Biomedical subjects

Jean-Pierre Timmermans

Publications and source records attributed to Jean-Pierre Timmermans.

52 records · Page 3Linked to original sources

PubMed2003

Functional morphology of pulmonary neuroepithelial bodies: extremely complex airway receptors.

Innervated groups of neuroendocrine cells, called neuroepithelial bodies (NEBs), are diffusely spread in the epithelium of intrapulmonary airways in many species. Our present understanding of the morphology of NEBs in mammalian lungs is comprehensive, but none of the proposed functional hypotheses have been proven conclusively. In recent reviews on airway innervation, NEBs have been added to the list of presumed physiological lung receptors. Microscopic data on the innervation of NEBs, however, have given rise to conflicting interpretations. Using neuronal tracing, denervation, and immunostaining, we recently demonstrated that the innervation of NEBs is much more complex than the almost unique vagal nodose sensory innervation suggested by other authors. The aim of the present work is to summarize our present understanding about the origin and chemical coding of the profuse nerve terminals that selectively contact pulmonary NEBs. A thorough knowledge of the complex interactions between the neuroendocrine cells and at least five different nerve fiber populations is essential for defining the position(s) of NEBs among the many pulmonary receptors characterized by lung physiologists.

Animals↗

PubMed2003

Reduced number of intrinsic pulmonary nitrergic neurons in Fawn-Hooded rats as compared to control rat strains.

The Fawn-Hooded rat (FHR) strain reveals a congenital predisposition to primary (idiopathic) pulmonary hypertension (PPH), and can therefore be regarded as an animal model in which to study possible mechanisms underlying an inherited susceptibility to pulmonary hypertension. Pulmonary hypertension can be induced in FHRs after a short exposure to mild hypoxia, presumably because of an altered peripheral oxygen sensitivity. Given the presence of pulmonary nitrergic neurons in rat lungs, the observed link between airway hypoxia and the expression of pulmonary neuronal nitric oxide synthase (nNOS), and the fact that nNOS appears to be involved in peripheral chemoreceptor sensitivity, we examined the intrinsic pulmonary nitrergic innervation in the FHR. In the present study the number of intrapulmonary nitrergic nerve cell bodies, detected by NADPH diaphorase (NADPHd) histochemistry, was quantified in the FHR and three control rat strains. Compared to the control rat strains, the FHR lungs revealed a highly significantly lower number of intrinsic nitrergic neurons, while no apparent differences were found in the number of enteric nitrergic neurons in the esophagus. In conclusion, the possible links between neuronal NO, hypersensitivity to airway hypoxia, and the development of PPH clearly deserve further investigation.

Animals↗

PubMed2003

Dual sensory innervation of pulmonary neuroepithelial bodies.

The characteristics of the different populations of sensory nerve terminals that selectively contact pulmonary neuroepithelial bodies (NEBs) in rat lungs were investigated after chemical denervation with capsaicin and compared with control lungs. Vagal calbindin D28k and P2X(3) purinoceptor immunoreactive (IR) afferent nerve terminals contacting NEBs appeared to have their origin in the nodose ganglion. Thick CB/P2X(3)-IR nerve fibers were seen to be myelinated and to lose their myelin sheaths just before branching and protruding intraepithelially between the NEB cells. This vagal sensory component of the innervation of NEBs was not affected by capsaicin nor expressed capsaicin receptors (vanilloid receptor subtype 1). A second sensory nerve fiber population that selectively innervates pulmonary NEBs in the rat lung consists of thin unmyelinated nonvagal substance P/calcitonin gene-related peptide IR nerve fibers, contacting mainly the basal pole of pulmonary NEBs, and having their origin in dorsal root ganglia. In concordance with vanilloid receptor 1 expression on these nerve terminals, the spinal sensory substance P/calcitionin gene-related peptide-IR component of the innervation of NEBs was depleted by systemic capsaicin treatment. The complex sensory innervation pattern of pulmonary NEBs characterized in the present study strongly suggests that, physiologically, pulmonary NEBs represent a group of intraepithelial receptors that may be able to accommodate various local and central reflex actions, in relation to both chemo- and mechanosensory stimuli.

