Practicality of multilayer round window reinforcement in the surgical management of superior semicircular canal dehiscence syndrome: a case report of long-term follow-up.

Several surgical techniques have been documented for approaching and repairing superior semicircular canal dehiscence syndrome (SCDS). These techniques encompass the trans-middle cranial fossa, transmastoid, endoscopic approaches, and round window reinforcement (RWR). RWR entails the placement of connective tissue with or without cartilage and around the round window niche, restricting the round window's movement to minimize the 3rd window effect and restore the bony labyrinth closer to its normal state. We employed the multilayer RWR technique, resulting in significant postoperative improvement and long-lasting effects for 3.7 years in 2 cases. Here, we present the clinical findings, surgical procedures, and the effectiveness of multilayer RWR. This technique can be the initial choice for surgical treatments of SCDS due to its high effectiveness, longer-lasting effect, and minimal risk of surgical complications.

Electrical impedance myography detects dystrophin-related muscle changes in mdx mice.

BACKGROUND: The lack of functional dystrophin protein in Duchenne muscular dystrophy (DMD) causes chronic skeletal muscle inflammation and degeneration. Therefore, the restoration of functional dystrophin levels is a fundamental approach for DMD therapy. Electrical impedance myography (EIM) is an emerging tool that provides noninvasive monitoring of muscle conditions and has been suggested as a treatment response biomarker in diverse indications. Although magnetic resonance imaging (MRI) of skeletal muscles has become a standard measurement in clinical trials for DMD, EIM offers distinct advantages, such as portability, user-friendliness, and reduced cost, allowing for remote monitoring of disease progression or response to therapy. To investigate the potential of EIM as a biomarker for DMD, we compared longitudinal EIM data with MRI/histopathological data from an X-linked muscular dystrophy (mdx) mouse model of DMD. In addition, we investigated whether EIM could detect dystrophin-related changes in muscles using antisense-mediated exon skipping in mdx mice. METHODS: The MRI data for muscle T2, the magnetic resonance spectroscopy (MRS) data for fat fraction, and three EIM parameters with histopathology were longitudinally obtained from the hindlimb muscles of wild-type (WT) and mdx mice. In the EIM study, a cell-penetrating peptide (Pip9b2) conjugated antisense phosphorodiamidate morpholino oligomer (PPMO), designed to induce exon-skipping and restore functional dystrophin production, was administered intravenously to mdx mice. RESULTS: MRI imaging in mdx mice showed higher T2 intensity at 6 weeks of age in hindlimb muscles compared to WT mice, which decreased at ≥ 9 weeks of age. In contrast, EIM reactance began to decline at 12 weeks of age, with peak reduction at 18 weeks of age in mdx mice. This decline was associated with myofiber atrophy and connective tissue infiltration in the skeletal muscles. Repeated dosing of PPMO (10 mg/kg, 4 times every 2 weeks) in mdx mice led to an increase in muscular dystrophin protein and reversed the decrease in EIM reactance. CONCLUSIONS: These findings suggest that muscle T2 MRI is sensitive to the early inflammatory response associated with dystrophin deficiency, whereas EIM provides a valuable biomarker for the noninvasive monitoring of subsequent changes in skeletal muscle composition. Furthermore, EIM reactance has the potential to monitor dystrophin-deficient muscle abnormalities and their recovery in response to antisense-mediated exon skipping.

Orexin 2 receptor-selective agonist danavorexton (TAK-925) promotes wakefulness in non-human primates and healthy individuals.

The orexin 2 receptor-selective agonist danavorexton (TAK-925) has been shown to produce wake-promoting effects in wild-type mice, narcolepsy-model mice, and individuals with narcolepsy type 1 and type 2. Here, we report wake-promoting effects of danavorexton in non-human primates and healthy men during their sleep phase. Electroencephalogram analyses revealed that subcutaneous administration of danavorexton significantly increased wakefulness in common marmosets (p < 0.05 at 0.1 mg kg-1 , and p < 0.001 at 1 mg kg-1 and 10 mg kg-1 ) and cynomolgus monkeys (p ≤ 0.05 at 1 mg kg-1 and 3 mg kg-1 ). In a phase 1b crossover, randomized, double-blind, placebo-controlled and active-controlled study in sleep-deprived healthy participants (ClinicalTrials.gov identifier: NCT03522506), modafinil 300 mg (used to demonstrate assay sensitivity) and continuous infusion of danavorexton 44 mg and danavorexton 112 mg showed statistically superior wake-promoting effects to placebo (n = 18). Measured using the Maintenance of Wakefulness Test, mean (standard deviation) sleep latencies during infusion of danavorexton 44 mg, danavorexton 112 mg and placebo were 21.4 (8.9), 31.8 (3.2) and 9.2 (6.4) min, respectively. Least-squares mean difference from placebo in average sleep latency was 16.8 min with danavorexton 44 mg and 30.2 min with danavorexton 112 mg (both p < 0.001). Karolinska Sleepiness Scale scores were statistically significantly lower (indicating decreased sleepiness) for participants receiving danavorexton than for those receiving placebo during infusion (danavorexton 44 mg, p = 0.010; danavorexton 112 mg, p < 0.001). Together, these results indicate that an orexin 2 receptor agonist increases wakefulness in non-human primates and healthy individuals during their sleep phase.

