Biomedical subjects

Jean-Pierre Timmermans

Publications and source records attributed to Jean-Pierre Timmermans.

At least 19 recordsLinked to original sources

PubMed2006

Sensory receptors in the visceral pleura: neurochemical coding and live staining in whole mounts.

Today, diagnosis and treatment of chest pain related to pathologic changes in the visceral pleura are often difficult. Data in the literature on the sensory innervation of the visceral pleura are sparse. The present study aimed at identifying sensory end-organs in the visceral pleura, and at obtaining more information about neurochemical coding. The immunocytochemcial data are mainly based on whole mounts of the visceral pleura of control and vagally denervated rats. It was shown that innervation of the rat visceral pleura is characterized by nerve bundles that enter in the hilus region and gradually split into slender bundles with a few nerve fibers. Separate nerve fibers regularly give rise to characteristic laminar terminals. Because of their unique association with the elastic fibers of the visceral pleura, we decided to refer to them as "visceral pleura receptors" (VPRs). Cryostat sections of rat lungs confirmed a predominant location on mediastinal and interlobar lung surfaces. VPRs can specifically be visualized by protein gene product 9.5 immunostaining, and were shown to express vesicular glutamate transporters, calbindin D28K, Na+/K+-ATPase, and P2X3 ATP-receptors. The sensory nerve fibers giving rise to VPRs appeared to be myelinated and to have a spinal origin. Because several of the investigated proteins have been reported as markers for sensory terminals in other organs, the present study revealed that VPRs display the neurochemical characteristics of mechanosensory and/or nociceptive terminals. The development of a live staining method, using AM1-43, showed that VPRs can be visualized in living tissue, offering an interesting model for future physiologic studies.

Animals↗

PubMed2006

The bidirectional communication between neurons and mast cells within the gastrointestinal tract.

Normal or disordered behaviour of the gastrointestinal tract is determined by a complex interplay between the epithelial barrier, immune cells, blood vessels, smooth muscle and intramurally located nerve elements. Mucosal mast cells (MMCs), which are able to detect noxious and antigenic threats and to generate or amplify signals to the other cells, are assigned a rather central position in this complex network. Signal input from MMCs to intrinsic enteric neurons is particularly crucial, because the enteric nervous system fulfils a pivotal role in the control of gastrointestinal functions. Activated enteric neurons are able to generate an alarm program involving alterations in motility and secretion. MMC signalling to extrinsic nerve fibres takes part in pathways generating visceral pain or extrinsic reflexes contributing to the disturbed motor and secretory function. Morphological and functional studies, especially studies concerning physiological stress, have provided evidence that, apart from the interaction between the enteric nervous system and MMCs, there is also a functional communication between the central nervous system and these mast cells. Psychological factors trigger neuronal pathways, which directly or indirectly affect MMCs. Further basic and clinical research will be needed to clarify in more detail whether basic patterns of this type of interactions are conserved between species including humans.

Animals↗

PubMed2006

Selective clearance of macrophages in atherosclerotic plaques by the protein synthesis inhibitor cycloheximide.

Macrophages are an essential component of unstable atherosclerotic plaques and play a pivotal role in the destabilization process. We have demonstrated previously that local delivery of the mammalian target of rapamycin (mTOR) inhibitor everolimus selectively clears macrophages in rabbit plaques. Because mTOR controls mRNA translation, inhibition of protein synthesis might induce selective macrophage cell death. We therefore investigated in the present study the effect of the protein synthesis inhibitor cycloheximide on macrophage and smooth muscle cell (SMC) viability. In vitro studies with cultured macrophages and SMCs showed that cycloheximide induced selective apoptosis of macrophages in a concentration- and time-dependent manner. Moreover, macrophages could be selectively depleted in rabbit carotid artery rings with collar-induced atherosclerotic plaques after in vitro treatment with cycloheximide. Local in vivo administration of cycloheximide via osmotic minipumps to rabbit carotid arteries with collar-induced atherosclerotic plaques significantly reduced the macrophage but not the SMC content. Cycloheximide-treated plaques showed signs of apoptosis (increased terminal deoxynucleotidyl transferase end labeling and fluorescein isothiocyanate-Val-Ala-dl-Asp(O-methyl)-fluoromethylketone labeling) that did not colocalize with SMCs. Organ chamber studies demonstrated that the functionality of SMCs and the endothelium were not influenced by cycloheximide treatment. All together, these findings demonstrate that cycloheximide decreases the macrophage load in atherosclerotic plaques by induction of apoptosis without changing SMC content or contractility.

