Divergent role for CRF1 and CRF2 receptors in the modulation of visceral pain

Research Progress of Central and Peripheral Corticotropin-Releasing Hormone in Irritable Bowel Syndrome with Comorbid Dysthymic Disorders

Irritable bowel syndrome (IBS) is considered a stress disorder characterized by psychological and gastrointestinal dysfunction. IBS patients not only suffer from intestinal symptoms such as abdominal pain, diarrhea, or constipation but also, experience dysthymic disorders such as anxiety and depression. Studies have found that corticotropin-releasing hormone plays a key role in IBS with comorbid dysthymic disorders. Next, we will summarize the effects of corticotropin-releasing hormone from the central nervous system and periphery on IBS with comorbid dysthymic disorders and relevant treatments based on published literatures in recent years.

Neural circuits regulating visceral pain

Visceral hypersensitivity, a common clinical manifestation of irritable bowel syndrome, may contribute to the development of chronic visceral pain, which is a major challenge for both patients and health providers. Neural circuits in the brain encode, store, and transfer pain information across brain regions. In this review, we focus on the anterior cingulate cortex and paraventricular nucleus of the hypothalamus to highlight the progress in identifying the neural circuits involved in visceral pain. We also discuss several neural circuit mechanisms and emphasize the importance of cross-species, multiangle approaches and the identification of specific neurons in determining the neural circuits that control visceral pain.

Stress-induced bladder hypersensitivity: Effect of corticotropin releasing factor receptors assessed by spinal neurophysiology and neurochemistry

Corticotropin releasing factor (CRF) receptors have been implicated in stress-induced hyperalgesia. The present study examined the role of CRF receptors Type 1&2 (CRFR1, CRFR2) in stress-induced bladder hyperalgesia in female rats by quantifying changes in receptor and agonist content following chronic (CFS, 7 daily episodes), acute (AFS, single episode) and control (NFS, no episodes) footshock protocols. ELISAs demonstrated that CFS lead to an increase in spinal thoracolumbar and lumbosacral spinal cord CRFR2 content and a decrease in lumbosacral spinal cord CRFR1 content. Content of the endogenous CRFR2 agonist, urocortin 2, was also increased in lumbosacral spinal cord and bladder tissues of CFS-pretreated rats, but urocortin 3 was decreased. Correlative single unit studies of lumbosacral dorsal horn neurons excited by bladder distension, in anesthetized rats that had undergone CFS, AFS or NFS protocols, used a before-after methodology with administration of a CRFR1 antagonist (antalarmin, 24 μg), CRFR2 antagonist (aSVG30, 12 μg) or normal saline topically to the exposed spinal cord following primary characterization. aSVG30 produced a reduction of neuronal responses evoked by bladder distension in CFS-pretreated rats but no statistically significant effects of aSVG30, antalarmin or vehicle were noted in other groups tested with the exception that antalarmin had an inhibitory effect on spontaneous activity in NFS-pretreated rats. The present findings are consistent with previous experiments using reflex responses to bladder distension as endpoints and further support a role for CRFR2-related mechanisms in stress-induced bladder hypersensitivity. This suggests CRFR2 antagonists may have efficacy in the treatment of bladder pain.

The Double Insult of Neonatal Cystitis Plus Adult Somatic Inflammation Results in Corticotropin Releasing Factor Type II Receptor-Dependent Bladder Hypersensitivity in Female Rats

The spinal mechanisms of visceral hypersensitivity are poorly understood, particularly when there is an interaction with somatic systems. Recently we demonstrated that rats which were pretreated with neonatal bladder inflammation (NBI) and subsequently pretreated as adults with bladder re-inflammation had augmented reflex and neuronal responses to urinary bladder distension via a corticotropin-releasing factor receptor type II (CRFR2) mechanism. Another insult producing similar augmented responses is somatic inflammation induced by Complete Freund's Adjuvant (CFA) in the hindlimb. Using neurochemical measures and both reflex and neuronal responses to urinary bladder distension as endpoints, the present study probed the role of CRFR2-related mechanisms in bladder hyperalgesia secondary to NBI and CFA-induced hindlimb inflammation. ELISA measures of the lumbosacral spinal cord demonstrated increased CRFR2 protein following pretreatment with NBI+CFA. Intrathecal CRFR2 antagonists blocked the augmentation of visceromotor responses to distension following pretreatment with both NBI+CFA. Lumbosacral dorsal horn neuronal responses to bladder distension in rats pretreated with NBI+CFA were attenuated by the spinal topical administration of a CRFR2 antagonist. These findings are the first demonstration of a somatovisceral interaction working via CRFR2 receptors and support the therapeutic value of these agents in the treatment of painful bladder disorders, particularly when triggered by somatic events. (Word Count 199). PERSPECTIVE: Bladder hypersensitivity occurs following neonatal cystitis and an adult insult such as somatic inflammation. This paper demonstrates that CRFR2-related mechanisms are associated with this hypersensitivity. This supports the therapeutic value of these agents in the treatment of painful bladder disorders, particularly when triggered by somatic events.

Peripheral CRF-R1/CRF-R2 antagonist, astressin C, induces a long-lasting blockade of acute stress-related visceral pain in male and female rats

Peptide CRF antagonists injected peripherally alleviate stress-induced visceral hypersensitivity (SIVH) to colorectal distension (CRD) in rodents. Here we further evaluated the dose and time-dependent inhibitory activity of several long-acting peptide CRF receptor antagonists related to astressin on SIVH, focusing on astressin C (AstC), which previously showed high efficacy on stress-related alterations of HPA axis and gut secretomotor functions. Male and female Sprague-Dawley rats pretreated subcutaneously (SC) with AstC were injected intraperitoneally (IP) with CRF 15 min later. The visceromotor responses (VMR) to graded phasic CRD (10, 20, 40 and 60 mmHg) were monitored at basal, 15 min and up to 1-8 days after pretreatment. Two other astressin analogs, hexanoyl-astressin D (Hex-AstD) and [CαMeVal^19,32]-AstC, were also tested. The response to IP CRF was sex-dependent with female rats requiring a higher dose to exhibit visceral hyperalgesia. Pretreatment with AstC (30-1000 µg/kg) resulted in a dose-related inhibition of IP CRF-induced SIVH and diarrhea in both sexes. The highest dose prevented SIVH and diarrhea up to 5-7 days after a single SC injection and was lost on day 7 (females) and day 8 (males) but reinstated after a second injection of AstC on day 8 or 9 respectively. [CαMeVal^19,32]-AstC and Hex-AstD (1000 µg/kg in males) also prevented SIVH. These data show the potent long-lasting anti-hyperalgesic effect of AstC in an acute model of SIVH in both male and female rats. This highlights the potential of long-acting peripheral CRF antagonists to treat stress-sensitive irritable bowel syndrome.

Neonatal cystitis leads to alterations in spinal corticotropin releasing factor receptor-type 2 content and function in adult rats following bladder re-inflammation

Spinal mechanisms associated with visceral hypersensitivity are poorly understood. One model of bladder hypersensitivity with phenotypic features similar to the disorder interstitial cystitis/bladder pain syndrome is the neonatal bladder inflammation (NBI) model. In this model, rat pup bladders are infused with zymosan solutions on post-partum days 14-16 and then rats are retested as adults. Studies of other sites of deep tissue hypersensitivity have suggested a role for corticotropin-releasing factor (CRF) receptors type 1 and 2 (CRFR1 and CRFR2). Using neurochemical measures, pharmacological manipulations and both reflex and neuronal responses to urinary bladder distension as endpoints, the present study probed the role of CRFR2s in bladder hyperalgesia secondary to NBI and acute bladder re-inflammation as an adult (ABI). ELISA measures of the lumbosacral spinal cord demonstrated increased CRFR1s and CRFR2s following pretreatment with both NBI + ABI as well as NBI-related increases in the CRFR2 agonist urocortin 2. Intrathecal CRFR2 antagonists, but not a CRFR1 antagonist, blocked the augmentation of visceromotor responses to distension following pretreatment with both NBI + ABI. Lumbosacral dorsal horn neuronal responses to distension in rats pretreated with NBI + ABI were attenuated by the spinal topical administration of a CRFR2 antagonist. These studies suggest therapeutic value of CRFR2 antagonists in the treatment of painful bladder disorders.

