Evaluation of gastrointestinal motility in awake rats: a learning exercise for undergraduate biomedical students

Role of atrial natriuretic peptide and oxytocin in gastric emptying delay induced by right atrial stretch in rats

Fluid volume and osmolality balance are maintained by complex neuroendocrine and liquid-salt intake behavior, cardiovascular and renal mechanisms, and gastrointestinal adjustments. Mechanical stretching of the right atrium [atrial stretch (AS)] enhances central venous pressure and heart rate while decreasing gastric emptying (GE) of liquid in rats. We evaluated the effect of AS on GE and plasma levels of atrial natriuretic peptide (ANP), oxytocin (OT), and corticosterone (CORT) to determine whether ANP contributes to the OT-mediated GE delay of liquids due to AS in awake rats. Initially, we performed thoracotomy followed by right appendectomy (AX) or sham thoracotomy. One week later, rats were randomly subjected to pretreatment with NaCl 0.15 M (control), atosiban (AT, OT-antagonist), anantin (ANT, ANP-antagonist), or dexamethasone (DEX). Afterward, 50 µL of AS was administered for 5 min or not (sham). Then, the rats were fed a test meal, and GE of liquids or solids was performed. The other animals were pretreated with NaCl 0.15 M, atosiban, anantin, or dexamethasone, followed by OT treatment for GE assessment. Compared with the sham group, 50 µL of AS decreased the GE of the liquid and solid test meals. This phenomenon was prevented by AT, ANT, DEX, and surgical procedures with AX. AS also increased plasma levels of ANP, OT, and CORT. In turn, oxytocin treatment decreased GE and increased plasma ANP, OT, and CORT levels, while AT, ANT, and DEX prevented OT-induced GE delay. Hence, AS delayed GE of liquid in rats, a phenomenon that involves oxytocinergic pathways and ANP activities.NEW & NOTEWORTHY We suggest a cardiogastric reflex with the participation of neuroendocrine mediators, which contributes to regulating liquid balance in the animal's body. Atrial natriuretic peptide and oxytocin are substances recognized for participating in diuresis and regulating the transit of liquids in the gastrointestinal tract in situations of cardiac volume overload, as was simulated with atrial stretching in the present experimental model.

The Rotenone-Induced Sporadic Parkinsonism Model: Timeline of Motor and Non-Motor Features

The prevalence of Parkinson's disease (PD) requires better characterized animal models, in particular of the PD prodrome. Since pesticide are well-established triggers of Parkinsonism, we now undertook a detailed characterization of the time-dependent onset of behavioural and neurochemical alterations after the repeated daily intraperitoneal administration to adult male rats of a low dose of rotenone (2.75 mg/kg) during weekdays for 21 days. The onset of motor (bradykinesia in the open field test) and coordination deficits (balance in the rotarod and rearing in the open field) occurred after 14 days of exposure to rotenone, linked to a nigrostriatal dopaminergic degeneration and increased accumulation of α-synuclein, which are key features of PD. Moreover, we identified several modifications pre-dating the onset of PD-like motor symptoms, encompassing gastrointestinal alterations and a modified whole-body composition together with olfactory dysfunction and memory and emotional impairments, which were typified by: i) a delayed gastric emptying of liquids (13CO2 analysis), which was evident from the third day of rotenone administration and was aggravated over subsequent days; ii) a loss of total, visceral and subcutaneous body fat and dehydration (bioimpedance spectroscopy); iii) olfactory dysfunction (discrimination test and food buried test). The characterization of this prodrome period in this robust model of PD offers a new window of opportunity to investigate the pathophysiological mechanisms of PD onset and to devise and test novel neuroprotective strategies.

New device for active gastric mechanical stimulation

BACKGROUND

Gastroparesis is a chronic stomach disorder and effective treatment is the aim of different strategies. Alternative therapies consist of an electrical stimulation of the stomach to evoke a response in the gastric activity. We present the development and in vivo application of an electromagnet system to induce a mechanical stimulus in the stomach aiming for gastric contractile responses.

