Fasting is a physiological stimulus of vagus-mediated enhancement of nociception in the female rat

Regular use of low-dose of opioids after gastrointestinal surgery may lead to postoperative gastrointestinal tract dysfunction in children: a Chinese national regional health center experience sharing

BACKGROUND

The need for pain management is increasing in pediatrics, but the side effects of overuse or abuse of analgesics can be harmful to children's health and even life-threatening in severe cases.

METHODS

Patients who underwent resection of Meckel's diverticulum at the Children's Hospital of Chongqing Medical University from July 1, 2019, to July 1, 2022, were included in this study. Opioids were administered through patient-controlled analgesia (PCA). Based on the preoperative choices made by the legal guardians, patients were stratified into two groups: PCA Group (PCAG) and Non-PCA Group (NPCAG). Data pertaining to the clinical characteristics and prognoses of these patients were subsequently collected and analyzed to assess the impact of opioid administration.

RESULTS

In the study, a total of 126 patients were enrolled, with 72 allocated to the Patient-Controlled Analgesia Group (PCAG) and 54 to the Non-Patient-Controlled Analgesia Group (NPCAG). When compared to the NPCAG, the PCAG exhibited a longer duration of postoperative fasting (median 72 vs. 62 h, p = 0.044) and increased utilization of laxatives (12[16.7%] vs. 2[3.7%], p = 0.022). However, the PCAG also experienced higher incidences of intestinal stasis and abnormal intestinal dilation (13[18.1%] vs. 3[5.6%], p = 0.037). No statistically significant differences were observed in pain assessments at the conclusion of the surgical procedure (0 vs. 1[1.9%], p = 0.429) or within the first 24 h postoperatively (16[22.2%] vs. 18[33.3%], p = 0.164). Additionally, NPCAG patients did not necessitate increased administration of rescue analgesics (2[2.8%] vs. 4[7.4%], p = 0.432).

CONCLUSIONS

The administration of opioids did not demonstrably ameliorate postoperative pain but was associated with a heightened incidence of postoperative gastrointestinal tract dysfunction. The retrospective nature of the current research should be considered and should be clarified further.

Gut Prevotellaceae-GABAergic septohippocampal pathway mediates spatial memory impairment in high-fat diet-fed ovariectomized mice

Clarifying the risk factors and mechanisms that contribute to the onset of cognitive impairment following estrogen depletion is essential for improving the quality of life of older females. In the current study, using behavioral tests, 16S rDNA sequencing, in vivo and in vitro electrophysiology, optogenetics and chemogenetics, we found that high-fat diet (HFD)-accelerated impairment of hippocampus-dependent memory, gut microbiota, and hippocampal theta rhythmogenesis in ovariectomized (OVX) mice and fecal microbiota transplantation rescued these phenomena. The identification of fasting-activated medial septal neurons showed that PV⁺ GABAergic neurons in the medial septal area (MSA) respond to gut sensory signals. Optogenetic activation of septohippocampal PV⁺ GABAergic fibers (but not cholinergic fibers) significantly rescued hippocampal theta rhythmogenesis and spatial memory in HFD-fed OVX mice. Resistant starch supplementation (RSHFD) rectified the gut Prevotellaceae and considerably alleviated reduced septal gut-responsive neurons, decreased hippocampal theta rhythm, and impaired hippocampus-dependent memory in HFD-fed OVX mice. Furthermore, chemogenetic inhibition of septal PV⁺ GABAergic neurons reversed the neuroprotective effects of resistant starch supplementation. These findings highlight the notable gut-sensory nature of medial septal PV⁺ GABAergic neurons. A HFD accelerates estrogen deficiency-induced cognitive impairment by disrupting the gut Prevotellaceae-septo-hippocampal pathway. This study contributes to a better understanding of the precise gut-brain control of cognition and cognitive impairment in postmenopausal females.