Functional and Anatomical Characterization of Corticotropin-Releasing Factor Receptor Subtypes of the Rat Spinal Cord Involved in Somatic Pain Relief

Corticotropin-releasing factor (CRF) orchestrates our body’s response to stressful stimuli. Pain is often stressful and counterbalanced by activation of CRF receptors along the nociceptive pathway, although the involvement of the CRF receptor subtypes 1 and/or 2 (CRF-R1 and CRF-R2, respectively) in CRF-induced analgesia remains controversial. Thus, the aim of the present study was to examine CRF-R1 and CRF-R2 expression within the spinal cord of rats with Freund’s complete adjuvant-induced unilateral inflammation of the hind paw using reverse transcriptase polymerase chain reaction, Western blot, radioligand binding, and immunofluorescence confocal analysis. Moreover, the antinociceptive effects of intrathecal (i.t.) CRF were measured by paw pressure algesiometer and their possible antagonism by selective antagonists for CRF-R1 and/or CRF-R2 as well as for opioid receptors. Our results demonstrated a preference for the expression of CRF-R2 over CRF-R1 mRNA, protein, binding sites and immunoreactivity in the dorsal horn of the rat spinal cord. Consistently, CRF as well as CRF-R2 agonists elicited potent dose-dependent antinociceptive effects which were antagonized by the i.t. CRF-R2 selective antagonist K41498, but not by the CRF-R1 selective antagonist NBI35965. In addition, i.t. applied opioid antagonist naloxone dose-dependently abolished the i.t. CRF- as well as CRF-R2 agonist-elicited inhibition of somatic pain. Importantly, double immunofluorescence confocal microscopy of the spinal dorsal horn showed CRF-R2 on enkephalin (ENK)-containing inhibitory interneurons in close opposition of incoming mu-opioid receptor-immunoreactive nociceptive neurons. CRF-R2 was, however, not seen on pre- or on postsynaptic sensory neurons of the spinal cord. Taken together, these findings suggest that i.t. CRF or CRF-R2 agonists inhibit somatic inflammatory pain predominantly through CRF-R2 receptors located on spinal enkephalinergic inhibitory interneurons which finally results in endogenous opioid-mediated pain inhibition.

Corticotropin-releasing factor neurons in the bed nucleus of the stria terminalis exhibit sex-specific pain encoding in mice

The bed nucleus of the stria terminalis (BNST) plays an emerging role in pain regulation. Pharmacological studies have found that inhibiting corticotropin-releasing factor (CRF) signaling in the BNST can selectively mitigate the sensory and affective-motivational components of pain. However, mechanistic insight on the source of CRF that drives BNST responses to these harmful experiences remains unknown. In the present study, we used a series of genetic approaches to show that CRF in the BNST is engaged in the processing and modulation of pain. We conducted cell-type specific in vivo calcium imaging in CRF-Cre mice and found robust and synchronized recruitment of BNSTCRF neurons during acute exposures to noxious heat. Distinct patterns of recruitment were observed by sex, as the magnitude and timing of heat responsive activity in BNSTCRF neurons differed for male and female mice. We then used a viral approach in Floxed-CRF mice to selectively reduce CRF expression in the BNST and found it decreased nociceptive sensitivity for both sexes and increased paw attending for females. Together, these findings reveal that CRF in the BNST influences multiple facets of the pain experience to impact the sex-specific expression of pain-related behaviors.

Amygdalar Corticotropin-Releasing Factor Signaling Is Required for Later-Life Behavioral Dysfunction Following Neonatal Pain

Neonatal pain such as that experienced by infants in the neonatal intensive care unit is known to produce later-life dysfunction including heightened pain sensitivity and anxiety, although the mechanisms remain unclear. Both chronic pain and stress in adult organisms are known to influence the corticotropin-releasing factor (CRF) system in the Central Nucleus of the Amygdala, making this system a likely candidate for changes following neonatal trauma. To examine this, neonatal rats were subjected to daily pain, non-painful handling or left undisturbed for the first week of life. Beginning on postnatal day, 24 male and female rats were subjected to a 4-day fear conditioning and sensory testing protocol. Some subjects received intra-amygdalar administration of either Vehicle, the CRF receptor 1 (CRF₁) receptor antagonist Antalarmin, or the CRF receptor 2 (CRF₂) receptor antagonist Astressin 2B prior to fear conditioning and somatosensory testing, while others had tissue collected following fear conditioning and CRF expression in the CeA and BLA was assessed using fluorescent in situ hybridization. CRF₁ antagonism attenuated fear-induced hypersensitivity in neonatal pain and handled rats, while CRF₂ antagonism produced a general antinociception. In addition, neonatal pain and handling produced a lateralized sex-dependent decrease in CRF expression, with males showing a diminished number of CRF-expressing cells in the right CeA and females showing a similar reduction in the number of CRF-expressing cells in the left BLA compared to undisturbed controls. These data show that the amygdalar CRF system is a likely target for alleviating dysfunction produced by early life trauma and that this system continues to play a major role in the lasting effects of such trauma into the juvenile stage of development.

The Role of Corticotropin-Releasing Hormone at Peripheral Nociceptors: Implications for Pain Modulation

Peripheral nociceptors and their synaptic partners utilize neuropeptides for signal transmission. Such communication tunes the excitatory and inhibitory function of nociceptor-based circuits, eventually contributing to pain modulation. Corticotropin-releasing hormone (CRH) is the initiator hormone for the conventional hypothalamic-pituitary-adrenal axis, preparing our body for stress insults. Although knowledge of the expression and functional profiles of CRH and its receptors and the outcomes of their interactions has been actively accumulating for many brain regions, those for nociceptors are still under gradual investigation. Currently, based on the evidence of their expressions in nociceptors and their neighboring components, several hypotheses for possible pain modulations are emerging. Here we overview the historical attention to CRH and its receptors on the peripheral nociception and the recent increases in information regarding their roles in tuning pain signals. We also briefly contemplate the possibility that the stress-response paradigm can be locally intrapolated into intercellular communication that is driven by nociceptor neurons. Such endeavors may contribute to a more precise view of local peptidergic mechanisms of peripheral pain modulation.

Neurobiological aspects of pain in the context of alcohol use disorder

Alcohol is an effective and widely utilized analgesic. However, the chronic use of alcohol can actually facilitate nociceptive sensitivity over time, a condition known as hyperalgesia. Excessive and uncontrollable alcohol drinking is also a hallmark feature of alcohol use disorder (AUD). Both AUD and chronic pain are typically accompanied by negative affective states that may underlie reinforcement mechanisms contributing to AUD maintenance or progression. Frequent utilization of alcohol to relieve pain in individuals suffering from AUD or other chronic pain conditions may thus represent a powerful negative reinforcement construct. This chapter will describe ties between alcohol-mediated pain relief and potential exacerbation of AUD. We describe neurobiological systems engaged in alcohol analgesia as well as systems recruited in the development and maintenance of AUD and hyperalgesia. Although few effective therapies exist for either chronic pain or AUD, the common interaction of these conditions will likely lead the way for promising new discoveries of more effective and even simultaneous treatment of AUD and co-morbid hyperalgesia. An abundance of neurobiological findings from multiple laboratories has implicated a potentiation of central amygdala (CeA) signaling in both pain and AUD, and these data also suggest that attenuation of stress-related systems (including corticotropin-releasing factor, vasopressin, and glucocorticoid receptor activity) would be particularly effective and comprehensive therapeutic strategies targeting the critical intersection of somatic and motivational mechanisms driving AUD, including alcohol-induced hyperalgesia.