METHODS

The electromagnet system consisted of an implantable magnet and an external drive coil. We implanted the magnet at the greater curvature of the gastric body in rats. We applied an alternating current to the drive coils, inducing mechanical stimulation of the gastric wall. We measured the gastric contraction activity and gastric electrical activity in response to the stimulus using AC biosusceptometry and electrogastrography. Moreover, we used the phenol red to evaluate the stimulus effects on gastrointestinal transit.

KEY RESULTS

The stimulus increased the spectral intensity and signal-to-noise ratio significantly of gastric contraction activity and gastric electrical activity. Furthermore, we found a lower phenol red retention in the stomach in rats without stimulus. No significant differences were found in frequency and root mean square amplitude.

CONCLUSIONS & INFERENCES

We developed a new simple electromagnet system that evoked a contraction and gastric electrical response using a mechanical stimulus and decreased gastric emptying time. The system is an accessible tool and may contribute to gastroparesis studies in animals.

An easy and low-cost biomagnetic methodology to study regional gastrointestinal transit in rats

The identification of gastrointestinal (GI) motility disorders requires the evaluation of regional GI transit, and the development of alternative methodologies in animals has a significant impact on translational approaches. Therefore, the purpose of this study was to validate an easy and low-cost methodology (alternate current biosusceptometry - ACB) for the assessment of regional GI transit in rats through images. Rats were fed a test meal containing magnetic tracer and phenol red, and GI segments (stomach, proximal, medial and distal small intestine, and cecum) were collected to assess tracer's retention at distinct times after ingestion (0, 60, 120, 240, and 360 min). Images were obtained by scanning the segments, and phenol red concentration was determined by the sample's absorbance. The temporal retention profile, geometric center, gastric emptying, and cecum arrival were evaluated. The correlation coefficient between methods was 0.802, and the temporal retention of each segment was successfully assessed. GI parameters yielded comparable results between methods, and ACB images presented advantages as the possibility to visualize intrasegmental tracer distribution and the automated scan of the segments. The imaging approach provided a reliable assessment of several parameters simultaneously and may serve as an accurate and sensitive approach for regional GI research in rats.

Role of cholecystokinin and oxytocin in slower gastric emptying induced by physical exercise in rats

Vigorous exercise can induce gastrointestinal disorders such decreased gastric emptying pace, while low-intensity exercise can accelerate gastric motility. However, the mechanisms of these effects are still unknown. We investigated the possible neurohumoral mechanisms involved in these phenomena. In sedentary (Sed) and acute exercise (Ex) groups of rats, we assessed the activation of c-Fos in NTS and DVMN and the plasma levels of CCK and OXT. Separate groups received pretreatment with the oxytocin antagonist atosiban (AT), the cholecystokinin antagonist devazepide (DVZ), or the TRPV1 receptor inhibitor capsazepine (CAPZ). AT, DVZ and CAPZ treatments prevented (p<0.05) slower gastric emptying induced by acute exercise. The gene expression of OXT decreased (P<0.05) while that of CCK increased (P<0.05) in the gastric fundus and pylorus of the Ex group, while the plasma levels of OXT rose (p<0.05) and of CCK declined (p<5.05). We also observed activation (p<0.05) of c-Fos-sensitive neurons in the NTS and DVMN of exercised rats. In conclusion, acute exercise slowed gastric emptying by the vagal afferent pathway, which involved activation of CCK1/OXT/TRPV1 sensitivity.

Helping students to understand physiological aspects of regional distribution of ventilation in humans: a experience from the electrical impedance tomography

