Interstitial cells of Cajal and human colon motility in health and disease.

Our understanding of human colonic motility, and autonomic reflexes that generate motor patterns, has increased markedly through high-resolution manometry. Details of the motor patterns are emerging related to frequency and propagation characteristics that allow linkage to interstitial cells of Cajal (ICC) networks. In studies on colonic motor dysfunction requiring surgery, ICC are almost always abnormal or significantly reduced. However, there are still gaps in our knowledge about the role of ICC in the control of colonic motility and there is little understanding of a mechanistic link between ICC abnormalities and colonic motor dysfunction. This review will outline the various ICC networks in the human colon and their proven and likely associations with the enteric and extrinsic autonomic nervous systems. Based on our extensive knowledge of the role of ICC in the control of gastrointestinal motility of animal models and the human stomach and small intestine, we propose how ICC networks are underlying the motor patterns of the human colon. The role of ICC will be reviewed in the autonomic neural reflexes that evoke essential motor patterns for transit and defecation. Mechanisms underlying ICC injury, maintenance, and repair will be discussed. Hypotheses are formulated as to how ICC dysfunction can lead to motor abnormalities in slow transit constipation, chronic idiopathic pseudo-obstruction, Hirschsprung's disease, fecal incontinence, diverticular disease, and inflammatory conditions. Recent studies on ICC repair after injury hold promise for future therapies.

The Sphincter of O'Beirne-Part 2: Report of a Case of Chronic Constipation with Autonomous Dyssynergia.

BACKGROUND: Chronic constipation can have one or more of many etiologies, and a diagnosis based on symptoms is not sufficient as a basis for treatment, in particular surgery. AIM: To investigate the cause of chronic constipation in a patient with complete absence of spontaneous bowel movements. METHODS: High-resolution colonic manometry was performed to assess motor functions of the colon, rectum, the sphincter of O'Beirne and the anal sphincters. RESULTS: Normal colonic motor patterns were observed, even at baseline, but a prominent high-pressure zone at the rectosigmoid junction, the sphincter of O'Beirne, was consistently present. In response to high-amplitude propagating pressure waves (HAPWs) that were not consciously perceived, the sphincter and the anal sphincters would not relax and paradoxically contract, identified as autonomous dyssynergia. Rectal bisacodyl evoked marked HAPW activity with complete relaxation of the sphincter of O'Beirne and the anal sphincters, indicating that all neural pathways to generate the coloanal reflex were intact but had low sensitivity to physiological stimuli. A retrograde propagating cyclic motor pattern initiated at the sphincter of O'Beirne, likely contributing to failure of content to move into the rectum. CONCLUSIONS: Chronic constipation without the presence of spontaneous bowel movements can be associated with normal colonic motor patterns but a highly exaggerated pressure at the rectosigmoid junction: the sphincter of O'Beirne, and failure of this sphincter and the anal sphincters to relax associated with propulsive motor patterns. The sphincter of O'Beirne can be an important part of the pathophysiology of chronic constipation.

A myogenic motor pattern in mice lacking myenteric interstitial cells of Cajal explained by a second coupled oscillator network.

