Normal and abnormal electrical propagation in the small intestine

Small Intestinal Slow Wave Dysrhythmia and Blunted Postprandial Responses in Diabetic Rats

BACKGROUND

Gastric dysmotility and gastric slow wave dysrhythmias have been well documented in patients with diabetes. However, little is known on the effect of hyperglycemia on small intestine motility, such as intestinal slow waves, due to limited options in measuring its activity. Moreover, food intake and digestion process have been reported to alter the small intestine motility in normal rats, but their roles in that of diabetic rats remains unknown. This study aimed to explore the effect of hyperglycemia on small intestinal myoelectrical activity (IMA) and responses to various meals in diabetic and normal rats.

METHODS

IMA was recorded via chronically implanted serosal electrodes in the proximal small intestine in rats with type 2 diabetes induced by high-fat diet feeding followed by a low dose of streptozotocin (30 mg/kg) and normal rats. The percentage of normal slow wave (%NSW), dominant power, and dominant frequency (DF) were assessed from the IMA under various conditions. Oral glucose tolerance test was performed, and blood was collected via the tail vein at baseline and 15, 30, 60, 90, 120, and 180 min after glucose administration for the measurement of blood glucose. Regular laboratory chow, high-fat diet, and small or large nutrient liquid meal were used to explore IMA responses to different meals in diabetic and normal rats.

RESULTS

(1) Compared with a postprandial increase in DF in normal rats (p = 0.007), diabetic rats showed a blunted postprandial response in DF (p = 0.145) after a regular chow. However, no difference was found in %NSW between diabetic and normal rats in both fasting and fed states; (2) In the fasting state, %NSW was correlated with the blood glucose level in diabetic rats (r = -0.817, p = 0.004, N = 8) as well as HbA1C (r = -0.871, p = 0.005, N = 8). After glucose administration, the increase in blood glucose was correlated with a decrease in %NSW (r = -0.655, p < 0.001, N = 8). (3) %NSW in diabetic rats during the 30-min postprandial state was not altered after a meal, either liquid or solid, regular or high-fat diet, small or large meal, suggesting an absence of gastric-small intestinal reflex.

CONCLUSIONS

In type 2 diabetic rats, the regularity of intestinal slow waves is negatively correlated with the blood glucose level in both fasting and fed states. Diabetic rats exhibit a blunted postprandial response in intestinal slow waves compared with normal rats. There seems to be a lack of gastric-small intestinal reflex upon food ingestion in diabetic rats.

Effects of Multiple High-Dose Methamphetamine Administration on Enteric Dopaminergic Neurons and Intestinal Motility in the Rat Model

Several studies have identified the effects of methamphetamine (MA) on central dopaminergic neurons, but its effects on enteric dopaminergic neurons (EDNs) are unclear. The aim of this study was to investigate the effects of MA on EDNs and intestinal motility. Male Sprague-Dawley rats were randomly divided into MA group and saline group. The MA group received the multiple high-dose MA treatment paradigm, while the controls received the same saline treatment. After enteric motility was assessed, different intestinal segments (i.e., duodenum, jejunum, ileum, and colon) were taken for histopathological, molecular biological, and immunological analysis. The EDNs were assessed by measuring the expression of two dopaminergic neuronal markers, dopamine transporter (DAT) and tyrosine hydroxylase (TH), at the transcriptional and protein levels. We also used c-Fos protein, a marker of neural activity, to detect the activation of EDNs. MA resulted in a significant reduction in TH and DAT mRNA expression as well as in the number of EDNs in the duodenum and jejunum (p < 0.05). MA caused a dramatic increase in c-Fos expression of EDNs in the ileum (p < 0.001). The positional variability of MA effects on EDNs paralleled the positional variability of its effect on intestinal motility, as evidenced by the marked inhibitory effect of MA on small intestinal motility (p < 0.0001). This study found significant effects of MA on EDNs with locational variability, which might be relevant to locational variability in the potential effects of MA on intestinal functions, such as motility.

