Excitatory effects of motilin in the hippocampus on gastric motility in rats

Why is motilin active in some studies with mice, rats, and guinea pigs, but not in others? Implications for functional variability among rodents

The gastrointestinal (GI) hormone motilin helps control human stomach movements during hunger and promotes hunger. Although widely present among mammals, it is generally accepted that in rodents the genes for motilin and/or its receptor have undergone pseudonymization, so exogenous motilin cannot function. However, several publications describe functions of low concentrations of motilin, usually within the GI tract and CNS of mice, rats, and guinea pigs. These animals were from institute-held stocks, simply described with stock names (e.g., "Sprague-Dawley") or were inbred strains. It is speculated that variation in source/type of animal introduces genetic variations to promote motilin-sensitive pathways. Perhaps, in some populations, motilin receptors exist, or a different functionally-active receptor has a good affinity for motilin (indicating evolutionary pressures to retain motilin functions). The ghrelin receptor has the closest sequence homology, yet in non-rodents the receptors have a poor affinity for each other's cognate ligand. In rodents, ghrelin may substitute for certain GI functions of motilin, but no good evidence suggests rodent ghrelin receptors are highly responsive to motilin. It remains unknown if motilin has functional relationships with additional bioactive molecules formed from the ghrelin and motilin genes, or if a 5-TM motilin receptor has influence in rodents (e.g., to dimerize with GPCRs and create different pharmacological profiles). Is the absence/presence of responses to motilin in rodents' characteristic for systems undergoing gene pseudonymization? What are the consequences of rodent supplier-dependent variations in motilin sensitivity (or other ligands for receptors undergoing pseudonymization) on gross physiological functions? These are important questions for understanding animal variation.

Gut Hormones as Potential Therapeutic Targets or Biomarkers of Response in Depression: The Case of Motilin

Recent research has identified the gut–brain axis as a key mechanistic pathway and potential therapeutic target in depression. In this paper, the potential role of gut hormones as potential treatments or predictors of response in depression is examined, with specific reference to the peptide hormone motilin. This possibility is explored through two methods: (1) a conceptual review of the possible links between motilin and depression, including evidence from animal and human research as well as clinical trials, based on a literature search of three scientific databases, and (2) an analysis of the relationship between a functional polymorphism (rs2281820) of the motilin (MLN) gene and cross-national variations in the prevalence of depression based on allele frequency data after correction for potential confounders. It was observed that (1) there are several plausible mechanisms, including interactions with diet, monoamine, and neuroendocrine pathways, to suggest that motilin may be relevant to the pathophysiology and treatment of depression, and (2) there was a significant correlation between rs2281820 allele frequencies and the prevalence of depression after correcting for multiple confounding factors. These results suggest that further evaluation of the utility of motilin and related gut peptides as markers of antidepressant response is required and that these molecular pathways represent potential future mechanisms for antidepressant drug development.

The Role of Gasotransmitters in Gut Peptide Actions

Although gasotransmitters nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H₂S) receive a bad connotation; in low concentrations these play a major governing role in local and systemic blood flow, stomach acid release, smooth muscles relaxations, anti-inflammatory behavior, protective effect and more. Many of these physiological processes are upstream regulated by gut peptides, for instance gastrin, cholecystokinin, secretin, motilin, ghrelin, glucagon-like peptide 1 and 2. The relationship between gasotransmitters and gut hormones is poorly understood. In this review, we discuss the role of NO, CO and H₂S on gut peptide release and functioning, and whether manipulation by gasotransmitter substrates or specific blockers leads to physiological alterations.

Translocator protein 18kDa antagonist ameliorates stress-induced stool abnormality and abdominal pain in rodent stress models

BACKGROUND

Irritable bowel syndrome (IBS) is a functional gastrointestinal (GI) disorder characterized by abdominal pain and abnormal bowel habits, both of which are exacerbated by psychological stress. The translocator protein 18kDa (TSPO) is a marker of reactive gliosis in a number of central nervous system (CNS) diseases and responsible for many cellular functions, including neurosteroidogenesis. Although it has been reported that psychological stress disturbs neurosteroids levels, the pathophysiological relevance of TSPO in IBS is poorly understood.

METHODS

We examined the effects of a TSPO antagonist, ONO-2952, on stress-induced stool abnormality and abdominal pain in rats, and on anxiety-related behavior induced by cholecystokinin.

KEY RESULTS

Oral administration of ONO-2952 attenuated stress-induced defecation and rectal hyperalgesia in rats with an efficacy equivalent to that of a 5-HT₃ receptor antagonist. In addition, ONO-2952 suppressed cholecystokinin-induced anxiety-like behavior with an efficacy equivalent to that of psychotropic drugs. On the other hand, ONO-2952 did not affect spontaneous defecation, gastrointestinal transit, visceral nociceptive threshold, and neurosteroid production in non-stressed rats even at a dose 10 times higher than its effective dose in the stress models.

CONCLUSIONS AND INFERENCES

These results suggest that TSPO antagonism results in antistress action, and that ONO-2952 is a promising candidate for IBS without side effects associated with current treatment.

Vagal Blocking for Obesity Control: a Possible Mechanism-Of-Action

BACKGROUND

Recently, the US FDA has approved "vagal blocking therapy or vBLoc® therapy" as a new treatment for obesity. The aim of the present study was to study the mechanism-of-action of "VBLOC" in rat models.

METHODS

Rats were implanted with VBLOC, an intra-abdominal electrical device with leads placed around gastric vagal trunks through an abdominal incision and controlled by wireless device. Body weight, food intake, hunger/satiety, and metabolic parameters were monitored by a comprehensive laboratory animal monitoring system. Brain-gut responses were analyzed physiologically.

RESULTS

VBLOC reduced body weight and food intake, which was associated with increased satiety but not with decreased hunger. Brain activities in response to VBLOC included increased gene expression of leptin and CCKb receptors, interleukin-1β, tumor necrosis factor, and transforming growth factor β1 in the brainstem; increased CCK, somatostatin, and tyrosine hydroxylase in the hippocampus; increased NPY, AgRP, and Foxa2 in the hypothalamus; and reduced CCKb receptor, melanocortin 4 receptor, and insulin receptor in the hypothalamus. Plasma concentrations of CCK, gastrin, glucagon, GLP-1, and PYY and gastric acid secretion were unchanged in response to VBLOC.

CONCLUSIONS

Based on the present study, we may suggest that VBLOC induces satiety through vagal signaling, leading to reduced food intake and loss of body weight.

