Enhanced responses of the anterior cingulate cortex neurones to colonic distension in viscerally hypersensitive rats

The role of experimental models in developing new treatments for irritable bowel syndrome

Irritable bowel syndrome (IBS) is characterized by chronic, recurrent abdominal pain and altered bowel habits and is currently defined by symptom criteria and the absence of detectable organic disease. The underlying pathophysiology remains incompletely understood. Despite considerable efforts by the scientific community and the pharmaceutical industry to develop novel pharmacological treatments aimed at chronic visceral pain, the traditional approach to identifying and evaluating novel drugs for this target have largely failed to translate into effective IBS treatments. However, several novel drugs aimed at normalizing bowel movements have produced clinical effects, not only on the primary target, but also on pain and discomfort. While some of the commonly used experimental animal models for the pain dimension of IBS have some face and construct validity, the predictive validity of most of the models is either unknown, or has been disappointing. A reverse translational approach is proposed, which is based on identification and characterization of brain endophenotypes in patients, followed by translation of these endophenotypes for pharmacological studies in rodent models.

Ascending multisynaptic pathways from the trigeminal ganglion to the anterior cingulate cortex

By means of retrograde transneuronal transport of rabies virus, ascending multisynaptic pathways from the trigeminal ganglion (TG) to the anterior cingulate cortex (ACC) were identified in the rat. After rabies injection into an electrophysiologically defined trigeminal projection region of the ACC, transsynaptic labeling of second-order neurons via the medial thalamus (including the parafascicular nucleus) was located in the spinal trigeminal nucleus pars caudalis. Third-order neuron labeling occurred in the TG. Most of these TG neurons were medium- or large-sized cells giving rise to myelinated Aδ or Aβ afferent fibers, respectively. By contrast, TG neurons labeled transsynaptically from the orofacial region of the primary somatosensory cortex contained many small cells associated with unmyelinated C afferent fibers. Furthermore, the TG neurons retrogradely labeled with fluorogold injected into the mental nerve were smaller in their sizes compared to those labeled with rabies. Our extracellular unit recordings revealed that a majority of ACC neurons responded to trigeminal nerve stimulation with latencies of shorter than 20ms. Thus, somatosensory information conveyed to the ACC by multisynaptic ascending pathways derived predominantly from myelinated primary afferents (i.e., the medial nociceptive system) and may be used to subserve affective-motivational aspects of pain. Lack of overlap with the lateral nociceptive system is notable and suggests that the medial and lateral nociceptive systems perform separate and non-overlapping functions.

The role of brain-derived neurotrophic factor in experimental inflammation of mouse gut

Previous studies suggested that brain-derived neurotrophic factor (BDNF) might act as an important modulator in chronic pain states. However, no systematic study has used knock-out mice to clarify its effect on visceral sensitivity. In the present study, 2,4,6-trinitrobenzene sulfonic acid (TNBS) was administered to heterozygous (BDNF(+/-)) knock-out and wild-type (BDNF(+/+)) mice to induce colitis. Visceral response to colorectal distension (CRD) and bladder reactivity were recorded. Results demonstrated that in normal state, BDNF(+/-) and BDNF(+/+) mice did not differ in the visceral response to CRD at <60 mm Hg pressure and the bladder reactivity; however, with 60 mm Hg pressure, BDNF(+/-) mice showed a weaker visceral response to CRD. In inflammatory state of colitis, TNBS induced upregulation of BDNF in dorsal root ganglia of both genotypes while BDNF(+/-) mice showing significantly lower sensitivity in the colon at 30 mm Hg and lower sensitivity in bladder than BDNF(+/+) mice. The two genotypes showed no significant difference in inflammatory severity. Thus, BDNF deficiency results in developmental changes in colonic nociception in both control and inflammatory states, which are more significant in inflammatory state. For bladder reactivity, BDNF deficiency leads to lower sensitization in inflammatory state but has no effect in control state.

