α-Synuclein pathology accumulates in sacral spinal visceral sensory pathways.

Urinary urgency and frequency are common in α-synucleinopathies such as Parkinson disease, Lewy body dementia, and multiple system atrophy. These symptoms cannot be managed with dopamine therapy, and their underlying pathophysiology is unclear. We show that in individuals with Parkinson disease, Lewy body dementia, or multiple system atrophy, α-synuclein pathology accumulates in the lateral collateral pathway, a region of the sacral spinal dorsal horn important for the relay of pelvic visceral afferents. Deposition of α-synuclein in this region may contribute to impaired micturition and/or constipation in Parkinson disease and other α-synucleinopathies.

P2X7 receptor-dependent intestinal afferent hypersensitivity in a mouse model of postinfectious irritable bowel syndrome.

The ATP-gated P2X(7) receptor (P2X(7)R) was shown to be an important mediator of inflammation and inflammatory pain through its regulation of IL-1ß processing and release. Trichinella spiralis-infected mice develop a postinflammatory visceral hypersensitivity that is reminiscent of the clinical features associated with postinfectious irritable bowel syndrome. In this study, we used P2X(7)R knockout mice (P2X(7)R(-/-)) to investigate the role of P2X(7)R activation in the in vivo production of IL-1ß and the development of postinflammatory visceral hypersensitivity in the T. spiralis-infected mouse. During acute nematode infection, IL-1ß-containing cells and P2X(7)R expression were increased in the jejunum of wild-type (WT) mice. Peritoneal and serum IL-1ß levels were also increased, which was indicative of elevated IL-1ß release. However, in the P2X(7)R(-/-) animals, we found that infection had no effect upon intracellular, plasma, or peritoneal IL-1ß levels. Conversely, infection augmented peritoneal TNF-α levels in both WT and P2X(7)R(-/-) animals. Infection was also associated with a P2X(7)R-dependent increase in extracellular peritoneal lactate dehydrogenase, and it triggered immunological changes in both strains. Jejunal afferent fiber mechanosensitivity was assessed in uninfected and postinfected WT and P2X(7)R(-/-) animals. Postinfected WT animals developed an augmented afferent fiber response to mechanical stimuli; however, this did not develop in postinfected P2X(7)R(-/-) animals. Therefore, our results demonstrated that P2X(7)Rs play a pivotal role in intestinal inflammation and are a trigger for the development of visceral hypersensitivity.

CB1 receptors mediate the analgesic effects of cannabinoids on colorectal distension-induced visceral pain in rodents.

Activation of cannabinoid receptors (CB(1), CB(2) and GPR(55)) produces analgesic effects in several experimental pain models, including visceral pain arising from the gastrointestinal tract. We assessed the role of CB(1), CB(2), and GPR(55) receptors and the endogenous cannabinoid system on basal pain responses and acute mechanical hyperalgesia during colorectal distension (CRD) in rodents. The effects of cannabinoid receptor agonists and antagonists on pain-related responses to CRD were assessed in rats and in wild-type and CB(1) receptor knock-out mice. The dual CB(1/2) agonist, WIN55,212-2, and the peripherally acting CB(1)-selective agonist, SAB-378, inhibited pain-related responses to repetitive noxious CRD (80 mmHg) in a dose-related manner in rats. The analgesic effects of WIN55,212-2 and SAB-378 were blocked by the selective CB(1) antagonist SR141716, but were not affected by the selective CB(2) antagonist SR144528. SR141716, per se, increased the responses to repetitive noxious CRD, indicative of hyperalgesia, and induced pain-related responses during non-noxious CRD (20 mmHg), indicative of allodynia. The cannabinoid receptor agonists anandamide, virodhamine and O-1602 had no effect. At analgesic doses, WIN55,212-2 did not affect colonic compliance. In accordance to the rat data, WIN55,212-2 produced analgesia, whereas SR141716 induced hyperalgesia, during noxious CRD (55 mmHg) in wild-type but not in CB(1)-knock-out mice. These data indicate that peripheral CB(1) receptors mediate the analgesic effects of cannabinoids on visceral pain from the gastrointestinal tract. The allodynic and hyperalgesic responses induced by SR141716 suggest the existence of an endogenous cannabinoid tone and the activation of CB(1) receptors during noxious CRD.

Post-inflammatory modification of colonic afferent mechanosensitivity.

