Motility Recordings Research Articles

Comparing parameter-reduction methods on a biophysical model of an auditory hair cell

Biophysical models describing complex cellular phenomena typically include systems of nonlinear differential equations with many free parameters. While experimental measurements can fix some parameters, those describing internal cellular processes frequently remain inaccessible. Hence, a proliferation of free parameters risks overfitting the data, limiting the model's predictive power. In this study, we develop systematic methods, applying statistical analysis and dynamical-systems theory, to reduce parameter count in a biophysical model. We demonstrate our techniques on a five-variable computational model designed to describe active, mechanical motility of auditory hair cells. Specifically, we use two statistical measures, the total-effect and PAWN indices, to rank each free parameter by its influence on selected, core properties of the model. With the resulting ranking, we fix most of the less influential parameters, yielding a five-parameter model with refined predictive power. We validate the theoretical model with experimental recordings of active hair-bundle motility, specifically by using Akaike and Bayesian information criteria after obtaining maximum-likelihood fits. As a result, we determine the system's most influential parameters, which illuminate the key biophysical elements of the cell's overall features. Even though we demonstrate with a concrete example, our techniques provide a general framework, applicable to other biophysical systems. Published by the American Physical Society 2024

Perinatal high-fat diet exposure alters oxytocin and corticotropin releasing factor inputs onto vagal neurocircuits controlling gastric motility.

Perinatal high-fat diet (pHFD) exposure alters the development of vagal neurocircuits that control gastrointestinal (GI) motility and reduce stress resiliency in offspring. Descending oxytocin (OXT; prototypical anti-stress peptide) and corticotropin releasing factor (CRF; prototypical stress peptide) inputs from the paraventricular nucleus (PVN) of the hypothalamus to the dorsal motor nucleus of the vagus (DMV) modulate the GI stress response. How these descending inputs, and their associated changes to GI motility and stress responses, are altered following pHFD exposure are, however, unknown. The present study used retrograde neuronal tracing experiments, cerebrospinal fluid extraction, in vivo recordings of gastric tone, motility and gastric emptying rates, and in vitro electrophysiological recordings from brainstem slice preparations to investigate the hypothesis that pHFD alters descending PVN-DMV inputs and dysregulates vagal brain-gut responses to stress. Compared to controls, rats exposed to pHFD had slower gastric emptying rates and did not respond to acute stress with the expected delay in gastric emptying. Neuronal tracing experiments demonstrated that pHFD reduced the number of PVNOXT neurons that project to the DMV, but increased PVNCRF neurons. Both in vitro electrophysiology recordings of DMV neurons and in vivo recordings of gastric motility and tone demonstrated that, following pHFD, PVNCRF -DMV projections were tonically active, and that pharmacological antagonism of brainstem CRF1 receptors restored the appropriate gastric response to brainstem OXT application. These results suggest that pHFD exposure disrupts descending PVN-DMV inputs, leading to a dysregulated vagal brain-gut response to stress. KEY POINTS: Maternal high-fat diet exposure is associated with gastric dysregulation and stress sensitivity in offspring. The present study demonstrates that perinatal high-fat diet exposure downregulates hypothalamic-vagal oxytocin (OXT) inputs but upregulates hypothalamic-vagal corticotropin releasing factor (CRF) inputs. Both in vitro and in vivo studies demonstrated that, following perinatal high-fat diet, CRF receptors were tonically active at NTS-DMV synapses, and that pharmacological antagonism of these receptors restored the appropriate gastric response to OXT. The current study suggests that perinatal high-fat diet exposure disrupts descending PVN-DMV inputs, leading to a dysregulated vagal brain-gut response to stress.

Brainstem astrocytes control homeostatic regulation of caloric intake.