Animals↗

PubMed2006

Time-dependent expression pattern of nitric oxide and superoxide after myocardial infarction in rats.

Previous experiments by our group have demonstrated a subacute increased contribution of nitric oxide (NO) to vasoreactivity after myocardial infarction in rats. However, the activation pattern of NO may be phasic after infarction and has been described to be strongly associated with superoxide production. Therefore, the present study evaluated the morphological distribution and time-dependent induction of NO and superoxide at the protein (via immunohistochemistry, chemiluminescence and spectrophotometry) and mRNA (via real-time RT-PCR) level after experimental induction of a myocardial infarction in rats. Myocardial infarction led to a modest but lasting upregulation of endothelial NO synthase (eNOS) in blood vessels and cardiomyocytes. In contrast, inducible NOS (iNOS) showed dramatic de novo formation 1 week after infarction, predominantly in the infarcted area and cardiomyocytes. In addition, a gradually increased myocardial production of superoxide was detected during remodelling, probably related by an upregulation of NADH oxidase in the peri-infarcted and remote myocardium. Furthermore, peroxynitrite formation was increased after myocardial infarction, indicating strong interaction between NO and superoxide. In conclusion, during the early remodelling phase after myocardial infarction mRNA concentrations and protein levels of eNOS and iNOS show an augmentation in a biphasic manner. Moreover, upregulation of NADH oxidase leads to increased presence of superoxide and peroxynitrite and thereby to a reduction of the bioavailability and compensatory effects of NO, as such influencing post-infarction remodelling.

Animals↗

PubMed2006

Evidence for a role of neuroepithelial bodies as complex airway sensors: comparison with smooth muscle-associated airway receptors.

The epithelium of intrapulmonary airways in many species harbors diffusely spread innervated groups of neuroendocrine cells, called neuroepithelial bodies (NEBs). Data on the location, morphology, and chemical coding of NEBs in mammalian lungs are abundant, but none of the proposed functions has so far been fully established. Besides C-fiber afferents, slowly adapting stretch receptors, and rapidly adapting stretch receptors, recent reviews have added NEBs to the list of presumed sensory receptors in intrapulmonary airways. Physiologically, the innervation of NEBs, however, remains enigmatic. This short overview summarizes our present understanding of the chemical coding and exact location of the receptor end organs of myelinated vagal airway afferents in intrapulmonary airways. The profuse populations that selectively contact complex pulmonary NEB receptors are compared with the much smaller group of smooth muscle-associated airway receptors. The main objective of our contribution was to stimulate the idea that the different populations of myelinated vagal afferents that selectively innervate intraepithelial pulmonary NEBs may represent subpopulations of the extensive group of known electrophysiologically characterized myelinated vagal airway receptors. Future efforts should be directed toward finding out which airway receptor groups are selectively coupled to the complex NEB receptors.

Animals↗

PubMed2006

Region-specific distribution of the P2Y4 receptor in enteric glial cells and interstitial cells of Cajal within the guinea-pig gastrointestinal tract.

Although there is pharmacological evidence to assume that the P2Y4 receptor is a regulator of epithelial ion transport, no detailed data about its distribution within the gut are available. Therefore, this study, using whole mounts and cryosections, aimed to reveal the expression pattern of P2Y4 along the entire guinea-pig gastrointestinal tract. P2Y4 immunoreactivity was absent from enteric neurons but present in enteric glial cells of the stomach, small and large intestine. In the esophagus, P2Y4 appeared to be exclusively located within striated muscle cells. P2Y4 showed also a region dependency regarding its presence in different subpopulations of interstitial cells of Cajal: in myenteric interstitial cells of Cajal in the stomach and ileum; in some intramuscular interstitial cells in the stomach and cecum; in some deep muscular plexus interstitial cells in the ileum; and in some submucosal surface interstitial cells in the colon. These results and the knowledge that P2Y4 activation causes intracellular Ca2+ recruitment led us to suggest that P2Y4 in enteric glia plays a modulatory role in intercellular Ca2+ waves, while P2Y4 in interstitial cells of Cajal modulates intracellular Ca2+ oscillations.

Animals↗

PubMed2006

Sensory receptors in the airways: neurochemical coding of smooth muscle-associated airway receptors and pulmonary neuroepithelial body innervation.

