Interplay between PACAP and NO in mouse ileum

Investigation of the Role of Pituitary Adenylate Cyclase-Activating Peptide (PACAP) and Its Type 1 (PAC1) Receptor in Uterine Contractility during Endometritis in Pigs

Uterine inflammation is a common pathology in animals, leading to disturbances in reproductive processes and reduced production profitability. Pituitary adenylate cyclase-activating peptide (PACAP) effects at the uterine level during inflammation are not known. In the current study, we analyzed the relative PACAP type 1 receptor (PAC1R) mRNA transcript and protein abundances in the myometrium (MYO), as well s PACAP and PAC1R involvement in the contractile function of inflamed pig uterus. To that end, E. coli suspension (E. coli group) or saline (SAL group) was injected into the uterine horns or laparotomy was performed (CON group). Eight days after the bacteria injections, severe acute endometritis and a reduced relative abundance of PAC1R protein in the MYO were observed. Compared to the period before PACAP in vitro administration, PACAP (10^-7 M) in the CON and SAL groups decreased in amplitude in the MYO and endometrium (ENDO)/MYO, whereas in the E. coli group, increased amplitude in the MYO and reduced amplitude in the ENDO/MYO were observed. In the E. coli group, PACAP enhanced the amplitude in the MYO (10^-7 M) and decreased the amplitude in the ENDO/MYO (10^-8 M) compared with other groups. PACAP (10^-7 M) increased the frequency of both kinds of strips in the CON and SAL groups compared with the pretreatment period. PACAP (both doses) did not significantly change the frequency in the E. coli group, whereas in response to PACAP (10^-7 M), the frequency was reduced compared to other groups. In the MYO, PAC1R antagonist decreased the amplitude reduction (CON and SAL groups) and reversed a rise in PACAP (10^-7 M)-evoked amplitude (E. coli group). PAC1R blocking reversed (MYO) and abolished (ENDO/MYO) the stimulatory effect of PACAP (10^-7 M) on the frequency (CON and SAL groups). PAC1R antagonist and PACAP (10^-7 M) evoked the appearance of frequency depression in both kinds of strips (E. coli group). In summary, in pigs, severe acute endometritis reduces the relative abundance of PAC1R protein in the MYO, and PAC1R mediates the influence of PACAP on inflamed uterus contractility.

Changes in the Neurochemical Characterization of Enteric Neurons in the Porcine Duodenum After Administration of Low-Dose Salmonella Enteritidis Lipopolysaccharides

Lipopolysaccharides (LPS), also known as lipoglycans or endotoxins, form part of the outer membrane of Gram-negative bacteria. Previous studies have described the various harmful impacts of LPS on humans and animals. Nevertheless, many aspects of these effects are still not fully explained. One of them is the influence of endotoxins on the neurochemical characterization of neurons within the enteric nervous system (ENS), which is found in the intestinal wall and plays important adaptive roles during pathological processes and exposures. In this study, the impact of a low single dose of Salmonella Enteritidis LPS on the duodenal enteric neurons immunoreactive to substance P (SP), vasoactive intestinal polypeptide (VIP), pituitary adenylate cyclase activating peptide (PACAP-27), and cocaine- and amphetamine-regulated transcript (CART) was studied using a double immunofluorescence technique. During the study, it was shown that even a low dose of LPS affects the number of enteric neurons containing the neuropeptides studied, and these changes were dependent on the type of the enteric plexus. The most visible changes concerned the SP-like immunoreactive (LI) neurons in the outer submucous plexus (LPS caused an increase in the percentage of these neurons from15.74 ± 0.61 to 21.72 ± 0.79%). Furthermore, the VIP-LI neurons in the inner submucous plexus were seen to decrease from 12.64 ± 0.83 to 5.96 ± 0.58%. The mechanisms behind these noted fluctuations are not clear, but it may be connected with the pro-inflammatory and neurotoxic activity of LPS.

Antibiotic-induced dysbiosis of the microbiota impairs gut neuromuscular function in juvenile mice

BACKGROUND AND PURPOSE

Gut microbiota is essential for the development of the gastrointestinal system, including the enteric nervous system (ENS). Perturbations of gut microbiota in early life have the potential to alter neurodevelopment leading to functional bowel disorders later in life. We examined the hypothesis that gut dysbiosis impairs the structural and functional integrity of the ENS, leading to gut dysmotility in juvenile mice.