Involvement of cannabinoid type 1 receptor in fasting-induced analgesia

The endocannabinoid system (ECS) is known to modulate not only food intake but also pain, especially via the cannabinoid type 1 receptor (CB1R) expressed throughout the central nervous system and the peripheral tissues. Our previous study demonstrated that fasting produces an analgesic effect in adult male mice, which is reversed by intraperitoneal (i.p.) administration of CB1R antagonist (SR 141716). In the present study, we further examined the effect of CB1R expressed in the peripheral tissues. In the formalin-induced inflammatory pain model, i.p. administration of peripherally restricted CB1R antagonist (AM 6545) reversed fasting-induced analgesia. However, intraplantar administration of SR 141716 did not affect fasting-induced analgesia. Furthermore, mRNA expression of CB1R did not change in the formalin model by fasting in the dorsal root ganglia. The formalin-induced c-Fos expression at the spinal cord level was not affected by fasting, and in vivo recording from the superficial dorsal horn of the lumbar spinal cord revealed that fasting did not affect formalin-induced neural activity, which indicates minimal involvement of the spinal cord in fasting-induced analgesia. Finally, when we performed subdiaphragmatic vagotomy to block the hunger signal from the gastrointestinal (GI) system, AM 6545 did not affect fasting-induced analgesia, but SR 141716 still reversed fasting-induced analgesia. Taken together, our results suggest that both peripheral and central CB1Rs contribute to fasting-induced analgesic effects and the CB1Rs in the GI system which transmit fasting signals to the brain, rather than those in the peripheral sensory neurons, may contribute to fasting-induced analgesic effects.

Is cervical region tightness related to vagal function and stomach symptoms?

The vagal nerve is a cranial nerve that carries mainly parasympathetic fibers (average 75%) with both sensory and motor functions. The vagal nerve contains a complex neuro-endocrine-immune network. The majority, at least 66%, of the gastric myenteric neurons receive direct cholinergic excitatory stimulation from the pre-enteric vagal nerve. Changes in vagal function may cause stomach problems, although the mechanisms that change the vagal function have not yet been fully illuminated. Considering the course of the vagal nerve in the cervical region, it is thought that conditions such as stiffness, tightness and decreased elasticity in this region may compress the vagal nerve andmay affect vagal function. According to this hypothesis, neuroinflammation and hyperalgesia may occur in the vagal nerve under mechanical pressure, resulting in increased complaints of pain and burning in the stomach increases. However, as the vagal nerve has various effects on the motility of the stomach and vagal dysfunction affects the motor function of the stomach, relaxation techniques applied to the soft tissues of the cervical region will provide mechanical relief in the nerve. Thus, the vagal nerve will be decompressed and be able to function optimally. According to our clinical observations, in patients whose soft tissues in the cervical region are relaxed, gastric symptoms are decreased. Based on research results and clinical experience, cervical region tightness can be considered to cause stomach problems through the vagal nerve, and soft tissue relaxation of the cervical region can be a promising treatment method for stomach symptoms.

Reduced Sensory-Evoked Locus Coeruleus-Norepinephrine Neural Activity in Female Rats With a History of Dietary-Induced Binge Eating

