[A family with developmental glaucoma and microcornea due to novel ADAMTS18 gene mutations]

This case report presents a family with developmental glaucoma accompanied by microcornea resulting from novel mutations in the ADAMTS18 gene. The index case involves a 5-year-old twin brother, who, during a routine examination, exhibited elevated intraocular pressure persisting for over a month. The peak intraocular pressure reached approximately 25 mmHg (1 mmHg=0.133 kPa) in both eyes, with a corneal diameter of less than 10 mm. Ocular examination revealed an enlarged cup-to-disc ratio, and optical coherence tomography (OCT) demonstrated thinning of the retinal nerve fiber layer and ganglion cell layer. Ultrasound biomicroscopy combined with gonioscopy indicated partial angle closure and abnormal anterior chamber angle development. The ocular manifestations in the twin brother were consistent with those observed in the twin sister. The clinical diagnosis was bilateral developmental glaucoma with microcornea. Genetic sequencing identified two novel compound heterozygous mutations in the ADAMTS18 gene in the twins: Mutation 1 (M1) involving the variant site 1 (c.3436C>T:p.R1146W) and Mutation 2 (M2) involving the variant site 2 (c.1454T>G:p.F485C). Ocular examinations of four additional family members were normal. Genetic testing revealed that the twins' father and sister carried M1, while the index case's mother and brother carried M2. This report underscores a unique association between ADAMTS18 gene mutations and developmental glaucoma with microcornea within a familial context, emphasizing the importance of genetic screening for early diagnosis and targeted management strategies.

Squalamine reverses age-associated changes of firing patterns of myenteric sensory neurons and vagal fibres

Vagus nerve signaling is a key component of the gut-brain axis and regulates diverse physiological processes that decline with age. Gut to brain vagus firing patterns are regulated by myenteric intrinsic primary afferent neuron (IPAN) to vagus neurotransmission. It remains unclear how IPANs or the afferent vagus age functionally. Here we identified a distinct ageing code in gut to brain neurotransmission defined by consistent differences in firing rates, burst durations, interburst and intraburst firing intervals of IPANs and the vagus, when comparing young and aged neurons. The aminosterol squalamine changed aged neurons firing patterns to a young phenotype. In contrast to young neurons, sertraline failed to increase firing rates in the aged vagus whereas squalamine was effective. These results may have implications for improved treatments involving pharmacological and electrical stimulation of the vagus for age-related mood and other disorders. For example, oral squalamine might be substituted for or added to sertraline for the aged.

Sequential left ventricular electro-mechanical changes in left bundle branch pacing vs right ventricular pacing a two-center study

Background

Left bundle branch pacing (LBBP) has been proved to maintain electrical synchrony better than RVP during mid to long-term follow-up, but little is known about the left ventricular (LV) mechanical changes over time. This study investigates if LBBP causes less sequential electro-mechanical alterations in LV that develop over time, compared with both conventional (CRVP) and leadless (LRVP) RVP.

Methods

Sixty-five patients with pacing indication for bradycardia were prospectively enrolled: Twenty-two were treated with LBBP, 23 with CRVP and 20 with LRVP. QRS duration (QRSd) was measured at baseline and during follow-up. All patients underwent echocardiography at baseline, one week after implantation and at one-year follow-up. LV volumes, ejection fraction (EF) and global longitudinal strain (GLS) were measured. Septal flash (SF), apical rocking and septal longitudinal strain patterns were assessed visually by two experienced readers.

Results

All the patients presented with normal strain pattern and no signs of SF or apical rocking at baseline. 100% of CRVP and 95% of LRVP patients had stage1 or 2 septal deformation patterns at week 1, and the majority (72.3% CRVP and 83.3% LRVP) progressed to stage≥2 at 12 months. On the contrary, over 2/3 of LBBP patients preserved normal strain patterns at week 1, and less than 1/3 had stage-1 pattern, 2 out of whom progressed to stage-2 during follow-up (Figure 1). At week 1 and 12 months, all RVP patients had SF, and most of them also exhibited apical rocking (87%-94.4% in CRVP and 80%-94.4% in LRVP). However, much less septal flash and apical rocking was induced in LBBP patients at week 1 and last follow-up (27.3%-37.5% and 22.7%-25%, P<0.001 vs RVP). Baseline QRSd were similar among three groups. At week 1, the paced QRSd increased least in LBBP compared to CRVP and LRVP and remained as such at 12 months. During one year follow-up, LVEF and LV GLS decreased more in CRVP group compared to LBBP (both P<0.05) (Figure 2).

Conclusion

LBBP causes less sequential changes in LV deformation patterns, septal flash and apical rocking, compared to CRVP and LRVP. With this, LBBP appears to preserve LV function better than RVP. CRVP and LRVP did not differ in electro-mechanical changes or LV remodeling.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Research Foundation Flanders (FWO) project grant

Left atrial appendage mechanical dispersion assessed by speckle-tracking echocardiography as a determinant of left atrial appendage stasis in patients with non-valvular atrial fibrillation

Background

We sought to investigate the relationship of left atrial appendage (LAA) mechanical dispersion (MD) with LAA dense spontaneous echo contrast (SEC) or thrombus, and to compare its usefulness in the identification of thrombogenesis with left atrial (LA) MD or LA/LAA strain parameters in patients with nonvalvular atrial fibrillation (AF).

Methods

We conducted a cross-sectional study of 493 consecutive patients with AF (median age 65, male 66.9%) who underwent echocardiography prior to catheter ablation. We measured the LAA and LA global longitudinal strain (GLS) using speckle-tracking echocardiography (STE). LAA MD and LA MD was defined as the standard deviation (SD) of time to peak positive strain corrected by the R-R interval.

Results

Patients with LAA dense SEC/thrombus (n=70) had significantly higher LAA MD than controls (n=423) (median 14.20% vs 9.35%). Areas under the receiver-operating curve for CHA2DS2-VASc score plus LAA MD, LAA GLS or LA GLS were comparable (0.830, 0.843 and 0.809) and superior to that combined with LA MD (0.762, all p<0.01). Multivariable analysis showed that LAA MD was an independent determinant of LAA dense SEC/thrombus in four different models (Odds ratio, 1.23–1.24; P<0.001), and provided additional diagnostic value over clinical and standard echocardiographic parameters. Whereas LA MD was not independently associated with LAA dense SEC/thrombus and had no incremental predictive value.

Conclusion

LAA mechanical dispersion provided incremental information over conventional risk factors in the identification of LAA dense SEC or thrombus in AF patients and is superior to LA mechanical dispersion.

Funding Acknowledgement

Type of funding sources: None.

Left bundle branch pacing is superior in preserving ventricular mechanical synchrony and cardiac function than right ventricular pacing: a two-center experience

Background

Left bundle branch pacing (LBBP) has emerged as a novel pacing modality. Although it has been proved to maintain electrical synchrony better than right ventricular pacing (RVP), little is known about the impact on mechanical synchrony. This study investigates if LBBP preserves mechanical synchrony and cardiac function better compared to conventional (CRVP) and leadless (LRVP) RVP.

