On the nature of synaptic receptors.
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Cell Membrane↗
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Characterization of a putative pheromone biosynthesis-activating neuropeptide (PBAN) receptor from the pheromone gland of Heliothis peltigera.
The binding of [(3)H]tyrosyl-PBAN28-33NH(2) to pheromone gland membranes of the moth Heliothis peltigera was investigated. The study describes the development of a pheromone biosynthesis-activating neuropeptide (PBAN) radioreceptor assay and demonstrates the presence of a putative PBAN binding site on the pheromone gland. It also describes synthesis of a radioligand and optimization of binding conditions with respect to membrane preparation, number of gland equivalents, kinetics of ligand binding and composition of the binding solution. Binding was found to be optimal when membranes were freshly prepared from frozen glands, incubated at a concentration of one gland equivalent per reaction tube in the presence of 10 mM HCO(3)(-) ions. Equilibrium of ligand binding was obtained after 20 min. Presence of other components such as NaCl, KCl or SH reagents did not have any effect on binding. Binding was found to be saturable, with a K(d) of 5.73 +/- 1.05 x 10(-6) M and a Bmax of 1.85 +/- 0.22 nmol/mg protein. Binding was effectively displaced by unlabeled PBAN1-33NH(2) and PBAN28-33NuEta(2) with a K(i) of 4.3 +/- 1.1 x 10(-6) M and 4.9 +/- 2.6 x 10(-6) M, respectively.
Animals↗
Cell communication in taste buds.
Taste bud cells communicate with sensory afferent fibers and may also exchange information with adjacent cells. Indeed, communication between taste cells via conventional and/or novel synaptic interactions may occur prior to signal output to primary afferent fibers. This review discusses synaptic processing in taste buds and summarizes results showing that it is now possible to measure real-time release of synaptic transmitters during taste stimulation using cellular biosensors. There is strong evidence that serotonin and ATP play a role in cell-to-cell signaling and sensory output in the gustatory end organs.
Adenosine Triphosphate↗
Brain stem lesions in the sudden infant death syndrome: variability in the hypoplasia of the arcuate nucleus.
In the present study we investigated quantitatively the incidence of hypoplasia of the arcuate nucleus (ARCn) of the medulla oblongata, reported earlier [Gozal D, Hathout GM, Kirlew KAT (1994) J Appl Physiol 76:207], as well as its distribution in 62 cases of sudden infant death syndrome (SIDS; mean age 14 postnatal weeks, 39 male and 23 female) and 25 controls (mean age 16 postnatal weeks, 14 male and 11 female), using detailed histopathological and morphometric analyses performed on serial sections of medulla oblongata. The SIDS cases were divided into four subtypes: SIDS A (27 cases, 43%) with histologically well-developed ARCn; SIDS B (16 cases, 26%) with severe bilateral hypoplasia along the whole length; SIDS C (11 cases, 18%) with partial bilateral hypoplasia, located mainly in the lateral portions of the caudal two thirds of the nucleus, and SIDS D (8 cases, 13%) with right monolateral hypoplasia of the ARCn. ARCn hypoplasia was detected in 56% of cases (35 cases). Three-dimensional volume reconstruction showed that in the SIDS A victims the mean volume was analogous to controls, whereas in the SIDS group with ARCn hypoplasia, severe or partial, the mean volume was significantly different from controls on both sides of the medulla oblongata (SIDS B group: P=0.003, P=0.002; SIDS C group: P=0.007, P=0.008). The mean ARCn volume in the SIDS D group was statistically significant only on the right side ( P=0.005). We also observed reduced neuron density of the ARCn, associated with a decrease in the total number of neurons over the whole length of the nucleus itself. On the basis of the morphometric results of neuronal population in the different portions of the ventrolateral medulla in SIDS cases, we hypothesized that infants without the full complement of neurons and neuropil (ARCn hypoplasia) are at risk for SIDS because they are unable to develop appropriate cardioventilatory control during this crucial developmental period.
Cell Count↗
Evidence for non-receptor odor discrimination using neuroblastoma cells as a model for olfactory cells.
