Sensitive Afferents Research Articles

Bladder hypersensitivity and transcriptional regulation of potassium channel subunit mRNA expression in mice with cystitis

Hyperexcitability in bladder primary afferents contributes to bladder overactivity and pain in pathological urological conditions. Target-derived growth factors can alter primary afferent expression of membrane-bound ion channels that regulate neuronal excitability, such as voltage-gated potassium (Kv) channels. Several Kv channels are expressed in primary afferent neurons and contain a binding site for repressor element-1-silencing transcription factor (REST). Growth factor-mediated, REST-induced, long-lasting downregulation of Kv channels may provide a mechanism through which persistent changes in bladder afferent sensitivity can occur.

Roles of TRPA1 in Pain Pathophysiology and Implications for the Development of a New Class of Analgesic Drugs

The Transient Receptor Potential A1 (TRPA1) ion channel has evolved in animals to respond to signals from a variety of sensory stimuli. Many structural determinants of its multimodal activation have been identified to date. TRPA1 activities include responses to exogenous chemical irritants, responses to endogenous inflammatory mediators, zinc, voltage, temperature or stretch and subtle yet critical modulation by calcium ions. TRPA1 has emerged as an important target for several types of pain and inflammatory conditions because of its limited expression profile and its demonstrated roles in mediating different types of pain and sensitization of peripheral sensory afferents. Despite observed species differences in channel pharmacology, recent genetic evidence in human brings some hope that preclinical efficacy in disease models will translate to patient condition. During the past decade, various groups have investigated the development of a new class of analgesic drugs or anti-tussive agents aimed at blocking TRPA1 activity in primary sensory afferents. Several companies are advancing toward clinical proof of concept studies. This review aims to summarize key advances in the understanding of TRPA1 with regard to its roles and implications for patient conditions.

Capsaicin-sensitive vagal afferent neurons contribute to the detection of pathogenic bacterial colonization in the gut

Vagal activation can reduce inflammation and disease activity in various animal models of intestinal inflammation via the cholinergic anti-inflammatory pathway. In the current model of this pathway, activation of descending vagal efferents is dependent on a signal initiated by stimulation of vagal afferents. However, little is known about how vagal afferents are activated, especially in the context of subclinical or clinical pathogenic bacterial infection. To address this question, we first determined if selective lesions of capsaicin-sensitive vagal afferents altered c-Fos expression in the nucleus of the solitary tract (nTS) after mice were inoculated with either Campylobacter jejuni or Salmonella typhimurium. Our results demonstrate that the activation of nTS neurons by intraluminal pathogenic bacteria is dependent on intact, capsaicin sensitive vagal afferents. We next determined if inflammatory mediators could cause the observed increase in c-Fos expression in the nTS by a direct action on vagal afferents. This was tested by the use of single-cell calcium measurements in cultured vagal afferent neurons. We found that tumor necrosis factor alpha (TNFα) and lipopolysaccharide (LPS) directly activate cultured vagal afferent neurons and that almost all TNFα and LPS responsive neurons were sensitive to capsaicin. We conclude that activation of the afferent arm of the parasympathetic neuroimmune reflex by pathogenic bacteria in the gut is dependent on capsaicin sensitive vagal afferent neurons and that the release of inflammatory mediators into intestinal tissue can be directly sensed by these neurons.

Hydrogen Sulfide Mediated Inhibitory Neurotransmission to the Pig Bladder Neck: Role of KATP Channels, Sensory Nerves and Calcium Signaling

