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PubMed2004

Endothelins and nitric oxide: vasoactive modulators of carotid body chemoreception.

The carotid body (CB) is the main arterial chemoreceptor that senses arterial PO2, PCO2 and pH. The structural unit of the CB is the glomoid, which is formed by clusters of chemoreceptor (glomus) cells located around the capillaries. The glomus cells are synaptically connected to nerve terminals of petrosal ganglion (PG) neurons and surrounded by sustentacular cells. The most accepted model of CB chemoreception states that glomus cells are the primary sensors. In response to hypoxia, hypercapnia and acidosis, glomus cells release one or more transmitters, which acting on the nerve terminals of sensory PG neurons, increase the chemosensory discharge. The CB has a high blood flow and an elevated metabolism that correlate to its oxygen-sensing function. Thus, vasoactive molecules produced within the CB may modulate the chemosensory process by controlling the CB blood flow and tissue PO2. In this review, we examine recent evidence supporting the idea that endothelins (ETs) and nitric oxide (NO) modulate the CB function acting upon chemoreceptor cells and chemosensory neurons or by regulating the blood flow through the CB parenchyma.

Animals↗
PubMed2004

Cellular mechanisms involved in CO(2) and acid signaling in chemosensitive neurons.

An increase in CO(2)/H(+) is a major stimulus for increased ventilation and is sensed by specialized brain stem neurons called central chemosensitive neurons. These neurons appear to be spread among numerous brain stem regions, and neurons from different regions have different levels of chemosensitivity. Early studies implicated changes of pH as playing a role in chemosensitive signaling, most likely by inhibiting a K(+) channel, depolarizing chemosensitive neurons, and thereby increasing their firing rate. Considerable progress has been made over the past decade in understanding the cellular mechanisms of chemosensitive signaling using reduced preparations. Recent evidence has pointed to an important role of changes of intracellular pH in the response of central chemosensitive neurons to increased CO(2)/H(+) levels. The signaling mechanisms for chemosensitivity may also involve changes of extracellular pH, intracellular Ca(2+), gap junctions, oxidative stress, glial cells, bicarbonate, CO(2), and neurotransmitters. The normal target for these signals is generally believed to be a K(+) channel, although it is likely that many K(+) channels as well as Ca(2+) channels are involved as targets of chemosensitive signals. The results of studies of cellular signaling in central chemosensitive neurons are compared with results in other CO(2)- and/or H(+)-sensitive cells, including peripheral chemoreceptors (carotid body glomus cells), invertebrate central chemoreceptors, avian intrapulmonary chemoreceptors, acid-sensitive taste receptor cells on the tongue, and pain-sensitive nociceptors. A multiple factors model is proposed for central chemosensitive neurons in which multiple signals that affect multiple ion channel targets result in the final neuronal response to changes in CO(2)/H(+).

Acids↗
PubMed2002

Lack of contribution of mitochondrial electron transport to acute O(2) sensing in model airway chemoreceptors.

We have recently reported that the model airway chemoreceptors, H146 cells, exhibit a significant component of their oxygen-sensing transduction pathway which cannot be explained by activity of NADPH oxidase. Using patch-clamp, we have studied the transduction system linking reduced O(2) to k(+) channel inhibition and report that, in complete contrast to recent suggestions in pulmonary vasculature, O(2) sensing by the model airway chemoreceptors, H146 cells, does not require functional mitochondria. These data show, for the first time, that mitochondrial production of reactive O(2) species is not the unifying mechanism in O(2) sensing.

Antimycin A↗
PubMed2002

Are there gap junctions between chief (glomus, type I) cells in the carotid body chemoreceptor? A review.

Since the dye- and electronic couplings between the carotid body chief cells have been demonstrated, the detection and localization of the gap junctions in the carotid body is crucial to understanding the functional mechanism of chemoreception. However, conventional electron microscopy has been unsuccessful in unquestionably detecting ultrastructural features equivalent to the gap junctions, such as close (2 nm in width) membrane appositions in ultrathin sections and aggregations of intramembranous particles in freeze-fracture replicas of the carotid body. We previously reported using a modified electron microscopic study by chemically fixed and subsequent rapid freezing and freeze-substitution method a number of close membrane appositions comparable to the gap junctions. However, we later found that the freeze-substitution also induces numerous close apposition of the membrane in sites where the gap junctions are not known to occur, indicating that the modified electron microscopy by freeze-substitution is not always confirmative in the detection of the gap junction. With regard to the molecular evidence for the gap junction in the carotid body, there have so far been few data on the immunohistochemical demonstration on connexin 32 and 43 in cultured chief cells, but not in the in situ cells.