1. The present review discusses interactions between the immune and nervous systems in post-infectious irritable bowel syndrome (PI-IBS). 2. Visceral pain is the single symptom that most affects the quality of life of patients with irritable bowel syndrome (IBS), yet it is the least successfully managed. An underlying hypersensitivity of colonic afferents to mechanical stimuli has long been implicated in visceral pain in IBS, but little more is known of the physiological aetiology. 3. The PI-IBS patients are a cohort of IBS patients who attribute their symptoms to a preceding gastrointestinal infection by pathogens such as Campylobacter or Salmonella. Current evidence suggests that the immune system remains activated in these patients and contributes to their visceral hypersensitivity. This is characterized by a shift in the phenotype of circulating immune cells towards a Type 1 (Th1 predominating) state. Products from these immune cells sensitize colonic afferents to mechanical stimuli. 4. Rectal instillation of trinitrobenzene sulphonic acid induces a Th1-mediated inflammatory response, consistent with clinical observations in PI-IBS. The visceral hypersensitivity observed in this model is biphasic, with an initial onset characterized by visceral hypersensitivity correlating with histological damage followed by a delayed phase that occurs after histological recovery. Interestingly, this chronic visceral hypersensitivity is mediated by afferents in closest apposition to blood vessels, but furthest from the initial site of damage. 5. Both clinical and experimental evidence indicates that chronic dysregulation of the immune system induces visceral afferent hypersensitivity and, therefore, may be the central mechanism underlying PI-IBS.

Taste perception abnormalities after acute stroke in postmenopausal women.

The study aims to elucidate the characteristics of post-stroke taste dysfunction in postmenopausal women. Taste function in 120 consecutive postmenopausal women with acute (<7 days) stroke was compared with that of age-matched control subjects (n=109). The agents used were: sodium chloride for saltiness, sucrose for sweetness, glacial acetic acid for sourness and quinine hemisulfate for bitterness. Detection and recognition thresholds were performed by the three-stimulus drop technique. Taste threshold values beyond two standard deviations of normal were considered "abnormal". For postmenopausal women after acute stroke, abnormal detection thresholds for the ability to taste sweetness, saltiness, sourness and bitterness were found in 33%, 21%, 35% and 30% of women, respectively, and abnormal recognition thresholds were found in 40%, 34%, 42% and 33% of women respectively. The taste dysfunction occurred ipsilaterally, contralaterally or bilaterally, and was not related to the side or location of the lesion. Large (>2 cm) lesions were more frequently associated with sweet and salty taste dysfunction than small lesions (p<0.05). Follow-up examination in 23 patients at 24 to 31 months (mean 27 months) after the initial evaluation showed that the taste abnormality persisted in 8 (35%) patients. Taste perception abnormalities are common and often persistent in stroke patients. The dysfunction can occur ipsilaterally, contralaterally or bilaterally.

Acute colonic ischaemia in rats results in long-term structural changes without alterations of colonic sensitivity.

Colonic ischaemia and mast cells have been involved in the pathophysiology of the functional gastrointestinal disorder irritable bowel syndrome, although the cause-effect relationships remain unknown. We assessed long-term histopathological and functional changes associated to an acute ischaemic episode (1 h) of the colon, followed by 8-week recovery, in rats. Functional colonic alterations [sensitivity during colorectal distension (CRD), compliance and propulsive motility] were assessed regularly during the recovery. Colonic histopathology (presence of inflammation, morphometric alterations and variations in neuronal density in the enteric nervous system) 8-week postischaemia was assessed. Following ischaemia, none of the functional parameters tested (motility, sensitivity and compliance) were affected. At necropsy, the colon presented an overall normal appearance with an increase in weight of the ischaemic area (mg/cm: 99 +/- 6; P < 0.05 vs. control: 81 +/- 4 or sham ischaemia: 81 +/- 3). Histopathological evaluations revealed the presence of a local infiltrate of mast cells in the area of ischaemia (nb of mast cells: 142 +/- 50; P < 0.05 vs. control, 31 +/- 14 or sham ischaemia: 40 +/- 16), without other significant alterations. Animals subjected to colonic ischaemia and treated 8 weeks later with the mast cell degranulator, compound 48/80, showed no changes in CRD-related pain responses. These studies show that acute colonic ischaemia is associated with the presence of a long-term local infiltration of mast cells, located within the serosa and muscle layers, despite the absence of functional changes, including colonic sensitivity. Considering the important pathophysiological functions of mast cells, the observed mast cell infiltration may be involved in ischaemia-induced functional changes yet to be characterized.