The interstitial cells of Cajal associated with the myenteric plexus (ICC-MP) are a network of coupled oscillators in the small intestine that generate rhythmic electrical phase waves leading to corresponding waves of contraction, yet rhythmic action potentials and intercellular calcium waves have been recorded from c-kit-mutant mice that lack the ICC-MP, suggesting that there may be a second pacemaker network. The gap junction blocker carbenoxolone induced a "pinstripe" motor pattern consisting of rhythmic "stripes" of contraction that appeared simultaneously across the intestine with a period of ~4 s. The infinite velocity of these stripes suggested they were generated by a coupled oscillator network, which we call X. In c-kit mutants rhythmic contraction waves with the period of X traveled the length of the intestine, before the induction of the pinstripe pattern by carbenoxolone. Thus X is not the ICC-MP and appears to operate under physiological conditions, a fact that could explain the viability of these mice. Individual stripes consisted of a complex pattern of bands of contraction and distension, and between stripes there could be slide waves and v waves of contraction. We hypothesized that these phenomena result from an interaction between X and the circular muscle that acts as a damped oscillator. A mathematical model of two chains of coupled Fitzhugh-Nagumo systems, representing X and circular muscle, supported this hypothesis. The presence of a second coupled oscillator network in the small intestine underlines the complexity of motor pattern generation in the gut.NEW & NOTEWORTHY Physiological experiments and a mathematical model indicate a coupled oscillator network in the small intestine in addition to the c-kit-expressing myenteric interstitial cells of Cajal. This network interacts with the circular muscle, which itself acts as a system of damped oscillators, to generate physiological contraction waves in c-kit (W) mutant mice.

Cancer pain and neuropathic pain are associated with A ß sensory neuronal plasticity in dorsal root ganglia and abnormal sprouting in lumbar spinal cord.

Evidence suggests that there are both nociceptive and neuropathic components of cancer-induced pain. We have observed that changes in intrinsic membrane properties and excitability of normally non-nociceptive Aß sensory neurons are consistent in rat models of peripheral neuropathic pain and cancer-induced pain. This has prompted a comparative investigation of the intracellular electrophysiological characteristics of sensory neurons and of the ultrastructural morphology of the dorsal horn in rat models of neuropathic pain and cancer-induced pain. Neuropathic pain model rats were induced with a polyethylene cuff implanted around a sciatic nerve. Cancer-induced pain model rats were induced with mammary rat metastasis tumour-1 rat breast cancer or MATLyLu rat prostate cancer cells implanted into the distal epiphysis of a femur. Behavioural evidence of nociception was detected using von Frey tactile assessment. Aß-fibre low threshold mechanoreceptor neurons in both cancer-induced pain and neuropathic pain models exhibited slower dynamics of action potential genesis, including a wider action potential duration and lower action potential amplitude compared to those in control animals. Enhanced excitability of Aß-fibre low threshold mechanoreceptor neurons was also observed in cancer-induced pain and neuropathic pain models. Furthermore, both cancer-induced pain and neuropathic pain models showed abundant abnormal axonal sprouting in bundles of myelinated axons in the ipsilateral spinal laminae IV and V. The patterns of changes show consistency between rat models of cancer-induced pain and neuropathic pain. These findings add to the body of evidence that animal models of cancer-induced pain and neuropathic pain share features that may contribute to the peripheral and central sensitization and tactile hypersensitivity in both pain states.

Rat model of cancer-induced bone pain: changes in nonnociceptive sensory neurons in vivo.

INTRODUCTION: Clinical data on cancer-induced bone pain (CIBP) suggest extensive changes in sensory function. In a previous investigation of an animal model of CIBP, we have observed that changes in intrinsic membrane properties and excitability of dorsal root ganglion (DRG) nociceptive neurons correspond to mechanical allodynia and hyperalgesia. OBJECTIVES: To investigate the mechanisms underlying changes in nonnociceptive sensory neurons in this model, we have compared the electrophysiological properties of primary nonnociceptive sensory neurons at <1 and >2 weeks after CIBP model induction with properties in sham control animals. METHODS: Copenhagen rats were injected with 106 MAT-LyLu rat prostate cancer cells into the distal femur epiphysis to generate a model of CIBP. After von Frey tactile measurement of mechanical withdrawal thresholds, the animals were prepared for acute electrophysiological recordings of mechanically sensitive neurons in the DRG in vivo. RESULTS: The mechanical withdrawal threshold progressively decreased in CIBP model rats. At <1 week after model induction, there were no changes observed in nonnociceptive Aß-fiber DRG neurons between CIBP model rats and sham rats. However, at >2 weeks, the Aß-fiber low-threshold mechanoreceptors (LTMs) in CIBP model rats exhibited a slowing of the dynamics of action potential (AP) genesis, including wider AP duration and lower AP amplitude compared with sham rats. Furthermore, enhanced excitability of Aß-fiber LTM neurons was observed as an excitatory discharge in response to intracellular injection of depolarizing current into the soma. CONCLUSION: After induction of the CIBP model, Aß-fiber LTMs at >2 weeks but not <1 week had undergone changes in electrophysiological properties. Importantly, changes observed are consistent with observations in models of peripheral neuropathy. Thus, Aß-fiber nonnociceptive primary sensory neurons might be involved in the peripheral sensitization and tumor-induced tactile hypersensitivity in CIBP.

