Estrogen and serotonin enhance stress-induced visceral hypersensitivity in female rats by up-regulating brain-derived neurotrophic factor in spinal cord

BACKGROUND

We previously reported that female offspring of dams subjected to chronic prenatal stress (CPS) develop enhanced visceral hypersensitivity (VHS) following exposure to chronic stress in adult life that is mediated by up-regulation of spinal cord BDNF. The aims of this study were to examine the roles of estrogen receptor alpha (ERα) and an increase in spinal serotonin signaling in promoting this enhanced VHS in female rats and up-regulation of spinal cord BDNF transcription.

METHODS

Pregnant dams were exposed to chronic stress from E11 until delivery. At 8 weeks, a chronic adult stress (CAS) protocol was applied for nine days.

KEY RESULTS

Ovariectomy before CAS or treatment with letrozole before and during CAS significantly prevented the development of enhanced VHS in female CPS+CAS rats. Intrathecal application of ERα siRNA significantly reduced VHS, decreased lumbar-sacral spinal cord expression of both ERα and BDNF, and reversed pro-transcriptional epigenetic modifications at BDNF promoter lX. Cerebrospinal fluid serotonin levels and 5HT3A receptor expression in the LS spinal cord were both significantly increased in female CPS+CAS rats. During CAS, intrathecal infusion of alosetron significantly decreased VHS, reduced BDNF and ERα expression in the LS spinal cord, and attenuated RNA pol II and ERα binding to the BNDF core promoter IX.

CONCLUSIONS & INFERENCES

Serotonin-mediated activation of 5HT3A receptors in the spinal cord drives the development of enhanced female-specific VHS in our two hit CPS+CAS through up-regulation of spinal cord ERα.

Estrogen augmented visceral pain and colonic neuron modulation in a double-hit model of prenatal and adult stress

BACKGROUND

Chronic stress during pregnancy may increase visceral hyperalgesia of offspring in a sex-dependent way. Combining adult stress in offspring will increase this sensitivity. Based on the evidence implicating estrogen in exacerbating visceral hypersensitivity in female rodents in preclinical models, we predicted that chronic prenatal stress (CPS) + chronic adult stress (CAS) will maximize visceral hyperalgesia; and that estrogen plays an important role in colonic hyperalgesia.

AIM

The aim was to illuminate the role of estrogen in colonic hyperalgesia and its underlying mechanisms.

METHODS

We established a CPS plus CAS rodent model in which the balloon was used to distend the colorectum. The single-fiber recording in vivo and patch clamp experiments in vitro were used to monitor the colonic neuron’s activity. The reverse transcription-polymerase chain reaction, western blot, and immunofluorescence were used to study the effects of CPS and CAS on colon primary afferent sensitivity. We used ovariectomy and letrozole to reduce estrogen levels of female rats respectively in order to assess the role of estrogen in female-specific enhanced primary afferent sensitization.

RESULTS

Spontaneous activity and single fiber activity were significantly greater in females than in males. The enhanced sensitization in female rats mainly came from low-threshold neurons. CPS significantly increased single-unit afferent fiber activity in L6-S2 dorsal roots in response. Activity was further enhanced by CAS. In addition, the excitability of colon-projecting dorsal root ganglion (DRG) neurons increased in CPS + CAS rats and was associated with a decrease in transient A-type K⁺ currents. Compared with ovariectomy, treatment with the aromatase inhibitor letrozole significantly reduced estrogen levels in female rats, confirming the gender difference. Moreover, mice treated with letrozole had decreased colonic DRG neuron excitability. The intrathecal infusion of estrogen increased brain-derived neurotrophic factor (BDNF) protein levels and contributed to the response to visceral pain. Western blotting showed that nerve growth factor protein was upregulated in CPS + CAS mice.

CONCLUSION

This study adds to the evidence that estrogen-dependent sensitization of primary afferent colon neurons is involved in the development of chronic stress-induced visceral hypersensitivity in female rats.

Neonatal Injury Increases Gut Permeability by Epigenetically Suppressing E-Cadherin in Adulthood

Altered intestinal epithelial integrity is an important susceptibility trait in inflammatory bowel disease (IBD), and early life stressors are reported to contribute to this disease susceptibility in adulthood. To identify disease mechanisms associated with early-life trauma that exacerbate IBD in adulthood, we used a "double-hit" neonatal inflammation (NI) and adult inflammation (AI) model that exhibits more severe mucosal injury in the colon later in life. In this study, we explore the underlying mechanisms of this aggravated injury. In rats exposed to both NI and AI, we found sustained increases in colonic permeability accompanied by significantly attenuated expression of the epithelial junction protein E-cadherin. Quantitative RT-PCR revealed a decreased Cdh1 (gene of E-cadherin) mRNA expression in NI + AI rats compared with NI or AI rats. Next, we performed microRNA microarrays to identify potential regulators of E-cadherin in NI + AI rats. We confirmed the overexpression of miR-155, a predicted regulator of E-cadherin, and selected it for further analysis based on reported significance in human IBD. Using ingenuity pathway analysis software, the targets and related canonical pathway of miR-155 were analyzed. Mechanistic studies identified histone hyperacetylation at the Mir155 promoter in NI + AI rats, concomitant with elevated RNA polymerase II binding. In vitro, E-cadherin knockdown markedly increased epithelial cell permeability, as did overexpression of miR-155 mimics, which significantly suppressed E-cadherin protein. In vivo, NI + AI colonic permeability was significantly reversed with administration of miR-155 inhibitor rectally. Our collective findings indicate that early-life inflammatory stressors trigger a significant and sustained epithelial injury by suppressing E-cadherin through epigenetic mechanisms.

Role of brain-derived neurotrophic factor in the pathogenesis of distention-associated abdominal pain in bowel obstruction

BACKGROUND

Previous studies found that visceral sensitivity is increased in bowel obstruction (BO). We hypothesized that mechanical stress-induced expression of BDNF in smooth muscle cells (SMC) of the distended bowel plays a critical role in visceral hypersensitivity in BO by altering voltage-gated K⁺ channel (K_v ) activity in sensory neurons.

METHODS

Partial colon obstruction was maintained in rats for 7 days. Colon-projecting neurons in the dorsal root ganglia (DRG, T13 to L2) were isolated for electrophysiological and gene expression studies.

KEY RESULTS

Compared to controls, membrane excitability of colon-projecting DRG neurons was markedly enhanced in BO. The densities of total K_v and transient A-type (I_A ) K⁺ currents, but not sustained delayed I_K current, were significantly reduced in the neurons in BO. The mRNA expression of I_A subtype K_v 1.4 in colon neurons was down-regulated in BO. Expression of BDNF mRNA and protein was dramatically increased in colonic smooth muscle of the distended segment, but not in the non-distended aboral segment. Mechanical stretch of colon SMC in vitro increased BDNF expression. Treatment with anti-BDNF antibody restored total K_v and I_A currents of neurons from BO rats. Administration of Trk B inhibitor ANA-12 blocked BO-associated changes of neuronal excitability, K_v activity and gene expression in obstruction.

CONCLUSIONS AND INFERENCES

Mechanical stress-induced expression of BDNF in colon SMC plays a critical role in visceral hypersensitivity in BO by suppressing A-type K⁺ currents and gene expression in sensory nerve. These findings help to identify therapeutic targets for distention-associated abdominal pain in the gut.

Neonatal immune challenge followed by adult immune challenge induces epigenetic-susceptibility to aggravated visceral hypersensitivity

BACKGROUND

Abdominal pain is one of the major symptoms of inflammatory Bowel Disease (IBD). The inflammatory mediators released by colon inflammation are known to sensitize the afferent neurons, which is one of the contributors to abdominal pain. However, not all IBD patients have abdominal pain, and some patients report abdominal pain during remission, suggesting contributions of other pathological factors to abdominal pain in IBD. Epidemiological studies found early-life gastrointestinal infections a risk factor for IBD symptoms and adult-life gastrointestinal infections may trigger the onset of IBD. We investigated the hypothesis that neonatal colon immune challenge followed by an adult colon immune challenge upregulates spinal cord BDNF that aggravates visceral sensitivity over and above that induced by adult colon immune challenge alone.