Prolonged high-fat diet (HFD) exposure is associated with hyperphagia, excess caloric intake and weight gain. After initial exposure to a HFD, a brief (24-48h) period of hyperphagia is followed by the regulation of caloric intake and restoration of energy balance within an acute (3-5day) period. Previous studies have demonstrated this occurs via a vagally mediated signalling cascade that increases glutamatergic transmission via activation of NMDA receptors located on gastric-projecting neurons of the dorsal motor nucleus of the vagus (DMV). The present study used electrophysiological recordings from thin brainstem slice preparations, in vivo recordings of gastric motility and tone, measurement of gastric emptying rates, and food intake studies to investigate the hypothesis that activation of brainstem astrocytes in response to acute HFD exposure is responsible for the increased glutamatergic drive to DMV neurons and the restoration of caloric balance. Pharmacological and chemogenetic inhibition of brainstem astrocytes reduced glutamatergic signalling and DMV excitability, dysregulated gastric tone and motility, attenuated the homeostatic delay in gastric emptying, and prevented the decrease in food intake that is observed during the period of energy regulation following initial exposure to HFD. Understanding the mechanisms involved in caloric regulation may provide critical insights into energy balance as well as into the hyperphagia that develops as these mechanisms are overcome. KEY POINTS: Initial exposure to a high fat diet is associated with a brief period of hyperphagia before caloric intake and energy balance is restored. This period of homeostatic regulation is associated with a vagally mediated signalling cascade that increases glutamatergic transmission to dorsal motor nucleus of the vagus (DMV) neurons via activation of synaptic NMDA receptors. The present study demonstrates that pharmacological and chemogenetic inhibition of brainstem astrocytes reduced glutamatergic signalling and DMV neuronal excitability, dysregulated gastric motility and tone and emptying, and prevented the regulation of food intake following high-fat diet exposure. Astrocyte regulation of glutamatergic transmission to DMV neurons appears to involve release of the gliotransmitters glutamate and ATP. Understanding the mechanisms involved in caloric regulation may provide critical insights into energy balance as well as into the hyperphagia that develops as these mechanisms are overcome.

High-resolution ultrasound and speckle tracking: a non-invasive approach to assess in vivo gastrointestinal motility during development.

Gastrointestinal motor activity has been extensively studied in adults; however, only few studies have investigated fetal motor skills. It is unknown when the gastrointestinal tract starts to contract during the embryonic period and how this function evolves during development. Here, we adapted a non-invasive high-resolution echography technique combined with speckle tracking analysis to examine the gastrointestinal tract motor activity dynamics during chick embryo development. We provided the first recordings of fetal gastrointestinal motility in living embryos without anesthesia. We found that, although gastrointestinal contractions appear very early during development, they become synchronized only at the end of the fetal period. To validate this approach, we used various pharmacological inhibitors and BAPX1 gene overexpression in vivo. We found that the enteric nervous system determines the onset of the synchronized contractions in the stomach. Moreover, alteration of smooth muscle fiber organization led to an impairment of this functional activity. Altogether, our findings show that non-invasive high-resolution echography and speckle tracking analysis allows visualization and quantification of gastrointestinal motility during development and highlight the progressive acquisition of functional and coordinated gastrointestinal motility before birth.

High-Resolution Spatiotemporal Quantification of Intestinal Motility With Free-Form Deformation.

To develop a method to quantify strain fields from in vivo intestinal motility recordings that mitigate accumulation of tracking error. The deforming geometry of the intestine in video sequences was modeled by a biquadratic B-spline mesh. Green-Lagrange strain fields were computed to quantify the surface deformations. A nonlinear optimization scheme was applied to mitigate the accumulation of tracking error associated with image registration. The optimization scheme maintained the RMS strain error under 1% and reduced the rate of strain error by 97% during synthetic tests. The algorithm was applied to map 64 segmental, 12 longitudinal, and 23 propagating circular contractions in the jejunum. Coordinated activity of the two muscle layers could be identified and the strain fields were able to map and quantify the anisotropic contractions of the intestine. Frequency and velocity were also quantified, from which two types of propagating circular contractions were identified: (i) [Formula: see text] strain contractions that originated spontaneously and propagated at [Formula: see text] mm/s in two pigs, and (ii) cyclic propagating contractions of [Formula: see text] strain occurred at [Formula: see text] cpm and propagated at [Formula: see text] mm/s in a rabbit. The algorithm simultaneously mapped the circular, longitudinal activity of the intestine with high spatial resolution and quantified anisotropic contractions and relaxations. The proposed algorithm can now be used to define the interactions of muscle layers during motility patterns. It can be integrated with high-resolution bioelectrical recordings to investigate the regulatory mechanisms of motility.

Antroduodenal motility recording identifies characteristic patterns in gastroparesis related to underlying etiology.

Gastroparesis (GP) is a gastrointestinal disorder associated with significant morbidity and healthcare costs. GP patients form a heterogeneous population with diverse etiology, and treatment is often challenging due to a poorly understood underlying pathophysiology. The aim of the present study was to assess antroduodenal motility patterns among the different GP etiologies. We reviewed antroduodenal manometry (ADM) recordings of patients with confirmed GP between 2009 and 2019. ADM measurements were evaluated for fed period duration, number of phase III contractions and migrating motor complexes (MMCs), motility index (MI), and presence of neuropathic patterns. A total of 167 GP patients (142 women, median age 45 [31-57]) were included. The following etiologies were identified: idiopathic n=101; post-surgery n=36; and diabetes n=30. Fed period duration was significantly longer in idiopathic (p<0.01) and diabetic GP patients (p<0.05) compared with post-surgery GP patients. Furthermore, the number and duration of phase III contractions and the number of MMCs were significantly lower in idiopathic and diabetic patients compared with post-surgery GP patients (p<0.01). Likewise, absence of MMCs during 6-h recording was more often observed in idiopathic and diabetes GP patients compared with post-surgery GP patients (resp. p<0.01 and p<0.05). Antroduodenal motility patterns are different among GP etiologies. A dysmotility spectrum was identified with different patterns ranging from post-surgery GP to idiopathic and diabetic GP.