Ionized calcium-binding adaptor molecule 1 positive macrophages and HO-1 up-regulation in intestinal muscularis resident macrophages.

Small intestinal muscularis externa macrophages have been associated with interstitial cells of Cajal. They have been proposed to play various roles in motility disorders and to take part in a microbiota-driven regulation of gastrointestinal motility. Our objective was to understand the reaction of resident macrophages of the musculature to a pro-inflammatory stimulator, lipopolysaccharide (LPS). Mice were injected with LPS or saline and sacrificed after 6 hr. Whole mounts were stained with antibodies toward CD169, ionized calcium-binding adaptor molecule 1 (iba1) (microglial/macrophage marker) and heme oxygenase-1 (HO-1). Cell densities were measured using unbiased stereology. RESULTS: iba1pos cells showed an overall higher density than CD169pos and HO-1pos cells. Most HO-1pos and iba1pos cells were positive for CD 169 in serosa and at Auerbach's plexus (AP). At the deep muscular plexus, mainly iba1pos cells were present, and were mostly CD169neg ; a few HO-1pos cells were present. CONCLUSIONS: A new subset of resident macrophages in the intestinal muscularis externa was discovered, identified as iba1pos CD169neg . HO-1 is constitutively present in most macrophages in serosa and at AP, suggesting a M2 phenotype. LPS-treatment results in an up-regulation of HO-1pos /CD169neg cells in serosa and at AP. Anat Rec, 300:1114-1122, 2017. © 2016 The Authors. The Anatomical Record published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.

Ano1 is a better marker than c-Kit for transcript analysis of single interstitial cells of Cajal in culture.

The interstitial cells of Cajal (ICC) drive the slow wave-associated contractions in the small intestine. A commonly used marker for these cells is c-Kit, but another marker named Ano1 was recently described. This study uses single-cell RT-PCR, qPCR and immunohistochemistry to determine if Ano1 could be reliably used as a molecular marker for ICC in single-cell mRNA analysis. Here, we report on the relationship between the expression of c-Kit and Ano1 in single ICC in culture. We observed that Ano1 is expressed in more than 60% of the collected cells, whereas c-Kit is found only in 22% of the cells (n = 18). When we stained ICC primary cultures for c-KIT and ANO1 protein, we found complete co-localization in all the preparations. We propose that this difference is due to the regulation of c-Kit mRNA in culture. This regulation gives rise to low levels of its transcript, while Ano1 is expressed more prominently in culture on day 4. We also propose that Ano1 is more suitable for single-cell expression analysis as a marker for cell identity than c-Kit at the mRNA level. We hope this evidence will help to validate and increase the success of future studies characterizing single ICC expression patterns.

Discrepancies between c-Kit positive and Ano1 positive ICC-SMP in the W/Wv and wild-type mouse colon; relationships with motor patterns and calcium transients.