Noradrenergic pathways have been implicated in eating pathologies. These experiments sought to examine how dietary-induced binge eating influences the neuronal activity of the locus coeruleus (LC)-norepinephrine (NE) system. Young adult female Sprague Dawley rats (7-8 weeks old) were exposed to a repeated intermittent (twice weekly) cycle of 30-min access to a highly palatable sweetened fat (i.e., vegetable shortening with 10% sucrose) with or without intermittent (24 h) calorie restriction (Restrict Binge or Binge groups, respectively). Age- and weight-matched female control rats were exposed to standard chow feeding (Naive group) or intermittent chow feeding (Restrict group). The Binge and Restrict Binge groups demonstrated an escalation in sweet-fat food intake after 2.5 weeks. On week 3, in vivo single-unit LC electrophysiological activity was recorded under isoflurane anesthesia. Restrict Binge (20 cells from six rats) and Binge (27 cells from six rats) had significantly reduced (approximate 20% and 26%, respectively) evoked LC discharge rates compared with naive rats (22 cells, seven rats). Spontaneous and tonic discharge rates were not different among the groups. Signal-to-noise ratio was reduced in the groups with intermittent sweetened fat exposure. In order to investigate the neuropeptide alterations as a consequence of dietary binge eating, relative gene expression of neuropeptide Y (NPY), glucagon-like peptide 1 receptor (GLP-1r), prodynorphin, and related genes were measured in LC and hypothalamic arcuate (Arc) regions. Glp-1r, Npy2r, and Pdyn in LC region were reduced with repeated intermittent restriction. Npy1r was reduced by approximately 27% in ARC of Restrict compared with Naive group. Such data indicate that dietary-induced binge eating alters the neural response of LC neurons to sensory stimuli and dampens the neural stress response.

Gut microbiota analysis and its significance in vasovagal syncope in children

BACKGROUND

Vasovagal syncope (VVS) is common in children and greatly affect both physical and mental health. But the mechanisms have not been completely explained. This study was designed to analyze the gut microbiota in children with VVS and explore its clinical significance.

METHODS

Fecal samples from 20 VVS children and 20 matched controls were collected, and the microbiota were analyzed by 16S rRNA gene sequencing. The diversity and microbiota compositions of the VVS cases and controls were compared with the independent sample t test or Mann-Whitney U test. The correlation between the predominant bacteria and clinical symptoms was analyzed using Pearson or Spearman correlation test.

RESULTS

No significant differences in diversity were evident between VVS and controls (P > 0.05). At the family level, the relative abundance of Ruminococcaceae was significantly higher in VVS children than in controls (median [Q1, Q3]: 22.10% [16.89%, 27.36%] vs. 13.92% [10.31%, 20.18%], Z = -2.40, P < 0.05), and LEfSe analysis revealed Ruminococcaceae as a discriminative feature (linear discriminant analysis [LDA] score > 4, P < 0.05). The relative abundance of Ruminococcaceae in VVS patients was positively correlated with the frequency of syncope (r = 0.616, P < 0.01). In terms of its correlation with hemodynamics, we showed that relative abundance of Ruminococcaceae was negatively correlated with the systolic and diastolic pressure reduction at the positive response in head-up tilt test (HUTT; r = -0.489 and -0.448, all P < 0.05), but was positively correlated with the mean pressure drop and decline rate (r = 0.489 and 0.467, all P < 0.05) as well as diastolic pressure drop and decline rate at the HUTT positive response (r = 0.579 and 0.589, all P < 0.01) in VVS patients.

CONCLUSION

Ruminococcaceae was the predominant gut bacteria and was associated with the clinical symptoms and hemodynamics of VVS, suggesting that gut microbiota might be involved in the development of VVS.

The Gut⁻Brain Axis in the Neuropsychological Disease Model of Obesity: A Classical Movie Revised by the Emerging Director "Microbiome"

The worldwide epidemic of obesity has become an important public health issue, with serious psychological and social consequences. Obesity is a multifactorial disorder in which various elements (genetic, host, and environment), play a definite role, even if none of them satisfactorily explains its etiology. A number of neurological comorbidities, such as anxiety and depression, charges the global obesity burden, and evidence suggests the hypothesis that the brain could be the seat of the initial malfunction leading to obesity. The gut microbiome plays an important role in energy homeostasis regulating energy harvesting, fat deposition, as well as feeding behavior and appetite. Dietary patterns, like the Western diet, are known to be a major cause of the obesity epidemic, probably promoting a dysbiotic drift in the gut microbiota. Moreover, the existence of a "gut⁻brain axis" suggests a role for microbiome on hosts' behavior according to different modalities, including interaction through the nervous system, and mutual crosstalk with the immune and the endocrine systems. In the perspective of obesity as a real neuropsychological disease and in light of the discussed considerations, this review focuses on the microbiome role as an emerging director in the development of obesity.