EXPERIMENTAL APPROACH

To induce gut dysbiosis, broad-spectrum antibiotics were administered by gavage to juvenile (3weeks old) male C57Bl/6 mice for 14 days. Bile acid composition in the intestinal lumen was analysed by liquid chromatography-mass spectrometry. Changes in intestinal motility were evaluated by stool frequency, transit of a fluorescent-labelled marker and isometric muscle responses of ileal full-thickness preparations to receptor and non-receptor-mediated stimuli. Alterations in ENS integrity were assessed by immunohistochemistry and Western blot analysis.

KEY RESULTS

Antibiotic treatment altered gastrointestinal transit, luminal bile acid metabolism and bowel architecture. Gut dysbiosis resulted in distorted glial network, loss of myenteric plexus neurons, altered cholinergic, tachykininergic and nitrergic neurotransmission associated with reduced number of nNOS neurons and different ileal distribution of the toll-like receptor TLR2. Functional defects were partly reversed by activation of TLR2 signalling.

CONCLUSIONS AND IMPLICATIONS

Gut dysbiosis caused complex morpho-functional neuromuscular rearrangements, characterized by structural defects of the ENS and increased tachykininergic neurotransmission. Altogether, our findings support the beneficial role of enteric microbiota for ENS homeostasis instrumental in ensuring proper gut neuromuscular function during critical stages of development.

Toll-Like Receptor 4 Modulates Small Intestine Neuromuscular Function through Nitrergic and Purinergic Pathways

Objective: Toll-like receptors (TLRs) play a pivotal role in the homeostatic microflora-host crosstalk. TLR4-mediated modulation of both motility and enteric neuronal survival has been reported mainly for colon with limited information on the role of TLR4 in tuning structural and functional integrity of enteric nervous system (ENS) and in controlling small bowel motility. Methods: Male TLR4 knockout (TLR4^-/-, 9 ± 1 weeks old) and sex- and age-matched wild-type (WT) C57BL/6J mice were used for the experiments. Alterations in ENS morphology and neurochemical code were assessed by immunohistochemistry whereas neuromuscular function was evaluated by isometric mechanical activity of ileal preparations following receptor and non-receptor-mediated stimuli and by gastrointestinal transit. Results: The absence of TLR4 induced gliosis and reduced the total number of neurons, mainly nNOS⁺ neurons, in ileal myenteric plexus. Furthermore, a lower cholinergic excitatory response with an increased inhibitory neurotransmission was found together with a delayed gastrointestinal transit. These changes were dependent on increased ileal non-adrenergic non-cholinergic (NANC) relaxations mediated by a complex neuronal-glia signaling constituted by P2X7 and P2Y1 receptors, and NO produced by nNOS and iNOS. Conclusion: We provide novel evidence that TLR4 signaling is involved in the fine-tuning of P2 receptors controlling ileal contractility, ENS cell distribution, and inhibitory NANC neurotransmission via the combined action of NO and adenosine-5'-triphosphate (ATP). For the first time, this study implicates TLR4 at regulating the crosstalk between glia and neurons in small intestine and helps to define its role in gastrointestinal motor abnormalities during dysbiosis.

Intravesical PAC1 Receptor Antagonist, PACAP(6-38), Reduces Urinary Bladder Frequency and Pelvic Sensitivity in NGF-OE Mice

Chronic NGF overexpression (OE) in the urothelium, achieved through the use of a highly urothelium-specific uroplakin II promoter, stimulates neuronal sprouting in the urinary bladder, produces increased voiding frequency and non-voiding contractions, and referred somatic sensitivity. Additional NGF-mediated pleiotropic changes might contribute to increased voiding frequency and pelvic hypersensitivity in NGF-OE mice such as neuropeptide/receptor systems including PACAP(Adcyap1) and PAC1 receptor (Adcyap1r1). Given the presence of PAC1-immunoreactive fibers and the expression of PAC1 receptor expression in bladder tissues, and PACAP-facilitated detrusor contraction, whether PACAP/receptor signaling contributes to increased voiding frequency and somatic sensitivity was evaluated in NGF-OE mice. Intravesical administration of the PAC1 receptor antagonist, PACAP(6-38) (300 nM), significantly (p ≤ 0.01) increased intercontraction interval (2.0-fold) and void volume (2.5-fold) in NGF-OE mice. Intravesical instillation of PACAP(6-38) also decreased baseline bladder pressure in NGF-OE mice. PACAP(6-38) had no effects on bladder function in WT mice. Intravesical administration of PACAP(6-38) (300 nM) significantly (p ≤ 0.01) reduced pelvic sensitivity in NGF-OE mice but was without effect in WT mice. PACAP/receptor signaling contributes to the increased voiding frequency and pelvic sensitivity observed in NGF-OE mice.