BACKGROUND: Interstitial cells of Cajal associated with the submuscular plexus (ICC-SMP) generate omnipresent slow-wave activity in the colon and are associated with prominent motor patterns. Our aim was to investigate colon motor dysfunction in W/W(v) mice in which the ICC are reportedly reduced. METHODS: Whole organ colon motility was studied using spatio-temporal mapping; immunohistochemical staining was carried out for c-Kit and Ano1; calcium imaging was applied to ICC-SMP. KEY RESULTS: Discrepancies between Ano1 and c-Kit staining were found in both wild-type and W/W(v) colon. ICC-SMP were reduced to ~50% in the W/W(v) mouse colon according to c-Kit immunohistochemistry, but Ano1 staining indicated a normal network of ICC-SMP. The latter was consistent with rhythmic calcium transients occurring at the submucosal border of the colon in W/W(v) mice, similar to the rhythmic transients in wild-type ICC-SMP. Furthermore, the motor pattern associated with ICC-SMP pacemaking, the so-called 'ripples' were normal in the W/W(v) colon. CONCLUSIONS & INFERENCES: c-Kit is not a reliable marker for quantifying ICC-SMP in the mouse colon. Ano1 staining revealed a normal network of ICC-SMP consistent with the presence of a normal 'ripples' motor pattern. We detected a class of Ano1 positive c-Kit negative cells that do not depend on Kit expression for maintenance, a feature shared with ICC progenitors.

Interstitial Cells of Cajal: Pathology, injury and repair.

Interstitial cells of cajal (ICC) are specialised cells located within the musculature of the gastrointestinal tract (GIT). Although they form only 5% of the cells in the musculature of the GIT, they play a critical role in regulating smooth muscle function and GIT motility in coordination with the enteric nervous system. C-kit is a transmembrane glycoprotein that plays a critical role in ICC development and maturation. Physiological conditions such as ageing, as well as pathological conditions that have different disease processes, negatively affect ICC networks and function. Absent or disordered ICC networks can be associated with disorders in GIT motility. This review highlights the mechanism of ICC recovery from various types of injury which entails understanding the development of ICC and the factors affecting it. ICC transformation into malignant tumours (gastrointestinal stromal tumours) and their potential as contributors to therapeutic resistance is also discussed.

On the origin of rhythmic calcium transients in the ICC-MP of the mouse small intestine.

Interstitial cells of Cajal associated with the myenteric plexus (ICC-MP) are pacemaker cells of the small intestine, producing the characteristic omnipresent electrical slow waves, which orchestrate peristaltic motor activity and are associated with rhythmic intracellular calcium oscillations. Our objective was to elucidate the origins of the calcium transients. We hypothesized that calcium oscillations in the ICC-MP are primarily regulated by the sarcoplasmic reticulum (SR) calcium release system. With the use of calcium imaging, study of the effect of T-type calcium channel blocker mibefradil revealed that T-type channels did not play a major role in generating the calcium transients. 2-Aminoethoxydiphenyl borate, an inositol 1,4,5 trisphosphate receptor (IP(3)R) inhibitor, and U73122, a phospholipase C inhibitor, both drastically decreased the frequency of calcium oscillations, suggesting a major role of IP(3) and IP(3)-induced calcium release from the SR. Immunohistochemistry proved the expression of IP(3)R type I (IP(3)R-I), but not type II (IP(3)R-II) and type III (IP(3)R-III) in ICC-MP, indicating the involvement of the IP(3)R-I subtype in calcium release from the SR. Cyclopiazonic acid, a SR/endoplasmic reticulum calcium ATPase pump inhibitor, strongly reduced or abolished calcium oscillations. The Na-Ca exchanger (NCX) in reverse mode is likely involved in refilling the SR because the NCX inhibitor KB-R7943 markedly reduced the frequency of calcium oscillations. Immunohistochemistry revealed 100% colocalization of NCX and c-Kit in ICC-MP. Testing a mitochondrial NCX inhibitor, we were unable to show an essential role for mitochondria in regulating calcium oscillations in the ICC-MP. In summary, ongoing IP(3) synthesis and IP(3)-induced calcium release from the SR, via the IP(3)R-I, are the major drivers of the calcium transients associated with ICC pacemaker activity. This suggests that a biochemical clock intrinsic to ICC determines the pacemaker frequency, which is likely directly linked to kinetics of the IP(3)-activated SR calcium channel and IP(3) metabolism.