Sensory Function and Chronic Pain in Multiple Sclerosis.

Objective: To examine whether hypoesthesia and chronic pain are related in patients with MS. Methods: Sixty-seven MS patients with pain and 80 persons without MS were included. Sensory functioning was tested by bedside neurological examination. Touch, joint position (dorsal column-medial lemniscus pathway), temperature sense, and pain (spinothalamic tract) were tested. Pain intensity was measured by the Colored Analogue Scale (CAS Intensity) and the Faces Pain Scale (FPS); pain affect was also measured by CAS Affect and Number of Words Chosen-Affective (NWC-A). Mood was assessed with the SCL-90 anxiety and depression subscales and the Beck Depression Inventory (BDI). Results: A significant negative relationship was found between pain intensity and the function of the dorsal column-medial lemniscal pathway, but not with the spinothalamic tract. Conclusion: In addition to the already known relation between hyperesthesia and pain, hypoesthesia for touch and joint position also seems to be related to chronic pain in MS patients.

Long-term regeneration of abdominal vagus: efferents fail while afferents succeed.

Vagal afferents regenerate, by 18 weeks after subdiaphragmatic transection, to reinnervate the gut and to differentiate into the two types of terminals normally found in the smooth muscle wall of the gastrointestinal (GI) tract (Phillips et al. [2000] J Comp Neurol. 421:325-346). Regeneration, however, is neither complete nor entirely accurate by 18 weeks. Moreover, the capacity of the vagal efferents to reinnervate the GI tract under comparable conditions has not been evaluated. Therefore, to determine whether a more extended postaxotomy survival interval would (1). result in more extensive reinnervation of smooth muscle, (2). facilitate correction of the inaccuracies of the regenerated axons and terminals, and (3). yield motor as well as sensory reinnervation of GI targets, Sprague-Dawley rats received either complete subdiaphragmatic vagotomies (n = 18) or sham surgeries (n = 12). Physiological endpoints that might normalize as vagal elements regenerated, including body weight, daily food intake, size of first daily meal, and metabolic efficiency, were monitored. At 45 weeks after the vagotomies, the animals were randomly assigned to afferent (wheat germ agglutinin-horseradish peroxidase) or efferent (cholera toxin subunit B-horseradish peroxidase) mapping conditions, and labeled axons and terminals in the stomach and first 8 cm of the small intestine were inventoried in whole-mounts. Afferent regeneration was more extensive at 45 weeks than previously observed at 18 weeks after surgery; however, the amount of GI innervation was still not comparable to the intact pattern of the sham rats. Furthermore, abnormal patterns of sensory organization occurred throughout the reinnervated field, with small bundles of axons forming complex tangles and some individual axons terminating in ectopic locations. The presence of growth cone profiles suggested that vagal reorganization was ongoing even 45 weeks after surgery. In contrast to this relatively extensive, albeit incomplete, sensory reinnervation of the gut, motor fibers had failed to reinnervate the GI tract. Thus, dramatic differences exist in the regenerative capacities of the sensory and motor arms of the vagus under the same surgical and maintenance conditions. Furthermore, the functional measures of disordered energy regulation did not normalize over the 45 weeks during which afferent but not efferent innervation was restored.

Deficits in visceral pain and hyperalgesia of mice with a disruption of the tachykinin NK1 receptor gene.

Studies in mice lacking genes encoding for substance P or its receptor (NK1), or with NK1 antagonists, have shown that this system contributes to nociception, but the data are complex. Here, we have further examined the role of NK1 receptors in pain and hyperalgesia by comparing nociceptive responses to mechanical and chemical stimulation of viscera and the resulting hyperalgesia and inflammation in NK1 knockout (-/-) and wild-type (+/+) mice. We concentrated on visceral nociception because substance P is expressed by a much greater proportion of visceral than cutaneous afferents. NK1 -/- mice showed normal responses to visceral mechanical stimuli, measured as behavioural responses to intraperitoneal acetylcholine or hypertonic saline or reflex responses to colon distension in anaesthetized mice, although -/- mice failed to encode the intensity of noxious colon distensions. In contrast, NK1 -/- mice showed profound deficits in spontaneous behavioural reactions to an acute visceral chemical stimulus (intracolonic capsaicin) and failed to develop referred hyperalgesia or tissue oedema. However, in an identical procedure, intracolonic mustard oil evoked normal spontaneous behaviour, referred hyperalgesia and oedema in -/- mice. The inflammatory effects of capsaicin were abolished by denervation of the extrinsic innervation of the colon in rats, whereas those of mustard oil were unchanged, showing that intracolonic capsaicin evokes neurogenic inflammation, but mustard oil does not. Tests of other neurogenic inflammatory stimuli in NK1 -/- mice revealed impaired behavioural responses to cyclophosphamide cystitis and no acute reflex responses or primary hyperalgesia to intracolonic acetic acid. We conclude that NK1 receptors have an essential role mediating central nociceptive and peripheral inflammatory responses to noxious stimuli that evoke neurogenic inflammation, and modulating responses to noxious mechanical stimuli. We propose that two separate hyperalgesia pathways exist, one of which is NK1 receptor dependent, whereas the other does not require intact substance P/NK1 signalling.