Methods

Sixty-five patients with pacing indication for bradycardia were prospectively enrolled: Twenty-two were treated with LBBP, 23 with CRVP and 20 with LRVP. All patients underwent echocardiography before and after implantation and at one-year follow-up. Left ventricular (LV) volumes, ejection fraction (EF) and global longitudinal strain (GLS) were measured. Regional septal (SW) and lateral wall work (LW) was calculated as the average from the respective basal and mid-ventricular segments in the apical four-chamber and three-chamber view. The lateral-septal work difference (LSWD) was used as a measure of mechanical dyssynchrony.

Results

At baseline, the QRS duration and LSWD were similar in all three groups. During follow-up, the QRS duration increased least in LBBP compared to CRVP and LRVP (+28.1±18.3ms vs +58.2±31.4 and 47.1±26.1ms, both P<0.01). SW was markedly decreased in CRVP and LRVP while LW work remained unchanged, resulting in a large LSWD compared to LBBP (1308.4±732.9 mmHg*% and 1451.3±606.1 mmHg*% vs. 286.0±479.9mmHg*%, both P<0.001). During one year follow-up, LVEF and LV GLS decreased more in CRVP compared to LBBP (both P<0.05).

Conclusion

LBBP causes less LV dyssynchrony than CRVP and LRVP as it preserves a more physiologic conduction pattern. With this, LBBP appears to preserve LV function better than CRVP. CRVP and LRVP did not differ in mechanical dyssynchrony or LV remodelling.

Funding Acknowledgement

Type of funding sources: None.

Left bundle branch pacing preserves ventricular mechanical synchrony better than right ventricular pacing-a two-center study

Funding Acknowledgements

Type of funding sources: None.

Background

Left bundle branch pacing (LBBP) has emerged as a novel pacing method. We sought to evaluate left ventricular (LV) mechanical synchrony under permanent LBBP and compare it with conventional and leadless right ventricular pacing (CRVP, LRVP).

Methods

Sixty-four patients with pacing indication for bradycardia were prospectively enrolled. Twenty-two patients received LBBP in the basal ventricular septum. Twenty-three patients received CRVP and 19 LRVP. All patients underwent echocardiography before and after device implantation. Myocardial work was estimated by pressure-strain analysis. Regional work in the septum (SEP) and lateral wall (LW) was calculated as the average from the respective basal and mid-ventricular segments in the apical four-chamber and three-chamber view. The absolute difference between work in LW and SEP (LW-S-work difference) was used as a measure of asymmetry in workload.

Results

Baseline characteristics were similar among the three groups. The electrocardiogram during LBBP showed a right bundle branch block pattern; during CRVP and LRVP a left bundle branch block pattern. The paced QRS duration was 114.27±9.9 ms in the LBBP group, significantly shorter than that in the CRVP and LRVP groups (153.9±25.26 ms and 159.1±13.99ms, respectively, both p<0.001). The SEP work decreased in all groups during ventricular pacing (all P<0.05), while the LW work remained similar. The paced LW-S work difference and work difference change between pacing on and off were more significant in the CRVP (1012.9±566.0mmHg*%) and LRVP group (1066.1±472.6mmHg*%) than the LBBP group (260.5±239.8mmHg*%, both P<0.001). In addition, LW-S work difference during ventricular pacing and work difference change between pacing and baseline were comparable in CRVP and LRVP group.

Conclusion

LBBP causes less LV dyssynchrony than CRVP and LRVP as it preserves a more physiologic conduction pattern. CRVP and LRVP did not differ in this respect. Further studies need to prove that LBBP has advantages over RVP with regards to preservation of LV synchrony and contractility.

Identification of SSRI-evoked antidepressant sensory signals by decoding vagus nerve activity

The vagus nerve relays mood-altering signals originating in the gut lumen to the brain. In mice, an intact vagus is required to mediate the behavioural effects of both intraluminally applied selective serotonin reuptake inhibitors and a strain of Lactobacillus with antidepressant-like activity. Similarly, the prodepressant effect of lipopolysaccharide is vagus nerve dependent. Single vagal fibres are broadly tuned to respond by excitation to both anti- and prodepressant agents, but it remains unclear how neural responses encode behaviour-specific information. Here we demonstrate using ex vivo experiments that for single vagal fibres within the mesenteric neurovascular bundle supplying the mouse small intestine, a unique neural firing pattern code is common to both chemical and bacterial vagus-dependent antidepressant luminal stimuli. This code is qualitatively and statistically discernible from that evoked by lipopolysaccharide, a non-vagus-dependent antidepressant or control non-antidepressant Lactobacillus strain and are not affected by sex status. We found that all vagus dependent antidepressants evoked a decrease in mean spike interval, increase in spike burst duration, decrease in gap duration between bursts and increase in intra-burst spike intervals. Our results offer a novel neuronal electrical perspective as one explanation for mechanisms of action of gut-derived vagal dependent antidepressants. We expect that our ex vivo individual vagal fibre recording model will improve the design and operation of new, extant electroceutical vagal stimulation devices currently used to treat major depression. Furthermore, use of this vagal antidepressant code should provide a valuable screening tool for novel potential oral antidepressant candidates in preclinical animal models.

Squalamine Restores the Function of the Enteric Nervous System in Mouse Models of Parkinson's Disease

BACKGROUND

Parkinson's disease (PD) is a progressive neurodegenerative disorder thought to be caused by accumulation of α-synuclein (α-syn) within the brain, autonomic nerves, and the enteric nervous system (ENS). Involvement of the ENS in PD often precedes the onset of the classic motor signs of PD by many years at a time when severe constipation represents a major morbidity. Studies conducted in vitro and in vivo, have shown that squalamine, a zwitterionic amphipathic aminosterol, originally isolated from the liver of the dogfish shark, effectively displaces membrane-bound α-syn.

OBJECTIVE

Here we explore the electrophysiological effect of squalamine on the gastrointestinal (GI) tract of mouse models of PD engineered to express the highly aggregating A53T human α-syn mutant.

METHODS

GI motility and in vivo response to oral squalamine in PD model mice and controls were assessed using an in vitro tissue motility protocol and via fecal pellet output. Vagal afferent response to squalamine was measured using extracellular mesenteric nerve recordings from the jejunum. Whole cell patch clamp was performed to measure response to squalamine in the myenteric plexus.

RESULTS

Squalamine effectively restores disordered colonic motility in vivo and within minutes of local application to the bowel. We show that topical squalamine exposure to intrinsic primary afferent neurons (IPANs) of the ENS rapidly restores excitability.

CONCLUSION

These observations may help to explain how squalamine may promote gut propulsive activity through local effects on IPANs in the ENS, and further support its possible utility in the treatment of constipation in patients with PD.

