Non-adrenergic Non-cholinergic Nerves Research Articles

Effects of 2-Hz and 100-Hz Electroacupuncture Stimulation on Respiratory Function and Heart Rate Variability: A Randomized Crossover Study

Background: Bronchial contraction and dilation is thought to be caused by non-adrenergic non-cholinergic nerves. Objective: To investigate the effects of low-frequency (1-5 Hz) and highfrequency (50-100 Hz) electric acupuncture (EA) stimulation on bronchial dilation. Design: Prospective, single-center study Setting: Teikyo Heisei University Subjects: Seventeen healthy male adults Randomization: We randomly assigned subjects to 2-Hz EA and 100-Hz EA groups in a crossover trial. The washout period was 2 weeks. Intervention: Both groups underwent a respiratory function test, followed by a 5-minute rest, followed a 5-minute rest or EA stimulation, followed by a 5min rest. Heart rate variability was measured at rest, followed by another respiratory function test. Acupuncture was delivered near the cervical ganglia at the level of the sixth cervical vertebra on the left side. EA stimuli were set to 2-Hz or 100-Hz, and stimulation intensity was set to a level where no pain was felt. Main outcome measures: Spirometry (forced vital capacity, forced expiratory volume in 1 s, and maximum respiratory flow), autonomic nerve activity (low-frequency component, high-frequency component, and their ratio), and heart rate variability. Results: Heart rate variability analysis showed significant differences in heart rate between the 2-Hz EA and 100-Hz EA groups. The 2-Hz EA group showed a significant increase in HF.Conclusions: 2-Hz EA stimulation resulted in decreased heart rate and increased HF during stimulation. This may be more effective for regulation of the autonomic nerves of the cardiopulmonary system than 100-Hz EA stimulation. Future studies are required to confirm our findings.

Pleasurable ways to spontaneously expulse distal ureteral stones: A systematic review and meta-analysis of randomized controlled trials

ABSTRACT Introduction Numerous non-invasive ways of managing distal ureteral stones have been recommended, such as administering treatments to inhibit receptors responsible for ureteral tone and peristaltic movement frequency. Nitric oxide, which is released during penile erection, causes smooth muscle relaxation by inhibiting the non-adrenergic non-cholinergic (NANC) nerves of the distal ureter and ureterovesical junction. Bladder neck contraction followed by relaxation, occurring during orgasm and ejaculation could also facilitate the passage of stones. However, the exact role of sexual activities involving these mechanisms has yet to be established. Objective This review aimed to evaluate the efficacy of sexual acts, including sexual intercourse and masturbation, to promote distal ureteral stones expulsion based on the findings of relevant randomized controlled trials (RCT)s. Methods A systematic search adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist was performed in the Embase, Scopus, and Medline databases in July 2021. The initial search generated 50 articles. The articles were screened based on the eligibility criteria. Their quality was assessed using the Cochrane Risk of Bias (RoB) tool 2 for randomized trials. Measured outcomes included stone expulsion rate, expulsion time, analgesic injections frequency, and the need for a ureteroscopic (URS) lithotripsy. A fixed effects model was used for analyzing parameters with homogeneity among studies, whereas a random effects model was used for heterogenous studies. The odds ratio (OR) and mean difference (MD) among studies were displayed in forest plots using the Review Manager software version 5.4.1. Results A total of five RCTs with an overall low risk of bias, consisting of 406 subjects, were included in this review. Four studies evaluated sexual intercourse and one study evaluated masturbation. Both interventions were instructed to be performed for three to four times a week. The stone expulsion rate was higher in the sexual activity group compared to the control group at the two-week follow-up (OR 5.77 95%CI 3.70 - 9.01, p<0.00001) and four-week follow-up (OR 4.44 95%CI 2.73 - 7.23, p<0.00001) with a significantly lower expulsion time of the sexual activity group (MD -3.79 95% CI -6.38 - -1.20, p=0.004). The number of subjects requiring additional analgesic injections (MD -0.62 95% CI -1.03 - -0.21, p=0.003) and URS lithotripsy (OR 0.22 95% CI 0.13 – 0.37, p<0.00001) was also lower in the sexual activity group compared to the control group. Conclusions Performing sexual intercourse or masturbation for three to four times a week is beneficial for promoting spontaneous expulsion of distal ureteral stones. It could also reduce the use of analgesic injections and the need for a URS lithotripsy.