Impaired nitrergic relaxation in pyloric sphincter of the 6-OHDA Parkinson's disease rat.

Patients with Parkinson's disease (PD) often suffer from delayed gastric emptying, but the underlying mechanism remains unclear. We have shown previously that a PD rat model comprising bilateral substantia nigra destruction by 6-hydroxydopamine (6-OHDA rats) exhibits gastroparesis with alteration of neural nitric oxide synthase (nNOS) and acetylcholine in gastric corpus. However, changes in pyloric motility in the 6-OHDA rats have not been characterized. Solid gastric emptying test, immunofluorescence, Western blot, and in vitro pyloric motility recordings were used to assess pyloric motor function in the 6-OHDA rats. The 6-OHDA-treated rats displayed delayed solid gastric emptying and a lower basal pyloric motility index. In the 6-OHDA rats, high K+-induced transient contractions were weaker in pyloric sphincters. Electric field stimulation (EFS)-induced pyloric sphincter relaxation was lower in the 6-OHDA rats. NG-nitro-l-arginine methyl ester (l-NAME), a nonselective inhibitor of NOS, markedly inhibited the EFS-induced relaxation in both control and 6-OHDA rats. Pretreatment of tetrodotoxin abolished the effect of EFS on the pyloric motility. In addition, nNOS-positive neurons were extensively distributed in the pyloric myenteric plexus, whereas the number of nNOS-immunoreactive neurons and the protein expression of nNOS were significantly decreased in the pyloric muscularis of 6-OHDA rats. However, sodium nitroprusside-induced pyloric relaxations were similar between the control and 6-OHDA rats. These results indicate that the pyloric sphincters of 6-OHDA rats exhibit both weakened contraction and relaxation. The latter may be due to reduced nNOS in the pyloric myenteric plexus. The dysfunction of the pyloric sphincter might be involved in the delayed gastric emptying.NEW & NOTEWORTHY Reduced nitrergic neurons in pyloric myenteric plexus potently contributed to the attenuated relaxation in 6-hydroxydopamine (6-OHDA) rats, subsequently affecting gastric emptying. SNP could well improve the relaxation of pylori in 6-OHDA rats. The present study provides new insight into the diagnosis and treatment of delayed gastric emptying in patients with PD.

Centrally Administered Neuropeptide-S Alleviates Gastrointestinal Dysmotility Induced by Neonatal Maternal Separation.

Neuropeptide-S (NPS) regulates autonomic outflow, stress response, and gastrointestinal (GI) motor functions. This study aimed to investigate the effects of NPS on GI dysmotility induced by neonatal maternal separation (MS). MS was conducted by isolating newborn pups from dams from postnatal day 1 to day 14. In adulthood, rats were also exposed to chronic homotypic stress (CHS). Visceral sensitivity was assessed by colorectal distension-induced abdominal contractions. Gastric emptying (GE) was measured following CHS, whereas fecal output was monitored daily. NPS or NPS receptor (NPSR) antagonist was centrally applied simultaneously with electrocardiography and gastric motility recording. Immunoreactivities for NPS, NPSR, corticotropin-releasing factor (CRF), choline acetyltransferase (ChAT), tyrosine hydroxylase (TH), and c-Fos were assessed by immunohistochemistry. NPS alleviated the MS-induced visceral hypersensitivity. Under basal conditions, central exogenous or endogenous NPS had no effect on GE and gastric motility. NPS restored CHS-induced gastric and colonic dysmotility in MS rats while increasing sympatho-vagal balance without affecting vagal outflow. NPSR expression was detected in CRF-producing cells of hypothalamic paraventricular nucleus, and central amygdala, but not in Barrington's nucleus. Moreover, NPSR was present in ChAT-expressing neurons in dorsal motor nucleus of the vagus (DMV), and nucleus ambiguus (NAmb) in addition to the TH-positive neurons in C1/A1, and locus coeruleus (LC). Neurons adjacent to the adrenergic cells in LC were found to produce NPS. NPS administration caused c-Fos expression in C1/A1 cells, while no immunoreactivity was detected in DMV or NAmb. NPS/NPSR system might be a novel target for the treatment of stress-related GI dysmotility.