A medial prefrontal cortex-nucleus acumens corticotropin-releasing factor circuitry for neuropathic pain-increased susceptibility to opioid reward

Recent studies have shown that persistent pain facilitates the response to morphine reward. However, the circuit mechanism underlying this process remains ambiguous. In this study, using chronic constriction injury (CCI) of the sciatic nerve in mice, we found that persistent neuropathic pain reduced the minimum number of morphine conditioning sessions required to induce conditioned place preference (CPP) behavior. This dose of morphine had no effect on the pain threshold. In the medial prefrontal cortex (mPFC), which is involved in both pain and emotion processing, corticotropin-releasing factor (CRF) expressing neuronal activity was increased in CCI mice. Chemogenetic inhibition of mPFC CRF neurons reversed CCI-induced morphine CPP facilitation. Furthermore, the nucleus acumens (NAc) received mPFC CRF functional projections that exerted excitatory effects on NAc neurons. Optogenetic inhibition of mPCF neuronal terminals or local infusion of the CRF receptor 1 (CRFR1) antagonist in the NAc restored the effects of neuropathic pain on morphine-induced CPP behavior, but not in normal mice. On a molecular level, in CCI mice, CRFR1 protein expression was increased in the NAc by a histone dimethyltransferase G9a-mediated epigenetic mechanism. Local G9a knockdown increased the expression of CRFR1 and mimicked CCI-induced hypersensitivity to acquiring morphine CPP. Taken together, these findings demonstrate a previously unknown and specific mPFC CRF engagement of NAc neuronal circuits, the sensitization of which facilitates behavioral responses to morphine reward in neuropathic pain states via CRFR1s.

Sound-stress-induced altered nociceptive behaviors are associated with increased spinal CRFR2 gene expression in a rat model of burn injury

Sound stress (SS) elicits behavioral changes, including pain behaviors. However, the neuronal mechanisms underlying SS-induced pain behaviors remain to be explored. The current study examined the effects of SS on nociceptive behaviors and changes in expression of the spinal corticotropin-releasing factor (CRF) system in male Sprague Dawley rats with and without thermal pain. We also studied the effects of SS on plasma corticosterone and fecal output. Rats were exposed to 3 days of SS protocol (n = 12/group). Changes in nociceptive behaviors were assessed using thermal and mechanical pain tests. Following the induction of SS, a subgroup of rats (n = 6/group) was inflicted with thermal injury and on day 14 postburn nociceptive behaviors were reassessed. Spinal CRF receptor mRNA expression was analyzed by semiquantitative reverse transcription polymerase chain reaction (RT-PCR). In addition, plasma corticosterone and spinal CRF concentrations were quantified using enzyme-linked immunosorbent assay (ELISA). Increased defecation was observed in SS rats. SS produced transient mechanical allodynia in naive rats, whereas it exacerbated thermal pain in thermally injured rats. Spinal CRFR2 mRNA expression was unaffected by stress or thermal injury alone, but their combined effect significantly increased its expression. SS had no effect on plasma corticosterone and spinal CRF protein in postburn rats. To conclude, SS is capable of exacerbating postburn thermal pain, which is linked to increased CRFR2 gene expression in the spinal cord. Future studies have to delineate whether attenuation of CRFR2 signaling at the spinal level prevents stress-induced exacerbation of burn pain.

Pharmacotherapy in smoking cessation: Corticotropin Releasing Factor receptors as emerging intervention targets

Smoking represents perhaps the single most important health risk factor and a global contributor to mortality that can unquestionably be prevented. Smoking is responsible for many diseases, including various types of cancer, chronic obstructive pulmonary disease, coronary heart disease, peripheral vascular disease and peptic ulcer, while it adversely affects fetal formation and development. Since smoking habit duration is a critical factor for mortality, the goal of treatment should be its timely cessation and relapse prevention. Drug intervention therapy is an important ally in smoking cessation. Significant positive steps have been achieved in the last few years in the development of supportive compounds. In the present review, we analyze reports studying the role of Corticotropin Releasing Factor (CRF), the principle neuroendocrine mediator of the stress response and its two receptors (CRF1 and CRF2) in the withdrawal phase as well as in the abstinence from nicotine use. Although still in pre-clinical evaluation, therapeutic implications of these data were investigated in order to highlight potential pharmaceutical interventions.

In vivo neutralization of IL-6 receptors ameliorates gastrointestinal dysfunction in dystrophin-deficient mdx mice

BACKGROUND

Duchenne muscular dystrophy (DMD) is a fatal disease characterized by progressive deterioration and degeneration of striated muscle. A mutation resulting in the loss of dystrophin, a structural protein which protects cells from contraction-induced damage, underlies DMD pathophysiology. Damage to muscle fibers results in chronic inflammation and elevated levels of proinflammatory cytokines such as interleukin-6 (IL-6). However, loss of cellular dystrophin also affects neurons and smooth muscle in the gastrointestinal (GI) tract with complaints such as hypomotility, pseudo-obstruction, and constipation reported in DMD patients.

METHODS

Using dystrophin-deficient mdx mice, studies were carried out to examine colonic morphology and function compared with wild-type mice. Treatment with neutralizing IL-6 receptor antibodies (xIL-6R) and/or the corticotropin-releasing factor (CRF) 2 receptor agonist, urocortin 2 (uro2) was tested to determine if they ameliorated GI dysfunction in mdx mice.

KEY RESULTS

Mdx mice exhibited thickening of colonic smooth muscle layers and delayed stress-induced defecation. In organ bath studies, neurally mediated IL-6-evoked contractions were larger in mdx colons. In vivo treatment of mdx mice with xIL-6R normalized defecation rates and colon lengths. Uro2 treatment did not affect motility or morphology. The potentiated colonic contractile response to IL-6 was attenuated by treatment with xIL-6R.

CONCLUSIONS & INFERENCES

These findings confirm the importance of dystrophin in normal GI function and implicate IL-6 as an important regulator of GI motility in the mdx mouse. Inhibition of IL-6 signaling may offer a potential new therapeutic strategy for treating DMD-associated GI symptoms.