PACAP Modulates Acetylcholine-Elicited Contractions at Nicotinic Neuromuscular Contacts of the Land Snail

In this study, we investigate the potentiating effect of PACAP27 on cholinergic neuromuscular transmission in the recently discovered flexor muscles of the land snail, Helix pomatia. Using immunohistochemistry, we show that PACAP and PAC1 receptors are present in nerve fibers innervating the flexor muscles but not in the muscle itself. We also observed that PACAP27 exerts both pre- and postsynaptic effects on the cholinergic synapse and performed tests using a broad spectrum of chemicals in order to explore the possible intracellular pathways through which PACAP mediates its stimulatory effect. Our pharmacological data demonstrate that PACAP27 presynaptically enhances the release of acetylcholine by activating the adenylate cyclase-cAMP-PKA pathway. Postsynaptically, PACAP27 was found to enhance muscle contractility by PKC-mediated signaling pathway resulting in an increased Ca(2+) release from intracellular stores. These findings suggest that regulation of Ca(2+) release may contribute to the stimulatory effect of PACAP. Our data are the first demonstration of the potentiating effect of PACAP27 at the molluscan excitatory neuromuscular contact.

The Influence of Low Doses of Zearalenone on Distribution of Selected Active Substances in Nerve Fibers Within the Circular Muscle Layer of Porcine Ileum

The aim of this study was to investigate, whether low doses (25 % of no observable adverse effect levels values) of zearalenone (ZEN) can affect the expression of active substances in nerve fibers in the muscular layer of porcine ileum. The study was performed on ten immature pigs divided into two groups: experimental group (n = 5), where zearalenone (10 μg/kg body weight) was given for 42 days, and control animals (n = 5), where placebo was administered. Fragments of ileum of all animals were processed for single-labelling immunofluorescence technique using the antibodies against vasoactive intestinal peptide, neuronal form of nitric oxide synthase, cocaine and amphetamine regulatory peptide, galanin, pituitary adenylate cyclase-activating peptide-27 and substance P. The number of nerve fibers immunoreactive to particular substances was evaluated by the counting of nerves per observation field (0.1 mm²). Low doses of zearalenone caused the clear changes in the expression of substances studied. The number of nerve fibers immunoreactive to the majority of substances increased in experimental animals. The exception was only galanin, the expression of which was less after administration of zearalenone. The obtained results for the first time show that even low doses of zearalenone can affect the nerve fibers in the digestive tract.

Hydrogen sulfide-mediated regulation of contractility in the mouse ileum with electrical stimulation: roles of L-cysteine, cystathionine β-synthase, and K+ channels

Hydrogen sulfide (H2S) is considered to be a signaling molecule. The precise mechanisms underlying H2S-related events, including the producing enzymes and target molecules in gastrointestinal tissues, have not been elucidated in detail. We herein examined the involvement of H2S in contractions induced by repeated electrical stimulations (ES). ES-induced contractions were neurotoxin-sensitive and increased by aminooxyacetic acid, an inhibitor of cystathionine β-synthase (CBS) and cystathionine γ-lyase, but not by D,L-propargylglycine, a selective inhibitor of cystathionine γ-lyase, in an ES trial-dependent manner. ES-induced contractions were markedly decreased in the presence of L-cysteine. This response was inhibited by aminooxyacetic acid and an antioxidant, and accelerated by L-methionine, an activator of CBS. The existence of CBS was confirmed. NaHS transiently inhibited ES- and acetylcholine-induced contractions, and sustainably decreased basal tone for at least 20 min after its addition. The treatment with glibenclamide, an ATP-sensitive K+ channel blocker, reduced both the L-cysteine response and NaHS-induced inhibition of contractions. The NaHS-induced decrease in basal tone was inhibited by apamin, a small conductance Ca2+-activated K+ channel blocker. These results suggest that H2S may be endogenously produced via CBS in ES-activated enteric neurons, and regulates contractility via multiple K+ channels in the ileum.

