Central oxytocin is involved in restoring impaired gastric motility following chronic repeated stress in mice

Paraventricular oxytocin neurons impact energy intake and expenditure: projections to the bed nucleus of the stria terminalis reduce sucrose consumption

Background

The part played by oxytocin and oxytocin neurons in the regulation of food intake is controversial. There is much pharmacological data to support a role for oxytocin notably in regulating sugar consumption, however, several recent experiments have questioned the importance of oxytocin neurons themselves.

Methods

Here we use a combination of histological and chemogenetic techniques to investigate the selective activation or inhibition of oxytocin neurons in the hypothalamic paraventricular nucleus (OxtPVH). We then identify a pathway from OxtPVH neurons to the bed nucleus of the stria terminalis using the cell-selective expression of channel rhodopsin.

Results

OxtPVH neurons increase their expression of cFos after both physiological (fast-induced re-feeding or oral lipid) and pharmacological (systemic administration of cholecystokinin or lithium chloride) anorectic signals. Chemogenetic activation of OxtPVH neurons is sufficient to decrease free-feeding in Oxt Cre:hM3Dq mice, while inhibition in Oxt Cre:hM4Di mice attenuates the response to administration of cholecystokinin. Activation of OxtPVH neurons also increases energy expenditure and core-body temperature, without a significant effect on locomotor activity. Finally, the selective, optogenetic stimulation of a pathway from OxtPVH neurons to the bed nucleus of the stria terminalis reduces the consumption of sucrose.

Conclusion

Our results support a role for oxytocin neurons in the regulation of whole-body metabolism, including a modulatory action on food intake and energy expenditure. Furthermore, we demonstrate that the pathway from OxtPVH neurons to the bed nucleus of the stria terminalis can regulate sugar consumption.

Protective effect of oxytocin on vincristine-induced gastrointestinal dysmotility in mice

Aims: Vincristine (VCR), an antineoplastic drug, induces peripheral neuropathy characterized by nerve damage, limiting its use and reducing the quality of life of patients. VCR causes myenteric neuron damage, inhibits gastrointestinal motility, and results in constipation or paralytic ileus in patients. Oxytocin (OT) is an endogenous neuropeptide produced by the enteric nerve system, which regulates gastrointestinal motility and exerts neuroprotective effects. This study aimed to investigate whether OT can improve VCR-induced gastrointestinal dysmotility and evaluate the underlying mechanism. Methods: Mice were injected either with saline or VCR (0.1 mg/kg/d, i. p.) for 14 days, and OT (0.1 mg/kg/d, i.p.) was applied 1 h before each VCR injection. Gastrointestinal transit and the contractile activity of the isolated colonic segments were assessed. The concentration of OT in plasma was measured using ELISA. Immunofluorescence staining was performed to analyze myenteric neurons and reactive oxygen species (ROS) levels. Furthermore, the indicators of oxidative stress were detected. The protein expressions of Nrf2, ERK1/2, P-ERK1/2, p38, and P-p38 in the colon were tested using Western blot. Results: VCR reduced gastrointestinal transit and the responses of isolated colonic segments to electrical field stimulation and decreased the amount of neurons. Furthermore, VCR reduced neuronal nitric oxide synthase and choline acetyltransferase immunopositive neurons in the colonic myenteric nerve plexus. VCR increased the concentration of OT in plasma. Exogenous OT pretreatment ameliorated the inhibition of gastrointestinal motility and the injury of myenteric neurons caused by VCR. OT pretreatment also prevented the decrease of superoxide dismutase activity, glutathione content, total antioxidative capacity, and Nrf2 expression, the increase of ROS levels, and the phosphorylation of ERK1/2 and p38 MAPK following VCR treatment. Conclusion: Our results suggest that OT pretreatment can protect enteric neurons from VCR-induced injury by inhibiting oxidative stress and MAPK pathways (ERK1/2, p38). This may be the underlying mechanism by which it alleviates gastrointestinal dysmotility.

Stress-induced neuroplasticity in the gastric response to brainstem oxytocin in male rats

Previous studies have shown that pharmacological manipulations with stress-related hormones such as corticotropin-releasing factor and thyrotropin-releasing hormone induce neuroplasticity in brainstem vagal neurocircuits, which modulate gastric tone and motility. The prototypical antistress hormone oxytocin (OXT) has been shown to modulate gastric tone and motility via vagal pathways, and descending hypothalamic oxytocinergic inputs play a major role in the vagally dependent gastric-related adaptations to stress. The aim of this study was to investigate the possible cellular mechanisms through which OXT modulates central vagal brainstem and peripheral enteric neurocircuits of male Sprague-Dawley rats in response to chronic repetitive stress. After chronic (5 consecutive days) of homotypic or heterotypic stress load, the response to exogenous brainstem administration of OXT was examined using whole cell patch-clamp recordings from gastric-projecting vagal motoneurons and in vivo recordings of gastric tone and motility. GABAergic currents onto vagal motoneurons were decreased by OXT in stressed, but not in naïve rats. In naïve rats, microinjections of OXT in vagal brainstem nuclei-induced gastroinhibition via peripheral release of nitric oxide (NO). In stressed rats, however, the OXT-induced gastroinhibition was determined by the release of both NO and vasoactive intestinal peptide (VIP). Taken together, our data indicate that stress induces neuroplasticity in the response to OXT in the neurocircuits, which modulate gastric tone and motility. In particular, stress uncovers the OXT-mediated modulation of brainstem GABAergic currents and alters the peripheral gastric response to vagal stimulation.NEW & NOTEWORTHY The prototypical antistress hormone, oxytocin (OXT), modulates gastric tone and motility via vagal pathways, and descending hypothalamic-brainstem OXT neurocircuits play a major role in the vagally dependent adaptation of gastric motility and tone to stress. The current study suggests that in the neurocircuits, which modulate gastric tone and motility, stress induces neuroplasticity in the response to OXT and may reflect the dysregulation observed in stress-exacerbated functional motility disorders.

Effectiveness and safety of kamikihito, a traditional Japanese medicine, in managing anxiety among female patients with intractable chronic constipation

BACKGROUND AND PURPOSE

The prevalence of anxiety in patients with chronic constipation is particularly high and these individuals are not necessarily satisfied by normal treatments targeting the gastrointestinal tract. Kamikihito, a traditional Japanese Kampo medicine, has been widely used to date in treating anxiety and neurosis in Japan. We conducted a single-arm, open-label pilot study of female patients with intractable chronic constipation and anxiety who took kamikihito by mouth for 12 weeks.

MATERIALS AND METHODS

Validated symptom questionnaires on anxiety and gastrointestinal symptoms [the Profile of Mood States, second edition (POMS2); the State-Trait Anxiety Inventory (STAI); and the Gastrointestinal Symptom Rating Scale (GSRS)] were completed at each study visit. Plasma, salivary, and stool samples were also assessed to evaluate levels of clinical bioactive substances linked to stress and inflammation, oxidative levels, the metabolome profile, and gut microbiota.

RESULTS

Twenty-four patients completed this study. Anxiety was significantly reduced at four and 12 weeks (Tension-Anxiety subscale of the POMS2, p = 0.006 and p = 0.039; Trait anxiety score of the STAI, p < 0.001 and p = 0.034), while the total GSRS score was improved at 12 weeks (p = 0.039). Targeted metabolomics in plasma showed significant alterations in some metabolites associated with psychological symptoms, such as O-phosphoethanolamine. No significant differences were found between pre- and posttreatment levels of clinical bioactive substances related to stress and inflammation, oxidative levels, and the gut microbiota in this cohort. No serious adverse events occurred.