DMV extrasynaptic NMDA receptors regulate caloric intake in rats.

Acute high-fat diet (aHFD) exposure induces a brief period of hyperphagia before caloric balance is restored. Previous studies have demonstrated that this period of regulation is associated with activation of synaptic N-methyl-D-aspartate (NMDA) receptors on dorsal motor nucleus of the vagus (DMV) neurons, which increases vagal control of gastric functions. Our aim was to test the hypothesis that activation of DMV synaptic NMDA receptors occurs subsequent to activation of extrasynaptic NMDA receptors. Sprague-Dawley rats were fed a control or high-fat diet for 3–5 days prior to experimentation. Whole-cell patch-clamp recordings from gastric-projecting DMV neurons; in vivo recordings of gastric motility, tone, compliance, and emptying; and food intake studies were used to assess the effects of NMDA receptor antagonism on caloric regulation. After aHFD exposure, inhibition of extrasynaptic NMDA receptors prevented the synaptic NMDA receptor–mediated increase in glutamatergic transmission to DMV neurons, as well as the increase in gastric tone and motility, while chronic extrasynaptic NMDA receptor inhibition attenuated the regulation of caloric intake. After aHFD exposure, the regulation of food intake involved synaptic NMDA receptor–mediated currents, which occurred in response to extrasynaptic NMDA receptor activation. Understanding these events may provide a mechanistic basis for hyperphagia and may identify novel therapeutic targets for the treatment of obesity.

Characterization of alternating neurogenic motor patterns in mouse colon.

Colonic motor complexes (CMCs) have been widely recorded in the large intestine of vertebrates. We have investigated whether in the smooth muscle, a single unified pattern of electrical activity, or different patterns of electrical activity give rise to the different neurogenic patterns of motility underlying CMCs in vitro. To study differences of the CMCs between proximal and distal colon, we used a novel combination of techniques to simultaneously record muscle diameter and force at multiple sites along the whole mouse colon ex vivo. In addition, electrical activity of smooth muscle was recorded by suction electrodes. Two distinct types of CMCs were distinguished; CMCs that propagated along the entire colon (complete CMC) and CMCs which were restricted to the proximal colon (incomplete CMC). The two types of CMC often occurred in the same preparations. Incomplete CMCs had longer bursts of smooth muscle action potentials than complete CMCs and propagated more slowly. Interestingly, both types of CMC were associated with similar frequency bursts of smooth muscle action potentials at ~2.4Hz. In the most proximal colon, an additional firing frequency was detected close to ~7Hz generating multiple peaks within each CMC. We report distinct characteristics underlying complete and incomplete CMCs in isolated mouse colon. Recognizing these distinct patterns of motility will be important for future interpretation of analysis of murine colonic motility recordings. The identification of alternating patterns of motor activity in proximal colon, but not distal colon may reflect specific neural mechanisms for fecal pellet formation.

SPARC: Chronic Simultaneous Recording of Gastric Motility and Ad Libitum Feeding Behavior in Awake, Freely Moving Rats with Vagal Nerve Simulation

ObjectiveIn spite of its apparent promise, bioelectric modulation of the vagal innervation of the stomach has had limited success modifying ingestive behavior. But, importantly, stimulation parameters in previous bioelectrical applications were arbitrarily employed without information as to their stimulus‐response relationships or optimal locations. With this in mind, we established a model of chronic vagal nerve stimulation (VNS) where we record GI motility continuously in unanesthetized, freely moving rats while their intake is monitored as they consume chow and water ad libitum (automated food and liquid intake monitors; BioDAQ, Research Diets Inc.).MethodsA patch electrode (MicroProbes) was attached to the muscle wall of the proximal forestomach of healthy adult male Sprague‐Dawley rats at a site known to contain the highest density of vagal mechanoreceptors. A strain gauge was similarly attached to the muscle wall of the antrum. Rats were maintained in their home cages equipped with BioDAQ feeders, while continuously tethered to overhead commutators. Following recovery, the feeding and drinking behavior as well as antral motility of individual rats was continuously monitored and recorded with and without concomitant VNS (pulse parameters, derived from acute studies: 0.3mA/0.2ms/10Hz; 20s On:40s Off). Subjects were exposed to each of the following four conditions on different days at the onset of lights off: a 2 h fast, a 2 h fast while being stimulated, 2 h ad lib access to chow, and 2 h ad lib access to chow while being stimulated. In a separate study, 2 days of strain gauge activity was continuously recorded: 24 h without stimulation followed by 24 h with stimulation.ResultsRats recovered quickly following surgery. Compared to the 2 h fasted condition, there was a 17% increase in antral peristalsis (change in amplitude and frequency expressed as area under the curve) when subjects were fasted while being stimulated; similarly, there was an 18% increase in antral peristalsis when subjects were stimulated while consuming chow compared to 2 h intake of chow without stimulation. The same pattern was observed in the 2 d study with a 23% increase in antral activity during 24 h of stimulation compared to 24 h pre‐stimulation. Interestingly, a 12% increase in total chow intake occurred when stimulated for 24 h while no difference was noted in water intake between the two conditions.ConclusionsInitial exposure to VNS results in a modest increase in antral activity with and without the presence of food in the stomach. Analyses are underway to tease apart the effect of stimulation on motility in relation to meal size. Finally, these findings confirm that our chronic VNS model has considerable potential for determining optimal stimulation parameters necessary for making meaningful changes in gut motility.Support or Funding InformationSPARC/NIH Office of the Director OT2 OD023847NIDDK/NIH R01 DK027627