The Impact of Prenatal Exposure to Dexamethasone on Gastrointestinal Function in Rats

Antenatal treatment with synthetic glucocorticoids is commonly used in pregnant women at risk of preterm delivery to accelerate tissue maturation. Exposure to glucocorticoids during development has been hypothesized to underlie different functional gastrointestinal (GI) and motility disorders. Herein, we investigated the impact of in utero exposure to synthetic glucocorticoids (iuGC) on GI function of adult rats. Wistar male rats, born from pregnant dams treated with dexamethasone (DEX), were studied at different ages. Length, histologic analysis, proliferation and apoptosis assays, GI transit, permeability and serotonin (5-HT) content of GI tract were measured. iuGC treatment decreased small intestine size and decreased gut transit. However, iuGC had no impact on intestinal permeability. iuGC differentially impacts the structure and function of the GI tract, which leads to long-lasting alterations in the small intestine that may predispose subjects prone to disorders of the GI tract.

The role of antisecretory factor in pancreatic exocrine secretion: studies in vivo and in vitro

NEW FINDINGS

What is the central question of this study? Antisecretory factor, an endogenous protein detected in many tissues of the body, is known as an inhibitor of intestinal secretion, but its role in pancreatic exocrine secretory function has not yet been investigated. What is the main finding and its importance? In a rodent model, we show that antisecretory factor reduces pancreatic exocrine secretion, probably via its direct action on the pancreatic acini and via modulation of the enteropancreatic reflexes involving cholecystokinin and sensory nerves. Antisecretory factor (AF) regulates ion and water transport through the intestinal cell membrane. Antisecretory factor inhibits intestinal secretion, but its effect on the exocrine pancreas has not yet been shown. We investigated the effect of AF on pancreatic amylase secretion in vivo and in vitro using pancreatic acini isolated by collagenase digestion. For the in vivo study, Wistar rats were surgically equipped with silicone catheters, inserted into the pancreaticobiliary duct and into the duodenum. Capsaicin was used to deactivate the sensory nerves in turn to assess their involvement in the effects of AF on the exocrine pancreas. Antisecretory factor (1, 3 or 10 μg kg(-1) i.p.) was given in basal conditions or following stimulation of pancreatic secretion with diversion of pancreaticobiliary juice. For the in vitro study, rat pancreatic acini were incubated in the presence of increasing doses of AF (from 10(-8) to 10(-5)  m) alone or in combination with caerulein (10(-12)  m). Cytoplasmic cholecystokinin 1 (CCK1 ) receptor protein was detected by Western blot and immunoprecipitation studies. Antisecretory factor markedly reduced the output of pancreatic amylase both in basal conditions and when stimulated by diversion of pancreaticobiliary juice. Deactivation of the sensory nerves with capsaicin completely reversed the inhibitory effects of AF on the exocrine pancreas. Caerulein-induced enzyme secretion from the pancreatic acini was inhibited by AF, whereas basal secretion was unaffected. Administration of AF to the rats significantly diminished the synthesis of CCK1 receptor protein. We conclude that AF inhibits pancreatic exocrine secretion indirectly via sensory nerves and directly decreases amylase release from isolated pancreatic acini. The direct inhibitory action of AF on the exocrine pancreas could be related, at least in part, to a reduction of CCK1 receptors on pancreatic acinar cells.

Nesfatin-1 signaling in the basom edial amygdala modulates the gastric distension-sensitive neurons discharge and decreases gastric motility via melanocortin 3/4 receptors and modified by the arcuate nucleus

Nesfatin-1 is a novel anorexigenic peptide that regulates feeding behavior and gastrointestinal function. This study aimed to explore the effects of nesfatin-1 on gastric distension (GD)-sensitive neurons in the basomedial amygdala (BMA) and the potential mechanism for nesfatin-1 to regulate gastric motility through the arcuate nucleus (Arc). The projection of nerve fiber and expression of nesfatin-1 were observed by retrograde tracing and fluo-immunohistochemistry staining. Single-unit discharges in the BMA were recorded extracellularly, and gastric motility in conscious rats was monitored. Results showed that the nesfatin-1/ fluorogold-double labeled neurons were observed in the Arc. Nesfatin-1 could excite the GD-excitatory neurons and inhibit the GD-inhibitory neurons in the BMA. Gastric motility and gastric emptying were significantly reduced by nesfatin-1 administration to the BMA in a dose-dependent manner. The effects of nesfatin-1 could be partially blocked by melanocortin 3/4 receptors antagonist, SHU9119. Electrical stimulation of the Arc significantly excited the response of GD neurons to nesfatin-1 and promoted gastric motility. Nevertheless, these effects could be mitigated by pretreatment with anti-NUCB2/nesfatin-1 antibody. It is suggested that nesfatin-1 in the BMA plays an important role in decreasing gastric motility and the Arc may be involved in this regulation process.

Mechanism of motilin-mediated inhibition on voltage-dependent potassium currents in hippocampal neurons

OBJECTIVE

The effects of motilin on voltage-dependent K+ currents in hippocampal neurons with the addition of L-arginine (L-AA), D-arginine (D-AA) and N-nitro-L-arginine methyl ester (L-NAME) were investigated in this study.

METHODS

Mice (1-3 days old) were randomly assigned to different groups according to the addition of motilin, L-AA, D-AA, and L-NAME. The K+ current signals were detected by the whole-cell patch-clamp technique.

RESULTS

Compared with the control group, the transient outward voltage-dependent K+ current was significantly inhibited by motilin added with L-AA. In contrast, the addition of motilin and L-NAME significantly increased the K+ current, while no significant change was detected by the addition of motilin accompanied with D-AA.

CONCLUSION

The inhibiting effects of motilin on the voltage-dependent K+ current in hippocampal neurons indicate that motilin acts as a regulatory factor for the nitric oxide pathway.

Effects of ghrelin on gastric distension sensitive neurons and gastric motility in the lateral septum and arcuate nucleus regulation

BACKGROUND

Ghrelin is an endogenous ligand for the growth hormone secretagogue receptor (GHS-R) and a peptide hormone that promotes food intake and gastric motility. Our aims are to explore the effects of ghrelin on gastric distension (GD) sensitive neurons in the lateral septum, and the possible regulation of gastric motility by ghrelin through the hypothalamic arcuate nucleus (ARC).

METHODS

Single-unit discharges were recorded, extracellularly, and the gastric motility was monitored by the administration of ghrelin in the lateral septum. The projection of nerve fiber and expression of ghrelin were observed by retrograde tracer and fluo-immunohistochemistry staining. The expression of GHS-R and ghrelin was determined by real-time polymerase chain reaction and western blotting analysis.