CONCLUSION

Kamikihito ameliorated psychological and gastrointestinal symptoms in patients with chronic constipation. In parallel with the onset of efficacy, kamikihito modulated some anxiety-related metabolites. Kamikihito was safe and well-tolerated.

Kamikihito, a traditional Japanese Kampo medicine, increases the secretion of oxytocin in rats with acute stress

ETHNOPHARMACOLOGICAL RELEVANCE

Kamikihito (KKT) is a Kampo medicine that is prescribed in Japan for the treatment of anemia, insomnia and mental anxiety in Japan. However, its precise mechanism of action remains unclear.

AIM OF THE STUDY

This study aimed to evaluate the possible antistress effect of KKT in rats with acute stress and the contribution of oxytocin to the process.

MATERIALS AND METHODS

Acute immobilization stress (AIS; for 90 min) was used to assess the effect of KKT on acute stress. Male Wistar rats were orally treated with KKT. Parameters of stress were evaluated, and concentrations of oxytocin in plasma and cerebrospinal fluid (CSF) were measured.

RESULTS

AIS-induced defecation and fecal weight were significantly decreased because of treatment with KKT. The plasma levels of stress-related hormones following AIS were investigated. The pre-administration of KKT significantly increased adrenocorticotrophic hormone (ACTH) and corticosterone (CORT) levels following AIS. Conversely, there was no significant change in the plasma oxytocin level. Microdialysis and hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC-MS/MS) were used to monitor the oxytocin secretion in CSF. Oxytocin level increased during AIS following the treatment of KKT. At 30 min after AIS, the level remained higher than before AIS. Furthermore, using an open field test, the locomotion (exploratory behavior) immediately after AIS was examined. The total traveled distance decreased after AIS; however, the decrease was significantly inhibited by the treatment of KKT. However, the effect of KKT was obstructed by the pre-administration of the oxytocin receptor antagonist.

CONCLUSIONS

These results suggest that KKT has antistress activity and increased oxytocin secretion may be a mechanism underlying this phenomenon.

Sensory Stimulation of Oxytocin Release Is Associated With Stress Management and Maternal Care

It has been shown that various types of stress initiate different physiological and neuroendocrine disorders. Oxytocin (OT) is mainly produced in the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus. Hypothalamic OT has antistress effects and attenuates the hypothalamic–pituitary–adrenal (HPA) axis. One mechanism behind the antistress effects of OT is mediated through the inhibition from GABA_A receptors on corticotropin-releasing factor (CRF) expression at the PVN. Various manual therapies such as acupuncture, transcutaneous electrical nerve stimulation (TENS), and massage initiate the stimulation of somatosensory neurons of the body. It is well-known that TENS simulates OT expression, while it inhibits CRF expression at the PVN following chronic stress loading in rodents. Upregulation of OT expression at the hypothalamus is activated by the somatosensory stimulation, which is mediated via the spinothalamic pathway (the connection between the spinal cord and hypothalamus). Thus, somatosensory stimulation is beneficial in treating stress-associated symptoms. Hypothalamic OT is associated with the social behaviors, including maternal care and affiliation. Childhood neglect and/or child abuse are severely responsible for deleterious long-term effects on the cognitive/social activity and behavioral development. At parturition, a profound amount of OT is released into the systemic circulation in response to vaginal and cervical stimulation caused by the body of fetus, which induces the onset of maternal behavior. Peridural anesthesia effectively impairs the sensitivity to vaginal and cervical stimulation at parturition. OT levels in cerebrospinal fluid is significantly reduced following peridural anesthesia. The vaginal delivery mothers had significantly more OT pulses than the caesarian section (CS) mothers. Due to low levels of endogenous OT, maternal behavior could be interrupted by epidural anesthesia and CS at parturition because of the reduction of the usual sensory input from the genitalia.

Hypothalamic-vagal oxytocinergic neurocircuitry modulates gastric emptying and motility following stress

KEY POINTS

Stress triggers and exacerbates the symptoms of functional gastrointestinal disorders, such as delayed gastric emptying and impaired gastric motility. Understanding the mechanisms by which the neural circuits, impaired by stress, are restored may help to identify potential targets for more effective therapeutic interventions. Oxytocin administration or release ameliorates the stress-induced delayed gastric emptying and motility. However, is it unclear whether the effects are mediated via the hypothalamic-pituitary-adrenocortical axis or the oxytocinergic projections from the paraventricular nucleus of the hypothalamus to brainstem neurones of the dorsal vagal complex. We used Cre-inducible designer receptors exclusively activated by designer drugs to demonstrate the fundamental role of the oxytocinergic hypothalamic-vagal projections in the gastric adaptation to stress.

ABSTRACT

Stress triggers and exacerbates the symptoms of functional gastrointestinal (GI) disorders, such as delayed gastric emptying and impaired gastric motility. The prototypical anti-stress hormone, oxytocin (OXT), plays a major role in the modulation of gastric emptying and motility following stress. It is not clear, however, whether the amelioration of dysregulated GI functions by OXT is mediated via an effect on the hypothalamic-pituitary-adrenocortical axis or the oxytocinergic projections from the paraventricular nucleus of the hypothalamus (PVN) to neurones of the dorsal vagal complex (DVC). In the present study we tested the hypothesis that the activity of hypothalamic-vagal oxytocinergic neurocircuits plays a major role in the gastric adaptation to stress. Cre-inducible designer receptors exclusively activated by designer drugs (DREADDs) were injected into the DVC of rats and retrogradely transported to allow selective expression in OXT neurones in the PVN. Following acute stress and either chronic heterotypic (CHe) or chronic homotypic (CHo) stress, gastric emptying was assessed via the [13 C]-octanoic acid breath test, and gastric tone and motility were assessed via strain gauges sewn on the surface of the stomach. Activation of the hypothalamic-vagal oxytocinergic neurocircuitry, by DREADD agonist clozapine-N-oxide (CNO), prevented the delayed gastric emptying observed following acute or CHe stress, and 4th ventricular administration of CNO increased gastric tone and motility. Conversely, CNO-mediated inhibition of the hypothalamic-vagal oxytocinergic neurocircuitry prevented the CHo-induced adaptation in gastric emptying, and an increase in gastric tone and motility. Taken together, the data support the hypothesis that hypothalamic-vagal oxytocinergic neurocircuits play a major role in the modulation of gastric emptying and motility following stress.

Intranasal Administration of Oxytocin Attenuates Stress Responses Following Chronic Complicated Stress in Rats

Background/Aims

Gastrointestinal (GI) symptoms may develop when we fail to adapt to various stressors of our daily life. Central oxytocin (OXT) can counteract the biological actions of corticotropin-releasing factor (CRF), and in turn attenuates stress responses. Administration (intracerebroventricular) of OXT significantly antagonized the inhibitory effects of chronic complicated stress (CCS) on GI dysmotility in rats. However, intracerebroventricular administration is an invasive pathway. Intranasal administration can rapidly deliver peptides to the brain avoiding stress response. The effects of intranasal OXT on hypothalamus-pituitary-adrenal axis and GI motility in CCS conditions have not been investigated.

Methods

A CCS rat model was set up, OXT 5, 10, or 20 μg were intranasal administered, 30 minutes prior to stress loading. Central CRF and OXT expression levels were analyzed, serum corticosterone and OXT concentrations were measured, and gastric and colonic motor functions were evaluated by gastric emptying, fecal pellet output, and motility recording system.