Animals↗
PubMed2000

Respiratory pacemaker cells responsive to CO(2) in the upper medulla: dose response and effects of mediators.

We previously reported on the presence of respiratory pacemaker cells that are highly sensitive to CO(2), in a region of the medulla oblongata in the fetal rat, 2 mm rostral to the obex. We now report on the CO(2) dose responses of these cells, as well as their responsiveness to certain chemical agents known to affect breathing in the fetus. Twenty-day-old fetal Sprague Dawley rats were block-dissected, and the cells of target areas were dissociated as previously described. Neuronal cells were plated on a medullary background and placed in the incubator with 10% CO(2) for 2-3 weeks. Cells were then studied using patch-clamp techniques. Pacemaker cells with single or bursting potentials showed responsiveness to CO(2) starting with pulses of 10 msec. Irregular beating or silent cells had poor or absent responsiveness to CO(2). Pacemaker cells responded to norepinephrine with increased firing potential; this action was blocked by metropolol. PGE(2) had no effect on pacemaker-cell activity, but indomethacin increased the spike frequency from 336+/-41 to 384+/- 65 spikes/min. Morphine stimulated the pacemaker cells from 205+/-25 to 272+/-29 spikes/min; this was blocked by naloxone. Finally, a placental extract, which inhibited breathing in the unanesthetized fetal sheep preparation, increased the activity of pacemaker cells from 301+/-35 to 452+/-52 spikes/min. In all of the above, irregular beating cells responded poorly and silent cells did not respond. The findings indicate that these pacemaker cells are uniquely designed to respond to CO(2) and have some properties which allow them to respond to certain chemical mediators in a manner similar to that of the whole respiratory system in vivo.

Animals↗
PubMed1988

Neurogenesis in the vomeronasal epithelium of adult garter snakes: 3. Use of H3-thymidine autoradiography to trace the genesis and migration of bipolar neurons.

Use of H3-thymidine autoradiography and unilateral vomeronasal (VN) axotomy has permitted us to demonstrate directly the existence of VN stem cells in the adult garter snake and to trace continuous bipolar neuron development and migration in the normal VN and deafferentated VN epithelium in the same animal. The vomeronasal epithelium and olfactory epithelium of adult garter snakes are both capable of incorporating H3-thymidine. In the sensory epithelium of the vomeronasal organ, H3-thymidine-labeled cells were initially restricted to the base of the undifferentiated cell layer in animals surviving 1 day following H3-thymidine injection. With increasing survival time, labeled cells progressively migrated vertically within the receptor cell column toward the apex of the bipolar neuron layer. In both the normal and denervated VN epithelium, labeled cells were observed through the 56 days of postoperative survival. In the normal epithelium, labeled cells were always located within the matrix of the intact receptor cell columns. However, labeled cells of the denervated epithelium were always located at the apical front of the newly formed cell mass following depletion of the original neuronal cell population. In addition, at postoperative days 28 and 56, labeled cells of the denervated VN epithelium achieved neuronal differentiation and maturation by migrating much farther away from the base of the receptor cell column than the labeled cells on the normal, unoperated contralateral side. This study directly demonstrates that basal cells initially incorporating H3-thymidine are indeed stem cells of the VN epithelium in adult garter snakes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2003

Distribution of transient receptor potential channels in the rat carotid chemosensory pathway.