PERSPECTIVE

This article highlights the role of BDNF in colonic and referred bladder hyperalgesia in mice. The findings might help in determining novel pharmaceutical interventions targeted at BDNF to relieve abdominal pain.

5-HT 3 receptors mediate the time-dependent vagal afferent modulation of nociception during chronic food allergen-sensitized visceral hyperalgesia in rats

Converging lines of evidence demonstrate a vagally mediated antinociceptive pathway in animals undergoing acute visceral insults, the contribution of this system to visceral pain following chronic noxious stimuli is unknown. 5-HT(3) receptor (5-HT(3)Rs) on spinal afferents are crucially involved in nociceptive processing, the role of 5-HT(3)Rs on vagal afferents is unclear. The aim of the present study was to determine the contribution of vagal afferents to visceral nociception in rats undergoing chronic luminal allergen stimulation and whether it involves vagal 5-HT(3)Rs. Sensitized rats received chicken egg albumin (EA, 1 mg mL(-1)) in drinking water for 2 weeks (day 1-14). Visceromotor response (VMR) to colorectal distension [colorectal distension (CRD), 60 mmHg] and the levels of mRNA encoding 5-HT(3)R (including 3A and 3B subunits) in the nodose ganglia (NG) were evaluated on day 2, 4, 8 and 15. Chronic EA challenge induced gradually increased visceral nociception, with a peak on day 15. Subdiaphragmatic vagotomy or functional deafferentation with capsaicin abolished this time-dependent manner, inducing hyperalgesia from day 2, lasting to day 15. Intraluminal infusion of a 5-HT(3)R antagonist (granisetron), whether alone or infused after local mucosa anaesthetic with 1% lidocaine, mimicked the effects of vagotomy. The mRNA levels for 5-HT(3B) or 5-HT(3A) subunit in the NG showed an opposite time-course to that of visceral pain, which increased from day 2, then decreased gradually to levels lower than those of controls. Our results demonstrate a time-dependent vagal afferent modulation of chronic allergen-sensitized visceral hyperalgesia, which may involve a 5-HT(3)R pathway.

Colorectal distension-induced prefrontal cortex activation in the Wistar-Kyoto rat: implications for irritable bowel syndrome

The prefrontal cortex plays a key role in the perception of painful stimuli, including those emerging from the viscera. Colorectal distension is a non-invasive stimulus used to study visceral pain processing in the nervous system. Visceral hypersensitivity is one of the main characteristics of the functional bowel disorder irritable bowel syndrome (IBS). Moreover, recent human neuroimaging studies have emphasized the importance of altered brain activity and circuitry in the manifestation of IBS symptom severity and reaction to visceral stimuli. It is unclear whether animal models of visceral hypersensitivity display a similar response. Therefore, in the present study, we have used c-Fos protein immunoreactivity as an indicator of cell activation, to compare the response of the viscerally hypersensitive Wistar-Kyoto (WKY) rat and control Sprague-Dawley (SD) rat strains to colorectal distension (CRD), a noxious visceral stimulus. Several corticolimbic structures were analysed including the prelimbic cortex, infralimbic cortex and the rostral and caudal anterior cingulate cortices. Moreover, visceral hypersensitivity was also assessed behaviourally in both strains. As previously described WKY rats had a lower pain threshold than SD controls in response to CRD. In all brain regions analysed, exposure to CRD induced an increase in c-Fos activation in both the WKY and SD rats. However, an exaggerated cell activation was found in the prelimbic, infralimbic and rostral anterior cingulate cortices of the WKY rat compared to SD animals. No significant difference was found in caudal anterior cingulate cortex activation when the strains were compared. These results demonstrate, to our knowledge, for the first time an augmented colorectal distension-induced prefrontal cortex activity in WKY rats similar to that seen in IBS patients, further supporting the use of this strain as a model in which to study brain-gut axis dysregulation observed in IBS.