Urine titin as a novel biomarker for Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD) is the most severe form of muscular dystrophy that is caused by lack of dystrophin, a critical structural protein in skeletal muscle. DMD treatments, and quantitative biomarkers to assess the efficacy of potential treatments, are urgently needed. Previous evidence has shown that titin, a muscle cell protein, is increased in the urine of patients with DMD, suggesting its usefulness as a DMD biomarker. Here, we demonstrated that the elevated titin in urine is directly associated with the lack of dystrophin and urine titin responses to drug treatment. We performed a drug intervention study using mdx mice, a DMD mouse model. We showed that mdx mice, which lack dystrophin due to a mutation in exon 23 of the Dmd gene, have elevated urine titin. Treatment with an exon skipper that targets exon 23 rescued muscle dystrophin level and dramatically decreased urine titin in mdx mice and correlates with dystrophin expression. We also demonstrated that titin levels were significantly increased in the urine of patients with DMD. This suggests that elevated urine titin level might be a hallmark of DMD and a useful pharmacodynamic marker for therapies designed to restore dystrophin levels.

Discovery of a Potent and Orally Bioavailable Melatonin Receptor Agonist.

To develop potent and orally bioavailable melatonin receptor (MT1 and MT2) agonists, a novel series of 5-6-5 tricyclic derivatives was designed, synthesized, and evaluated. The synthesized indeno[5,4-d][1,3]oxazole, cyclopenta[c]pyrazolo[1,5-a]pyridine, indeno[5,4-d][1,3]thiazole, and cyclopenta[e]indazole derivatives showed potent binding affinities for MT1/MT2 receptors. Further optimization of these derivatives based on their metabolic stability in human hepatic microsomes revealed that (S)-3b ((S)-N-[2-(2-methyl-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]acetamide) was a potent MT1 and MT2 ligand (MT1, Ki = 0.031 nM; MT2, Ki = 0.070 nM) with good metabolic stability in human hepatic microsomes. Moreover, compound (S)-3b showed good BBB permeability in rats, and its in vivo pharmacological effects were confirmed by its sleep-promotion ability in cats.

TAK-915, a phosphodiesterase 2A inhibitor, ameliorates the cognitive impairment associated with aging in rodent models.

Changes in the cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) signaling are implicated in older people with dementia. Drugs that modulate the cAMP/cGMP levels in the brain might therefore provide new therapeutic options for the treatment of cognitive impairment in aging and elderly with dementia. Phosphodiesterase 2A (PDE2A), which is highly expressed in the forebrain, is one of the key phosphodiesterase enzymes that hydrolyze cAMP and cGMP. In this study, we investigated the effects of PDE2A inhibition on the cognitive functions associated with aging, such as spatial learning, episodic memory, and attention, in rats with a selective, brain penetrant PDE2A inhibitor, N-{(1S)-1-[3-fluoro-4-(trifluoromethoxy)phenyl]-2-methoxyethyl-7-methoxy-2-oxo-2,3-dihydropyrido[2,3-b]pyrazine-4(1H)-carboxamide (TAK-915). Repeated treatment with TAK-915 (3 mg/kg/day, p.o. for 4 days) significantly reduced escape latency in aged rats in the Morris water maze task compared to the vehicle treatment. In the novel object recognition task, TAK-915 (1, 3, and 10 mg/kg, p.o.) dose-dependently attenuated the non-selective muscarinic antagonist scopolamine-induced memory deficits in rats. In addition, oral administration of TAK-915 at 10 mg/kg significantly improved the attentional performance in middle-aged, poorly performing rats in the 5-choice serial reaction time task. These findings suggest that PDE2A inhibition in the brain has the potential to ameliorate the age-related cognitive decline.