Glomus cells in the carotid body respond to decreases in oxygen tension of the blood and transmit this sensory information in the carotid sinus nerve to the brain via neurons in the petrosal ganglion. G-protein-coupled membrane receptors linked to phospholipase C may play an important role in this response through the activation of the cation channels formed by the transient receptor potential (TRP) proteins. In the present study, expression of TRPC proteins in the rat carotid body and petrosal ganglion was examined using immunohistochemical techniques. TRPC3, TRPC4, TRPC5, TRPC6, and TRPC7 were present in neurons throughout the ganglion. TRPC1 was expressed in only 28% of petrosal neurons, and of this population, 45% were tyrosine hydroxylase (TH)-positive, accounting for essentially all the TH-expressing neurons in the ganglion. Because TH-positive neurons project to the carotid body, this result suggests that TRPC1 is selectively associated with the chemosensory pathway. Confocal images through the carotid body showed that TRPC1/3/4/5/6 proteins localize to the carotid sinus nerve fibers, some of which were immunoreactive to an anti-neurofilament (NF) antibody cocktail. TRPC1 and TRPC3 were present in both NF-positive and NF-negative fibers, whereas TPRC4, TRPC5, and TRPC6 expression was primarily localized to NF-negative fibers. Only TRPC1 and TRPC4 were localized in the afferent nerve terminals that encircle individual glomus cells. TRPC7 was not expressed in sensory fibers. All the TRPC proteins studied were present in type I glomus cells. Although their role as receptor-activated cation channels in the chemosensory pathway is yet to be established, the presence of TRPC channels in glomus cells and sensory nerves of the carotid body suggests a role in facilitating and/or sustaining the hypoxic response.

Animals↗
PubMed2004

Localized ablation of olfactory receptor neurons induces both localized regeneration and widespread replacement of neurons in spiny lobsters.

The peripheral olfactory system of the spiny lobster Panulirus argus--located on paired antennules--undergoes continual postembryonic development. This process includes continuous addition of olfactory receptor neurons (ORNs) related to indeterminate growth, continuous replacement, and regeneration when necessitated by damage. We have shown previously that new olfactory tissue is continually added to the proximal margin of these populations, called the proximal proliferation zone (PPZ). Here, we show that focal damage to mature portions of the olfactory system causes localized degeneration of ORNs over 1-10 days after damage. Studies using the cell proliferation marker 5-bromo-2'-deoxyuridine show that localized degeneration was followed by rapid and localized regeneration of olfactory tissue. Rapidly dividing cells were recorded up to 40 days after damage, with regeneration of ORN clusters complete within 80 days. Focal damage appeared to stimulate widespread cell replacement (cell death and proliferation) within mature, undamaged ORN clusters. This response was observed in ORN clusters outside the damaged zone, including mature clusters in the contralateral antennule. The degree of widespread cell replacement was less than local repair after local damage, but it increased with more extensive damage. However, changes in on-going proliferation in the PPZ were not detected, at least not 20 days or longer after damage, suggesting damage-induced widespread proliferation may be specific to mature populations of ORNs. We speculate that localized regeneration involves activity of resident precursor cells not destroyed by the ablation and that unidentified regulatory signals released in response to localized damage induce widespread ORN replacement.

Animals↗
PubMed1983

Fetal development of primate chemosensory corpuscles. I. Synaptic relationships in late gestation.

Fetal macaque chemosensory corpuscles during the last part of gestation contained chemosensory, sustentacular, and undifferentiated basal cells. Sustentacular cells had apical secretory granules and no specialized contacts with axons. Chemosensory cells contained basal collections of 80-100 nm dense core granules, and specialized axonal contacts of three types--afferent synapses, efferent synapses, and subsurface cisternae. Afferent synapses were commonly present on electron opaque cells with many 80-100-nm granules, typical 40-60-nm synaptic vesicles, and a few cisternae of smooth or granular endoplasmic reticulum. Cells with subsurface cisternae and/or efferent synapses were usually electron lucent, lacked vesicles and granules, and contained numerous intracytoplasmic cisternal elements. A continuum of intermediate forms was observed. It is postulated that transition of synaptic arrays accompanies the maturation of individual chemosensory cells.

Animals↗
PubMed1985

Anterograde axonal transport and intercellular transfer of WGA-HRP in trigeminal-innervated sensory receptors of rat incisive papilla.