Animals↗

PubMed2003

Intrinsic choroidal neurons in the human eye: projections, targets, and basic electrophysiological data.

PURPOSE: The chemical coding of intrinsic choroidal neurons (ICNs) has features in common with extrinsic fibers (e.g., from the pterygopalatine ganglion) making it impossible to assess whether a neuronal nitric oxide synthase (nNOS)/vasoactive intestinal polypeptide (VIP)-immunoreactive nerve fiber is of intrinsic or extrinsic origin. Neurobiotin injections into single neurons allow the visualization of projections of these cells and the determination of the origin of target innervation. Thus, this technique was used in the present study to help characterize the organization of the ICN in the human eye. METHODS: ICNs were visualized with the fluorescent vital dye 4-Di-2-ASP. Electrophysiological properties were determined by means of intracellular recordings. The impaled neurons were iontophoretically filled with neurobiotin. After fixation, immunohistochemistry for neuronal nitric oxide synthase (nNOS), alpha-smooth muscle actin, and calcitonin gene-related peptide (CGRP) was conducted. RESULTS: ICN processes were traced over distances of up to 2.612 micro m. They were found in the immediate vicinity of other nNOS-positive or -negative ICNs and were also found apposed to smooth muscle fibers (vascular and stromal nonvascular). CGRP-positive fibers forming boutons were observed closely associated with ICNs. Electrophysiological recording showed phasic firing without slow afterhyperpolarization, no spontaneous activity, an input resistance of 136 +/-73 MOmega, and a membrane time constant of 7 +/- 1 ms. CONCLUSIONS: Apart from the first functional characterization of ICNs, this study provided more precise evidence of reciprocal ICN-to-ICN contacts and innervation of both choroidal nonvascular and vascular smooth muscle. The presented technique offers promising perspectives to further investigate the function of ICNs in ocular homeostasis.

Actins↗

PubMed2003

Role of nitric oxide and oxidative stress in ischaemic myocardial injury and preconditioning.

Nitric oxide (NO) plays an important role in the physiologic modulation of coronary artery tone and myocardial function. However, increased formation of NO within the myocardium can also have detrimental effects, contributing to the pathophysiology of myocardial dysfunction in ischaemic heart diseases. The role of reactive nitrogen species in the pathogenesis of myocardial dysfunction after ischaemia has been investigated in numerous studies. They reveal divergent and opposed effects of nitric oxide: from a cardioprotective action leading to ischaemic preconditioning after short ischaemic periods to a cardiodepressive action after severe ischaemia/reperfusion injury and heart failure. This review describes the determining role of reactive oxygen species on these opposite myocardial effects of NO. The final action of NO, whether cardioprotective or cardiodepressive, strongly depends on the level of oxidative stress in the myocardium. Nitric oxide disrupts free radical and oxidant-mediated reactions, due to a strong attraction and interaction with superoxide.The level of oxidative stress is positively related to the severity of the ischaemic injury, making the results in different myocardial syndromes more concordant. If the increased production of NO is well in balance with a moderate increase in oxygen radicals, then NO will exert beneficial effects. However, if the oxygen radicals are produced in excess of NO as in prolonged ischaemic injury, then deleterious effects will be induced. Consequently, the balance between NO and free oxygen radicals is crucial in modulating the outcome after an ischaemic insult.

Animals↗

PubMed2002

Investigation of the potential modulatory effect of biliverdin, carbon monoxide and bilirubin on nitrergic neurotransmission in the pig gastric fundus.