BDNF augments rat internal anal sphincter smooth muscle tone via RhoA/ROCK signaling and nonadrenergic noncholinergic relaxation via increased NO release.

Presently, there are no studies examining the neuromodulatory effects of brain-derived neurotropic factor (BDNF) on the basal internal anal sphincter (IAS) tone and nonadrenergic noncholinergic (NANC) relaxation. To examine this, we determined the neuromuscular effects of BDNF on basal IAS smooth muscle tone and the smooth muscle cells (SMCs) and the effects of NANC nerve stimulation before and after high-affinity receptor tyrosine kinase receptor B (TrkB) antagonist K252a. We also investigated the mechanisms underlying BDNF-augmented increase in the IAS tone and NANC relaxation. We found that BDNF-increased IAS tone and SMC contractility were TTX resistant and attenuated by K252a. TrkB-specific agonist 7,8-dihydroxyflavone, similar to BDNF, also produced a concentration-dependent increase in the basal tone, whereas TrkB inhibitors K252a and ANA-12 produced a decrease in the tone. In addition, BDNF produced leftward shifts in the concentration-response curves with U46619 and ANG II (but not with bethanechol and K+ depolarization), and these shifts were reversed by K252a. Effects of Y27632 and Western blot data indicated that the BDNF-induced increase in IAS tone was mediated via RhoA/ROCK. BDNF-augmented NANC relaxation by electrical field stimulation was found to be mediated via the nitric oxide (NO)/soluble guanylate cyclase (sGC) pathway rather than via increased sensitivity to NO. In conclusion, the net effect of BDNF was that it caused an increase in the basal IAS tone via RhoA/ROCK signaling. BDNF also augmented NANC relaxation via NO/sGC. These findings may have relevance to the role of BDNF in the pathophysiology and therapeutic targeting of the IAS-associated rectoanal motility disorders.NEW & NOTEWORTHY These studies for the first time to our knowledge demonstrate that increased levels of brain-derived neurotrophic factor (BDNF; conceivably released from smooth muscle cells and/or the enteric neurons) has two major effects. First, BDNF augments the internal anal sphincter (IAS) tone via tyrosine kinase receptor B/thromboxane A2-receptor, angiotensin II receptor type 1/RhoA/ROCK signaling; and second, it increases nonadrenergic noncholinergic relaxation via nitric oxide/soluble guanylate cyclase. These studies may have relevance in therapeutic targeting in the anorectal motility disorders associated with the IAS.

Antinicotinic activity of some 2-aminotetralin derivatives. A structure-activity relationship study.

The antagonistic potencies of some methoxy-2-aminotetralin derivatives on nicotinic type acetylcholine receptors were compared in rat anococcygeus muscle and frog rectus abdominis muscle preparations. Stimulation of intrinsic non-adrenergic non-cholinergic (NANC) nerves with nicotine (100 mumol/l) produced a 65.7 +/- 3.2% relaxation in phenylephrine (1 mumol/l) precontracted (2.53 +/- 0.20 g) preparations (n = 17). 2-Aminotetralin derivatives inhibited the nicotine-induced relaxations in rat anococcygeus muscle in a concentration-dependent manner with the following order of potency: BDI-60 > BDI-85 > BDI-51. Preincubation of frog rectus abdominis muscles with the test compounds caused noncompetitive antagonism as reflected by significant reductions in the maximum contractions obtained with nicotine. The order of potency according to their pD2' values was BDI-60 > BDI-85 > BDI-51. All three compounds possess antagonistic action with the same order of potency on both neuronal and muscular type nicotinic acetylcholine receptors. It has been concluded that doubling the n-propyl residue on the 2-amino moiety causes an increase in the antagonistic potency on nicotonic type acetylcholine receptors, while shifting of the 8-methoxy residue to the fifth position reduces it.