The role of vagal visceral afferents in the control of nociception.

We have shown that activity in subdiaphragmatic vagal afferents modulates mechanical hyperalgesic behavior in the rat. Subdiaphragmatic vagotomy decreases paw-withdrawal threshold to mechanical stimulation (baseline and after intradermal injection of bradykinin), thus enhancing mechanical hyperalgesic behavior. Most of this decrease is generated by an endocrine signal released by the adrenal medullae because denervation or removal of the adrenal medullae prevents or reverses these changes. This novel mechanism may imply that: (a) the brain is able to regulate sensitivity of nociceptors all over the body by a neuroendocrine mechanisms, (b) sensitivity of nociceptors can be influenced by changes in parts of the body which are remote from the location of the sensitized nociceptors and (c) circulating catecholamines can influence nociceptors in a way which is different from those reported so far (see Jänig and McLachlan, 1994; Jänig, 1996a; Jänig et al., 1996).

Telemetric blood pressure monitoring in conscious rats before and after compression injury of spinal cord.

Abnormal cardiovascular control after spinal cord injury (SCI) results in hypotension soon after injury. Later, paroxysmal hypertension and bradycardia in response to sensory stimulation below the level of injury develop in most people with SCI. In this study, we used a radiotelemetry system, in rats (n = 7), to investigate the effect of a clinically relevant compression model of SCI at T5 spinal segment on mean arterial pressure (MAP) and heart rate (HR) at rest and in response to colorectal distension. The transducers were implanted 1 month before clip compression (50-g) injury and continuous recording of MAP and HR was established for a period of 2.5 months. SCI was associated with hypotension (86+/-3 mm Hg) at 1 day after injury. In the following 2 days, MAP gradually returned to preinjury levels. By contrast, HR increased at 1 day after SCI and remained unchanged thereafter. Three days after SCI, colorectal distension caused an increase in MAP of 8+/-2 mm Hg accompanied by bradycardia (-18 bpm). One week after SCI, colorectal distension induced an increase in MAP of 9+/-2 mm Hg and bradycardia (-41 bpm). In the following days, the magnitude of reflex hypertension gradually increased, reaching 21+/-4 mm Hg at 1.5 months after SCI. In summary, our data show that resting MAP rapidly returns to control values after SCI. Episodic hypertension associated with autonomic dysreflexia can develop in rats within 1 month after incomplete SCI.

Absence of protective role of afferent nerves in early intestinal mucosal alterations induced by abdominal irradiation in rats.

PURPOSE: To assess the early effects of primary afferent nerve suppression by systemic treatment with the neurotoxin capsaicin in an acute model of abdominal irradiation in rats (10Gy, gamma). MATERIALS AND METHODS: Changes in myeloperoxidase (MPO) activity, calcitonin gene-related peptide (CGRP) tissue content, number of mast cells and apoptotic cells were determined in jejunum and ileum in four groups of rat male Wistar (vehicle sham-irradiated, vehicle irradiated, capsaicin sham-irradiated and capsaicin irradiated) at 1 and 3 days post-irradiation. RESULTS: In vehicle irradiated rats, CGRP was significantly increased from the first day after irradiation in jejunal mucosa; MPO activity increased in both segments at day 3 but not at day 1 after irradiation; the number of detectable mucosal mast cells dropped to nearly zero on days 1 and 3, while the apoptotic cells in the intestinal mucosa were significantly increased at day 1. Similar results were obtained for mast cells and apoptosis in capsaicin irradiated rats as compared to capsaicin sham-irradiated rats, while MPO activity was significantly increased and CGRP concentration in jejunal mucosa significantly decreased from the first day in these rats in comparison with capsaicin sham-irradiated rats. CONCLUSIONS: Intestinal sensory innervation seems not to have a major protective role against a radiation-induced intestinal inflammatory reaction.

