscle was recorded by suction electrodes.

KEY RESULTS

Two distinct types of CMCs were distinguished; CMCs that propagated along the entire colon (complete CMC) and CMCs which were restricted to the proximal colon (incomplete CMC). The two types of CMC often occurred in the same preparations. Incomplete CMCs had longer bursts of smooth muscle action potentials than complete CMCs and propagated more slowly. Interestingly, both types of CMC were associated with similar frequency bursts of smooth muscle action potentials at ~2.4 Hz. In the most proximal colon, an additional firing frequency was detected close to ~7 Hz generating multiple peaks within each CMC.

CONCLUSIONS & INFERENCES

We report distinct characteristics underlying complete and incomplete CMCs in isolated mouse colon. Recognizing these distinct patterns of motility will be important for future interpretation of analysis of murine colonic motility recordings. The identification of alternating patterns of motor activity in proximal colon, but not distal colon may reflect specific neural mechanisms for fecal pellet formation.

Control of colonic motility using electrical stimulation to modulate enteric neural activity

Electrical stimulation of the enteric nervous system (ENS) is an attractive approach to modify gastrointestinal transit. Colonic motor complexes (CMCs) occur with a periodic rhythm, but the ability to elicit a premature CMC depends, at least in part, upon the intrinsic refractory properties of the ENS, which are presently unknown. The objectives of this study were to record myoelectric complexes (MCs, the electrical correlates of CMCs) in the smooth muscle and 1) determine the refractory periods of MCs, 2) inform and evaluate closed-loop stimulation to repetitively evoke MCs, and 3) identify stimulation methods to suppress MC propagation. We dissected the colon from male and female C57BL/6 mice, preserving the integrity of intrinsic circuitry while removing the extrinsic nerves, and measured properties of spontaneous and evoked MCs in vitro. Hexamethonium abolished spontaneous and evoked MCs, confirming the necessary involvement of the ENS for electrically evoked MCs. Electrical stimulation reduced the mean interval between evoked and spontaneous CMCs (24.6 ± 3.5 vs. 70.6 ± 15.7 s, P = 0.0002, n = 7). The absolute refractory period was 4.3 s (95% confidence interval (CI) = 2.8-5.7 s, R2 = 0.7315, n = 8). Electrical stimulation applied during fluid distention-evoked MCs led to an arrest of MC propagation, and following stimulation, MC propagation resumed at an increased velocity (n = 9). The timing parameters of electrical stimulation increased the rate of evoked MCs and the duration of entrainment of MCs, and the refractory period provides insight into timing considerations for designing neuromodulation strategies to treat colonic dysmotility.NEW & NOTEWORTHY Maintained physiological distension of the isolated mouse colon induces rhythmic cyclic myoelectric complexes (MCs). MCs evoked repeatedly by closed-loop electrical stimulation entrain MCs more frequently than spontaneously occurring MCs. Electrical stimulation delivered at the onset of a contraction temporarily suppresses the propagation of MC contractions. Controlled electrical stimulation can either evoke MCs or temporarily delay MCs in the isolated mouse colon, depending on timing relative to ongoing activity.

Advances in colonic motor complexes in mice

The primary functions of the gastrointestinal (GI) tract are to absorb nutrients, water, and electrolytes that are essential for life. This is accompanied by the capability of the GI tract to mix ingested content to maximize absorption and effectively excrete waste material. There have been major advances in understanding intrinsic neural mechanisms involved in GI motility. This review highlights major advances over the past few decades in our understanding of colonic motor complexes (CMCs), the major intrinsic neural patterns that control GI motility. CMCs are generated by rhythmic coordinated firing of large populations of myenteric neurons. Initially, it was thought that serotonin release from the mucosa was required for CMC generation. However, careful experiments have now shown that neither the mucosa nor endogenous serotonin are required, although, evidence suggests enteroendocrine (EC) cells modulate CMCs. The frequency and extent of propagation of CMCs are highly dependent on mechanical stimuli (circumferential stretch). In summary, the isolated mouse colon emerges as a good model to investigate intrinsic mechanisms underlying colonic motility and provides an excellent preparation to explore potential therapeutic agents on colonic motility, in a highly controlled in vitro environment. In addition, during CMCs, the mouse colon facilitates investigations into the emergence of dynamic assemblies of extensive neural networks, applicable to the nervous system of different organisms.