Desflurane and neural control of airway tone

The study by Myers et al. in this edition of the Journal adds to our understanding of the role of desflurane in reactive airway disease. The authors compare the ability of sevoflurane with that of desflurane to alter respiratory mechanics following a cholinergic contraction in normal or sensitized rabbits whose lungs were ventilated through a tracheostomy. This study is an important addition to a growing body of literature which addresses an important clinical question: Does the choice of volatile anesthetic matter in patients with reactive airway disease, and more specifically, is desflurane a bad choice in patients with reactive airway disease? The airway is exposed to two primary irritants during general anesthesia with a volatile anesthetic, i.e., a foreign body (endotracheal tube or laryngeal mask airway device [LMAD]) acting as a mechanical irritant and a volatile anesthetic which can elicit a chemical irritation. C-fibres, including excitatory non-adrenergic non-cholinergic (eNANC) nerves, innervate the upper airway and are activated by transient receptor potential (TRP) channels to release tachykinins which can elicit smooth muscle contraction. Desflurane has been shown to activate TRP A1 receptors on C-fibres, inducing a tachykinin-mediated airway response. A secondary important neural reflex pathway which responds to airway irritation is the cholinergic pathway whereby parasympathetic nerve fibres travelling within the vagus nerve release acetylcholine which induces airway smooth muscle contraction. The current study was designed to evaluate the effect of desflurane on the neurotransmitter of this latter neural pathway, namely, acetylcholine. The authors demonstrate that desflurane is comparable with sevoflurane in its ability to attenuate bronchoconstriction induced by activation of muscarinic receptors on airway smooth muscle by intravenous methacholine. These results are consistent with previous studies which implicated TRP channels on C-fibres as the culprit of desflurane-induced bronchoconstriction observed in clinical studies. Although not a topic of the current study, desflurane activation of C-fibres would also account for the frequently observed clinical complication of cough. In isolated human bronchi, desflurane was equally potent as halothane and isoflurane at relaxing proximal but not distal bronchi. This finding is also consistent with the present study since neural innervation is thought to be primarily cholinergic in large central airways and eNANC in peripheral airways. In previous studies of isolated airways or tracheostomized and ventilated lungs of animals from multiple species, desflurane was shown to be at least as effective as other volatile anesthetics in directly relaxing airway smooth muscle. Taken together, these studies, which are performed in the absence of intact innervation, suggest that clinical difficulties with desflurane and the airway are not likely related to direct airway smooth muscle effects but are mediated by differential effects on irritant neural reflexes. The current study is an important addition to our mechanistic understanding of differential effects of volatile anesthetics on bronchoconstriction. This study demonstrates that sevoflurane and desflurane are similar in their abilities to prevent bronchoconstriction of cholinergic origin occurring in sensitized airways. It should be emphasized that desflurane was delivered to an intubated trachea (or isolated airway tissue) in this and previous C. W. Emala, MD (&) Department of Anesthesiology, Columbia University, 622 West 168th St., P&S Box 46, New York, NY 10032, USA e-mail: cwe5@columbia.edu

Are Antimuscarinic Drugs Effective Against Urinary Frequency Mediated by Atropine-Resistant Contractions?

In the disease states of urinary frequency and urgency, atropine-resistant contractions are known to be involved, in addition to contractions mediated by cholinergic nerves. This study was undertaken to investigate the mechanism underlying the development of atropine-resistant contractions using the representative antimuscarinic drugs solifenacin and tolterodine and also propiverine that has Ca2+ channel–antagonizing activity in addition to antimuscarinic activity. Rat models of urinary frequency were established by intravesical infusion of acetylcholine (ACh) (cholinergic nerve–mediated urinary frequency model), acetic acid (AcOH) [non-adrenergic noncholinergic nerve (NANC)-mediated urinary frequency model], or CaCl2 (atropine-resistant contractions-mediated urinary frequency model). Cystometrograms were obtained to measure the micturition parameters following oral administration of the aforementioned drugs. Propiverine increased the micturition weight in all the urinary frequency models. Solifenacin and tolterodine increased the micturition weight in the ACh-induced urinary frequency model but neither had any effect in the AcOH- or CaCl2-induced urinary frequency models. While antimuscarinic drugs are, in general, effective for the control of urinary frequency and incontinence, use of drugs possessing inhibitory effects on contractions mediated by cholinergic as well as NANC nerve transmission or Ca2+ influx into smooth muscles is recommended for management of the symptoms in disease states in which atropine-resistant contractions, such as Ca2+- and capsaicin-sensitive sensory nerves, are involved.