Inhibition of the mechanical activity of mouse ileum by cactus pear (Opuntia Ficus Indica, L, Mill.) fruit extract and its pigment indicaxanthin

We investigated, using an organ bath technique, the effects of a hydrophilic extract from Opuntia ficus indica fruit pulp (cactus fruit extract, CFE) on the motility of mouse ileum, and researched the extract component(s) responsible for the observed responses. CFE (10-320 mg of fresh fruit pulp equivalents/mL of organ bath) reduced dose-dependently the spontaneous contractions. This effect was unaffected by tetrodotoxin, a neuronal blocker, N(omega)-nitro-l-arginine methyl ester, a nitric oxide synthase blocker, tetraethylammonium, a potassium channel blocker, or atropine, a muscarinic receptor antagonist. CFE also reduced the contractions evoked by carbachol, without affecting the contractions evoked by high extracellular potassium. Indicaxanthin, but not ascorbic acid, assayed at concentrations comparable with their content in CFE, mimicked the CFE effects. The data show that CFE is able to exert direct antispasmodic effects on the intestinal motility. The CFE inhibitory effects do not involve potassium channels or voltage-dependent calcium channels but rather pathways of calcium intracellular release. The fruit pigment indicaxanthin appears to be the main component responsible for the CFE-induced effects.

PACAP/VIP and receptor characterization in micturition pathways in mice with overexpression of NGF in urothelium

Urothelium-specific overexpression of nerve growth factor (NGF) in the urinary bladder of transgenic mice stimulates neuronal sprouting or proliferation in the urinary bladder, produces urinary bladder hyperreflexia, and results in increased referred somatic hypersensitivity. Additional NGF-mediated changes might contribute to the urinary bladder hyperreflexia and pelvic hypersensitivity observed in these transgenic mice such as upregulation of neuropeptide/receptor systems. Chronic overexpression of NGF in the urothelium was achieved through the use of a highly urothelium-specific, uroplakin II promoter. In the present study, we examined pituitary adenylate cyclase activating polypeptide (PACAP), vasoactive intestinal polypeptide (VIP), and associated receptor (PAC1, VPAC1, VPAC2) transcripts or protein expression in urothelium and detrusor smooth muscle and lumbosacral dorsal root ganglia in NGF-overexpressing and littermate wildtype mice using real-time quantitative reverse transcription-polymerase chain reaction and immunohistochemical approaches. Results demonstrate upregulation of PAC1 receptor transcript and PAC1-immunoreactivity in urothelium of NGF-OE mice whereas PACAP transcript and PACAP-immunoreactivity were decreased in urothelium of NGF-OE mice. In contrast, VPAC1 receptor transcript was decreased in both urothelium and detrusor smooth muscle of NGF-OE mice. VIP transcript expression and immunostaining was not altered in urinary bladder of NGF-OE mice. Changes in PACAP, VIP, and associated receptor transcripts and protein expression in micturition pathways resemble some, but not all, changes observed after induction of urinary bladder inflammation known to involve NGF production.

PACAP stimulation of maturational gonadotropin secretion in goldfish involves extracellular signal-regulated kinase, but not nitric oxide or guanylate cyclase, signaling

In goldfish, nitric oxide synthase (NOS) immunoreactivity is present in gonadotropes and extracellular signal-regulated protein kinase (ERK) mediates GnRH stimulation of gonadotropin release and synthesis. In this study, we tested the possible involvement of nitric oxide (NO) and ERK in mediating PACAP-stimulated maturational gonadotropin (GTH-II) release from primary cultures of dispersed goldfish pituitary cells. In static incubation experiments, PACAP-induced GTH-II release was unaffected by two inhibitors of NOS synthase, AGH and 1400W; whereas addition of a NO donor, SNAP, elevated GTH-II secretion. In perifusion experiments, neither NOS inhibitors (AGH, 1400W and 7-Ni) nor NO scavengers (PTIO and rutin hydrate) attenuated the GTH-II response to pulse applications of PACAP. In addition, the GTH-II responses to PACAP and the NO donor SNP were additive while PTIO blocked SNP action. Although dibutyryl cGMP increased GTH-II secretion in static incubation, inhibition of guanylate cyclase (GC), a known down-stream target for NO signaling, did not reduce the GTH-II response to pulse application of PACAP. On the other hand, GTH-II responses to PACAP in perifusion were attenuated in the presence of two inhibitors of ERK kinase (MEK), U 0126 and PD 98059. These results suggest that although increased availability of NO and cGMP can lead to increased GTH-II secretion, MEK/ERK signaling, rather than NOS/NO/GC activation, mediates PACAP action on GTH-II release in goldfish.