The ultrastructure and identification of WGA-HRP-labeled sensory receptors in the rat incisive papilla (the most anterior part of hard palate) were studied using semiserial thin sections. Various sensory receptors were organized according to three locations: dome region (ventral), chemosensory corpuscle region (medial to orifice of incisive canal), and lateral labium (apposing the incisive canal). In the dome region, the sensory receptors were localized in three sensory zones that were associated with surface ridges (one medial and two lateral). In each of these zones, intraepithelial receptor axons and Merkel receptors occurred in the epithelium, while simple unencapsulated corpuscles, glomerular-Meissner corpuscles, and incisive (encapsulated) corpuscles occurred in the lamina propria. In the chemosensory corpuscle region, chemosensory corpuscles and intraepithelial receptor axons were located in the epithelium, and incisive corpuscles were present in the lamina propria. In the lateral labium, only intraepithelial receptor axons were prominent. In all these sensory receptors, the preterminal axons and axon terminals were labeled with the tracer protein. In addition, some nonneuronal cells closely associated with the axon terminals were selectively labeled, e.g., terminal Schwann cells, lamellar Schwann cells, Merkel cells, corpuscular basal cells and chemosensory cells. Other adjacent cells were not labeled, e.g., unspecialized epithelial cells, capsular cells, corpuscular sustentacular cells, and fibroblasts. In both labeled axons and cells, WGA-HRP was incorporated into vesicles, tubules, and vacuolar organelles. The specific intercellular transfer of tracer protein may indicate trophic interactions between axon terminals and support cells in sensory receptors. The specific organization of multiple sensory receptors in the rat incisive papilla may provide a useful alternative system for studying somatosensory physiology.

Animals↗
PubMed2004

Control of bract formation in Drosophila: poxn, kek1, and the EGF-R pathway.

In Drosophila, the sensory organs are formed by cells that derive from a precursor cell through a fixed lineage. One exception to this rule is the bract cell that accompanies some of the adult bristles. The bract cell is derived from the surrounding epidermis and is induced by the bristle cells. On the adult tibia, bracts are associated with all mechanosensory bristles, but not with chemosensory bristles. The differences between chemosensory and mechanosensory lineages are controlled by the selector gene pox-neuro (poxn). Here we show that poxn is also involved in suppressing bract formation near the chemosensory bristles. We have identified the gene kek1, described as an inhibitor of the EGF-R signaling pathway, in a screen for poxn downstream genes. We show that kek1 can suppress bract formation and can interfere with other steps of sensory development, including SMC determination and shaft differentiation.

Animals↗
PubMed1990

TAR independent activation of the human immunodeficiency virus in phorbol ester stimulated T lymphocytes.

Multiple regulatory elements in the human immunodeficiency virus long terminal repeat (HIV LTR) are required for activation of HIV gene expression. Previous transfection studies of HIV LTR constructs linked to the chloramphenicol acetyltransferase gene indicated that multiple regulatory regions including the enhancer, SP1, TATA and TAR regions were important for HIV gene expression. To characterize these regulatory elements further, mutations in these regions were inserted into both the 5' and 3' HIV LTRs and infectious proviral constructs were assembled. These constructs were transfected into either HeLa cells, Jurkat cells or U937 cells in both the presence and absence of phorbol esters which have previously been demonstrated to activate HIV gene expression. Viral gene expression was assayed by the level of p24 gag protein released from cultures transfected with the proviral constructs. Results in all cell lines indicated that mutations of the SP1, TATA and the TAR loop and stem secondary structure resulted in marked decreases in gene expression while mutations of the enhancer motif or TAR primary sequence resulted in only slight decreases. However, viruses containing mutations in either the TAR loop sequences or stem secondary structure which were very defective for gene expression in untreated Jurkat cells, gave nearly wild-type levels of gene expression in phorbol ester-treated Jurkat cells but not in phorbol ester-treated HeLa or U937 cells. High level gene expression of these TAR mutant constructs in phorbol ester-treated Jurkat cells was eliminated by second site mutations in the enhancer region or by disruption of the tat gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial Proteins↗
PubMed2004

Olfactory receptors in the mouse septal organ.