RESULTS

There were GD neurons in the lateral septum. The administration of ghrelin could excite both GD-excitatory (GD-E) and GD-inhibitory (GD-I) neurons in the lateral septum. Gastric motility was significantly enhanced by the administration of ghrelin in the lateral septum in a dose-dependent manner. Pretreatment with [D-Lys-3]-GHRP-6, however, could completely abolish the ghrelin-induced effects. Electrical stimulation of the ARC could significantly excite the response of GD neurons to ghrelin, increase ghrelin protein expression in the lateral septum and promote gastric motility. Nevertheless, these effects could be mitigated by pretreatment of [D-Lys-3]-GHRP-6. Electrical lesion of the lateral septum resulted in decreased gastric motility. The GHS-R and Ghrelin/FG-double labeled neurons were observed in the lateral septum and ARC, respectively.

CONCLUSIONS

It is suggested that the lateral septum may receive afferent information from the gastrointestinal tract and promote gastric motility. Ghrelin plays an important role in promoting gastric motility in the lateral septum. The ARC may be involved in the regulation of the lateral septum's influence on gastric motility.

Heterotrimeric guanosine triphosphate-binding protein-coupled modulatory actions of motilin on K+ channels and postsynaptic γ-aminobutyric acid receptors in mouse medial vestibular nuclear neurons

Some central nervous system neurons express receptors of gastrointestinal hormones, but their pharmacological actions are not well known. Previous anatomical and unit recording studies suggest that a group of cerebellar Purkinje cells express motilin receptors, and motilin depresses the spike discharges of vestibular nuclear neurons that receive direct cerebellar inhibition in rats or rabbits. Here, by the slice-patch recording method, we examined the pharmacological actions of motilin on the mouse medial vestibular nuclear neurons (MVNs), which play an important role in the control of ocular reflexes. A small number of MVNs, as well as cerebellar floccular Purkinje cells, were labeled with an anti-motilin receptor antibody. Bath application of motilin (0.1 μm) decreased the discharge frequency of spontaneous action potentials in a group of MVNs in a dose-dependent manner (K(d) , 0.03 μm). The motilin action on spontaneous action potentials was blocked by apamin (100 nm), a blocker of small-conductance Ca(2+) -activated K(+) channels. Furthermore, motilin enhanced the amplitudes of inhibitory postsynaptic currents (IPSCs) and miniature IPSCs, but did not affect the frequencies of miniature IPSCs. Intracellular application of pertussis toxin (PTx) (0.5 μg/μL) or guanosine triphosphate-γ-S (1 mm) depressed the motilin actions on both action potentials and IPSCs. Only 30% of MVNs examined on slices obtained from wild-type mice, but none of the GABAergic MVNs that were studied on slices obtained from vesicular γ-aminobutyric acid transporter-Venus transgenic mice, showed such a motilin response on action potentials and IPSCs. These findings suggest that motilin could modulate small-conductance Ca(2+) -activated K(+) channels and postsynaptic γ-aminobutyric acid receptors through heterotrimeric guanosine triphosphate-binding protein-coupled receptor in a group of glutamatergic MVNs.

Ghrelin microinjected into the hypothalamic arcuatus nucleus regulates gastric motility in a diabetic rat model

AIM: To study the effect of Ghrelin microinjected into the hypothalamic arcuatus nucleus (ARC) on gastric motility in rats with diabetic gastroparesis (DGP).

METHODS: Two hundred and forty Wistar rats were randomly divided into 10 groups: control group (C), saline group (NS), low-dose Ghrelin group (L), high-dose Ghrelin group (H), high-dose Ghrelin plus D-Lys6-GHRP-6 (DLS) group (H+D), DGP group (DGP), saline-treated DGP group (DGP+NS), low-dose Ghrelin-treated DGP group (DGP+L), high-dose Ghrelin-treated DGP group (DGP+H), high-dose Ghrelin plus D-Lys6-GHRP-6 (DLS)-treated DGP group (DGP+H+D). A rat diabetic model was established by intraperitoneal injection of streptozotocin (STZ). Fluorescent immunohistochemistry, reverse transcription-polymerase chain reaction (RT-PCR) and real-time quantitative polymerase chain reaction (real-time PCR) were performed to evaluate the protein and mRNA expression of Ghrelin receptor (GHS-R) in the ARC of rats. The effect of Ghrelin injection into ARC on gastric motility was observed.

RESULTS: The number of GHS-R immunoreactive neurons and the relative level of GHS-R mRNA/β-actin in the ARC of normal rats were 10.0/mm² ± 2.1/mm² and 0.48 ± 0.13, while in DGP rats the values decreased to 3.0/mm² ± 0.7/mm² and 0.21 ± 0.10 (both P < 0.05). Microinjection of 0.05 or 0.5 nmol Ghrelin into the ARC could increase the amplitude of gastric motility in a dose-dependent manner (L: 14.6 g ± 2.2 g vs NS: 8.14 g ± 1.58 g, P < 0.05; H: 22.28 g ± 4.10 g vs NS: 8.14 g ± 1.58 g, P < 0.01; NS: 8.14 g ± 1.58 g vs L: 14.6 g ± 2.2 g, P < 0.05), and the frequency of gastric motility was also increased significantly (L: 7.45/min ± 0.87/min vs NS: 5.18/min ± 0.61/min, P < 0.05; H: 10.98/min ± 1.03/min vs NS: 5.18/min ± 0.61/min, P < 0.01; H: 10.98/min ± 1.03/min vs L: 7.45/min ± 0.87/min, P < 0.05). In DGP rats, gastric motility decreased with an enhanced amplitude (2.21 g ± 0.89 g vs 8.14 g ± 1.58 g, P < 0.05) and an increased frequency (1.81/min ± 0.2/min vs 5.18/min ± 0.61/min, P < 0.05). The administration of 0.5 mmol Ghrelin into the ARC could increase gastric motility in DGP rats (amplitude: DGP + H: 5.04 g ± 1.11 g vs DGP + NS: 2.14 g ± 0.23 g or DGP + L: 3.58 g ± 1.11 g, P < 0.05; frequency: DGP + H: 3.81/min ± 0.43/min vs DGP + NS: 1.8/min ± 0.19/min or DGP + L: 2.3/min ± 0.29/min, P < 0.05). The GHS-R antagonist, D-Lys3-GHRP-6, could totally block the effects of Ghrelin.

CONCLUSION: Gastric motility disorder in diabetic rats is partly caused by decreased expression of GHS-R in the hypothalamus. Ghrelin could regulate the genesis of DGP through the GHS-R in the ARC.