METHODS

We induced neonatal and adult colon immune challenges by intraluminal administration of trinitrobenzene sulfonic acid to the rat colon.

KEY RESULTS

We found that neonatal immune challenge triggers epigenetic programming that upregulates tyrosine hydroxylase in the locus ceruleus when these rats are subjected to an adult colon immune challenge. The upregulation of locus ceruleus tyrosine hydroxylase, upregulates norepinephrine in the cerebrospinal fluid that acts on adrenergic receptors to enhance pCREB binding to the cAMP response element, which recruits histone acetylene transferase (HAT) to the BDNF gene to enhance its transcription resulting in aggravated visceromotor response to colorectal distension. HAT and adrenergic receptor antagonists block the aggravation of visceral sensitivity.

CONCLUSION & INFERENCES

HAT and adrenergic receptor inhibitors may serve as alternates to opioids and NSAIDS in suppressing abdominal pain in IBD.

Enhanced sympathetic nerve activity induced by neonatal colon inflammation induces gastric hypersensitivity and anxiety-like behavior in adult rats

Gastric hypersensitivity (GHS) and anxiety are prevalent in functional dyspepsia patients; their underlying mechanisms remain unknown largely because of lack of availability of live visceral tissues from human subjects. Recently, we demonstrated in a preclinical model that rats subjected to neonatal colon inflammation show increased basal plasma norepinephrine (NE), which contributes to GHS through the upregulation of nerve growth factor (NGF) expression in the gastric fundus. We tested the hypothesis that neonatal colon inflammation increases anxiety-like behavior and sympathetic nervous system activity, which upregulates the expression of NGF to induce GHS in adult life. Chemical sympathectomy, but not adrenalectomy, suppressed the elevated NGF expression in the fundus muscularis externa and GHS. The measurement of heart rate variability showed a significant increase in the low frequency-to-high frequency ratio in GHS vs. the control rats. Stimulus-evoked release of NE from the fundus muscularis externa strips was significantly greater in GHS than in the control rats. Tyrosine hydroxylase expression was increased in the celiac ganglia of the GHS vs. the control rats. We found an increase in trait but not stress-induced anxiety-like behavior in GHS rats in an elevated plus maze. We concluded that neonatal programming triggered by colon inflammation upregulates tyrosine hydroxylase in the celiac ganglia, which upregulates the release of NE in the gastric fundus muscularis externa. The increase of NE release from the sympathetic nerve terminals concentration dependently upregulates NGF, which proportionately increases the visceromotor response to gastric distention. Neonatal programming concurrently increases anxiety-like behavior in GHS rats.

Noninflammatory upregulation of nerve growth factor underlies gastric hypersensitivity induced by neonatal colon inflammation

Gastric hypersensitivity is one of the key contributors to the postprandial symptoms of epigastric pain/discomfort, satiety, and fullness in functional dyspepsia patients. Epidemiological studies found that adverse early-life experiences are risk factors for the development of gastric hypersensitivity. Preclinical studies found that neonatal colon inflammation elevates plasma norepinephrine (NE), which upregulates expression of nerve growth factor (NGF) in the muscularis externa of the gastric fundus. Our goal was to investigate the cellular mechanisms by which NE upregulates the expression of NGF in gastric hypersensitive (GHS) rats, which were subjected previously to neonatal colon inflammation. Neonatal colon inflammation upregulated NGF protein, but not mRNA, in the gastric fundus of GHS rats. Western blotting showed upregulation of p110γ of phosphatidylinositol 4,5-bisphosphate 3-kinase (PI3K), phosphoinositide-dependent kinase-1 (PDK1), pAKT(Ser473), and phosphorylated 4E-binding protein (p4E-BP1)(Thr70), suggesting AKT activation and enhanced NGF protein translation. AKT inhibitor MK-2206 blocked the upregulation of NGF in the fundus of GHS rats. Matrix metalloproteinase 9 (MMP-9), the major NGF-degrading protease, was suppressed, indicating that NGF degradation was impeded. Incubation of fundus muscularis externa with NE upregulated NGF by modulating the protein translation and degradation pathways. Yohimbine, an α2-adrenergic receptor antagonist, upregulated plasma NE and NGF expression by activating the protein translation and degradation pathways in naive rats. In contrast, a cocktail of adrenergic receptor antagonists suppressed the upregulation of NGF by blocking the activation of the protein translation and degradation pathways. Our findings provide evidence that the elevation of plasma NE induces NGF expression in the gastric fundus.

Genesis of anxiety, depression, and ongoing abdominal discomfort in ulcerative colitis-like colon inflammation

Psychological disorders are prevalent in patients with inflammatory bowel disease; the underlying mechanisms remain unknown. We tested the hypothesis that ulcerative colitis-like inflammation induced by dextran sodium sulfate (DSS) exacerbates the ongoing spontaneous activity in colon-projecting afferent neurons that induces abdominal discomfort and anxiety, and depressive-like behaviors in rats. In this study, we used the conditioned place preference and standard tests for anxiety- and depression-like behaviors. DSS rats developed anxiety- and depression-like behaviors 10 to 20 days after the start of inflammation. Single-fiber recordings showed an increase in the frequency of spontaneous activity in L6-S1 dorsal root ganglion (DRG) roots. Prolonged desensitization of transient receptor potential vanilloid 1 (TRPV1)-expressing colonic afferents by resiniferatoxin (RTX) suppressed the spontaneous activity, as well as the anxiety- and depressive-like behaviors. Reduction in spontaneous activity in colon afferents by intracolonic administration of lidocaine produced robust conditioned place preference (CPP) in DSS rats, but not in control rats. Patch-clamp studies demonstrated a significant decrease in the resting membrane potential, lower rheobase, and sensitization of colon-projecting L6-S1 DRG neurons to generate trains of action potentials in response to current injection in DSS rats. DSS inflammation upregulated the mRNA levels of transient receptor potential ankyrin 1 and TRPV1 channels and downregulated that of Kv1.1 and Kv1.4 channels. Ulcerative colitis-like inflammation in rats induces anxiety- and depression-like behaviors, as well as ongoing abdominal discomfort by exacerbating the spontaneous activity in the colon-projecting afferent neurons. Alterations in the expression of voltage- and ligand-gated channels are associated with the induction of mood disorders following colon inflammation.

Chronic prenatal stress epigenetically modifies spinal cord BDNF expression to induce sex-specific visceral hypersensitivity in offspring

BACKGROUND

Irritable bowel syndrome (IBS) is a heterogeneous disorder with abdominal pain as one of the primary symptoms. The etiology of IBS remains unknown. Epidemiological studies found that a subset of these patients have a history of adverse early-life experiences. We tested the hypothesis that chronic prenatal stress (CPS) epigenetically enhances brain-derived neurotrophic factor (BDNF) in spinal cord to aggravate colon sensitivity to colorectal distension (CRD) differentially in male and female offspring.

METHODS

We used heterotypic intermittent chronic stress (HeICS) protocols in pregnant dams from E11 until delivery.

KEY RESULTS

Chronic prenatal stress induced significant visceral hypersensitivity (VHS) to CRD in male and female offspring. A second exposure to HeICS in adult offspring exacerbated VHS greater in female offspring that persisted longer than in male offspring. Chronic prenatal stress upregulated BDNF expression in the lumbar-sacral dorsal horn that correlated with the exacerbation of VHS in female, but not in male offspring. The upregulation of BDNF was due to a significant increase in RNA Pol II binding, histone H3 acetylation, and significant decrease in histone deacetylase 1 association with the core promoter of BDNF in female offspring. Other chronic prenatal and neonatal stress protocols were less effective than HeICS.