PACAP-mediated ATP release from rat urothelium and regulation of PACAP/VIP and receptor mRNA in micturition pathways after cyclophosphamide (CYP)-induced cystitis

Pituitary adenylate cyclase-activating peptide (PACAP) peptides are expressed in micturition pathways, and PACAP expression is regulated by urinary bladder inflammation. Previous physiological studies have demonstrated roles for PACAP27 and PACAP38 in detrusor smooth muscle (DSM) contraction and a PAC1 receptor antagonist reduced cyclophosphamide (CYP)-induced bladder hyperreflexia. To gain insight into PACAP signaling in micturition and regulation with cystitis, receptor characterization by real-time quantitative polymerase chain reaction and physiological assays were performed. PACAP receptors were identified in tissues of rat micturition pathway, including DSM, urothelium (U), and dorsal root ganglia (DRG) after acute (4 h), intermediate (48 h) or chronic (8 days) CYP-induced cystitis. PAC1 messenger RNA expression significantly (p < or = 0.05) increased in U and DSM after 48 h and chronic CYP-induced cystitis after an initial decrease at 4 h. VPAC1 and VPAC2 transcripts increased in U and DSM after acute and intermediate CYP-induced cystitis followed by a decrease in VPAC2 expression with chronic cystitis. Application of PACAP27 (100 nM) to cultured urothelial cells evoked adenosine triphosphate (ATP) release that was blocked by the PAC1 specific antagonist, M65 (1 microM). PACAP38 (100 nM) also evoked ATP release from cultured urothelial cells, but ATP release was less than that observed with PACAP27. PACAP transcripts were increased in the U with intermediate and chronic cystitis, whereas vasoactive intestinal polypeptide (VIP) expression in both tissues was very low and showed no regulation with cystitis. Regulation of PACAP, galanin, and substance P transcripts expression was observed in lumbosacral DRG, but no regulation for VIP was observed. The current data demonstrate PACAP and PAC1 regulation in micturition pathways with inflammation and PACAP-mediated ATP release from urothelium.

Involvements of PHI-nitric oxide and PACAP-BK channel in the sustained relaxation of mouse gastric fundus

The roles of nitric oxide (NO) and K(+) channels in sustained relaxation induced by electrical field stimulation (EFS) in the presence of atropine and guanethidine were studied in circular muscle strips of mouse gastric fundus. In the wild-type mouse, N(G)-nitro-l-arginine (l-nitroarginine), a nitric oxide synthase inhibitor, significantly inhibited the sustained relaxation in addition to the rapid relaxation. The sustained relaxation in pituitary adenylate cyclase-activating peptide (PACAP)-knockout mouse, which was smaller than that of the wild-type mouse, was also inhibited by l-nitroarginine. l-Nitroarginine inhibited the relaxation induced by the peptide histidine isoleucine (PHI), but not that induced by PACAP. S-Nitroso-N-acetyl-dl-penicillamine (SNAP), a NO donor, -induced relaxation was not affected by PACAP(6-38). EFS-induced sustained relaxation was inhibited by iberiotoxin, a big conductance calcium-activated K(+) (BK) channel inhibitor, but not by apamin, a small conductance calcium-activated K(+) (SK) channel inhibitor, and glibenclamide, an ATP-sensitive K(+) channel inhibitor. The relaxation that remained after the iberiotoxin-treatment was significantly inhibited by l-nitroarginine. Iberiotoxin inhibited PACAP-induced relaxation, while it had no effect on both PHI- and SNAP-induced relaxation. Immunoreactivities to anti-BK channel and anti-PHI antibodies were found in the circular muscle and the myenteric plexus layers, respectively. These results suggest interplay between PHI and NO in the sustained relaxation of the mouse gastric fundus, and that BK channels are involved in the PACAP-component of the sustained relaxation.