Microvesicles from Lactobacillus reuteri (DSM-17938) completely reproduce modulation of gut motility by bacteria in mice

Microvesicles are small lipid, bilayer structures (20–400 nm in diameter) secreted by bacteria, fungi, archaea and parasites involved in inter-bacterial communication and host-pathogen interactions. Lactobacillus reuteri DSM-17938 (DSM) has been shown to have clinical efficacy in the treatment of infantile colic, diarrhea and constipation. We have shown previously that luminal administration to the mouse gut promotes reduction of jejunal motility but increases that in the colon. The production of microvesicles by DSM has been characterized, but the effect of these microvesicles on gastrointestinal motility has yet to be evaluated. To investigate a potential mechanism for the effects of DSM on the intestine, the bacteria and its products have here been tested for changes in velocity, frequency, and amplitude of contractions in intact segments of jejunum and colon excised from mice. The effect of the parent bacteria (DSM) was compared to the conditioned media in which it was grown, and the microvesicles it produced. The media used to culture the bacteria (broth) was tested as a negative control and the conditioned medium was tested after the microvesicles had been removed. DSM, conditioned medium, and the microvesicles all produced comparable effects in both the jejunum and the colon. The treatments individually decreased the velocity and frequency of propagating contractile cluster contractions in the jejunum and increased them in the colon to a similar degree. The broth control had little effect in both tissues. Removal of the microvesicles from the conditioned medium almost completely eradicated their effect on motility in both tissues. These results show that the microvesicles from DSM alone can completely reproduce the effects of the whole bacteria on gut motility. Furthermore, they suggest a new approach to the formulation of orally active bacterial therapeutics and offer a novel way to begin to identify the active bacterial components.

Oral selective serotonin reuptake inhibitors activate vagus nerve dependent gut-brain signalling

The vagus nerve can transmit signals to the brain resulting in a reduction in depressive behavior as evidenced by the long-term beneficial effects of electrical stimulation of the vagus in patients with intractable depression. The vagus is the major neural connection between gut and brain, and we have previously shown that ingestion of beneficial bacteria modulates behaviour and brain neurochemistry via this pathway. Given the high levels of serotonin in the gut, we considered if gut-brain signaling, and specifically the vagal pathway, might contribute to the therapeutic effect of oral selective serotonin reuptake inhibitors (SSRI). Mesenteric nerve recordings were conducted in mice after treatment with SSRI to ascertain if this class of drugs resulted in increased vagal excitability. Patch clamp recordings of enteric neurons were carried out to measure activity of primary afferent neurons in the gut in response to SSRI and to assess the importance of gut epithelium in transducing signal. The tail suspension test (TST) was used following 14d feeding of SSRI in vagotomised and surgical sham mice to measure depressive-like behaviour. Brain mRNA expression was examined via PCR and the intestinal microbiome was assessed. Mesenteric nerve recordings in BALB/c mice demonstrated that oral treatment with SSRI leads to a significant increase in vagal activity. This effect was not observed in mice treated with a representative noradrenaline-dopamine reuptake inhibitor. It is known that signals from the gut can be transmitted to the vagus via the enteric nervous system. Exposure of the gut to SSRI increased the excitability of intrinsic primary afferent neurons in the myenteric plexus, through an intestinal epithelium dependent mechanism, and alpha-diversity of gut microbiota was altered. Critically, blocking vagal signaling from gut to brain, via subdiaphragmatic vagotomy, abolished the antidepressive effects of oral SSRI treatment as determined by the tail suspension test. This work suggests that vagus nerve dependent gut-brain signaling contributes to the effects of oral SSRI and further, highlights the potential for pharmacological approaches to treatment of mood disorders that focus on vagal stimulation and may not even require therapeutic agents to enter the circulation.

Colonic Motility and Jejunal Vagal Afferent Firing Rates Are Decreased in Aged Adult Male Mice and Can Be Restored by an Aminosterol

There is a general decline in gastrointestinal function in old age including decreased intestinal motility, sensory signaling, and afferent sensitivity. There is also increased prevalence of significant constipation in aged populations. We hypothesized this may be linked to reduced colonic motility and alterations in vagal-gut-brain sensory signaling. Using in vitro preparations from young (3 months) and old (18–24 months) male CD1 mice we report functional age-related differences in colonic motility and jejunal mesenteric afferent firing. Furthermore, we tested the effect of the aminosterol squalamine on colonic motility and jejunal vagal firing rate. Old mice had significantly reduced velocity of colonic migrating motor complexes (MMC) by 27% compared to young mice (p = 0.0161). Intraluminal squalamine increased colonic MMC velocity by 31% in old mice (p = 0.0150), which also had significantly reduced mesenteric afferent single-unit firing rates from the jejunum by 51% (p < 0.0001). The jejunal vagal afferent firing rate was reduced in aged mice by 62% (p = 0.0004). While the time to peak response to squalamine was longer in old mice compared to young mice (18.82 ± 1.37 min vs. 12.95 ± 0.99 min; p = 0.0182), it significantly increased vagal afferent firing rate by 36 and 56% in young and old mice, respectively (p = 0.0006, p = 0.0013). Our results show for the first time that the jejunal vagal afferent firing rate is reduced in aged-mice. They also suggest that there is translational potential for the therapeutic use of squalamine in the treatment of age-related constipation and dysmotility.

The TRPV1 channel in rodents is a major target for antinociceptive effect of the probiotic Lactobacillus reuteri DSM 17938

Certain probiotic bacteria have been shown to reduce distension-dependent gut pain, but the mechanisms involved remain obscure. Live luminal Lactobacillus reuteri (DSM 17938) and its conditioned medium dose dependently reduced jejunal spinal nerve firing evoked by distension or capsaicin, and 80% of this response was blocked by a specific TRPV1 channel antagonist or in TRPV1 knockout mice. The specificity of DSM action on TRPV1 was further confirmed by its inhibition of capsaicin-induced intracellular calcium increases in dorsal root ganglion neurons. Another lactobacillus with ability to reduce gut pain did not modify this response. Prior feeding of rats with DSM inhibited the bradycardia induced by painful gastric distension. These results offer a system for the screening of new and improved candidate bacteria that may be useful as novel therapeutic adjuncts in gut pain. Certain bacteria exert visceral antinociceptive activity, but the mechanisms involved are not determined. Lactobacillus reuteri DSM 17938 was examined since it may be antinociceptive in children. Since transient receptor potential vanilloid 1 (TRPV1) channel activity may mediate nociceptive signals, we hypothesized that TRPV1 current is inhibited by DSM. We tested this by examining the effect of DSM on the firing frequency of spinal nerve fibres in murine jejunal mesenteric nerve bundles following serosal application of capsaicin. We also measured the effects of DSM on capsaicin-evoked increase in intracellular Ca(2+) or ionic current in dorsal root ganglion (DRG) neurons. Furthermore, we tested the in vivo antinociceptive effects of oral DSM on gastric distension in rats. Live DSM reduced the response of capsaicin- and distension-evoked firing of spinal nerve action potentials (238 ± 27.5% vs. 129 ± 17%). DSM also reduced the capsaicin-evoked TRPV1 ionic current in DRG neuronal primary culture from 83 ± 11% to 41 ± 8% of the initial response to capsaicin only. Another lactobacillus (Lactobacillus rhamnosus JB-1) with known visceral anti-nociceptive activity did not have these effects. DSM also inhibited capsaicin-evoked Ca(2+) increase in DRG neurons; an increase in Ca(2+) fluorescence intensity ratio of 2.36 ± 0.31 evoked by capsaicin was reduced to 1.25 ± 0.04. DSM releasable products (conditioned medium) mimicked DSM inhibition of capsaicin-evoked excitability. The TRPV1 antagonist 6-iodonordihydrocapsaicin or the use of TRPV1 knock-out mice revealed that TRPV1 channels mediate about 80% of the inhibitory effect of DSM on mesenteric nerve response to high intensity gut distension. Finally, feeding with DSM inhibited perception in rats of painful gastric distension. Our results identify a specific target channel for a probiotic with potential therapeutic properties.