TAK-071, a muscarinic M1 receptor positive allosteric modulator, attenuates scopolamine-induced quantitative electroencephalogram power spectral changes in cynomolgus monkeys.

Activation of the muscarinic M1 receptor is a promising approach to improve cognitive deficits associated with cholinergic dysfunction in Alzheimer's disease, dementia with Lewy bodies, and schizophrenia. TAK-071 is an M1-selective positive allosteric modulator that improves cognitive deficits induced by scopolamine, a non-selective muscarinic receptor antagonist, with reduced side effects on gastrointestinal function in rats. In this study, we explored changes in quantitative electroencephalography (qEEG) power bands, with or without scopolamine challenge, as a non-invasive translational biomarker for the effect of TAK-071 in cynomolgus monkeys. Scopolamine has been reported to increase theta and delta power bands and decrease alpha power band in healthy volunteers. In line with the clinical observations, scopolamine (25-100 µg/kg, subcutaneous administration [s.c.]) increased theta and delta power bands in cynomolgus monkeys in a dose-dependent manner, whereas it had the opposite effect on alpha power band. The effects of TAK-071 on scopolamine (25 µg/kg, s.c.)-induced qEEG spectral changes were examined using an acetylcholinesterase inhibitor donepezil and a muscarinic M1/M4 receptor agonist xanomeline as comparative cholinomimetics. TAK-071 (0.3-3 mg/kg, oral administration [p.o.]), donepezil (3 mg/kg, p.o.), and xanomeline (1 mg/kg, s.c.) suppressed the scopolamine-induced increases in alpha, theta, and delta power bands. These results suggest that changes in specific qEEG power bands, in particular theta and delta power bands in the context of scopolamine challenge, could be used as translational biomarkers for the evaluation of TAK-071 in clinical studies.

Phosphodiesterase 2A Inhibitor TAK-915 Ameliorates Cognitive Impairments and Social Withdrawal in N-Methyl-d-Aspartate Receptor Antagonist-Induced Rat Models of Schizophrenia.

The pathophysiology of schizophrenia has been associated with glutamatergic dysfunction. Modulation of the glutamatergic signaling pathway, including N-methyl-d-aspartate (NMDA) receptors, can provide a new therapeutic target for schizophrenia. Phosphodiesterase 2A (PDE2A) is highly expressed in the forebrain, and is a dual substrate enzyme that hydrolyzes both cAMP and cGMP, which play pivotal roles as intracellular second messengers downstream of NMDA receptors. Here we characterize the in vivo pharmacological profile of a selective and brain-penetrant PDE2A inhibitor, (N-{(1S)-1-[3-fluoro-4-(trifluoromethoxy)phenyl]-2-methoxyethyl}-7-methoxy-2-oxo-2,3-dihydropyrido[2,3-b]pyrazine-4(1H)-carboxamide) (TAK-915) as a novel treatment of schizophrenia. Oral administration of TAK-915 at 3 and 10 mg/kg significantly increased cGMP levels in the frontal cortex, hippocampus, and striatum of rats. TAK-915 at 10 mg/kg significantly upregulated the phosphorylation of α-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid receptor subunit GluR1 in the rat hippocampus. TAK-915 at 3 and 10 mg/kg significantly attenuated episodic memory deficits induced by the NMDA receptor antagonist (+)-MK-801 hydrogen maleate (MK-801) in the rat passive avoidance test. TAK-915 at 10 mg/kg significantly attenuated working memory deficits induced by MK-801 in the rat radial arm maze test. Additionally, TAK-915 at 10 mg/kg prevented subchronic phencyclidine-induced social withdrawal in social interaction in rats. In contrast, TAK-915 did not produce antipsychotic-like activity; TAK-915 had little effect on MK-801- or methamphetamine-induced hyperlocomotion in rats. These results suggest that TAK-915 has a potential to ameliorate cognitive impairments and social withdrawal in schizophrenia.

Discovery of a Novel Series of Pyrazolo[1,5-a]pyrimidine-Based Phosphodiesterase 2A Inhibitors Structurally Different from N-((1S)-1-(3-Fluoro-4-(trifluoromethoxy)phenyl)-2-methoxyethyl)-7-methoxy-2-oxo-2,3-dihydropyrido[2,3-b]pyrazine-4(1H)-carboxamide (TAK-915), for the Treatment of Cognitive Disorders.