CONCLUSIONS & INFERENCES

The development of VHS, which contributes to the symptom of intermittent abdominal pain, is a two-step process, chronic in utero stress followed by chronic stress in adult-life. This two-step process induces aggravated and persistent colon hypersensitivity in female than in male offspring. Our preclinical model explains several clinical features in IBS patients.

Inflammation induced by mast cell deficiency rather than the loss of interstitial cells of Cajal causes smooth muscle dysfunction in W/W(v) mice

The initial hypothesis suggested that the interstitial cells of Cajal (ICC) played an essential role in mediating enteric neuronal input to smooth muscle cells. Much information for this hypothesis came from studies in W/W^v mice lacking ICC. However, mast cells, which play critical roles in regulating inflammation in their microenvironment, are also absent in W/W^v mice. We tested the hypothesis that the depletion of mast cells in W/W^v mice generates inflammation in fundus muscularis externa (ME) that impairs smooth muscle reactivity to Ach, independent of the depletion of ICC. We performed experiments on the fundus ME from wild type (WT) and W/W^v mice before and after reconstitution of mast cells by bone marrow transplant. We found that mast cell deficiency in W/W^v mice significantly increased COX-2 and iNOS expression and decreased smooth muscle reactivity to Ach. Mast cell reconstitution or concurrent blockade of COX-2 and iNOS restored smooth muscle contractility without affecting the suppression of c-kit in W/W^v mice. The expression of nNOS and ChAT were suppressed in W/W^v mice; mast cell reconstitution did not restore them. We conclude that innate inflammation induced by mast cell deficiency in W/W^v mice impairs smooth muscle contractility independent of ICC deficiency. The impairment of smooth muscle contractility and the suppression of the enzymes regulating the synthesis of Ach and NO in W/W^v mice need to be considered in evaluating the role of ICC in regulating smooth muscle and enteric neuronal function in W/W^v mice.

Developmental origins of colon smooth muscle dysfunction in IBS-like rats

Epidemiological studies show that subsets of adult and pediatric patients with irritable bowel syndrome (IBS) have prior exposures to psychological or inflammatory stress. We investigated the cellular mechanisms of colonic smooth muscle dysfunction in adult rats subjected to neonatal inflammation. Ten-day-old male rat pups received 2,4,6-trinitrobenzene sulfonic acid to induce colonic inflammation. Colonic circular smooth muscle strips were obtained 6 to 8 wk later. We found that about half of the neonate pups subjected to inflammatory insult showed a significant increase in expression of the pore-forming α1C-subunit of Cav1.2b channels in adult life. These were the same rats in whom Vip mRNA increased in the colon muscularis externae. Additional experiments showed reduced interaction of histone deacetylase (HDAC) 3 with α1C1b promoter that increased the acetylation of histone H3 lysine 9 (H3K9) in the core promoter region. Vasoactive intestinal peptide (VIP) treatment of naïve muscularis externae swiftly recruited CREB-binding protein (CBP) to the α1C1b promoter and dissociated HDAC3 from this region to initiate transcription. The CBP interaction with the α1C1b promoter was transient, but the dissociation of HDAC3 persisted to sustain H3K9 hyperacetylation and increase in transcription. Intraperitoneal treatment of adult naïve rats with butyrate mimicked the effects of neonatal colon inflammation. We concluded that neonatal inflammation upregulates VIP in the colon muscularis externae, which modulates epigenetic events at the α1C1b promoter to activate α1C1b gene transcription. Inflammatory insult in early life may be one of the etiologies of smooth muscle dysfunction in adult life, which contributes to the altered motility function in patients with diarrhea-predominant IBS.

Are interstitial cells of Cajal involved in mechanical stress-induced gene expression and impairment of smooth muscle contractility in bowel obstruction?

BACKGROUND AND AIMS

The network of interstitial cells of Cajal (ICC) is altered in obstructive bowel disorders (OBD). However, whether alteration in ICC network is a cause or consequence of OBD remains unknown. This study tested the hypothesis that mechanical dilation in obstruction disrupts the ICC network and that ICC do not mediate mechanotranscription of COX-2 and impairment of smooth muscle contractility in obstruction.

METHODS

Medical-grade silicon bands were wrapped around the distal colon to induce partial obstruction in wild-type and ICC deficient (W/W(v)) mice.

RESULTS

In wild-type mice, colon obstruction led to time-dependent alterations of the ICC network in the proximal colon segment. Although unaffected on days 1 and 3, the ICC density decreased markedly and the network was disrupted on day 7 of obstruction. COX-2 expression increased, and circular muscle contractility decreased significantly in the segment proximal to obstruction. In W/W(v) control mice, COX-2 mRNA level was 4.0 (±1.1)-fold higher (n=4) and circular muscle contractility was lower than in wild-type control mice. Obstruction further increased COX-2 mRNA level in W/W(v) mice to 7.2 (±1.0)-fold vs. W/W(v) controls [28.8 (±4.1)-fold vs. wild-type controls] on day 3. Obstruction further suppressed smooth muscle contractility in W/W(v) mice. However, daily administration of COX-2 inhibitor NS-398 significantly improved muscle contractility in both W/W(v) sham and obstruction mice.

CONCLUSIONS

Lumen dilation disrupts the ICC network. ICC deficiency has limited effect on stretch-induced expression of COX-2 and suppression of smooth muscle contractility in obstruction. Rather, stretch-induced COX-2 plays a critical role in motility dysfunction in partial colon obstruction.

Paradoxical regulation of ChAT and nNOS expression in animal models of Crohn's colitis and ulcerative colitis

Morphological and functional changes in the enteric nervous system (ENS) have been reported in inflammatory bowel disease. We examined the effects of inflammation on the expression of choline acetyltransferase (ChAT) and nNOS in the muscularis externae of two models of colonic inflammation, trinitrobenzene sulfonic acid (TNBS)-induced colitis, which models Crohn's disease-like inflammation, and DSS-induced colitis, which models ulcerative Colitis-like inflammation. In TNBS colitis, we observed significant decline in ChAT, nNOS, and protein gene product (PGP) 9.5 protein and mRNA levels. In DSS colitis, ChAT and PGP9.5 were significantly upregulated while nNOS levels did not change. The nNOS dimer-to-monomer ratio decreased significantly in DSS- but not in TNBS-induced colitis. No differences were observed in the percentage of either ChAT (31 vs. 33%)- or nNOS (37 vs. 41%)-immunopositive neurons per ganglia or the mean number of neurons per ganglia (55 ± 5 vs. 59 ± 5, P > 0.05). Incubation of the distal colon muscularis externae in vitro with different types of inflammatory mediators showed that cytokines decreased ChAT and nNOS expression, whereas H₂O₂, a component of oxidative stress, increased their expression. NF-κB inhibitor MG-132 did not prevent the IL-1β-induced decline in either ChAT or nNOS expression. These findings showed that TNBS- and DSS-induced inflammation differentially regulates the expression of two critical proteins expressed in the colonic myenteric neurons. These differences are likely due to the exposure of the myenteric plexus neurons to different combinations of Th1-type inflammatory mediators and H₂O₂ in each model.

Developmental origins of functional dyspepsia-like gastric hypersensitivity in rats

BACKGROUND & AIMS

Gastric hypersensitivity (GHS) contributes to epigastric pain in patients with functional dyspepsia (FD); the etiology and cellular mechanisms of this dysfunction remain unknown. We investigated whether inflammatory insult to the colons of neonatal rats induced GHS in adult life.

METHODS

We used cellular, molecular, and in vivo approaches to investigate the mechanisms of GHS in adult rats subjected to neonatal colonic insult by intraluminal administration of trinitrobenzene sulfonic acid; controls received saline. Six to 8 weeks later, rats were evaluated for GHS and tissue was collected for molecular experiments.