The bioelectrical conduction system around the ileocecal junction defined through in vivo high-resolution mapping in rabbits

Coordinated contractions across the small and large intestines via the ileocecal junction (ICJ) are critical to healthy gastrointestinal function and are in part governed by myoelectrical activity. In this study, the spatiotemporal characteristics of the bioelectrical conduction across the ICJ and its adjacent regions were quantified in anesthetized rabbits. High-resolution mapping was applied from the terminal ileum (TI) to the sacculus rotundus (SR), across the ICJ and into the beginning of the large intestine at the cecum ampulla coli (AC). Orally propagating slow wave patterns in the SR did not entrain the TI. However, aborally propagating patterns from the TI were able to entrain the SR. Bioelectrical activity was recorded within the ICJ and AC, revealing complex interactions of slow waves, spike bursts, and bioelectrical quiescence. This suggests the involvement of myogenic coordination when regulating motility between the small and large intestines. Mean slow wave frequency between regions did not vary significantly (13.74-17.16 cycles/min). Slow waves in the SR propagated with significantly faster speeds (18.51 ± 1.57 mm/s) compared with the TI (14.05 ± 2.53 mm/s, P = 0.0113) and AC (9.56 ± 1.56 mm/s, P = 0.0001). Significantly higher amplitudes were observed in both the TI (0.28 ± 0.13 mV, P = 0.0167) and SR (0.24 ± 0.08 mV, P = 0.0159) within the small intestine compared with the large intestine AC (0.03 ± 0.01 mV). We hypothesize that orally propagating slow waves facilitate a motor-brake pattern in the SR to limit outflow into the ICJ, similar to those previously observed in other gastrointestinal regions.NEW & NOTEWORTHY Competing slow wave pacemakers were observed in the terminal ileum and sacculus rotundus. Prevalent oral propagation in the sacculus rotundus toward the terminal ileum potentially acts as a brake mechanism limiting outflow. Slow waves and periods of quiescence at the ileocecal junction suggest that activation may depend on the coregulatory flow and distention pathways. Slow waves and spike bursts in the cecum impart a role in the coordination of motility.

Characterization of Slow Wave Activity in Ex-vivo Porcine Small Intestine Segments

The motility of the gut is central to digestion and is coordinated, in part, by bioelectrical events known as slow waves. While the nature of these events is well defined in-vivo, the temporal response of ex-vivo gastrointestinal myoelectrical activity without perfusion is poorly understood. To achieve a fundamental understanding of ex-vivo electrophysiology, slow wave activity was measured from excised porcine intestinal segments and characterized over time. In this study, slow wave frequencies and amplitudes, along with the duration of sustained activity were quantified. Slow wave amplitudes and frequencies decreased from initial values of 46 ± 34 µV and 9.6 ± 5.9 cpm to electrical quiescence over a period of 12.2 ± 2.3 minutes. Mean slow wave amplitude and frequency uniformly declined before electrical quiescence was reached. This study demonstrated the successful acquisition of gastrointestinal myoelectrical activity in excised tissue segments without perfusion. Key slow wave characteristics may contribute to future diagnostics, transplantations and treatments for motility disorders.Clinical Relevance- The ability to characterize excised slow wave activity in organs lacking perfusion will be a critical advancement in developing clinical solutions. Findings will assist in establishing the efficacy of bioelectrical activity in excised tissue samples for organ transplantation. In addition, the ex-vivo setting can be used to represent compromised electrophysiological states to evaluate novel therapies.

A pipeline for phase-based analysis of in vitro micro-electrode array recordings of gastrointestinal slow waves

Motility of the gastrointestinal tract (GI) is governed by an bioelectrical event termed slow waves. Accurately measuring the characteristics of GI slow waves is critical to understanding its role in clinical applications. High-resolution (HR) bioelectrical mapping involves placing a spatially dense array of electrodes directly over the surface of the GI wall to record the spatiotemporal changes in slow waves. A micro-electrode array (MEA) with spatial resolution of 200 μm in an 8x8 configuration was employed to record intestinal slow waves using isolated tissues from small animals including rodents, shrews and ferrets. A filtering, processing, and analytic pipeline was developed to extract useful metrics from the recordings. The pipeline relied on CWT and Hilbert Transform to identify the frequency and phase of the signals, from which the individual activation times of slow waves were identified and clustered using k-means. A structural similarity index was applied to group the major activation patterns. Overall, the pipeline identified 91 cycles of slow waves from 300 s of recordings in mice, with an average frequency of 20.68 ± 0.71 cpm, amplitude of 7.94 ± 2.15 µV, and velocity of 3.64 ± 1.75 mm s^-1. Three major propagation patterns were identified during this period. The findings of this study will inform the development of a high throughput software platform for future in vitro pharmacological studies using the MEA.