It has been hypothesized that selective inhibition of phosphodiesterase (PDE) 2A could potentially be a novel approach to treat cognitive impairment in neuropsychiatric and neurodegenerative disorders through augmentation of cyclic nucleotide signaling pathways in brain regions associated with learning and memory. Following our earlier work, this article describes a drug design strategy for a new series of lead compounds structurally distinct from our clinical candidate 2 (TAK-915), and subsequent medicinal chemistry efforts to optimize potency, selectivity over other PDE families, and other preclinical properties including in vitro phototoxicity and in vivo rat plasma clearance. These efforts resulted in the discovery of N-((1S)-2-hydroxy-2-methyl-1-(4-(trifluoromethoxy)phenyl)propyl)-6-methyl-5-(3-methyl-1H-1,2,4-triazol-1-yl)pyrazolo[1,5-a]pyrimidine-3-carboxamide (20), which robustly increased 3',5'-cyclic guanosine monophosphate (cGMP) levels in the rat brain following an oral dose, and moreover, attenuated MK-801-induced episodic memory deficits in a passive avoidance task in rats. These data provide further support to the potential therapeutic utility of PDE2A inhibitors in enhancing cognitive performance.

Autophosphorylation of Specific Threonine and Tyrosine Residues in Arabidopsis CERK1 is Essential for the Activation of Chitin-Induced Immune Signaling.

Pattern recognition receptors on the plant cell surface mediate the recognition of microbe/damage-associated molecular patterns (MAMPs/DAMPs) and activate downstream immune signaling. Autophosphorylation of signaling receptor-like kinases is a critical event for the activation of downstream responses but the function of each phosphorylation site in the regulation of immune signaling is not well understood. In this study, 41 Ser/Thr/Tyr and 15 Ser/Thr residues were identified as in vitro and in vivo autophosphorylation sites of Arabidopsis CERK1, which is essential for chitin signaling. Comprehensive analysis of transgenic plants expressing mutated CERK1 genes for each phosphorylation site in the cerk1-2 background indicated that the phosphorylation of T479 in the activation segment and Y428 located upstream of the catalytic loop is important for the activation of chitin-triggered defense responses. Contribution of the phosphorylation of T573 to the chitin responses was also suggested. In vitro evaluation of kinase activities of mutated kinase domains indicated that the phosphorylation of T479 and T573 is directly involved in the regulation of kinase activity of CERK1 but the phosphorylation of Y428 regulates chitin signaling independently of the regulation of kinase activity. These results indicated that the phosphorylation of specific residues in the kinase domain contributes to the regulation of downstream signaling either through the regulation of kinase activity or the different mechanisms, e.g. regulation of protein-protein interactions.

Regulatory mechanism of the gastric hyperemic response following barrier disruption: roles of cyclooxygenase-1, the prostaglandin E2/EP1 receptor and sensory neurons.

We herein reviewed the mechanism underlying the gastric hyperemic response following barrier disruption, with a focus on cyclooxygenase (COX) isozymes, prostaglandin (PG) E2, and capsaicin-sensitive afferent neurons. Mucosal damage was induced by exposing the stomach to 20 mM taurocholate (TC) with 50 mM HCl. The TC treatment disrupted surface epithelial cells, and then increased acid back-diffusion and mucosal blood flow (GMBF) in the stomachs of rats or wild-type mice. This hyperemic response in the rat stomach was inhibited by indomethacin without affecting acid back-diffusion, which resulted in the aggravation of lesions. The effect of indomethacin was mimicked by loxoprofen and the selective COX-1 inhibitor, SC-560, but not by the selective COX-2 inhibitor, celecoxib. The GMBF responses induced by TC were similarly observed in the stomachs of wild-type mice and EP3 receptor knockout mice, but not in mice lacking the EP1 receptor or pretreated with an EP1 antagonist. The increase in the GMBF response associated with acid back-diffusion after the TC treatment was also inhibited by the chemical ablation of capsaicin-sensitive afferent neurons, but not capsazepine, a TRPV1 antagonist. Thus, endogenous PGE2 produced by COX-1 plays a role in the gastric hyperemic response following barrier disruption of the stomach by interacting with capsaicin-sensitive afferent neurons, mainly through EP1 receptors, and facilitating the GMBF response to acid back-diffusion. These findings have also contributed to a deeper understanding of mucosal defensive mechanisms following barrier disruption and the development of new strategies for the treatment of gastrointestinal diseases.

Selective regulation of the chitin-induced defense response by the Arabidopsis receptor-like cytoplasmic kinase PBL27.