Interstitial cells of Cajal: pacemaker cells of the pancreatic duct?

OBJECTIVES: Ramon y Cajal discovered interstitial cells in the pancreas associated with intrinsic nerves. It was our aim to provide evidence for or against the hypothesis that the pancreatic duct harbors interstitial cells of Cajal (ICCs) that may function as pacemakers for duct motility. METHODS: We used immunohistochemistry using c-Kit as the ICC marker and protein gene product 9.5 for nerves. Electron microscopy further characterized the cells and their interrelationships. RESULTS: c-Kit-positive cells were associated with smooth muscle cells and nerve fibers of the duct wall and were rich in mitochondria, rough endoplasmic reticulum, and intermediate filaments; they possessed occasional caveolae and had a discontinuous basal lamina. They were connected by small gap junctions to each other and to smooth muscle cells. c-Kit-positive cells around large blood vessels were similar. c-Kit-positive cells within acini were similar in structure but were not associated with smooth muscle cells. CONCLUSIONS: The c-Kit-positive cells around the main duct were identified as ICCs and have the morphological criteria to likely function as pacemaker cells for the previously observed spontaneous rhythmic pancreatic duct contractions. Interstitial cells of Cajal around the large blood vessels likely affect vessel wall rhythmicity.

Ether-a-go-go-related gene 3 is the main candidate for the E-4031-sensitive potassium current in the pacemaker interstitial cells of Cajal.

The interstitial cells of Cajal (ICC), as pacemaker cells of the gut, contribute to rhythmic peristalsis and muscle excitability through initiation of slow-wave activity, which subsequently actively propagates into the musculature. An E-4031-sensitive K(+) current makes a critical contribution to membrane potential in ICC. This study provides novel features of this current in ICC in physiological solutions and seeks to identify the channel isoform. In situ hybridization and Kit immunohistochemistry were combined to assess ether-a-go-go-related gene (ERG) mRNA expression in ICC in mouse jejunum, while the translated message was assessed by immunofluorescence colocalization of ERG and Kit proteins. E-4031-sensitive currents in cultured ICC were studied by the whole cell patch-clamp method, with physiological K(+) concentration in the bath and the pipette. In situ hybridization combined with Kit immunohistochemistry detected m-erg1 and m-erg3, but not m-erg2, mRNA in ICC. ERG3 protein was colocalized with Kit-immunoreactive ICC in jejunum sections, but ERG1 protein was visualized only in the smooth muscle cells. At physiological K(+) concentration, the E-4031-sensitive outward current in ICC was different from its counterpart in cardiac and gut smooth muscle cells. In particular, inactivation upon depolarization and recovery from inactivation by hyperpolarization were modest in ICC. In summary, the E-4031-sensitive currents influence the kinetics of the pacemaker activity in ICC and contribute to maintenance of the resting membrane potential in smooth muscle cells, which together constitute a marked effect on tissue excitability. Whereas this current is mediated by ERG1 in smooth muscle, it is primarily mediated by ERG3 in ICC.

Nitric oxide decreases the excitability of interstitial cells of Cajal through activation of the BK channel.