Autonomic control of the urogenital tract

The urogenital tract houses many of the organs that play a major role in homeostasis, in particular those that control water and salt balance, and reproductive function. This review focuses on the anatomical and functional innervation of the kidneys, urinary ducts and bladders of the urinary system, and the gonads, gonadal ducts, and intromittent organs of the reproductive tract. The literature, especially in recent years, is overwhelmingly skewed toward the situation in mammals. Nevertheless, where specific neurochemical markers have been investigated, common patterns of innervation can be found in representatives from most vertebrate classes. Not surprisingly the vasculature, epithelia and smooth muscle of all urogenital organs receives adrenergic innervation. These nerves may contain non-adrenergic non-cholinergic (NANC) neurotransmitters such as ATP and NPY. Cholinergic nerves increase motility in most urogenital organs with the exception of the kidney. The major NANC nerves found to influence urogenital organs include those containing VIP/PACAP, galanin and neuronal nitric oxide synthase. These can be found associated with both smooth muscle and epithelia. The role these nerves play, and the circumstances where they are activated are for the most part unknown.

Role of L‐Citrulline/L‐Arginine Cycle in Hyperoxia‐Induced Decrease of Airway Smooth Muscle Relaxation

It was shown that inhibitory nonadrenergic noncholinergic (iNANC) nerve–induced nitric oxide (NO) production and airway smooth muscle (ASM) relaxation are impared after exposure to hyperoxia due to decrease of L‐arginine bioavailability to NO synthase (NOS). Therefore, we tested the hypothesis that L‐citrulline/L‐arginine cycle is active in rat pup airways and supplementation of tissues with L‐citrulline, restores impaired relaxation of ASM after exposure to hyperoxia. Tracheal rings were excised from rat pups 12 days old, exposed to hyperoxia or room air for seven days. In precontracted tracheal smooth muscle (TSM), electrical field stimulation (EFS) was applied to induce relaxation. In hyperoxic group, relaxation was reduced as compare to control group. Incubation of tissues with NOS inhibitor (L‐NAME), reduced relaxant responses in control group. In vitro supplementation of tissues with L‐citrulline reversed EFS‐induced relaxation of TSM of hyperoxic group at control level, but did not have any effect in control group under basal condition. Inhibition of enzymes involved in L‐citrulline recycling, prevented this effect of L‐citrulline.The data demonstrate that L‐citrulline/L‐arginine cycle is active in rat pup TSM and is effective under conditions of reduced bioavailability of L‐arginine to NOS. Presence of L‐citrulline restores hyperoxia‐induced decrease of ASM relaxation.

Mechanisms of hypertonic saline-induced bronchoconstriction in guinea pigs

We examined whether inhalation of hypertonic saline can induce bronchoconstriction in guinea pigs, and also studied the mechanisms of this bronchoconstriction. Twenty-five male Hartley guinea pigs were divided into the following 5 groups: G-1, 0.9% saline inhalation; G-2. non-treatment and inhalation of hypertonic saline; G-3, capsaicin pretreatment and inhalation of hypertonic salines; G-4, ipratropium bromide pretreatment and inhalation of hypertonic saline; G-5, chlorpheniramine pretreatment and inhalation of hypertonic saline. RL and Cdyn were serially measured to assess bronchoconstriction, and the percent increase in RL from the value measured before inhalation of hypertonic saline (%RL) was analyzed. The maximum %RL was 9.2 +/- 3.8% in G-1, 90.6 +/- 6.6% in G-2, 11.2 +/- 5.7% in G-3, 9.0 +/- 6.0% in G-4, and 47.8 +/- 4.0% in G-5. The values in G-3 and G-4 were significantly lower than in G-2. We conclude that inhalation of hypertonic saline causes concentration dependent bronchoconstriction in guinea pigs and that both non-adrenergic non-cholinergic nerves and cholinergic nerves may play an important role in this bronchoconstriction.