A Novel Mode of Sympathetic Reflex Activation Mediated by the Enteric Nervous System

Enteric viscerofugal neurons provide a pathway by which the enteric nervous system (ENS), otherwise confined to the gut wall, can activate sympathetic neurons in prevertebral ganglia. Firing transmitted through these pathways is currently considered fundamentally mechanosensory. The mouse colon generates a cyclical pattern of neurogenic contractile activity, called the colonic motor complex (CMC). Motor complexes involve a highly coordinated firing pattern in myenteric neurons with a frequency of ∼2 Hz. However, it remains unknown how viscerofugal neurons are activated and communicate with the sympathetic nervous system during this naturally-occurring motor pattern. Here, viscerofugal neurons were recorded extracellularly from rectal nerve trunks in isolated tube and flat-sheet preparations of mouse colon held at fixed circumferential length. In freshly dissected preparations, motor complexes were associated with bursts of viscerofugal firing at 2 Hz that aligned with 2-Hz smooth muscle voltage oscillations. This behavior persisted during muscle paralysis with nicardipine. Identical recordings were made after a 4- to 5-d organotypic culture during which extrinsic nerves degenerated, confirming that recordings were from viscerofugal neurons. Single unit analysis revealed the burst firing pattern emerging from assemblies of viscerofugal neurons differed from individual neurons, which typically made partial contributions, highlighting the importance and extent of ENS-mediated synchronization. Finally, sympathetic neuron firing was recorded from the central nerve trunks emerging from the inferior mesenteric ganglion. Increased sympathetic neuron firing accompanied all motor complexes with a 2-Hz burst pattern similar to viscerofugal neurons. These data provide evidence for a novel mechanism of sympathetic reflex activation derived from synchronized firing output generated by the ENS.

The asymmetric innervation of the circular and longitudinal muscle of the mouse colon differently modulates myogenic slow phasic contractions

BACKGROUND

Neuromuscular transmission has been extensively studied in the circular layer of the mouse colon where a co-transmission of purines acting on P2Y₁ receptors and NO has been previously described. However, the corresponding mechanisms in the longitudinal layer are less known.

METHODS

Electrophysiological and myography techniques were used to evaluate spontaneous phasic contractions (SPC) and neural-mediated responses in the proximal, mid, and distal colon devoid of CD1 mice. Immunohistochemistry against c-kit and PDGFRα was performed in each colonic segment.

KEY RESULTS

SPC were recorded in both muscle layers at a similar frequency being about four contractions per minute (c.p.m.) in the proximal and distal colon compared to the mid colon (2 c.p.m.). In non-adrenergic, non-cholinergic conditions, L-NNA (1 mmol/L) increased contractility in the circular but not in the longitudinal layer. In the longitudinal muscle, both electrophysiological and mechanical neural-mediated inhibitory responses were L-NNA and ODQ (10 µmol/L) sensitive. NaNP (1 µmol/L) caused cessation of SPC and the response was blocked by ODQ. Neither ADPßS (10 µmol/L) nor CYPPA (10 µmol/L), which both targeted the purinergic pathway, altered longitudinal contractions. PDGFRα + cells were located in both muscle layers and were more numerous compared with cKit + cells, which both formed a heterologous cellular network. A decreasing gradient of the PDGFRα labeling was observed along the colon.

CONCLUSION

An inhibitory neural tone was absent in the longitudinal layer and neuronal inhibitory responses were mainly nitrergic. Despite the presence of PDGFRα + cells, purinergic responses were absent. Post-junctional pathways located in different cell types might be responsible for neurotransmitter transduction.

