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At least 523 records · Page 29Linked to original sources
PubMed1999

Cooperative mechanism for improving the discriminating ability in the chemoreceptor neuron binomial case.

The discriminating ability (selectivity) of the chemoreceptor neuron is compared with that of its receptor proteins. The process of neuronal triggering is expected to be cooperative and threshold type in a sense that the neuron fires a spike if and only if the number of receptor proteins which are bound with odor molecules is above a definite threshold. The binomial distribution is utilized to estimate the firing probability if a definite odor is applied. It is established that a chemoreceptor neuron can have a much higher selectivity than its individual receptor proteins, provided that the chemical stimuli are presented at low concentrations. A possibility for the above mechanism to be valid in other sensory systems is discussed.

Animals↗
PubMed2005

Solitary chemoreceptor cell proliferation in adult nasal epithelium.

Nasal trigeminal chemosensitivity in mice and rats is mediated in part by solitary chemoreceptor cells (SCCs) in the nasal epithelium (Finger et al., 2003). Many nasal SCCs express the G-protein alpha-gustducin as well as other elements of the bitter-taste signaling cascade including phospholipase Cbeta2, TRPM5 and T2R bitter-taste receptors. While some populations of sensory cells are replaced throughout life (taste and olfaction), others are not (hair cells and carotid body chemoreceptors). These experiments were designed to test whether new SCCs are generated within the epithelium of adult mice. Wild type C57/B6 mice were injected with the thymidine analog 5-bromo-2'-deoxyuridine (BrdU) to label dividing cells. At various times after injection (1-40 days), the mice were perfused with 4% paraformaldehyde and prepared for dual-label immunocytochemistry. Double labeled cells were detected as early as 3 days post BrdU injection and remained for as long as 12 days post-injection suggesting that SCCs do undergo turnover like the surrounding nasal epithelium. No BrdU labeled cells were detected after 24 days suggesting relatively rapid replacement of the SCCs.

Animals↗
PubMed1995

Ultrastructure and immunohistochemistry of the coronary chemoreceptor in human and canine hearts.

Ultrastructure of the coronary chemoreceptor that causes a hypertensive reflex was studied immunohistochemically in human and canine hearts. Both cytologic and histologic features were similar in human beings and dogs, consisting of chief cells, sustentacular cells, Schwann cells, nerve fibers, blood vessels, and connective tissue. Three or four chief cells were typically surrounded by one Schwann cell, making a glomoid cluster about 20 microns across. Volume fractions of chief cells compared to capillaries were about 1:2 in dog and 1:4 in human chemoreceptors. Abundant osmiophilic dense granules filled the chief cells. Complex junctions between nerve fibers, chief cells, and sustentacular cells or Schwann cells exhibited a characteristic fine structure. Immunohistochemically, serotonin reactivity was observed mainly in the vicinity of junctions between nerve endings and chief cells, but some large granules in chief cells also stained positively. These new morphologic findings provide further support for the probable role of serotonin in the activation of the cardiogenic hypertensive chemoreflex in both human and canine hearts.

Adolescent↗
PubMed1993

Calretinin, calbindin-D28k and parvalbumin-like immunoreactivity in mouse chemoreceptor neurons.

Calretinin immunoreactivity was demonstrated in adult mouse olfactory receptor neurons and in the vomeronasal and septal chemoreceptor neurons, whereas parvalbumin expression was restricted to the vomeronasal receptor neurons. Calbindin-D28k-like immunoreactivity was primarily localized in the vomeronasal and septal chemoreceptor neurons although an occasional neuronal staining with calbindin-D28k was also found in restricted areas of the main olfactory epithelium.

Animals↗
PubMed1983

Nucleus tractus solitarii respiratory neurons in the chemoreceptor pathway activated by almitrine.

In anaesthetized, paralysed and artificially ventilated dogs, activities were recorded from the phrenic nerve and from respiratory units within the nucleus tractus solitarii (NTS). The inspiratory neurons were classified according to their discharge pattern and their response to lung inflation. Two categories of cells with an augmenting discharge pattern were detected: the R alpha inspiratory neurons (18 units) inhibited by lung inflation and the R beta cells (10 units) activated by inflation. Prolonged stimulation of peripheral chemoreceptors by almitrine (50 micrograms/kg i.v.) induced an increase in the firing rate of R alpha and R beta inspiratory neurons. In addition almitrine stimulated R beta cells classified as expiratory-inspiratory units. Two expiratory neurons were found in the NTS and the firing rate of these cells was enhanced by almitrine. It is concluded that the NTS respiratory neurons are strongly involved in the chemoreceptor pathway activated by almitrine.