Bioelectrical Signals for the Diagnosis and Therapy of Functional Gastrointestinal Disorders

Coordinated contractions and motility patterns unique to each gastrointestinal organ facilitate the digestive process. These motor activities are coordinated by bioelectrical events, sensory and motor nerves, and hormones. The motility problems in the gastrointestinal tract known as functional gastrointestinal disorders (FGIDs) are generally caused by impaired neuromuscular activity and are highly prevalent. Their diagnosis is challenging as symptoms are often vague and difficult to localize. Therefore, the underlying pathophysiological factors remain unknown. However, there is an increasing level of research and clinical evidence suggesting a link between FGIDs and altered bioelectrical activity. In addition, electroceuticals (bioelectrical therapies to treat diseases) have recently gained significant interest. This paper gives an overview of bioelectrical signatures of gastrointestinal organs with normal and/or impaired motility patterns and bioelectrical therapies that have been developed for treating FGIDs. The existing research evidence suggests that bioelectrical activities could potentially help to identify the diverse etiologies of FGIDs and overcome the drawbacks of the current clinically adapted methods. Moreover, electroceuticals could potentially be effective in the treatment of FGIDs and replace the limited existing conventional therapies which often attempt to treat the symptoms rather than the underlying condition.

Characteristics of myoelectrical activities along the small intestine and their responses to test meals of different glycemic index in rats

The purpose of this study was to characterize intestinal myoelectrical activity along the small intestine and investigate its responses to test meals with different glycemic index at different locations. Sixteen rats were implanted with electrodes in the serosal surface of the duodenum, jejunum, and ileum. Intestinal myoelectrical activities were recorded from these electrodes for 30 min in the fasting state and 3 h after four kinds of meals with different glycemic index, together with the assessment of blood glucose. The results were as follows: 1) in the fasting state, the percentage of normal intestinal slow waves (%NISW) showed no difference; however, the dominant frequency (DF), power (DP), and percentage of spike activity superimposed on the intestinal slow wave (NS/M) were progressively decreased along the entire small intestine; 2) regular solid meal and Ensure solicited no changes in any parameters of intestinal myoelectrical activity; whereas glucose and glucose + glucagon significantly altered the %NISW, DF, DP, and NS/M, and the effects on the proximal intestine were opposite to those in the distal intestine; and 3) postprandial blood glucose level was significantly correlated with %NISW along the entire small intestine. We found that that, in addition to the well-known frequency gradient, there is also a gradual decrease in the DP and spikes along the small intestine in the fasting state. Glucose and hyperglycemic meals inhibit myoelectrical activities in the proximal small intestine but result in enhanced but more dysrhythmic intestinal myoelectrical activities. There is a significant negative correlation between the normality of intestinal slow waves and blood glucose.

Dynamic slow-wave interactions in the rabbit small intestine defined using high-resolution mapping

BACKGROUND

The motility in the small intestine is governed in part by myogenic bio-electrical events, known as slow waves. High-resolution multi-electrode mapping has improved our understanding of slow-wave propagation in the small intestine but has been applied in a limited number of in vivo animal studies. This study applied high-resolution mapping to investigate slow waves in the rabbit small intestine.

METHODS

A high-resolution flexible printed circuit board array (256 electrodes; 4 mm spacing) was applied in vivo to the rabbit intestine. Extracellular slow-wave activity was acquired sequentially along the length of the intestine.

KEY RESULTS AND CONCLUSIONS

The majority of the slow waves propagated in the antegrade direction (56%) while retrograde patterns were primarily observed in the distal intestine (29%). Colliding slow-wave events were observed across the length of the small intestine (15%). The interaction of competing pacemakers was mapped in spatiotemporal detail. The frequency and velocity of the slow waves were highest in the duodenum compared to ileum (20.0 ± 1.2 cpm vs 10.5 ± 0.9 cpm, P < 0.001; 14.4 ± 3.4 mm/s vs 12.3 ± 3.4 mm/s; P < 0.05).