Exploring the impact of real-life dosing conditions on intraluminal and systemic concentrations of atazanavir in parallel with gastric motility recording in healthy subjects

This work strived to explore gastrointestinal (GI) dissolution, supersaturation and precipitation of the weakly basic drug atazanavir in humans under different ‘real-life’ intake conditions. The impact of GI pH and motility on these processes was thoroughly explored. In a cross-over study, atazanavir (Reyataz®) was orally administered to 5 healthy subjects with (i) a glass of water, (ii) a glass of Coca-Cola® and (iii) a glass of water under hypochlorhydric conditions (induced by concomitant intake of a proton-pump inhibitor (PPI)). After intake, GI fluids were aspirated from the stomach and the duodenum and, subsequently, analyzed for atazanavir. In parallel, blood samples were collected to assess systemic concentrations. In general, the results of this study revealed that the acidic gastric pH in combination with gastric residence time played a crucial role in the dissolution of atazanavir along the GI tract. After intake of atazanavir with a glass of water (i.e., reference condition), complete gastric dissolution was observed. After GI transfer, supersaturation was noticed for a limited amount of time (1.25 h). With respect to the Coca-Cola® condition, complete gastric dissolution was also observed. A delay in gastric emptying, highly likely caused by the caloric content (101 kcal), was responsible for delayed arrival of atazanavir into the upper small intestine, creating a longer time window of supersaturated concentrations in the duodenal segment (3.25 h) compared to the water condition. The longer period of supersaturated concentrations resulted in a slightly higher systemic exposure of atazanavir compared to the condition when atazanavir was taken with a glass of water. A remarkable observation was the creation (when the drug was given in the migrating motor complex (MMC) phase 2) or maintenance (when the drug was given in MMC phase 1) of a quiescent phase for up to 80 min. With respect to the PPI condition, negligible gastric and intestinal concentrations were observed, resulting in minimal systemic exposure for all subjects. It can be concluded that gastric pH and residence time play a pivotal role in the intestinal disposition of atazanavir in order to generate sufficiently high concentrations further down in the intestinal tract for a sufficient period of time, thus creating a beneficial driving force for intestinal absorption.

The inhibitory effect of somatostatin on gastric motility in Suncus murinus.

Gastric contractions show two specific patterns in many species, migrating motor contractions (MMC) and postprandial contractions (PPCs), that occur in the fasted and fed states, respectively. In this study, we examined the role of somatostatin (SST) in gastric motility both in vivo and in vitro using the Asian house shrew (Suncus murinus). We performed in vivo recordings of gastric motility and in vitro organ bath experiments using S. murinus, which was recently established as a small laboratory animal for use in tests of gastrointestinal motility. SST (1.65 µg kg−1 min−1) was intravenously administered during phase II of MMC and PPCs. Next, the effect of SST on motilin-induced gastric contractions at phase I of MMC was measured. Cyclosomatostatin (CSST), an SST receptor antagonist, was administered at the peak of phase III of MMC. In addition, the effect of SST (10−11–10−9 M) on motilin-induced gastric contractions was evaluated using an organ bath experiment in vitro. In conscious, free-moving S. murinus, the administration of SST decreased the occurrence of the spontaneous phase II of MMC and PPCs. Pretreatment with SST and octreotide suppressed the induction of motilin-induced gastric contractions both in vivo and in vitro. Administration of CSST before the peak of spontaneous phase III contractions had no effect on gastric contractions. Endogenous SST is not involved in the regulation of gastric MMC and PPCs, but exogenous SST suppresses spontaneous gastric contractions. Thus, SST would be good for treating abnormal gastrointestinal motility disorders.