Analgesic effect of paeoniflorin in rats with neonatal maternal separation-induced visceral hyperalgesia is mediated through adenosine A(1) receptor by inhibiting the extracellular signal-regulated protein kinase (ERK) pathway

Paeoniflorin (PF), a chief active ingredient in the root of Paeonia lactiflora Pall (family Ranunculaceae), is effective in relieving colorectal distention (CRD)-induced visceral pain in rats with visceral hyperalgesia induced by neonatal maternal separation (NMS). This study aimed at exploring the underlying mechanisms of PF's analgesic effect on CRD-evoked nociceptive signaling in the central nervous system (CNS) and investigating whether the adenosine A(1) receptor is involved in PF's anti-nociception.

RESULTS

CRD-induced visceral pain as well as phosphorylated-extracellular signal-regulated protein kinase (p-ERK) and phospho-cAMP response element-binding protein (p-CREB) expression in the CNS structures of NMS rats were suppressed by NMDA receptor antagonist dizocilpine (MK-801) and ERK phosphorylation inhibitor U0126. PF could similarly inhibit CRD-evoked p-ERK and c-Fos expression in laminae I-II of the lumbosacral dorsal horn and anterior cingulate cortex (ACC). PF could also reverse the CRD-evoked increased glutamate concentration by CRD as shown by dynamic microdialysis monitoring in ACC, whereas, DPCPX, an antagonist of adenosine A(1) receptor, significantly blocked the analgesic effect of PF and PF's inhibition on CRD-induced p-ERK and p-CREB expression. These results suggest that PF's analgesic effect is possibly mediated by adenosine A(1) receptor by inhibiting CRD-evoked glutamate release and the NMDA receptor dependent ERK signaling.

Up-regulation of anterior cingulate cortex NR2B receptors contributes to visceral pain responses in rats

BACKGROUND & AIMS

Electrophysiologic and behavioral studies have shown that increased N-methyl-D-aspartate (NMDA)-receptor activation of anterior cingulate cortex (ACC) neurons has a critical role in modulating visceral pain responses in viscerally hypersensitive (VH) rats. This study aimed to identify the NMDA receptor subtypes in perigenual ACC (pACC) neurons involved in the facilitation of visceral nociception.

METHODS

We performed in vivo electrophysiologic recordings of pACC neurons and examined the visceromotor response (VMR) to colorectal distention (CRD) in normal and VH rats induced by colonic anaphylaxis. The NR2A-subtype-receptor antagonist [(R)-[(S)-1-(4-bromo-phenyl)-ethylamino]-(2,3-dioxo-1,2,3,4-tetrahydroquinoxalin-5-yl)-methyl]-phosphonic acid (NVP-AAM077) and the NR2B-receptor-antagonist Ro25-6981 were microinjected into the pACC. To down-regulate NR2B-receptor gene expression, an NR2B-specific small interfering RNA (siRNA) and a plasmid (pEGFP-N1) that expressed the green fluorescent protein were administered into ACC neurons by electroporation.

RESULTS

Reverse microdialysis of NVP-AAM077 had no effect on basal and CRD-induced ACC neuronal firing in VH and control groups. In VH rats, Ro25-6981 (500 micromol/L) inhibited ACC neuronal firing, evoked by 30 and 50 mm Hg CRD, by 98% and 52%, respectively. NVP-AAM077 did not affect the VMR in either group. Ro25-6981 significantly suppressed the VMR in VH but not normal rats. Immunoblot analysis showed increased NR2B-receptor expression in the pACC of VH rats. NR2B siRNA-treated VH rats showed a significant reduction in the VMR, compared with controls.