Recognition of microbe-associated molecular patterns (MAMPs) initiates pattern-triggered immunity in host plants. Pattern recognition receptors (PRRs) and receptor-like cytoplasmic kinases (RLCKs) are the major components required for sensing and transduction of these molecular patterns. However, the regulation of RLCKs by PRRs and their specificity remain obscure. In this study we show that PBL27, an Arabidopsis ortholog of OsRLCK185, is an immediate downstream component of the chitin receptor CERK1 and contributes to the regulation of chitin-induced immunity in Arabidopsis. Knockout of PBL27 resulted in the suppression of several chitin-induced defense responses, including the activation of MPK3/6 and callose deposition as well as in disease resistance against fungal and bacterial infections. On the other hand, the contribution of PBL27 to flg22 signaling appears to be very limited, suggesting that PBL27 selectively regulates defense signaling downstream of specific PRR complexes. In vitro phosphorylation experiments showed that CERK1 preferentially phosphorylated PBL27 in comparison to BIK1, whereas phosphorylation of PBL27 by BAK1 was very low compared with that of BIK1. Thus, the substrate specificity of the signaling receptor-like kinases, CERK1 and BAK1, may determine the preference of downstream RLCKs.

Discovery of potent, selective, orally active benzoxazepine-based Orexin-2 receptor antagonists.

During our efforts to identify a series of potent, selective, orally active human Orexin-2 Receptor (OX2R) antagonists, we elucidated structure-activity relationship (SAR) on the 7-position of a benzoxazepine scaffold by utilizing Hammett σ(p) and Hansch-Fujita π value as aromatic substituent constants. The attempts led to the discovery of compound 1m, possessing good in vitro potency with over 100-fold selectivity against OX1R, good metabolic stability in human and rat liver microsome, good oral bioavailability in rats, and in vivo antagonistic activity in rats by oral administration.

Synthesis of a novel series of tricyclic dihydrofuran derivatives: discovery of 8,9-dihydrofuro[3,2-c]pyrazolo[1,5-a]pyridines as melatonin receptor (MT1/MT2) ligands.

Novel tricyclic dihydrofuran derivatives were designed, synthesized, and evaluated as melatonin receptor (MT(1)/MT(2)) ligands based on the previously reported 1,6-dihydro-2H-indeno[5,4-b]furan 1a. By screening the central tricyclic cores, we identified 8,9-dihydrofuro[3,2-c]pyrazolo[1,5-a]pyridine as a potent scaffold with a high ligand-lipophilicity efficiency (LLE) value. Subsequent optimization of the side chains led to identification of the potent MT(1)/MT(2) agonist 4d (MT(1), K(i) = 0.062 nM; MT(2), K(i) = 0.420 nM) with good oral absorption and blood-brain barrier (BBB) penetration in rats. The oral administration of compound 4d exhibited a sleep-promoting action in freely moving cats at 0.1 mg/kg.

[IgG4-related Mikulicz's disease: a report of 3 cases].

INTRODUCTION: We report three cases of hyper-IgG4 disease with synchronous or asynchronous lymphocytic infiltration onset, IgG4 positive plasma cell infiltration, and fibril formation in multiple exocrine glands and extranodal organs. IgG4-related sialadenitis attracting recent attention has yet to be clarified as a clinical entity. CASE REPORT: Case 1, a 61-year-old man, had a submandibular gland sample showing IgG4-positive plasma cell infiltration. Case 2, a 61-year-old man, was diagnosed with IgG4-related Mikulicz's disease confirmed by a sublingual gland sample. Case 3, a 57-year-old woman, had a diagnosis of IgG4-related Mikulicz's disease confirmed based on labial and sublingual gland samples. All reported oral dryness and bilateral submandibular swelling. Cases 1 and 2 recovered following Predonine administration tapered from 30 or 20 mg. DISCUSSION: IgG4-related Mikulicz's disease must be recognized as a clinical entity, together with its diagnostic criteria and treatment. Sublingual gland biopsy should be done to confirm its diagnosis following sublingual gland swelling.

A case of nasal natural killer/T lymphoma revealed by repeated deep neck abscess.

A diagnosis of natural killer (NK)/T-cell lymphoma was clarified after repeated deep neck abscess in a 63-year-old man. The absolute number of lymphocytes was mildly decreased. Lymphopenia induced by latent malignant lymphoma in this case likely caused the immunodeficiency, which induced repeated infection in the head and neck region. We conclude that it is always necessary to consider diseases caused by immunodeficiency conditions, such as malignant lymphoma, into consideration in a case of repeated deep neck abscess.

