Search PubMed⌕ Search

Biomedical subjects

H Breer

Publications and source records attributed to H Breer.

At least 73 records · Page 4Linked to original sources
PubMed1997

Second messenger-controlled membrane conductance in locust (Locusta migratoria) olfactory neurons.

The membrane conductance of olfactory neurons of Locusta migratoria was examined using the whole-cell configuration of the patch-clamp technique. Intracellular application of the second messenger inositol 1,4,5 trisphosphate (IP(3)) via a dual pipette technique elicited a clear increase in the membrane conductance. The IP(3)-induced conductance increased due to a rise in the extracellular concentration of calcium from 100&mgr;M to 4mM. Micromolar concentrations of ruthenium red partially blocked the IP(3)-induced increase in membrane conductance. Stimulating olfactory neurons with odour (hexenoic acid) resulted in an increase in the membrane conductance partially similar to that mediated IP(3). These findings suggest that stimulation with appropriate odours as well as intracellular application of IP(3) activate the same calcium-permeable ion channels in the plasma membrane of insect olfactory neurons.

Journal Article↗
PubMed1997

Sodium/calcium exchanger in rat olfactory neurons.

The chemo-electrical transduction process in olfactory neurons is accompanied by a rapid and transient increase in intracellular calcium concentrations. The notion that Na+/Ca2+ exchanger activities may play a major role in extruding calcium ions out of the cell and maintaining Ca2+ homeostasis in olfactory receptor cells was assessed by means of laser scanning confocal microscopy in combination with the fluorescent indicators Fluo-3 and Fura-Red. The data indicate that high exchanger activity, which was inhibited by amiloride derivatives, is located in the dendritic knob and probably in the olfactory cilia. This result was supported by experiments using specific antiserum raised against retinal Na+/Ca2+ exchanger protein which labelled an immunoreactive protein of 230 kDa in Western blots from olfactory tissue and strongly stained the ciliary layer of the olfactory epithelium.

Animals↗
PubMed1997

Subfamily of olfactory receptors characterized by unique structural features and expression patterns.

The complex chemospecificity of the olfactory system is probably due to the large family of short-looped, heptahelical receptor proteins expressed in neurons widely distributed throughout one of the several zones within the nasal neuroepithelium. In this study, a subfamily of olfactory receptors has been identified that is characterized by distinct structural features as well as a unique expression pattern. Members of this receptor family are found in mammals, such as rodents and opossum, but not in lower vertebrates. All identified subtypes comprise an extended third extracellular loop that exhibits amphiphilic properties and contains numerous charged amino acids in conserved positions. Olfactory sensory neurons expressing these receptor types are segregated in small clusters on the tip of central turbinates, thus representing a novel pattern of expression for olfactory receptors. In mouse, genes encoding the new subfamily of receptors were found to be harbored within a small contiguous segment of genomic DNA. Based on species specificity as well as the unique structural properties and expression pattern, it is conceivable that the novel receptor subfamily may serve a special function in the olfactory system of mammals.

Amino Acid Sequence↗
PubMed1997

Value of magnetic-resonance cholangio-pancreatography (MRCP) after unsuccessful endoscopic-retrograde cholangio-pancreatography (ERCP).

BACKGROUND AND STUDY AIMS: The present study tries to evaluate the success rate of MRCP when two attempts by experts to perform ERCP in a center failed. PATIENTS AND METHODS: From March 1996 to December 1996 thirteen patients fulfilled the inclusion criteria. The MR cholangiopancreatograms were acquired using commercially available software in a clinical MR scanner (Magnetom Expert 1 T-Scanner, Siemens, Erlangen, Germany). MRCP utilized heavily T2-weighted turbo-spin echo sequences with fat supression (HASTE). Maximum intensity projection (MIP) of the pancreatic duct and biliary tree was then carried out. Additionally, T1-weighted sequences were obtained using the breath-hold technique. RESULTS: The MRCP images were of diagnostic quality in all 13 patients. In five cases the diagnoses detected by MRCP were followed by an interventional procedure. One patient showed a pancreatic pseudocyst, that was percutaneously drained using ultrasound guidance. In three cases we found benign bile duct obstruction, all of which were successfully treated by percutaneous transhepatic drainage. In one patient choledocholithiasis was diagnosed, the stone was successfully managed by percutaneous transhepatic extraction. CONCLUSION: MRCP is the method of choice in cases where ERCP is incomplete or where duct cannulation is not possible. A further advantage of MR imaging is the fact that it may provide complementary information about the whole region of interest, thus detecting the cause of duct pathology in many cases.

Aged↗
PubMed1997

The calcium-binding protein VILIP in olfactory neurons: regulation of second messenger signaling.