CONCLUSIONS

The NR2B subunit of the NMDA receptor has a critical role in the modulation of ACC sensitization and visceral pain responses in VH rats.

fMRI of supraspinal areas after morphine and one week pancreatic inflammation in rats

Abdominal pain is a major reason patients seek medical attention yet relatively little is known about neuronal pathways relaying visceral pain. We have previously characterized pathways transmitting information to the brain about visceral pain. Visceral pain arises from second order neurons in lamina X surrounding the spinal cord central canal. Some of the brain regions of interest receiving axonal terminations directly from lamina X were examined in the present study using enhanced functional magnetic resonance imaging (fMRI) before and one week after induction of a rat pancreatitis model with persistent inflammation and behavioral signs of increased nociception. Analysis of imaging data demonstrates an increase in MRI signal for all the regions of interest selected including the rostral ventromedial medulla, dorsal raphe, periaqueductal grey, medial thalamus, and central amygdala as predicted by the anatomical data, as well as increases in the lateral thalamus, cingulate/retrosplenial and parietal cortex. Occipital cortex was not activated above threshold in any condition and served as a negative control. Morphine attenuated the MRI signal, and the morphine effect was antagonized by naloxone in lower brainstem sites. These data confirm activation of these specific regions of interest known as integration sites for nociceptive information important in behavioral, affective, emotional and autonomic responses to ongoing noxious visceral activation.

Epileptiform synchronization in the cingulate cortex

PURPOSE

The anterior cingulate cortex (ACC)--which plays a role in pain, emotions and behavior--can generate epileptic seizures. To date, little is known on the neuronal mechanisms leading to epileptiform synchronization in this structure. Therefore, we investigated the role of excitatory and inhibitory synaptic transmission in epileptiform activity in this cortical area. In addition, since the ACC presents with a high density of opioid receptors, we studied the effect of opioid agonism on epileptiform synchronization in this brain region.

METHODS

We used field and intracellular recordings in conjunction with pharmacological manipulations to characterize the epileptiform activity generated by the rat ACC in a brain slice preparation.

RESULTS

Bath-application of the convulsant 4-aminopyridine (4AP, 50 microM) induced both brief and prolonged periods of epileptiform synchronization resembling interictal- and ictal-like discharges, respectively. Interictal events could occur more frequently before the onset of ictal activity that was contributed by N-methyl-D-aspartate (NMDA) receptors. Mu-opioid receptor activation abolished 4AP-induced ictal events and markedly reduced the occurrence of the pharmacologically isolated GABAergic synchronous potentials. Ictal discharges were replaced by interictal events during GABAergic antagonism; this GABA-independent activity was influenced by subsequent mu-opioid agonist application.

CONCLUSIONS

Our results indicate that both glutamatergic and GABAergic signaling contribute to epileptiform synchronization leading to the generation of electrographic ictal events in the ACC. In addition, mu-opioid receptors appear to modulate both excitatory and inhibitory mechanisms, thus influencing epileptiform synchronization in the ACC.

Regional brain activation in conscious, nonrestrained rats in response to noxious visceral stimulation

Preclinical drug development for visceral pain has largely relied on quantifying pseudoaffective responses to colorectal distension (CRD) in restrained rodents. However, the predictive value of changes in simple reflex responses in rodents for the complex human pain experience is not known. Male rats were implanted with venous cannulas and with telemetry transmitters for abdominal electromyographic (EMG) recordings. [(14)C]-iodoantipyrine was injected during noxious CRD (60 mmHg) in the awake, nonrestrained animal. Regional cerebral blood flow (rCBF)-related tissue radioactivity was quantified by autoradiography and analyzed in the three-dimensionally reconstructed brain by statistical parametric mapping. 60-mmHg CRD, compared with controls (0 mmHg) evoked significant increases in EMG activity (267+/-24% vs. 103+/-8%), as well as in behavioral pain score (77+/-6% vs. 3+/-3%). CRD elicited significant increases in rCBF as expected in sensory (insula, somatosensory cortex), and limbic and paralimbic regions (including anterior cingulate cortex and amygdala). Significant decreases in rCBF were seen in the thalamus, parabrachial nucleus, periaqueductal gray, hypothalamus and pons. Correlations of rCBF with EMG and with behavioral pain score were noted in the cingulate, insula, lateral amygdala, dorsal striatum, somatosensory and motor regions. Our findings support the validity of measurements of cerebral perfusion during CRD in the freely moving rat as a model of functional brain changes in human visceral pain. However, not all regions demonstrating significant group differences correlated with EMG or behavioral measures. This suggests that functional brain imaging captures more extensive responses of the central nervous system to noxious visceral distension than those identified by traditional measures.