RESULTS

Inflammatory insult to the colon on post-natal day 10 caused an aberrant increase of corticosterone on post-natal day 15 and induced GHS in adult life. We called these FD-like rats. Inhibition of glucocorticoid receptors after neonatal insult blocked the induction of GHS in adult rats. The aberrant increase of plasma corticosterone in neonates increased the plasma concentration of norepinephrine, nerve growth factor in the gastric fundus muscularis externae, brain-derived neurotrophic factor in the thoracic dorsal root ganglia and spinal cord, and down-regulated K(v)1.1 messenger RNA in thoracic dorsal root ganglia without affecting the expression of K(v)1.4, Na(v)1.8, TrpA1, TrpV1, or P2X3 in FD-like rats. Inhibition of glucocorticoid receptors during neonatal insult or the inhibition of adrenergic receptors, nerve growth factor, or brain-derived neurotrophic factor in FD-like rats suppressed GHS. The intrathecal administration of small interfering RNAs against K(v)1.1 increased GHS in naive rats.

CONCLUSIONS

Inflammatory insult to the colons of rat pups leads to GHS in adult life. GHS is caused by altered expression of genes encoding neurotrophins and ion channels, and altered activity of the sympathetic nervous system.

Differential immune and genetic responses in rat models of Crohn's colitis and ulcerative colitis

Crohn's disease and ulcerative colitis are clinically, immunologically, and morphologically distinct forms of inflammatory bowel disease (IBD). However, smooth muscle function is impaired similarly in both diseases, resulting in diarrhea. We tested the hypothesis that differential cellular, genetic, and immunological mechanisms mediate smooth muscle dysfunction in two animal models believed to represent the two diseases. We used the rat models of trinitrobenzene sulfonic acid (TNBS)- and dextran sodium sulfate (DSS)-induced colonic inflammations, which closely mimic the clinical and morphological features of Crohn's disease and ulcerative colitis, respectively. DSS inflammation induced oxidative stress initially in mucosa/submucosa, which then propagated to the muscularis externa to impair smooth muscle function. The muscularis externa showed no increase of cytokines/chemokines. On the other hand, TNBS inflammation almost simultaneously induced oxidative stress, recruited or activated immune cells, and generated cytokines/chemokines in both mucosa/submucosa and muscularis externa. The generation of cytokines/chemokines did not correlate with the recruitment and activation of immune cells. Consequently, the impairment of smooth muscle function in DSS inflammation was primarily due to oxidative stress, whereas that in TNBS inflammation was due to both oxidative stress and proinflammatory cytokines. The impairment of smooth muscle function in DSS inflammation was due to suppression of Gα(q) protein of the excitation-contraction coupling. In TNBS inflammation, it was due to suppression of the α(1C)1b subunit of Ca(v)1.2b channels, CPI-17 and Gα(q). TNBS inflammation increased IGF-1 and TGF-β time dependently in the muscularis externa. IGF-1 induced smooth muscle hyperplasia; both IGF-1 and TGF-β induced hypertrophy. In conclusion, both TNBS and DSS induce transmural inflammation, albeit with different types of inflammatory mediators. The recruitment or activation of immune cells does not correlate directly with the intensity of generation of inflammatory mediators. The inflammatory mediators in TNBS and DSS inflammations target different genes to impair smooth muscle function.

Ameliorating effects of mirtazapine on visceral hypersensitivity in rats with neonatal colon sensitivity

BACKGROUND

The aim was to investigate the effects of mirtazapine on visceral hypersensitivity and gastric emptying in an established rodent model of colonic sensitization.

METHODS

Twenty colonic sensitized rats and 20 matched controls were used. Visceral sensitivity during colorectal distension (CRD) was assessed by the measurement of abdominal electromyogram (EMG) with the pressures of 20, 40, and 60 mmHg. Mirtazapine with doses of 1, 5, and 10 mg kg(-1) were administered orally. Gastric emptying and small intestinal transit were performed in a separated experiment after gavage of 1.5 mL of phenol red solution.

KEY RESULTS

(i) Visceral hypersensitivity after neonatal colonic sensitization was confirmed. (ii) Mirtazapine dose-dependently reduced visceral hypersensitivity in the colonic sensitized rats. The increases in EMG during CRD at 40, 60 mmHg were, 17.59 +/- 6.49 and 26.04 +/- 8.30, respectively, with saline session, and substantially reduced to 10.0 +/- 5.95 (P = 0.02 vs corresponding saline) and 12.58 +/- 7.43 (P < 0.001 vs saline) with mirtazapine at 10 mg kg(-1). Similar findings were noted at doses of 5 and 1 mg kg(-1) at a lesser degree. In the control rats, mirtazapine-reduced visceral sensitivity only during CRD at 60 mmHg. (iii) Mirtazapine 10 mg kg(-1) significantly accelerated gastric emptying (P = 0.045) but slightly and marginally delayed intestinal transit (P = 0.058) the colonic sensitized rats.

CONCLUSIONS & INFERENCES

Mirtazapine dose-dependently ameliorates visceral hypersensitivity in colonic sensitized rats. Mirtazapine at a high dose improves delayed gastric emptying in colonic sensitized rats but slightly and marginally delays small intestinal transit. Its roles in altering gastrointestinal motility need further investigation.

Adrenergic stimulation mediates visceral hypersensitivity to colorectal distension following heterotypic chronic stress

BACKGROUND & AIMS

Chronic stress exacerbates or causes relapse of symptoms such as abdominal pain and cramping in patients with irritable bowel syndrome. We investigated whether chronic stress increases plasma norepinephrine and sensitizes colon-specific dorsal root ganglion (DRG) neurons by increasing expression of nerve growth factor (NGF) in the colon wall.

METHODS

Heterotypic chronic stress (HeCS) was applied to male Wistar rats and neurologic and molecular responses were analyzed. Tissues were analyzed for NGF expression.

RESULTS

HeCS significantly increased visceromoter response to colorectal distension; expression of NGF increased in colonic muscularis externa and mucosa/submucosa. Rheobase decreased, resting membrane potential was depolarized, and electrogenesis of action potentials increased in colon-specific thoracolumbar DRG neurons. Luminal administration of resiniferatoxin in distal colon, systemic administration of anti-NGF antibody, or inhibition of the NGF receptor trkA by k252a or antisense oligonucleotides in thoracolumbar DRG blocked the chronic stress-induced visceral hypersensitivity to colorectal distension. Blockade of alpha1/alpha2- and beta1/beta2-adrenergic receptors prevented the stress-induced visceral hypersensitivity and increased expression of NGF in the colon wall. HeCS did not induce any inflammatory response in the colon wall.

CONCLUSIONS

The peripheral stress mediator norepinephrine induces visceral hypersensitivity to colorectal distension in response to HeCS by increasing the expression of NGF in the colon wall, which sensitizes primary afferents in the absence of an inflammatory response.

Electroacupuncture attenuates visceral hyperalgesia and inhibits the enhanced excitability of colon specific sensory neurons in a rat model of irritable bowel syndrome

The causes of irritable bowel syndrome remain elusive and there are few effective treatments for pain in this syndrome. Electroacupunture (EA) is used extensively for treatment of various painful conditions including chronic visceral hyperalgesia (CVH). However, mechanism of its analgesic effect remains unknown. This study was designed to investigate effect of EA on colon specific dorsal root ganglion (DRG) neurons in rats with CVH. CVH was induced by intracolonic injection of acetic acid (AA) in 10-day-old rats. Electromyography and patch clamp recordings were performed at age of 8-10 weeks. Colon DRG neurons were labelled by injection of DiI into the colon wall. EA was given at ST36 in both hindlimbs. As adults, neonatal AA-injected rats displayed an increased sensitivity to colorectal distension (CRD) and an enhanced excitability of colon DRG neurons. EA treatment for 40 min significantly attenuated the nociceptive responses to CRD in these rats; this attenuation was reversed by pretreatment with naloxone. EA treatment for 40 min per day for 5 days produced a prolonged analgesic effect and normalized the enhanced excitability of colon DRG neurons. Furthermore, in vitro application of [D-Ala(2), N-MePhe(4), Gly(5)-Ol] enkephalin (DAMGO) suppressed the enhanced excitability of colon neurons from rats with CVH. These findings suggest that EA produced-visceral analgesia, which might be mediated in a large part by endogenous opioids pathways, is associated with reversal of the enhanced excitability of colon DRG neurons in rats with CVH.