Correlation between the brain-gut interaction and acupuncture treatment of functional gastrointestinal disorders

Acupuncture has been proven to be effective in treating functional gastrointestinal disorders (FGIDs), which are common digestive diseases. Recent studies have proven that dysfunction of the "Brain-Gut-Axis" (BGA) might be an important pathogenetic factor for FGIDs. The curative effect of acupuncture on FGIDs could mainly be attributed to its modulation effect on the BGA. Increasing attention has been paid to the study of the interaction between the central nervous system and brain-gut peptide in patients with FGIDs due to the development of functional imaging and the progress in research of the brain-gut peptide. Acupuncture has been extensively used in treating FGIDs clinically. Substantial studies have shown that acupuncture could modulate the central nervous system and the brain-gut peptide. In this article we are going to summarize the correlation between the brain-gut interaction and the curative effect of acupuncture in terms of central nervous system and the metabolism of brain-gut peptide.

The paraventricular nucleus modulates thyroidal motilin release and rat gastric motility

Motilin, an important endocrine regulator of gastrointestinal motility, was once considered to be produced in the gastrointestinal tract and brain. In recent years, however, motilin has been found in the human thyroid, as well as in that of the guinea pig. The physiological function and central modulation of thyroidal motilin remain poorly understood. To determine the functional role of thyroidal motilin, we observed the concentration of motilin in the plasma and also gastric motility before and after thyroidectomy. Our studies show that both the concentration of plasma motilin and gastric motility were decreased after thyroidectomy. To explore modulation-related nuclei, a c-Fos immune response experiment was carried out. The PVN of the hypothalamus was the main area of reactivity after thyroidectomy. Subsequently, we studied the effects of electrical excitation and PVN lesions on gastric motility and the expression of motilin in the thyroid and plasma. Excitation of the PVN was shown to prompt gastric motility that was partly prevented by the motilin receptor antagonist, GM-109. The effects of PVN excitation on gastric contraction were significantly reduced in thyroidectomised rats. In addition, the expression of motilin in the thyroid was significantly increased after PVN excitation and decreased after PVN lesions. The changes in the concentration of motilin in plasma induced by PVN stimulation were positively correlated with changes of gastric motility. In our in vitro study, the motilin secreted from TT cells (a parafollicular cell line originating from human thyroid medullary carcinoma) gradually increased on day 6 of culture, and motilin and calcitonin (CT) were co-expressed in TT cells. These results demonstrate that motilin from the thyroid could be secreted into the peripheral plasma and affect gastric motility and that PVN was a central nucleus for modulating gastric motility and motilin expression in the thyroid.

Effect of motilin on gastric distension sensitive neurons in arcuate nucleus and gastric motility in rat

BACKGROUND

Intestinal motilin is known to stimulate gastrointestinal (GI) motility and the arcuate nucleus (Arc) of hypothalamus is shown to be involved in the regulation of GI motility.

METHODS

Single unit discharges in the Arc were recorded extracellularly by implantation of a force transducer into the stomach in rats, to evaluate the effect of motilin on gastric motility. Projection of nerve fiber and expression of motilin were observed by retrograde tracer deposits of Fluoro-Gold (FG) and fluo-immunohistochemistry staining.

KEY RESULTS

65.5% of neurons in Arc responded to gastric distension (GD), 55.6% of which showed excitation (GD-E), and 44.4% showed inhibition (GD-I). After GD, the firing rate of GD-E neurons significantly increased (P<0.01), but decreased for GD-I neurons (P<0.01). Most of both GD-E and GD-I neurons were activated by motilin (P<0.05). The frequency and amplitude of gastric contractions significantly increased by administration of motilin in Arc with a dose dependent manner (P<0.05-0.01). However, pretreatment with GM109 could abolish the responses of neurons and excitatory effect of gastric motility induced by motilin. Motilin immunoreactive neurons were increased in Arc via gastric distention (P<0.05). Motilin/FG-labeled neurons were detected in hypothalamus paraventricular nucleus (PVN).

CONCLUSIONS & INFERENCES

Our findings suggest that motilin neurons in Arc may accept peripheral somatosensory afferent inputs from gastric mechanoreceptors of the stomach, and also may acts as a stimulatory factor in Arc to regulate gastric motility via some inferior nucleus relay pathway. The results provide insight into the role of Arc in the control of digestion mediated via motilin.

Erythromycin inhibited glycinergic inputs to gastric vagal motoneurons in brainstem slices of newborn rats

BACKGROUND

Motilin has been known to stimulate the motility of digestive organs peripherally via activation of motilin receptors located at gastrointestinal (GI) cholinergic nerve endings and/or smooth muscle cells. Recent studies have indicated that motilin may also promote GI motility via actions in the central nervous system; however the sites of action and the mechanisms are not clear yet. The present study aimed to test the hypothesis that motilin receptor agonist erythromycin alters the synaptic inputs of preganglionic gastric vagal motoneurons (GVMs) located in the dorsal motor nucleus of the vagus (DMV).

METHODS

Gastric vagal motoneurons were retrogradely labeled by fluorescent tracer from the stomach wall of newborn rats. Fluorescently labeled GVMs in DMV were recorded using whole-cell patch-clamp in brainstem slices and the effects of motilin receptor agonist erythromycin on the synaptic inputs were examined.

KEY RESULTS

Erythromycin (100 nmol L(-1), 1 μmol L(-1), 10 μmol L(-1)) significantly inhibited the frequency of glycinergic spontaneous inhibitory postsynaptic currents (sIPSCs) of GVMs and significantly inhibited the amplitude at the concentration of 10 μmol L(-1). These responses were prevented by GM-109, a selective motilin receptor antagonist. In the pre-existence of tetradotoxin (TTX, 1 μmol L(-1)), erythromycin (10 μmol L(-1)) caused significant decreases of the glycinergic miniature inhibitory postsynaptic currents (mIPSCs), in both the frequency and the amplitude. However, erythromycin (10 μmol L(-1)) didn't cause significant changes of the GABAergic sIPSCs.

CONCLUSIONS & INFERENCES

Erythromycin selectively inhibits the glycinergic inputs of GVMs.