Cannabinoid CB(1) receptor activation modulates spontaneous contractile activity in mouse ileal longitudinal muscle

The purpose of the present study was to examine whether cannabinoid receptor agonists influence spontaneous contractile activity of longitudinal muscle in mouse ileum in vitro. Isolated segments of mouse ileum displayed spontaneous contractions with an amplitude and frequency of about 300 mg and 30 cpm, respectively. The endocannabinoid anandamide (1-100 microM), the selective cannabinoid CB(1) receptor agonist, ACEA (0.1 microM-10 microM), but not the selective cannabinoid CB(2) receptor agonist, JWH 133 (0.1 microM-10 microM), reduced in a concentration-dependent manner the spontaneous mechanical activity. The inhibitory effect consisted in a decrease of the mean amplitude of longitudinal spontaneous contractions, without changes in the resting tone. The inhibitory effect induced by cannabinoids was significantly antagonized by the selective cannabinoid CB(1) receptor antagonist, SR141716A (0.1 microM), but not by the selective cannabinoid CB(2) receptor antagonist, AM630 (0.1 microM). None of the cannabinoid antagonists, at the concentration used, did affect the spontaneous mechanical activity. The ACEA-induced reduction of spontaneous contractions was almost abolished by tetrodotoxin, atropine or apamin and it was unaffected by hexamethonium or N(omega)-nitro-l-arginine methyl ester (l-NAME), inhibitor of nitric oxide synthase. The myogenic contractions evoked by carbachol were not affected by ACEA. In conclusion, the present results suggest that activation of neural cannabinoid CB(1) receptors may play a role in the control of spontaneous mechanical activity through inhibition of acetylcholine release from cholinergic nerve. Activation of small conductance Ca(2+)-dependent K(+) channels is involved in this action.

Regulation of basal tone, relaxation and contraction of the lower oesophageal sphincter. Relevance to drug discovery for oesophageal disorders

The lower oesophageal sphincter (LOS) is a specialized region of the oesophageal circular smooth muscle that allows the passage of a swallowed bolus to the stomach and prevents the reflux of gastric contents into the oesophagus. The anatomical arrangement of the LOS includes semicircular clasp fibres adjacent to the lesser gastric curvature and sling fibres following the greater gastric curvature. Such anatomical arrangement together with an asymmetric intrinsic innervation and distinct proportion of neurotransmitters in both regions produces an asymmetric pressure profile. The LOS tone is myogenic in origin and depends on smooth muscle properties that lead to opening of L-type Ca(2+) channels; however it can be modulated by enteric motor neurons, the parasympathetic and sympathetic extrinsic nervous system and several neurohumoral substances. Nitric oxide synthesized by neuronal NOS is the main inhibitory neurotransmitter involved in LOS relaxation. Different putative neurotransmitters have been proposed to play a role together with NO. So far, only ATP or related purines have shown to be co-transmitters with NO. Acetylcholine and tachykinins are involved in the LOS contraction acting through acetylcholine M(3) and tachykinin NK(2) receptors. Nitric oxide can also be involved in the regulation of LOS contraction. The understanding of the mechanisms that originate and modulate LOS tone, relaxation and contraction and the characterization of neurotransmitters and receptors involved in LOS function are important to develop new pharmacological tools to treat primary oesophageal motor disorders and gastro-oesophageal reflux disease.

Role for pituitary adenylate cyclase activating polypeptide in cystitis-induced plasticity of micturition reflexes

Pituitary adenylate cyclase activating polypeptide (PACAP) peptides are expressed and regulated in sensory afferents of the micturition pathway. Although these studies have implicated PACAP in bladder control, the physiological significance of these observations has not been firmly established. To clarify these issues, the roles of PACAP and PACAP signaling in micturition and cystitis were examined in receptor characterization and physiological assays. PACAP receptors were identified in various tissues of the micturition pathway, including bladder detrusor smooth muscle and urothelium. Bladder smooth muscle expressed heterogeneously PAC(1)null, PAC(1)HOP1, and VPAC(2) receptors; the urothelium was more restricted in expressing preferentially the PAC(1) receptor subtype only. Immunocytochemical studies for PAC(1) receptors were consistent with these tissue distributions. Furthermore, the addition of 50-100 nM PACAP27 or PACAP38 to isolated bladder strips elicited transient contractions and sustained increases in the amplitude of spontaneous phasic contractions. Treatment of the bladder strips with tetrodotoxin (1 muM) did not alter the spontaneous phasic contractions suggesting direct PACAP effects on bladder smooth muscle. PACAP also increased the amplitude of nerve-evoked contractions. By contrast, vasoactive intestinal polypeptide had no direct effects on bladder smooth muscle. In a rat cyclophosphamide (CYP)-induced cystitis paradigm, intrathecal or intravesical administration of PAC(1) receptor antagonist, PACAP6-38, reduced cystitis-induced bladder overactivity. In summary, these studies support roles for PACAP in micturition and suggest that inflammation-induced plasticity in PACAP expression in peripheral and central micturition pathways contribute to bladder dysfunction with cystitis.