Mainly due to the lack of conclusive morphological data, correlation between functionally and morphologically defined lung receptors has so far been unsatisfactory. In the present study, multiple immunocytochemical stainings with a panel of markers for (mechanso)sensory nerve fibres were performed in order to visualise putative receptor terminals in rat intrapulmonary airways. We first focussed on determining the location, morphology and neurochemical coding of subepithelial receptor-like structures that have been sporadically reported in the wall of large diameter airways. Immunostaining with antibodies against Na+/K+-ATPase alpha3, vesicular glutamate transporter 1 (VGLUT1) and VGLUT2 revealed branching laminar subepithelial receptor endings associated with airway smooth muscle. The latter nerve terminals appeared to further express calbindin D28k (CB), and the ATP receptor P2X3, but were calcitonin gene-related peptide (CGRP)-negative. The nerve fibres that give rise to these terminals were shown to be myelinated and have a vagal sensory origin. Because of the close association between the laminar terminals of this receptor-like structures and airway smooth muscle, we will further refer to these clearly morphologically identifiable sensory end organs as 'smooth muscle-associated airway receptors (SMARs)'. Secondly, we further explored the sensory innervation of pulmonary neuroepithelial bodies (NEBs). NEBs are intraepithelial groups of neuroendocrine cells, contacted by several nerve fibre populations, at least three of which are sensory. The spinal sensory innervation of NEBs expresses CGRP and substance P, contacts NEBs at their basal pole, and is capsaicin-sensitive. The intraepithelial vagal sensory innervation of NEBs, on the other hand, appears to be myelinated and could be labelled by antibodies against VGLUT1, VGLUT2, CB and P2X3 receptors. Na+/K+-ATPase alpha3 immunostaining additionally labelled part of the vagal sensory innervation of rat pulmonary NEBs. The neurochemical coding and receptor-like appearance of SMARs and of the complex vagal sensory innervation of NEBs appeared to be almost identical and reminiscent of mechanosensors. Both SMARs and vagal nodose nerve terminals in NEBs therefore likely represent the morphological counterparts of subgroups of the extensive population of physiologically characterised myelinated vagal airway receptors, the majority of which are mechanosensitive. Electrophysiological data based on 'local' stimuli should be interpreted with caution, because of the regular close apposition of SMARs and NEBs and the very similar characteristics of their nerve terminals.

Animals↗

PubMed2006

Macrophages but not smooth muscle cells undergo benzyloxycarbonyl-Val-Ala-DL-Asp(O-Methyl)-fluoromethylketone-induced nonapoptotic cell death depending on receptor-interacting protein 1 expression: implications for the stabilization of macrophage-rich atherosclerotic plaques.

Several lines of evidence suggest that macrophages play a key role in atherosclerotic plaque destabilization and rupture. Therefore, selective removal of macrophages from plaques via pharmacological therapy could represent a promising approach to stabilize "vulnerable," rupture-prone lesions. Yet, how macrophages can be eliminated from plaques without influencing other cell types, including smooth muscle cells (SMCs), is unknown. In the present study, we report that benzyloxycarbonyl-Val-Ala-DL-Asp(O-methyl)-fluoromethylketone (z-VAD-fmk), a caspase inhibitor with broad specificity, induces nonapoptotic cell death of J774A.1 and RAW264.7 macrophages but not of SMCs. Cell death was characterized by bulk degradation of long-lived proteins, processing of microtubule-associated protein light chain 3, and cytoplasmic vacuolization, which are all markers of autophagy. However, necrosis also occurred, and the number of necrotic cells rapidly increased during z-VAD-fmk treatment. Primary mouse peritoneal macrophages were resistant to z-VAD-fmk-mediated cell death, but unlike SMCs, they underwent z-VAD-fmk-mediated necrosis after pretreatment with interferon-gamma. Further evidence indicated that the expression level of receptor-interacting protein 1 (RIP1) mediates the sensitivity to z-VAD-fmk. Importantly, upon z-VAD-fmk treatment, J774A.1 macrophages overexpressed and secreted several chemokines and cytokines, including tumor necrosis factor (TNF) alpha. The combination of z-VAD-fmk and TNFalpha, but not TNFalpha alone, induced SMCs necrosis via a mechanism that required RIP1 expression. These results suggest that z-VAD-fmk, despite its selective cell death inducing capacity, would be detrimental for the stability of atherosclerotic plaques due to enlargement of the necrotic core, stimulation of inflammatory responses, and indirect induction of SMC death.