Undergraduate biomedical students often have difficulties in understanding basic concepts of respiratory physiology, particularly respiratory mechanics. In this study, we report the use of electrical impedance tomography (EIT) to improve and consolidate the knowledge about physiological aspects of normal regional distribution of ventilation in humans. Initially, we assessed the previous knowledge of a group of medical students ( n = 39) about regional differences in lung ventilation. Thereafter, we recorded the regional distribution of ventilation through surface electrodes on a healthy volunteer adopting four different decubitus positions: supine, prone, and right and left lateral. The recordings clearly showed greater pulmonary ventilation in the dependent lung, mainly in the lateral decubitus. Considering the differences in pulmonary ventilation between right and left lateral decubitus, only 33% of students were able to notice it correctly beforehand. This percentage increased to 84 and 100%, respectively ( P < 0.01), after the results of the ventilation measurements obtained with EIT were examined and discussed. A self-assessment questionnaire showed that students considered the practical activity as an important tool to assist in the understanding of the basic concepts of respiratory mechanics. Experimental demonstration of the physiological variations of regional lung ventilation in volunteers by using EIT is feasible, effective, and stimulating for undergraduate medical students. Therefore, this practical activity may help faculty and students to overcome the challenges in the field of respiratory physiology learning.

Status of research on physiology education in Brazil

Physiology education research aims to investigate teaching-learning aspects and methods specifically applied to physiology teaching and learning. In this paper exploring Brazilian research public data and information from the Brazilian Physiological Society Teaching Committee, we investigated the status of this research topic (physiology education) in Brazil. The data showed that physiology education research needs to be more recognized and supported in Brazil, and more physiologists may become interested in research in this field. Thus this field will become more developed during the physiologists' education.

A hybrid transducer to evaluate stomach emptying by ultrasound and susceptometric measurements: an in vivo feasibility study

Gastric emptying reflects a diversity of important physiological functions. Alternating current biosusceptometry (ACB) is an inexpensive, radiation-free, and minimally invasive method to evaluate gastric emptying, but its response depends on the spatial distribution of the magnetized material and does not provide precise anatomical information. The hybrid transducer, which combines ACB and an ultrasound probe, is an alternative to improve susceptometry measurements, namely the spatial localization of the magnetized source. In this study, initial stomach emptying, in rats, was monitored with the aid of the hybrid transducer. Yogurt mixed with ferrite particles was injected into the rat's stomach. The hybrid transducer was placed on the rat's abdomen during experiments, and the susceptometry signal and magnetomotive ultrasound (MMUS) images were saved and postprocessed. MMUS highlighted the movement of magnetic particles due to magnetic force from ACB excitation coils, and showed the rat's stomach location. In this feasibility study, we monitored the stomach emptying of 4 rats for 20 min. The mean relative ACB signal decayed by 4.6 ± 0.1%, and the mean relative area of MMUS images decreased by 4.5 ± 0.2%, after 20 min postingestion of the magnetic meal due to stomach emptying. In a second experiment, 3-D MMUS images from axial sequences were obtained by spatially translating the hybrid transducer, providing details of the stomach wall, which may enable minimally invasive detection of abnormalities. In conclusion, the MMUS image increased ACB spatial resolution and furnished additional anatomical information.

Subtotal nephrectomy inhibits the gastric emptying of liquid in awake rats

Homeostasis of blood volume (BV) is attained through a functional interaction between the cardiovascular and renal systems. The gastrointestinal tract also adjusts its permeability and motor behavior after acute BV imbalances. We evaluated the effect of progressive nephron loss on gut motility. Male Wistar rats were subjected or not (sham) to 5/6 partial nephrectomy (PNX) in two steps (0 and 7th day). After further 3, 7, or 14 days, PNX and sham operation (control) rats were instrumented to monitor mean arterial pressure (MAP), central venous pressure (CVP), heart rate (HR), and blood collection for biochemical analysis. The next day, they were gavage fed with a liquid test meal (phenol red in glucose solution), and fractional dye recovery determined 10, 20, or 30 min later. The effect of nonhypotensive hypovolemia and the role of neuroautonomic pathways on PNX-induced gastric emptying (GE) delay were also evaluated. Compared with the sham-operated group, PNX rats exhibited higher (P < 0.05) MAP and CVP values as well as increased values of gastric dye recovery, phenomenon proportional to the BV values. Gastric retention was prevented by prior hypovolemia, bilateral subdiaphragmatic vagotomy, coelic ganglionectomy + splanchnicectomy, guanethidine, or atropine pretreatment. PNX also inhibited (P < 0.05) the marker's progression through the small intestine. In anesthetized rats, PNX increased (P < 0.05) gastric volume, measured by a balloon catheter in a barostat system. In conclusion, the progressive loss of kidney function delayed the GE rate, which may contribute to gut dysmotility complaints associated with severe renal failure.