Because neuronal released endogenous H2S has a key role in relaxation of the bladder outflow region, we investigated the mechanisms involved in H2S dependent inhibitory neurotransmission to the pig bladder neck. Bladder neck strips were mounted in myographs for isometric force recording and simultaneous measurement of intracellular Ca(2+) and tension. On phenylephrine contracted preparations electrical field stimulation and the H2S donor GYY4137 evoked frequency and concentration dependent relaxation, which was reduced by desensitizing capsaicin sensitive primary afferents with capsaicin, and the blockade of adenosine 5'-triphosphate dependent K(+) channels, cyclooxygenase and cyclooxygenase-1 with glibenclamide, indomethacin and SC560, respectively. Inhibition of vanilloid, transient receptor potential A1, transient receptor potential vanilloid 1, vasoactive intestinal peptide/pituitary adenylyl cyclase-activating polypeptide and calcitonin gene-related peptide receptors with capsazepine, HC030031, AMG9810, PACAP6-38 and CGRP8-37, respectively, also decreased electrical field stimulation and GYY4137 responses. H2S relaxation was not changed by guanylyl cyclase, protein kinase A, or Ca(2+) activated or voltage gated K(+) channel inhibitors. GYY4137 inhibited the contractions induced by phenylephrine and by K(+) enriched (80 mM) physiological saline solution. To a lesser extent it decreased the phenylephrine and K(+) induced increases in intracellular Ca(2+). H2S produces pig bladder neck relaxation via activation of adenosine 5'-triphosphate dependent K(+) channel and by smooth muscle intracellular Ca(2+) desensitization dependent mechanisms. H2S also promotes the release of sensory neuropeptides and cyclooxygenase-1 pathway derived prostanoids from capsaicin sensitive primary afferents via transient receptor potential A1, transient receptor potential vanilloid 1 and/or related ion channel activation.

Mast cells and the cyclooxygenase pathway mediate colonic afferent nerve sensitization in a murine colitis model

Intestinal inflammation alters colonic afferent nerve sensitivity which may contribute to patients' perception of abdominal discomfort. We aimed to explore whether mast cells and the cyclooxygenase pathway are involved in altered afferent nerve sensitivity during colitis. C57Bl6 mice received 3% dextran-sulfate sodium (DSS) in drinking water for 7 days to induce colitis. Control animals received regular water. On day 8 inflammation was assessed in the proximal colon by morphology and histology. Extracellular afferent nerve discharge was recorded from the mesenteric nerve of a 2 cm colonic segment. Subgroups were treated in vitro with the mast cell stabilizer doxantrazole (10⁻⁴M) or the cyclooxygenase inhibitor naproxen (10⁻⁵M). DSS colitis resulted in morphological and histological signs of inflammation. At baseline, peak firing was 11±2 imp s⁻¹ in colitis segments and 5±1 imp s⁻¹ in uninflamed control segments (p<0.05; mean ± SEM; each n=6). In colitis segments, afferent nerve discharge to bradykinin (0.5 μM) was increased to 47±7 compared to 23±6 imp s⁻¹ in recordings from non-inflamed control tissue (p<0.05). Mechanosensitivity during luminal ramp distension (0-80 cm H₂O) was increased reaching 24±5 imp s⁻¹ at 80 cm H₂O during colitis compared to 14±2 in non-inflamed controls (p<0.05). Doxantrazole or naproxen reduced afferent discharge to bradykinin and luminal ramp distension in colitis segments to control levels. Intestinal inflammation sensitizes mesenteric afferent nerve fibers to bradykinin and mechanical stimuli. The underlying mechanism responsible for this sensitization seems to involve mast cells and prostaglandins.

Activation of p38 mitogen-activated protein kinase in the dorsal root ganglion contributes to pain hypersensitivity after plantar incision

BackgroundThe phosphorylation of p38 mitogen-activated protein kinase (MAPK) in the dorsal root ganglion (DRG) promotes primary afferent sensitization. The role of p38MAPK signaling in the DRG in the pathogenesis of plantar incision hyperalgesia has not been investigated. ResultsLevels of phosphorylated p38MAPK (p-p38MAPK) obviously increased in the DRG after plantar incision. Unmyelinated and myelinated DRG neurons that express p-p38MAPK contained small to medium cell bodies, suggesting that p-p38MAPK expression is induced in neurons with C- and Aδ-fibers. The p-p38MAPK inhibitors FR167653 or SB203580 inhibited incision-induced mechanical hypersensitivity and spontaneous pain behavior. The systemic administration of tumor necrosis factor-α (TNF-α) inhibitor prevented subsequent incision-induced activation of p38MAPK in the DRG and alleviated mechanical hypersensitivity after the incision. Conclusionsp38MAPK signaling in the DRG plays a crucial role in the development of primary afferent sensitization and pain behavior caused by plantar incision.