Results

Rats in CCS condition showed significantly increased CRF expression and corticosterone concentration, which resulted in delayed gastric emptying and increased fecal pellet output, attenuated gastric motility and enhanced colonic motility were also recorded. OXT 10 μg or 20 μg significantly reduced CRF mRNA expression and the corticosterone concentration, OXT 20 μg also helped to restore GI motor dysfunction induced by CCS.

Conclusion

Intranasal administration of OXT has an anxiolytic effect and attenuates the hypothalamus-pituitary-adrenal axis in response to CCS, and gave effects which helped to restore GI dysmotility, and might be a new approach for the treatment of stress-induced GI motility disorders.

Oxytocin and Vasopressin Systems in Obesity and Metabolic Health: Mechanisms and Perspectives

PURPOSE OF REVIEW

The neurohypophysial endocrine system is identified here as a potential target for therapeutic interventions toward improving obesity-related metabolic dysfunction, given its coinciding pleiotropic effects on psychological, neurological and metabolic systems that are disrupted in obesity.

RECENT FINDINGS

Copeptin, the C-terminal portion of the precursor of arginine-vasopressin, is positively associated with body mass index and risk of type 2 diabetes. Plasma oxytocin is decreased in obesity and several other conditions of abnormal glucose homeostasis. Recent data also show non-classical tissues, such as myocytes, hepatocytes and β-cells, exhibit responses to oxytocin and vasopressin receptor binding that may contribute to alterations in metabolic function. The modulation of anorexigenic and orexigenic pathways appears to be the dominant mechanism underlying the effects of oxytocin and vasopressin on body weight regulation; however, there are apparent limitations associated with their use in direct pharmacological applications. A clearer picture of their wider physiological effects is needed before either system can be considered for therapeutic use.

Central control of gastrointestinal motility

PURPOSE OF REVIEW

This review summarizes the organization and structure of vagal neurocircuits controlling the upper gastrointestinal tract, and more recent studies investigating their role in the regulation of gastric motility under physiological, as well as pathophysiological, conditions.

RECENT FINDINGS

Vagal neurocircuits regulating gastric functions are highly plastic, and open to modulation by a variety of inputs, both peripheral and central. Recent research in the fields of obesity, development, stress, and neurological disorders highlight the importance of central inputs onto these brainstem neurocircuits in the regulation of gastric motility.

SUMMARY

Recognition of the pivotal role that the central nervous system exerts in the regulation, integration, and modulation of gastric motility should serve to encourage research into central mechanisms regulating peripheral motility disorders.

Stress Adaptation Upregulates Oxytocin within Hypothalamo-Vagal Neurocircuits

Stress plays a pivotal role in the development and/or exacerbation of functional gastrointestinal (GI) disorders. The paraventricular nucleus of the hypothalamus (PVN) contains neurons that are part of the hypothalamic-pituitary-adrenal axis as well as preautonomic neurons innervating, among other areas, gastric-projecting preganglionic neurons of the dorsal vagal complex (DVC). The aim of the present study was to test the hypothesis that stress adaptation upregulates oxytocin (OXT) within PVN-brainstem vagal neurocircuitry. The retrograde tracer cholera toxin B (CTB) was injected into the DVC of rats which, after post-surgical recovery, were pair-housed and exposed to either homo- or heterotypic stress for five consecutive days. Fecal pellets were counted at the end of each stress load. Two hours after the last stressor, the whole brain was excised. Brainstem and hypothalamic nuclei were analyzed immunohistochemically for the presence of both OXT-immunopositive cells in identified preautonomic PVN neurons as well as OXT fibers in the DVC. Rats exposed to chronic homotypic, but not chronic heterotypic stress, had a significant increase in both number of CTB+ OXT co-localized neurons in the PVN as well as density of OXT-positive fibers in the DVC compared to control rats. These data suggest that preautonomic OXT PVN neurons and their projections to the DVC increase following adaptation to stress, and suggest that the possible up-regulation of OXT within PVN-brainstem vagal neurocircuitry may play a role in the adaptation of GI responses to stress.

Inhibitory effect of the Kampo medicinal formula Yokukansan on acute stress-induced defecation in rats

OBJECTIVES

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder with symptoms of abnormal defecation and abdominal discomfort. Psychological factors are well known to be involved in onset and exacerbation of IBS. A few studies have reported effectiveness of traditional herbal (Kampo) medicines in IBS treatment. Yokukansan (YKS) has been shown to have anti-stress and anxiolytic effects. We investigated the effect of YKS on defecation induced by stress and involvement of oxytocin (OT), a peptide hormone produced by the hypothalamus, in order to elucidate the mechanism of YKS action.

METHODS AND RESULTS

Male Wistar rats were divided into four groups; control, YKS (300 mg/kg PO)-treated non-stress (YKS), acute stress (Stress), and YKS (300 mg/kg PO)-treated acute stress (Stress+YKS) groups. Rats in the Stress and Stress+YKS groups were exposed to a 15-min psychological stress procedure involving novel environmental stress. Levels of plasma OT in the YKS group were significantly higher compared with those in the Control group (P < 0.05), and OT levels in the Stress+YKS group were remarkably higher than those in the other groups (P < 0.01). Next, rats were divided into four groups; Stress, Stress+YKS, Atosiban (OT receptor antagonist; 1 mg/kg IP)-treated Stress+YKS (Stress+YKS+B), and OT (0.04 mg/kg IP)-treated acute stress (Stress+OT) groups. Rats were exposed to acute stress as in the previous experiment, and defecation during the stress load was measured. Administration of YKS or OT significantly inhibited defecation; however, administration of Atosiban partially abolished the inhibitory effect of YKS. Finally, direct action of YKS on motility of isolated colon was assessed. YKS (1 mg/mL, 5 mg/mL) did not inhibit spontaneous contraction.

CONCLUSION

These results suggested that YKS influences stress-induced defecation and that increased OT secretion may be a mechanism underlying this phenomenon.

Vagally mediated gastric effects of brain stem α2-adrenoceptor activation in stressed rats

Chronic stress exerts vagally dependent effects to disrupt gastric motility; previous studies have shown that, among other nuclei, A2 neurons are involved in mediating these effects. Several studies have also shown robust in vitro and in vivo effects of α2-adrenoceptor agonists on vagal motoneurons. We have demonstrated previously that brainstem vagal neurocircuits undergo remodeling following acute stress; however, the effects following brief periods of chronic stress have not been investigated. Our aim, therefore, was to test the hypothesis that different types of chronic stress influence gastric tone and motility by inducing plasticity in the response of vagal neurocircuits to α2-adrenoreceptor agonists. In rats that underwent 5 days of either homotypic or heterotypic stress loading, we applied the α2-adrenoceptor agonist, UK14304, either by in vitro brainstem perfusion to examine its ability to modulate GABAergic synaptic inputs to vagal motoneurons or in vivo brainstem microinjection to observe actions to modulate antral tone and motility. In neurons from naïve rats, GABAergic currents were unresponsive to exogenous application of UK14304. In contrast, GABAergic currents were inhibited by UK14304 in all neurons from homotypic and, in a subpopulation of neurons, heterotypic stressed rats. In control rats, UK14304 microinjection inhibited gastric tone and motility via withdrawal of vagal cholinergic tone; in heterotypic stressed rats, the larger inhibition of antrum tone was due to a concomitant activation of peripheral nonadrenergic, noncholinergic pathways. These data suggest that stress induces plasticity in brainstem vagal neurocircuits, leading to an upregulation of α2-mediated responses. NEW & NOTEWORTHY Catecholaminergic neurons of the A2 area play a relevant role in stress-related dysfunction of the gastric antrum. Brief periods of chronic stress load induce plastic changes in the actions of adrenoceptors on vagal brainstem neurocircuits.