Subdiaphragmatic vagal afferent nerves modulate visceral pain

Activation of the vagal afferents by noxious gastrointestinal stimuli suggests that vagal afferents may play a complex role in visceral pain processes. The contribution of the vagus nerve to visceral pain remains unresolved. Previous studies reported that patients following chronic vagotomy have lower pain thresholds. The patient with irritable bowel syndrome has been shown alteration of vagal function. We hypothesize that vagal afferent nerves modulate visceral pain. Visceromotor responses (VMR) to graded colorectal distension (CRD) were recorded from the abdominal muscles in conscious rats. Chronic subdiaphragmatic vagus nerve sections induced 470, 106, 51, and 54% increases in VMR to CRD at 20, 40, 60 and 80 mmHg, respectively. Similarly, at light level of anesthesia, topical application of lidocaine to the subdiaphragmatic vagus nerve in rats increased VMR to CRD. Vagal afferent neuronal responses to low or high-intensity electrical vagal stimulation (EVS) of vagal afferent Adelta or C fibers were distinguished by calculating their conduction velocity. Low-intensity EVS of Adelta fibers (40 microA, 20 Hz, 0.5 ms for 30 s) reduced VMR to CRD at 40, 60, and 80 mmHg by 41, 52, and 58%, respectively. In contrast, high-intensity EVS of C fibers (400 microA, 1 Hz, 0.5 ms for 30 s) had no effect on VMR to CRD. In conclusion, we demonstrated that vagal afferent nerves modulate visceral pain. Low-intensity EVS that activates vagal afferent Adelta fibers reduced visceral pain. Thus EVS may potentially have a role in the treatment of chronic visceral pain.

Role for NMDA receptors in visceral nociceptive transmission in the anterior cingulate cortex of viscerally hypersensitive rats

We have identified colorectal distension (CRD)-responsive neurons in the anterior cingulate cortex (ACC) and demonstrated that persistence of a heightened visceral afferent nociceptive input to the ACC induces ACC sensitization. In the present study, we confirmed that rostral ACC neurons of sensitized rats [induced by chicken egg albumin (EA)] exhibit enhanced spike responses to CRD. Simultaneous in vivo recording and reverse microdialysis of single ACC neurons showed that a low dose of glutamate (50 microM) did not change basal ACC neuronal firing in normal rats but increased ACC neuronal firing in EA rats from 18 +/- 2 to 32 +/- 3.8 impulses/10 s. A high dose of glutamate (500 microM) produced 1.95-fold and a 4.27-fold increases of ACC neuronal firing in sham-treated rats and in EA rats, respectively, suggesting enhanced glutamatergic transmission in the ACC neurons of EA rats. Reverse microdialysis of the 3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kainite receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 10 microM) reduced basal and abolished CRD-induced ACC neuronal firing in normal rats. In contrast, microdialysis of N-methyl-d-aspartate (NMDA) receptor antagonist AP5 had no effect on ACC neuronal firing in normal rats. However, AP5 produced 86% inhibition of ACC neuronal firing evoked by 50 mmHg CRD in the EA rats. In conclusion, ACC nociceptive transmissions are mediated by glutamate AMPA receptors in the control rats. ACC responses to CRD are enhanced in viscerally hypersensitive rats. The enhancement of excitatory glutamatergic transmission in the ACC appears to mediate this response. Furthermore, NMDA receptors mediate ACC synaptic responses after the induction of visceral hypersensitivity.