Intranasal Administration of Oxytocin Attenuates Stress Responses Following Chronic Complicated Stress in Rats.

Background/AimsGastrointestinal (GI) symptoms may develop when we fail to adapt to various stressors of our daily life. Central oxytocin (OXT) can counteract the biological actions of corticotropin-releasing factor (CRF), and in turn attenuates stress responses. Administration (intracerebroventricular) of OXT significantly antagonized the inhibitory effects of chronic complicated stress (CCS) on GI dysmotility in rats. However, intracerebroventricular administration is an invasive pathway. Intranasal administration can rapidly deliver peptides to the brain avoiding stress response. The effects of intranasal OXT on hypothalamus-pituitary-adrenal axis and GI motility in CCS conditions have not been investigated.MethodsA CCS rat model was set up, OXT 5, 10, or 20 μg were intranasal administered, 30 minutes prior to stress loading. Central CRF and OXT expression levels were analyzed, serum corticosterone and OXT concentrations were measured, and gastric and colonic motor functions were evaluated by gastric emptying, fecal pellet output, and motility recording system.ResultsRats in CCS condition showed significantly increased CRF expression and corticosterone concentration, which resulted in delayed gastric emptying and increased fecal pellet output, attenuated gastric motility and enhanced colonic motility were also recorded. OXT 10 μg or 20 μg significantly reduced CRF mRNA expression and the corticosterone concentration, OXT 20 μg also helped to restore GI motor dysfunction induced by CCS.ConclusionIntranasal administration of OXT has an anxiolytic effect and attenuates the hypothalamus-pituitary-adrenal axis in response to CCS, and gave effects which helped to restore GI dysmotility, and might be a new approach for the treatment of stress-induced GI motility disorders.

Acute High‐Fat Diet Induced Modulation of Glutamatergic Currents in Dorsal Motor Nucleus of the Vagus Neurons is Dependent on Activation of Extrasynaptic NMDA Receptors

Following HFD exposure, both humans and experimental animals undergo a brief period of hyperphagia (1–2 days), before caloric balance is restored (3–5 days). We showed previously that acute HFD increases glutamatergic transmission to neurons of the dorsal motor nucleus of the vagus (DMV) via activation of synaptic NMDA receptors (NMDA‐R), increasing motoneuron excitability and efferent control of gastric function (PMID: 29368945) although the mechanism responsible has not been elucidated. Previous studies have suggested, however, that activation of extrasynaptic NMDA‐Rs may cause sufficient local depolarization to remove the Mg2+ block on NMDA‐Rs, allowing for their activation. The purpose of this study is to test the hypothesis that the increased synaptic NMDA‐R activation in DMV neurons following acute HFD exposure occurs subsequent to activation of extrasynaptic NMDA‐R.Whole‐cell patch clamp recordings were made from gastric‐projecting DMV neurons in thin (300μm) brainstem slices of Sprague‐Dawley rats, 4–6 weeks of age. Rats were fed control or HFD (14% and 60% kcal from fat, respectively) for 3–5 days prior to experimentation. The effects of increasing (from 1.2mM to 2.4mM) or decreasing (to 0.6mM) extracellular levels of Mg2+, the NMDA‐R antagonist memantine (30μM), and the glutamate uptake inhibitor, dihydrokainate (DHK; 30μM), on NMDA‐mediated miniature excitatory postsynaptic currents (mEPSCs) and DMV neuronal excitability (action potential firing rate; AP) were assessed. In vivo recordings of gastric tone and motility were made in response to brainstem microinjection of DHK or 4th ventricular application of memantine (60pmol/60nL and 50pmol/2mL, respectively).Following acute HFD, the NMDA‐R antagonist AP5 (25mM) decreases mEPSC frequency and AP firing rate in DMV neurons; these actions were blocked by memantine (65.1±9% vs. 12.6±9% and 78.9±14% vs. 18.1±8%, respectively n=5–13, P<0.05). In control rate, however, increasing extracellular glutamate concentration with DHK uncovered inhibitory actions of AP5 on mEPSCs and AP firing rate (115.7±12% vs. 77.2%±6% and 87.6%±14% vs. 70.5%±16% respectively, n=5–15, P<0.05). Furthermore, increasing extracellular [Mg2+] blocked the effects of AP5 following acute HFD exposure (89.0±25%, n=4, p>0.05) whereas decreasing the extracellular [Mg2+] uncovered synaptic NMDA‐R mediated synaptic currents in control rats (48.6±5%, n=4, P<0.05). Preliminary in vivo recordings suggest that brainstem microinjection of memantine attenuated the glutamate‐dependent decrease in gastric tone and motility following acute HFD exposure, whereas DHK uncovered this effect in control rats.These data suggest that the acute HFD‐induced increase in synaptic NMDA‐R activation occurs following extrasynaptic NMDA‐R activation, although the source of this extrasynaptic glutamate remains to be elucidated. Understanding these mechanisms and, importantly, how they are lost following continued HFD exposure, may provide a mechanistic understanding of hyperphagia and weight gain as well as identify potential therapeutic targets for the treatment of obesity.Support or Funding InformationNIH DK111667 to KNBThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Colonic Electromechanical Abnormalities Underlying Post-operative Ileus: A Systematic and Critical Review.