Impact of caveolin-1 knockout on NANC relaxation in circular muscles of the mouse small intestine compared with longitudinal muscles

Recently, we showed that caveolin-1 (cav1) knockout mice (Cav1(-/-) mice) have impaired nitric oxide (NO) function in the longitudinal muscle (LM) layer of the small intestine. The defect was a reduced responsiveness of the muscles to NO compensated by an increase in the function of apamin-sensitive, nonadrenergic, noncholinergic (NANC) mediators. In the present study, we examined similarly the effects of cav1 knockout on the relaxation in circular muscle (CM) of the mouse small intestine. CM of Cav1(-/-) mice also showed defective NO function, but less than in LM, as well as more activation of apamin-sensitive NANC mediators. CM of Cav1(-/-) mice, like LM, lacked cav1 but retained small amounts of cav3 and caveolae in the outer CM layer. In addition, we also examined the effects of a soluble guanylate cyclase inhibitor, 1H-[1,2,4]oxadiazolo-[4,3-alpha]quinazolin-1-one (ODQ), on electric field stimulation (EFS)-mediated relaxation in both LM and CM. ODQ had an effect similar to the block of NO synthesis. Moreover, we compared the actions of two NO donors in the LM and CM of control and Cav1(-/-) mice. Similar to LM, CM of Cav1(-/-) mice showed a reduced responsiveness to the NO donors sodium nitroprusside and S-nitroso-N-acetyl penicillamine. However, both ODQ and apamin blocked the inhibitory effects of the NO donors in LM, whereas apamin had no effect in CM. In conclusion, cav1 knockout affects NO function in both LM and CM, but its effects in CM differ significantly.

Caveolin-1 gene knockout impairs nitrergic function in mouse small intestine

Caveolin-1 is a plasma membrane-associated protein that is responsible for caveolae formation. It plays an important role in the regulation of the function of different signaling molecules, among which are the different isoforms of nitric oxide synthase (NOS). Nitric oxide (NO) is known to be an important inhibitory mediator in the mouse gut. Caveolin-1 knockout mice (Cav1(-/-)) were used to examine the effect of caveolin-1 absence on the NO function in the mouse small intestine (ileum and jejunum) compared to their genetic controls and BALB/c controls. Immunohistochemical staining showed loss of caveolin-1 and NOS in the jejunal smooth muscles and myenteric plexus interstitial cells of Cajal (ICC) of Cav1(-/-) mice; however, nNOS immunoreactive nerves were still present in myenteric ganglia. Under nonadrenergic noncholinergic (NANC) conditions, small intestinal tissues from Cav1(-/-) mice relaxed to electrical field stimulation (EFS), as did tissues from control mice. Relaxation of tissues from control mice was markedly reduced by N-omega-nitro-L-arginine (10(-4) M), but relaxation of Cav1(-/-) animals was affected much less. Also, Cav1(-/-) mice tissues showed reduced relaxation responses to sodium nitroprusside (100 microM) compared to controls; yet there were no significant differences in the relaxation responses to 8-bromoguanosine-3': 5'-cyclic monophosphate (100 microM). Apamin (10(-6) M) significantly reduced relaxations to EFS in NANC conditions in Cav1(-/-) mice, but not in controls. The data from this study suggest that caveolin-1 gene knockout causes alterations in the smooth muscles and the ICC, leading to an impaired NO function in the mouse small intestine that could possibly be compensated by apamin-sensitive inhibitory mediators.