In porcine gastric fundus, we have investigated the colocalization of the bile pigment biosynthetic enzymes heme oxygenase-2 and biliverdin reductase with neuronal nitric oxide synthase (nNOS), the effect of carbon monoxide (CO) on fundic circular smooth muscle and the possible modulatory effect of the bile pigments biliverdin and bilirubin on CO-mediated relaxations and on nitrergic relaxation. Heme oxygenase-2 and biliverdin reductase immunoreactivity was present in all nNOS containing myenteric neurons. CO induced a concentration-dependent relaxation of fundic circular smooth muscle strips, which was completely blocked by the specific guanylate cyclase inhibitor 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ). 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (YC-1), biliverdin and bilirubin strongly enhanced the amplitude of the CO-induced relaxation. Tin protoporphyrin had no effect on electrically induced nitrergic relaxation, but spectrophotometric analysis learned that incubation of porcine gastric fundus circular muscle strips with tin protoporphyrin did not influence heme oxygenase activity. In conclusion, our data suggest that nitrergic neurons in the pig gastric fundus are able to produce biliverdin and bilirubin, and that these agents potentiate the relaxant effect of CO, which is formed concomitantly with biliverdin by heme oxygenase-2.

Animals↗

PubMed2002

L-citrulline recycling by argininosuccinate synthetase and lyase in rat gastric fundus.

The aim of this study was to investigate in rat gastric fundus whether L-citrulline, the co-product in the nitric oxide (NO) biosynthesis catalyzed by neuronal nitric oxide synthase (nNOS), can be converted back to the nNOS substrate L-arginine. Immunohistochemistry showed that argininosuccinate synthetase and argininosuccinate lyase, that mediate transformation of L-citrulline to L-arginine in the ureum cycle in hepatocytes, co-localize with nNOS. In longitudinal smooth muscle strips, L-arginine as well as L-citrulline (10(-3) M) was capable of completely respectively partially preventing the N(G)-nitro-L-arginine methyl ester (L-NAME) (3 x 10(-5) M)-induced inhibition of electrically induced nitrergic relaxations, whereas D-citrulline (10(-3) M) was not. The L-citrulline-mediated prevention of the L-NAME-induced inhibition was reduced by L-glutamine (3 x 10(-3) M), the putative L-citrulline uptake inhibitor, and by succinate, an argininosuccinate lyase inhibitor. The results demonstrate that the L-citrulline recycling mechanism is active in rat gastric fundus. Recycling of L-citrulline might play a role in providing sufficient amounts of nNOS substrate during long-lasting relaxations in gastric fundus after food intake.

Animals↗

PubMed2002

Distribution, immunohistochemical characteristics and nerve pathways of primary sensory neurons supplying the porcine vas deferens.

The present study investigated: (1) the distribution and chemical coding of primary sensory neurons supplying the vas deferens in juvenile pigs by the use of retrograde tracing combined with double-labelling immunofluorescence, (2) nerve pathways from dorsal root ganglia (DRG) to the vas deferens by means of denervation procedures involving transection of the hypogastric or pelvic nerve combined with a retrograde tracing method, and (3) possible interactions of the substance P (SP)/calcitonin gene-related peptide (CGRP)-immunoreactive varicose nerve fibres on vas deferens projecting neurons (VDPN) in the anterior pelvic ganglion (APG). The vast majority of VDPN were found mainly in the lumbar L2, L3 and sacral S2, S3 pairs of DRG and showed a clear ipsilaterally organized projection pattern. Immunohistochemistry revealed that most of these neurons contained SP and/or CGRP, occasionally coexpressed with galanin. Interestingly, pronounced differences in the expression of SP and/or CGRP were observed between the lumbar and sacral VDPN in that most of the lumbar but less than half of the sacral neurons stained for these peptides. Denervation experiments showed that the neurons located within the lumbar DRG project through the ipsilateral hypogastric nerve, whereas those found within the sacral DRG send their processes through the ipsilateral and contralateral pelvic nerve. In the nerve-lesioned animals, especially in those with the hypogastric nerve cut, a dramatic reduction in the number of SP and/or CGRP-containing nerve terminals surrounding the efferent VDPN within the APG was observed. This study has disclosed the distribution and, for the first time, chemical coding and nerve pathways of vas deferens-projecting primary sensory neurons in a mammalian species, the pig. The results obtained also provide some novel information about the possible morphological and functional relationship between vas deferens-projecting primary sensory and pelvic efferent nerve cells.