Nitrergic nerves are structurally and functionally associated with ICC. To further understand mechanisms of communication, the hypothesis was investigated that NO might affect large conductance K channels. To that end, we searched for IbTX-sensitive currents in ICC obtained through explant cultures from the mouse small intestine and studied effects of the NOS inhibitor omega N-nitro-L-arginine (LNNA) and the NO donor sodium nitroprusside (SNP). IbTX-sensitive currents acquired in the whole-cell configuration through nystatin perforated patches exhibited high noise levels but relatively low amplitude, whereas currents obtained in the conventional whole-cell configuration exhibited less noise and higher amplitudes; depolarization from -80 to + 40 mV evoked 357 +/- 159 pA current in the nystatin perforated patch configuration and 1075 +/- 597 pA using the conventional whole-cell configuration. Immunohistochemistry showed that ICC associated with ganglia and Auerbach's plexus nerve fibers were immunoreactive to BK antibodies. The IbTX-sensitive currents were increased by SNP and inhibited by LNNA. BK blockers suppressed spontaneous transit outward currents in ICC. After block of BK currents, or before these currents became prominent, calcium currents were activated by depolarization in the same cells. Their peak amplitude occurred at -25 mV and the currents were increased with increasing extracellular calcium and inhibited by cobalt. The hypothesis is warranted that nitrergic innervation inhibits ICC excitability in part through activation of BK channels. In addition, NO is an intracellular regulator of ICC excitability.

Increase in stretch-induced rhythmic motor activity in the diabetic rat colon is associated with loss of ICC of the submuscular plexus.

Diabetes affects many aspects of gastrointestinal motility, in part due to changes in interstitial cells of Cajal (ICC). The effect of diabetes on the colon, however, is not well characterized, and the aim of the present study was to investigate possible relationships between altered colonic motility as a consequence of streptozotocin-induced diabetes and injury to ICC. Physiological, immunohistochemical, and ultrastructural techniques were employed. The motor pattern of the rat colon was dominated by rhythmic high-amplitude, low-frequency contractions that were primarily myogenic in origin. These rhythmic contractions were induced by stretch associated with increased tension; the amplitude of the superimposed rhythmic contractions increased with increasing applied tension. In diabetic rats, the stretch-induced rhythmic contractile activity remained robust and of similar frequency but was significantly higher in amplitude compared with that in control rats. At 700 mg of applied tension, the force of contraction in circular colonic muscle strips of the diabetic rats was 370% of control values. This robust presence of low-frequency contractions is consistent with the unaffected pacemaker, the ICC associated with Auerbach's plexus, and the increased amplitude correlates with loss of and injury to ICC of the submuscular plexus and intramuscular ICC. Loss of inhibitory nitrergic nerves does not appear to be a factor based on unaltered nNOS immunoreactivity.

Muscarinic regulation of ether-a-go-go-related gene K+ currents in interstitial cells of Cajal.

The interstitial cells of Cajal (ICC) of the myenteric plexus generate a set of currents that evoke a pacemaker potential that sets the initial conditions for the contraction frequency and duration of the electrically coupled intestinal musculature. The synapse-like contacts between ICC and myenteric motor nerves highlight the potential role of the enteric nervous system in regulating the pacemaking currents in ICC. The objective of the present study was to investigate muscarinic regulation of the ether-a-go-go-related gene (ERG) K(+) current. Immunoreactivity of the M(3) receptor (M(3)R) but not the M(2) receptor was detected on murine jejunal ICC-Auerbach's plexus (ICC-AP). The muscarinic agonist bethanechol reduced hyperpolarization-evoked peak ERG currents at -100 mV by 23 +/- 1% and increased both fast and slow time constants of deactivation, resulting in increased steady-state currents between -55 and -35 mV. Bethanechol also increased depolarization-evoked steady-state currents by 59 +/- 10% at -40 mV, whereas currents were decreased at potentials positive to 0 mV. The half-maximal voltage of activation was shifted 11.9 mV leftward. Interestingly, the time constant of activation increased only at -40 mV. Atropine prevented and 2 muM E4031 [1-[2-(6-methyl-2-pyridyl)-ethyl-4-(methylsulfonylaminobenzoyl)piperidine] inhibited bethanechol-affected currents. The effect of bethanechol was mimicked by protein kinase C (PKC) activation and diminished by PKC inhibition. Our results indicate that the ERG K(+) channel in ICC is affected by stimulation of muscarinic receptors, probably the M(3)R, via a PKC-dependent mechanism. Modulation of the ERG K(+) current in ICC-AP will affect the kinetics of pacemaking in the intestinal musculature.