Neurotransmitters in Airway Parasympathetic Neurons Altered by Neurotrophin-3 and Repeated Allergen Challenge

Changes in airway nerves associated with chronic inflammation may underlie the pathogenesis and symptoms of lower airway diseases, such as asthma. The molecules most likely causing such alterations are neurotrophins (NTs) and/or related neurokines. In several species, including humans, lower airway parasympathetic postganglionic neurons that project axons to airway smooth muscle are either cholinergic or nonadrenergic noncholinergic (NANC), the latter synthesizing vasoactive intestinal peptide and nitric oxide, but not acetylcholine. In guinea pig trachealis smooth muscle, cholinergic nerve terminals arise from ganglionic neurons located near the tracheal smooth muscle, whereas the source of NANC nerve fibers is from neurons in ganglia located in the adjacent myenteric plexus of the esophagus, making this an ideal species to study regulation of parasympathetic neurotransmitter phenotypes. In the present study, we determined that, 48 hours after repeated allergen challenge, the NANC phenotype of airway parasympathetic ganglionic neurons changed to a cholinergic phenotype, and NT-3 mimicked this change. Nerve growth factor, brain-derived neurotrophic factor, leukemia inhibitory factor, or IL-1β had no effect on either phenotype, and they did not induce these neurons to synthesize substance P or tyrosine hydroxylase. These results indicate a role for inflammation and NT-3 in regulating biochemical and anatomical characteristics of principal neurons in adult airway parasympathetic ganglia.

Imaging of Nitric Oxide in Nitrergic Neuromuscular Neurotransmission in the Gut

BackgroundNumerous functional studies have shown that nitrergic neurotransmission plays a central role in peristalsis and sphincter relaxation throughout the gut and impaired nitrergic neurotransmission has been implicated in clinical disorders of all parts of the gut. However, the role of nitric oxide (NO) as a neurotransmitter continues to be controversial because: 1) the cellular site of production during neurotransmission is not well established; 2) NO may interacts with other inhibitory neurotransmitter candidates, making it difficult to understand its precise role.Methodology/Principal FindingsImaging NO can help resolve many of the controversies regarding the role of NO in nitrergic neurotransmission. Imaging of NO and its cellular site of production is now possible. NO forms quantifiable fluorescent compound with diaminofluorescein (DAF) and allows imaging of NO with good specificity and sensitivity in living cells. In this report we describe visualization and regulation of NO and calcium (Ca2+) in the myenteric nerve varicosities during neurotransmission using multiphoton microscopy. Our results in mice gastric muscle strips provide visual proof that NO is produced de novo in the nitrergic nerve varicosities upon nonadrenergic noncholinergic (NANC) nerve stimulation. These studies show that NO is a neurotransmitter rather than a mediator. Changes in NO production in response to various pharmacological treatments correlated well with changes in slow inhibitory junction potential of smooth muscles.Conclusions/SignificanceDual imaging and electrophysiologic studies provide visual proof that during nitrergic neurotransmission NO is produced in the nerve terminals. Such studies may help define whether NO production or its signaling pathway is responsible for impaired nitrergic neurotransmission in pathological states.

Type 1 and Type 2 Diabetic‐Erectile Dysfunction: Same Diagnosis (ICD‐9), Different Disease?