Afferent Pathways↗

PubMed2002

Neuroepithelial bodies: a morphologic substrate for the link between neuronal nitric oxide and sensitivity to airway hypoxia?

Currently, the significance of nitric oxide (NO) in the respiratory tract is a matter of great interest because NO is believed to play a major role in the physiological regulation of airway function but also in lung pathology. What is especially intriguing with respect to the present investigation, are reports that the pulmonary expression of neuronal NO synthase (nNOS) is altered as a result of airway hypoxia. We examined the possible relationship between intrapulmonary nitrergic structures and pulmonary neuroepithelial bodies (NEBs), chemoreceptor-like epithelial cell groups that are known to have all necessary components for oxygen perception. Tyramide-enhanced immunostaining for nNOS was combined with known markers for NEBs in an ontogenetic study of rat lungs. From postnatal day 2 onward, nNOS-immunoreactive (-IR) neuronal cell bodies, present mainly in the lamina propria at all levels of intrapulmonary airways, were seen to give rise to remarkable intraepithelial terminal arborizations that invariably colocalized with NEBs. nNOS immunoreactivity was absent from the vagal calbindin D28k(CB) -IR and the spinal calcitonin gene-related peptide(CGRP) -IR extrinsic sensory nerve fiber populations that our group reported earlier to selectively contact NEBs. Quantitative analysis showed that all NEBs receiving nNOS-IR terminals were also contacted by CGRP-IR nerve fibers, whereas approximately 55% were additionally contacted by CB-IR nerves. The reported nitrergic neurons did not express the cholinergic marker vesicular acetylcholine transporter and were always surrounded by a basket of CGRP-IR nerve terminals. In conclusion, part of the pulmonary NEBs selectively receive extensive nitrergic nerve terminals that originate from intrinsic neurons. Together with literature data on lung physiology and pharmacology, some interesting suggestions for the functional significance of the association between pulmonary CGRP-IR NEBs, nNOS-IR neurons, and CGRP-IR afferents described in the present study, are discussed.

Airway Obstruction↗

PubMed2002

Neurochemical identification of enteric neurons expressing P2X(3) receptors in the guinea-pig ileum.

It was hypothesised that P2X(3) receptors, predominantly labelling spinal and cranial sensory ganglionic neurons, are also expressed in intrinsic sensory enteric neurons, although direct evidence is lacking. The aim of this study was to localise P2X(3) receptors in the enteric nervous system of the guinea-pig ileum, and to neurochemically identify the P2X(3)-expressing neurons. In the submucous plexus, cholinergic neurons expressing calretinin (CRT), were immunostained for P2X(3). These neurons made up about 12% of the submucous neurons. In the myenteric plexus, approximately 36% of the neurons expressed P2X(3). Half of the latter neurons were immunoreactive for CRT, whereas about 20% were immunoreactive for nitric oxide synthase (NOS). Based on earlier neurochemical analysis of enteric neurons in the guinea-pig, the myenteric neurons exhibiting P2X(3)/CRT immunoreactivity were identified as longitudinal muscle motor neurons, and those expressing P2X(3)/NOS immunoreactivity as short inhibitory circular muscle motor neurons. In both plexuses, no colocalisation was observed between P2X(3) and calbindin, a marker for intrinsic sensory neurons. Multiple staining with antisera raised against somatostatin, neuropeptide Y, substance P or neurofilament protein did not reveal any costaining. It can be concluded that in the guinea-pig ileum, intrinsic sensory neurons do not express P2X(3) receptors. However, this does not negate the possibility that extrinsic sensory nerves expressing P2X(3) are involved in a purinergic mechanosensory transduction pathway as demonstrated in other organs.