Functional GI disorders: from animal models to drug development

Despite considerable efforts by academic researchers and by the pharmaceutical industry, the development of novel pharmacological treatments for irritable bowel syndrome (IBS) and other functional gastrointestinal (GI) disorders has been slow and disappointing. The traditional approach to identifying and evaluating novel drugs for these symptom-based syndromes has relied on a fairly standard algorithm using animal models, experimental medicine models and clinical trials. In the current article, the empirical basis for this process is reviewed, focusing on the utility of the assessment of visceral hypersensitivity and GI transit, in both animals and humans, as well as the predictive validity of preclinical and clinical models of IBS for identifying successful treatments for IBS symptoms and IBS-related quality of life impairment. A review of published evidence suggests that abdominal pain, defecation-related symptoms (urgency, straining) and psychological factors all contribute to overall symptom severity and to health-related quality of life. Correlations between readouts obtained in preclinical and clinical models and respective symptoms are small, and the ability to predict drug effectiveness for specific as well as for global IBS symptoms is limited. One possible drug development algorithm is proposed which focuses on pharmacological imaging approaches in both preclinical and clinical models, with decreased emphasis on evaluating compounds in symptom-related animal models, and more rapid screening of promising candidate compounds in man.

Neurocognitive processing of esophageal central sensitization in the insula and cingulate gyrus

The cingulate and insular cortices are parts of the limbic system that process and modulate gastrointestinal sensory signals. We hypothesized that sensitization of these two limbic area may operate in esophageal sensitization. Thus the objective of the study was to elucidate the neurocognitive processing in the cingulate and insular cortices to mechanical stimulation of the proximal esophagus following infusion of acid or phosphate buffer solution (PBS) into the esophagus. Twenty-six studies (14 to acid and 12 to PBS infusion) were performed in 20 healthy subjects (18-35 yr) using high-resolution (2.5 x 2.5 x 2.5 mm(3) voxel size) functional MRI (fMRI). Paradigm-driven, 2-min fMRI scans were performed during randomly timed 15-s intervals of proximal esophageal barostatically controlled distentions and rest, before and after 30-min of distal esophageal acid or PBS perfusion (0.1 N HCl or 0.1 M PBS at 1 ml/min). Following distal esophageal acid infusion, at subliminal and liminal levels of proximal esophageal distentions, the number of activated voxels in both cingulate and insular cortices showed a significant increase compared with before acid infusion (P < 0.05). No statistically significant change in cortical activity was noted following PBS infusion. We conclude that 1) acid stimulation of the esophagus results in sensitization of the cingulate and insular cortices to subliminal and liminal nonpainful mechanical stimulations, and 2) these findings can have ramifications with regard to the mechanisms of some esophageal symptoms attributed to reflux disease.

Anterior cingulate cortex modulates visceral pain as measured by visceromotor responses in viscerally hypersensitive rats

BACKGROUND & AIMS

We have identified that the anterior cingulate cortex (ACC) neurons are responsive to colorectal distention (CRD) and shown that sensitization of ACC neurons occurs in viscerally hypersensitive rats. However, the role of the ACC in pain response has not been clearly defined. We aimed to determine if ACC neuron activation enhances visceral pain in viscerally hypersensitive rats and to identify the receptor involved in facilitation of visceral pain.

METHODS

The nociceptive response (visceromotor response [VMR]) to CRD was recorded in normal and viscerally hypersensitive rats induced by colonic anaphylaxis. The ACC was stimulated electrically, and ACC lesions were generated with ibotenic acid. l-glutamate, alpha-amino-3-hydroxy-5-methyl-isoxozole propionic acid receptor antagonist cyanonitroquinoxaline dione, and N-methyl-d-aspartate receptor antagonist aminophosphonopentanoic acid were microinjected into the rostral ACC.