Antinociceptive effects of caloric restriction on post-incisional pain in nonobese rats

Caloric restriction (CR) increases lifespan, retards physiological signs of aging, and delays a variety of diseases. Reduction of inflammatory response was proposed as one of the molecular mechanisms for how CR exerts beneficial effects. The present study investigated the effects of CR on postoperative pain in rats. Adult nonobese rats were divided into two dietary groups, an ad libitum fed group (AL) and a caloric restriction group (CR) that was provided with 60% of the food intake of AL rats. After 6 weeks, the effects of CR on pain behaviors and inflammation induced by plantar incision were examined. CR rats displayed significantly reduced nonevoked pain, mechanical allodynia and thermal hyperalgesia induced by incision, and showed decreased levels of pro-inflammatory cytokines in serum, peri-incisional skin tissue and ipsilateral spinal cord dorsal horn at 6 h and 24 h after incision. The analgesic efficiency of parecoxib and morphine, two agents widely used for the management of postoperative pain clinically, was reinforced by CR. Together, CR generates antinociceptive effects on postoperative incisional pain in rats, perhaps providing some improvement of QOL in patients with postoperative pain, and the beneficial effects may be attributable to the inhibition of excessive inflammation induced by surgical injury.

The effects of female sexual steroids on gastric function and barrier resistance of gastrointestinal tract following traumatic brain injury

AIM

The aim was to assess the alteration of gastric function and barrier function of gastrointestinal (GI) tract following diffuse brain injury in varying ovarian hormone status.

MATERIALS AND METHODS

Diffuse traumatic brain injury (TBI) was induced by Marmarou method. Rats were randomly assigned into 10 groups: Intact, sham + ovariectomized female (OVX), TBI, TBI + OVX, vehicle, estradiol (E2), progesterone (P), E2 + P, estrogen receptor alpha agonist and estrogen receptor beta agonist (DPN). Endotoxin levels were measured using enzyme-linked immunosorbent assay method. All the parameters were measured 5 days after TBI.

RESULTS

Intragastric pressure was significantly decreased in TBI as compared to the intact group (P < 0.001) and this was lower in TBI group versus TBI + OVX group (P < 0.05). Pretreatment with steroid hormones and their agonists did not have any effect on the gastric pressure compared to TBI + OVX or vehicle groups. Inflammation, congestion, ulcer and erosion were seen in the TBI rats. All treatment groups worsen the tissue condition so that the presence of thrombosis also was seen. The trauma induction did not have any effect on the serum and intestinal endotoxin levels. DPN had caused a significant reduction in serum levels of endotoxin compared with OVX + TBI group (P < 0.05).

CONCLUSION

Pretreatment with sexual steroids is not useful in the treatment of GI dysfunction induced by TBI. The treatment with all sexual female hormones worsens the gastric tissue condition. Furthermore, the applied weight was not enough for releasing of endotoxin. It seems that estrogen reduced the endotoxin levels by estrogen beta receptor.

Effect of food deprivation on formalin-induced nociceptive behaviors and β-endorphin and sex hormone concentration in rats

BACKGROUND

The present study examined the possible role of endogenous opioidergic system in effect of food deprivation on formalin-induced nociceptive behaviors in male and female rats. Also, we investigated the effect of food deprivation on the plasma level of beta-endorphin and sex hormones.

METHODS

Food was withdrawn 48 h prior to performing the formalin test, but water continued to be available ad libitum. The formalin was injected into hind plantar paw.

RESULTS

There is significant difference between male and female control rats during phase 2B. Following 48-h food deprivation, both male and female rats exhibited enhanced nociceptive behavior in response to formalin. Food deprivation for 12 and 24 h increased and for 48 h decreased beta-endorphin level in male and female rats. Food deprivation for 24 h decreased testosterone level in male, while it had no significant effect on female rats and food deprivation for 48 h decreased testosterone level in both sexes. Food deprivation for 24 h increased estradiol level in female and that for 48 h had no significant effect on male and female rats.