VEMPの基礎研究の可能性

In humans, intense air- and bone-conducted sound has been reported to evoke cervical vestibular evoked myogenic potentials (cVEMP) on the sternocleidomastoid muscle. In addition, these stimuli can evoke ocular vestibular evoked myogenic potentials (oVEMP) on the extraocular muscles. In this study, basic studies into the cVEMP and oVEMP were reviewed. First, the sensitivity of primary vestibular afferents in the internal auditory meatus was investigated. These studies suggested that irregular primary otoliths afferent from both utricular and saccular maculae might respond to both air- and bone-conducted sound. Second, the differences between utricle and saccule-activated neural circuitry in both vestibulo-ocular reflex (VOR) and vestibulocollic reflex (VCR) systems were evaluated. These studies described that utricular afferents have a strong projection to the VOR system, whereas the saccular afferents have a strong projection to the VCR system. Third, identifying the appropriate animal models for both cVEMP and oVEMP was also important to resolve the questions about the neural pathways underlying these responses.

Acid Sensitization of Esophageal Mucosal Afferents

Sensitization of esophageal chemoreceptors, either directly by intermittent acid exposure or indirectly through esophagitis-associated inflammatory mediators, is likely to be the mechanism underlying the perception of heartburn. To compare basal esophageal sensitivity with electrical stimulation and acid, and to compare the degree of acid-induced sensitization in controls and in patient groups across the entire spectrum of gastroesophageal reflux disease: erosive oesophagitis (EO), nonerosive reflux disease (NERD), and functional heartburn (FH). Esophageal sensory and pain thresholds to electrical stimulation were measured before, 30, and 60 minutes after an intraesophageal infusion of saline or HCl. Patients received a 30-minute infusion of 0.15 M HCl and controls were randomized to receive either HCl (n = 11) or saline (n = 10). After electrical sensory threshold testing, participants received another 30-minute infusion of HCl to determine whether sensitivity to acid is increased by prior acid exposure All patient groups had higher basal sensory thresholds than healthy controls (controls, 13 ± 1.4 mA; FH, 20 ± 5.1 mA; NERD, 21 ± 5.1 mA; EO, 23 ± 5.4 mA; P < 0.05). Acute esophageal acid exposure reduced sensory thresholds to electrical stimulation in FH and NERD patients (P < 0.05). The level of acid sensitivity during the first HCl infusion was comparable between all patient groups and controls. The secondary infusion caused increased discomfort in all participants (P < 0.01). This acid-induced sensitization to HCl was significantly elevated in the patient groups ( P < 0.05). (1) Esophageal acid infusion sensitizes it to subsequent electrical and chemical stimulation. (2) The acid-related sensitization is greater in gastroesophageal reflux disease than in controls and may influence in part symptom perception in this population. (3) Acid-related sensitization within the gastroesophageal reflux disease population is not dependant on mucosal inflammation.

Air-Conducted oVEMPs Provide the Best Separation Between Intact and Superior Canal Dehiscent Labyrinths

First, to define the best single-step suprathreshold screening test for superior canal dehiscence syndrome (SCDS); second, to obtain further insight into the relative sensitivity of vestibular afferents to sound vibration in the presence of a superior canal dehiscence. Prospective study. Tertiary referral center. Eleven patients with surgically confirmed SCDS (mean, 50 yr; range, 32-66 yr) and 11 age-matched, healthy subjects (right ear only) with no hearing or vestibular deficits (mean, 50 yr; range, 33-66 yr). All subjects completed ocular and cervical vestibular evoked myogenic potential (o- and cVEMP) testing in response to air conduction (click and 500 Hz tone burst) and midline bone conduction (reflex hammer and Mini-shaker) stimulation. OVEMP n10 amplitude and cVEMP corrected peak-to-peak amplitude. OVEMP n10 amplitudes were significantly higher in SCDS when compared with healthy controls in response to all stimuli with the exception of reflex hammer. Likewise, cVEMP-corrected peak-to-peak amplitudes were significantly higher in SCDS when compared with healthy controls for air conduction stimulation (click and 500 Hz toneburst). However, there were no significant differences between groups for midline taps (reflex hammer or mini-shaker). Receiver operating characteristic curves demonstrated that oVEMPs in response to air conduction stimulation provided the best separation between SCDS and healthy controls. OVEMPs in response to air conduction stimulation (click and 500 Hz toneburst) provide the best separation between SCDS and healthy controls and are therefore the best single-step screening test for SCDS.