Selective vagal afferent dysfunction in dogs with congenital idiopathic megaoesophagus.

Congenital idiopathic megaoesophagus (CIM) is a rare, naturally occurring disorder of the dog that is characterised by deficient motility and dilatation of the oesophagus. Recent studies indicate that the vagal sensory system mediating reflexes induced by oesophageal distension is defective in, and may underlie the pathomechanism of this disorder. We sought to establish whether other distension sensitive vagal afferent systems were impaired in CIM, or whether the vagal afferent dysfunction was selective. Thus, we examined the Hering-Breuer lung inflation reflex (HBR), which is subserved by a contiguous and physiologically similar vagal afferent system, in five dogs with CIM in which oesophageal vagal afferent dysfunction had been demonstrated. At varying levels of lung inflation, we found the HBR to be normally graded and of normal strength in affected dogs and that this result was unlikely to be influenced by other factors known to alter the strength of the reflex. These observations provide evidence for an organ specific, selective vagal afferent dysfunction in dogs with CIM. It is possible that similar processes may be active in disorders of visceral organ systems subserved by vagal afferents in other species, including man.

Degeneration of sensory afferent nerves enhances pulmonary inflammatory alterations in acute myocardial infarction in rats.

BACKGROUND: Evidence suggests proinflammatory changes in the lungs during acute myocardial infarction and a participation of neural mechanisms and substance P in the pathology. This study was undertaken to investigate the role and the mechanisms by which sensory afferent degeneration at neonatal stages exacerbates the pulmonary inflammatory responses to acute myocardial infarction in the adult rats. METHODS: The degeneration of capsaicin-sensitive afferent nerves was induced by administration of capsaicin to neonatal rats. The pulmonary inflammatory changes following coronary artery occlusion (CAO) were assessed by the analysis of the infiltration of neutrophils and tissue morphology in the lungs. RESULTS: Significant increases in the pulmonary infiltration of neutrophils, up to 240% and 218% of the sham controls at 3 and 6 h, respectively, after CAO (P<.05) and marked pulmonary edema were observed. Degeneration of capsaicin-sensitive afferent nerves or antagonism of endogenous neurokinin (NK)-1 receptor exacerbated the pulmonary infiltration of neutrophils (up to 214% and 254% of the controls, respectively) and pulmonary tissue edema following the CAO. CONCLUSION: The findings indicate that degeneration of sensory afferent nerves enhances the pulmonary inflammatory changes in acute myocardial infarction, in which the endogenous NK may play a role.

Function and expression pattern of TRPM8 in bladder afferent neurons associated with bladder outlet obstruction in rats.

We investigated the function and expression pattern of the transient receptor potential melastatin-8 (TRPM8) in urinary bladder afferent neurons from control and bladder outlet obstruction (BOO) rats. BOO was produced and, after six weeks, the effects of intravesical infusion of menthol, the agonist of TRPM8, were investigated using unanesthetized cystometry. The intravesical infusion of menthol produced an increase in the micturition pressure in both sham surgery and BOO rats. In BOO rats, increased basal and threshold pressure and a decreased micturition interval were observed. Next, the population of TRPM8-positive and the co-expression proportion of TRPM8 with neurochemical markers (NF200 or TRPV1) in the bladder afferent neurons were each compared between the control and BOO rats using retrograde tracing and immunohistochemistry. The population of TRPM8-immunoreactive bladder afferent neurons was larger in BOO rats (3.28±0.43%) than in the control rats (1.33±0.18%). However, there were no statistical differences between the control and BOO rats in the co-expression proportion of neither TRPM8-NF200 (84.1±4.3% vs 79.7±2.7%, p=0.41) nor TRPM8-TRPV1 (33.3±3.6% vs 40.8±2.6%, p=0.08) in the bladder afferent neurons. The present results suggest that the neuronal input through TRPM8-positive bladder afferent neurons are augmented after BOO, however, the neurochemical phenotype of the up-regulated TRPM8-positive bladder afferent neurons is not changed after BOO.

Postinflammatory visceral sensitivity and pain mechanisms.