Amino Acid Chloromethyl Ketones↗

PubMed2006

Cadmium and zinc induction of ZnT-1 mRNA in an established carp cell line.

The cDNA of a zinc transporter-1 (ZnT-1) gene was cloned from an established cell line derived from common carp (Cyprinus carpio) using rapid amplification of cDNA ends (RACE). Using real-time quantitative PCR, we showed that both zinc (Zn) and cadmium (Cd) transiently upregulate ZnT-1 mRNA to comparable levels. The loosely bound cellular Zn pool, as estimated using the Zn-specific probe FluoZin-3, was increased threefold after exposure to 250 microM ZnCl(2). Correspondingly, the ZnT-1 mRNA level at 24 h was induced about fivefold, reflecting the need for more zinc export capacity. Total cellular zinc levels were not different from the controls after 72 h of exposure to 10, 50, or 250 microM ZnCl(2). A loss of total cellular Zn but little labile zinc changes were observed with up to 25 microM Cd. At 72 h, the total Zn was partially restored to the control levels, only 1 microM Cd allowed for a full recovery. Downregulation of ZnT-1 mRNA and partial loss of loosely bound Zn were observed with 50 microM Cd. Our results clearly show that although Zn and Cd can both regulate Zn export in EPC cells, the effects on the cellular Zn pools are quite different.

Amino Acid Sequence↗

PubMed2006

Tracing of labile zinc in live fish hepatocytes using FluoZin-3.

Intracellular zinc levels are homeostatically regulated and although most is bound, a pool of labile Zn(II) is present in cells. We show here that the zinc probe FluoZin-3 is useful to monitor zinc fluxes during fluorescent imaging of the trout hepatic cell line D11. Nuclei and bulk cytosol appeared to lack detectable labile zinc, while the punctuate staining pattern colocalized with a lysosome-specific probe. Applying extracellular zinc alone resulted in vesicular sequestration of the metal ion. Together with Na-pyrithione a delayed and toxic rise in cellular fluorescence was triggered. When using another ionophore, 4-Br A23187, a zinc buffering effect of the vesicular pools was evident. Secondly, N-ethylmaleimide induced a homogeneous fluorescence rise, which was strongly enhanced by addition of Zn-pyrithione and disappeared after TPEN washing. This suggests the involvement of thiol residues in controlling available cytosolic zinc. Our observations have implications for the interpretation of calculated intracellular Zn2+ concentrations.

Animals↗

PubMed2005

Neurochemical characterisation of sensory receptors in airway smooth muscle: comparison with pulmonary neuroepithelial bodies.

Descriptions of morphologically well-defined sensory airway receptors are sparse, in contrast to the multiplicity of airway receptors that have been identified electrophysiologically. The present study aimed at further determining the location, morphology and neurochemical coding of subepithelial receptor-like structures that have been sporadically reported in the wall of large diameter airways. The results were compared with those obtained for pulmonary neuroepithelial bodies (NEBs), which are complex intraepithelial sensory airway receptors. Multiple immunocytochemical staining showed branching laminar subepithelial receptor-like endings, which were found to intercalate in the smooth muscle layer of intrapulmonary conducting airways in rats. Because of the consistent intimate association with the airway smooth muscle, the laminar terminals will further be referred to as 'smooth muscle-associated airway receptors (SMARs)'. SMARs were characterised by their Na(+)/K(+)-ATPase alpha3, vesicular glutamate transporter 1 (VGLUT1) and VGLUT2-immunoreactivity, expression of the ATP receptor P2X(3), and the presence of calcium-binding proteins. Nerve fibres giving rise to SMARs were shown to be myelinated and to have a vagal origin. Interestingly, the neurochemical coding and receptor-like appearance of SMARs appeared to be almost identical to at least part of the complex vagal sensory terminals in NEBs. Intraepithelial nerve endings in pulmonary NEBs were indeed also shown to originate from myelinated vagal afferent nerve fibres, and to express Na(+)/K(+)-ATPase alpha3, VGLUT1, VGLUT2, P2X(3) and calcium-binding proteins. Since several of the latter proteins have been reported as markers for mechanoreceptor terminals in other organs, both SMARs and the vagal nodose nerve terminals in NEBs seem good candidates to represent the morphological counterparts of at least subsets of the extensive population of physiologically characterised myelinated vagal airway mechanoreceptors. The observation that SMARs and NEBs are regularly found in each other's immediate neighbourhood, and the very similar characteristics of their nerve terminals, point out that the interpretation of electrophysiological data based on 'local' stimuli should be made with great caution.