In this study we have identified a repertoire of chemosensory receptors expressed in the septal organ (SO). The results suggest that septal organ neurons are specified to express receptor genes belonging to class II olfactory receptors that are also expressed in the main olfactory epithelium. We found no evidence for the expression of members from the vomeronasal receptor gene families. In the SO, no topography analogous to the receptor expression zones of the main olfactory epithelium was evident. The majority of identified receptors corresponds to genes with restricted expression in the medial and lateral zones of the main olfactory epithelium. This coincides with the expression of olfactory cell adhesion molecule (OCAM) throughout the SO, which is considered as a marker for the medial-lateral zones. In contrast, NADPH:quinone oxidoreductase 1 expression, a characteristic marker for the dorsal zone, was lacking in the SO. Most of the receptor types were found to be expressed in rather few SO neurons; as an exception, the receptor mOR244-3 was observed in a very high proportion of cells. Although a very high fraction of SO neurons expressed mOR244-3, we found no evidence for the coexpression of different receptors in individual cells.

Animals↗
PubMed1998

Age-related changes in the dendrites of olfactory receptor neurons in the male silkmoth Antheraea peryni (Insecta, Lepidoptera: Saturniidae).

A study was conducted to evaluate the changes that occur with aging at the dendrite level of the olfactory receptor neuron in the male silkmoth Antheraea pernyi. Using calcein AM/ethidium homodimer-1 solutions, we found increased numbers of dendrites with damaged membrane with aging. Correspondingly there was an overall decrease in the electrophysiological activity as evidenced by the decreased number of cells discharging nerve impulse in response to female pheromone. It was also seen that the number of membrane swellings increased with age. In young animals aged 1-4 days, swellings showed intact membrane, and in older animals aged 5-15 days, they showed damaged membranes. With TUNEL assay that detects fragmented DNA in dying cells, an increased number of dendrites showing cytoplasmic labelling with age was found. The presence of fragmented DNA within aged dendrites was also confirmed in polyacrylamide gels after DNA extraction and PCR amplification. When tested for reversal of phosphatidylserine from the inner leaflet to the outer leaflet of plasma membrane no reactivity was seen. It appears that changes that occur during aging of dendrites may reflect some of the recognized symptoms of both apoptosis and necrosis.

Animals↗
PubMed1995

The inositol 1,4,5-triphosphate receptor expression in Drosophila suggests a role for IP3 signalling in muscle development and adult chemosensory functions.

Inositol 1,4,5-triphosphate (IP3) is generated as a second messenger in many diverse cellular signalling pathways. In general these signalling pathways activate a membrane-bound phospholipase C, which cleaves the phospholipid phosphatidylinositol bisphosphate to generate IP3 and diacylglycerol. IP3 binds to a specific intracellular receptor, which is a membrane protein and a ligand-gated Ca2+ channel, that causes Ca2+ release from intracellular stores. The inositol 1,4,5-triphosphate receptor (IP3R) is thus an integral part of the IP3 signalling pathway and can be used as a marker to identify biological processes that use IP3 as a second messenger. We have used an affinity-purified antibody, directed against a bacterial fusion protein and containing 339 amino acids of the Drosophila IP3R, to detect this protein in adult heads and during embryonic and pupal development. Our results suggest that in Drosophila the IP3 signalling pathway is used during muscle development, primarily when myoblasts undergo rapid multiplication, in both embryos and pupae. In adults, IP3 is probably a second messenger in more than one sensory transduction pathway, as well as in other as yet undefined brain and muscle functions.

Animals↗
PubMed2001

Spatially restricted expression of regulators of G-protein signaling in primary olfactory neurons.

The intracellular signal transduction machinery of heterotrimeric G-protein coupled odorant and putative pheromone receptors converts odorous information into a cellular response. We have investigated for the presence of 18 members of the family termed "regulators of G-protein signaling" (RGS) in primary olfactory sensory neurons of the main as well as the accessory (vomeronasal) system of the mouse. Unexpectedly, expression of a few RGS members show spatial restrictions correlating with the patterns described for G-protein coupled receptors in these two types of olfactory neurons. RGS3 was selectively coexpressed with the Galphai2 G-protein subunit in a subpopulation of vomeronasal neurons. The mutually exclusive spatial extents of RGS9 and RGSZ1 expression in main olfactory neurons corresponded precisely to that of certain odorant receptor zones. This renders these RGS members the first described intracellular signal transduction components with a potential role in the spatially organized sensory coding in the main olfactory system.

Animals↗