The inflammatory reaction is normally tightly regulated, and as soon as the original insult has been cleared, a resolution phase starts that aims at leading the tissues back to a normal physiological state. However, after intestinal inflammation, a number of patients develop postinflammatory hypersensitivity symptoms, which can be defined as an excessive sensitivity to gut nociceptive stimulation. The pain experienced by those patients has been largely studied in the context of postinfectious intestinal diseases. The mechanisms of postinflammatory persistent visceral pain involve peripheral and central neuroplastic changes, low-grade chronic inflammation that sensitizes visceral afferent pathways and sensitization of non-neuronal resident cells of the gut. Several molecular determinants such as neurokinins, serotonin, proteases and voltage-gated ion channels seem to play a significant role in the control of postinflammatory visceral sensation. This review tries to give insights into the mechanisms of persistent visceral pain following the resolution of intestinal inflammation and tries to identify what needs to be done to further advance the field of postinflammatory hypersensitivity clinical management.

Intractable hiccup and nausea with periaqueductal lesions in neuromyelitis optica.

Intractable hiccup and nausea (IHN) was found in eight of 47 cases of relapsing neuromyelitis optica (NMO) (17%) but in none of 130 cases of multiple sclerosis (MS). IHN resolved with methylprednisolone. In six cases, MRI detected linear medullary lesions involving the pericanal region, the area postrema, and the nucleus tractus solitarius. Like long and centrally located myelitis, a linear medullary lesion causing IHN may distinguish NMO from MS.

Changes in pituitary adenylate cyclase activating polypeptide expression in urinary bladder pathways after spinal cord injury.

These studies examined changes in the pituitary adenylate cyclase activating polypeptide (PACAP) expression in micturition reflex pathways after spinal cord injury (SCI) of various durations. In spinal-intact animals, PACAP immunoreactivity (IR) was expressed in fibers in the superficial dorsal horn in all segmental levels examined (L1, L2, L4-S1). Bladder-afferent cells (35-45%) in the dorsal root ganglia (DRG; L1, L2, L6, S1) from spinal-intact animals also exhibited PACAP-IR. After SCI (6 weeks), PACAP-IR was dramatically increased in spinal segments and DRG (L1, L2, L6, S1) involved in micturition reflexes. The density of PACAP-IR was increased in the superficial laminae (I-II) of the L1, L2, L6, and S1 spinal segments. No changes in PACAP-IR were observed in the L4-L5 segments. Staining was also dramatically increased in a fiber bundle extending ventrally from Lissauer's tract (LT) in lamina I along the lateral edge of the dorsal horn to the sacral parasympathetic nucleus (SPN) in the L6-S1 spinal segments (lateral collateral pathway of Lissauer, LCP). After SCI (range 48 h to 6 weeks), PACAP-IR in cells in the L1, L2, L6, and S1 DRG significantly (P < or = 0.001) increased and the percentage of bladder-afferent cells expressing PACAP-IR also significantly (P < or = 0.001) increased (70-92%). No changes were observed in the L4-L5 DRG. PACAP-IR was reduced throughout the urothelium and detrusor smooth muscle whole mounts after SCI. These studies demonstrate changes in PACAP expression in micturition reflex pathways after SCI that may contribute to urinary bladder dysfunction or reemergence of primitive voiding reflexes after SCI.

Visceral nociception.

Visceral pain is of great concern to the medical community because it remains particularly resistant to current clinical treatments. A serendipitous and initially unexplainable clinical finding that a punctate midline dorsal column lesion is effective in eliminating visceral pain, however, has initiated a resurgence of interest in the study of the basic mechanisms of visceral nociception. Clinical and anatomic findings have determined that visceral pain either of thoracic or pelvic origin can be relieved by carefully placed lesions directed at the lateral edge or the medial edge of the gracile fasciculus, respectively. Studies are demonstrating that visceral pain is quite unique from cutaneous pain.

Visceral pain.

Visceral pain, although different from somatic pain in several important features, is not as widely researched and consequently our knowledge of neurophysiologic mechanisms as well as clinical management of visceral pain states remains unsatisfactory. Several recent studies have employed different visceral pain animal models to provide insight into the peripheral and central nervous system mechanisms underlying pain originating from the urinary bladder, ureter, and gastrointestinal tract. The effects of opioid and nonopioid drugs in these models have also been evaluated and are reviewed in this article. The importance of anatomic pathways relaying pain sensation in the central nervous system, particularly the newly described dorsal column pathway, is also discussed. In human subjects, new techniques like positron emission tomography are now being used to better understand visceral pain perception. Such findings deriving from basic animal research and human studies summarized in the present overview lead to a better understanding of visceral pain states and may be helpful in developing better treatment strategies to combat visceral pain states in the clinical setting.