Insulin and hippocampus activation in response to images of high-calorie food in normal weight and obese adolescents

Responsiveness to food cues, especially those associated with high-calorie nutrients may be a factor underlying obesity. An increased motivational potency of foods appears to be mediated in part by the hippocampus. To clarify this, we investigated by means of 3-T magnetic resonance imaging (MRI) the activation of the hippocampus and associated brain structures in response to pictures of high-calorie and low-calorie foods in 12 obese and 12 normal-weight adolescents. To investigate the relationship between neuronal activation patterns (e.g., hippocampus) to the caloric content of food images and plasma insulin levels, we performed a multiple regression analysis. Interestingly, a significant positive correlation between fasting plasma levels of insulin, waist circumference, and right hippocampal activation was seen after stimulation with high-caloric food images. BMI values did not correlate significantly with the hippocampal activation. On the other hand, we found a significant negative correlation in response to high-caloric food images and the plasma levels of insulin in the medial right gyrus frontalis superior and in the left thalamus. In summary, our data show that insulin is importantly involved in the central regulation of food intake. The significant positive relationship between hippocampal activation after stimulation with high-caloric food images, plasma insulin levels, and waist circumference suggests a permissive role of insulin signaling pathways in the hippocampal control of eating behavior. Interestingly, only the waist circumference, as a main indicator of abdominal obesity, correlated significantly with the hippocampal activation patterns, and not the BMI.

Alterations in the hippocampal endocannabinoid system in diet-induced obese mice

The endocannabinoid (eCB) system plays central roles in the regulation of food intake and energy expenditure. Its alteration in activity contributes to the development and maintenance of obesity. Stimulation of the cannabinoid receptor type 1 (CB(1) receptor) increases feeding, enhances reward aspects of eating, and promotes lipogenesis, whereas its blockade decreases appetite, sustains weight loss, increases insulin sensitivity, and alleviates dysregulation of lipid metabolism. The hypothesis has been put forward that the eCB system is overactive in obesity. Hippocampal circuits are not directly involved in the neuronal control of food intake and appetite, but they play important roles in hedonic aspects of eating. We investigated the possibility whether or not diet-induced obesity (DIO) alters the functioning of the hippocampal eCB system. We found that levels of the two eCBs, 2-arachidonoyl glycerol (2-AG) and anandamide, were increased in the hippocampus from DIO mice, with a concomitant increase of the 2-AG synthesizing enzyme diacylglycerol lipase-alpha and increased CB(1) receptor immunoreactivity in CA1 and CA3 regions, whereas CB(1) receptor agonist-induced [(35)S]GTPgammaS binding was unchanged. eCB-mediated synaptic plasticity was changed in the CA1 region, as depolarization-induced suppression of inhibition and long-term depression of inhibitory synapses were enhanced. Functionality of CB(1) receptors in GABAergic neurons was furthermore revealed, as mice specifically lacking CB(1) receptors on this neuronal population were partly resistant to DIO. Our results show that DIO-induced changes in the eCB system affect not only tissues directly involved in the metabolic regulation but also brain regions mediating hedonic aspects of eating and influencing cognitive processes.

[Promotility drugs use in critical care: indications and limits?]

Enteral feeding is often limited by gastric and intestinal motility disturbances in critically ill patients, particularly in patients with shock. So, promotility agents are frequently used to improve tolerance to enteral nutrition. This review summaries the pathophysiology, presents the available pharmacological strategies, the clinical data, the counter-indications and the principal limits. The clinical data are poor. No study demonstrates a positive effect on clinical outcomes. Metoclopramide and erythromycin seems to be the more effective. Considering the risk of antibiotic resistance, the first line use of erythromycin should be avoided in favor of metoclopramide.

Effects of gastric electric stimulation on gastric distention responsive neurons and expressions of CCK in rodent hippocampus

OBJECTIVE

Gastric electrical stimulation (GES) has been introduced for treating obesity. The hippocampus is known to be involved in the regulation of gastrointestinal motility. Changes in hypathalumus cholecystokinin (CCK) have been observed in genetically obese rodents. This experiment was to study the effect of GES on the activities of neurons and the expression of CCK in the hippocampus.

METHODS AND PROCEDURES

We investigated the effect of GES (GES-I: pulse train of standard parameters; GES-2: reduced train-on time; GES-3: increased pulse width; GES-4: reduced pulse frequency) on neurons responsive to gastric distention (GD) by recording extracellular potentials of single neurons and observing the expression of CCK in the rodent hippocampus by immunohistochemistry staining, radioimmunoassay, and real-time PCR.

RESULTS

92.1% of neurons in the CA2-3 region responded to GD, 53.2% of which showed excitation (GD-E), and 46.8% showed inhibition (GD-I). 64.8% GD-responsive neurons were excited by GES. The response was associated with stimulation strength, pulse width, and frequency; 70.6, 57.1, 94.4, and 66.7% of GD-E and 72.7, 57.1, 86.4, and 50% of GD-I neurons showed excitatory responses to GES-I, -2, -3, and -4, respectively. CCK immunoreactive positive neurons (P<0.001), the content of CCK-like materials (P<0.05) and the amount of CCK mRNA were significantly increased after GES (P<0.05).

DISCUSSION

These findings suggest the central, neuronal, and hormonal mechanisms of GES. GES may excite the activity of GD-sensitive neurons and increase the expression of CCK in the hippocampus. These excitatory effects of GES seem to be related to the parameters of stimulation.

Effect of motilin on the discharge of rat hippocampal neurons responding to gastric distension and its potential mechanism

The study aims to find the effect of motilin on neuronal activity of gastric distension-responsive neurons in rat hippocampus and its possible mechanism. Single unit discharges in the hippocampal CA1 region were recorded extracellularly by means of four-barrel glass micropipettes in anesthetized rats and the expression of nNOS in hippocampus was observed by fluo-immunohistochemistry staining. Of the 171 recorded neurons, 76.0% were GD-excitatory (GD-E) neurons and 24.0% were GD-inhibited (GD-I) neurons. The 57.6% of GD-E neurons showed an excitatory response to motilin and the same effect was observed in 51.7% GD-I neurons. However, when NOS inhibitor nitro-l-arginine methyl ester (l-NAME) was administrated previously, the followed motilin-induced excitatory responsiveness of GD-responsive neurons was reduced. In contrast, discharge activity of GD-responsive neurons with motilin was enhanced by pretreatment of NO precursor l-arginine. The expression of nNOS-IR positive neurons was significantly increased in CA1 after administration of motilin. Our findings suggested that motilin excited the GD-responsive neurons in the hippocampal CA1 region and the excitatory effect of motilin may be mediated by the endogenous NO.

Distribution and electrophysiological effects of motilin in Purkinje cells

Evidence exists that motilin immunoreactivity is highly expressed in Purkinje cells. In this study, immunohistochemistry and whole-cell patch-clamp recording were performed to investigate the spatial distribution and electrophysiological effects of motilin receptors in the cerebellum. We show here that motilin receptors are strongly expressed in Purkinje cells of the human and rat cerebellum. Motilin at 10 nM depolarized Purkinje cells of the rat cerebellum, and this was mimicked by the motilin receptor agonist erythromycin. The depolarization evoked by motilin persisted in the presence of tetrodotoxin, glutamate and gamma-amino-n-butyric acid receptor antagonists, indicating that motilin excited the Purkinje cells by activating the receptor expressed on the neurons recorded. We suggest that motilin may serve specific neural functions in the cerebellum.