Activation of corticotropin-releasing factor neurons and microglia in paraventricular nucleus precipitates visceral hypersensitivity induced by colorectal distension in rats

Visceral hypersensitivity is a major contributor to irritable bowel syndrome and other disorders with visceral pain. Substantial evidence has established that glial activation and neuro-glial interaction play a key role in the establishment and maintenance of visceral hypersensitivity. We recently demonstrated that activation of spinal microglial toll-like receptor 4 (TLR4)/myeloid differentiation factor 88 (MyD88)/nuclear factor κB (NF-κB) signaling facilitated the development of visceral hypersensitivity in a rat model developed by neonatal and adult colorectal distensions (CRDs). Hypothalamic paraventricular nucleus (PVN) plays a pivotal role in the pathogenesis of chronic pain. In this study, we examined the mechanism by which microglia and neurons in PVN establish and maintain visceral hypersensitivity and the involvement of TLR4 signaling. Visceral hypersensitivity was precipitated by adult colorectal distension (CRD) only in rats that experienced neonatal CRDs. Visceral hypersensitivity was associated with an increase in the expression of c-fos, corticotropin-releasing factor (CRF) protein and mRNA in PVN, which could be prevented by intra-PVN infusion of lidocaine or small interfering RNA targeting the CRF gene. These results suggest PVN CRF neurons modulate visceral hypersensitivity. Adult CRD induced an increase in the expression of Iba-1 (a microglial marker), TLR4 protein, and its downstream effectors MyD88, NF-κB, as well as proinflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) only in rats that experienced neonatal CRDs. Intra-PVN infusion of minocycline, a nonselective microglial inhibitor, attenuated the hyperactivity of TLR4 signaling cascade, microglial activation, and visceral hypersensitivity. Taken together, these data suggest that neonatal CRDs induce a glial activation in PVN. Adult CRD potentiates the glial and CRF neuronal activity, and precipitates visceral hypersensitivity and pain. TLR4 signaling and proinflammatory cytokines TNF-α and IL-1β may participate in neuro-glial interaction during the pathogenesis of visceral hypersensitivity.

Water avoidance stress induces visceral hyposensitivity through peripheral corticotropin releasing factor receptor type 2 and central dopamine D2 receptor in rats

BACKGROUND

Water avoidance stress (WAS) is reported to induce functional changes in visceral sensory function in rodents, but the results which have been demonstrated so far are not consistent, i.e., hypersensitivity or hyposensitivity. We determined the effect of WAS on visceral sensation and evaluated the mechanisms of the action.

METHODS

Visceral sensation was assessed by abdominal muscle contractions induced by colonic balloon distention, i.e., visceromotor response (VMR), measured electrophysiologically in conscious rats. The electromyogram electrodes were acutely implanted under anesthesia on the day of the experiment. The threshold of VMR was measured before and after WAS for 1 h. To explore the mechanisms of WAS-induced response, drugs were administered 10 min prior to the initiation of WAS.

KEY RESULTS

WAS significantly increased the threshold of VMR, and this effect was no longer detected at 24 h after. Intraperitoneal injection of astressin2 -B (200 μg/kg), a corticotropin releasing factor (CRF) receptor type 2 antagonist abolished the response by WAS. Subcutaneous (sc) injection of sulpiride (200 mg/kg), a dopamine D2 receptor antagonist blocked the response, while sc domperidone (10 mg/kg), a peripheral dopamine D2 receptor antagonist did not alter it. Naloxone (1 mg/kg, sc), an opioid antagonist did not modify it either.

CONCLUSIONS & INFERENCES

WAS induced visceral hyposensitivity through peripheral CRF receptor type 2 and central dopamine D2 receptor, but not through opioid pathways. As altered pain inhibitory system was reported to be observed in the patients with irritable bowel syndrome, CRF and dopamine signaling might contribute to the pathophysiology.

Stress and the Microbiota-Gut-Brain Axis in Visceral Pain: Relevance to Irritable Bowel Syndrome

Visceral pain is a global term used to describe pain originating from the internal organs of the body, which affects a significant proportion of the population and is a common feature of functional gastrointestinal disorders (FGIDs) such as irritable bowel syndrome (IBS). While IBS is multifactorial, with no single etiology to completely explain the disorder, many patients also experience comorbid behavioral disorders, such as anxiety or depression; thus, IBS is described as a disorder of the gut-brain axis. Stress is implicated in the development and exacerbation of visceral pain disorders. Chronic stress can modify central pain circuitry, as well as change motility and permeability throughout the gastrointestinal (GI) tract. More recently, the role of the gut microbiota in the bidirectional communication along the gut-brain axis, and subsequent changes in behavior, has emerged. Thus, stress and the gut microbiota can interact through complementary or opposing factors to influence visceral nociceptive behaviors. This review will highlight the evidence by which stress and the gut microbiota interact in the regulation of visceral nociception. We will focus on the influence of stress on the microbiota and the mechanisms by which microbiota can affect the stress response and behavioral outcomes with an emphasis on visceral pain.

Intrathecal urocortin I in the spinal cord as a murine model of stress hormone-induced musculoskeletal and tactile hyperalgesia

Stress is antinociceptive in some models of pain, but enhances musculoskeletal nociceptive responses in mice and muscle pain in patients with fibromyalgia syndrome. To test the hypothesis that urocortins are stress hormones that are sufficient to enhance tactile and musculoskeletal hyperalgesia, von Frey fibre sensitivity and grip force after injection of corticotropin-releasing factor (CRF), urocortin I and urocortin II were measured in mice. Urocortin I (a CRF1 and CRF2 receptor ligand) produced hyperalgesia in both assays when injected intrathecally (i.t.) but not intracerebroventricularly, and only at a large dose when injected peripherally, suggesting a spinal action. Morphine inhibited urocortin I-induced changes in nociceptive responses in a dose-related fashion, confirming that changes in behaviour reflect hyperalgesia rather than weakness. No tolerance developed to the effect of urocortin I (i.t.) when injected repeatedly, consistent with a potential to enhance pain chronically. Tactile hyperalgesia was inhibited by NBI-35965, a CRF1 receptor antagonist, but not astressin 2B, a CRF2 receptor antagonist. However, while urocortin I-induced decreases in grip force were not observed when co-administered i.t. with either NBI-35965 or astressin 2B, they were even more sensitive to inhibition by astressin, a non-selective CRF receptor antagonist. Together these data indicate that urocortin I acts at CRF receptors in the mouse spinal cord to elicit a reproducible and persistent tactile (von Frey) and musculoskeletal (grip force) hyperalgesia. Urocortin I-induced hyperalgesia may serve as a screen for drugs that alleviate painful conditions that are exacerbated by stress.

A balance theory of peripheral corticotropin-releasing factor receptor type 1 and type 2 signaling to induce colonic contractions and visceral hyperalgesia in rats

Several recent studies suggest that peripheral corticotropin-releasing factor (CRF) receptor type 1 (CRF1) and CRF2 have a counter regulatory action on gastrointestinal functions. We hypothesized that the activity balance of each CRF subtype signaling may determine the changes in colonic motility and visceral sensation. Colonic contractions were assessed by the perfused manometry, and contractions of colonic muscle strips were measured in vitro in rats. Visceromotor response was determined by measuring contractions of abdominal muscle in response to colorectal distensions (CRDs) (60 mm Hg for 10 min twice with a 30-min rest). All drugs were administered through ip route in in vivo studies. CRF increased colonic contractions. Pretreatment with astressin, a nonselective CRF antagonist, blocked the CRF-induced response, but astressin2-B, a selective CRF2 antagonist, enhanced the response by CRF. Cortagine, a selective CRF1 agonist, increased colonic contractions. In in vitro study, CRF increased contractions of muscle strips. Urocortin 2, a selective CRF2 agonist, itself did not alter the contractions but blocked this increased response by CRF. Visceromotor response to the second CRD was significantly higher than that of the first. Astressin blocked this CRD-induced sensitization, but astressin2-B or CRF did not affect it. Meanwhile, astressin2-B together with CRF significantly enhanced the sensitization. Urocortin 2 blocked, but cortagine significantly enhanced, the sensitization. These results indicated that peripheral CRF1 signaling enhanced colonic contractility and induced visceral sensitization, and these responses were modulated by peripheral CRF2 signaling. The activity balance of each subtype signaling may determine the colonic functions in response to stress.