Visinin-like-protein (VILIP), a member of the neuronal subfamily of EF-hand calcium-sensor proteins is shown to be expressed in olfactory sensory cells of the rat nasal epithelium. Its prominent localization in cilia and dendritic knobs-the chemosensory compartments of olfactory neurons-suggests that the calcium-binding protein could be involved in olfactory signal transduction. Consistent with this assumption, it was found that recombinant VILIP attenuates in a calcium-dependent manner odorant-induced cAMP formation in olfactory cilia preparations. Kinetic data indicate that VILIP does not interfere with odorant-induced receptor desensitization. Since VILIP inhibits the forskolin-induced formation of cAMP, it is conceivable that VILIP may directly affect the olfactory adenylyl cyclase. Thus, VILIP may play a role in adaptation of olfactory neurons.

Animals↗
PubMed1996

Expression of an olfactory receptor in Escherichia coli: purification, reconstitution, and ligand binding.

An olfactory receptor has been expressed in bacterial cells as a fusion protein with glutathione S-transferase (GST). Overexpression of receptor protein yielding about 10% of the cell protein was achieved with mutants lacking the N-terminus and the first transmembrane region or with mutants carrying three positively charged residues in the first intracellular loop. The overexpressed fusion protein accumulated in inclusion bodies and could be solubilized in detergent. It was purified by metal chelation chromatography based on a C-terminal 6-histidine tag, and the GST portion was removed after proteolytic cleavage. The purified receptor was reconstituted into lipid vesicles and specific binding of odor ligands was shown by photoaffinity labeling and tryptophan fluorescence measurements. Thus, for the first time, an odorant receptor/ligand pair becomes available in large amounts for biophysical and screening studies.

Amino Acid Sequence↗
PubMed1996

Pheromone-induced second messenger signaling in the hamster vomeronasal organ.

Compounds present in estrous hamster vaginal discharge modulate male attraction and mounting behavior. These compounds are differentially processed by chemosensory neurons in the main olfactory epithelium (MOE) and vomeronasal organ (VNO). The transduction cascade responsible for this processing is unclear in the VNO, although studies of the MOE suggest that the second messengers cAMP or IP3 may be involved. Here we demonstrate that purified aphrodisin, a hamster mounting pheromone, modulates IP3 production in male VNO membranes without altering cAMP production. Aphrodisin does not alter the concentration of either second messenger in membranes from the MOE. These results confirm the specificity of the VNO in the processing of mounting pheromones and establishes the importance of IP3 cascades in mammalian reproductive behavior.

Animals↗
PubMed1996

Phosphatase 2A regulates the responsiveness of olfactory cilia.

The odorant-induced second messenger response in olfactory cilia was monitored in the presence of phosphatase modulators. Okadaic acid, a phosphatase inhibitor, attenuated the odorant-induced cAMP-response in a dose-dependent manner, half maximal inhibition was obtained at 1.5 nM okadaic acid indicating that phosphatase 2A may be involved. Protamine, a selective activator of phosphatase 2A, led to significantly stronger cAMP-responses. Western blot and immunohistochemical analysis employing specific antibodies revealed that phosphatase 2A is present in olfactory tissues in particular in olfactory cilia. The results suggest that phosphatase 2A may play a regulatory role in governing the responsiveness of olfactory neurons.

Animals↗
PubMed1996

Regulation of olfactory signalling via cGMP-dependent protein kinase.

Strong odor stimuli elicit a slow and sustained increase of the cGMP concentration in isolated rat olfactory cilia. Elevated cGMP levels appear to attenuate the primary response to odorant stimulation. Incubating cilia with membrane-permeable cGMP derivates caused a significantly reduced cAMP signal in response to odorant stimulation. This inhibitory effect was mimicked by 8-(4-chlorophenlythio)-cGMP, a selective activator of cGMP-activated protein kinases; in contrast, a selective inhibitor, [8-(4-chlorophenylthio)-guanosine-3',5'-cyclic monophosphorothioate] of cGMP kinases enhanced the reactivity to odorant stimulation. The data suggest that the responsiveness of olfactory sensory cells is governed by a cGMP-dependent protein kinase. Western-blot analysis using subtype-specific antibodies indicated that cytosolic type-I cGMP kinase, but not the membrane-associated type-II cGMP kinase, is expressed in olfactory sensory neurons.

Animals↗
PubMed1996

Molecular genetics of mammalian olfaction.

Olfaction plays a crucial role in the survival of most animal species; it is remarkable in its ability to recognize and discriminate numerous airborne molecules, yet is one of the least understood senses. The advent of molecular genetic approaches has greatly contributed to disclosing some of the mysteries in olfaction. The identification of olfactory-specific proteins, the discovery of the large receptor gene family, and the first insight into the mechanisms governing chemosensory gene expression hold great promise for an eventually detailed understanding of a sensory system that was previously considered as hardly accessible for research at the molecular level.