The gut microbiome restores intrinsic and extrinsic nerve function in germ-free mice accompanied by changes in calbindin

BACKGROUND

The microbiome is essential for normal myenteric intrinsic primary afferent neuron (IPAN) excitability. These neurons control gut motility and modulate gut-brain signaling by exciting extrinsic afferent fibers innervating the enteric nervous system via an IPAN to extrinsic fiber sensory synapse. We investigated effects of germ-free (GF) status and conventionalization on extrinsic sensory fiber discharge in the mesenteric nerve bundle and IPAN electrophysiology, and compared these findings with those from specific pathogen-free (SPF) mice. As we have previously shown that the IPAN calcium-dependent slow afterhyperpolarization (sAHP) is enhanced in GF mice, we also examined the expression of the calcium-binding protein calbindin in these neurons in these different animal groups.

METHODS

IPAN sAHP and mesenteric nerve multiunit discharge were recorded using ex vivo jejunal gut segments from SPF, GF, or conventionalized (CONV) mice. IPANs were excited by adding 5 μM TRAM-34 to the serosal superfusate. We probed for calbindin expression using immunohistochemical techniques.

KEY RESULTS

SPF mice had a 21% increase in mesenteric nerve multiunit firing rate and CONV mice a 41% increase when IPANs were excited by TRAM-34. For GF mice, this increase was barely detectable (2%). TRAM-34 changed sAHP area under the curve by -77 for SPF, +3 for GF, or -54% for CONV animals. Calbindin-immunopositive neurons per myenteric ganglion were 36% in SPF, 24% in GF, and 52% in CONV animals.

CONCLUSIONS & INFERENCES

The intact microbiome is essential for normal intrinsic and extrinsic nerve function and gut-brain signaling.

Gut commensal microvesicles reproduce parent bacterial signals to host immune and enteric nervous systems

Ingestion of a commensal bacteria, Lactobacillus rhamnosus JB-1, has potent immunoregulatory effects, and changes nerve-dependent colon migrating motor complexes (MMCs), enteric nerve function, and behavior. How these alterations occur is unknown. JB-1 microvesicles (MVs) are enriched for heat shock protein components such as chaperonin 60 heat-shock protein isolated from Escherichia coli (GroEL) and reproduce regulatory and neuronal effects in vitro and in vivo. Ingested labeled MVs were detected in murine Peyer's patch (PP) dendritic cells (DCs) within 18 h. After 3 d, PP and mesenteric lymph node DCs assumed a regulatory phenotype and increased functional regulatory CD4(+)25(+)Foxp3+ T cells. JB-1, MVs, and GroEL similarly induced phenotypic change in cocultured DCs via multiple pathways including C-type lectin receptors specific intercellular adhesion molecule-3 grabbing non-integrin-related 1 and Dectin-1, as well as TLR-2 and -9. JB-1 and MVs also decreased the amplitude of neuronally dependent MMCs in an ex vivo model of peristalsis. Gut epithelial, but not direct neuronal application of, MVs, replicated functional effects of JB-1 on in situ patch-clamped enteric neurons. GroEL and anti-TLR-2 were without effect in this system, suggesting the importance of epithelium neuron signaling and discrimination between pathways for bacteria-neuron and -immune communication. Together these results offer a mechanistic explanation of how Gram-positive commensals and probiotics may influence the host's immune and nervous systems.

The gut-brain axis rewired: adding a functional vagal nicotinic "sensory synapse"

It is generally accepted that intestinal sensory vagal fibers are primary afferent, responding nonsynaptically to luminal stimuli. The gut also contains intrinsic primary afferent neurons (IPANs) that respond to luminal stimuli. A psychoactive Lactobacillus rhamnosus (JB-1) that affects brain function excites both vagal fibers and IPANs. We wondered whether, contrary to its primary afferent designation, the sensory vagus response to JB-1 might depend on IPAN to vagal fiber synaptic transmission. We recorded ex vivo single- and multiunit afferent action potentials from mesenteric nerves supplying mouse jejunal segments. Intramural synaptic blockade with Ca(2+) channel blockers reduced constitutive or JB-1-evoked vagal sensory discharge. Firing of 60% of spontaneously active units was reduced by synaptic blockade. Synaptic or nicotinic receptor blockade reduced firing in 60% of vagal sensory units that were stimulated by luminal JB-1. In control experiments, increasing or decreasing IPAN excitability, respectively increased or decreased nerve firing that was abolished by synaptic blockade or vagotomy. We conclude that >50% of vagal afferents function as interneurons for stimulation by JB-1, receiving input from an intramural functional "sensory synapse." This was supported by myenteric plexus nicotinic receptor immunohistochemistry. These data offer a novel therapeutic target to modify pathological gut-brain axis activity.-Perez-Burgos, A., Mao, Y.-K., Bienenstock, J., Kunze, W. A. The gut-brain axis rewired: adding a functional vagal nicotinic "sensory synapse."

Bacteroides fragilis polysaccharide A is necessary and sufficient for acute activation of intestinal sensory neurons

Symbionts or probiotics are known to affect the nervous system. To understand the mechanisms involved, it is important to measure sensory neuron responses and identify molecules responsible for this interaction. Here we test the effects of adding Lactobacillus rhamnosus (JB-1) and Bacteroides fragilis to the epithelium while making voltage recordings from intestinal primary afferent neurons. Sensory responses are recorded within 8 s of applying JB-1 and excitability facilitated within 15 min. Bacteroides fragilis produces similar results, as does its isolated, capsular exopolysaccharide, polysaccharide A. Lipopolysaccharide-free polysaccharide A completely mimics the neuronal effects of the parent organism. Experiments with a mutant Bacteroides fragilis devoid of polysaccharide A shows that polysaccharide A is necessary and sufficient for the neuronal effects. Complex carbohydrates have not been reported before as candidates for such signalling between symbionts and the host. These observations indicate new neuronal targets and invite further study of bacterial carbohydrates as inter-kingdom signalling molecules between beneficial bacteria and sensory neurons.

The microbiome is essential for normal gut intrinsic primary afferent neuron excitability in the mouse

BACKGROUND

The role of intestinal microbiota in the development and function of host physiology is of high interest, especially with respect to the nervous system. While strong evidence has accrued that intestinal bacteria alter host nervous system function, mechanisms by which this occurs have remained elusive. For this reason, we have carried out experiments examining the electrophysiological properties of neurons in the myenteric plexus of the enteric nervous system (ENS) in germ-free (GF) mice compared with specific pathogen-free (SPF) control mice and adult germ-free mice that have been conventionalized (CONV-GF) with intestinal bacteria.