Mechanisms underlying the inhibitory effects induced by pituitary adenylate cyclase-activating peptide in mouse ileum

The aim of this study was to investigate the signal transduction mechanisms underlying the inhibitory effect induced by pituitary adenylate cyclase activating peptide (PACAP-27) on the spontaneous contractile activity of longitudinal muscle of mouse ileum. Mechanical activity of ileal segments was recorded isometrically in vitro. PACAP-27 produced apamin-sensitive reduction of the amplitude of the spontaneous contractions. 9-(Tetrahydro-2-furanyl)-9H-purin-6-amine (SQ 22,536), adenylate cyclase inhibitor, or genistein and tyrphostin 25, tyrosine kinase inhibitors, had negligible effects on PACAP-27-induced inhibition. PACAP-27 effects were significantly inhibited by U-73122, phopholipase C (PLC) inhibitor, by 2-aminoethoxy-diphenylborate (2-APB), permeable blocker of inositol 1,4,5-triphosphate (IP3) receptors and by depletion of Ca2+ stores with cyclopiazonic acid or thapsigargin. Ryanodine did not reduce PACAP-27-inhibitory responses. We suggest that, in mouse ileum, the inhibitory responses to PACAP-27 involve stimulation of PLC, increased production of IP3 and localised Ca2+ release from intracellular stores, which could provide the opening of apamin-sensitive Ca2+-dependent K+ channels.

Gastrointestinal Function Regulation by Nitrergic Efferent Nerves

Gastrointestinal (GI) smooth muscle responses to stimulation of the nonadrenergic noncholinergic inhibitory nerves have been suggested to be mediated by polypeptides, ATP, or another unidentified neurotransmitter. The discovery of nitric-oxide (NO) synthase inhibitors greatly contributed to our understanding of mechanisms involved in these responses, leading to the novel hypothesis that NO, an inorganic, gaseous molecule, acts as an inhibitory neurotransmitter. The nerves whose transmitter function depends on the NO release are called "nitrergic", and such nerves are recognized to play major roles in the control of smooth muscle tone and motility and of fluid secretion in the GI tract. Endothelium-derived relaxing factor, discovered by Furchgott and Zawadzki, has been identified to be NO that is biosynthesized from l-arginine by the constitutive NO synthase in endothelial cells and neurons. NO as a mediator or transmitter activates soluble guanylyl cyclase and produces cyclic GMP in smooth muscle cells, resulting in relaxation of the vasculature. On the other hand, NO-induced GI smooth muscle relaxation is mediated, not only by cyclic GMP directly or indirectly via hyperpolarization, but also by cyclic GMP-independent mechanisms. Numerous cotransmitters and cross talk of autonomic efferent nerves make the neural control of GI functions complicated. However, the findingsrelated to the nitrergic innervation may provide us a new way of understanding GI tract physiology and pathophysiology and might result in the development of new therapies of GI diseases. This review article covers the discovery of nitrergic nerves, their functional roles, and pathological implications in the GI tract.

Mechanisms underlying the nitric oxide inhibitory effects in mouse ileal longitudinal muscle

We investigated the mechanisms involved in the nitric oxide (NO)-induced inhibitory effects on longitudinal smooth muscle of mouse ileum, using organ bath technique. Exogenously applied NO, delivered as sodium nitroprusside (SNP; 0.1–100 µmol/L) induced a concentration-dependent reduction of the ileal spontaneous contractions. 1H-[1,2,4]oxadiazolol[4,3,a]quinoxalin-1-one (ODQ; 1 µmol/L), a guanilyl cyclase inhibitor, reduced the SNP-induced effects. Tetraethylammonium chloride (20 mmol/L), a non-selective K+ channel blocker, and charybdotoxin (0.1 µmol/L), blocker of large conductance Ca2+-dependent K+ channels, significantly reduced SNP-induced inhibitory effects. In contrast, apamin (0.1 µmol/L), blocker of small conductance Ca2+-dependent K+ channels, was not able to affect the response to SNP. Ciclopiazonic acid (10 µmol/L) or thapsigargin (0.1 µmol/L), sarcoplasmatic reticulum Ca2+-ATPase inhibitors, decreased the SNP-inhibitory effects. Ryanodine (10 µmol/L), inhibitor of Ca2+ release from ryanodine-sensitive intracellular stores, significantly reduced the SNP inhibitory effects. The membrane permeable analogue of cGMP, 8-bromoguanosine 3′,5′-cyclic monophosphate (100 µmol/L), also reduced spontaneous mechanical activity, and its effect was antagonized by ryanodine. The present study suggests that NO causes inhibitory effects on longitudinal smooth muscle of mouse ileum through cGMP which in turn would activate the large conductance Ca2+-dependent K+ channels, via localized ryanodine-sensitive Ca2+ release.Key words: nitric oxide, mouse ileum, potassium channels, calcium stores.