The endogenous hydrogen sulfide producing enzyme cystathionine-beta synthase contributes to visceral hypersensitivity in a rat model of irritable bowel syndrome

Background

The pathogenesis of visceral hypersensitivity, a characteristic pathophysiological feature of irritable bowel syndrome (IBS), remains elusive. Recent studies suggest a role for hydrogen sulfide (H₂S) in pain signaling but this has not been well studied in visceral models of hyperalgesia. We therefore determined the role for the endogenous H₂S producing enzyme cystathionine-β-synthetase (CBS) in a validated rat model of IBS-like chronic visceral hyperalgesia (CVH). CVH was induced by colonic injection of 0.5% acetic acid (AA) in 10-day-old rats and experiments were performed at 8–10 weeks of age. Dorsal root ganglion (DRG) neurons innervating the colon were labeled by injection of DiI (1,1'-dioleyl-3,3,3',3-tetramethylindocarbocyanine methanesulfonate) into the colon wall.

Results

In rat DRG, CBS-immunoreactivity was observed in approximately 85% of predominantly small- and medium-sized neurons. Colon specific DRG neurons revealed by retrograde labeling DiI were all CBS-positive. CBS-positive colon neurons co-expressed TRPV1 or P2X3 receptors. Western blotting analysis showed that CBS expression was significantly increased in colon DRGs 8 weeks after neonatal AA-treatment. Furthermore, the CBS inhibitor hydroxylamine markedly attenuated the abdominal withdrawal reflex scores in response to colorectal distention in rats with CVH. By contrast, the H₂S donor NaHS significantly enhanced the frequency of action potentials of colon specific DRG neurons evoked by 2 times rheobase electrical stimulation.

Conclusion

Our results suggest that upregulation of CBS expression in colonic DRG neurons and H₂S signaling may play an important role in developing CVH, thus identifying a specific neurobiological target for the treatment of CVH in functional bowel syndromes.

P2X receptor-mediated visceral hyperalgesia in a rat model of chronic visceral hypersensitivity

BACKGROUND

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder characterised by abdominal pain and bloating in association with altered bowel movements. Its pathogenesis and the underlying molecular mechanisms of visceral hyperalgesia remain elusive. Recent studies of somatic and other visceral pain models suggest a role for purinergic signalling mediated by the P2X receptor (P2XR) family.

AIMS

To examine the role of P2XR signalling in the pathogenesis in a rat model of IBS-like visceral hyperalgesia.

METHODS

Visceral hypersensitivity was induced by colonic injection of 0.5% acetic acid (AA) in 10-day-old rats and experiments were conducted at 8 weeks of age. Dorsal root ganglion (DRG) neurons innervating the colon were labelled by injection of DiI (1,1'-dioleyl-3,3,3',3-tetramethylindocarbocyanine methanesulfonate) fluorescence into the colon wall.

RESULTS

Visceral hypersensitivity was reversed by TNP-ATP (2'-(or-3')-O-(trinitrophenyl) ATP), a potent P2X1, P2X3 and P2X2/3 receptor antagonist. Rapid application of ATP (20 microM) induced a fast inactivating current in colon-specific DRG neurons from both control and AA-treated rats. There was a twofold increase in the peak ATP responses in neurons from AA-treated rats. These currents were sensitive to TNP-ATP (100 nM). Under current-clamped conditions, ATP evoked a larger membrane depolarisation in neurons from neonatal AA-treated rats than in controls. P2X3R protein expression was significantly enhanced in colon-specific DRGs 8 weeks after neonatal AA treatment.

CONCLUSIONS

These data suggest that the large enhancement of P2XR expression and function may contribute to the maintenance of visceral hypersensitivity, thus identifying a specific neurobiological target for the treatment of chronic visceral hyperalgesia.

A rat model of chronic gastric sensorimotor dysfunction resulting from transient neonatal gastric irritation

BACKGROUND & AIMS

Although several pathophysiologic abnormalities have been noted in functional dyspepsia (FD), their pathogenesis is poorly understood. We hypothesized that chronic gastric hypersensitivity and gastric motor dysfunction seen in FD patients can be modeled in rats by transient gastric irritation during the neonatal period, a time of known neuronal vulnerability to long-term plasticity.

METHODS

Ten-day-old male rats received 0.2 mL 0.1% iodoacetamide (IA) in 2% sucrose daily by oral gavages for 6 days; controls received 2% sucrose. Rats in both groups were then followed to adulthood (8-10 weeks) at which point behavioral, visceromotor, and great splanchnic nerve responses to graded gastric balloon distention (GD; 20-80 mm Hg) and gastric motor function were tested.

RESULTS

IA-treated rats exhibited hypersensitivity to GD in a dose-dependent manner, as compared with the control group. The threshold of afferent nerve activation was lower and nerve responses to GD were significantly increased in IA-treated rats. Although IA-treated rats ingested food at a lower rate, gastric emptying was not significantly different between IA and control groups. However, gastric accommodation was significantly reduced in the IA group. No significant gastric pathology was seen in hypersensitive adult rats compared with controls.

CONCLUSIONS

These studies demonstrate that gastric irritation in the neonatal period can result in chronic gastric hypersensitivity and gastric motor dysfunction in adults even in the absence of significant detectable gastric pathology. Our results offer insight into the pathogenesis of chronic functional dyspepsia and provide a potential model for further study to this important clinical problem.

Transient receptor potential vanilloid 1 mediates hyperalgesia and is up-regulated in rats with chronic pancreatitis

BACKGROUND & AIMS

The neurobiologic basis of pancreatic hyperalgesia in chronic pancreatitis (CP) is understood poorly and there is a need to identify novel therapeutic targets. Our aim was to study the role of the transient receptor potential vanilloid 1 (TRPV1), a key integrator of noxious stimuli, in the pathogenesis of pancreatic pain in a rat model of CP.

METHODS

CP was induced in rats by intraductal injection of trinitrobenzene sulfonic acid. TRPV1 currents in pancreas-specific DRG neurons were measured using perforated patch-clamp techniques. Reverse-transcription polymerase chain reaction was used to measure mRNA expression of TRPV1 in these neurons after laser capture microdissection. Immunofluorescence and Western blot analysis, using TRPV1-specific antibodies, also were performed. Pancreatic hyperalgesia was assessed by rat's nocifensive behavior to electrical stimulation of the pancreas.

RESULTS

CP was associated with a 4-fold increase in capsaicin-induced current density (P < .02), along with an increase in the proportion of pancreas-specific DRG neurons that responded to capsaicin (52.9% in controls vs 79.0% in CP; P < .05). CP also was associated with a significant increase in TRPV1 expression both at the messenger RNA and protein level in whole thoracic DRGs and pancreas-specific sensory neurons. Systemic administration of the TRPV1 antagonist SB-366791 markedly reduced both visceral pain behavior and referred somatic hyperalgesia in rats with CP, but not in control animals.

CONCLUSIONS

TRPV1 up-regulation and sensitization is a specific molecular mechanism contributing to hyperalgesia in CP and represents a useful target for treating pancreatic hyperalgesia caused by inflammation.