ABSTRACT Introduction Although hyperglycemia is a common defining feature of both type 1 and type 2 diabetes, many unique characteristics distinguish these diseases, including insulin and lipid levels, obesity status, and inflammatory agent profiles. In the laboratory, the presence of erectile dysfunction (ED) has been established in animal models of both type 1 and type 2 diabetes. Aim The purpose of this study was to determine whether unique mechanisms underlie ED in type 1 vs. type 2 diabetic animal models. Main Outcome Measures Many mechanisms can underlie ED, including impaired dilatory signaling, heightened contractile sensitivity, and veno-occlusive disorder. Methods Using PubMed, the literature was mined to evaluate what is known about which mechanism underlie ED in type 1 vs. type 2 diabetic animal models. Results Impaired cavernosal vasodilation has been established in type 1 diabetic rodents. This dysfunction appears to be mediated by a severe defect in non-adrenergic–non-cholinergic nerve signaling, as well as impairment in penile endothelial function. In contrast, type 2 diabetic animals appear to have minimal impairment in parasympathetic-mediated dilatory function, but do have evidence of endothelial dysfunction. Type 2 diabetic models also exhibit a significant and striking increase in cavernosal contractile sensitivity, and a significant veno-occlusive disorder, neither of which is consistently reported in type 1 diabetic animals. Conclusions With the distinct mechanisms underlying the ED phenotype in animal models of type 1 and type 2 diabetes, tailoring therapeutic treatments for diabetic-ED to the specific mechanisms underlying this disease complication may be warranted. Further examination of mechanisms underlying ED in diabetic human patients may thus lead to significant changes in the way urologists diagnose, code, and treat diabetic-ED.

The GABAA agonist muscimol attenuates induced airway constriction in guinea pigs in vivo

GABA(A) channels are ubiquitously expressed on neuronal cells and act via an inward chloride current to hyperpolarize the cell membrane of mature neurons. Expression and function of GABA(A) channels on airway smooth muscle cells has been demonstrated in vitro. Airway smooth muscle cell membrane hyperpolarization contributes to relaxation. We hypothesized that muscimol, a selective GABA(A) agonist, could act on endogenous GABA(A) channels expressed on airway smooth muscle to attenuate induced increases in airway pressures in anesthetized guinea pigs in vivo. In an effort to localize muscimol's effect to GABA(A) channels expressed on airway smooth muscle, we pretreated guinea pigs with a selective GABA(A) antagonist (gabazine) or eliminated lung neural control from central parasympathetic, sympathetic, and nonadrenergic, noncholinergic (NANC) nerves before muscimol treatment. Pretreatment with intravenous muscimol alone attenuated intravenous histamine-, intravenous acetylcholine-, or vagal nerve-stimulated increases in peak pulmonary inflation pressure. Pretreatment with the GABA(A) antagonist gabazine blocked muscimol's effect. After the elimination of neural input to airway tone by central parasympathetic nerves, peripheral sympathetic nerves, and NANC nerves, intravenous muscimol retained its ability to block intravenous acetylcholine-induced increases in peak pulmonary inflation pressures. These findings demonstrate that the GABA(A) agonist muscimol acting specifically via GABA(A) channel activation attenuates airway constriction independently of neural contributions. These findings suggest that therapeutics directed at the airway smooth muscle GABA(A) channel may be a novel therapy for airway constriction following airway irritation and possibly more broadly in diseases such as asthma and chronic obstructive pulmonary disease.

Purines as Neurotransmitters and Neuromodulators in Blood Vessels

ATP is an important neurotransmitter being released with noradrenaline (NA) and neuropeptide Y (NPY) from perivascular sympathetic nerves; it acts at postjunctional P2X receptors to evoke vascular smooth muscle contraction, often synergising with the effects of NA acting at alpha-adrenoceptors. There is growing evidence for ATP as a neurotransmitter in perivascular non-adrenergic non-cholinergic nerves. In addition, ATP can act as a facilitatory and inhibitory neuromodulator via prejunctional P2 receptors. ATP is rapidly broken down, by ectonucleotidases, to adenosine which can also regulate the release of neurotransmitters via inhibitory prejunctional A(1) adenosine receptors. The relative contributions of ATP and NA as functional cotransmitters varies with species, age, type and size of blood vessel, frequency and duration of stimulation, the tone/pressure of the blood vessel, and in disease. Blood vessel tone/pressure itself can be influenced by the vasocontractile and vasorelaxant actions of purines at different subtypes of P1 and P2 receptors, following release from the endothelium, smooth muscle, erythrocytes and platelets, as well as from perivascular nerves. This review focuses on the role of ATP as a cotransmitter in perivascular nerves in physiological and pathophysiological conditions; neuromodulator roles of purines are also discussed.