Interactions between adenosine, angiotensin II and nitric oxide on the afferent arteriole influence sensitivity of the tubuloglomerular feedback

Adenosine, via activation of A1 receptors on the afferent arteriole (AA), mediates the tubuloglomerular feedback (TGF) mechanism. Angiotensin II and nitric oxide (NO) can modulate the sensitivity of the TGF mechanism. However, the interaction among these substances in regulating the TGF resetting phenomenon has been debated. Studies in isolated perfused AA have shown a biphasic response to accumulating doses of adenosine alone. In the nanomolar range adenosine has a weak contractile effect (7%), whereas vasodilatation is observed at high concentrations. However, a synergistic interaction between the contractile response by adenosine and that of angiotensin II has been demonstrated. Adenosine in low concentrations strongly enhances the response to angiotensin II. At the same time, angiotensin II in physiological concentrations increases significantly the contractile response to adenosine. Moreover, addition of a NO donor (spermine NONOate) to increase NO bioavailability abolished the contractile response from combined application of angiotensin II and adenosine. These mutual modulating effects of adenosine and angiotensin II, and the effect of NO on the response of AA can contribute to the resetting of the TGF sensitivity.

Spinal Cord FAAH in Normal Micturition Control and Bladder Overactivity in Awake Rats

We assessed whether spinal inhibition of the cannabinoid degrading enzyme FAAH would have urodynamic effects in normal rats and rats with bladder overactivity induced by partial urethral obstruction or prostaglandin E2. We also determined the expression of FAAH, and the cannabinoid receptors CB1 and CB2 in the sacral spinal cord. We used 44 rats for functional (cystometry) and Western blot experiments. The FAAH inhibitor oleoyl ethyl amide (3 to 300 nmol) was administered intrathecally (subarachnoidally) or intravenously. The expression of FAAH and CB1/CB2 receptors was determined by Western blot. Oleoyl ethyl amide given intrathecally affected micturition in normal rats and rats with bladder overactivity but effects were more pronounced in the latter. In normal rats oleoyl ethyl amide only decreased micturition frequency, while it decreased frequency and bladder pressures in rats with bladder overactivity. Intravenous oleoyl ethyl amide (3 to 300 nmol) had no urodynamic effect. FAAH and CB1/CB2 receptors were expressed in the rat sacral spinal cord. The expression of CB1/CB2 receptors but not FAAH was higher in obstructed than in normal rats. FAAH inhibition in the sacral spinal cord by oleoyl ethyl amide resulted in urodynamic effects in normal rats and rats with bladder overactivity. The spinal endocannabinoid system may be involved in normal micturition control and it appears altered when there is bladder overactivity.

The endogenous cytokine profile and nerve fibre density in mouse ear Leishmania major-induced lesions related to nociceptive thresholds

Several reports have shown that cutaneous leishmaniasis lesions are painless, suggesting that Leishmania infection interferes with pain perception. Comparisons of inflammation-induced hyperalgesia between BALB/c and C57BL/6 mice have been little explored in the literature, and comparative data regarding nociception in leishmaniasis are non-existent. In susceptible BALB/c mice and resistant C57BL/6 mice that were intradermally inoculated with a low dose of Leishmania major in the ear, we investigated the variation in nociception over a 12-wk period post-infection and this variation's association with the structure of nerve fibres and the presence of endogenous cytokines that are classically considered hyper- or hypo-nociceptive. Infected BALB/c mice presented susceptibility and severe lesions. Infected C57BL/6 mice exhibited resistance and healing lesions. The immune response involved pro- and anti-inflammatory cytokine secretion, respectively. The infection-induced hypoalgesia in BALB/c mice after wks 9 was accompanied by decreased levels of IL-6 and IL-10 in ear tissue with intact nerves. C57BL/6 mice showed short-lived hyperalgesia in wks 2, which was related to increased local levels of IL-6, KC/CXCL-1, TNF-α and IL-10 and a decrease in nerve density. The increase in pro-inflammatory cytokine IL-6, KC/CXCL-1 and TNF-α levels during hyperalgesia suggested a role for these mediators in afferent nerve sensitisation, which was secondary to the inflammatory damage of nerve fibres stained by PGP 9.5. In contrast, the mechanisms of hypoalgesia may include the downregulation of cytokines, the preservation of the structure of nerve endings, and as yet uninvestigated unidentified differences in neurotransmitter release or a direct role of the parasites in the context of the progressive and permissive inflammatory response of BALB/c mice.