METHODS

Segments of jejunum from 8 to 12 week old GF, SPF, and CONV-GF mice were dissected to expose the myenteric plexus. Intracellular recordings in current-clamp mode were made by impaling cells with sharp microelectrodes. Action potential (AP) shapes, firing thresholds, the number of APs fired at 2× threshold, and passive membrane characteristics were measured.

KEY RESULTS

In GF mice, excitability was decreased in myenteric afterhyperpolarization (AH) neurons as measured by a lower resting membrane potential and by the number of APs generated at 2× threshold. The post AP slow afterhyperpolarization (sAHP) was prolonged for GF compared with SPF and CONV-GF animals. Passive membrane characteristics were also altered in GF mice by a decrease in input resistance.

CONCLUSIONS & INFERENCES

Here, we report the novel finding that commensal intestinal microbiota are necessary for normal excitability of gut sensory neurons and thus provide a potential mechanism for the transfer of information between the microbiota and nervous system.

Psychoactive bacteria Lactobacillus rhamnosus (JB-1) elicits rapid frequency facilitation in vagal afferents

Mounting evidence supports the influence of the gut microbiome on the local enteric nervous system and its effects on brain chemistry and relevant behavior. Vagal afferents are involved in some of these effects. We previously showed that ingestion of the probiotic bacterium Lactobacillus rhamnosus (JB-1) caused extensive neurochemical changes in the brain and behavior that were abrogated by prior vagotomy. Because information can be transmitted to the brain via primary afferents encoded as neuronal spike trains, our goal was to record those induced by JB-1 in vagal afferents in the mesenteric nerve bundle and thus determine the nature of the signals sent to the brain. Male Swiss Webster mice jejunal segments were cannulated ex vivo, and serosal and luminal compartments were perfused separately. Bacteria were added intraluminally. We found no evidence for translocation of labeled bacteria across the epithelium during the experiment. We recorded extracellular multi- and single-unit neuronal activity with glass suction pipettes. Within minutes of application, JB-1 increased the constitutive single- and multiunit firing rate of the mesenteric nerve bundle, but Lactobacillus salivarius (a negative control) or media alone were ineffective. JB-1 significantly augmented multiunit discharge responses to an intraluminal distension pressure of 31 hPa. Prior subdiaphragmatic vagotomy abolished all of the JB-1-evoked effects. This detailed exploration of the neuronal spike firing that encodes behavioral signaling to the brain may be useful to identify effective psychoactive bacteria and thereby offer an alternative new perspective in the field of psychiatry and comorbid conditions.

Luminal administration ex vivo of a live Lactobacillus species moderates mouse jejunal motility within minutes

Gut commensals modulate host immune, endocrine, and metabolic functions. They also affect peripheral and central neural reflexes and function. We have previously shown that daily ingestion of Lactobacillus reuteri (LR) for 9 d inhibits the pseudoaffective cardiac response and spinal single-fiber discharge evoked by visceral distension, and decreases intestinal motility and myenteric AH cell slow afterhyperpolarization (sAHP) by inhibiting a Ca-activated K (IK(Ca)) channel. We tested whether luminal LR could acutely decrease motility in an ex vivo perfusion model of naive Balb/c jejunum. Live LR dose dependently decreased motor complex pressure wave amplitudes with 9- to 16-min onset latency and an IC(50) of 5 × 10(7) cells/ml Krebs. Heat-killed LR or another live commensal, Lactobacillus salivarius, were without effect. The IK(Ca) channel blocker TRAM-34, but neither the opener (DCEBIO) nor the hyperpolarization-activated cationic channel inhibitor ZD7288 (5 μM) (or TTX 1 μM), mimicked the LR effect on motility acutely ex vivo. We provide evidence for a rapid, strain-specific, dose-dependent action of a live Lactobacillus on small intestinal motility reflexes that recapitulates the long-term effects of LR ingestion. These observations may be useful as a first step to unraveling the pathways involved in bacteria to the nervous system communication.

Lactobacillus reuteri ingestion prevents hyperexcitability of colonic DRG neurons induced by noxious stimuli

Lactobacillus species ingestion can decrease autonomic responses and spinal fiber discharge to nociceptive colorectal distension (CRD), even in the absence of inflammation. The present study aimed to determine whether dorsal root ganglion (DRG) somas could be a locus where the antinociceptive probiotic may have an effect. Healthy rats were fed with Lactobacillus reuteri or vehicle control for 9 days whereupon they were anesthetized, and intermittent distal colonic CRD at 80 mmHg distension was either performed for 1 h or not. The animals were immediately euthanized and patch-clamp recordings taken after isolation and overnight culture from those DRG that projected to the distal colon. CRD decreased the threshold for action potential generation and increased the number of spikes discharged during a standard depolarizing test stimulus, and this effect was blocked by prior probiotic ingestion. The increase in excitability was paralleled by an increase in DRG capacitance, which was not altered by Lactobacillus reuteri ingestion. CRD did not increase tissue weight or myeloperoxidase activity. We suggest that the effects of CRD may have been caused by activity-dependent neurotransmission between DRG somas. CRD evoked increases in action potential upstroke speed, which suggests that it may also have led to augmentation of sodium channel conductances. Probiotic ingestion may have interfered with this hypothetical mechanism since it blocked the effect of CRD on the action potential.

Lactobacillus reuteri enhances excitability of colonic AH neurons by inhibiting calcium-dependent potassium channel opening

Probiotics are live non-pathogenic commensal organisms that exert therapeutic effects in travellers' diarrhea, irritable bowel syndrome and inflammatory bowel disease. Little is known about mechanisms of action of commensal bacteria on intestinal motility and motility-induced pain. It has been proposed that probiotics affect intestinal nerve function, but direct evidence for this has thus far been lacking. We hypothesized that probiotic effects might be mediated by actions on colonic intrinsic sensory neurons. We first determined whether sensory neurons were present in rat colon by their responses to chemical mucosal stimulation and identified them in terms of physiological phenotype and soma morphotype. Enteric neuron excitability and ion channel activity were measured using patch clamp recordings. We fed 10(9)Lactobacillus reuteri (LR) or vehicle control to rats for 9 days. LR ingestion increased excitability (threshold for evoking action potentials) and number of action potentials per depolarizing pulse, decreased calcium-dependent potassium channel (IK(Ca)) opening and decreased the slow afterhyperpolarization (sAHP) in sensory AH neurons, similar to the IK(Ca) antagonists Tram-34 and clotrimazole. LR did not affect threshold for action potential generation in S neurons. Our results demonstrate that LR targets an ion channel in enteric sensory nerves through which LR may affect gut motility and pain perception.