About the presence of interstitial cells of Cajal outside the musculature of the gastrointestinal tract.

Santiago Ramon y Cajal observed a special cell type that appeared to function as endstructures of the intrinsic nervous system in several organs. These cells were structurally and functionally further characterized in the gut musculature and named interstitial cells of Cajal (ICC). In recent years, interstitial cells have been identified in the vasculature, urinary tract, glands and other organs. Their morphologies and functions are just beginning to be clarified. It is likely that amongst them, subtypes will be discovered that warrant the classification of interstitial cells of Cajal. This "point of view" continues the discussion on the criteria that should be used to identify ICC outside the musculature of the gut.

ERG K+ currents regulate pacemaker activity in ICC.

Ether-à-go-go-related gene (ERG) K channels have been implicated in the generation of pacemaker activities in the heart. To study the presence and function of ERG K channels in the pacemaker cells of the small intestine [the interstitial cells of Cajal (ICC)], a combination of patch-clamp techniques, tissue and live cell immunohistochemistry, RT-PCR, and in vitro functional studies were performed. Nonenzymatically isolated ICC in culture were identified by vital staining and presence of rhythmic inward currents. RT-PCR showed the presence of ERG mRNA in the intestinal musculature, and immunohistochemistry on tissue and cultured cells demonstrated that protein similar to human ERG was concentrated on ICC in the Auerbach's plexus region. Whole cell ERG K+ currents were evoked on hyperpolarization from 0 mV (but not from -70 mV) up to -120 mV and showed strong inward rectification. The currents were inhibited by E-4031, cisapride, La3+, and Gd3+ but not by 50 microM Ba2+. The ERG K+ inward current had a typical transient component with fast activation and inactivation kinetics followed by significant steady-state current. E-4031 also inhibited tetraethylammonium (TEA)-insensitive outward current indicating that the ERG K+ current is operating at depolarizing potentials. In contrast to TEA, blockers of the ERG K+ currents caused marked increase in tissue excitability as reflected by an increase in slow-wave duration and an increase in superimposed action potential activity. In summary, ERG K channels in ICC contribute to the membrane potential and play a role in regulation of pacemaker activity of the small intestine.

Pathology of interstitial cells of Cajal in relation to inflammation revealed by ultrastructure but not immunohistochemistry.

The role of interstitial cells of Cajal associated with Auerbach's plexus (ICC-AP) in the pathophysiology of inflammation-induced abnormalities in gut motor activity is poorly understood. Therefore we applied a well-described model of inflammation (infection by Trichinella spiralis) to the mouse small intestine where the structure and function of ICC-AP are best known. Electron microscopic evaluation revealed that 1 to 3 days after infection, selective and patchy damage to the ICC processes occurred, thereby disrupting contacts between these ICC and smooth muscle cells as well as ICC and nerves, which was associated with disordered electrical activity and abnormal peristalsis. Ten to 15 days after infection, damage to ICC-AP was maximal and now involving the cell body and major processes. Marked synthetic activity and regrowth of their processes occurred from day 3 onward and recovery was completed at day 40 after infection. No changes to the network of ICC-AP were seen with c-Kit immunohistochemistry. From day 1 after infection, macrophages infiltrated the AP area, making close contact including peg-and-socket-like junctions with smooth muscle cells and ICC-AP but up to day 6 after infection without any sign of phagocytosis. By day 6 after infection, lymphocytes entered the musculature forming close contacts with ICC-AP. This was not associated with damage to ICC-AP but with proliferation of rough endoplasmic reticulum. From day 23 onward, immune cells withdrew from the musculature except macrophages, resulting in a markedly increased population of macrophages in the AP area at day 60 after infection.