INFERENCES

In summary, extracellular serosal slow-wave activity was quantified spatiotemporally along the length of the rabbit intestine. In particular, the study provides evidence toward the presence and interaction of slow-wave pacemakers acting along the small intestine and how they may contribute to the slow-wave frequency gradient along the length of the intestine.

Characteristics of Intestinal Myoelectrical and Motor Activities in Diet-Induced Obese Rats: Obesity and Motility

BACKGROUND

Gastrointestinal motility has been reported to be altered in obesity. However, it is unknown whether intestinal myoelectrical activity (IMA) is also changed in obesity.

AIMS

The aim of this study was to characterize intestinal myoelectrical and motility activities in the fasting state, during feeding, and postprandial state after various test meals in diet-induced obese (DIO) rats in comparison with regular rats.

METHODS

IMA was recorded in the fasting, feeding, and postprandial states in DIO and regular rats. Regular laboratory chow, high-fat solid food, and high-fat liquid food were used to test IMA responses to different meals.

RESULTS

(1) The intestinal slow waves in the DIO rats were not different from those in normal rats in the fasting or postprandial state. Neither intestinal transit nor the number of intestinal contractions per minute was altered in DIO rats although gastric emptying was accelerated. (2) Both DIO rats and normal rats showed altered IMA during the first minute of feeding (cephalic stimulation). (3) The intestinal slow waves in both DIO rats and regular rats were impaired slightly but significantly after intake of a high-fat meal.

CONCLUSIONS

Our study demonstrates that intestinal myoelectrical activity is not altered in DIO rats and its postprandial responses to various meals are not altered either. High-fat meals induce intestinal dysrhythmia but do not have a chronic impact on intestinal slow waves in DIO rats.

Recent advances in intestinal smooth muscle research: from muscle strips and single cells, via ICC networks to whole organ physiology and assessment of human gut motor dysfunction

Gastrointestinal smooth muscle research has evolved from studies on muscle strips to spatiotemporal mapping of whole organ motor and electrical activities. Decades of research on single muscle cells and small sections of isolated musculature from animal models has given us the groundwork for interpretation of human in vivo studies. Human gut motility studies have dramatically improved by high-resolution manometry and high-resolution electrophysiology. The details that emerge from spatiotemporal mapping of high-resolution data are now of such quality that hypotheses can be generated as to the physiology (in healthy subjects) and pathophysiology (in patients) of gastrointestinal (dys) motility. Such interpretation demands understanding of the musculature as a super-network of excitable cells (neurons, smooth muscle cells, other accessory cells) and oscillatory cells (the pacemaker interstitial cells of Cajal), for which mathematical modeling becomes essential. The developing deeper understanding of gastrointestinal motility will bring us soon to a level of precision in diagnosis of dysfunction that is far beyond what is currently available.

Phase waves and trigger waves: emergent properties of oscillating and excitable networks in the gut

The gut is enmeshed by a number of cellular networks, but there is only a limited understanding of how these networks generate the complex patterns of activity that drive gut contractile functions. Here we review two fundamental types of cell behaviour, excitable and oscillating, and the patterns that networks of such cells generate, trigger waves and phase waves, respectively. We use both the language of biophysics and the theory of nonlinear dynamics to define these behaviours and understand how they generate patterns. Based on this we look for evidence of trigger and phase waves in the gut, including some of our recent work on the small intestine.

Intra-operative high-resolution mapping of slow wave propagation in the human jejunum: Feasibility and initial results

BACKGROUND

Bioelectrical slow waves are a coordinating mechanism of small intestine motility, but extracellular human studies have been restricted to a limited number of sparse electrode recordings. High-resolution (HR) mapping has offered substantial insights into spatiotemporal intestinal slow wave dynamics, but has been limited to animal studies to date. This study aimed to translate intra-operative HR mapping to define pacemaking and conduction profiles in the human small intestine.