Oxytocin and the warm outer glow: Thermoregulatory deficits cause huddling abnormalities in oxytocin-deficient mouse pups

Oxytocin is a social and reproductive hormone that also plays critical roles in a range of homeostatic processes, including thermoregulation. Here, we examine the role of oxytocin (OT) as a mediator of brown adipose tissue (BAT) thermogenesis, cold-induced huddling, and thermotaxis in eight-day-old (PD8) OT 'knock out' (OTKO) mouse pups. We tested OTKO and wildtype (WT) pups in single- and mixed-genotype groups of six, exposing these to a period of ambient warmth (~35°C) followed by a period of cold (~21.5°C). Whether huddling exclusively with other OTKO or alongside WT pups, OTKO pups showed reduced BAT thermogenesis and were significantly cooler when cold-challenged. Huddles of OTKO pups were also significantly less cohesive than WT huddles during cooling, suggesting that thermoregulatory deficits contribute to contact abnormalities in OTKO pups. To further explore this issue, we examined thermotaxis in individuals and groups of four OTKO or WT pups placed on the cool end of a thermocline and permitted to freely locomote for 2h. When tested individually, male OTKO pups displayed abnormal thermotaxis, taking significantly longer to move up the thermocline and settling upon significantly lower temperatures than WT pups during the 2h test. OTKO mouse pups thus appear to have deficits in both thermogenesis and thermotaxis-the latter deficit being specific to males. Our results add to a growing body of work indicating that OT plays critical roles in thermoregulation and also highlight the entanglement of social and thermoregulatory processes in small mammals such as mice.

Role of the nitrergic pathway in motor effects of oxytocin in rat proximal colon

BACKGROUND

Oxytocin (OT) reduces rat duodenal tone and mouse intestinal transit; however, the underlying mechanisms are not totally understood. Consequently, this study was designed to investigate the influence of OT on spontaneous mechanical activity and neurally evoked responses, to characterize the mechanisms of the action, and to determine the distribution of the OT receptor (OTR) in rat proximal colonic muscle strips.

METHODS

The organ bath technique with electrical field stimulation, western blotting, and immunofluorescence were used.

KEY RESULTS

In rat proximal colon, exogenous OT induced a concentration-dependent reduction of the spontaneous mechanical activity without affecting the resting basal tone, which was abolished by atosiban, an OTR antagonist, by tetrodotoxin (TTX), a neural blocker or by Nω-propyl-l-arginine hydrochloride, an inhibitor of neuronal nitric oxide synthase (nNOS). The inhibitory effects of OT were not affected by atropine or the vasoactive intestinal peptide (VIP) receptor antagonist [Lys1, Pro2,5, Arg3,4, Tyr6]-VIP (VIPHyb). Proximal colon responses to electrical field stimulation were characterized by nonadrenergic, noncholinergic (NANC) relaxation, which was followed by an off-contraction. Oxytocin enhanced only NANC relaxation. Oxytocin stimulated spontaneous NO release from the longitudinal muscle myenteric plexus preparation of rat proximal colon. Western blot and immunohistochemistry experiments showing the presence of the OTR in proximal colon, and its co-localization with nNOS established that myenteric nitrergic neurons express OTR.

CONCLUSIONS & INFERENCES

The activation of OTR located on nitrergic neurons may negatively modulate colonic spontaneous contraction and enhance electrically evoked NANC relaxation through excitation of NO release.

The Impact of Prenatal Exposure to Dexamethasone on Gastrointestinal Function in Rats

Antenatal treatment with synthetic glucocorticoids is commonly used in pregnant women at risk of preterm delivery to accelerate tissue maturation. Exposure to glucocorticoids during development has been hypothesized to underlie different functional gastrointestinal (GI) and motility disorders. Herein, we investigated the impact of in utero exposure to synthetic glucocorticoids (iuGC) on GI function of adult rats. Wistar male rats, born from pregnant dams treated with dexamethasone (DEX), were studied at different ages. Length, histologic analysis, proliferation and apoptosis assays, GI transit, permeability and serotonin (5-HT) content of GI tract were measured. iuGC treatment decreased small intestine size and decreased gut transit. However, iuGC had no impact on intestinal permeability. iuGC differentially impacts the structure and function of the GI tract, which leads to long-lasting alterations in the small intestine that may predispose subjects prone to disorders of the GI tract.

Vagal neurocircuitry and its influence on gastric motility

A large body of research has been dedicated to the effects of gastrointestinal peptides on vagal afferent fibres, yet multiple lines of evidence indicate that gastrointestinal peptides also modulate brainstem vagal neurocircuitry, and that this modulation has a fundamental role in the physiology and pathophysiology of the upper gastrointestinal tract. In fact, brainstem vagovagal neurocircuits comprise highly plastic neurons and synapses connecting afferent vagal fibres, second order neurons of the nucleus tractus solitarius (NTS), and efferent fibres originating in the dorsal motor nucleus of the vagus (DMV). Neuronal communication between the NTS and DMV is regulated by the presence of a variety of inputs, both from within the brainstem itself as well as from higher centres, which utilize an array of neurotransmitters and neuromodulators. Because of the circumventricular nature of these brainstem areas, circulating hormones can also modulate the vagal output to the upper gastrointestinal tract. This Review summarizes the organization and function of vagovagal reflex control of the upper gastrointestinal tract, presents data on the plasticity within these neurocircuits after stress, and discusses the gastrointestinal dysfunctions observed in Parkinson disease as examples of physiological adjustment and maladaptation of these reflexes.

Arginine Vasopressin Injected into the Dorsal Motor Nucleus of the Vagus Inhibits Gastric Motility in Rats

Background. Until now, the effect of arginine vasopressin (AVP) in the DMV on gastric motility and the possible modulating pathway between the DMV and the gastrointestinal system remain poorly understood. Objectives. We aimed to explore the role of AVP in the DMV in regulating gastric motility and the possible central and peripheral pathways. Material and Methods. Firstly, we microinjected different doses of AVP into the DMV and investigated its effects on gastric motility in rats. Then, the possible central and peripheral pathways that regulate gastric motility were also discussed by microinjecting SR49059 (a specific AVP receptor antagonist) into the DMV and intravenous injection of hexamethonium (a specific neuronal nicotinic cholinergic receptor antagonist) before AVP microinjection. Results. Following microinjection of AVP (180 pmol and 18 pmol) into the DMV, the gastric motility (including total amplitude, total duration, and motility index of gastric contraction) was significantly inhibited (P < 0.05). Moreover, the inhibitory effect of AVP (180 pmol) on gastric motility could be blocked completely by both SR49059 (320 pmol) and hexamethonium (8 μmol). Conclusions. It is concluded that AVP inhibits the gastric motility by acting on the specific AVP receptor in the DMV, with the potential involvement of the parasympathetic preganglionic cholinergic fibers.