Primary laryngeal natural killer/T-cell lymphoma--report of a rare case.

BACKGROUND: Natural killer (NK)/T-cell lymphoma involving the larynx is a rare entity, and its clinical picture has not been described. METHODS AND RESULTS: A 73-year-old man had a granulomatous tumor involving the larynx. Multiple biopsies over 1 year were needed to reach an accurate diagnosis of NK/T-cell lymphoma. This patient died of the disease despite the use of chemotherapy. CONCLUSION: To the best of our knowledge, this is the second case of primary laryngeal NK/T-cell that illustrates its clinical picture. In the early stage of the disease, this type of tumor can present as granulous tumor-like lesion without a definite destructive lesion. This tumor type should be kept in mind in tumors that are difficult to diagnose, especially in Asian populations.

Tonsillar cyst of the false vocal cord.

OBJECTIVES/HYPOTHESIS: To report, for the first time, tonsillar cyst of the false vocal cord. STUDY DESIGN: Case report. METHODS: Case presentation and literature review. RESULTS: A 74-year-old woman with a mass in the false vocal cord presented with hoarseness. Histopathological examination revealed tonsillar cyst. Marsupialization via microlaryngeal approach failed. Finally the cyst was resected successfully through a lateral cervical approach with concomitant tracheotomy. CONCLUSIONS: This is the first report of tonsillar cyst in the false vocal cord in English literature. The cyst was finally resected through the lateral cervical approach with success.

Peritonsillar abscess with parapharyngeal and retropharyngeal involvement: incidence and intraoral approach.

CONCLUSION: This study illustrates common sites of infection seen in peritonsillar abscesses with involvement of the pharyngeal space and retropharyngeal space. Abscesses behind and/or inferior to the tonsil were encountered more frequently than expected. In these cases, the drainage had to be placed in the inferior pole of the tonsil and these types were frequently seen in older patients. OBJECTIVES: The aim of this study was to assess to what extent abscesses spread in patients with peritonsillar abscess and to determine to what extent pus can be drained intraorally. PATIENTS AND METHODS: The clinical charts of 45 patients with peritonsillar abscess involvement of the parapharyngeal space and/or retropharyngeal space were retrospectively reviewed. RESULTS: In 45 cases, 21 patients were diagnosed with the superior type, and we could drain the pus intraorally in 90% of the patients. On the other hand, 24 cases were diagnosed with the inferior type and they were drained intraorally in 58% of the cases.

No role for prostacyclin IP receptors in duodenal HCO3- secretion induced by mucosal acidification in mice--comparison with capsaicin-induced response.

BACKGROUND/AIM: We investigated the role of prostacyclin (PGI2) IP receptors in the acid-induced secretion of HCO3- using IP receptor knockout [IP (-/-)] mice, in comparison with capsaicin-induced secretion. METHODS: Male C57/BL6 mice, both wild-type [WT] and [IP (-/-)], fasted for 18 h were used. Under urethane anesthesia, a proximal duodenal loop was perfused with saline, and the secretion of HCO3- was measured at pH 7.0 using a pH-stat method and by adding 2 mM HCl. The secretion was stimulated by exposure of the loop to 10 mM HCl, capsaicin, PGE2 or cicaprost (a PGI2 agonist) for 10 min. RESULTS: PGE2 stimulated HCO3- secretion in both WT and IP (-/-) mice, while cicaprost increased it in WT but not IP (-/-) mice. Luminal acidification increased the mucosal level of PGE2 as well as 6-keto-PGF1alpha, yet stimulated HCO3- secretion in both WT and IP (-/-) mice, in an indomethacin-inhibitable and sensory neuron-dependent manners. Perfusion of the duodenum with 20 mM HCl for 4 h caused severe damage in WT mice pretreated with indomethacin, but not in control WT or IP (-/-) mice. Capsaicin increased duodenal HCO3- secretion in WT mice, in an indomethacin-sensitive manner, yet no such response was observed in the animals lacking IP receptors. CONCLUSION: The presence of IP receptors is not essential for acid-induced HCO3- secretion and mucosal defense against acid injury in the duodenum, although activation of IP receptors results in stimulation of HCO3- secretion. Although duodenal HCO3- secretion induced by both acid and capsaicin depends on afferent neurons, it seems that the mode of interaction with the afferent neurons differs regarding dependency on the PGI2/IP receptors.