The ClC-3 Chloride Transport Protein Traffics through the Plasma Membrane via Interaction of an N-terminal Dileucine Cluster with Clathrin

ClC-3 is a ubiquitously expressed chloride transport protein that is present in synaptic vesicles and endosome/lysosome compartments. It is largely intracellular but has been observed at the plasma membrane as well. The aim of this study was to identify the pathways and regulation of ClC-3 trafficking to intracellular sites. At the steady state, approximately 94% of transfected ClC-3 was localized intracellularly, and only 6% was at the plasma membrane. Pulse labeling with [(35)S]methionine and biotinylation demonstrated that about 25% of newly synthesized ClC-3 traffics through the plasma membrane. We used both immunofluorescence microscopy and biotinylation assays to assess the trafficking of ClC-3. Plasma membrane ClC-3 was rapidly endocytosed (t((1/2)) approximately 9 min); a portion entered a recycling pool that returned to the cell surface after internalization, and the remainder trafficked to more distal intracellular compartments. ClC-3 associated with clathrin at the plasma membrane. Coimmunoprecipitation and glutathione S-transferase pulldown assays demonstrated that the N terminus of ClC-3 binds to clathrin. Alanine replacement of a dileucine acidic cluster within the cytosolic N terminus (amino acids 13-19) resulted in a molecule that had decreased endocytosis and increased surface expression. This replacement also abolished interaction with clathrin as assessed both by coimmunoprecipitation and glutathione S-transferase pulldown assays. We conclude that ClC-3 is primarily an intracellular transport protein that is transiently inserted into the plasma membrane where it is rapidly endocytosed. Internalization of ClC-3 depends on the interaction between an N-terminal dileucine cluster and clathrin.

A computerized analysis of robotic versus laparoscopic task performance

INTRODUCTION

Robotic technology has been postulated to improve performance in advanced surgical skills. We utilized a novel computerized assessment system to objectively describe the technical enhancement in task performance comparing robotic and laparoscopic instrumentation.

METHODS AND PROCEDURES

Advanced laparoscopic surgeons (2-10 yrs experience) performed three unique task modules using laparoscopic and Telerobotic surgical instrumentation (Intuitive Surgical, Sunnyvale, CA). Performance was evaluated using a computerized assessment system (ProMIS, Dublin, Ireland) and results were recorded as time (s), path (mm) and precision. Each surgeon had an initial training session followed by two testing sessions for each module. A paired Student's t-test was used to analyze the data.

RESULTS

Ten surgeons completed the study. 8/10 surgeons had significant technical enhancement utilizing robotic technology.

CONCLUSIONS

The ProMIS computerized assessment system can be modified to objectively obtain task performance data with robotic instrumentation. All the tasks were performed faster and with more precision using the robotic technology than standard laparoscopy.

Hirschsprung's disease in a young adult: report of a case and review of the literature

Hirschsprung's disease (HD) in adults is rare and often undiagnosed or misdiagnosed. We report a case of HD in a 26-year-old woman who had a history of chronic constipation that required laxatives and enemas since early childhood. She developed severe intestinal obstruction and presented to the emergency department with significant abdominal distension. A computed tomographic scan confirmed significant fecal loading of the entire colon and rectum. An anal manometry revealed lack of normal rectoanal inhibitory reflex. A rectal biopsy showed hypoganglionic anorectum, suspicious for HD. Because of the severe fecal retention that was refractory to conservative management, total proctocolectomy with ileal pouch-anal anastomosis was performed. The entire colon showed massive dilatation and marked wall thickening. Histologic examination showed absence of ganglion cells in submucosal (Meissner's) and myenteric (Auerbach's) plexuses in the distal rectum. A diagnosis of adult HD was made. Her postoperative course was uneventful with complete resolution of the symptoms. Hirschsprung's disease should be considered in adults who have long-standing and refractory constipation.

Enhanced excitability and suppression of A-type K+ current of pancreas-specific afferent neurons in a rat model of chronic pancreatitis

Chronic pancreatitis (CP) is a relatively common disorder, characterized by glandular insufficiency and chronic, often intractable, pain. The mechanism of pain in CP is poorly understood. We have previously developed a model of trinitrobenzene sulphonic acid (TNBS)-induced CP that results in nociceptive sensitization in rats. This study was designed to examine changes in the excitability and alteration of voltage-gated K(+) currents of dorsal root ganglia (DRG) neurons innervating the pancreas. CP was induced in adult rats by an intraductal injection of TNBS. DRG neurons innervating the pancreas were identified by 1,1'-dioleyl-3,3,3',3-tetramethylindocarbocyanine methanesulfonate fluorescence labeling. Perforated patch-clamp recordings were made from acutely dissociated DRG neurons from control and TNBS-treated rats. Pancreas-specific DRG neurons displayed more depolarized resting potentials in TNBS-treated rats than those in controls (P < 0.02). Some neurons from the TNBS-treated group exhibited spontaneous firings. TNBS-induced CP also resulted in a dramatic reduction in rheobase (P < 0.05) and a significant increase in the number of action potentials evoked at twice rheobase (P < 0.05). Under voltage-clamp conditions, neurons from both groups exhibited transient A-type (I(A)) and sustained outward rectifier K(+) currents (I(K)). Compared with controls, the average I(A) but not the average I(K) density was significantly reduced in the TNBS-treated group (P < 0.05). The steady-state inactivation curve for I(A) was displaced by approximately 20 mV to more hyperpolarized levels after the TNBS treatment. These data suggest that TNBS treatment increases the excitability of pancreas-specific DRG neurons by suppressing I(A) density, thus identifying for the first time a specific molecular mechanism underlying chronic visceral pain and sensitization in CP.

Molecular and behavioral changes in nociception in a novel rat model of chronic pancreatitis for the study of pain

The approach to the management of painful chronic pancreatitis has been empirical, primarily due to the lack of information about biological mechanisms producing pain. To facilitate research into pain mechanisms, our aim was to assess a rat model of chronic pancreatitis induced by pancreatic infusion of trinitrobenzene sulfonic acid as a model of painful pancreatitis. Nociception was assessed by measuring mechanical sensitivity of the abdomen and by recording the number of nocifensive behaviors in response to electrical stimulation of the pancreas. Expression of neuropeptides calcitonin gene-related peptide (CGRP) and substance P (SP) in the thoracic dorsal root ganglia receiving input from the pancreas and nerve growth factor (NGF) in the pancreas were measured. Rats with pancreatitis exhibited marked increase in sensitivity to mechanical probing of the abdomen and increased sensitivity to noxious electrical stimulation of the pancreas. There were significant increases in NGF protein in the pancreas and in expression of neuropeptides CGRP and SP in the sensory neurons from dorsal root ganglia receiving input from the pancreas. We have established quantitative measures of referred nociception and pancreatic hyperalgesia in a rat model of chronic pancreatitis that bears histological similarities to the human disease. This model has considerable construct, face and predictive validity for the human condition. It is of importance for the study of the pathogenesis of pain in this condition and can facilitate the development of new therapeutic options.

Traumatic brain injury and hemorrhagic hypotension suppress neuroprotective gene expression in injured hippocampal neurons

BACKGROUND

After traumatic brain injury, memory dysfunction is due in part to damage to the hippocampus. To study the molecular mechanisms of this selective vulnerability, the authors used laser capture microdissection of neurons stained with Fluoro-Jade to directly compare gene expression in injured (Fluoro-Jade-positive) and adjacent uninjured (Fluoro-Jade-negative) rat hippocampal neurons after traumatic brain injury and traumatic brain injury plus hemorrhagic hypotension.

METHODS

Twelve isoflurane-anesthetized Sprague-Dawley rats underwent moderate (2.0 atm) fluid percussion traumatic brain injury followed by either normotension or hemorrhagic hypotension. Animals were killed 24 h after injury. Frozen brain sections were double stained with 1% cresyl violet and 0.001% Fluoro-Jade. RNA from 10 Fluoro-Jade-positive neurons and 10 Fluoro-Jade-negative neurons, obtained from the hippocampal CA1, CA3, and dentate gyrus subfields using laser capture microdissection, was linearly amplified and analyzed by quantitative ribonuclease protection assay for nine neuroprotective and apoptosis-related genes.