The mouse neuroblastoma cell (N-18 clone), which is independent of an olfactory cell, was depolarized by 20 odorants examined, suggesting that specific proteins are not required for reception of odorants. The mechanism of non-receptor-mediated odor discrimination was examined using the N-18 cell. Changes in the membrane fluidity of the cell induced by adsorption of odorants were measured with various fluorescence probes, which monitor the fluidity at the different depth and in the different phase of the membrane. The profiles of the membrane fluidity changes monitored with these dyes were different from one species of odorants to another, suggesting that odorants having different odors are adsorbed at different sites in the membranes. The alteration of the lipid composition of the cell membrane brought about by exogenous application of stearic acid and cholesterol led to modification of the responses (magnitude of depolarization) to various odorants. The extent and direction (increase or decrease) of changes in the responses greatly varied among species of odorants. The following mechanism on odor discrimination was proposed. A membrane composition of each olfactory cell is postulated to be different from cell to cell. Different combinations of lipids and proteins in the membranes provide different adsorption sites for odorants. Relative amounts of the membrane potential changes in many olfactory cells in response to an odorant are characteristic of the species of the odorant. The response profiles at the cell level determine the quality of the odor.
Animals↗
Autoradiographic evidence for receptor cell renewal in the olfactory epithelium of a snail.
The tentacles of the terrestrial snail Achatina fulica contain an epithelium at their tips which is specialized for olfaction. The histology of the snail's olfactory organ bears a striking resemblance to that of the olfactory mucosa in the nose of vertebrates, where the receptor cell population is known to undergo a continuous process of renewal. In the present experiments, [3H]thymidine was delivered as a single pulse that was determined to have a maximum duration of about 1 h. Thirty minutes after an injection of [3H]thymidine, presumptive precursor cells were found labeled within, or at the edges of, receptor cell lobules. At later survival times, label was seen over cells that were identified as receptors. The mean position of the labeled cells within the layer of receptor cells became progressively more superficial with increasing survival times, indicating an upward migration of newly differentiated cells. The labeling index in the snail is ca. 0.7%, compared to 0.9% in the mouse. The turnover time is about 45 days, compared to 30-45 days in the mouse.
Animals↗
Electrophysiological evidence for the reconstitution of chemosensory units in co-cultures of carotid body and nodose ganglion neurons.
The electrophysiological characteristics of nodose ganglion sensory neurons, cultured alone or co-cultured with carotid body tissue, were compared. Some properties of the neurons and their response to acid (a carotid body 'natural' stimulus) changed in the presence of this tissue. (a) The evoked action potential after-hyperpolarization was smaller and longer whereas spike amplitude and duration, and the passive membrane properties remained unaltered. (b) Spontaneously occurring action potentials happened more frequently (16% vs 3%). (c) Acid solutions induced appreciable depolarization, an increased discharge, or both, only in a population of co-cultured neurons. These changes probably arose because of synaptic and/or trophic interactions between neurons and glomus cells.
Action Potentials↗
Development of acetylcholine sensitivity during myogenesis.
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Acetylcholine↗
Genetics of chemotactic behavior in bacteria.
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Alcohols↗
Bacterial motility and signal transduction.
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Bacterial Physiological Phenomena↗
Protein localization and asymmetry in the bacterial cell.
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Animals↗
Ontogenesis of glucose sensitivity in the rat lateral hypothalamus: a brain slice study.
The development of glucose-sensitive neurons in the lateral hypothalamus (LHA) brain slices was examined. In 60-100-day-old rats, 20% of LHA neurons were sensitive, that is, their firing rates decreased upon increase in the glucose concentration in the perfusate and increased upon decrease in glucose concentration. In 2-, 3- and 7-day-old rats, 16% of the neurons were glucose sensitive. Results confirm glucose-sensitivity in the LHA at a very early stage of ontogeny.
Animals↗
Early development of olfactory receptor cell axons.
An electron microscope study was done on development of olfactory receptor cell axons in rat fetuses 13-17 days after conception (E13-E17). Initiation of axon outgrowth was first seen on E13. On E14, small bundles of olfactory axons, accompanied by epithelial cells, grow out of the epithelium and, by so doing, breach the basal lamina. Close examination of these epithelial cells from E14 fetuses has revealed that they can be grouped into two types, one containing a ribosome-rich, dense cytoplasm, the other containing fewer free ribosomes and a more lucent cytoplasm. The first of these types is present infrequently or not at all at later times in development. The fate of the migrating cells is not known. Another notable observation was the indentation of olfactory epithelium by blood vessels during the developmental stages studied. There is very close association between processes of vascular endothelium and cells of the olfactory epithelium, so close, in fact, that a basal lamina is frequently absent. It is possible that vascular endothelium plays a role in breakdown of basal lamina, thus enabling olfactory axons to breach this barrier as they leave the epithelium.