Importance of CRF receptor-mediated mechanisms of the bed nucleus of the stria terminalis in the processing of anxiety and pain

Corticotropin-releasing factor (CRF)-mediated mechanisms in the bed nucleus of the stria terminalis (BNST) have a pivotal role in stress-induced anxiety and hyperalgesia. Although CRF is known to activate two receptor subtypes, CRF1 and CRF2, attempts to delineate the specific role of each subtype in modulating anxiety and nociception have been inconsistent. Here we test the hypothesis that CRF1 and CRF2 receptor activation in the anteriolateral BNST (BNSTAL) facilitates divergent mechanisms modulating comorbid anxiety and hyperalgesia. Microinfusions of the specific antagonists CP376395 and Astressin2B into the BNSTAL were used to investigate CRF1 and CRF2 receptor functions, respectively. We found that CRF1 and CRF2 receptors in the BNSTAL had opposing effects on exploratory behavior in the elevated plus-maze, somatic mechanical threshold, and the autonomic and endocrine response to stress. However, CRF1 or CRF2 receptor antagonism in the BNSTAL revealed complementary roles in facilitating the acoustic startle and visceromotor reflexes. Our results suggest that the net effect of CRF1 and CRF2 receptor activation in the BNSTAL is pathway-dependent and provides important insight into the CRF receptor-associated circuitry that likely underpins stress-induced pathologies.

Effects of contact dermatitis on hepatic gene expression in broilers

1. Severe foot and hock dermatitis in broiler chickens can reduce growth rate and increase susceptibility to bacterial infection, affecting both profitability and welfare. However, little is known about the underlying physiological changes associated with foot and hock lesions. 2. This study compared global hepatic gene expression in control birds and those with ammonia-induced foot and hock lesions using Agilent 44 K chicken oligonucleotide microarrays (8 birds per group). 3. In total, 417 genes were differentially expressed of which 174 could be mapped onto the genome. Genes associated with energy metabolism, thyroid hormone activity and cellular control were affected, while there was also evidence of an up-regulation of genes linked to a pro-inflammatory response. 4. It is conceivable that pain is the underlying cause for the observed changes in energy metabolism genes. 5. Changes in hepatic gene expression provide new information on how a chicken's physiological mechanisms alter to cope with foot and hock lesions. The findings support other data indicating that birds with increased severity of lesions are likely to be in pain and that growth will be compromised. Reduction of the incidence of dermatitis by improved husbandry should therefore benefit both welfare and commercial performance.

Effects of corticotropin-releasing factor on intermediolateral cell column neurons of newborn rats

Corticotropin-releasing factor (CRF) is a neuropeptide that mediates neuroendocrine, autonomic, and behavioral processes associated with the stress response. CRF-containing fibers and receptors are found in various regions of the central nervous system including the spinal cord. Here, we report excitatory effects of CRF on sympathetic preganglionic neurons in the intermediolateral cell column (IML) of in vitro spinal cord preparations from newborn rats. We also examine the receptor subtypes that are involved in the CRF effects. Application of CRF significantly depolarized the IML neurons and increased the frequency of excitatory postsynaptic potentials (EPSPs) in the IML neurons. These effects were blocked by the CRF receptor 1 antagonist, antalarmin. Menthol, a transient receptor potential channel M8 agonist, depressed EPSPs enhanced by CRF. Our findings suggested that CRF depolarized the IML neurons via direct postsynaptic action and CRF-affected interneurons located in the spinal cord send EPSPs to IML neurons. These excitatory effects of CRF may be caused through CRF1 receptors but not CRF2 receptors.

Systemic urocortin 2, but not urocortin 1 or stressin 1-A, suppresses feeding via CRF2 receptors without malaise and stress

BACKGROUND AND PURPOSE

Infusion of corticotropin-releasing factor (CRF)/urocortin (Ucn) family peptides suppresses feeding in mice. We examined whether rats show peripheral CRF/Ucn-induced anorexia and determined its behavioural and pharmacological bases.

EXPERIMENTAL APPROACH

Male Wistar rats (n= 5-12 per group) were administered (i.p.) CRF receptor agonists with different subtype affinities. Food intake, formation of conditioned taste aversion and corticosterone levels were assessed. In addition, Ucn 1- and Ucn 2-induced anorexia was studied in fasted CRF(2) knockout (n= 11) and wild-type (n= 13) mice.

KEY RESULTS

Ucn 1, non-selective CRF receptor agonist, reduced food intake most potently (~0.32 nmol·kg(-1) ) and efficaciously (up to 70% reduction) in fasted and fed rats. The peptides' rank-order of anorexic potency was Ucn 1 ≥ Ucn 2 > >stressin(1) -A > Ucn 3, and efficacy, Ucn 1 > stressin(1) -A > Ucn 2 = Ucn 3. Ucn 1 reduced meal frequency and size, facilitated feeding bout termination and slowed eating rate. Stressin(1) -A (CRF(1) agonist) reduced meal size; Ucn 2 (CRF(2) agonist) reduced meal frequency. Stressin(1) -A and Ucn 1, but not Ucn 2, produced a conditioned taste aversion, reduced feeding efficiency and weight regain and elicited diarrhoea. Ucn 1, but not Ucn 2, also increased corticosterone levels. Ucn 1 and Ucn 2 reduced feeding in wild-type, but not CRF(2) knockout, mice.

CONCLUSIONS AND IMPLICATIONS

CRF(1) agonists, Ucn 1 and stressin(1) -A, reduced feeding and induced interoceptive stress, whereas Ucn 2 potently suppressed feeding via a CRF(2) -dependent mechanism without eliciting malaise. Consistent with their pharmacological differences, peripheral urocortins have diverse effects on appetite.

Pain is a salient "stressor" that is mediated by corticotropin-releasing factor-1 receptors

Corticotropin-releasing factor (CRF) plays a major role in controlling the body's response to stress. Because painful conditions are inherently stressful, we hypothesize that CRF may act via CRF-1 receptors to contribute to the pain experience. Studies were designed to investigate whether blocking CRF-1 receptors with selective antagonists or reducing their expression with CRF-Saporin, would attenuate ulcer, inflammatory- and neuropathic-like pain. Five experimental designs were undertaken. In experiment 1, ulcer pain was induced in mice following oral administration of indomethacin, while in experiments 2 and 3, inflammatory pain was induced in rats with either carrageenan or FCA, respectively. For these studies, animals were dosed with CP-154,526 (3, 10, 30 mg/kg) and NBI 27914 (1-30 mg/kg) 1 h prior to the assessment of tactile, thermal or mechanical hypersensitivity, respectively. In experiment 4, neuropathic pain was induced. Twenty-one days following spinal nerve ligation (SNL), animals received CRF-Saporin or control. Three weeks later tactile allodynia was assessed. Similarly, in experiment 5, a separate set of rats received CRF-Saporin or control. Twenty-one days later, mechanical hyperalgesia was assessed following intraplantar carrageenan. Results from the antagonist studies showed that CP-154,526 and NBI 27914 either fully or partially reversed the referred ulcer pain with minimal effective doses (MED) equal to 3 and 10 mg/kg, respectively. Similarly, both NBI 27914 and CP-154,526 reversed the thermal and mechanical hypersensitivity elicited by carrageenan and FCA with MEDs </= 5 and 10 mg/kg, respectively. Findings from the two CRF-Saporin studies determined that pre-treatment with this toxin significantly attenuated SNL- and carrageenan-induced tactile hypersensitivity. Together, these findings suggest that CRF-1 receptors mediate pain and implicate CRF in this regard.