Animals↗

PubMed2002

Dense-core senile plaques in the Flemish variant of Alzheimer's disease are vasocentric.

Alzheimer's disease (AD) is characterized by deposition of beta-amyloid (Abeta) in diffuse and senile plaques, and variably in vessels. Mutations in the Abeta-encoding region of the amyloid precursor protein (APP) gene are frequently associated with very severe forms of vascular Abeta deposition, sometimes also accompanied by AD pathology. We earlier described a Flemish APP (A692G) mutation causing a form of early-onset AD with a prominent cerebral amyloid angiopathy and unusually large senile plaque cores. The pathogenic basis of Flemish AD is unknown. By image and mass spectrometric Abeta analyses, we demonstrated that in contrast to other familial AD cases with predominant brain Abeta42, Flemish AD patients predominantly deposit Abeta40. On serial histological section analysis we further showed that the neuritic senile plaques in APP692 brains were centered on vessels. Of a total of 2400 senile plaque cores studied from various brain regions from three patients, 68% enclosed a vessel, whereas the remainder were associated with vascular walls. These observations were confirmed by electron microscopy coupled with examination of serial semi-thin plastic sections, as well as three-dimensional observations by confocal microscopy. Diffuse plaques did not associate with vessels, or with neuritic or inflammatory pathology. Together with earlier in vitro data on APP692, our analyses suggest that the altered biological properties of the Flemish APP and Abeta facilitate progressive Abeta deposition in vascular walls that in addition to causing strokes, initiates formation of dense-core senile plaques in the Flemish variant of AD.

Alzheimer Disease↗

PubMed2002

Localization of 5-HT2A, 5-HT3, 5-HT5A and 5-HT7 receptor-like immunoreactivity in the rat cerebellum.

Although serotonin (5-hydroxytryptamine, 5-HT) is known to exert a modulatory action on cerebellar function, our current knowledge of the nature of receptor subtypes mediating serotonergic activity in this part of the brain remains fragmentary. In this study, we report the presence and distribution of 5-HT3, 5-HT5A and 5-HT7 receptor-like immunoreactivity in the rat cerebellum using immunofluorescence histochemistry. 5-HT3 immunoreactivity was found in fibers sparsely distributed throughout the cerebellum. Most of them were seen in the cerebellar cortex as fine varicose 5-HT3-positive axonal processes. 5-HT5A immunoreactivity, on the other hand, was observed in neuronal somata of the cerebellar cortex and deep cerebellar nuclei. Based upon cell morphology and the use of cell-specific markers, Purkinje cells, molecular layer interneurons and Golgi cells were found to be 5-HT5A immunopositive. In addition, the use of cell-specific markers allowed us to identify previously reported large 5-HT2A-positive cells in the granular layer as being Golgi cells. Finally, 5-HT7 immunoreactivity was observed only in Purkinje cells. Corroborating previous radioligand-binding, in situ hybridization and immunohistochemical studies, our data relate serotonin receptor subtypes to specific cerebellar cell types and may consequently contribute to the elucidation of serotonergic actions in the cerebellum.

Animals↗

PubMed2002

Temporal distribution of distinct mast cell phenotypes during intestinal schistosomiasis in mice.

Mastocytosis is a common feature of helminth infection in most host species. We examined the temporal distribution and phenotype of mast cells during intestinal schistosomiasis in mice, using antibodies directed against histamine, a general mast cell marker, against mouse mast cell protease-1 (MMCP-1), a mucosal mast cell (MMC) marker, and against tryptase, a predominantly connective tissue mast cell (CTMC) marker. Ileal paraffin and/or cryosections of control, 8- and 15-week-infected mice were quantitatively analysed. In the intestinal wall of non- and unisexual infected mice, a few dispersed mast cells were detected. In infected mice, a transient increase of mast cells in the mucosa and a gradual increase in the outer muscle layer were observed. MMCP-1 expressing MMCs were predominantly present in the mucosa during the acute phase [8 weeks postinfection (p.i.)], while tryptase and histamine immunoreactivity demonstrated that two subsets of CTMCs were predominantly present in the outer muscle layer at 15 weeks p.i. (chronic phase). In conclusion, these results reveal that, in mice, both MMCs and CTMCs are involved in the inflammatory response during schistosomiasis. The recruitment of each mast cell population is time-dependent and occurs at different locations. These data suggest that mastocytosis is associated with motility-related gastrointestinal symptoms and egg excretion.