Purinergic receptors as future targets for treatment of functional GI disorders

The concept of purinergic signalling arose from experiments designed to find the identity of the non-adrenergic, non-cholinergic (NANC) inhibitory neurotransmitter in the gut.1 However, it has taken many years for...

Investigation of a possible interaction between the heme oxygenase/biliverdin reductase and nitric oxide synthase pathway in murine gastric fundus and jejunum

This study investigated the possible interaction between the heme oxygenase (HO)/biliverdin reductase (BVR) and nitric oxide synthase (NOS) pathway in murine gastric fundus and jejunum, since previous studies have shown that both HO-2 and BVR are expressed in interstitial cells of Cajal (ICCs) and co-localized with neuronal NOS in a large proportion of myenteric neurons along the gastrointestinal tract. Neither HO inhibition by chromium mesoporphyrin (CrMP) nor co-incubation with CO or biliverdin/bilirubin affected nitrergic neurotransmission — i.e. relaxations induced by non-adrenergic non-cholinergic (NANC) nerve stimulation or exogenous NO — under normal physiological conditions. However, biliverdin/bilirubin reversed the inhibitory effect of the superoxide generator LY83583 on exogenous NO-induced relaxations in both tissues. When gastric fundus muscle strips were depleted of the endogenous antioxidant Cu/Zn superoxide dismutase (SOD) by the Cu-chelator DETCA, electrically induced NANC relaxations were also affected by LY82583; however, biliverdin/bilirubin could not substitute for the loss of Cu/Zn SOD when this specific antioxidant enzyme was depleted. In jejunal muscle strips, the combination DETCA plus LY83583 nearly abolished contractile phasic activity and, hence, did not allow studying nitrergic relaxation in these experimental conditions. In conclusion, this study does not establish a role for HO/CO in inhibitory NANC neurotransmission in murine gastric fundus and jejunum under normal physiological conditions. However, the antioxidants biliverdin/bilirubin might play an important role in the protection of the nitrergic neurotransmitter against oxidative stress.

DOCA-salt treatment enhances responses to endothelin-1 in murine corpus cavernosumThis article is one of a selection of papers published in the special issue (part 1 of 2) on Forefronts in Endothelin.

The penis is kept in the flaccid state mainly via a tonic activity of norepinephrine and endothelins (ETs). ET-1 is important in salt-sensitive forms of hypertension. We hypothesized that cavernosal responses to ET-1 are enhanced in deoxycorticosterone acetate (DOCA)-salt mice and that blockade of ETA receptors prevents abnormal responses of the corpus cavernosum in DOCA-salt hypertension. Male C57BL/6 mice were unilaterally nephrectomized and treated for 5 weeks with both DOCA and water containing 1% NaCl and 0.2% KCl. Control mice were uninephrectomized and received tap water with no added salt. Animals received either the ETA antagonist atrasentan (5 mg x day(-1) x kg(-1) body weight) or vehicle. DOCA-salt mice displayed increased systolic blood pressure (SBP), and treatment with atrasentan decreased SBP in DOCA-salt mice. Contractile responses in cavernosal strips from DOCA-salt mice were enhanced by ET-1, phenylephrine, and electrical field stimulation (EFS) of adrenergic nerves, whereas relaxations were not altered by IRL-1620 (an ETB agonist), acetylcholine, sodium nitroprusside, and EFS of nonadrenergic noncholinergic nerves. PD59089 (an ERK1/2 inhibitor), but not Y-27632 (a Rho-kinase inhibitor), abolished enhanced contractions to ET-1 in cavernosum from DOCA-salt mice. Treatment of DOCA-salt mice with atrasentan did not normalize cavernosal responses. In summary, DOCA-salt treatment in mice enhances cavernosal reactivity to contractile, but not to relaxant, stimuli, via ET-1/ETA receptor-independent mechanisms.