Analgesic actions of corticotropin-releasing factor (CRF) on somatic pain sensitivity: involvement of glucocorticoid and CRF-2 receptors

The aim of the present work was to study the involvement of glucocorticoid receptors and corticotropin-releasing factor type 2 receptors (CRF-2 receptors) in mediating the analgesic effects of CRF on somatic pain sensitivity. The involvement of glucocorticoid and CRF-2 receptors in the development of analgesia evoked by systemic administration of CRF was studied by blockade of these receptors by their specific antagonists RU 38486 and astressin 2-B, respectively, in anesthetized rats. Pain sensitivity was tested before and 30 min after administration of CRF in terms of the threshold of the pain reaction induced by stimulation of the rat's tail with an electric current. Blockade of glucocorticoid receptors induced partial suppression of the analgesic action of CRF, while blockade of CRF-2 receptors produced complete suppression of the analgesic effect. These results provide evidence that glucocorticoid and CRF-2 receptors are involved in mediating the analgesic effects of CRF.

Footshock-induced urinary bladder hypersensitivity: role of spinal corticotropin-releasing factor receptors

Stress-induced hyperalgesia (SIH), a common clinical observation associated with multiple painful diseases including functional urinary disorders, presently has no mechanistic explanation. Using a footshock treatment, a classic stressor, to magnify physiological responses in a model of urinary bladder pain, we examined one potential group of mediators of SIH, the corticotropin-releasing factor (CRF)-related neuropeptides. Exposure to a footshock treatment produced bladder hypersensitivity in female Sprague-Dawley rats, manifested as significantly more vigorous visceromotor responses (VMRs) to urinary bladder distension (UBD) compared with rats that were exposed to a non-footshock treatment. This bladder hypersensitivity was significantly attenuated by blocking spinal CRF(2) receptors but not CRF(1) receptors. Furthermore, spinal administration of urocortin 2, a CRF(2) receptor agonist, augmented UBD-evoked VMRs in a way similar to what was observed after exposure to Footshock, an effect significantly attenuated by pretreatment with spinal aSVG30, a CRF(2) receptor antagonist. Surprisingly, neither spinal administration of CRF nor the CRF(1) receptor antagonist antalarmin had an effect on bladder nociceptive responses. The results of the present study not only provide further support for a role of stress in the exacerbation of bladder pain but also implicate spinal urocortins and their endogenous receptor, the CRF(2) receptor, as potential mediators of this effect.

PERSPECTIVE

This study presents evidence that spinal urocortins and CRF(2) receptors are involved in stress-induced hypersensitivity related to the urinary bladder. This provides a basis for investigating how urocortins mediate SIH, ultimately leading to more effective treatment options for patients with painful bladder syndromes as well as stress-exacerbated chronic pain.

Corticotropin-releasing hormone receptor 1 antagonist blocks colonic hypersensitivity induced by a combination of inflammation and repetitive colorectal distension

Gastroenteritis is one of the risk factors for developing irritable bowel syndrome (IBS). However, the precise mechanism of postinfectious IBS is still unknown. We tested the hypothesis that a combination of previous inflammation and repetitive colorectal distention (CRD) makes the colon hypersensitive and that treatment with a corticotropin-releasing hormone receptor 1 (CRH-R1) antagonist blocks this colonic hypersensitivity. Rats were pretreated with vehicle or 2,4,6-trinitrobenzene sulphonic acid (TNBS) 6 weeks before CRD. For the CRD experiment, the colorectum was distended once a day for six consecutive days. The CRH-R1 antagonist (CP-154,526, 20 mg kg(-1)) or vehicle was injected subcutaneously 30 min before CRD. Visceral perception was quantified as visceromotor response (VMR) using an electromyograph. For histological examination, the rats were killed on the last day of CRD experiment, and haematoxylin and eosin-staining of colon segments was performed. Although from the first to the third day of CRD, VMRs increased in both the vehicle-treated rats and TNBS-treated rats, they were significantly higher in TNBS-treated rats than those in vehicle-treated controls. On the fifth day of CRD, however, VMRs in the vehicle-treated rats were significantly greater than those in TNBS-treated rats. Pretreatment of rats with CP-154,526 significantly attenuated the increase in VMR induced by repetitive CRD with previous inflammation. Finally, we found that repetitive CRD and repetitive CRD after colitis induced visceral inflammation. These results indicate that a combination of previous inflammation and repetitive CRD induces visceral hypersensitivity and that a CRH-R1 antagonist attenuates this response in rats.

Visceral analgesics: drugs with a great potential in functional disorders?

Irritable bowel syndrome remains an incompletely understood, common syndrome with significant unmet medical needs. In IBS patients, abdominal pain is a primary factor related to quality of life impairment, symptom severity and health care utilization, and chronic visceral hyperalgesia has been identified as an important aspect of IBS pathophysiology. However, the development of therapies aimed at reducing this hyperalgesia (visceral analgesics) has been only partially successful despite preclinical evidence supporting the potential usefulness of several preclinical compounds aimed at peripheral as well as central targets.

Postnatal expression of corticotropin releasing factor (CRF) in rat urinary bladder

Corticotropin releasing factor (CRF) is a neuropeptide expressed in micturition reflex circuitry and different roles in these reflexes have been suggested. These studies examined the expression of CRF/CRF receptors in the urinary bladder during postnatal development in the rat. Urinary bladder was harvested from rats (postnatal (P) day 0-adult) euthanized by isoflurane (4%) and thoracotomy. CRF protein expression significantly (p<or=0.01) decreased in the urothelium with increasing postnatal age. In contrast, CRF-immunoreactivity (IR) was increased in nerve fibers in the suburothelial plexus during the second-third postnatal week. Total CRF protein from urinary bladder significantly increased during the second-third postnatal weeks as determined with ELISAs. CRF receptor 2 (CRFR(2)) transcript was expressed in urinary bladder of all postnatal ages examined whereas no CRFR(1) transcript was expressed at any postnatal age examined. We also demonstrated changes in urinary bladder mRNA expression for the neuropeptides, galanin, substance P, vasoactive intestinal polypeptide and pituitary adenylate cyclase activating polypeptide during postnatal development. These studies demonstrate changes in the CRF expression in urinary bladder, specifically in the urothelium and nerve fibers of the suburothelial plexus during postnatal development. Changes in CRF expression and neuropeptide expression in general in the urinary bladder may contribute to the emergence of mature voiding reflexes.

Differential mechanisms of CRF1 and CRF2 receptor functions in the amygdala in pain-related synaptic facilitation and behavior

A major site of extrahypothalamic expression of corticotropin-releasing factor (CRF) and its G-protein-coupled CRF1 and CRF2 receptors is the amygdala, a key player in emotions and affective disorders. Pain-related plasticity in the laterocapsular division of the central nucleus of the amygdala (CeLC) generates emotional-affective responses and anxiety-like behavior. CRF1 receptor antagonists have anxiolytic effects. Although both CRF1 and CRF2 receptors couple positively to adenylyl cyclase, they can have opposite effects, but the underlying mechanism is unknown. This study addressed CRF1 and CRF2 receptor functions and mechanisms in the amygdala in a model of arthritic pain. Using whole-cell patch-clamp recordings of CeLC neurons, we found that a selective CRF1 receptor antagonist (NBI27914 [5-chloro-4-(N-(cyclopropyl)methyl-N-propylamino)-2-methyl-6-(2,4,6-trichlorophenyl)]) amino-pyridine inhibited synaptic facilitation in brain slices from arthritic rats through a postsynaptic mechanism. Inhibition of the NMDA receptor-mediated synaptic component was occluded by a protein kinase A (PKA) inhibitor, consistent with our previous demonstration of PKA-dependent increased NMDA receptor function in arthritis pain-related plasticity. NBI27914 also decreased neuronal excitability through inhibition of highly tetraethylammonium (TEA)-sensitive ion channels that contribute to action potential repolarization and firing rate. In contrast, a CRF2 receptor antagonist (astressin-2B [cyclo(31-34) [d-Phe11,His12,C alphaMeLeu13,39, Nle17, Glu31, Lys34] Ac-Sauvagine(8-40)]) facilitated synaptic transmission through presynaptic inhibition of GABAergic transmission (disinhibition). NBI27914 inhibited arthritis pain-related behaviors (audible and ultrasonic vocalizations and hindlimb withdrawal reflexes). Astressin-2B had no significant behavioral effect. The data suggest that endogenous CRF1 receptor activation in the amygdala contributes to pain-related synaptic facilitation, increased excitability, and pain behavior through a postsynaptic mechanism involving activation of PKA and highly TEA-sensitive K(+)-currents. Presynaptic CRF2 receptor-mediated inhibition does not reach behavioral significance.