Arginosuccinate synthetase, arginosuccinate lyase and NOS in canine gastrointestinal tract: immunocytochemical studies

Nitric oxide synthase (NOS) requires the substrate L-arginine for NO production to support multiple gastrointestinal functions. We asked, 'Where do enzymes to regenerate L-arginine from L-citrulline exist?'. We examined loci of immunoreactivities in the canine gastrointestinal tract for arginosuccinate synthetase and arginosuccinate lyase, enzymes that resynthesize L-arginine from L-citrulline, in relation to the distribution of nNOS immunoreactivity or NADPH-diaphorase histochemistry. Arginosuccinate synthetase and lyase were present in many neurones and nerve fibres in the myenteric plexus of the lower oesophageal sphincter (LOS), antrum, pylorus, ileum and colon; in the submucosal plexus of ileum and colon; in longitudinal muscle of ileum and colon; and in nerve bundles in circular muscle everywhere. LOS muscle was also immunoreactive for both enzymes. Circular and longitudinal muscle cells of the ileum and colon and cells resembling interstitial cells of Cajal in the deep muscular plexus of the ileum and the submuscular plexus of the colon also appeared immunoreactive. In neurones, arginosuccinate synthetase and nNOS were usually co-localized. NADPH diaphorase activity was present in LOS and likely in pylorus, but not in muscularis externa of ileum or colon. We conclude that resynthesis of L-arginine probably occurs in enteric nerves, interstitial cells of Cajal (ICC) and LOS muscle; also apparently in some cells without NOS to utilize it.

Myogenic NOS in canine lower esophageal sphincter: enzyme activation, substrate recycling, and product actions

Depolarization elicited outward K+ currents from canine lower esophageal sphincter (LES) muscle cells, primarily through iberiotoxin (IbTX)- and tetraethylammonium-sensitive Ca(2+)-dependent K+ channels. Current magnitudes varied with pipette Ca2+ concentration (EC50 = 108.5 nM). NG-nitro-L-arginine (L-NNA, 10(-4)M), IbTX (10(-8)M), or buffering intracellular Ca2+ to 8 nM decreased outward currents > 80%. Sodium nitroprusside (NaNP, 10(-4)M) restored L-NNA-inhibited or low intracellular Ca2+ concentration (not IbTX)-inhibited currents. L-NNA or IbTX application depolarized LES cells from -43 to -35 mV. NaNP restored the membrane potential to -46 mV after L-NNA but not after IbTX application. Nifedipine (30 microM) reduced outward currents and abolished or reduced L-NNA or NaNP effects, respectively. Immunocytochemistry revealed the presence of both argininosuccinate synthetase and argininosuccinate lyase in LES muscle cells. L-Citrulline, like L-arginine, reversed L-NNA inhibition of outward currents; only L-arginine reversed inhibition of outward currents by an antibody to argininosuccinate synthetase. Therefore, endogenous nitric oxide production, activated by Ca2+ entrance involving L-type Ca2+ channels, may continuously enhance outward currents to modulate LES muscle cell membrane potential and excitability.

Myogenic nitric oxide synthase activity in canine lower oesophageal sphincter: morphological and functional evidence

1. Studies on canine lower oesophageal sphincter (LOS) evaluated the existence and function of a myogenic, nitric oxide synthase (NOS) by use of immunocytochemistry for NOS isozymes, NADPH-d histochemistry, [3H]-L-arginine to [3H]-L-citrulline transformation. In addition, functional studies in the muscle bath were performed. 2. Smooth muscle bundles or freshly isolated smooth muscle cells of LOS were NADPH-d reactive but did not recognize some antibodies against neural, endothelial or inducible NOS. NADPH-d reactivity and immunoreactivity to a neural NOS antibody were colocalized in LOS enteric nerves. Muscle plasma membrane-enriched fractions from fresh and cultured LOS cells converted [3H]-L-arginine to [3H]-L-citrulline; activity was mostly Ca2+/calmodulin-dependent. 3. N-Nitro-L-arginine (L-NOARG) persistently increased tone (blocked by L-arginine) in muscle strips despite blockade of nerve function. Nifedipine prevented or abolished L-NOARG-induced, but not carbachol-induced, contraction showing that tone increase by L-NOARG required functional L-Ca channels. 4. Membrane-bound, myogenic NOS in canine LOS may release NO continuously when Ca2+ entry through L-Ca channels occurs under physiological conditions and thereby modulate tone in LOS.

Locations and molecular forms of PACAP and sites and characteristics of PACAP receptors in canine ileum

In canine ileum we investigated the distribution of pituitary adenylate cyclase-activating peptide (PACAP), using immunofluorescence and radioimmunoassay and the binding of 125I-PACAP-27 to membranes. Nerve profiles immunoreactive to PACAP-27, and often to vasoactive intestinal polypeptide (VIP) as well, were found in all plexi, but PACAP was present in approximately 100-fold lesser amounts than VIP. High-performance liquid chromatography analysis of deep muscular plexus (DMP) synaptosomes suggested the presence of PACAP-38, PACAP-27, and a third unidentified molecular form. High- and low-affinity 125I-PACAP-27 binding sites were found in DMP synaptosomes and circular smooth muscle (CM) plasma membranes. In competition studies with DMP membranes, high (H)- and low (L)-affinity dissociation constants (Kd) and maximal binding capacities (Bmax) were as follows: KdH = 66.9 pM, BmaxH = 101 fmol/mg; KdL = 2.18 nM, BmaxL = 580 fmol/mg protein. The binding of 125I-PACAP-27 was fast. Dissociation was slow and incomplete in the presence of unlabeled PACAP-27 but accelerated by pretreatment with guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S). GTP gamma S or cholera toxin treatment eliminated high-affinity binding in both membranes. VIP had approximately 100-fold lower affinity than PACAP-27 in both membranes. Cross-linking studies identified an approximately 70-kDa PACAP receptor in each membrane. Thus PACAP coexists with VIP in ileal enteric nerves and acts on PACAP-preferring, possibly Gs-coupled, receptors in DMP synaptosomes and CM membranes.

Colocalization of inhibitory mediators, NO, VIP and galanin, in canine enteric nerves

The colocalization of three putative inhibitory mediators of enteric nerves, vasoactive intestinal peptide (VIP), galanin (GAL) and nitric oxide synthase (nNOS), was examined in the myenteric plexus of canine antrum, intestine and colon. Many ileal and colonic neurons contained nNOS-immunoreactive (nNOS-IR) activity with some also containing VIP-IR; only a few neurons also contained GAL-IR. Ileal and colonic VIP-IR nerves often appeared to be interneurons innervating nNOS nerves. Many antral neurons contained VIP-IR with nearly all also containing GAL-IR. A few also contained nNOS-IR. The predominance of nNOS-IR neurons relative to VIP-IR and GAL-IR neurons in the ileal and colonic, but not the antral, myenteric plexus is consistent with NO being the primary inhibitory mediator in the intestine but not in the antrum.

The distribution of NPY-containing nerves and the catecholamine contents of canine enteric nerve plexuses

Our previous study demonstrated that PYY was a major neuropeptide in the canine enteric nervous system, the present study defines the locations of NPY-containing enteric neurons. NPY-positive nerve cell bodies and fibers were numerous in gastric and pyloric myenteric plexuses as were positive nerve fibers in antral and pyloric muscle layers, pyloric sphincter muscle layers, and surrounding blood vessels. In contrast to findings for PYY, there were considerably fewer NPY-positive nerve cell bodies and fibers in the canine ileum and colon. Noradrenaline was the predominant catecholamine in all plexuses, the rank order of its contents being: deep muscular > submucous > myenteric plexus. The dopamine/noradrenaline ratio was constant in all plexuses; adrenaline was present in minor amounts. PYY is the more abundant neuropeptide in ileum and colon, and NPY has a greater presence in the gastric antrum, pylorus, and surrounding blood vessels. PYY and NPY may play different functional roles in the GI tract.