A novel method for quantifying periodicity and time delay in dynamic neural networks using unstable subaction potential threshold depolarizations

Techniques to identify and correlate the propagation of electrical signals (like action potentials) along neural networks are well described, using multisite recordings. In these cases, the waveform of action potentials is usually relatively stable and discriminating relevant electrical signals straightforward. However, problems can arise when attempting to identify and correlate the propagation of signals when their waveforms are unstable (e.g., fluctuations in amplitude or time course). This makes correlation of the degree of synchronization and time lag between propagating electrical events across two or more recording sites problematic. Here, we present novel techniques for the determination of the periodicity of electrical signals at individual sites. When recording from two independent sites, we present novel analytical techniques for joint determination of periodicity and time delay. The techniques presented exploit properties of the cross-correlation function, rather than utilizing the time lag at which the cross-correlation function is maximized. The approach allows determination of directionality of the spread of excitation along a neural network based on measurements of the time delay between recording sites. This new method is particularly applicable to analysis of signals in other biological systems that have unstable characteristics in waveform that show dynamic variability.NEW & NOTEWORTHY The determination of frequency(s) at which two sources are synchronized, and relative time delay between them, is a fundamental problem for a wide a range of signal-processing applications. In this methodology paper, we present novel procedures for periodicity estimation for single time series and joint periodicity and time delay estimation for two time series. The methods use properties of the cross-correlation function rather than the cross-correlation function explicitly.

Diversity of neurogenic smooth muscle electrical rhythmicity in mouse proximal colon

The mechanisms underlying electrical rhythmicity in smooth muscle of the proximal colon are incompletely understood. Our aim was to identify patterns of electrical rhythmicity in smooth muscle of the proximal region of isolated whole mouse colon and characterize their mechanisms of origin. Two independent extracellular recording electrodes were used to record the patterns of electrical activity in smooth muscle of the proximal region of whole isolated mouse colon. Cross-correlation analysis was used to quantify spatial coordination of these electrical activities over increasing electrode separation distances. Four distinct neurogenic patterns of electrical rhythmicity were identified in smooth muscle of the proximal colon, three of which have not been identified and consisted of bursts of rhythmic action potentials at 1-2 Hz that were abolished by hexamethonium. These neurogenic patterns of electrical rhythmicity in smooth muscle were spatially and temporally synchronized over large separation distances (≥2 mm rosto-caudal axis). Myogenic slow waves could be recorded from the same preparations, but they showed poor spatial and temporal coordination over even short distances (≤1 mm rostro-caudal axis). It is not commonly thought that electrical rhythmicity in gastrointestinal smooth muscle is dependent upon the enteric nervous system. Here, we identified neurogenic patterns of electrical rhythmicity in smooth muscle of the proximal region of isolated mouse colon, which are dependent on synaptic transmission in the enteric nervous system. If the whole colon is studied in vitro, recordings can preserve novel neurogenic patterns of electrical rhythmicity in smooth muscle.NEW & NOTEWORTHY Previously, it has not often been thought that electrical rhythmicity in smooth muscle of the gastrointestinal tract is dependent upon the enteric nervous system. We identified patterns of electrical rhythmicity in smooth muscle of the mouse proximal colon that were abolished by hexamethonium and involved the temporal synchronization of smooth muscle membrane potential over large spatial fields. We reveal different patterns of electrical rhythmicity in colonic smooth muscle that are dependent on the ENS.

First translational consensus on terminology and definitions of colonic motility in animals and humans studied by manometric and other techniques

Alterations in colonic motility are implicated in the pathophysiology of bowel disorders, but high-resolution manometry of human colonic motor function has revealed that our knowledge of normal motor patterns is limited. Furthermore, various terminologies and definitions have been used to describe colonic motor patterns in children, adults and animals. An example is the distinction between the high-amplitude propagating contractions in humans and giant contractions in animals. Harmonized terminology and definitions are required that are applicable to the study of colonic motility performed by basic scientists and clinicians, as well as adult and paediatric gastroenterologists. As clinical studies increasingly require adequate animal models to develop and test new therapies, there is a need for rational use of terminology to describe those motor patterns that are equivalent between animals and humans. This Consensus Statement provides the first harmonized interpretation of commonly used terminology to describe colonic motor function and delineates possible similarities between motor patterns observed in animal models and humans in vitro (ex vivo) and in vivo. The consolidated terminology can be an impetus for new research that will considerably improve our understanding of colonic motor function and will facilitate the development and testing of new therapies for colonic motility disorders.