Animals↗

PubMed2002

Vestibular dysfunction in the epistatic circler mouse is caused by phenotypic interaction of one recessive gene and three modifier genes.

Vestibular dysfunction is a frequent clinical problem, leading to dizziness and imbalance. Genes play an important role in its etiology, but the genetics are complex and poorly understood. In this study we have analyzed the complex inheritance pattern in the Epistatic circler mouse, which shows circling behavior indicative of vestibular dysfunction in the mouse. This phenotype exists in a proportion of the F2-generation from an intercross between C57L/J and SWR/J mouse strains. Genetic investigation indicates that the circling behavior is caused by a major recessively inherited gene derived from the SWR/J strain (the Ecs-gene) in combination with at least three different modifier genes derived from C57L/J (the Ecl-genes). Genetic mapping made it possible to localize the Ecs-gene to chromosome 14 and the Ecl-genes to chromosome 3, 4, and 13. This study illustrates the feasibility of identifying genes for multifactorial traits in mice.

Animals↗

PubMed2002

Triple immunofluorescence staining with antibodies raised in the same species to study the complex innervation pattern of intrapulmonary chemoreceptors.

A general problem in immunocytochemistry is the development of a reliable multiple immunolabeling method when primary antibodies must be used that originate in the same species. We have developed a protocol for the immunodetection of three antigens in a single tissue preparation, using unconjugated primary antibodies raised in the same species. Immunocytochemical detection of neuronal nitric oxide synthase, calcitonin gene-related peptide, and calbindin D28k in the lung of rats demonstrated that part of the pulmonary neuroepithelial bodies are selectively contacted by at least three different nerve fiber populations. The first antigen was detected using tyramide signal amplification, a very sensitive method allowing a dilution of the first primary antibody far beyond the detection limit of fluorescently labeled secondary antibodies. The second antigen was visualized by a fluorophore-conjugated secondary monovalent Fab antibody that at the same time blocks the access of the third secondary antibody to the second primary antibody. Moreover, the monovalence of the Fab fragment prevents the third primary antibody from binding with the second-step secondary antibody. The triple staining technique described here is generally applicable, uses commercially available products only, and allows the detection of three antigens in the same preparation with primary antibodies that are raised in the same species.

Animals↗

PubMed2002

Supercontracting muscle: producing tension over extreme muscle lengths.

Muscle mechanics dictates a trade-off between the ability of a muscle to generate isometric force and its length. This intrinsic trade-off is the result of the need for overlap between thick and thin filaments upon extension of the sarcomere and of the limitations imposed by the physical interference between the thin filaments and the thick filaments with the Z-disk upon contraction. However, previously published data indicate that chameleons are able to produce a nearly constant tongue retraction force over a wide range of tongue extension lengths, made possible by the presence of supercontracting muscle in the tongue retractors. Investigation of the length/tension properties and ultrastructure of the tongue retractor in a closely related agamid lizard (Pogona vitticeps) indicates that the ability to generate tension at extreme elongation is probably a derived feature for chameleons. Whereas chameleons are unique among vertebrates in possessing supercontracting muscle, this seems to be a common phenomenon in invertebrates. However, the presence of supercontracting muscle in chameleons and in several invertebrate groups seems to be coupled to the need to generate tension over large changes in muscle length and might be a more general solution for this problem.

Actin Cytoskeleton↗