Peptide YY receptor in submucosal and myenteric plexus synaptosomes of canine small intestine

PYY receptors were characterized and their loci determined in canine small intestine. The density of 125I-labeled peptide tyrosine tyrosine (PYY) binding was highest in myenteric (MY) and submucosal (SUB) plexus fractions enriched in synaptosomes. Two binding sites [high affinity (H) and low affinity (L)] were found in the submucosal synaptosome-enriched membrane: dissociation constant (Kd)H = 7.6 pM, maximal binding capacity (Bmax)H = 28 fmol/mg; KdL = 0.18 nM, BmaxL = 120 fmol/mg protein. The binding of 125I-PYY reached a maximum within 30 min; dissociation was incomplete in the presence of unlabeled PYY. The rate of dissociation was enhanced after exposure of synaptosomes to guanosine 5'-O-(3-thiotriphosphate). Binding of 125I-PYY was completely inhibited by neuropeptide Y (NPY)-(13-36) (in SUB and MY) and by [Leu31,Pro34]NPY (in MY) but only partially by [Leu31,Pro34]NPY in SUB, suggesting the presence of Y2 receptor in SUB and the presence of Y1 and Y2 receptors in MY. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the PYY receptor complex revealed a radioactive band at 70 kDa. The PYY receptors in the canine small intestinal myenteric and submucosal plexus correspond in location to that of PYY in synaptosomes and are coupled with G proteins. Different subtypes are present in different loci.

Characterization of neurokinin type 1 receptor in canine small intestinal muscle

The binding of [3H]substance P (SP) was localized and characterized in canine small intestine. The highest density of [3H]SP binding occurred in the fraction enriched in circular muscle membranes (Bmax 148 +/- 14 fmol/mg; Kd 0.81 +/- 0.01 nM). In the kinetics studies binding was reversible, yielding a similar Kd value. NK1 agonists and antagonists fully displaced, but ligands at the NK2 and NK3 receptor only partially displaced, [3H]SP binding. The potency order of displacement resembled that for the human NK1 receptor ortholog rather than the rat NK1 receptor. Densities of [3H]SP binding were lower in myenteric plexus and longitudinal muscle membrane fractions, but suggested binding in both neural and muscle membranes. The conclusion is that NK1 receptors occur primarily in canine intestine circular muscle plasma membrane.

Heterogeneity of motilin receptors in the gastrointestinal tract of the rabbit

Motilin, a 22-amino acid peptide synthesized in endocrine cells of intestinal mucosa, stimulates GI smooth muscle contractility. To elucidate the mode of action of motilin, we attempted to determine whether motilin receptors are localized on nerve cells or on smooth muscle cells of the GI tract. Mucosa-free tissues from rabbit antrum and duodenum were homogenized separately with a Polytron prior to differential centrifugation to obtain synaptosome or plasma membrane-enriched fractions, as determined by the distribution of [3H]saxitoxin (SAX) binding (neural membranes) and 5' nucleotidase (5'N) activity (smooth muscle plasma membranes). Motilin binding was evaluated by the displacement of [125I]motilin by motilin (1-22) on the various membrane fractions. In the antrum, motilin binding was highly correlated with SAX binding (r = 0.81, p < 0.0005), and also significantly with 5'N activity (r = 0.54, p < 0.05). In the duodenum, motilin binding correlated significantly with 5'N activity (r = 0.67, p < 0.005), but not with SAX binding (r = -0.11, NS). Receptor affinity, for the motilin antagonist MOT(1-12)[CH2NH]10-11, for motilin(1-22), and for the motilin agonist erythromycin lactobionate was significantly (p < 0.001, p < 0.001, and p < 0.05, respectively) higher in SAX-enriched fractions from the antrum than in 5'N-enriched fractions from the duodenum. Therefore, in the rabbit: 1) motilin receptors appear to be predominantly located on nerve tissues in the antrum and restricted to smooth muscle cells in the duodenum, and 2) antral receptors and duodenal receptors displayed different pharmacological characteristics, probably corresponding to two specific and heterogeneous motilin receptor subtypes.

Characterization of cholecystokinin receptors in canine intestinal circular muscle

We localized and characterized the binding of [3H](+/-)-L364,718 in canine small intestine circular muscle. The highest densities of [3H]L364,718 binding were located in the fraction enriched in deep muscular plexus synaptosomal membranes. In this fraction [3H]L364,718 binding was of high density (Bmax 136.78 +/- 53.66 fmol/mg) and high affinity (Kd 1.67 +/- 0.74 nM). Kinetics studies revealed that binding was reversible and yielded a similar Kd value. L364,718, CCK-8-S, and L365,260 fully displaced [3H]L364,718 binding, but ligands at CCKB receptors, gastrin-17, and YM022 did not. Therefore, CCKA receptors in canine intestine circular muscle are located on nerve endings.

Distribution of galanin-immunoreactive nerves in the canine gastrointestinal tract

The distribution of nerves containing galanin immunoreactivity (GAL-IR) in the canine gastrointestinal tract was determined by immunohistochemistry. GAL-IR was observed in nerve cell bodies and nerve fibers in all layers of the lower esophagus, gastric antrum, pylorus, ileum, and colon, and in the sphincters of lower esophagus and pylorus. There were numerous GAL-IR-containing nerve cell bodies in the myenteric plexus of gastric antrum. GAL-IR nerve somata were also common in the myenteric plexus of lower esophagus, ileum, pylorus, and colon, and in the submucous plexus of stomach, ileum, and colon. GAL-IR-positive nerve fibers were also observed around submucous blood vessels of the stomach. GAL-IR nerves are distributed more widely in the canine enteric nervous system than previously recognized.

Distribution and characterization of vasoactive intestinal polypeptide binding in canine lower esophageal sphincter

BACKGROUND

Vasoactive intestinal polypeptide (VIP) may be a nonadrenergic, noncholinergic inhibitory transmitter in the lower esophageal sphincter (LES). There is no biochemical evidence of VIP receptors in the LES.

METHODS

Using membranes from canine LES, VIP receptor distribution and characterization were analyzed by radioligand binding and cross-linking experiments.

RESULTS

High densities of saturable VIP receptors were found (maximum bound [Bmax], 539.2 fmol/mg in the synaptosome-enriched fraction [P2] and 732.7 fmol/mg in the smooth muscle, plasma membrane-enriched fraction [Mic II]), with high affinity for 125I-VIP (dissociation constant [Kd], 1.38 nmol/L in P2 and 1.40 nmol/L in Mic II). Competition binding studies suggested the presence of two binding sites, a high-affinity (inhibitor constant [Ki1], 0.064 nmol/L) and a low-affinity (Ki2, 2.68 nmol/L) binding site in P2 membranes, but only one binding site (Ki, 1.18 nmol/L) in Mic II membranes. Guanosine triphosphate-gamma-s pretreatment eliminated high-affinity binding in P2 membranes by conversion to binding sites of lower affinity (Ki, 2.82 nmol/L). Studies with a cross-linking agent identified VIP receptors in synaptosomal and smooth muscle plasma membrane fractions; a single polypeptide of approximately 60 kilodaltons was found in each membrane.