Post-operative ileus (POI) is an inevitable consequence of major abdominal surgery, and may be prolonged in up to 30% of patients. Ileus is commonly presumed to result from paralysis of the GI tract, though there is little direct evidence to support this view. The aim of this review is to systematically search and critically review the literature investigating post-operative colonic electrical and mechanical activity. MEDLINE and Embase databases were systematically searched for articles investigating post-operative colonic motor or electrical activity in human patients. Nineteen original articles investigating post-operative colonic motor or electrical activity were identified. Most studies have used low-resolution techniques, with intermittent recordings of colonic motility. Numerous studies have shown that colonic electrical and motor activity does not cease routinely following surgery, but is of abnormal character for 3–6 days following laparotomy. One recent high-resolution manometry study identified hyperactive cyclic motor patterns occurring in the distal colon on the first post-operative day. Low-resolution studies have shown colonic slow waves are not inhibited by surgery, and are present even in the immediate post-operative period. Recovery of normal motility appears to occur in a proximal to distal direction and is temporally correlated with the clinical return of bowel function. No studies have investigated motility specifically in prolonged POI. Future studies should use high-resolution techniques to accurately characterise abnormalities in electrical and mechanical function underlying POI, and correlate these changes with clinical recovery of bowel function.

Arcuate Nucleus Orexin-A Signaling Alleviates Cisplatin-Induced Nausea and Vomiting Through the Paraventricular Nucleus of the Hypothalamus in Rats.

The most common side effects of cisplatin chemotherapy are nausea and vomiting, and the overwhelming majority of research studies on the mechanism of cisplatin-induced nausea have been focused on the “vomiting center.” As a modulatory center of gastric motility, the roles of the hypothalamus in nausea and vomiting remain unclear. In the present study, we investigated the effects of exogenous orexin-A injected into the arcuate nucleus (ARC) on cisplatin-induced nausea and vomiting, and the possible underlying mechanism. Kaolin intake was calculated daily in cisplatin-treated and saline-treated rats. Gastric motility recording, injections into the ARC, and lesions of the paraventricular nucleus (PVN) were used to study the effects of orexin-A and the hypothalamic nucleus on disorders of gastrointestinal function in cisplatin-treated rats. The pathway from the ARC to the PVN was observed through Fluoro-Gold retrograde tracing. Furthermore, an NPY Y1 receptor antagonist was administered to explore the possible mechanisms involved in the effects of orexin-A in the ARC. We illustrated that exogenous orexin-A injected into the ARC reduced kaolin intake and promoted gastric motility in cisplatin-treated rats, and these effects could have been blocked by an ipsilateral PVN lesion or co-injected antagonist of orexin-A-SB334867. Additional results showed that orexin-A-activated neurons in the ARC communicated directly with other neurons in the PVN that express neuropeptide Y (NPY). Furthermore, activation of the downstream NPY pathway was required for the observed effects of orexin in the ARC on cisplatin-induced nausea and vomiting. These findings reveal a novel neurobiological circuit from the ARC to the PVN that might provide a potential target for the prevention and treatment of cisplatin-induced nausea and vomiting.

Elobixibat, an ileal bile acid transporter inhibitor, induces giant migrating contractions during natural defecation in conscious dogs.