RESULTS

In injured CA3 neurons, expression of the neuroprotective genes glutathione peroxidase 1, heme oxygenase 1, and brain-derived neurotrophic factor was significantly decreased compared with that of adjacent uninjured neurons. Superimposition of hemorrhagic hypotension was associated with down-regulation of neuroprotective genes in both injured and uninjured neurons of all subregions. Expression of apoptosis-related genes did not vary between injured and uninjured neurons, with or without superimposed hemorrhage.

CONCLUSIONS

The authors show, in the first direct comparison of messenger RNA levels in injured and uninjured hippocampal neurons, that injured neurons express lower levels of neuroprotective genes than adjacent uninjured neurons.

The role of mast cells in the pathogenesis of pain in chronic pancreatitis

BACKGROUND

The biological basis of pain in chronic pancreatitis is poorly understood. Mast cells have been implicated in the pathogenesis of pain in other conditions. We hypothesized that mast cells play a role in the pain of chronic pancreatitis. We examined the association of pain with mast cells in autopsy specimens of patients with painful chronic pancreatitis. We explored our hypothesis further using an experimental model of trinitrobenzene sulfonic acid (TNBS) -induced chronic pancreatitis in both wild type (WT) and mast cell deficient mice (MCDM).

METHODS

Archival tissues with histological diagnoses of chronic pancreatitis were identified and clinical records reviewed for presence or absence of reported pain in humans. Mast cells were counted. The presence of pain was assessed using von Frey Filaments (VFF) to measure abdominal withdrawal responses in both WT and MCDM mice with and without chronic pancreatitis.

RESULTS

Humans with painful chronic pancreatitis demonstrated a 3.5-fold increase in pancreatic mast cells as compared with those with painless chronic pancreatitis.WT mice with chronic pancreatitis were significantly more sensitive as assessed by VFF pain testing of the abdomen when compared with MCDM.

CONCLUSION

Humans with painful chronic pancreatitis have an increased number of pancreatic mast cells as compared with those with painless chronic pancreatitis. MCDM are less sensitive to mechanical stimulation of the abdomen after induction of chronic pancreatitis as compared with WT. Mast cells may play an important role in the pathogenesis of pain in chronic pancreatitis.

Trypsin mediates nociception via the proteinase-activated receptor 2: a potentially novel role in pancreatic pain

BACKGROUND & AIMS

The pathogenesis of pain in pancreatitis remains poorly understood. We hypothesized that trypsin, a key inflammatory mediator in this condition, can also activate nociceptive neurons via the proteinase-activated receptor 2.

METHODS

Double immunohistochemical staining of T8 to T12 dorsal root ganglia sections was performed with antibodies against proteinase-activated receptor 2 and vanilloid receptor 1, a marker for primary nociceptive neurons. In vivo nociceptive activity was measured by FOS immunoreactivity in thoracic spinal dorsal horn segments after intrapancreatic administration of proteinase-activated receptor 2 agonists. Pain behavior was assessed by visceromotor reflex activity in response to noxious stimulation of the pancreas with proteinase-activated receptor 2 agonists.

RESULTS

Proteinase-activated receptor 2 was expressed by virtually all nociceptive neurons in thoracic dorsal root ganglia. Intraductal trypsin, in subinflammatory concentrations, activated spinal dorsal horn neurons in a dose-dependent manner, as measured by FOS expression. Both trypsin and a proteinase-activated receptor 2-specific peptide agonist induced a behavioral pain response when infused into the pancreatic duct of awake rats. Preinfusion of the pancreatic duct with proteinase-activated receptor 2-specific activating peptide desensitized the response to trypsin.

CONCLUSIONS

Our findings suggest a novel proteinase-activated receptor 2-mediated role for trypsin in the pathogenesis of pancreatic pain and one that is independent of its inflammatory effect.

Acute pancreatitis results in referred mechanical hypersensitivity and neuropeptide up-regulation that can be suppressed by the protein kinase inhibitor k252a

Although pain is a cardinal feature of pancreatitis, its pathogenesis is poorly understood and treatment remains difficult. Nociceptive sensitization in several somatic pain models has been associated with activation of protein kinases including trkA, protein kinase C, and protein kinase A. We therefore tested the hypothesis that systemic treatment with a kinase inhibitor, k252a, known to inhibit all of these kinases would alleviate pain in an animal model of pancreatitis. Von Frey filament testing of somatic referral regions was evaluated as a method to measure referred pain in a rat model of acute necrotizing pancreatitis induced by L-arginine. Rats with pancreatitis showed increased sensitivity to abdominal stimulation with Von Frey filament. This referred mechanical sensitivity was associated with an 8-fold increase in levels of phosphorylated trkA in the pancreas and with significant up-regulation of both calcitonin gene-related peptide and preprotachykinin mRNA expression in thoracic dorsal root ganglia and with increased calcitonin gene-related peptide and substance P immunoreactivity in spinal cord segment T10. Treatment with the kinase inhibitor k252a suppressed the phosphorylation of trkA in the pancreas as well as reversed both the behavioral changes and the increase in neuropeptide expression associated with pancreatitis.

Intraductal administration of an NK1 receptor antagonist attenuates the inflammatory response to retrograde infusion of radiological contrast in rats: implications for the pathogenesis and prevention of ERCP-induced pancreatitis

INTRODUCTION

The neurogenic inflammatory mediator, substance P (SP), has been implicated in the pathogenesis of acute secretagogue-induced pancreatitis. We hypothesized that it may also play an important role in the development of acute pancreatitis after endoscopic retrograde cholangiopancreatography (ERCP). AIMS Our aim was to evaluate the effectiveness of CP-96345, a NK1 receptor antagonist, in diminishing post-ERCP pancreatitis in a rat model.

METHODS

The effects of CP-96345, when mixed with the contrast agent, were studied in a rat model of pancreatitis caused by retrograde contrast infusion. After 24 hours, histology, edema, and myeloperoxidase activity (MPO) of pancreas, plasma amylase, and NK1 receptor endocytosis in pancreatic acinar cells were evaluated.

RESULTS

Intraductal contrast infusion caused increases in plasma amylase, edema, histologic grade, and MPO of pancreas, and NK1 receptor internalization in pancreatic acinar cells. The addition of CP-96345 to the infusate significantly reduced pancreatic edema, MPO activity, and the histologic grade of pancreatitis accompanied by a decrease in NK1 receptor internalization.

CONCLUSIONS

When an NK1 receptor antagonist is delivered along with the contrast media there is significant reduction in the pancreatic inflammation caused by intraductal contrast infusion. These results provide some insight into the pathogenesis of ERCP induced pancreatitis as well as present novel pharmacological targets for its prevention.

Characterization of the neurotrophic response to acute pancreatitis

INTRODUCTION

Interesting preliminary data on changes in the neurotrophin system in various digestive diseases have recently begun to emerge.

AIMS

To measure changes in messenger RNA (mRNA) levels of neurotrophins and to identify cell types expressing neurotrophins in the pancreas of rats with L-arginine-induced pancreatitis.

METHODOLOGY

Rats were killed at time points from 2 hours to 4 weeks after the induction of pancreatitis, and responses were measured by assay.

RESULTS

By RNase protection assay, ciliary neurotrophic factor (CNTF) mRNA expression showed a rapid response (sixfold increase over control) in the inflamed pancreas at 2 hours. The levels of mRNA expression of brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4) in the inflamed pancreas reached a peak at 1 week (2.5-fold, twofold, fourfold, and fivefold increase, respectively). By immunohistochemistry, immunoreactivity for all neurotrophins examined was observed in the islets of Langerhans in the control pancreas at all time points, but it was markedly reduced in the islets in the inflamed pancreas at 2 and 6 hours. Acinar and ductal cells, inflammatory cells, and neural elements were immunoreactive for those neurotrophins in the inflamed pancreas from 2 hours to 2 weeks.