Animals↗
The growth of olfactory neurons in short-term cultures of rat olfactory epithelium.
We have found that purified astrocytes will support the growth of olfactory epithelial neurons ( OENs ) in vitro. Candidate OENs were visible by light microscopy within one day after plating of dissociated cells from neonatal rat ethmoturbinates . Electron microscopy showed that OENs expressed the unique ultrastructural features which characterize these cells in situ, showing that regulation of neuronal morphology and ultrastructure can function independently of contact with other cells of the appropriate tissue. Characteristics of the cultures are such that this in vitro system would be useful in electrophysiological investigations of the chemosensory olfactory neurons.
Animals↗
Intracellular recordings from isolated salamander olfactory receptor neurons.
Isolated receptor cells were obtained by enzymatic dissociation of nasal sacs from the land-phase tiger salamander. The isolated cells have an ovoid soma, a dendrite of variable length which terminates in a cilia-bearing knob and an axon, also of variable length. Intracellular recordings were obtained using patch pipettes. Good recordings were characterized by resting potentials of -40 mV, high input impedance and the presence of fast overshooting action potentials upon depolarization or rebound excitation. With one cell, chemical stimulation evoked large depolarizations which produced action potentials. The reversal potential of this response was +2.7 mV. The results show that these cells can be dissociated for patch recordings, and they support previous studies indicating that transduction of olfactory stimuli leads to a depolarization of vertebrate olfactory receptor neurons.
1-Butanol↗
The gene poxn controls different steps of the formation of chemosensory organs in Drosophila.
The gene poxn codes for a transcriptional regulator that specifies poly-innervated (chemosensory), as opposed to mono-innervated (mechanosensory), organs in Drosophila. The ectopic expression of poxn during metamorphosis results in a transformation of the morphology and central projection of adult mechanosensory organs toward those of chemosensory organs. Here we show, by electron microscopy analysis of normal and transformed bristles and by Dil labeling of the innervating neurons, that poxn also controls the number of neurons. To determine whether poxn can transform not only the sense organ precursor cells but also their daughter cells, we examine the effects of the ectopic expression of poxn at different stages of the lineage, and we conclude that poxn can act at a late stage to affect the fate of the undifferentiated neuron.
Animals↗
Effect of prenylcysteine analogues on chemoattractant receptor-mediated G protein activation.
The hypothesis that carboxylmethylation of gamma subunits plays a role in G protein activation was tested by examining the ability of N-acetyl-S-farnesyl-L-cysteine (AFC) and its methyl ester (AFC-ME) to inhibit G protein-mediated signalling in intact HL-60 granulocytes and isolated HL-60 plasma membranes. Incubation of HL-60 granulocytes with AFC or AFC-ME inhibited superoxide release stimulated by fMet-Leu-Phe, but not by opsonized bacteria. AFC-ME, but not AFC, inhibited NaF- and PMA-stimulated superoxide release. Addition of AFC to HL-60 membranes inhibited fMet-Leu-Phe-, leukotriene B4- (LTB4) and C5a-stimulated GTP gamma S binding and GTP hydrolysis more potently than it inhibited basal guanine nucleotide exchange. AFC-ME inhibited basal- and ligand-stimulated G protein activation with equal potency, but less potently than AFC. AFC also inhibited mastoparan-stimulated GTP gamma S binding. Binding of fMet-Leu-Phe and LTB4 to HL-60 membranes was completely inhibited by AFC, while AFC-ME inhibited ligand binding by less than 50%. Neither AFC nor AFC-ME inhibited pertussis toxin or cholera toxin-catalysed ADP-ribosylation of alpha i. It was concluded that AFC interrupts signal propagation in G protein-dependent pathways by multiple mechanisms, including inhibition of ligand-receptor interactions, of receptor-G protein coupling and of guanine nucleotide binding to G proteins. Carboxylmethylation alters the specificity of AFC interruption of signal propagation in intact cells and isolated membranes.
Acetylcysteine↗
Pheromone response in yeast.
In response to peptide pheromones, yeast cells prepare themselves for mating; changes include arrest of the cell cycle and induction of transcription. Proteins involved in this signal transduction pathway include the pheromone receptors, subunits of a G protein, protein kinases and DNA-binding proteins. Understanding of this pathway has been facilitated by yeast genetics, which has allowed the genes encoding all of these proteins to be identified and characterized.
Cell Cycle↗