Involvement of soluble guanylate cyclase α1 and α2, and SKCa channels in NANC relaxation of mouse distal colon

In distal colon, both nitric oxide (NO) and ATP are involved in non-adrenergic non-cholinergic (NANC) inhibitory neurotransmission. The role of the soluble guanylate cyclase (sGC) isoforms α1β1 and α2β1, and of the small conductance Ca2+-dependent K+ channels (SKCa channels) in the relaxation of distal colon by exogenous NO and by NANC nerve stimulation was investigated, comparing wild type (WT) and sGCα1 knockout (KO) mice. In WT strips, the relaxation induced by electrical field stimulation (EFS) at 1 Hz but not at 2–8 Hz was significantly reduced by the NO-synthase inhibitor l-NAME or the sGC inhibitor ODQ. In sGCα1 KO strips, the EFS-induced relaxation at 1 Hz was significantly reduced and no longer influenced by l-NAME or ODQ. The SKCa channel blocker apamin alone had no inhibitory effect on EFS-induced relaxation, but combined with ODQ or l-NAME, apamin inhibited the relaxation induced by EFS at 2–8 Hz in WT strips and at 8 Hz in sGCα1 KO strips. Relaxation by exogenous NO was significantly attenuated in sGCα1 KO strips, but could still be reduced further by ODQ. Basal cGMP levels were lower in sGCα1 KO strips but NO still significantly increased cGMP levels versus basal. In conclusion, in the absence of sGCα1β1, exogenous NO is able to partially act through sGCα2β1. NO, acting via sGCα1β1, is the principal neurotransmitter in EFS-evoked responses at 1 Hz. At higher stimulation frequencies, NO, acting at sGCα1β1 and/or sGCα2β1, functions together with another transmitter, probably ATP acting via SKCa channels, with some degree of redundancy.

The journey to establish purinergic signalling in the gut

Although the concept of purinergic signalling arose from experiments designed to find the identity of the non-adrenergic, non-cholinergic (NANC) inhibitory neurotransmitter in the gut, it has taken many years for the more general importance of the various roles of ATP as a physiological messenger in the gut to be recognized. Firstly, vasoactive intestitial polypeptide (VIP) and later nitric oxide (NO) were considered the NANC transmitter and it was only later, after the concept of cotransmission was established, that ATP, NO and VIP were recognized as cotransmitters in NANC nerves, although the proportions vary in different gut regions. Recently, many purinoceptor subtypes have been identified on myenteric, submucosal motor, sensory and interneurons involved in synaptic neurotransmission and neuromodulation and reflex activity of several kinds, including ascending excitatory and descending inhibitory reflex pathways. Nucleotide receptors have been shown to be expressed on enteric glial cells and interstitial cells of Cajal. Purinergic mechanosensory transduction, involving release of ATP from mucosal epithelial cells during distension to stimulate subepithelial nerve endings of intrinsic and extrinsic sensory nerves to modulate peristalsis and initiate nociception respectively, is attracting current attention. Exciting new areas of interest about purinergic signalling in the gut include: involvement of purines in development, ageing and regeneration, including the role of stem cells; studies of the involvement of nucleotides in the activity of the gut of invertebrates and lower vertebrates; and the pathophysiology of enteric purinergic signalling in diseases including irritable bowel syndrome, postoperative ileus, oesophageal reflux, constipation, diarrhoea, diabetes, Chaga's and Hirschprung's disease.

Enterik Sinir Sistemi: Nitrik Oksit ve Vazoaktif İntestinal Polipeptid Arasindaki İlişki

Nitric oxide and vasoactive intestinal polypeptide are the primary neurotransmitters of the non-adrenergic non-cholinergic nerves with relaxing effects on smooth muscle cells. The relationship of these two molecules is still a matter of debate. In this review, the results obtained from the studies conducted so far have been presented.