Sodium bicarbonate treatment prevents gastric emptying delay caused by acute exercise in awake rats

Physical exercise, mainly after vigorous activity, may induce gastrointestinal dysmotility whose mechanisms are still unknown. We hypothesized that physical exercise and ensuing lactate-related acidemia alter gastrointestinal motor behavior. In the present study, we evaluated the effects of short-term exercise on gastric emptying rate in awake rats subjected to 15-min swimming sessions against a load equivalent to 5% of their body weight. After 0, 10, or 20 min of exercise testing, the rats were gavage fed with 1.5 ml of a liquid test meal (0.5 mg/ml of phenol red in 5% glucose solution) and euthanized 10 min postprandially to measure fractional gastric dye recovery. In addition to inducing acidemia and increasing blood lactate levels, acute exercise increased (P < 0.05) gastric retention. Such a phenomenon presented a positive correlation (P < 0.001) between blood lactate levels and fractional gastric dye recovery. Gastric retention and other acidbase-related changes were all prevented by NaHCO3 pretreatment. Additionally, exercise enhanced (P < 0.05) the marker's progression through the small intestine. In anesthetized rats, exercise increased (P < 0.05) gastric volume, measured by a balloon catheter in a barostat system. Compared with sedentary control rats, acute exercise also inhibited (P < 0.05) the contractility of gastric fundus strips in vitro. In conclusion, acute exercise delayed the gastric emptying of a liquid test meal by interfering with the acid-base balance.

Aortocaval fistula delays gastric emptying of liquid test meal in awake rats

Arteriovenous anastomoses disrupt cardiovascular and renal homeostasis, eliciting hemodynamic adjustments, resetting the humoral pattern, and inducing cardiac hypertrophy. Because acute circulatory imbalance alters gut motor behavior, we studied the effects of arteriovenous fistula placement on the gastric emptying (GE) of a liquid meal in awake rats. After laparotomy, we created an aortocaval fistula (ACF) by aorta and cava wall puncture with a 21-, 23-, or 26-gauge needle. The ACF was not created in the control group, which underwent sham operation. After 12, 24, or 48 h, mean arterial pressure, heart rate, and central venous pressure were continuously recorded, and cardiac output was estimated by thermal dilution. The rats were then gavage fed a test meal (i.e., phenol red in glucose solution), and fractional dye retention was determined 10, 20, or 30 min later. The effect of prior bleeding on ACF-induced GE delay, the role of neuroautonomic pathways, and changes in plasma hormone levels (i.e., angiotensin II, arginine vasopressin, atrial natriuretic peptide, corticosterone, and oxytocin) were evaluated. When compared with the sham-operated group, ACF rats exhibited arterial hypotension, higher ( P < 0.05) heart rate, central venous pressure, and cardiac output values and increased ( P < 0.05) gastric dye retention, a phenomenon prevented by bilateral subdiaphragmatic vagotomy and hexamethonium treatment. Pirenzepine also impaired the occurrence of gastric delay in subjects with ACF. In addition to causing hyperkinetic circulation, ACF placement delayed the GE of liquid in awake rats, an effect that likely involves a parasympathetic pathway.

Atrial stretch delays gastric emptying of liquids in awake rats

AIMS

We previously reported that mechanical atrial stretch (AS) by balloon distention increased gastric tonus in anesthetized rats. The present study evaluated the effect of AS on the gastric emptying of a liquid test meal in awake rats and its underlying neural mechanisms.

MAIN METHODS

Anesthetized male rats received a balloon catheter into the right atrium and a gastrostomy cannula. The next day, mean arterial pressure (MAP), heart rate (HR), central venous pressure (CVP), and cardiac output (CO) were continuously monitored. After the first 20min of monitoring (basal interval), the balloon was either distended or not (control) with 30, 50, or 70μl saline for 5min. Fifteen minutes later, the rats received the test meal (glucose solution with phenol red), and fractional gastric dye retention was determined 10, 20, or 30min later.