Vagus Nerve Stimulation at the Interface of Brain-Gut Interactions

The vagus nerve, a key component of the cross-communication between the gut and the brain, is a major element of homeostasis sensing the "milieu intérieur" and boosting the nervous and endocrine responses to maintain the gastrointestinal health status. This nerve has anti-inflammatory properties regulating the gut through the activation of the hypothalamic-pituitary-adrenal axis and the release of cortisol and through a vagovagal reflex, which has an anti-tumor necrosis factor (TNF) effect called the cholinergic anti-inflammatory pathway. Stimulating this nerve is an interesting tool as a nondrug therapy for the treatment of gastrointestinal diseases in which brain-gut communication is dysfunctional, such as inflammatory bowel disorders and others. This review presents the rationale of vagal gastrointestinal physiology and diseases and the most recent advances in vagus nerve stimulation. It also highlights the main issues to be addressed in the future to improve this bioelectronic therapy for gastrointestinal disorders.

Protocol for a scoping review study to identify and map treatments for dysphagia following moderate to severe acquired brain injury

INTRODUCTION

Dysphagia is highly prevalent in patients with acquired brain injury (ABI) and is associated with high morbidity and mortality. However, dysphagia management varies greatly between units and internationally, and there is currently no consensus, standard intervention or treatment. A review mapping the existing literature on dysphagia treatment is needed. In this paper, the protocol for a scoping review to identify and map dysphagia treatment following ABI is outlined.

OBJECTIVE

The objective of the scoping review is to systematically map the existing research literature to answer the research question: Which non-surgical, non-pharmacological interventions are used in the treatment of dysphagia in patients with moderate and severe acquired brain injury in the acute and subacute phase? METHODS AND ANALYSIS: The methodological framework for the study is based on methodology by Arksey and O'Malley and methodological advancement by Levac et al. We will search electronic databases in June 2019: MEDLINE (Ovid); Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library); EMBASE (Ovid); CINAHL (EBSCO); PsycINFO; Science Citation Index Expanded on Web of Science; OTseeker; Speechbite and PEDro. The search terms will be limited to patients with moderate to severe ABI and dysphagia. Four review authors will independently conduct an initial screening of title and abstract and subsequent full-text review of included studies. Data will be extracted and summarised in diagrammatic or tabular form (numerical summary), and a descriptive format (narrative summary). The strategy for data synthesis entails qualitative methods to categorise the interventions based on the treatment modality and subgroup diagnosis.

ETHICS AND DISSEMINATION

Scoping the existing literature will provide a foundation for further evaluating and developing our dysphagia treatment and inform future studies assessing the effectiveness of treatments. The review is part of an ongoing expansive research into dysphagia. The results will be disseminated through a peer-reviewed publication and conference presentations.

Cell-specific effects of nitric oxide on the efficiency and frequency of long distance contractions in murine colon

BACKGROUND

Nitric oxide (NO) mediates inhibitory neurotransmission and is a critical component of neuronal programs that generate propulsive contractions. NO acts via its receptor NO-sensitive guanylyl cyclase (NO-GC) which is expressed in smooth muscle cells (SMC) and interstitial cells of Cajal (ICC). Organ bath studies with colonic rings from NO-GC knockout mice (GCKO) have indicated NO-GC to modulate spontaneous contractions. The cell-specific effects of NO-GC on the dominant pan-colonic propulsive contraction, the long distance contractions (LDCs), of whole colon preparations have not yet been described.

METHODS

Contractions of whole colon preparations from wild type (WT), global, and cell-specific GCKO were recorded. After transformation into spatiotemporal maps, motility patterns were analyzed. Simultaneous perfusion of the colon enabled the correlation of outflow with LDCs to analyze contraction efficiency.

KEY RESULTS

Deletion of NO-GC in both ICC and SMC (ie, in GCKO and SMC/ICC-GCKO) caused loss of typical LDC activity and instead generated high-frequency LDC-like contractions with inefficient propulsive activity. Frequency was also increased in WT, SMC-GCKO, and ICC-GCKO colon in the presence of L-NAME to block neuronal NO synthase. LDC efficiency was dependent on NO-GC in SMC as it was reduced in GCKO, SMC-GCKO, and ICC/SMC-GCKO colon; LDC efficiency was decreased in all genotypes in the presence of L-NAME.