Central nervous system control of gastrointestinal motility and secretion and modulation of gastrointestinal functions

Although the gastrointestinal (GI) tract possesses intrinsic neural plexuses that allow a significant degree of autonomy over GI functions, the central nervous system (CNS) provides extrinsic neural inputs that regulate, modulate, and control these functions. While the intestines are capable of functioning in the absence of extrinsic inputs, the stomach and esophagus are much more dependent upon extrinsic neural inputs, particularly from parasympathetic and sympathetic pathways. The sympathetic nervous system exerts a predominantly inhibitory effect upon GI muscle and provides a tonic inhibitory influence over mucosal secretion while, at the same time, regulates GI blood flow via neurally mediated vasoconstriction. The parasympathetic nervous system, in contrast, exerts both excitatory and inhibitory control over gastric and intestinal tone and motility. Although GI functions are controlled by the autonomic nervous system and occur, by and large, independently of conscious perception, it is clear that the higher CNS centers influence homeostatic control as well as cognitive and behavioral functions. This review will describe the basic neural circuitry of extrinsic inputs to the GI tract as well as the major CNS nuclei that innervate and modulate the activity of these pathways. The role of CNS-centered reflexes in the regulation of GI functions will be discussed as will modulation of these reflexes under both physiological and pathophysiological conditions. Finally, future directions within the field will be discussed in terms of important questions that remain to be resolved and advances in technology that may help provide these answers.

Stress-induced visceral pain: toward animal models of irritable-bowel syndrome and associated comorbidities

Visceral pain is a global term used to describe pain originating from the internal organs, which is distinct from somatic pain. It is a hallmark of functional gastrointestinal disorders such as irritable-bowel syndrome (IBS). Currently, the treatment strategies targeting visceral pain are unsatisfactory, with development of novel therapeutics hindered by a lack of detailed knowledge of the underlying mechanisms. Stress has long been implicated in the pathophysiology of visceral pain in both preclinical and clinical studies. Here, we discuss the complex etiology of visceral pain reviewing our current understanding in the context of the role of stress, gender, gut microbiota alterations, and immune functioning. Furthermore, we review the role of glutamate, GABA, and epigenetic mechanisms as possible therapeutic strategies for the treatment of visceral pain for which there is an unmet medical need. Moreover, we discuss the most widely described rodent models used to model visceral pain in the preclinical setting. The theory behind, and application of, animal models is key for both the understanding of underlying mechanisms and design of future therapeutic interventions. Taken together, it is apparent that stress-induced visceral pain and its psychiatric comorbidities, as typified by IBS, has a multifaceted etiology. Moreover, treatment strategies still lag far behind when compared to other pain modalities. The development of novel, effective, and specific therapeutics for the treatment of visceral pain has never been more pertinent.

Social functions of individual vasopressin-oxytocin cell groups in vertebrates: what do we really know?

Vasopressin-oxytocin (VP-OT) nonapeptides modulate numerous social and stress-related behaviors, yet these peptides are made in multiple nuclei and brain regions (e.g., >20 in some mammals), and VP-OT cells in these areas often exhibit overlapping axonal projections. Furthermore, the magnocellular cell groups release peptide volumetrically from dendrites and soma, which gives rise to paracrine modulation in distal brain areas. Nonapeptide receptors also tend to be promiscuous. Hence, behavioral effects that are mediated by any given receptor type (e.g., the OT receptor) in a target brain region cannot be conclusively attributed to either VP or OT, nor to a specific cell group. We here review what is actually known about the social behavior functions of nonapeptide cell groups, with a focus on aggression, affiliation, bonding, social stress, and parental behavior, and discuss recent studies that demonstrate a diversity of sex-specific contributions of VP-OT cell groups to gregariousness and pair bonding.

Plasticity in the brainstem vagal circuits controlling gastric motor function triggered by corticotropin releasing factor

Stress impairs gastric emptying, reduces stomach compliance and induces early satiety via vagal actions. We have shown recently that the ability of the anti-stress neuropeptide oxytocin (OXT) to modulate vagal brainstem circuits undergoes short-term plasticity via alterations in cAMP levels subsequent to vagal afferent fibre-dependent activation of metabotropic glutamate receptors. The aim of the present study was to test the hypothesis that the OXT-induced gastric response undergoes plastic changes in the presence of the prototypical stress hormone, corticotropin releasing factor (CRF). Whole cell patch clamp recordings showed that CRF increased inhibitory GABAergic synaptic transmission to identified corpus-projecting dorsal motor nucleus of the vagus (DMV) neurones. In naive brainstem slices, OXT perfusion had no effect on inhibitory synaptic transmission; following exposure to CRF (and recovery from its actions), however, re-application of OXT inhibited GABAergic transmission in the majority of neurones tested. This uncovering of the OXT response was antagonized by pretreatment with protein kinase A or adenylate cyclase inhibitors, H89 and di-deoxyadenosine, respectively, indicating a cAMP-mediated mechanism. In naive animals, OXT microinjection in the dorsal vagal complex induced a NO-mediated corpus relaxation. Following CRF pretreatment, however, microinjection of OXT attenuated or, at times reversed, the gastric relaxation which was insensitive to l-NAME but was antagonized by pretreatment with a VIP antagonist. Immunohistochemical analyses of vagal motoneurones showed an increased number of oxytocin receptors present on GABAergic terminals of CRF-treated or stressed vs. naive rats. These results indicate that CRF alters vagal inhibitory circuits that uncover the ability of OXT to modulate GABAergic currents and modifies the gastric corpus motility response to OXT.

Vagal afferent fibres determine the oxytocin-induced modulation of gastric tone

Oxytocin (OXT) inputs to the dorsal vagal complex (DVC; nucleus of the tractus solitarius (NTS) dorsal motor nucleus of the vagus (DMV) and area postrema) decrease gastric tone and motility. Our first aim was to investigate the mechanism(s) of OXT-induced gastric relaxation. We demonstrated recently that vagal afferent inputs modulate NTS-DMV synapses involved in gastric and pancreatic reflexes via group II metabotropic glutamate receptors (mGluRs). Our second aim was to investigate whether group II mGluRs similarly influence the response of vagal motoneurons to OXT. Microinjection of OXT in the DVC decreased gastric tone in a dose-dependent manner. The OXT-induced gastric relaxation was enhanced following bethanechol and reduced by l-NAME administration, suggesting a nitrergic mechanism of gastroinhibition. DVC application of the group II mGluR antagonist EGLU induced a gastroinhibition that was not dose dependent and shifted the gastric effects of OXT to a cholinergic-mediated mechanism. Evoked and miniature GABAergic synaptic currents between NTS and identified gastric-projecting DMV neurones were not affected by OXT in any neurones tested, unless the brainstem slice was (a) pretreated with EGLU or (b) derived from rats that had earlier received a surgical vagal deafferentation. Conversely, OXT inhibited glutamatergic currents even in naive slices, but their responses were unaffected by EGLU pretreatment. These results suggest that the OXT-induced gastroinhibition is mediated by activation of the NANC pathway. Inhibition of brainstem group II mGluRs, however, uncovers the ability of OXT to modulate GABAergic transmission between the NTS and DMV, resulting in the engagement of an otherwise silent cholinergic vagal neurocircuit.

Effect of DA-9701, a novel prokinetic agent, on stress-induced delayed gastric emptying and hormonal changes in rats

BACKGROUND

DA-9701 is a novel prokinetic agent formulated with Pharbitis Semen and Corydalis Tuber. This study aimed to evaluate the effect of DA-9701 on stress-induced delay in gastric emptying and changes in plasma adrenocorticotropic hormone and ghrelin levels in rats.

METHODS

Changes in gastric emptying in response to different durations of stress were evaluated. Gastric emptying was compared between the following groups: (i) nonstressed vehicle- or DA-9701-treated group, (ii) nonstressed vehicle- or mosapride-treated group, (iii) 2-h stressed vehicle- or DA-9701-treated group, and (iv) 2-h stressed vehicle- or mosapride-treated group. Water immersion restraint stress was used as the stressor. DA-9701 or mosapride at 3 mg kg(-1) was administered to the rats after subjecting them to 2-h stress, and then gastric emptying was measured using the phenol red method.