Da-Cheng-Qi-Tang promotes the recovery of gastrointestinal motility after abdominal surgery in humans

In order to examine the effects of Da-Cheng-Qi-Tang (DCQT) on gastrointestinal motility functions after abdominal surgery in humans, 33 patients with abdominal surgeries and 36 patients with cholecystectomies were divided into the DCQT and the control groups at random. Electrogastrography (EGG) and gastroduodenojejunal manometry was performed and the levels of plasma motilin were measured by radioimmunoassay. The results were as follows: (1) on the day of surgery, the ratio of EGG normal frequency in the DCQT group was higher than in the control group (P=0.0016); (2) the power of EGG in the DCQT group was higher than in the control group on the second and third days after surgeries (P=0.0011 and P=0.0215, respectively); (3) the percentage of normal bowel peristalsis was significantly higher in the DCQT group than in the control group (P<0.01); and (4) in the DCQT group, the plasma motilin level reached its peak earlier than in the control group. Our results suggest that DCQT can increase plasma motilin, enhance gastrointestinal motility, improve gastric dysrythmia, and reduce gastroparesis after abdominal surgery.

Effects of gastric electrical stimulation on hippocampus gastric distension responsive neurons and the expression of motilin and neuronal nitric oxide synthase in rats

AIM: To explore the effects of gastric electrical stimulation (GES) on gastric distension (GD) responsive neurons in rat hippocampus, and study the expression of neuronal nitric oxide synthase (nNOS) and motilin (MTL) in rat brain for exploring the central mechanism of GES.

METHODS: Fifty adult Wistar rats were used in this experiment. The effects of GES on GD responsive neurons in hippocampus CA1 area were observed by recording extracellular potentials of single neuron. GD responsive neurons were classified as GD-excitatory (GD-E) and GD-inhibitory (GD-I) neurons according to their responses to GD. GES with 3 sets of parameters were applied for 1 minute respectively: GES-A (6 mA, 0.3 ms, 40 Hz, 2 s-on, 3 s-off) with standard pulse trains; GES-B with increased wave width to 3 ms and GES-C with decreased frequency to 20 Hz. Two hours after GES-A was applied, we observed the expression of nNOS immunoreactive positive neurons in hippocampus by fluorescent immunohistochemistry and the content of motilin in rat brain by radioimmunoassay.

RESULTS: Eighty-seven neurons in hippocampus CA1 area were recorded and 79 responded to gastric distension (GD, 3-5 mL, 10-30 s). Of the 79 GD responsive neurons, 40 (50.6%) were GD-E neurons and 39 (49.4%) were GD-I ones. 62.5%, 100% and 62.3% of GD-E neurons were excited by GES-A, -B, and -C respectively. GES-B excited more GD-E neurons than GES-C (P = 0.016). Among the GD-I neurons, 63.6%, 85.7% and 50.0% neurons were excited by GES-A, -B and -C respectively. GES-C was noted to be less effective comparing with GES-A (P = 0.041) or GES-B (P = 0.021). Two hours after GES-A was used, the expressions of nNOS positive neurons significantly decreased in the CA1 and CA2-3 area of hippocampus (16.75 ± 0.91 cells/mm²vs 20.46 ± 1.30 cells/mm², P < 0.05; 14.91 ± 1.17 cells/mm²vs 18.73 ± 1.10 cells/mm², P < 0.05) and the content of motilin peptide decreased obviously in the hypothalamus (48.93 ± 6.98 fmol/mg vs 96.23 ± 12.93 fmol/mg, P < 0.01), mesencephalon (53.17 ± 8.96 fmol/mg vs 30.96 ± 4.86 fmol/mg, P < 0.05), medulla oblongata (46.27 ± 7.83 fmol/mg vs 73.86 ± 9.37 fmol/mg, P < 0.05) and hippocampus (32.23 ± 6.51 fmol/mg vs 62.72 ± 10.07 fmol/mg, P < 0.05) by radioimmunoassay.

CONCLUSION: GES may activate the gastric distension responsive neurons in hippocampus CA1 area and the excitatory effect of GES is related to the frequency and wave width of stimulation. Decreased expression of nNOS and motilin in the brain may also take part in the central mechanism of GES.

Expression of motilin in the hypothalamus and the effect of central erythromycin on gastric motility in diabetic rats

OBJECTIVE

To investigate the expression of motilin-immunoreactive neurons in the hypothalamus and the effect of central administration of erythromycin (EM) on the regulation of gastric motility in diabetic rats.

METHODS

The motilin immunoreactive neurons in the hypothalamus and the hippocampus were detected by immunohistochemistry with rabbit anti-motilin polyclonal antibody. To measure the gastric motility, force transducers were surgically affixed to the gastric serosa. A microinjection syringe was connected via a plastic tube to an injection cannula, which was connected with a stainless steel guide cannula. The syringe was inserted into the right lateral cerebral ventricle for microinjecting the chemicals.

RESULTS

Diabetic mellitus was successfully induced in cohorts of rats. Motilin-immunoreactive neurons significantly increased in the paraventricular (PVN) and supraoptic nuclei (SON) of the hypothalamus in the diabetic rats. Intracerebroventricular (i.c.v.) administration of EM, a motilin receptor agonist, stimulated the gastric motility of diabetic rats. EM (91.56 nmol, i.c.v.) dose-dependently increased the amplitude by (174.82 +/- 48.62)% (P<0.05), and increased the frequency by (70.43 +/- 27.11)% (P < 0.05) in 5 min. The stimulatory effect lasted more than 15 min to the end of the measurement, and can be blocked partially by the prior treatment of motilin receptor antagonist GM-109.

CONCLUSION

Motilin-immunoreactive neurons are increased in the PVN and SON of the hypothalamus in diabetic rats. Centrally administered EM may regulate gastric motility by binding to the central motilin receptors, and central motilin might be involved in regulation of gastric motility in diabetic rats.