CONCLUSIONS

Specific VIP receptors exist in both synaptosomal and smooth muscle plasma membrane of canine LES.

VIP receptors on canine submucosal synaptosomes

The present study characterized [125I]VIP binding to synaptosomes from the submucosa of canine small intestine. Studies of saturation, competition binding, and kinetic studies revealed high- and low-affinity binding sites. Studies with GTP-gamma-S and cholera toxin suggested that the receptor was coupled to a G-protein, possibly Gs. Competition with VIP analogs suggested that the N-terminal end of the molecule played the major role in determining affinity and that this receptor was for VIP, not PACAP. Cross-linking VIP to the receptor revealed a single peptide (M(r) congruent to 60,000). We suggest that VIP may act to modulate mediator release from enteric nerve endings.

Differential catabolic fate of neuromedin N and neurotensin in the canine intestinal mucosa

We have established the peptidase content of a P2 fraction (enriched in synaptosomes) and plasma membranes prepared from canine intestinal mucosa. Fourteen exo- and endopeptidases were assayed with fluorimetric or chromogenic substrates and identified by means of specific peptidase inhibitors. Post-proline dipeptidyl aminopeptidase IV, aminopeptidase M, and carboxypeptidase A were the most abundant exopeptidases, while aminopeptidases A and B, dipeptidyl aminopeptidase, pyroglutamyl peptide hydrolase I, and carboxypeptidase B displayed little, if any, activity. Endopeptidase 24.11 was the only endopeptidase that was detected in high amount. By contrast, proline endopeptidase exhibited a low activity, while angiotensin-converting enzyme, endopeptidase 24.15, endopeptidase 24.16, and cathepsin B and D-like activities were not detected. The catabolic rates of the two related neuropeptides, neurotensin (NT) and neuromedin N (NN), established that NN was inactivated 16 to 24 times faster than NT by plasma membrane and P2 fractions, respectively. Furthermore, the two peptides underwent qualitatively distinct mechanisms of degradation. A phosphoramidon-sensitive formation of NT(1-10) was detected as the major NT catabolite, indicating that NT was susceptible to an endoproteolytic cleavage elicited by endopeptidase 24.11. By contrast, NN was inactivated by the action of an exopeptidase at its N-terminus, leading to the formation of [des-Lys1]NN. The occurrence of this NN metabolite was prevented by bestatin and actinonin, but not by the aminopeptidase B inhibitor, arphamenine B, indicating that the release of the N-terminal residue of NN was likely due to aminopeptidase M.(ABSTRACT TRUNCATED AT 250 WORDS)

PYY: a neuropeptide in the canine enteric nervous system

This study re-examined the anatomical locations of PYY in the canine gastrointestinal tract. Immunohistochemical studies with two relatively selective PYY antisera demonstrated PYY-LI immunoreactivity in nerve cell bodies and nerve fibres in the intestinal and gastric myenteric plexus and the intestinal submucosal plexus and in nerve fibres of the intestinal deep muscular plexus. Immunoreactive PYY-LI was also present in ileal endocrine cells. All PYY-LI immunoreactivity was completely abolished by pre-incubation of the antibodies with synthetic PYY but was unaltered by pre-incubation with synthetic NPY. Individual synaptosomal preparations obtained from canine intestinal and gastric myenteric plexus, and intestinal deep muscular plexus and submucous plexus, contained considerable quantities of PYY-LI which, on reverse-phase HPLC, co-eluted with a synthetic canine/porcine PYY standard. In contrast, isolated myenteric ganglia from rat and guinea pig did not contain detectable amounts of PYY-LI. These studies demonstrate that PYY is not confined to distal intestinal endocrine cells in the dog but is also an enteric neuropeptide with maximal concentrations being present in the intestinal myenteric plexus.

An endothelial cell-line contains functional vasoactive intestinal polypeptide receptors: they control inwardly rectifying K+ channels

Bovine endothelial cells cultured from pulmonary artery (ATCC cell line No. 209) were found to contain a high density of 125I-VIP (vasoactive intestinal polypeptide) binding sites. These were found to be saturable and to be fit by a single binding site model (Kd 1.8 nM; Bmax 534 fmol/mg protein). Studies of association and dissociation of 125I-VIP to this site revealed that binding was fully reversible and yielded a Kd value similar to that from equilibrium binding. However competition studies showed that VIP competed for binding at two sites (Ki1 1.2 x 10(-11) M, Ki2 4.7 x 10(-9) M; N1 = 21%, N2 = 77%; Ki a dissociation constant for inhibitor; N percentage of occupied receptors). [Phe1]VIP also competed at two sites, but VIP-(10-28), PHM, [4-Cl-D-Phe6,Leu17]VIP and [D-Ala4]VIP displaced all specific VIP binding in a simple competitive manner. These VIP binding sites were shown to be functional. In patch clamp studies VIP 10(-8)-10(-7) M inhibited opening of inwardly rectifying K+ channels on hyperpolarization. These channels were affected appropriately by alteration in the K(+)-gradient and by Ba2+ or Cs+. The VIP antagonist [4-Cl-D-Phe6, Leu17]VIP prevented or reversed the effects of VIP. These results show that functional VIP receptors are present in high density in a endothelial cell line and provide a possible model for analysis of the molecular biology of these receptors.

Distribution of vasoactive intestinal polypeptide (VIP) binding in circular muscle and characterization of VIP binding in canine small intestinal mucosa

The present study examined the localization and characterization of [125I]vasoactive intestinal polypeptide (VIP) binding to synaptosomes and enterocyte membranes using preparations made from homogenized canine intestinal mucosa and compared it to [3H]saxitoxin binding and VIP-immunoreactive content (markers for synaptosomes). The highest [125I]VIP binding was located in the P2 fraction and was correlated with the locations of maximal [3H]saxitoxin binding and VIP-immunoreactive content. This correlation indicates that VIP receptors are present on synaptosomes of canine small intestinal mucosa. A fraction enriched in synaptosomes contained a high density of saturable VIP receptors (352 +/- 26.40 fmol/mg) having high affinity (Kd, 0.23 nM) for [125I]VIP. Studies of association and dissociation of [125I]VIP to this site revealed that binding was fully reversible and yielded a Kd value similar to that from equilibrium binding. Competition binding experiments suggested the presence of two binding sites, a high and a low affinity binding site. The order of competition potency was VIP greater than peptide histidine isoleucine greater than secretin greater than peptide histidine methionine greater than or equal to [D-Ala4]VIP greater than or equal to [Phe1]VIP greater than VIP10-28 greater than [4-Cl-D-Phe6-Leu17]VIP. All these competitors displaced all specifically bound VIP. VIP, peptide histidine isoleucine and secretin interacted differentially with each of the two binding sites. Peptide histidine methionine, [D-Ala4]VIP, [Phe1]VIP, VIP10-28 and [4-Cl-D-Phe6-Leu17]VIP interacted with a single low affinity at all binding sites. Other VIP binding sites were sought in circular muscle and submucosa.(ABSTRACT TRUNCATED AT 250 WORDS)