METHODS

Immediately following laparotomy, flexible-printed-circuit arrays were applied around the serosa of the proximal jejunum (128-256 electrodes; 4-5.2 mm spacing; 28-59 cm² ). Slow wave propagation patterns were mapped, and frequencies, amplitudes, downstroke widths, and velocities were calculated. Pacemaking and propagation patterns were defined.

KEY RESULTS

Analysis comprised nine patients with mean recording duration of 7.6 ± 2.8 minutes. Slow waves occurred at a frequency of 9.8 ± 0.4 cpm, amplitude 0.3 ± 0.04 mV, downstroke width 0.5 ± 0.1 seconds, and with faster circumferential velocity than longitudinal (10.1 ± 0.8 vs 9.0 ± 0.7 mm/s; P = .001). Focal pacemakers were identified and mapped (n = 4; mean frequency 9.9 ± 0.2 cpm). Disordered slow wave propagation was observed, including wavefront collisions, conduction blocks, and breakout and entrainment of pacemakers.

CONCLUSIONS & INFERENCES

This study introduces HR mapping of human intestinal slow waves, and provides first descriptions of intestinal pacemaker sites and velocity anisotropy. Future translation to other intestinal regions, disease states, and postsurgical dysmotility holds potential for improving the basic and clinical understanding of small intestine pathophysiology.

Reduced interstitial cells of Cajal and increased intraepithelial lymphocytes are associated with development of small intestinal bacterial overgrowth in post-infectious IBS mouse model

OBJECTIVE

Intestinal dysmotility and immune activation are likely involved in the pathogenesis of small intestinal bacteria overgrowth (SIBO) in irritable bowel syndrome (IBS). We aimed at investigating the role of interstitial cells of Cajal (ICC) and intestinal inflammation in the development of SIBO using a post-infectious IBS (PI-IBS) mouse model.

MATERIALS AND METHODS

NIH mice were randomly infected with Trichinella spiralis. Visceral sensitivity and stool pattern were assessed at 8-weeks post-infection (PI). Intestinal bacteria counts from jejunum and ileum were measured by quantitative real-time PCR to evaluate the presence of SIBO. ICC density, intraepithelial lymphocytes (IELs) counts, and intestinal cytokine levels (IL1-β, IL-6, toll-like receptor-4 (TLR-4), IL-10) in the ileum were examined.

RESULTS

PI-IBS mice demonstrated increased visceral sensitivity compared with the control group. One-third of the PI-IBS mice developed SIBO (SIBO+/PI-IBS) and was more likely to have abnormal stool form compared with SIBO negative PI-IBS (SIBO-/PI-IBS) mice but without difference in visceral sensitivity. SIBO+/PI-IBS mice had decreased ICC density and increased IELs counts in the ileum compared with SIBO-/PI-IBS mice. No difference in inflammatory cytokine expression levels were detected among the groups except for increased TLR-4 in PI-IBS mice compared with the control group.

CONCLUSIONS

Development of SIBO in PI-IBS mice was associated with reduced ICC density and increased IELs counts in the ileum. Our findings support the role of intestinal dysmotility and inflammation in the pathogenesis of SIBO in IBS and may provide potential therapeutic targets.

Minimally invasive wireless motility capsule to study canine gastrointestinal motility and pH

The aim of this study was to describe the feasibility of using a gastrointestinal tract wireless motility capsule (WMC) that measured intraluminal pressure, pH and transit time through the gastrointestinal tract, in dogs in their home environment. Forty-four adult healthy dogs, eating a standard diet, were prospectively enrolled. The WMC was well tolerated by all dogs and provided data from the different sections of the gastrointestinal tract. Median gastric emptying time was 20h (range, 6.3-119h), demonstrating a large range. The gastric pressure pattern and pH depended on the phase of food consumption. The small bowel transit time was 3.1h (range, 1.6-5.4h) with average contraction pressures of 6.5mmHg (range, 1.1-21.4mmHg) and pH 7.8 (range, 7-8.9). The large bowel transit time was 21h (range, 1-69h) with average contractions pressures of 0.9mmHg (range, 0.3-2.7mmHg) and pH 6.4 (range, 5.3-8.2). There was considerable individual variation in motility patterns and transit times between dogs. No difference was observed between the sexes. No relationships between any transit time, bowel pH or pressure pattern and bodyweights were identified. The WMC likely represents movement of a large non-digestible particle rather than normal ingesta. Due to its large size, the WMC should not be use in smaller dogs. The WMC is a promising minimally invasive tool to assess GIT solid phase transit times, pressures and pH. However, further studies are necessary due to the current limitations observed.