Human Dendritic Cell Heterogeneity: Opportunities and Challenges for the Control of Immunity

Abstract SCI-21Dendritic cells (DCs) comprise a heterogeneous population of potent antigen-presenting cells, which are master orchestrators of the immune response. DCs initiate immunity, and just as importantly, control its quality and outcome. DCs accomplish this by capitalizing on their defined subsets, which exert discrete functions in responding to different types of antigens and factors in the microenvironment. DCs, therefore, provide the immune system with an essential and robust flexibility to discriminate between enormous numbers of harmful and benign agents and to mount functionally distinct and appropriate responses in the contexts of innate and adaptive immunity. Our lab has focused on the contrasting functions of conventional human DC subsets, primarily monocyte-derived DCs (moDCs) versus CD34+ hematopoietic progenitor cell-derived Langerhans-type DCs (LCs). Recent findings that have defined the afferent sensitization of different types of immune responses by these distinct DC subtypes will be discussed. For example, LCs use an endogenous IL-15R-α/IL-15 mechanism to generate potent cytotoxic T lymphocytes and break tolerance against a self-differentiation tumor antigen like WT1. This contrasts with the potency of moDCs in maturing and stimulating NK cells by their production of IL-12p70, whereas LCs can only ensure NK-cell viability. The application of these findings to the holy grail of separating graft-versus-leukemia from the deleterious aspects of graft-versus-host disease in allotransplantation, at the level of afferent sensitization by these distinct DC subtypes, as well as the novel use of small-molecule inhibitors of JAK-STAT signaling in DC-stimulated T cells, will also be addressed. Disclosures:Off Label Use: JAK2 inhibitors (potentially several) for inhibition of dendritic cell stimulated alloreactivity - but all data will be in vitro, so perhaps this is not off-label drug use because it is not in vivo in humans.

Expression of nicotinic acetylcholine receptor subunit mRNA in mouse bladder afferent neurons

Nicotinic acetylcholine receptors (nAChR) influence bladder afferent activity and reflex sensitivity, and have been suggested as potential targets for treating detrusor overactivity. Mechanisms may include indirect effects, e.g. involving the urothelium, and direct action on nAChR expressed by afferent neurons. Here we determined the nAChR repertoire of bladder afferent neurons by retrograde neuronal tracing and laser-assisted microdissection/reverse transcriptase polymerase chain reaction (RT–PCR), and quantified retrogradely labelled nAChRα3-subunit-expressing neurons by immunohistochemistry in nAChR α3β4α5 cluster enhanced green fluorescent protein (eGFP) reporter mice. Bladder afferents distinctly expressed mRNAs encoding for nAChR-subunits α3, α6, α7, β2–4, and weakly α4. Based upon known combinatorial patterns of subunits, this predicts the expression of at least three basically different subunits of nAChR – α3∗, α6∗ and α7∗ – and of additional combinations with β-subunits and α5. Bladder afferents were of all sizes, and their majority (69%; n=1367) were eGFP–nAChRα3 positive. Immunofluorescence revealed immunoreactivities to neurofilament 68 (NF68), transient receptor potential cation channel vanilloid 1 (TRPV1), substance P (SP) and calcitonin gene-related peptide (CGRP) in eGFP–nAChRα3-positive and -negative neurons. For each antigen, all possible combinations of colocalisation with eGFP–nAChRα3 were observed, with eGFP–nAChRα3-positive bladder neurons without additional immunoreactivity being most numerous, followed by triple-labelled neurons. In conclusion, more than one population of bladder afferent neurons expresses nAChR, indicating that peripheral nicotinic initiation and modulation of bladder reflexes might result, in addition to indirect effects, from the direct activation of sensory terminals. The expression of multiple nAChR subunits offers the potential of selectively addressing functional aspects and/or sensory neuron subpopulations.