CONCLUSION

The temporal and spatial expression of neurotrophins in the course of experimental pancreatitis suggests that their upregulation is a critical component of the response of the pancreas to injury in this model.

Molecular cloning of the rat proteinase-activated receptor 4 (PAR4)

BACKGROUND

The proteinase-activated receptor 4 (PAR4) is a G-protein-coupled receptor activated by proteases such as thrombin and trypsin. Although activation of PAR4 has been shown to modulate rat gastrointestinal motility, the rat PAR4 sequence was unknown until now. This study aimed to identify the rat PAR4 cDNA.

RESULTS

The cDNA coding for the rat PAR4 homologue was cloned from the duodenum. Northern blots demonstrated a 3.0 kb transcript in the duodenum. Protein homology with mouse and human counterparts was 90% and 75% respectively. PAR4 is expressed predominantly in the esophagus, stomach, duodenum and the spleen. When expressed in COS cells, PAR4 is activated by trypsin (1 nM), thrombin (50 nM), mouse PAR4 specific peptide (500 microM) and a putative rat PAR4 specific activating peptide (100 microM), as measured by intracellular Ca2+-changes.

CONCLUSIONS

We have identified and characterized cDNA encoding the rat PAR4 homologue. PAR4 is expressed predominantly in the upper gastrointestinal tract. It is activated by trypsin, thrombin and its newly identified rat PAR4 specific activating peptide.

The proteinase-activated receptor 2 is involved in nociception

The proteinase-activated receptor 2 is expressed on a subset of primary afferent neurons and may participate in the neurogenic component of inflammation. We hypothesized that this receptor may also play a role in neuronal sensitization and contribute to the pathogenesis of pain in inflammatory conditions such as pancreatitis. Using a specific proteinase-activated receptor 2 activating peptide, we found evidence of such sensitization in vitro in the form of enhanced capsaicin- and KCl-evoked release of calcitonin gene-related peptide, a marker for nociceptive signaling. We then demonstrated that injection of the proteinase-activated receptor 2 activating peptide into the pancreatic duct can activate and sensitize pancreas-specific afferent neurons in vivo, as measured by Fos expression in the dorsal horn of the spinal cord. These observations suggest that proteinase-activated receptor 2 contributes to nociceptive signaling and may provide a novel link between inflammation and pain.

Regulation of forestomach-specific expression of the murine adenosine deaminase gene

The maturation of stratified squamous epithelium of the upper gastrointestinal tract is a highly ordered process of development and differentiation. Information on the molecular basis of this process is, however, limited. Here we report the identification of the first murine forestomach regulatory element using the murine adenosine deaminase (Ada) gene as a model. In the adult mouse, Ada is highly expressed in the terminally differentiated epithelial layer of upper gastrointestinal tract tissues. The data reported here represent the identification and detailed analysis of a 1. 1-kilobase (kb) sequence located 3.4-kb upstream of the transcription initiation site of the murine Ada gene, which is sufficient to target cat reporter gene expression to the forestomach in transgenic mice. This 1.1-kb fragment is capable of directing cat reporter gene expression mainly to the forestomach of transgenic mice, with a level comparable to the endogenous Ada gene. This expression is localized to the appropriate cell types, confers copy number dependence, and shows the same developmental regulation. Mutational analysis revealed the functional importance of multiple transcription factor-binding sites.

Rat trehalase: cDNA cloning and mRNA expression in adult rat tissues and during intestinal ontogeny

A partial rat trehalase cDNA has been cloned and used to examine trehalase mRNA expression. Northern blotting with total RNA from 11 adult rat tissues showed a trehalase transcript only in small intestine, where it was abundant in proximal regions but declined steeply toward the ileum. During development, trehalase mRNA was not detectable in jejunum until postnatal day 19 and then increased markedly through day 25. Modest levels in trehalase mRNA were induced precociously by administration of dexamethasone, with increasing responsiveness evident between the first and second postnatal weeks. In contrast, analysis of sucrase-isomaltase mRNA on the same blots showed maximal induction at both ages. In adrenalectomized animals, the ontogenic increase of trehalase mRNA began as usual but proceeded more slowly than in control animals. Overall, trehalase mRNA expression in the rat displayed both similarities and differences compared with rabbit. Moreover, the differences revealed in glucocorticoid responsiveness of trehalase mRNA and sucrase-isomaltase mRNA suggest that the actions of these hormones on the developing intestine may be more complex than previously recognized.

Diverse genetic regulatory motifs required for murine adenosine deaminase gene expression in the placenta

Murine adenosine deaminase (ADA) is a ubiquitous purine catabolic enzyme whose expression is subject to developmental and tissue-specific regulation. ADA is enriched in trophoblast cells of the chorioallantoic placenta and is essential for embryonic and fetal development. To begin to understand the genetic pathway controlling Ada gene expression in the placenta, we have identified and characterized a 770-base pair fragment located 5.4 kilobase pairs upstream of the Ada transcription initiation site, which directs reporter gene expression to the placenta of transgenic mice. The expression pattern of the reporter gene reflected that of the endogenous Ada gene in the placenta. Sequence analysis revealed potential binding sites for bHLH and GATA transcription factors. DNase I footprinting defined three protein binding regions, one of which was placenta-specific. Mutations in the potential protein binding sites and footprinting regions resulted in loss of placental expression in transgenic mice. These findings indicate that multiple protein binding motifs are necessary for Ada expression in the placenta.

An intron 1 regulatory region from the murine adenosine deaminase gene can activate heterologous promoters for ubiquitous expression in transgenic mice

Ubiquitously expressed genes contain regulatory features which allow expression in virtually all cell types. In an effort to understand the molecular basis for this regulatory feature, the chromatin structure of the murine adenosine deaminase gene was examined by DNase I digestion in nuclei of several tissues. The promoter contained a strong hypersensitive site in all tissues examined, including those with very high and very low levels of ADA expression. Transgenic mouse studies revealed that a 3.3 kb EcoRI (3.3EE) fragment from intron I was required to generate a strong promoter DNase I hypersensitive site, and to produce ubiquitous expression. The 3.3EE fragment also contained a thymic enhancer activity which mapped to sequences conserved with the human ADA gene T-lymphocyte enhancer. Mutational analysis indicated that ubiquitous expression was not dependent on the presence of a functional thymic enhancer. Both the thymic enhancer and the ubiquitous activator within the 3.3EE fragment functioned with heterologous promoters in transgenic mice.

5' flanking sequences of the murine adenosine deaminase gene direct expression of a reporter gene to specific prenatal and postnatal tissues in transgenic mice

Adenosine deaminase (ADA), an enzyme of purine metabolism, is highly expressed in four tissues of the mouse: the maternal decidua, the fetal placenta, the keratinizing epithelium of the upper alimentary tract (tongue, esophagus, and forestomach), and the absorptive epithelium of the proximal small intestine. ADA is produced at relatively low levels in all other tissues. To identify genetic elements that direct appropriate prenatal and postnatal expression of the ADA gene, a segment of DNA including the ADA promoter and 6.4 kilobases of the adjacent 5' flanking region was tested for the ability to direct the expression of a reporter gene in transgenic mice. In seven lines of transgenic mice studied, this construct directed high levels of reporter gene expression in the placenta and forestomach and exhibited correct developmental regulation in these tissues. This construct failed to direct significant reporter gene expression to either the maternal decidua or the proximal small intestine. Thus, different gene regulatory elements are required to target high expression to the four tissues characterized by high levels of ADA.

Malignant islet cell adenoma in a pancreatic cyst. Report of a case

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