RESULTS

Electrical stimulation of the rostral ACC enhanced the VMR to CRD in normal rats. ACC lesions caused a decrease in the VMR in viscerally hypersensitive rats but had no effect in normal rats. ACC microinjection of 2 mmol/L glutamate increased the VMR to CRD (10 mm Hg) in viscerally hypersensitive rats, and 20 mmol/L glutamate induced a more potent VMR in viscerally hypersensitive than in normal rats. Cyanonitroquinoxaline dione did not affect the VMR in either group. Aminophosphonopentanoic acid significantly suppressed the VMR in viscerally hypersensitive rats but not in normal rats.

CONCLUSIONS

The ACC plays a critical role in the modulation of visceral pain responses in viscerally hypersensitive rats. This process appears to be mediated by enhanced activities of glutamate N-methyl-d-aspartate receptors.

Distribution and properties of visceral nociceptive neurons in rabbit cingulate cortex

Human imaging localizes most visceral nociceptive responses to anterior cingulate cortex (ACC), however, imaging in conscious subjects cannot completely control anticipatory and reflexive activity or resolve neuron activity. This study overcame these shortcomings by recording individual neuron responses in 12 anesthetized and paralyzed rabbits to define the visceronociceptive response pattern by region and layer. Balloon distension was applied to the colon at innocuous (15 mmHg) or noxious (60 mmHg) intensities, and innocuous and noxious mechanical, thermal and electrical stimuli were applied to the skin. Simultaneous recording from multiple regions assured differences were not due to anesthesia and neuron responses were resolved by spike sorting using principal components analysis. Of the total 346 neurons, 48% were nociceptive; responding to noxious levels of visceral or cutaneous stimulation, or both. Visceronociceptive neurons were most frequent in ACC (39%) and midcingulate cortex (MCC, 36%) and infrequent in retrosplenial cortex (RSC, 12%). In contrast, cutaneous nociceptive units were higher in MCC (MCC, 43%; ACC, 32%; RSC, 23%). Visceral-specific neurons were proportionately more frequent in ACC (37%), while cutaneous-specific units predominated in RSC (62.5%). Visceral nociceptive response durations were longer than those for cutaneous responses. Postmortem analysis of electrode tracks confirmed regional designations, and laminar analysis found inhibitory responses mainly in superficial layers and excitatory in deep layers. Thus, cingulate visceral nociception extends beyond ACC, this is the first report of nociceptive activity in RSC including nociceptive cutaneous responses, and these regional differences require a new model of cingulate nociceptive processing.

Allergy and intestinal dysmotility--evidence of genuine causal linkage?

PURPOSE OF REVIEW

The relationship between allergy and motility has been controversial. There is, however, accumulating evidence demonstrating that mucosal allergic responses may disrupt gut motility, and may also potentially alter nociceptive pathways to cause visceral hyperalgesia.

RECENT FINDINGS

Experimental studies implicate T helper 2 cells and the cytokines interleukin-4 and -13 in antigen-induced dysmotility, and interleukin-5 in the pathogenesis of mucosal eosinophilia. Both mast cells and eosinophils play obligatory roles in different forms of experimental antigen-induced dysmotility. Overall clinical findings appear to implicate eosinophil infiltration in proximal and distal dysmotility syndromes (oesophageal, gastric and colorectal), and induced mast cell degranulation in mid-gut dysmotility. There is also evidence that mucosal allergic responses may induce long-term changes in visceral perception, including alteration of limbic response, leading to sustained abnormality in visceral sensation.

SUMMARY

Clinical evidence implicating mucosal allergic responses in dysmotility has been extended to include disorders considered previously entirely functional, such as in some cases of irritable bowel syndrome. Only a proportion of cases are, however, caused by food allergy and a future challenge is to differentiate patients with similar symptoms, but induced by different mechanisms.

N/A

N/A