Motilin activates neurons in the rat amygdala and increases gastric motility

Motilin and motilin receptors have been found in most regions of the brain, including the amygdala, one of the most important parts of the limbic system. Our previous study found that administration of motilin in the hippocampus stimulates gastric motility. We now explore the effect of motilin in the amygdala on gastric motility. In conscious rats, gastric motility was recorded after microinjection of motilin, motilin receptor antagonist (GM-109) or a mixture of the two into the basomedial amygdala nucleus (BMA). In anesthetized rats the changes of spontaneous discharges of gastric distention sensitive neurons (GDSN) in the BMA were recorded after intracerebroventricular (i.c.v.) microinjection of motilin or GM-109. In conscious rats the amplitude of gastric contractions increased dose-dependently after microinjection of motilin in the BMA, and decreased after microinjection of GM-109. The excitatory or inhibitory effects induced by motilin or GM-109 alone, were weakened by microinjection of a mixture solution of both. The spontaneous discharge frequency of gastric distention excitatory neuron (GDEN) was mainly inhibited by i.c.v. microinjection of motilin but excited by GM-109. In contrast, the spontaneous discharge frequency of gastric distention inhibitory neuron (GDIN) was mainly excited by motilin, but inhibited by GM-109. Our findings suggest that motilin may regulate gastric motility by modulating neural pathways in the BMA.

Gastric stimulation in obese subjects activates the hippocampus and other regions involved in brain reward circuitry

The neurobiological mechanisms underlying overeating in obesity are not understood. Here, we assessed the neurobiological responses to an Implantable Gastric Stimulator (IGS), which induces stomach expansion via electrical stimulation of the vagus nerve to identify the brain circuits responsible for its effects in decreasing food intake. Brain metabolism was measured with positron emission tomography and 2-deoxy-2[18F]fluoro-D-glucose in seven obese subjects who had the IGS implanted for 1-2 years. Brain metabolism was evaluated twice during activation (on) and during deactivation (off) of the IGS. The Three-Factor Eating Questionnaire was obtained to measure the behavioral components of eating (cognitive restraint, uncontrolled eating, and emotional eating). The largest difference was in the right hippocampus, where metabolism was 18% higher (P < 0.01) during the "on" than "off" condition, and these changes were associated with scores on "emotional eating," which was lower during the on than off condition and with "uncontrolled eating," which did not differ between conditions. Metabolism also was significantly higher in right anterior cerebellum, orbitofrontal cortex, and striatum during the on condition. These findings corroborate the role of the vagus nerve in regulating hippocampal activity and the importance of the hippocampus in modulating eating behaviors linked to emotional eating and lack of control. IGS-induced activation of regions previously shown to be involved in drug craving in addicted subjects (orbitofrontal cortex, hippocampus, cerebellum, and striatum) suggests that similar brain circuits underlie the enhanced motivational drive for food and drugs seen in obese and drug-addicted subjects, respectively.

Excitatory effects of gastric electrical stimulation on gastric distension responsive neurons in ventromedial hypothalamus (VMH) in rats

INTRODUCTION

Gastric electrical stimulation (GES) has been used for the treatment of obesity with unclear central mechanisms. The purpose of this study was to investigate the effects of GES on the neuronal activity in the ventromedial hypothalamus (VMH).

METHODS

Extracellular potentials of single neurons in VMH were recorded in 52 anesthetized rats. Neurons were classified as gastric distension-excitatory (GD-E) neurons or GD-inhibitory (GD-I) neurons. GES with four sets of parameters was applied for comparison.

RESULTS

Eighty two neurons out of 96 (85.41%) in VMH responded to gastric distension (GD). 37.8% were GD-E neurons and 51(62.2%) were GD-I neurons. 55.0%, 17.6%, 77.8%, 14.3% of GD-E neurons were excited by four sets of parameters: GES1 (standard), GES2 (reduced pulse numbers), GES3 (increased pulse width) and GES4 (reduced frequency), respectively. More GD-E neurons were excited by GES3 (P < 0.05 versus GES2 or GES4) and by GES1 (P < 0.02 versus GES2 or GES4). Among the GD-I neurons, 63.6, 37.9, 73.3, and 51.9% neurons were excited by GES1-4, respectively.

CONCLUSION

GES with parameters used for treating obesity excites GD-responsive neurons in VMH. The excitatory effect of GES is related to the strength of stimulation, including pulse frequency and width as well as pulse train on-time.

Effect of exogenous motilin in amygdaloid nucleus on gastric motility and its underlying mechanism in rats

AIM: To investigate the effect of motilin microinjection into bilateral basomedial amygdaloid nucleus (BMA) on the gastric motility in rats, and explore its underlying mechanism.

METHODS: Forty male Wistar rats were used for four sets of experiments (Exp). Exp 1: Animals received bilateral injections of motilin (MT, 1 mg/side) or normal saline (NS, 0.5 mL/side) into BMA, and both intragastric pressure (IGP) and gastric motility frequency (GMF) were recorded to estimate the gastric motility (n = 14). Exp 2: Pretreatment of vagotomy was carried out in 12 rats, and then MT or NS was injected into BMA as in Exp1. Exp3: Sixty minutes after MT or NS injection into BMA, c-Fos protein expression was detected in the paraventricular nucleus (PVA, n = 7). Exp 4: Motilin contents were measured in five brain areas (hypothalamus, midbrain, pons, medulla, and pituitary gland), using radioimmunoassay (RIA) method (n = 7).

RESULTS: Exogenous motilin in BMA enhanced the gastric motility in rats, and this action lasted about 15 min. At the 10^th, 15^th, 20^th, 25^th min after motilin injection, the changes of IGP percentage were 19.7% ± 6.5%(P = 0.023), 62.9% ± 4.7% (P < 0.01), 45.1% ± 7.9% (P < 0.01), 29.3% ± 10.3% (P = 0.029). The changes of GMF percentage at the 15^th, 20^th min were 36.7% ± 8.5% (P < 0.01) and 19.5% ± 6.0% (P = 0.015), respectively. No obvious changes in both IGP and GMF were observed in normal saline controls. Pretreatment of subdiaphragmal vagotomy abolished the enhanced gastric motility induced by motilin injection. Motilin injection into bilateral BMA induced increased numbers of c-Fos positive cells in PVN, as compared with the saline control (53.4 ± 8.9 vs 22.5 ± 5.2, P < 0.01). Among the five tested brain areas, the highest motilin level was found in the hypothalamus area (74.3 ± 19.6 mg/kg). The motilin contents in the other four areas ranged from 7.8 ± 2.2 mg/kg to 17.3 ± 6.6 mg/kg.

CONCLUSION: Exogenous motilin in BMA can enhance the gastric motility in rats, which might rely on the amygdala-hypothalamus and brain stem-vagus pathway.

Effects of gastric electrical stimulation on responsive neurons to gastric distension and expression of orexin in rats

AIM: To investigate the effects of gastric electri-cal stimulation (GES) on responsive neurons to gastric distension (GD) in ventromedia hypotha-lamus (VMH) and the expression of orexin in rat brain.