Problems with extracellular recording of electrical activity in gastrointestinal muscle

Motility patterns of the gastrointestinal tract are important for efficient processing of nutrients and waste. Peristalsis and segmentation are based on rhythmic electrical slow waves that generate the phasic contractions fundamental to gastrointestinal motility. Slow waves are generated and propagated actively by interstitial cells of Cajal (ICC), and these events conduct to smooth muscle cells to elicit excitation-contraction coupling. Extracellular electrical recording has been utilized to characterize slow-wave generation and propagation and abnormalities that might be responsible for gastrointestinal motility disorders. Electrode array recording and digital processing are being used to generate data for models of electrical propagation in normal and pathophysiological conditions. Here, we discuss techniques of extracellular recording as applied to gastrointestinal organs and how mechanical artefacts might contaminate these recordings and confound their interpretation. Without rigorous controls for movement, current interpretations of extracellular recordings might ascribe inaccurate behaviours and electrical anomalies to ICC networks and gastrointestinal muscles, bringing into question the findings and validity of models of gastrointestinal electrophysiology developed from these recordings.

Pancreatic islet blood flow and its measurement

Pancreatic islets are richly vascularized, and islet blood vessels are uniquely adapted to maintain and support the internal milieu of the islets favoring normal endocrine function. Islet blood flow is normally very high compared with that to the exocrine pancreas and is autonomously regulated through complex interactions between the nervous system, metabolites from insulin secreting β-cells, endothelium-derived mediators, and hormones. The islet blood flow is normally coupled to the needs for insulin release and is usually disturbed during glucose intolerance and overt diabetes. The present review provides a brief background on islet vascular function and especially focuses on available techniques to measure islet blood perfusion. The gold standard for islet blood flow measurements in experimental animals is the microsphere technique, and its advantages and disadvantages will be discussed. In humans there are still no methods to measure islet blood flow selectively, but new developments in radiological techniques hold great hopes for the future.

The virtual intestine: in silico modeling of small intestinal electrophysiology and motility and the applications

The intestine comprises a long hollow muscular tube organized in anatomically and functionally discrete compartments, which digest and absorb nutrients and water from ingested food. The intestine also plays key roles in the elimination of waste and protection from infection. Critical to all of these functions is the intricate, highly coordinated motion of the intestinal tract, known as motility, which is coregulated by hormonal, neural, electrophysiological and other factors. The Virtual Intestine encapsulates a series of mathematical models of intestinal function in health and disease, with a current focus on motility, and particularly electrophysiology. The Virtual Intestine is being cohesively established across multiple physiological scales, from sub/cellular functions to whole organ levels, facilitating quantitative evaluations that present an integrative in silico framework. The models are also now finding broad physiological applications, including in evaluating hypotheses of slow wave pacemaker mechanisms, smooth muscle electrophysiology, structure-function relationships, and electromechanical coupling. Clinical applications are also beginning to follow, including in the pathophysiology of motility disorders, diagnosing intestinal ischemia, and visualizing colonic dysfunction. These advances illustrate the emerging potential of the Virtual Intestine to effectively address multiscale research challenges in interdisciplinary gastrointestinal sciences.

Slow wave conduction patterns in the stomach: from Waller's foundations to current challenges

This review provides an overview of our understanding of motility and slow wave propagation in the stomach. It begins by reviewing seminal studies conducted by Walter Cannon and Augustus Waller on in vivo motility and slow wave patterns. Then our current understanding of slow wave patterns in common laboratory animals and humans is presented. The implications of slow wave arrhythmic patterns that have been recorded in animals and patients suffering from gastroparesis are discussed. Finally, current challenges in experimental methods and techniques, slow wave modulation and the use of mathematical models are discussed.