Corticotropin-releasing factor type 1 receptors mediate the visceral hyperalgesia induced by repeated psychological stress in rats

Visceral hypersensitivity has been implicated as an important pathophysiological mechanism in functional gastrointestinal disorders. In this study, we investigated whether the sustained visceral hyperalgesia induced by repeated psychological stress in rats involves the activation of CRF(1) signaling system using two different antagonists. Male Wistar rats were exposed to 10 consecutive days of water avoidance stress (WAS) or sham stress for 1 h/day, and the visceromotor response to phasic colorectal distension (CRD) was assessed before and after the stress period. Animals were injected subcutaneously with the brain penetrant CRF(1) antagonist, CP-154,526, acutely (30 min before the final CRD) or chronically (via osmotic minipump implanted subcutaneously, during stress) or with the peripherally restricted, nonselective CRF(1) and CRF(2) antagonist, astressin, chronically (15 min before each stress session). Repeated WAS induced visceral hypersensitivity to CRD at 40 and 60 mmHg. CP-154,526 injected acutely significantly reduced stress-induced visceral hyperalgesia at 40 mmHg but not at 60 mmHg. Chronic subcutaneous delivery of astressin reduced the stress-induced visceral hyperalgesia to baseline at all distension pressures. Interestingly, chronically administered CP-154,526 eliminated hyperalgesia and produced responses below baseline at 40 mmHg and 60 mmHg, indicating a hypoalgesic effect of the compound. These data support a major role for CRF(1) in both the development and maintenance of visceral hyperalgesia induced by repeated stress and indicate a possible role of peripheral CRF receptors in such mechanisms.

Intestinal electrical stimulation improves delayed gastric emptying and vomiting induced by duodenal distension in dogs

The aim of this study was to investigate the effects of short-pulse intestinal electrical stimulation (IES) on duodenal distention-induced delayed gastric emptying and vomiting in dogs and its possible mechanisms. The study was performed in 12 dogs with jejunal electrodes and a duodenal cannula in three separate experiments to investigate the effects of IES on duodenal distension (DD)-induced delayed gastric emptying and discomfort signs, vagal efferent activity, and jejunal tone. We found that: (i) IES significantly accelerated gastric emptying of liquid delayed by distension (18.05 +/- 4.06%vs. 7.18 +/- 1.99%, P = 0.036 at 60 min). (ii) IES significantly reduced vomiting and discomfort/pain induced by distension. The average signs score was 15.33 +/- 1.37 during distension which decreased to 6.50 +/- 0.91 (P = 0.0002) with IES. (iii) IES did not change vagal afferent activity, which was assessed by the spectral analysis of the heart rate variability. (iv) IES decreased jejunal tone. In conclusion, IES with parameters commonly used in gastric electrical stimulation for nausea and vomiting associated with gastroparesis improves DD-induced delayed gastric emptying and prevents DD-induced vomiting and discomfort signs. Further studies are warranted to investigate the therapeutic potential of IES for gastrointestinal symptoms associated with disturbances in motility and sensory function in small intestine.

Pro- and anti-nociceptive effects of corticotropin-releasing factor (CRF) in central amygdala neurons are mediated through different receptors

Corticotropin-releasing factor (CRF) is not only a stress hormone but also acts as a neuromodulator outside the hypothalamic-pituitary-adrenocortical axis, playing an important role in anxiety, depression, and pain modulation. The underlying mechanisms remain to be determined. A major site of extra-hypothalamic expression of CRF and its receptors is the amygdala, a key player in affect-related disorders such as anxiety. The latero-capsular division of the central nucleus of the amygdala (CeLC) is also important for pain modulation and pain affect. This study analyzed the effects of CRF on nociceptive processing in CeLC neurons and the contribution of CRF1 and CRF2 receptors and protein kinases A and C. Extracellular single-unit recordings were made from CeLC neurons in anesthetized adult rats. All neurons responded more strongly to noxious than innocuous mechanical stimulation of the knee. Evoked responses and background activity were measured before and during administration of CRF into the CeLC by microdialysis. CRF was administered alone or together with receptor antagonists or protein kinase inhibitors. CRF (0.01-1 microM; concentrations in microdialysis probe; 15 min) facilitated the evoked responses more strongly than background activity; a higher concentration (10 microM) had inhibitory effects. Facilitation by CRF (0.1 microM) was reversed by a selective CRF1 receptor antagonist (NBI27914, 10 microM) but not a CRF2 receptor antagonist (astressin-2B, 100 microM) and by a protein kinase A (PKA) inhibitor (KT5720, 100 microM) but not a protein kinase C inhibitor (GF109203X, 100 microM). Inhibitory effects of CRF (10 microM) were reversed by astressin-2B. These data suggest that CRF has dual effects on amygdala neurons: CRF1 receptor-mediated PKA-dependent facilitation and CRF2 receptor-mediated inhibition.

Inhibition of inflammatory pain by CRF at peripheral, spinal and supraspinal sites: involvement of areas coexpressing CRF receptors and opioid peptides

There is conflicting evidence on the antinociceptive effects of corticotropin-releasing factor (CRF) along the neuraxis of pain transmission and the responsible anatomical sites of CRF's action at the level of the brain, spinal cord and periphery. In an animal model of tonic pain, that is, Freunds complete adjuvant (FCA) hindpaw inflammation, we systematically investigated CRF's ability to modulate inflammatory pain at those three levels of pain transmission by algesiometry following the intracerebroventricular, intrathecal, and intraplantar application of low, systemically inactive doses of CRF. At each level, CRF elicits potent antinociceptive effects, which are dose dependent and antagonized by local, but not systemic CRF receptor antagonist alpha-helical CRF indicating CRF receptor specificity. Consistently, we have identified by immunohistochemistry multiple brain areas, inhibitory interneurons within the dorsal horn of the spinal cord as well as immune cells within subcutaneous tissue--but not peripheral sensory neurons--that coexpress both CRF receptors and opioid peptides. In line with these anatomical findings, local administration of CRF together with the opioid receptor antagonist naloxone dose-dependently reversed CRF's antinociceptive effects at each of these three levels of pain transmission. Therefore, local application of low, systemically inactive doses of CRF at the level of the brain, spinal cord and periphery inhibits tonic inflammatory pain most likely through an activation of CRF receptors on cells that coexpress opioid peptides which results in opioid-mediated pain inhibition. Future studies have to delineate whether endogenous CRF at these three levels contributes to the body's response to cope with the stressful stimulus pain in an opioid-mediated manner.