CONCLUSIONS

The present study demonstrates the existence of food deprivation for 48 h causes enhancement of nociception in the formalin test in male and female rats that has correlation with decrease in plasma beta-endorphin and testosterone levels.

Is eating behavior manipulated by the gastrointestinal microbiota? Evolutionary pressures and potential mechanisms

Microbes in the gastrointestinal tract are under selective pressure to manipulate host eating behavior to increase their fitness, sometimes at the expense of host fitness. Microbes may do this through two potential strategies: (i) generating cravings for foods that they specialize on or foods that suppress their competitors, or (ii) inducing dysphoria until we eat foods that enhance their fitness. We review several potential mechanisms for microbial control over eating behavior including microbial influence on reward and satiety pathways, production of toxins that alter mood, changes to receptors including taste receptors, and hijacking of the vagus nerve, the neural axis between the gut and the brain. We also review the evidence for alternative explanations for cravings and unhealthy eating behavior. Because microbiota are easily manipulatable by prebiotics, probiotics, antibiotics, fecal transplants, and dietary changes, altering our microbiota offers a tractable approach to otherwise intractable problems of obesity and unhealthy eating.

Food Deprivation Sensitizes Pain Perception

While food deprivation has known effects on sympathovagal balance, little is known about hunger’s influence on the perception of pain. Since autonomic activities influence many cognitive and emotional processes, this suggests that food deprivation should interact with the perception of pain. This study analyzed the possible effects of short-term food deprivation on pain sensitivity in healthy female participants. This study was comprised of 32 healthy female participants who underwent a 48-hr inpatient hospital investigation. Prior to testing, heart rate and heart rate variability were assessed. After a standardized breakfast, day 1 measurements were taken. Food intake was then not allowed again until the following evening for 22 participants (experimental group), while 12 participants were served standard meals (control group). Pain threshold and tolerance were assessed at 10:00 a.m. on both days using a pressure algometer. Additionally pain experience was examined. Food deprivation significantly reduced pain thresholds and tolerance scores in the experimental group. Additionally, the sympathovagal balance changed, characterized by a decrease in parasympathetic activation. Higher vagal withdrawal after food deprivation was associated with higher pain sensitivity in the experimental group. Furthermore, perceived unpleasantness and pain intensity increased for threshold and tolerance stimuli in the experimental group. We conclude that short-term food deprivation sensitized pain perception in healthy females. An imbalance in sympathovagal activation evoked by food deprivation accounted for this effect. Our results might be a pathogenic mechanism for the development of emotional difficulties associated with disturbed eating behavior.

Estrogen and its role in gastrointestinal health and disease

INTRODUCTION

While the concept of a role of estrogen in gastrointestinal (in particular, colonic) malignancy has generated excitement in recent years, no review has examined the role of this potent and omnipresent steroid hormone in physiological states or its contribution to the development of benign pathological processes. Understanding these effects (and mechanisms therein) may provide a platform for a deeper understanding of more complex disease processes.

METHODS

A literature search was conducted using the PubMed database and the search terms were "estrogen," "estrogen AND gastrointestinal tract," "estrogen AND colon," "estrogen AND esophagus," "estrogen AND small intestine," "estrogen AND stomach," "estrogen AND gallbladder," and "estrogen AND motility." Bibliographies of extracted studies were further cross-referenced. In all, 136 full-text articles were selected for review. A logical organ-based approach was taken to enable extraction of data of clinical relevance and meaningful interpretation thereof. Insight is provided into the hypotheses, theories, controversies, and contradictions generated over the last five decades by extensive investigation of estrogen in human, animal, and cell models using techniques as diverse as autoradiographic studies of baboons to human population analysis.