Animals↗

PubMed2005

Cytoplasmic, but not nuclear, expression of the neuronal nuclei (NeuN) antibody is an exclusive feature of Dogiel type II neurons in the guinea-pig gastrointestinal tract.

This study aimed to reveal if NeuN, a neuronal nuclei (NeuN) antibody, is a selective marker of intrinsic primary afferent neurons (IPANs) in the guinea-pig gastrointestinal tract as previously hypothesised. The NeuN immunoreactivity was found in the enteric nervous system with exception of the esophagus. Two groups of NeuN-expressing neurons were observed: neurons with immunostained nuclei and cytoplasm (NeuN(NC)) and neurons only expressing immunoreactivity in their nuclei (NeuN(N)). The NeuN(N)-immunoreactive neurons were found in the myenteric plexus of the stomach and the colon. In the stomach, none of the NeuN(N)-expressing neurons, of which 55+/-3% co-expressed calbindin, had a Dogiel type I or II morphology. The NeuN(N)-positive neurons of the colon, which did not express calbindin, did not resemble a Dogiel type II morphology either, but were small-sized neurons. The NeuN(NC)-immunoreactive neurons were observed in both the small and large intestine. These neurons were smooth-contoured and bigger-sized, resembling a Dogiel type II morphology. Some of these neurons co-expressed calbindin. The present data reveal the existence of two populations of Dogiel type II neurons, exhibiting NeuN(NC)+/calbindin+ or NeuN(NC)+/calbindin- immunoreactivity, in the intestine. Assuming that all IPANs exhibit a Dogiel type II morphology, we conclude that the cytoplasmic expression of NeuN is an exclusive feature of IPANs.

Animals↗

PubMed2005

Subtractive hybridization unravels a role for the ion cotransporter NKCC1 in the murine intestinal pacemaker.

In the small intestine, interstitial cells of Cajal (ICC) surrounding the myenteric plexus generate the pacemaking slow waves that are essential for an efficient intestinal transit. The underlying molecular mechanisms of the slow wave are poorly known. Our aim was to identify ICC-specific genes and their function in the mouse jejunum. Suppression subtractive hybridization using two independent ICC-deficient mouse models identified 56 genes putatively downregulated in the muscularis propria compared with wild-type littermates. Differential expression was confirmed by real-time quantitative PCR for the tyrosine kinase receptor KIT, the established marker for ICC, and for the Na(+)-K(+)-2Cl(-) cotransporter (NKCC1). Immunoreactivity for NKCC1 was detected in myenteric ICC but not in the ICC population located at the deep muscular plexus. NKCC1 was also expressed in enteric neurons and mucosal crypts. Bumetanide, an NKCC1 inhibitor, reversibly affected the shape, amplitude, and frequency of the slow waves. Similar alterations were observed in NKCC1 knockout mice. These data support the hypothesis that NKCC1 expressed in myenteric ICC is involved in the mechanism of slow waves in the murine jejunum.

Action Potentials↗

PubMed2005

Domain analysis of Kv6.3, an electrically silent channel.

The subunit Kv6.3 encodes a voltage-gated potassium channel belonging to the group of electrically silent Kv subunits, i.e. subunits that do not form functional homotetrameric channels. The lack of current, caused by retention in the endoplasmic reticulum (ER), was overcome by coexpression with Kv2.1. To investigate whether a specific section of Kv6.3 was responsible for ER retention, we constructed chimeric subunits between Kv6.3 and Kv2.1, and analysed their subcellular localization and functionality. The results demonstrate that the ER retention of Kv6.3 is not caused by the N-terminal A and B box (NAB) domain nor the intracellular N- or C-termini, but rather by the S1-S6 core protein. Introduction of individual transmembrane segments of Kv6.3 in Kv2.1 was tolerated, with the exception of S6. Indeed, introduction of the S6 domain of Kv6.3 in Kv2.1 was enough to cause ER retention, which was due to the C-terminal section of S6. The S4 segment of Kv6.3 could act as a voltage sensor in the Kv2.1 context, albeit with a major hyperpolarizing shift in the voltage dependence of activation and inactivation, apparently caused by the presence of a tyrosine in Kv6.3 instead of a conserved arginine. This study suggests that the silent behaviour of Kv6.3 is largely caused by the C-terminal part of its sixth transmembrane domain that causes ER retention of the subunit.

