[3H]Spiroperidol binding in normal and denervated carotid bodies

Producción CientíficaSpecific dopamine receptors were studied in freshly dissected, unhomogenized rabbit carotid bodies incubated in [3H]spiroperidol. Total binding and non-specific binding were determined in the absence and presence of 0.2 #M (+)-butaclamol, respectively. Specific binding in normal carotid bodies incubated at near saturating concentrations (0.38 nM) was 1.63 _+ 0.58 pmol/g of tissue. Chronic section of the carotid sinus nerve (14 days) resulted in a 64070 reduction (P < 0.05) in specific binding. We conclude that the majority of specific dopaminergic receptors are located on carotid sinus nerve afferent terminals

Localization and Function of Cat Carotid Body Nicotinic Receptors

Producción CientíficaAcetylcholine and nicotinic agents excite cat carotid body chemoreceptors and modify their response to natural stimuli. The present experiments utilized [125I]a-bungarotoxin ([125I]a-BGT) to localize within the chemosensory tissue the possible sites of action of exogenous and endogenous nicotinic cholinergic substances. In vitro equilibrium binding studies of intact carotid bodies determined a K d of 5.57 nM and a Bma x of 9.21 pmol/g of tissue. Chronic section (12-15 days) of the carotid sinus nerve (CSN) did not change the amount of displaceable toxin binding. In contrast, the specific binding was reduced by 46% following removal of the superior cervical ganglion. Light microscope autoradiography of normal, CSN-denervated and sympathectomized carotid bodies revealed displaceable binding sites concentrated in lobules of type I and type II cells. Treatment of carotid bodies with 50 nM a-BGT in vitro reduced by 50% the release of [3H]dopamine (synthesized from [3H]tyrosine) caused by hypoxia or nicotine, and also significantly reduced the stimulus-. evoked discharges recorded from the CSN. The data suggest (1) an absence of ct-BGT binding sites on the afferent terminals of the CSN and (2) that nicotinic receptors located within parenchymal cell lobules may modulate the release of catecholamines from these cells

Alpha-bungarotoxin binding in cat carotid body

Producción CientíficaThe carotid body is an arterial chemosensory organ which detects changes in blood gas tensions and pH, and reflexly contributes to the cardiorespiratory adjustments which occur during hypoxia, hypercapnia and acidosis. However, the sensory mechanisms involved in carotid chemoreception remain to be elucidated. Morphologically, the carotid body consists of an association of elemental units, or glomeruli, within a connective tissue stroma penetrated by a dense capillary net 5. The glomeruli are comprised of catecholamine-rich type I, or chief cells, which are enveloped by glial-like processes of type II, or sustentacular, cellsa,4,19. Sensory fibers from the carotid sinus nerve penetrate the glomeruli to terminate in synaptic-like apposition on type I cellst,18, 21

Differential stimulus coupling to dopamine and norepinephrine stores in rabbit carotid body type I cells

Recent studies suggest that preneural type I (glomus) cells in the arterial chemoreceptor tissue of the carotid body act as primary transducer elements which respond to natural stimuli (low 02, pH or increased CO2) by releasing chemical transmitter agents capable of exciting the closely apposed afferent nerve terminals. These type I cells contain multiple putative transmitters, but the identity of the natural excitatory agents remains an unresolved problem in carotid body physiology. Characterization of putative transmitter involvement in the response to natural and pharmacological stimuli has therefore become fundamental to further understanding of chemotransmission in this organ. The present study demonstrates that a natural stimulus (hypoxia) evokes the release of dopamine (DA) and norepinephrine (NE) in approximate proportion to their unequal stores in rabbit carotid body (DA release/NE release = 8.2). In contrast, nicotine (100/~M), a cholinornimetic agent thought to act on the nicotinic receptors present on the type I cells, evokes the preferential release of NE (DA release/NE release = 0.17). These findings suggest that distinct mechanisms are involved in a differential mobilization of these two cateeholamines from the rabbit carotid body

A chronic pain: inflammation-dependent chemoreceptor adaptation in rat carotid body

Producción CientíficaExperiments in recent years have revealed labile electrophysiological and neurochemical phenotypes in primary afferent neurons exposed to specific stimulus conditions associated with the development of chronic pain. These studies collectively demonstrate that the mechanisms responsible for functional plasticity are primarily mediated by novel neuroimmune interactions involving circulating and resident immune cells and their secretory products, which together induce hyperexcitability in the primary sensory neurons. In another peripheral sensory modality, namely the arterial chemoreceptors, sustained stimulation in the form of chronic hypoxia (CH) elicits increased chemoafferent excitability from the mammalian carotid body. Previous studies which focused on functional changes in oxygen-sensitive type I cells in this organ have only partially elucidated the molecular and cellular mechanisms which initiate and control this adaptive response. Recent studies in our laboratory indicate a unique role for the immune system in regulating the chemo-adaptive response of the carotid body to physiologically relevant levels of hypoxia