Physiology, pharmacology, and therapeutic relevance of urocortins in mammals: ancient CRF paralogs

Urocortins, three paralogs of the stress-related peptide corticotropin-releasing factor (CRF) found in bony fish, amphibians, birds, and mammals, have unique phylogenies, pharmacologies, and tissue distributions. As a result and despite a structural family resemblance, the natural functions of urocortins and CRF in mammalian homeostatic responses differ substantially. Endogenous urocortins are neither simply counterpoints nor mimics of endogenous CRF action. In their own right, urocortins may be clinically relevant molecules in the pathogenesis or management of many conditions, including congestive heart failure, hypertension, gastrointestinal and inflammatory disorders (irritable bowel syndrome, active gastritis, gastroparesis, and rheumatoid arthritis), atopic/allergic disorders (dermatitis, urticaria, and asthma), pregnancy and parturition (preeclampsia, spontaneous abortion, onset, and maintenance of effective labor), major depression and obesity. Safety trials for intravenous urocortin treatment have already begun for the treatment of congestive heart failure. Further understanding the unique functions of urocortin 1, urocortin 2, and urocortin 3 action may uncover other therapeutic opportunities.

Corticotropin-releasing factor, urocortin 1, and their receptors in the mouse spinal cord

Corticotropin-releasing factor (CRF) and urocortin 1 (Ucn1) are involved in stress adaptation. CRF receptor 1 (CRF1) binds CRF and Ucn1 with similar high affinity, but CRF receptor 2 (CRF2) binds Ucn1 with higher affinity than CRF. We tested the hypothesis that in the spinal cord CRF and Ucn1 control peripheral components of the stress response, by assessing the distribution of CRF- and Ucn1-containing fibers, CRF1 and CRF2 mRNAs, and CRF receptor protein (CRFR) in the mouse spinal cord, by using immunofluorescence and in situ hybridization. CRF, Ucn1, and CRFR occurred throughout the spinal cord. CRF fibers predominated in laminae I, V-VII, and X of Rexed. Ucn1 fibers occurred mainly in laminae VII and X and occasionally in lamina IX. Both CRFR mRNAs occurred in all laminae except the superficial laminae of the dorsal horn, but they exhibited different distributions, CRF2 mRNA having a wider occurrence (laminae III-X) than CRF1 mRNA (laminae III-VIII). Double immunofluorescence indicated that CRF and Ucn1 fibers contacted CRFR-containing neurons, mainly in laminae VII and X. The strongest co-distribution of CRF1 and CRF2 mRNAs with CRF and Ucn1 fibers appeared in lamina VII. CRF2 mRNA predominated in lamina IX together with Ucn1, whereas CRF2 mRNA predominated in lamina X, where it had similar distributions with each ligand. In view of the lamina-specific and similar distributions of the two CRF receptor mRNAs with their ligands, we suggest that CRF1 and CRF2 are involved in peripheral stress adaptation processes, such as modulation of stress-induced analgesia and the mediation of visceral nociceptive information by CRF2.

Stress signaling pathways activated by weaning mediate intestinal dysfunction in the pig

Weaning in the piglet is a stressful event associated with gastrointestinal disorders and increased disease susceptibility. Although stress is thought to play a role in postweaning intestinal disease, the mechanisms by which stress influences intestinal pathophysiology in the weaned pig are not understood. The objectives of these experiments were to investigate the impact of weaning on gastrointestinal health in the pig and to assess the role of stress signaling pathways in this response. Nineteen-day-old pigs were weaned, and mucosal barrier function and ion transport were assessed in jejunal and colonic tissues mounted on Ussing chambers. Weaning caused marked disturbances in intestinal barrier function, as demonstrated by significant (P < 0.01) reductions in transepithelial electrical resistance and increases in intestinal permeability to [3H]mannitol in both the jejunum and colon compared with intestinal tissues from age-matched, unweaned control pigs. Weaned intestinal tissues exhibited increased intestinal secretory activity, as demonstrated by elevated short-circuit current that was sensitive to treatment with tetrodotoxin and indomethacin, suggesting activation of enteric neural and prostaglandin synthesis pathways in weaned intestinal tissues. Western blot analyses of mucosal homogenates showed increased expression of corticotrophin-releasing factor (CRF) receptor 1 in the jejunum and colon of weaned intestinal tissues. Pretreatment of pigs with the CRF receptor antagonist alpha-helical CRF(9-41), which was injected intraperitoneally 30 min prior to weaning, abolished the stress-induced mucosal changes. Our results indicate that weaning stress induces mucosal dysfunction mediated by intestinal CRF receptors and activated by enteric nerves and prostanoid pathways.

Enhanced pelvic responses to stressors in female CRF-overexpressing mice

Acute stress affects gut functions through the activation of corticotropin-releasing factor (CRF) receptors. The impact of acute stress on pelvic viscera in the context of chronic stress is not well characterized. We investigated the colonic, urinary, and locomotor responses monitored as fecal pellet output (FPO), urine voiding, and ambulatory activity, respectively, in female and male CRF-overexpressing (CRF-OE) mice, a chronic stress model, and their wild-type littermates (WTL). Female CRF-OE mice, compared with WTL, had enhanced FPO to 2-min handling (150%) and 60-min novel environment (155%) but displayed a similar response to a 60-min partial restraint stress. Female CRF-OE mice, compared with WTL, also had a significantly increased number of urine spots (7.3 +/- 1.4 vs. 1.3 +/- 0.8 spots/h) and lower locomotor activity (246.8 +/- 47.8 vs. 388.2 +/- 31.9 entries/h) to a novel environment. Male CRF-OE mice and WTL both responded to a novel environment but failed to show differences between them in colonic and locomotor responses. Male WTL, compared with female WTL, had higher FPO (113%). In female CRF-OE mice, the CRF(1)/CRF(2) receptor antagonist astressin B and the selective CRF(2) receptor agonist mouse urocortin 2 (injected peripherally) prevented the enhanced defecation without affecting urine or locomotor responses to novel environment. RT-PCR showed that CRF(1) and CRF(2) receptors are expressed in the mouse colonic tissues. The data show that chronic stress, due to continuous central CRF overdrive, renders female CRF-OE mice to have enhanced pelvic and altered behavioral responses to superimposed mild stressors and that CRF(1)-initiated colonic response is counteracted by selective activation of CRF(2) receptor.

Acute inflammatory and neuropathic pain in Lewis and Fischer rats

Inbred, histocompatible Lewis and Fischer 344 rats (LEW and FIS) have been used to identify an inverse relationship between hypothalamic-pituitary-adrenal (HPA) axis activity and susceptibility to autoimmune and chronic inflammatory disorders, with LEW showing blunted HPA axis activity and increased susceptibility toward the development of autoimmunity and chronic inflammation, and FIS showing the opposite relationship. In the present study, LEW and FIS were used to determine the relationship between HPA axis function and acute inflammatory pain (carrageenan-induced hindpaw inflammation) and neuropathic pain (partial sciatic nerve ligation; PSNL). The results showed that carrageenan-induced thermal and mechanical allodynia and hyperalgesia were greater in FIS than in LEW. Similarly, FIS showed more carrageenan-induced hindpaw swelling and higher levels of myeloperoxidase (a measure of neutrophils) in the carrageenan-inflamed hindpaw. After PSNL, LEW showed a profound mechanical allodynia and hyperalgesia, whereas mechanical sensitivity in FIS was unaltered. However, FIS, but not LEW, developed thermal allodynia and hyperalgesia after PSNL. These results provide strong evidence for a positive relationship between HPA axis activity and acute inflammatory pain. The results also support a relationship between HPA axis activity and neuropathic pain, but the relationship is complex and may depend on the pain assay.