METHODS: Fifty-two adult Wistar rats were used in this experiment. The effects of GES on GD responsive neurons in VMH were observed by recording extracellular potentials of single neuron. GD responsive neurons were classified as GD-excitatory (GD-E) and GD-inhibitory (GD-I) ones according to their responses to GD. GES with three sets of parameters were applied for one minute respectively: GES1 (6 mA, 0.3 ms, 40 Hz, 2 s-on, 3 s-off) with standard pulse trains; GES2 with reduced on-time to 0.1 s and GES3 with decreased frequency to 20 Hz. After GES1 was using for 2 h, we observed the expression of orexin-A immunoreactive (orexin-A-IR) positive neurons in lateral hypothalamus area (LHA) by fluorescent immunohistochemistry and the content of orexin in rat brain by radioimmunoassay.

RESULTS: Ninety neurons in VMH were recorded, of which 82 (85.41%) responded to GD (3-5 mL, 10-30 s). Of the 82 GD responsive neurons, 31 (37.8%) were GD-E neurons and 51 (62.2%) were GD-I neurons. 55.0%, 17.6%, and 14.3% of GD-E neurons were excited by GES1, GES2, and GES3 respectively. More GD-E neurons were excited by GES1 than by GES2 and GES3 (P = 0.002 and 0.016, respectively). Of the GD-I neurons, 63.6%, 37.9%, and 51.9% neurons were excited by GES1, GES2, and GES3, respectively. GES2 was noted to be less effective in comparison with GES1 (P = 0.043). After GES1 was in application for 2 h, the levels of orexin-A-IR positive neurons were significantly decreased in LHA as comopared with those in control group (6.97 ± 1.51/0.1 mm2 vs 26.62 ± 8.30/0.1 mm2, P < 0.01), and the content of orexin peptide was decreased obviously in the hypothalamus (112.54 ± 11.58 fmol/mg vs 185.23 ± 15.22 fmol/mg, P < 0.01), mesencephalon (71.95 ± 8.45 fmol/mg vs 98.48 ± 12.02 fmol/mg, P < 0.05), medulla oblongata (72.36 ± 6.58 fmol/mg vs 101.29 ± 15.22 fmol/mg, P < 0.05), solitary tract nucleus (69.12 ± 4.99 fmol/mg vs 89.21 ± 9.23 fmol/mg, P < 0.05) by radioimmunoassay. However, the content of orexin peptide had no significant change in pons.

CONCLUSION: GES may activate the GD responsive neurons in VMH and the excitatory effect of GES is related to the frequency and time of stimulation. Decreased expression of orexin in the brain may also take part in the central mechanism of GES.

Antisecretory factor modulates GABAergic transmission in the rat hippocampus

Antisecretory Factor (AF) is a protein that has been implicated in the suppression of intestinal hypersecretion and inflammation. Intestinal secretion and inflammation are partly under local and central neural control raising the possibility that AF might exert its action by modulating neural signaling. In the present study we have investigated whether AF can modulate central synaptic transmission. Evoked glutamatergic and GABAergic synaptic transmissions were investigated using extracellular recordings in the CA1 region of hippocampal slices from adult rats. AF (0.5 microg/ml) suppressed GABA(A)-mediated synaptic transmission by about 40% while having no effect on glutamatergic transmission. Per oral administration of cholera toxin as well as feeding of rats with a diet containing hydrothermally processed cereals, known to upregulate endogenous AF plasma activity, mimicked the effect of exogenously administered AF on hippocampal GABAergic transmission. Our results identify AF as a neuromodulator and further raise the possibility that the hippocampus and AF are involved in a gut-brain loop controlling intestinal secretion and inflammation.

Central, but not peripheral application of motilin increases c-Fos expression in hypothalamic nuclei in the rat brain

Previous immunocytochemical studies have shown the presence of motilin-immunoreactive neurons in specific brain areas of rats and autoradiographic studies in rabbits demonstrated motilin-binding sites in the central nervous system as well. Therefore, the aim of this study was to determine the anatomical localisation and neurochemical features of neurons activated by central administration of motilin (Mo) in rats. One week after cannulation, an intracerebroventricular injection of Mo (ICV, 3 microg/6 mul 0.9% saline) was given. For comparative purposes, a group of animals received an intravenous injection of motilin (IV, 9 microg/300 mul 0.9% saline) or an equal volume of saline. Neuronal excitation was assessed by c-Fos immunocytochemistry and combined with immunostaining for neurotransmitter markers. In contrast to the IV motilin-treated animals, the ICV motilin-treated animals displayed a significant increase in c-Fos expression in the supraoptic nuclei (SO) and paraventricular nuclei of the hypothalamus (PVH). At the level of the dorsomedial, ventromedial and lateral hypothalamic nuclei, ICV administration of motilin did not induce changes in c-Fos expression. In addition, the cerebellum did not show c-Fos expression after ICV motilin administration either. These findings might suggest distinct pathways and actions of centrally released and systemic motilin, but, particularly in rodents, do not rule out the possibility that the effects seen in the SO and PVH after ICV application are aspecific in nature. At present, we cannot exclude the fact that the results observed with motilin in rodents are due to cross-interaction with other related (e.g. ghrelin) or not yet identified receptors.

Effects of motilin and ursodeoxycholic acid on gastrointestinal myoelectric activity of different origins in fasted rats

AIM: To investigate gastrointestinal migrating myoelectric complex (MMC) and the effects of porcine motilin and ursodeoxycholic acid (UDCA) on MMC of gastrointestinal tract of different origins in fasted rats.

METHODS: Three bipolar silver electrodes were chronically implanted on the antrum, duodenum and jejunum. Seven days later 24 experimental rats were divided into 2 groups. One group was injected with porcine motilin via sublingual vein at a dose of 20 μg/kg, the other group was perfused into stomach with UDCA. The gastrointestinal myoelectric activity was recorded 1 h before and 2 h after the test substance infusions into the rats.

RESULTS: In all fasted rats a typical pattern of MMC was observed. Among the totally 68 activity fronts recorded in fasted rats under control, 67% started in duodenum, and 33% in antrum. MMC cycle duration and duration of phase III of antral origin were longer than those of duodenal origin. Administration of 20 μg/kg porcine motilin induced a premature antral phase III of antral origin. But perfusion into stomach with UDCA resulted in shorter MMC cycle duration, longer duration of phase III of duodenal origin, which were followed with shorter cycle duration and duration of antral phase III.

CONCLUSION: In fasted rats, MMC could originate from antrum and duodenum respectively. The characteristics of MMC of different origins may contribute to the large variations within subjects. The mechanisms of different origins of phase III may be different. Porcine motilin and UDCA could affect MMC of different origins of the gastrointestinal tract in fasted state, respectively.