Amino Acid Sequence↗

PubMed2005

Thickness of the gerbil tympanic membrane measured with confocal microscopy.

Thickness data for the gerbil tympanic membrane, an extremely thin biological membrane, are presented. Thickness measurements were performed on fresh material using fluorescence images taken perpendicular through the membrane with a commercial confocal microscope. Thickness varies strongly across the membrane. Similar thickness distributions in all samples (pars tensa n = 11; pars flaccida n = 3) were observed. The pars tensa has a rather constant thickness of about 7 microm in the central region curving as a horse shoe upwards around the manubrium. In the most superior parts of the pars tensa thickness becomes gradually twice as large. Thickness increases also steeply from the central region towards the edges (about 35 microm near the annulus and 20 microm near the manubrium). A pronounced, local thickening of about 30 microm is present close to the edge and extends as a ring along the entire annular periphery of the pars tensa. Overall, the pars flaccida is thicker than the pars tensa and has a rugged surface. Its central region has a mean thickness of about 24 microm with a mean variation of about 4 microm. The average thickness in the inferior region is slightly larger than in the superior region. The pars flaccida thickens steeply, up to about 80 microm, near the edges.

Animals↗

PubMed2005

Role of nitric oxide during coronary endothelial dysfunction after myocardial infarction.

This study aimed to investigate whether permanent ischaemia influences subacute vasodilatation responses of non-infarcted rat coronary vasculature, and to characterise these coronary changes. Ischaemia led to a significant impairment of the endothelium-dependent vasodilator response, while coronary vasodilatory capacity remained unaltered. In normal coronary circulation, nitric oxide (NO) and prostanoids contributed to vasodilatation, while basal involvement of endothelium-derived hyperpolarising factor was limited. Vasodilatory impairment following myocardial infarction did not originate from alterations in the prostanoid pathway, and only a slightly increased influence of K+ channels was observed. However, NO-mediated vasodilatation was significantly increased after ischaemia, as also confirmed by higher mRNA and protein levels of iNOS and eNOS. Additionally, the amount of superoxide was enhanced following infarction. We conclude that subacute postinfarction remodeling is accompanied by endothelial dysfunction in non-infarcted coronary arteries. Although the NO-mediated response is increased after ischaemia, its final action is restricted due to the presence of superoxide.

Adenosine↗

PubMed2005

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.

Animals↗

PubMed2005

Evidence for the presence of motilin, ghrelin, and the motilin and ghrelin receptor in neurons of the myenteric plexus.

Motilin, a 22-amino acid gastrointestinal peptide, and ghrelin, the natural ligand of the growth hormone secretagogue receptor, form a new group of structurally related peptides. Several lines of evidence suggest that motilin and ghrelin are involved in the control of gastrointestinal motility by the activation of receptors on enteric neurons. The aim of this study was to look for the existence of motilin, ghrelin, and their respective receptors in the myenteric plexus of the guinea pig. We used longitudinal muscle/myenteric plexus (LMMP) preparations and cultures of myenteric neurons of the guinea pig ileum, immunohistochemistry, and reverse transcriptase-polymerase chain reaction (RT-PCR). Most of the motilin-immunoreactive (IR; 72.8%) and motilin receptor-IR (68.9%) neurons were also positive for neuronal nitric oxide synthase (nNOS), 72.8% and 68.9%, few for choline acetyl transferase (ChAT), 11.4% and 11.9%, respectively. In contrast, ghrelin was mainly colocalized with ChAT (72.2%), and only 3.6% of ghrelin-positive cells showed nNOS-IR in the LMMP. Neither motilin nor the motilin receptor or ghrelin colocalized with calbindin. RT-PCR studies revealed motilin, ghrelin, and ghrelin receptor mRNA transcripts in LMMP preparations and in cultured myenteric neurons. In conclusion, this study, for the first time, provides direct evidence for the existence of motilin and ghrelin in myenteric neurons and suggests that both peptides may play a role in the activation of the enteric nervous system and hence in the regulation of gastrointestinal motility.

Animals↗