CONCLUSIONS AND INFERENCES

NO/cGMP signaling is critical for normal peristaltic movements; as NO-GC in both SMC and ICC is essential, both cell types appear to work in synchrony. The efficiency of contractions to expel fluid is particularly influenced by NO-GC in SMC.

Identification of multiple distinct neurogenic motor patterns that can occur simultaneously in the guinea pig distal colon

In the guinea pig distal colon, nonpropulsive neurally mediated motor patterns have been observed in different experimental conditions. Isolated segments of guinea pig distal colon were used to investigate these neural mechanisms by simultaneously recording wall motion, intraluminal pressure, and smooth muscle electrical activity in different conditions of constant distension and in response to pharmacological agents. Three distinct neurally dependent motor patterns were identified: transient neural events (TNEs), cyclic motor complexes (CMC), and distal colon migrating motor complexes (DCMMC). These could occur simultaneously and were distinguished by their electrophysiological, mechanical, and pharmacological features. TNEs occurred at irregular intervals of ~3s, with bursts of action potentials at 9 Hz. They propagated orally at 12 cm/s via assemblies of ascending cholinergic interneurons that activated final excitatory and inhibitory motor neurons, apparently without involvement of stretch-sensitive intrinsic primary afferent neurons. CMCs occurred during maintained distension and consisted of clusters of closely spaced TNEs, which fused to cause high-frequency action potential firing at 7 Hz lasting ~10 s. They generated periodic pressure peaks mediated by stretch-sensitive intrinsic primary afferent neurons and by cholinergic interneurons. DCMMCs were generated by ongoing activity in excitatory motor neurons without apparent involvement of stretch-sensitive neurons, cholinergic interneurons, or inhibitory motor neurons. In conclusion, we have identified three distinct motor patterns that can occur concurrently in the isolated guinea pig distal colon. The mechanisms underlying the generation of these neural patterns likely involve recruitment of different populations of enteric neurons with distinct temporal activation properties.

Different distributions of interstitial cells of Cajal and platelet-derived growth factor receptor-α positive cells in colonic smooth muscle cell/interstitial cell of Cajal/platelet-derived growth factor receptor-α positive cell syncytium in mice

AIM

To investigate the distribution and function of interstitial cells of Cajal (ICCs) and platelet-derived growth factor receptor-α positive (PDGFRα⁺) cells in the proximal and distal colon.

METHODS

The comparison of colonic transit in the proximal and distal ends was performed by colonic migrating motor complexes (CMMCs). The tension of the colonic smooth muscle was examined by smooth muscle spontaneous contractile experiments with both ends of the smooth muscle strip tied with a silk thread. Intracellular recordings were used to assess electrical field stimulation (EFS)-induced inhibitory junction potentials (IJP) on the colonic smooth muscle. Western blot analysis was used to examine the expression levels of ICCs and PDGFRα in the colonic smooth muscle.

RESULTS

Treatment with NG-nitro-L-arginine methyl ester hydrochloride (L-NAME) significantly increased the CMMC frequency and spontaneous contractions, especially in the proximal colon, while treatment with MRS2500 increased only distal CMMC activity and smooth muscle contractions. Both CMMCs and spontaneous contractions were markedly inhibited by NPPB, especially in the proximal colon. Accordingly, CyPPA sharply inhibited the distal contraction of both CMMCs and spontaneous contractions. Additionally, the amplitude of stimulation-induced nitric oxide (NO)/ICC-dependent slow IJPs (sIJPs) by intracellular recordings from the smooth muscles in the proximal colon was larger than that in the distal colon, while the amplitude of electric field stimulation-induced purinergic/PDGFRα-dependent fast IJPs (fIJPs) in the distal colon was larger than that in the proximal colon. Consistently, protein expression levels of c-Kit and anoctamin-1 (ANO1) in the proximal colon were much higher, while protein expression levels of PDGFRα and small conductance calcium-activated potassium channel 3 (SK3) in the distal colon were much higher.

CONCLUSION

The ICCs are mainly distributed in the proximal colon and there are more PDGFRα⁺ cells are in the distal colon, which generates a pressure gradient between the two ends of the colon to propel the feces to the anus.