Molecular Pharmacological Approaches to Effects of Capsaicinoids and of Classical Antisecretory Drugs on Gastric Basal Acid Secretion and on Indomethacin-Induced Gastric Mucosal Damage in Human Healthy Subjects (Mini Review)

Actions of various drugs have been tested on the gastric acid basal secretion and on the drug (Indomethacin)- induced gastric mucosal damage; however their physiological and pharmacological mechanisms have not been compared. The effects of capsaicinoids, atropine, cimetidine, omeprazole, famotidine and ranitidine were studied on gastric basal acid output, whereas the gastric mucosal preventive effects of capsaicinoids (capsaicin), atropine and cimetidine were tested on the indomethacin-induced gastric mucosal microbleedings in human healthy subjects. Results were presented by molecular pharmacological method; affinity (pD) and intrinsic activity (α-values) were calculated. Intrinsic activity curves are based on comparison to atropine effect (α(atropine)= 1.00). For evaluation of physiological and pharmacological effects of compounds molar doses of pD(2) (necessary doses to produce 50% inhibition) and pA(2) (50% inhibion on intrinsic activity) were calculated from affinity and intrinsic activity curves. The pD(2) values for compounds were as follows: 5.88 for capsaicinoids, 5.40 for atropine , 2.23 for cimetidine, 3.33 for ranitidine, 3.77 for famotidine and 3.97 for omeprazole. α - value results for compounds were: 0.76 for capsaicinoids, and 1.00 for atropine, cimetidine, ranitidine, famotidine and omeprazole all equal to 1.00 on gastric acid basal secretion. The pD(2) values on indomethacin-induced gastric mucosal microbleeding were found as follows: 6.00 for capsaicinoids, 5.50 for atropine, and 3.50 for cimetidine, meanwhile α-values resulted 0.76 for capsaicinoids, 1.00 for atropine and cimetidine. Comparison classical antisecretory drugs acting on different pathways but in much more higher molar concentrations. The atropine and capsaicinoids act in about the same molar concentration which suggests a significant physiological role for capsaicin sensitive afferent nerves in the regulation of gastric basal acid secretion and in the prevention of chemically- induced gastric mucosal protection in human healthy subjects, suggesting a novel physiological pathway in regulation. These results clearly indicate the molecular pharmacological backgrounds of actions of classical antisecretory drugs and physiological role of capsaicin- sensitive afferent nerves in human healty subjects on the gastric basal secretion and on the prevention of drug-induced gastric mucosal damage.

Molecular Pharmacological Approaches to Effects of Capsaicinoids and of Classical Antisecretory Drugs on Gastric Basal Acid Secretion and on Indomethacin-Induced Gastric Mucosal Damage in Human Healthy Subjects (Mini Review)