KEY RESULTS

Gastric emptying was significantly delayed in the 2-h stressed group compared with the nonstressed group. Mosapride administration resulted in significant recovery from the stress-induced delay in gastric emptying. Gastric emptying in the rats that underwent 2-h stress followed by DA-9701 administration was not significantly different from that in the nonstressed group. The plasma adrenocorticotropic hormone and active ghrelin levels in the 2-h stressed group were significantly higher than those in the nonstressed group. These increases were significantly inhibited by DA-9701.

CONCLUSIONS & INFERENCES

The administration of DA-9701 improved delayed gastric emptying and inhibited the hormonal changes induced by stress, suggesting that DA-9701 can be used as a gastroprokinetic agent for the treatment of delayed gastric emptying, particularly that associated with stress.

Social interaction attenuates stress responses following chronic stress in maternally separated rats

Early life stress has been implicated as a risk factor for functional gastrointestinal (GI) disorders. Hypothalamic oxytocin (OXT) is well known to regulate social interactions and affiliative behaviors. We have shown that maternal separation (MS) induces GI dysmotility and impair hypothalamic OXT expression in response to chronic homotypic stress (CHS). We studied whether social interaction can improve GI dysmotility and OXT expression in MS rats. Male neonatal SD rats were exposed to MS for 180 min from postnatal day (PND)-2 to PND-14. After weaning, 3MS rats were housed together (pure MS). In another group, 1MS rat was housed with 2 control rats (mixed MS). Anxiety-like behaviors were evaluated in elevated plus maze (EPM). Solid gastric emptying (GE) and colonic transit (CT) were measured following CHS loading. Expression of corticotropin releasing factor (CRF) and OXT in the paraventricular nucleus (PVN) were evaluated by real time RT-PCR and immunohistochemistry. Pure MS rats demonstrated increased anxiety-like behaviors, which were significantly reduced in mixed MS rats. Delayed GE (31.5±2.8%, n=6) and accelerated CT [Geometric center (GC) =8.9±0.8, n=6] observed in pure MS rats were restored in mixed MS rats (GE=67.8±3.8%, GC=6.7±1.2, n=6, P<0.05) following CHS. OXT mRNA expression was upregulated, while CRF mRNA expression was downregulated in mixed MS rats, compared to pure MS rats. The number of OXT-immunoreactive cells was significantly increased following CHS at the PVN in mixed MS rats. Our study may contribute to the treatment strategies for GI motility disorders associated with early life stress.

Anti-stress effects of transcutaneous electrical nerve stimulation (TENS) on colonic motility in rats

BACKGROUND

Disorders of colonic motility may contribute to symptoms in patients with irritable bowel syndrome (IBS), and stress is widely believed to play a major role in developing IBS. Stress increases corticotropin releasing factor (CRF) of the hypothalamus, resulting in acceleration of colonic transit in rodents. In contrast, hypothalamic oxytocin (OXT) has an anti-stress effect via inhibiting CRF expression and hypothalamic-pituitary-adrenal axis activity. Although transcutaneous electrical nerve stimulation (TENS) and acupuncture have been shown to have anti-stress effects, the mechanism of the beneficial effects remains unknown.

AIMS

We tested the hypothesis that TENS upregulates hypothalamic OXT expression resulting in reduced CRF expression and restoration of colonic dysmotility in response to chronic stress.

METHODS

Male SD rats received different types of stressors for seven consecutive days (chronic heterotypic stress). TENS was applied to the bilateral hind limbs every other day before stress loading. Another group of rats did not receive TENS treatment.

RESULTS

TENS significantly attenuated accelerated colonic transit induced by chronic heterotypic stress, which was antagonized by a central injection of an OXT antagonist. Immunohistochemical study showed that TENS increased OXT expression and decreased CRF expression at the paraventricular nucleus (PVN) following chronic heterotypic stress.

CONCLUSIONS

It is suggested that TENS upregulates hypothalamic OXT expression which acts as an anti-stressor agent and mediates restored colonic dysmotility following chronic stress. TENS may be useful to treat gastrointestinal symptoms associated with stress.

Impaired adaptation of gastrointestinal motility following chronic stress in maternally separated rats

Exposure to early life stress causes increased stress responsiveness and permanent changes in the central nervous system. We recently showed that delayed gastric emptying (GE) and accelerated colonic transit (CT) in response to acute restraint stress (ARS) were completely restored following chronic homotypic stress (CHS) in rats via upregulation of hypothalamic oxytocin (OXT) expression. However, it is unknown whether early life stress affects hypothalamic OXT circuits and gastrointestinal motor function. Neonatal rats were subjected to maternal separation (MS) for 180 min/day for 2 wk. Anxiety-like behaviors were evaluated by the elevated-plus-maze test. GE and CT were measured under nonstressed (NS), ARS, and CHS conditions. Expression of corticotropin-releasing factor (CRF) and OXT in the paraventricular nucleus (PVN) of the hypothalamus was evaluated by real time RT-PCR and immunohistochemistry. MS increased anxiety-like behaviors. ARS delayed GE and accelerated CT in control and MS rats. After CHS, delayed GE and accelerated CT were restored in control, but not MS, rats. CRF mRNA expression was significantly increased in response to ARS in control and MS rats. Increased CRF mRNA expression was still observed following CHS in MS, but not control, rats. In response to CHS, OXT mRNA expression was significantly increased in control, but not MS, rats. The number of OXT-immunoreactive cells was increased following CHS in the magnocellular part of the PVN in control, but not MS, rats. MS impairs the adaptation response of gastrointestinal motility following CHS. The mechanism of the impaired adaptation involves downregulation of OXT and upregulation of CRF in the hypothalamus in MS rats.

Hypothalamic circuit regulating colonic transit following chronic stress in rats

Although acute stress accelerates colonic transit, the effect of chronic stress on colonic transit remains unclear. In this study, rats received repeated restraint stress (chronic homotypic stress) or various types of stress (chronic heterotypic stress) for 5 and 7 days, respectively. Vehicle saline, oxytocin (OXT), OXT receptor antagonist or corticotropin-releasing factor (CRF) receptor antagonists were administered by intracerebroventricular (ICV) injection prior to restraint stress for 90 min. Immediately after the stress exposure, the entire colon was removed and the geometric center (GC) of Na51CrO4 (a nonabsorbable radioactive marker; 0.5 μCi) distribution was calculated to measure the transit. Gene expression of OXT and CRF in the paraventricular nucleus (PVN) was evaluated by in situ hybridization. Accelerated colonic transit with the acute stressor was no longer observed following chronic homotypic stress. This restored colonic transit was reversed by ICV injection of an OXT antagonist. In contrast, chronic heterotypic stress significantly accelerated colonic transit, which was attenuated by ICV injection of OXT and by a CRF receptor 1 antagonist. OXT mRNA expression in the PVN was significantly increased following chronic homotypic stress, but not chronic heterotypic stress. However, CRF mRNA expression in the PVN was significantly increased following acute and chronic heterotypic stress, but not chronic homotypic stress. These results indicate that central OXT and CRF play a pivotal role in mediating the colonic dysmotility following chronic stress in rats.