Optogenetic Induction of Colonic Motility in Mice

BACKGROUND & AIMS

Strategies are needed to increase gastrointestinal transit without systemic pharmacologic agents. We investigated whether optogenetics, focal application of light to control enteric nervous system excitability, could be used to evoke propagating contractions and increase colonic transit in mice.

METHODS

We generated transgenic mice with Cre-mediated expression of light-sensitive channelrhodopsin-2 (ChR2) in calretinin neurons (CAL-ChR2 Cre+ mice); Cre- littermates served as controls. Colonic myenteric neurons were analyzed by immunohistochemistry, patch-clamp, and calcium imaging studies. Motility was assessed by mechanical, electrophysiological, and video recording in vitro and by fecal output in vivo.

RESULTS

In isolated colons, focal light stimulation of calretinin enteric neurons evoked classic polarized motor reflexes (50/58 stimulations), followed by premature anterograde propagating contractions (39/58 stimulations). Light stimulation could evoke motility from sites along the entire colon. These effects were prevented by neural blockade with tetrodotoxin (n = 2), and did not occur in control mice (n = 5). Light stimulation of proximal colon increased the proportion of natural fecal pellets expelled over 15 minutes in vitro (75% ± 17% vs 32% ± 8% for controls) (P < .05). In vivo, activation of wireless light-emitting diodes implanted onto the colon wall significantly increased hourly fecal pellet output in conscious, freely moving mice (4.2 ± 0.4 vs 1.3 ± 0.3 in controls) (P < .001).

CONCLUSIONS

In studies of mice, we found that focal activation of a subset of enteric neurons can increase motility of the entire colon in vitro, and fecal output in vivo. Optogenetic control of enteric neurons might therefore be used to modify gut motility.

Identification of a Rhythmic Firing Pattern in the Enteric Nervous System That Generates Rhythmic Electrical Activity in Smooth Muscle

The enteric nervous system (ENS) contains millions of neurons essential for organization of motor behavior of the intestine. It is well established that the large intestine requires ENS activity to drive propulsive motor behaviors. However, the firing pattern of the ENS underlying propagating neurogenic contractions of the large intestine remains unknown. To identify this, we used high-resolution neuronal imaging with electrophysiology from neighboring smooth muscle. Myoelectric activity underlying propagating neurogenic contractions along murine large intestine [also referred to as colonic migrating motor complexes, (CMMCs)] consisted of prolonged bursts of rhythmic depolarizations at a frequency of ∼2 Hz. Temporal coordination of this activity in the smooth muscle over large spatial fields (∼7 mm, longitudinally) was dependent on the ENS. During quiescent periods between neurogenic contractions, recordings from large populations of enteric neurons, in mice of either sex, revealed ongoing activity. The onset of neurogenic contractions was characterized by the emergence of temporally synchronized activity across large populations of excitatory and inhibitory neurons. This neuronal firing pattern was rhythmic and temporally synchronized across large numbers of ganglia at ∼2 Hz. ENS activation preceded smooth muscle depolarization, indicating rhythmic depolarizations in smooth muscle were controlled by firing of enteric neurons. The cyclical emergence of temporally coordinated firing of large populations of enteric neurons represents a unique neural motor pattern outside the CNS. This is the first direct observation of rhythmic firing in the ENS underlying rhythmic electrical depolarizations in smooth muscle. The pattern of neuronal activity we identified underlies the generation of CMMCs.SIGNIFICANCE STATEMENT How the enteric nervous system (ENS) generates neurogenic contractions of smooth muscle in the gastrointestinal (GI) tract has been a long-standing mystery in vertebrates. It is well known that myogenic pacemaker cells exist in the GI tract [called interstitial cells of Cajal (ICCs)] that generate rhythmic myogenic contractions. However, the mechanisms underlying the generation of rhythmic neurogenic contractions of smooth muscle in the GI tract remains unknown. We developed a high-resolution neuronal imaging method with electrophysiology to address this issue. This technique revealed a novel pattern of rhythmic coordinated neuronal firing in the ENS that has never been identified. Rhythmic neuronal firing in the ENS was found to generate rhythmic neurogenic depolarizations in smooth muscle that underlie contraction of the GI tract.