Animals↗
PubMed1996

Laminar segregation of odorant receptor expression in the olfactory epithelium.

The laminar segregation of sensory neurons expressing a distinct receptor type was determined in tissue sections through the olfactory epithelium by in situ hybridization employing receptor-specific probes. Reactive cells were restricted to the mid-zone of the epithelium, the location of mature neurons. Detailed analyses revealed that neurons expressing a distinct receptor type were distributed in a characteristic manner throughout the layers of the neuronal zone, i.e. they were preferentially located in a particular laminar zone of the epithelium. Cells expressing different receptor types displayed different distribution patterns. In addition, sets of several reactive neurons within the same laminar zone were found to be arranged in an orderly fashion and were positioned at well-defined intervals. These results indicate that the localization of sensory neurons expressing a distinct receptor type is under stringent control leading to characteristic expression patterns.

Animals↗
PubMed1996

Calcium controls second-messenger signalling in olfactory cilia.

The increase in intracellular calcium concentration elicited by odorant stimulation seems to be involved in down-regulating the responsiveness of olfactory neurons to subsequent stimuli. The present study suggests that this regulatory effect may be due to a calcium-dependent attenuation of the olfactory signalling cascade; the odor-induced cyclic adenosine monophosphate (cAMP) response in olfactory cilia is diminished by calcium in a dose-dependent manner. This reduced cAMP signal is not due to an activation of phosphodiesterases by elevated calcium levels, but rather seems to be mediated by the inhibition of adenylate cyclase by calcium ions.

1-Methyl-3-isobutylxanthine↗
PubMed1996

Binding proteins from the antennae of Bombyx mori.

From an antennal library of Bombyx mori cDNA clones encoding different binding proteins have been isolated. The deduced amino acid sequences showed only moderate homology to each other but shared several common structural features. Based on a sequence comparison with the antennal binding proteins from different moth species, one of the clones appears to encode a pheromone binding protein, whereas two others represent new members of the two general odorant binding protein families. A fourth clone encodes a protein which is related to antennal binding proteins so far found only in Drosophila melanogaster.

Amino Acid Sequence↗
PubMed1996

Rapid kinetics of second messenger production in bitter taste.

The tasting of bitter compounds may have evolved as a protective mechanism against ingestion of potentially harmful substances. We have identified second messengers involved in bitter taste and show here for the first time that they are rapid and transient. Using a quench-flow system, we have studied bitter taste signal transduction in a pair of mouse strains that differ in their ability to taste the bitter stimulus sucrose octaacetate (SOA); however, both strains taste the bitter agent denatonium. In both strains of mice, denatonium (10 mM) induced a transient and rapid increase in levels of the second messenger inositol 1,4,5-trisphosphate (IP3) with a maximal production near 75-100 ms after stimulation. In contrast, SOA (100 microM) brought about a similar increase in IP3 only in SOA-taster mice. The response to SOA was potentiated in the presence of GTP (1 microM). The GTP-enhanced SOA-response supports a G protein-mediated response for this bitter compound. The rapid kinetics, transient nature, and specificity of the bitter taste stimulus-induced IP3 formation are consistent with the role of IP3 as a second messenger in the chemoelectrical transduction of bitter taste.

Animals↗
PubMed1995

Calcium signals in olfactory neurons.

Laser scanning confocal microscopy in combination with the fluorescent calcium indicators Fluo-3 and Fura-Red was employed to estimate the intracellular concentration of free calcium ions in individual olfactory receptor neurons and to monitor temporal and spatial changes in the Ca(2+)-level upon stimulation. The chemosensory cells responded to odorants with a significant increase in the calcium concentration, preferentially in the dendritic knob. Applying various stimulation paradigma, it was found that in a population of isolated cells, subsets of receptor neurons display distinct patterns of responsiveness.

Aniline Compounds↗
PubMed1995

Receptor expression in olfactory neurons during rat development: in situ hybridization studies.

In situ hybridization approaches have been employed to explore the onset and time course of odorant receptor expression during the prenatal development of rats. The critical phase for the maturation of the olfactory system from embryonic day (E) 12 to E18 was analysed. The onset of expression of four receptor genes (OR5, OR14, OR37 and OR124) was found between day E12 and E14. In the early phase of development (E14) a distinct receptor subtype was expressed only in a few hundred neurons; the number increased about two-' to three-fold within a 2 day interval. From the very beginning, spatial segregation of receptor subtypes in distinct expression zones was observed.

Animals↗