Oxytocin-immunoreactive innervation of identified neurons in the rat dorsal vagal complex

BACKGROUND

Oxytocin (OXT) has been implicated in reproduction and social interactions and in the control of digestion and blood pressure. OXT-immunoreactive axons occur in the dorsal vagal complex (DVC; nucleus tractus solitarius, NTS, dorsal motor nucleus of the vagus, DMV, and area postrema, AP), which contains neurons that regulate autonomic homeostasis. The aim of the present work is to provide a systematic investigation of the OXT-immunoreactive innervation of dorsal motor nucleus of the vagus (DMV) neurons involved in the control of gastrointestinal (GI) function.

METHODS

We studied DMV neurons identified by (i) prior injection of retrograde tracers in the stomach, ileum, or cervical vagus or (ii) induction of c-fos expression by glucoprivation with 2-deoxyglucose. Another subgroup of DMV neurons was identified electrophysiologically by stimulation of the cervical vagus and then juxtacellularly labeled with biotinamide. We used two- or three-color immunoperoxidase labeling for studies at the light microscopic level.

KEY RESULTS

Close appositions from OXT-immunoreactive varicosities were found on the cell bodies, dendrites, and axons of DMV neurons that projected to the GI tract and that responded to 2-deoxyglucose and juxtacellularly labeled DMV neurons. Double staining for OXT and choline acetyltransferase revealed that OXT innervation was heavier in the caudal and lateral DMV than in other regions. OXT-immunoreactive varicosities also closely apposed a small subset of tyrosine hydroxylase-immunoreactive NTS and DMV neurons.

CONCLUSIONS & INFERENCES

Our results provide the first anatomical evidence for direct OXT-immunoreactive innervation of GI-related neurons in the DMV.

Stress and visceral pain: from animal models to clinical therapies

Epidemiological studies have implicated stress (psychosocial and physical) as a trigger of first onset or exacerbation of irritable bowel syndrome (IBS) symptoms of which visceral pain is an integrant landmark. A number of experimental acute or chronic exteroceptive or interoceptive stressors induce visceral hyperalgesia in rodents although recent evidence also points to stress-related visceral analgesia as established in the somatic pain field. Underlying mechanisms of stress-related visceral hypersensitivity may involve a combination of sensitization of primary afferents, central sensitization in response to input from the viscera and dysregulation of descending pathways that modulate spinal nociceptive transmission or analgesic response. Biochemical coding of stress involves the recruitment of corticotropin releasing factor (CRF) signaling pathways. Experimental studies established that activation of brain and peripheral CRF receptor subtype 1 plays a primary role in the development of stress-related delayed visceral hyperalgesia while subtype 2 activation induces analgesic response. In line with stress pathways playing a role in IBS, non-pharmacologic and pharmacologic treatment modalities aimed at reducing stress perception using a broad range of evidence-based mind-body interventions and centrally-targeted medications to reduce anxiety impact on brain patterns activated by visceral stimuli and dampen visceral pain.

Stress and visceral pain: from animal models to clinical therapies

Epidemiological studies have implicated stress (psychosocial and physical) as a trigger of first onset or exacerbation of irritable bowel syndrome (IBS) symptoms of which visceral pain is an integrant landmark. A number of experimental acute or chronic exteroceptive or interoceptive stressors induce visceral hyperalgesia in rodents although recent evidence also points to stress-related visceral analgesia as established in the somatic pain field. Underlying mechanisms of stress-related visceral hypersensitivity may involve a combination of sensitization of primary afferents, central sensitization in response to input from the viscera and dysregulation of descending pathways that modulate spinal nociceptive transmission or analgesic response. Biochemical coding of stress involves the recruitment of corticotropin releasing factor (CRF) signaling pathways. Experimental studies established that activation of brain and peripheral CRF receptor subtype 1 plays a primary role in the development of stress-related delayed visceral hyperalgesia while subtype 2 activation induces analgesic response. In line with stress pathways playing a role in IBS, non-pharmacologic and pharmacologic treatment modalities aimed at reducing stress perception using a broad range of evidence-based mind-body interventions and centrally-targeted medications to reduce anxiety impact on brain patterns activated by visceral stimuli and dampen visceral pain.

Sustained acceleration of colonic transit following chronic homotypic stress in oxytocin knockout mice

Acute restraint stress delays gastric emptying and accelerates colonic transit via central corticotropin releasing factor (CRF) in rats. In contrast, central oxytocin has anxiolytic effects and attenuates the hypothalamus-pituitary-adrenal (HPA) axis in response to stress. Our recent study showed that up regulated oxytocin expression attenuates hypothalamic CRF expression and restores impaired gastric motility following chronic homotypic stress in mice. We studied the effects of acute and chronic homotypic stress on colonic transit and hypothalamic CRF mRNA expression in wild type (WT) and oxytocin knockout (OXT-KO) mice. Colonic transit was measured following acute restraint stress or chronic homotypic stress (repeated restraint stress for 5 consecutive days). (51)Cr was injected via a catheter into the proximal colon. Ninety minutes after restraint stress loading, the entire colon was removed. The geometric center (GC) was calculated to evaluate colonic transit. Expression of CRF mRNA in the supraoptic nucleus (SON) was measured by real time RT-PCR. Colonic transit was significantly accelerated following acute stress in WT (GC=8.1±0.8; n=7) and OXT KO mice (GC=9.4±0.3; n=7). The accelerated colonic transit was significantly attenuated in WT mice (GC=6.6±0.5; n=9) following chronic homotypic stress while it was still accelerated in OXT KO mice (GC=9.3±0.5; n=8). The increase in CRF mRNA expression at the SON was much greater in OXT-KO mice, compared to WT mice following chronic homotypic stress. It is suggested that oxytocin plays a pivotal role in mediating the adaptation mechanism following chronic homotypic stress in mice.

Sustained delayed gastric emptying during repeated restraint stress in oxytocin knockout mice

We have recently shown that impaired gastric motility observed in acute restraint stress was restored following repeated restraint stress in mice. Repeated restraint stress up-regulates oxytocin mRNA expression and down-regulates corticotrophin-releasing factor (CRF) mRNA expression at the hypothalamus. Oxytocin knockout mice (OXT-KO) have been widely used to study the central oxytocin signalling pathways in response to various stressors. We studied the effects of acute and repeated restraint stress on solid gastric emptying and hypothalamic CRF mRNA expression in wild-type (WT) and OXT-KO mice. Heterozygous (HZ) parents (B6; 129S-Oxt(tm1Wsy)/J mice) were bred in our animal facility. Male OXT-KO, WT and HZ littermates were used for the study. Solid gastric emptying was measured following acute restraint stress (for 90 min) or repeated restraint stress (for five consecutive days). Expression of CRF mRNA in the paraventricular nucleus (PVN) was measured by real-time reverse transcriptase-polymerase chain reaction. There were no significant differences of gastric emptying in WT (68.4 ± 4.1%, n = 6), HZ (71.8 ± 3.1%, n = 6) and OXT-KO (70.6 ± 3.1%, n = 6) mice in nonstressed conditions. Acute stress significantly delayed gastric emptying in OXT-KO mice (33.10 ± 2.5%, n = 6) WT (39.1 ± 1.1%, n = 6) and HZ mice (35.8 ± 1.2%, n = 6). Following repeated restraint stress loading, gastric emptying was significantly restored in WT (68.3 ± 4.5%, n = 6) and HZ mice (63.1 ± 2.6%, n = 6). By contrast, gastric emptying was still delayed in OXT-KO mice (34.7 ± 1.3%, n = 6) following repeated restraint stress. The increase in CRF mRNA expression at the PVN was much pronounced in OXT-KO mice compared to WT or HZ mice following repeated restraint stress. These findings suggest that central oxytocin plays a pivotal role in mediating the adaptation mechanism following repeated restraint stress in mice.