CONCLUSIONS

Effects from esophagus through to the colon and rectum are summarized in this first concise collection of data pertaining to estrogenic actions in gastrointestinal health and disease. Mechanisms of these actions are discussed where possible. Undoubtedly, this hormone exerts many actions yet to be elucidated, and its potential therapeutic applications remain, as yet, largely unexplored.

Formalin-induced acute pain upregulates the expression of annexin 5 mRNA in the stomach and submandibular gland of rats

AIM: To investigate the effects of formalin-induced acute pain on the expression of annexin 5 mRNA in the stomach and submandibular gland of Sprague-Dawley (SD) rats.

METHODS: Acute pain was induced in SD rats by subcutaneous injection of 2 mL of 50 g/L formalin into the plantar surface of the left hindpaw. Control rats were injected with equal volume of normal saline solution. The samples of the stomach and submandibular gland were collected under terminal anaesthesia with ketamine (40 mg/kg) at 1, 6, 24 and 72 h after formalin injection. The expression of annexin 5 mRNA in the stomach and submandibular gland was analyzed by fluorescent quantitative polymerase chain reaction (PCR).

RESULTS: Fluorescent quantitative PCR showed that the expression of annexin 5 mRNA in the stomach significantly increased at 1 h after formalin injection compared to that in control mice (7.43 ± 2.67 vs 1.00 ± 0.00, P < 0.01), and then decreased to basic level at 6 h (P > 0.05). In the submandibular gland, the expression of annexin 5 mRNA also increased at 1 h after formalin injection (4.33 ± 1.50 vs 1.00 ± 0.00, P < 0.01), and returned to normal level at 72 h (P > 0.05).

CONCLUSION: Formalin injection-induced acute pain upregulats the expression of annexin 5 mRNA in the stomach and submandibular gland of rats. Annexin 5 may be an acute stress response protein in the digestive system.

Subdiaphragmatic vagal afferent nerves modulate visceral pain

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

Neurogenic inflammation and arthritis

Inflammation and inflammatory diseases are sexually dimorphic, but the underlying causes for this observed sexual dimorphism are poorly understood. We discuss neural-immune mechanisms that underlie sexual dimorphism in three critical aspects of the inflammatory process-plasma extravasation, neutrophil function, and inflammatory hyperalgesia. Plasma extravasation and accumulation/activation of leukocytes into tissues are critical components in inflammation and are required for several other aspects of the inflammatory response. Pain (hyperalgesia) also markedly influences the magnitude of other components of the inflammatory response and induces a feedback control of plasma extravasation and neutrophil function. More important, this feedback control itself is powerfully modulated by vagal afferent activity and both the function of the primary afferent nociceptor and the modulation of inflammatory hyperalgesia by vagal afferent activity are highly sexually dimorphic.

Nociception and locomotor activity are increased in ketogenic diet fed rats

Ketogenic diets have been used to treat epilepsy in children for almost 80 years. However, there are only few studies concerning behavioral effects of these diets, besides their efficacy in treating seizure disorders induced by kainic acid or pentylenetetrazol in rats. Here, rats were fed with a ketogenic diet and locomotion, anxiety and nociception were investigated after 10 weeks. Male Wistar rats were weight matched and divided into two groups: control rats, that received regular laboratory ration, and KD rats, that received ketogenic diet (70% fat, 24% protein and no carbohydrate). Behavioral tests were applied after 10-12 weeks of treatment, and included tests to evaluate exploration (habituation to the open field), anxiety (plus-maze), and nociception (tail-flick measurement). Performance of the animals in the open field revealed a significant difference in the number of crossings, suggesting a higher locomotor activity in animals fed with a ketogenic diet. No differences in anxiety were observed, as evaluated by the plus-maze test. Nociception was measured by the latency in the tail-flick test, and ketogenic rats presented a hypernociceptive response. Yet, these animals responded to a stressor with the classic analgesia, similarly to the controls. The response of ketogenic diet fed rats to the stressor, however, was more prolonged. Exposure to a ketogenic diet may induce higher locomotor activity, together with a hypernociceptive state in the animals, possibly as a result of some alteration in the neural systems involved in the modulation of these behaviors.