Chronic constipation affects 14%-17% of the population. Elobixibat, a novel, ileal bile acid transporter (IBAT) inhibitor, has been approved as a new chronic constipation drug in Japan in January 2018. The present study aimed to examine the pharmacological effects of elobixibat on colonic motility in conscious dogs using a telemetry system. Six male beagle dogs were surgically implanted with strain gauge force transducers for gastrointestinal (GI) motility recording. The motility index was calculated from GI motility at each recording site in conscious and nonrestraint dogs. The fasted dogs were orally administered elobixibat (3, 10, or 30mg kg-1 ) or 30mg kg-1 of sennoside as positive control or vehicle using a crossover design and washout period of more than 6days. One hour after drug administration, the dogs were fed chow, and GI motility and defecation were observed for 10hours; GI motility was quantified to calculate giant migrating contractions (GMCs). Fecal bile acids (BAs) were determined as well. Elobixibat and sennoside significantly increased the number of defecations, fecal wet weight, and water content within 10hours after administration. Elobixibat dose-dependently decreased the time to first bowel movement, increased the amount of total fecal BAs, and rapidly induced mild GMCs during defecation; however, higher strength of GMCs was observed with sennoside. Elobixibat induces bowel movements faster than sennoside through a different mechanism. Elobixibat locally inhibits IBAT in the ileal lumen, leading to elevated fecal BAs in the colon and induced mild GMCs during defecation.

Rasagiline, an inhibitor of MAO-B, decreases colonic motility through elevating colonic dopamine content.

Dopamine (DA) is a negative modulator of gut motility. Monoamine oxidase-B (MAO-B) is an important metabolic enzyme degrading DA. Rasagiline, an irreversible MAO-B inhibitor, is used to treat Parkinson's disease because of its neuroprotective effect and increasing central DA. However, it is unclear whether MAO-B exists in the colon and rasagiline increases colonic DA, thereby affecting colonic motility. Immunohistochemistry, western blotting, enzyme activity assay, colonic motility recording, gut transit test, and high-performance liquid chromatography-electrochemical detection were employed in this study. Monoamine oxidase-B was distributed in the colonic muscular layers including neurons and glias of rat and human. When oral treatment of rats with rasagiline for 4weeks, in vitro colonic motility was significantly reduced, but it was greatly reversed by SCH-23390, an antagonist of DA D1 receptor. The rasagiline-treated rats also manifested decreased MAO-B activity and increased DA content in the colonic muscular layer, but no alterations were detected in the protein expressions of D1 and D2 receptors, and MAO-A and MAO-B, as well as in the content of 5-hydroxytryptamine and noradrenaline. Moreover, acute administration of rasagiline did not affect the colonic motility in vitro and the colonic DA level in rats, although MAO-B activity was significantly inhibited. Monoamine oxidase-B is abundant in the colonic muscular layer including myenteric plexus of rat and human. Long-term administration of rasagiline can increase colonic DA thereby inhibiting colonic motility, suggesting that colonic MAO-B could be a potential drug target for colonic dysmotility.

A novel flush technique to simulate natural dispersal of spermatozoa in the female reproductive tract and expedite motility assessment of fresh ejaculated Merino (<i>Ovis aries</i>) sperm

Motility is an important criterion in the assessment and quantification of the quality of ejaculated and epididymal sperm samples. Ovine sperm spermatozoa are particularly susceptible to cryodamage, and shortening the interval from collection to cryostorage may potentially minimize the negative effects of cryopreservation, thereby improving the post-thaw viability of ram spermatozoa. The use of the swim-up technique (SUT) in quantifying spermatozoa motility is well documented, especially for the isolation of highly motile spermatozoa for assisted reproductive purposes. However, this technique is time consuming and involves a swim-up period of 10 minutes before the motility of a sample is recorded by using computer-assisted sperm analysis (CASA) software such as the Sperm Class Analyser® (SCA®). The novel flush technique (FT) allows for capturing of sperm motility tracks via the SCA® system shortly after semen collection, that is, within a minute. This study compared fresh ejaculated sperm motility traits by using the SUT and FT. Motility evaluations were performed using 45 semen samples obtained from 15 adult Merino rams (Ovis aries) at weekly intervals. Motility recordings were captured at 100 frames per second, using a calibrated 20 μm deep Leja slide. The percentage total motile spermatozoa of samples subjected to the FT was 89.2%, which was significantly higher than that recorded by the SUT (83.9%). The results also indicated that the wobble (WOB) parameter showed significantly higher values when using the FT, and parameters curvilinear velocity (VCL) and amplitude of the lateral head displacement (ALH) indicated significantly higher values when using the SUT. Establishing the ideal spermatozoa concentration and analysis of sperm subpopulation motility characteristics would assist in the optimization of the FT, and its use in CASA motility analysis of ovine spermatozoa. Standardization of CASA analysis of ovine semen samples, which would enable the selection of quality spermatozoa samples for use in field insemination (fresh samples) or in vitro fertilization programs, and laparoscopic AI cryopreserved samples warrants further investigation.Keywords: Cryopreservation, merino, sperm class analyser, sperm motility, sperm separation technique