Hypothalamic oxytocin mediates adaptation mechanism against chronic stress in rats

Accumulation of continuous life stress (chronic stress) often causes gastric symptoms. Although central oxytocin has antistress effects, the role of central oxytocin in stress-induced gastric dysmotility remains unknown. Solid gastric emptying was measured in rats receiving acute restraint stress, 5 consecutive days of repeated restraint stress (chronic homotypic stress), and 7 consecutive days of varying types of stress (chronic heterotypic stress). Oxytocin and oxytocin receptor antagonist were administered intracerebroventricularly (icv). Expression of corticotropin-releasing factor (CRF) mRNA and oxytocin mRNA in the paraventricular nucleus (PVN) of the hypothalamus was evaluated by real-time RT-PCR. The changes of oxytocinergic neurons in the PVN were evaluated by immunohistochemistry. Acute stress delayed gastric emptying, and the delayed gastric emptying was completely restored after 5 consecutive days of chronic homotypic stress. In contrast, delayed gastric emptying persisted following chronic heterotypic stress. The restored gastric emptying following chronic homotypic stress was antagonized by icv injection of an oxytocin antagonist. Icv injection of oxytocin restored delayed gastric emptying induced by chronic heterotypic stress. CRF mRNA expression, which was significantly increased in response to acute stress and chronic heterotypic stress, returned to the basal levels following chronic homotypic stress. In contrast, oxytocin mRNA expression was significantly increased following chronic homotypic stress. The number of oxytocin-immunoreactive cells was increased following chronic homotypic stress at the magnocellular part of the PVN. Icv injection of oxytocin reduced CRF mRNA expression induced by acute stress and chronic heterotypic stress. It is suggested that the adaptation mechanism to chronic stress may involve the upregulation of oxytocin expression in the hypothalamus, which in turn attenuates CRF expression.

Central oxytocin attenuates augmented gastric postprandial motility induced by restraint stress in rats

Restraint stress delays gastric emptying via uncoordinated motility pattern in rats. Central oxytocin has anxiolytic effects and attenuates the hypothalamic-pituitary-adrenal (HPA) axis in response to stress and facilitates stress-induced delayed gastric emptying. However, the role of central oxytocin in regulating gastric motility remains unknown. Postprandial gastric motility was recorded via a strain-gauge transducer, implanted on the antrum in Sprague-Dawley (SD) rats. To investigate whether central and peripheral oxytocin are involved in gastric motility, oxytocin (10 microg) was administered intracerebroventricularly (icv) and intraperitoneally (ip). Central and peripheral oxytocin administration did not affect the postprandial gastric motility under non-stressed conditions. Restraint stress augmented gastric contractions. Central administration of oxytocin, but not peripheral administration, abolished the augmented postprandial gastric contractions induced by restraint stress. Oxytocin facilitates stress-induced delayed gastric emptying via alleviating uncoordinated gastric motility. Oxytocin might be a candidate for the treatment of stress-induced GI motility disorders.

Beneficial effects of social attachment to overcome daily stress

Accumulation of daily life stress (chronic stress) often causes functional gastrointestinal diseases. Central oxytocin plays an important role in attenuating stress responses and regulating positive social interactions. Adult male rats were either paired or singly housed 1 week prior to the stress loading. Solid gastric emptying was measured after 7 consecutive days of chronic heterotypic stress. To study whether endogenous oxytocin is involved in restoring the delayed gastric emptying after paired housing, an oxytocin antagonist was injected intracerebroventricularly (icv) before the gastric emptying study. CRF and oxytocin mRNA expression in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) was evaluated by real time RT-PCR. In singly housed rats, chronic heterotypic stress significantly delayed gastric emptying (35.1+/-2.8%, n=6, P<or=0.01), compared to that of non-stressed rats (53.2+/-1.3%, n=6). Delayed gastric emptying observed in singly housed rats induced by chronic heterotypic stress was significantly improved by paired housing (54.8+/-3.5%, n=8, P<0.05). Central-administration of oxytocin antagonist attenuated the restored gastric emptying in paired housed rats (33.2+/-4.1%, n=6) following chronic heterotypic stress. Increased CRF mRNA expression at the PVN and SON observed in singly housed rats was significantly reduced in paired housed rats following chronic heterotypic stress. In contrast, oxytocin mRNA expression at the PVN and SON was significantly increased in paired housed rats. Social attachment restores delayed gastric emptying following chronic heterotypic stress, via down-regulating CRF expression and up-regulating oxytocin mRNA expression. Our study may provide the scientific benefit of social attachment in our daily life.

The role of 5-HT3 and 5-HT4 receptors in the adaptive mechanism of colonic transit following the parasympathetic denervation in rats

BACKGROUND

Clinical studies show that disturbed colonic motility induced by extrinsic nerves damage is restored over time. We studied whether 5-HT3 and 5HT4 receptors are involved in mediating the adaptive mechanisms following parasympathetic denervation.

METHODS

Parasympathetic denervation of the entire colon was achieved by bilateral pelvic nerve transection and truncal vagotomy in rats. Colonic transit was measured by calculating the geometric center (GC) of 51Cr distribution. Expression of 5-HT3 and 5HT4 receptor mRNA was determined by real time RT-PCR.

RESULTS

Parasympathetic denervation caused a significant delay in colonic transit (GC=4.36) at postoperative day (POD) 1, compared with sham operation (GC=6.31). Delayed transit was gradually restored by POD 7 (GC=5.99) after the denervation. Restored colonic transit was antagonized by the administration of 5-HT3 and 5HT4 receptors antagonists at POD 7. 5-HT3 and 5HT4 receptors mRNA expression were significantly increased in the mucosal/submucosal layer at POD 3 or POD 7, whereas no significant difference was observed in the longitudinal muscle layers adherent with the myenteric plexus (LMMP).

CONCLUSIONS

It is suggested that up-regulation of 5-HT3 and 5-HT4 receptors expression in the mucosal/submucosal layer is involved to restore the delayed transit after the parasympathetic denervation in rats.

The role of 5-HT3 and 5-HT4 receptors in the adaptive mechanism of colonic transit following the parasympathetic denervation in rats

BACKGROUND

Clinical studies show that disturbed colonic motility induced by extrinsic nerves damage is restored over time. We studied whether 5-HT3 and 5HT4 receptors are involved in mediating the adaptive mechanisms following parasympathetic denervation.

METHODS

Parasympathetic denervation of the entire colon was achieved by bilateral pelvic nerve transection and truncal vagotomy in rats. Colonic transit was measured by calculating the geometric center (GC) of 51Cr distribution. Expression of 5-HT3 and 5HT4 receptor mRNA was determined by real time RT-PCR.

RESULTS

Parasympathetic denervation caused a significant delay in colonic transit (GC=4.36) at postoperative day (POD) 1, compared with sham operation (GC=6.31). Delayed transit was gradually restored by POD 7 (GC=5.99) after the denervation. Restored colonic transit was antagonized by the administration of 5-HT3 and 5HT4 receptors antagonists at POD 7. 5-HT3 and 5HT4 receptors mRNA expression were significantly increased in the mucosal/submucosal layer at POD 3 or POD 7, whereas no significant difference was observed in the longitudinal muscle layers adherent with the myenteric plexus (LMMP).

CONCLUSIONS

It is suggested that up-regulation of 5-HT3 and 5-HT4 receptors expression in the mucosal/submucosal layer is involved to restore the delayed transit after the parasympathetic denervation in rats.