Analgesic effects of dietary caloric restriction in adult mice

Nociception was studied in male mice, mostly of the C57BL/6 strain, during continuous or prolonged restriction of caloric intake (60% of ad-libitum) from midlife to senescence (up to 105 weeks). Restricted mice showed fewer licking or biting responses 20-60 min after hind paw injection of 5% formalin at 46 and 70 weeks, but not at 93 weeks. Also, they showed longer response latencies around 46 weeks of age in the 52 degrees C hot-plate test, which partial tail amputation failed to affect, although it did produce at least 2 weeks of chronic neuropathic hypersensitivity in ad libitum controls. Injection of collagen subcutaneously at 36-42 weeks led to chronic hyperalgesia in the DBA/1 but not the C57BL/6 strain, measured weekly by the barely nociceptive 50 degrees C hot-plate test to minimize damage. This collagen-induced arthritic hyperalgesia was then gradually and reversibly blocked during 9-15 weeks of caloric restriction starting at 53-58 weeks. In longitudinal trials on normal mice, performed every 2-4 weeks between 42 and 105 weeks with the 50 degrees C hot-plate, caloric restriction led to altered latencies (higher relative to controls) only in the last 10-20 weeks, perhaps because it delayed the onset of age-related peripheral neuropathies. In conclusion, long-term caloric restriction leads to significant hypoalgesia in pre-senescent mice subjected to above-threshold pain of widely different durations, the effect disappearing at later ages unless spontaneous neuropathies become influential. A reduction in cumulative food intake thus appears to generate antinociceptive signals in adult male mice, perhaps serving specifically to promote riskier behavior during prolonged food shortages.

Postoperative Gastrointestinal Tract Dysfunction

Postoperative gastrointestinal (GI) tract dysfunction (PGID) is common and is associated with increased patient suffering and cost of care. The pathogenesis of PGID is complex and multifactorial. Traditional measures intended to reduce the incidence of PGID, such as the use of prokinetic drugs, nasogastric tube drainage, and the avoidance of early fluid and/or food intake, are apparently not beneficial. The administration of larger volumes of IV fluids to achieve predetermined increases in cardiac output has been shown in randomized trials to improve gut perfusion and reduce the incidence of PGID. A multimodal approach that includes limited surgical incision, regional local anesthesia, early mobilization, and enteral feeding has been associated with a dramatic reduction in postoperative complications, PGID, and length of hospital stay. However, none of these approaches has been validated in adequately powered multicenter prospective randomized controlled trials.

Mechanosensitive duodenal afferents contribute to vagal modulation of inflammation in the rat

Noxious stimuli inhibit inflammation by activating neuroendocrine stress axes, an effect that is potently attenuated by ongoing activity in subdiaphragmatic vagal afferents. Because this vagal afferent activity is carried in the coeliac and coeliac accessory branches of the subdiaphragmatic vagus, we tested the hypothesis that the activity arises from vagal afferents that innervate a proximal segment of the gastrointestinal tract. Surgical removal of the duodenum, but not the stomach, produces a marked (six orders of magnitude) leftward shift in the dose-response curve for intraplantar capsaicin-induced inhibition of synovial plasma extravasation induced by the potent inflammatory mediator bradykinin, in the knee joint; this is similar in magnitude to the inhibition produced by subdiaphragmatic or by coeliac plus coeliac accessory branch vagotomy. Fasting, to unload mechanically sensitive polymodal afferents in the proximal gastrointestinal tract, produces a similar leftward shift in the dose-response curve for the inhibitory effect of capsaicin, an effect that is reversed by balloon distension in the duodenum in fasted rats, while balloon distension postvagotomy had no effect. These results suggest that activation of mechanically sensitive vagal afferents in the duodenum contributes vagal afferent activity that modulates neuroendocrine control of the inflammatory response.