Nitrergic signaling via interstitial cells of Cajal and smooth muscle cells influences circular smooth muscle contractility in murine colon

BACKGROUND

Regulation of gastrointestinal motility involves excitatory and inhibitory neurotransmission. Nitric oxide (NO), the major inhibitory neurotransmitter, acts via its receptor NO-sensitive guanylyl cyclase (NO-GC). In the GI tract, NO-GC is expressed in several cell types such as smooth muscle cells (SMC) and interstitial cells of Cajal (ICC). Using cell-specific knockout mice, we have previously shown that NO-GC modulates spontaneous contractions in colonic longitudinal smooth muscle. However, its detailed role in the colonic circular smooth muscle is still unclear.

METHODS

Myography was performed to evaluate spontaneous contractions in rings of proximal colon (2.5 mm) from global (GCKO) and cell-specific knockout mice for NO-GC. Immunohistochemistry and in situ hybridization were used to specify NO-GC expression.

KEY RESULTS

Colonic circular smooth muscle showed three different contraction patterns: high-frequency ripples, slow phasic contractions, and large contractions. Ripples formed independently of NO-GC. Slow phasic contractions occurred intermittently in WT, SMC-GCKO, and ICC-GCKO tissue, whereas they were more prominent and prolonged in GCKO and SMC/ICC-GCKO tissue. Tetrodotoxin and the NO-GC inhibitor ODQ transformed slow phasic contractions of WT and single cell-specific knockout into GCKO-like contractions. ODQ increased the frequency of large contractions in WT and ICC-GCKO colon but not in GCKO, SMC-GCKO, and SMC/ICC-GCKO preparations. Tetrodotoxin and hexamethonium abolished large contractions.

CONCLUSIONS AND INFERENCES

We conclude that short rings of murine colon can be effectively used to record spontaneous contractions. Although NO-GC in SMC determines smooth muscle tone, concerted action of NO-GC in both SMC and ICC modulates slow phasic contractions and large contractions.

Synaptic activation of putative sensory neurons by hexamethonium-sensitive nerve pathways in mouse colon

The gastrointestinal tract contains its own independent population of sensory neurons within the gut wall. These sensory neurons have been referred to as intrinsic primary afferent neurons (IPANs) and can be identified by immunoreactivity to calcitonin gene-related peptide (CGRP) in mice. A common feature of IPANs is a paucity of fast synaptic inputs observed during sharp microelectrode recordings. Whether this is observed using different recording techniques is of particular interest for understanding the physiology of these neurons and neural circuit modeling. Here, we imaged spontaneous and evoked activation of myenteric neurons in isolated whole preparations of mouse colon and correlated recordings with CGRP and nitric oxide synthase (NOS) immunoreactivity, post hoc. Calcium indicator fluo 4 was used for this purpose. Calcium responses were recorded in nerve cell bodies located 5-10 mm oral to transmural electrical nerve stimuli. A total of 618 recorded neurons were classified for CGRP or NOS immunoreactivity. Aboral electrical stimulation evoked short-latency calcium transients in the majority of myenteric neurons, including ~90% of CGRP-immunoreactive Dogiel type II neurons. Activation of Dogiel type II neurons had a time course consistent with fast synaptic transmission and was always abolished by hexamethonium (300 μM) and by low-calcium Krebs solution. The nicotinic receptor agonist 1,1-dimethyl-4-phenylpiperazinium iodide (during synaptic blockade) directly activated Dogiel type II neurons. The present study suggests that murine colonic Dogiel type II neurons receive prominent fast excitatory synaptic inputs from hexamethonium-sensitive neural pathways. NEW & NOTEWORTHY Myenteric neurons in isolated mouse colon were recorded using calcium imaging and then neurochemically defined. Short-latency calcium transients were detected in >90% of calcitonin gene-related peptide-immunoreactive neurons to electrical stimulation of hexamethonium-sensitive pathways. Putative sensory Dogiel type II calcitonin gene-related peptide-immunoreactive myenteric neurons may receive widespread fast synaptic inputs in mouse colon.