Background: Actions of various drugs have been tested on the gastric acid basal secretion and on the drug (Indomethacin)- induced gastric mucosal damage; however their physiological and pharmacological mechanisms have not been compared. Aims: The effects of capsaicinoids, atropine, cimetidine, omeprazole, famotidine and ranitidine were studied on gastric basal acid output, whereas the gastric mucosal preventive effects of capsaicinoids (capsaicin), atropine and cimetidine were tested on the indomethacin-induced gastric mucosal microbleedings in human healthy subjects. Results were presented by molecular pharmacological method; affinity (pD) and intrinsic activity (α-values) were calculated. Intrinsic activity curves are based on comparison to atropine effect (α atropine&equals; 1.00). For evaluation of physiological and pharmacological effects of compounds molar doses of pD2 (necessary doses to produce 50&percnt; inhibition) and pA2 (50&percnt; inhibion on intrinsic activity) were calculated from affinity and intrinsic activity curves. Results: The pD2 values for compounds were as follows: 5.88 for capsaicinoids, 5.40 for atropine , 2.23 for cimetidine, 3.33 for ranitidine, 3.77 for famotidine and 3.97 for omeprazole. α - value results for compounds were: 0.76 for capsaicinoids, and 1.00 for atropine, cimetidine, ranitidine, famotidine and omeprazole all equal to 1.00 on gastric acid basal secretion. The pD2 values on indomethacin-induced gastric mucosal microbleeding were found as follows: 6.00 for capsaicinoids, 5.50 for atropine, and 3.50 for cimetidine, meanwhile α-values resulted 0.76 for capsaicinoids, 1.00 for atropine and cimetidine. Conclusions: Comparison classical antisecretory drugs acting on different pathways but in much more higher molar concentrations. The atropine and capsaicinoids act in about the same molar concentration which suggests a significant physiological role for capsaicin sensitive afferent nerves in the regulation of gastric basal acid secretion and in the prevention of chemically- induced gastric mucosal protection in human healthy subjects, suggesting a novel physiological pathway in regulation. These results clearly indicate the molecular pharmacological backgrounds of actions of classical antisecretory drugs and physiological role of capsaicin- sensitive afferent nerves in human healty subjects on the gastric basal secretion and on the prevention of drug-induced gastric mucosal damage. Keywords: Capsaicinoids, gastric acid inhibitory drugs, indomethacin-induced gastric mucosal damage, molecular pharmacology, physiological and pharmacological regulations of afferent and efferent vagal nerve, atropine, cimetidine, omeprazole, famotidine, anitidine

New perspectives concerning feedback influences on cardiorespiratory control during rhythmic exercise and on exercise performance

The cardioaccelerator and ventilatory responses to rhythmic exercise in the human are commonly viewed as being mediated predominantly via feedforward 'central command' mechanisms, with contributions from locomotor muscle afferents to the sympathetically mediated pressor response. We have assessed the relative contributions of three types of feedback afferents on the cardiorespiratory response to voluntary, rhythmic exercise by inhibiting their normal 'tonic' activity in healthy animals and humans and in chronic heart failure. Transient inhibition of the carotid chemoreceptors during moderate intensity exercise reduced muscle sympathetic nerve activity (MSNA) and increased limb vascular conductance and blood flow; and reducing the normal level of respiratory muscle work during heavier intensity exercise increased limb vascular conductance and blood flow. These cardiorespiratory effects were prevented via ganglionic blockade and were enhanced in chronic heart failure and in hypoxia. Blockade of μ opioid sensitive locomotor muscle afferents, with preservation of central motor output via intrathecal fentanyl: (a) reduced the mean arterial blood pressure (MAP), heart rate and ventilatory responses to all steady state exercise intensities; and (b) during sustained high intensity exercise, reduced O(2) transport, increased central motor output and end-exercise muscle fatigue and reduced endurance performance. We propose that these three afferent reflexes - probably acting in concert with feedforward central command - contribute significantly to preserving O(2) transport to locomotor and to respiratory muscles during exercise. Locomotor muscle afferents also appear to provide feedback concerning the metabolic state of the muscle to influence central motor output, thereby limiting peripheral fatigue development.

Altered colorectal afferent function associated with TNBS-induced visceral hypersensitivity in mice

Inflammation of the distal bowel is often associated with abdominal pain and hypersensitivity, but whether and which colorectal afferents contribute to the hypersensitivity is unknown. Using a mouse model of 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis, we investigated colorectal hypersensitivity following intracolonic TNBS and associated changes in colorectum and afferent functions. C57BL/6 mice were treated intracolonically with TNBS or saline. Visceromotor responses to colorectal distension (15-60 mmHg) were recorded over 8 wk in TNBS- and saline-treated (control) mice. In other mice treated with TNBS or saline, colorectal inflammation was assessed by myeloperoxidase assay and immunohistological staining. In vitro single-fiber recordings were conducted on both TNBS and saline-treated mice to assess colorectal afferent function. Mice exhibited significant colorectal hypersensitivity through day 14 after TNBS treatment that resolved by day 28 with no resensitization through day 56. TNBS induced a neutrophil- and macrophage-based colorectal inflammation as well as loss of nerve fibers, all of which resolved by days 14-28. Single-fiber recordings revealed a net increase in afferent drive from stretch-sensitive colorectal afferents at day 14 post-TNBS and reduced proportions of mechanically insensitive afferents (MIAs) at days 14-28. Intracolonic TNBS-induced colorectal inflammation was associated with the development and recovery of hypersensitivity in mice, which correlated with a transient increase and recovery of sensitization of stretch-sensitive colorectal afferents and MIAs. These results indicate that the development and maintenance of colorectal hypersensitivity following inflammation are mediated by peripheral drive from stretch-sensitive colorectal afferents and a potential contribution from MIAs.