KEY FINDINGS

Heart rate and CVP values were transiently increased by 50 or 70μl AS but not 30μl AS, whereas gastric emptying was slower after 30, 50, or 70μl AS than after sham distention. Subdiaphragmatic vagotomy or splanchnicotomy+celiac ganglionectomy and capsaicin, ondansetron, hexamethonium, L-NAME, and glibenclamide treatment prevented the AS-induced delay in gastric emptying, whereas atropine and guanethidine treatment failed to prevent it.

SIGNIFICANCE

Atrial stretch inhibited the gastric emptying of liquid via non-adrenergic and non-cholinergic pathways that activate nitric oxide-K(+)ATP channels.

Active physiology learning in a diverse class: an analysis of medical student responses in terms of sex, home language, and self-reported test performance

The student body at the Nelson R. Mandela School of Medicine (NRMSM) is very diverse, representing many cultures, religions, and languages. Research has shown that weakness in English can impact student performance. Recent studies have also highlighted sex-based differences in students' learning and listening styles. These factors pose both challenges and opportunities for teachers of physiology. Student presentations were incorporated for a number of years into the traditional didactic second-year medical physiology curriculum at the NRMSM. Feedback obtained about the perceived benefits of these presentations for the learning of gastrointestinal and endocrine physiology included demographic data pertaining to students' sex, home language, and self-reported performance in tests. Analysis of the 50-item questionnaire responses, obtained over a 2-yr period, provided some interesting insights. Student responses to the items differed significantly in 27 of the 50 items in the questionnaire, based on sex alone (22%), sex and home language (7%), home language alone (37%), performance alone (26%), and performance and home language (7%). Our analyses of student perceptions support the findings of other studies and show that factors such as sex, home language, and student performance can play an important role in the way students are motivated to learn. In designing active learning strategies, academics need to take into account the potential influences that might affect student learning in diverse, multicultural, and multilingual classes.

Employment of a noninvasive magnetic method for evaluation of gastrointestinal transit in rats

AC Biosusceptometry (ACB) was previously employed towards recording gastrointestinal motility. Our data show a reliable and successful evaluation of gastrointestinal transit of liquid and solid meals in rats, considering the methods scarcity and number of experiments needed to endorsement of drugs and medicinal plants. ACB permits real time and simultaneous experiments using the same animal, preserving the physiological conditions employing both meals with simplicity and accuracy.

Student perceptions of the use of presentations as a method of learning endocrine and gastrointestinal pathophysiology

Second-year medical students at the Nelson R. Mandela School of Medicine (Durban, South Africa) were given a brief to prepare oral presentations on topics related to disorders of the gastrointestinal tract and endocrine system in the form of "patient-doctor" role play and to submit written documents about their topics. This initiative was introduced to assist medical students in their application and understanding of physiology to clinical situations. The aims of the student presentations were to improve the understanding of the physiological basis of diseases; promote independent research, active, and group-based learning; encourage social interactions; and develop presentation and peer review skills. Students rose to the challenge, producing a variety of presentations reflecting a wealth of creativity, humour, sensitivity to local cultural issues, and analytic thinking skills. The quality of the supporting posters and computer-generated slides was outstanding. Numerous "fun" prizes for specific individual and group performances were given based on peer and staff evaluations. This exercise ran over a 5-yr period before the introduction of a problem-based learning medical curriculum. Student feedback obtained over these years is reported here. Students were asked to complete semistructured questionnaires, which elicited feedback on various aspects of the learning exercise, including whether it should be continued and how it could be improved upon, especially if they were in groups that did not function well. The feedback obtained revealed that most students perceived the presentations to be fun, informative, creative/innovative, and, most importantly, beneficial to their learning. The majority of students felt that this exercise improved their understanding of pathophysiology, taught them to research independently, and encouraged better class interactions and group learning. The inclusion of such initiatives is beneficial not only to students' understanding and their experience in studying physiology but also for the development of skills useful in their future careers.