Muscarinic receptor localization and function in rabbit carotid body

Producción CientíficaAcetylcholine and muscarinic agonists inhibit chemosensory activity in the rabbit carotid sinus nerve (CSN). Because the mechanism of this inhibition is poorly understood, we have investigated the kinetics and distribution of muscarinic receptors in the rabbit carotid body with the specific muscarinic antagonist [SH]quinuclidinylbenzitate ([3H]QNB). Equilibrium binding experiments identified displaceable binding sites (1/~M atropine) with a K d = 71.46 pM and a Bm~ x = 9.23 pmol/g tissue. These binding parameters and the pharmacology of the displaceable [SH]QNB binding sites are similar to specific muscannic receptors identified in numerous other nervous, muscular and glandular tissues. Comparisons of specific binding in normal and chronic CSN-denervated carotid bodies suggest that musearinic receptors are absent on afferent terminals in the carotid body; however, nearly 50% of the specific [3H]QNB binding is lost following chronic sympathectomy, suggesting the presence of presynaptic muscarinic receptors on the sympathetic innervation supplying the carotid body vasculature. Autoradiographic studies have localized the remainder of [3H]QNB binding sites to Iobules of type I and type II parenchymal cells. In separate experiments, the muscarinic agonists, oxotremorine (100/~M) and bethanechol (100 ~tM) were shown to inhibit both the release of catecholamines and the increased CSN activity evoked by nicotine (50/~M) stimulation of the in vitro carotid body, Our data suggest that muscarinic inhibition in the rabbit carotid body is mediated by receptors located on type I cells which are able to modulate the excitatory actions of acetylcholine at nicotinic sites

Evidence for two types of nicotinic receptors in the cat carotid body chemoreceptor cells

Producción CientíficaCurrent concepts on the location and functional significance of nicotinic receptors in the carotid body rest on a-bungarotoxin binding and autoradiographic studies. Using an in vitro preparation of the cat carotid body whose catecholamine deposits have been labeled by prior incubation with the tritiated natural precursor w3Hxtyrosine, we have found that nicotine induces release of w3Hxcatecholamines in a dose-dependent manner IC50s9.81 mM.. We also found that mecamylamine 50 mM. completely abolished the nicotine-induced release, while a-bungarotoxin 100 nM; f20 times its binding Kd. only reduced the release by 56%. These findings indicate that chemoreceptor cells, and perhaps other carotid body structures, contain nicotinic receptors that are not sensitive to a-bungarotoxin and force a revision of the current concepts on cholinergic mechanisms in the carotid body chemoreception

A physics-based earthquake simulator replicates seismic hazard statistics across California

Seismic hazard models are important for society, feeding into building codes and hazard mitigation efforts. These models, however, rest on many uncertain assumptions and are difficult to test observationally because of the long recurrence times of large earthquakes. Physics-based earthquake simulators offer a potentially helpful tool, but they face a vast range of fundamental scientific uncertainties. We compare a physics-based earthquake simulator against the latest seismic hazard model for California. Using only uniform parameters in the simulator, we find strikingly good agreement of the long-term shaking hazard compared with the California model. This ability to replicate statistically based seismic hazard estimates by a physics-based model cross-validates standard methods and provides a new alternative approach needing fewer inputs and assumptions for estimating hazard

The role of NADPH oxidase in carotid body arterial chemoreceptors

Producción CientíficaO2-sensing in the carotid body occurs in neuroectoderm-derived type I glomus cells where hypoxia elicits a complex chemotransduction cascade involving membrane depolarization, Ca2+ entry and the release of excitatory neurotransmitters. Efforts to understand the exquisite O2-sensitivity of these cells currently focus on the coupling between local PO2 and the open-closed state of K+-channels. Amongst multiple competing hypotheses is the notion that K+-channel activity is mediated by a phagocytic-like multisubunit enzyme, NADPH oxidase, which produces reactive oxygen species (ROS) in proportion to the prevailing PO2. In O2-sensitive cells of lung neuroepithelial bodies (NEB), multiple studies confirm that ROS levels decrease in hypoxia, and that EM and K+-channel activity are indeed controlled by ROS produced by NADPH oxidase. However, recent studies in our laboratories suggest that ROS generated by a non-phagocyte isoform of the oxidase are important contributors to chemotransduction, but that their role in type I cells differs fundamentally from the mechanism utilized by NEB chemoreceptors. Data indicate that in response to hypoxia, NADPH oxidase activity is increased in type I cells, and further, that increased ROS levels generated in response to low-O2 facilitate cell repolarization via specific subsets of K+-channels

Building sensory receptors on the tongue

Neurotrophins, neurotrophin receptors and sensory neurons are required for the development of lingual sense organs. For example, neurotrophin 3 sustains lingual somatosensory neurons. In the traditional view, sensory axons will terminate where neurotrophin expression is most pronounced. Yet, lingual somatosensory axons characteristically terminate in each filiform papilla and in each somatosensory prominence within a cluster of cells expressing the p75 neurotrophin receptor (p75NTR), rather than terminating among the adjacent cells that secrete neurotrophin 3. The p75NTR on special specialized clusters of epithelial cells may promote axonal arborization in vivo since its over-expression by fibroblasts enhances neurite outgrowth from overlying somatosensory neurons in vitro . Two classical observations have implicated gustatory neurons in the development and maintenance of mammalian taste buds—the early arrival times of embryonic innervation and the loss of taste buds after their denervation in adults. In the modern era more than a dozen experimental studies have used early denervation or neurotrophin gene mutations to evaluate mammalian gustatory organ development. Necessary for taste organ development, brain-derived neurotrophic factor sustains developing gustatory neurons. The cardinal conclusion is readily summarized: taste buds in the palate and tongue are induced by innervation. Taste buds are unstable: the death and birth of taste receptor cells relentlessly remodels synaptic connections. As receptor cells turn over, the sensory code for taste quality is probably stabilized by selective synapse formation between each type of gustatory axon and its matching taste receptor cell. We anticipate important new discoveries of molecular interactions among the epithelium, the underlying mesenchyme and gustatory innervation that build the gustatory papillae, their specialized epithelial cells, and the resulting taste buds.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47466/1/11068_2005_Article_3332.pd