Role for NGF in augmented sympathetic nerve response to activation of mechanically and metabolically sensitive muscle afferents in rats with femoral artery occlusion

Arterial blood pressure and heart rate responses to static contraction of the hindlimb muscles are greater in rats whose femoral arteries were previously ligated than in control rats. Also, the prior findings demonstrate that nerve growth factor (NGF) is increased in sensory neurons-dorsal root ganglion (DRG) neurons of occluded rats. However, the role for endogenous NGF in engagement of the augmented sympathetic and pressor responses to stimulation of mechanically and/or metabolically sensitive muscle afferent nerves during static contraction after femoral artery ligation has not been specifically determined. In the present study, both afferent nerves and either of them were activated by muscle contraction, passive tendon stretch, and arterial injection of lactic acid into the hindlimb muscles. Data showed that femoral occlusion-augmented blood pressure response to contraction was significantly attenuated by a prior administration of the NGF antibody (NGF-Ab) into the hindlimb muscles. The effects of NGF neutralization were not seen when the sympathetic nerve and pressor responses were evoked by stimulation of mechanically sensitive muscle afferent nerves with tendon stretch in occluded rats. In addition, chemically sensitive muscle afferent nerves were stimulated by lactic acid injected into arterial blood supply of the hindlimb muscles after the prior NGF-Ab, demonstrating that the reflex muscle responses to lactic acid were significantly attenuated. The results of this study further showed that NGF-Ab attenuated an increase in acid-sensing ion channel subtype 3 (ASIC3) of DRG in occluded rats. Moreover, immunohistochemistry was employed to examine the number of C-fiber and A-fiber DRG neurons. The data showed that distribution of DRG neurons with different thin fiber phenotypes was not notably altered when NGF was infused into the hindlimb muscles. However, NGF increased expression of ASIC3 in DRG neurons with C-fiber but not A-fiber. Overall, these data suggest that 1) NGF is amplified in sensory nerves of occluded rats and contributes to augmented reflex sympathetic and blood pressure responses evoked by stimulation of chemically, but not mechanically, sensitive muscle afferent nerves and 2) NGF likely plays a role in modulating the muscle metaboreflex via enhancement of ASIC3 expression in C-fiber of DRG neurons.

Exercise pressor reflex function in female rats fluctuates with the estrous cycle

In women, sympathoexcitation during static handgrip exercise is reduced during the follicular phase of the ovarian cycle compared with the menstrual phase. Previous animal studies have demonstrated that estrogen modulates the exercise pressor reflex, a sympathoexcitatory mechanism originating in contracting skeletal muscle. The present study was conducted in female rats to determine whether skeletal muscle contraction-evoked reflex sympathoexcitation fluctuates with the estrous cycle. The estrous cycle was judged by vaginal smear. Plasma concentrations of estrogen were significantly (P < 0.05) higher in rats during the proestrus phase of the estrus cycle than those during the diestrus phase. In decerebrate rats, either electrically induced 30-s continuous static contraction of the hindlimb muscle or 30-s passive stretch of Achilles tendon (a maneuver that selectively stimulates mechanically sensitive muscle afferents) evoked less renal sympathoexcitatory and pressor responses in the proestrus animals than in the diestrus animals. Renal sympathoexcitatory response to 1-min intermittent (1- to 4-s stimulation to relaxation) bouts of static contraction was also significantly less in the proestrus rats than that in the diestrus rats. In ovariectomized female rats, 17β-estradiol applied into a well covering the dorsal surface of the lumbar spinal cord significantly reduced skeletal muscle contraction-evoked responses. These observations demonstrate that the exercise pressor reflex function and its mechanical component fluctuate with the estrous cycle in rats. Estrogen may cause these fluctuations through its attenuating effects on the spinal component of the reflex arc.