Almitrine↗
PubMed1984

Increased sensitivity of rabbit carotid body chemoreceptors to dopamine after chronic treatment with domperidone.

An increase in specific dopamine D2 receptor binding sites was observed in membranes prepared from the carotid bodies of rabbits treated for 8 weeks and then withdrawn for 4-9 days from the D2 antagonist domperidone (2-5 mg/kg per day). Recordings of chemoreceptor afferent discharge from the carotid body also revealed that this change in receptor density was accompanied by an increased sensitivity to the chemodepressant effects of exogenous dopamine. The chemoreceptor responsiveness of the carotid body to hypoxia is blunted in rabbits treated chronically with domperidone, but this can be restored to normal by an acute dose of the D2 antagonist. These experiments provide evidence that is compatible with a chemo-inhibitory role for endogenous dopamine in the rabbit's carotid body. Furthermore, these results suggest that the carotid body provides a useful model for the functional studies of dopamine D2 receptors.

Animals↗
PubMed1984

Ventrolateral medullary respiratory neurons and peripheral chemoreceptor stimulation by almitrine.

In anaesthetized, paralysed and artificially ventilated dogs, activities were recorded from the phrenic nerve and from respiratory units within the nucleus ambiguus (nA) and within the nucleus retroambigualis (nRA). The respiratory neurons were classified according to their discharge pattern. Almitrine (50 micrograms/kg i.v.) induced an increase in the firing rate of late peak inspiratory neurons (40 units) and in early burst inspiratory cells (10 units) of the nA. In the nRA, almitrine (50 micrograms/kg i.v.) also stimulated late peak expiratory neurons (17 units) and early burst expiratory cells (9 units). It is concluded that the chemoreceptor pathway is not restricted to the inspiratory neurons of the nTS and that both inspiratory and expiratory neurons of the nA and nRA are involved in the chemoreceptor pathway activated by almitrine.

Almitrine↗
PubMed1986

Desensitization by covalent modification of the chemoreceptor of Escherichia coli.

Chemoreceptors in Escherichia coli were studied in situ in chemotactic mutants, deficient in the ability to modify the receptors, by using membrane vesicles prepared from the mutants. The affinity of the receptors for the ligands is related to the level of modification of the receptors. Unmodified serine receptor had a dissociation constant of 0.8 microM, while modified receptor had a dissociation constant that was at least 100-times higher. The results are discussed in relation to the two-state model of the chemoreceptor.

Aspartic Acid↗
PubMed1984

Lethal respiratory disturbance in neonatal rats after arterial chemoreceptor denervation.

The role of afferent feedback from arterial chemoreceptors in the maintenance of rhythmic respiration during early development was studied by section of carotid sinus and aortic nerves of rat pups at different ages from 3 days to 3 weeks postnatally. This deafferentation produced a severe, episodic respiratory disturbance, limited to pups younger than 21 days and associated with mortality rates near 50% during the 2 weeks following surgery. These findings may have implications for the role of peripheral chemoreceptors in the periodic apneas of premature infants and in the Sudden Infant Death Syndrome.

Analysis of Variance↗
PubMed1976

Response to CO2 of intrapulmonary chemoreceptors in the emu.

We studied discharge frequencies of 12 intrapulmonary chemoreceptors in the paleopulmonic lung of an emu (Dromiceius novaechollandiae) during unidirectional, artificial ventilation when step changes and static CO2 concentrations were given. Discharge frequency in afferent neurons from the receptors increased as intrapulmonary CO2 decreased. The response of the receptors to various static intrapulmonary CO2 concentrations was similar to that previously demonstrated for the duck and chicken. The median sensitivity of the emu receptors at one-half maximal discharge was 4.6 imp-(sec-0.01 F1CO2)-1. Discharge frequencies altered phasically in nine of 12 receptors when step changes in CO2 of 3.3% at 1.6 Hz were given in the unidirectional gas stream while four of 12 modulated their discharge when the CO2 changes were as rapid as 3.2 Hz. Hence, some receptors can respond to rapid fluctuations in CO2 in their microencironment. We conclude that intrapulmonary chemoreceptors in the paleopulmonic lung of the emu exhibit similar characteristics to those in birds that possess varying amounts of neopulmonic parabronchi, such as the duck and chicken.

Animals↗
PubMed1977

Ventilatory responses to CO2 in the chicken: intrapulmonary and systemic chemoreceptors.

The independent effects of pulmonary and arterial Pco2 on respiratory amplitude (RA) and respiratory frequency (f) were studied in unidirectionally ventilated chickens anesthetized with phenobarbital (160 mg-kg-1). Pulmonary Pco2 was set by the level of PIco2 ventilating the vascularly isolated right lung (VIL), whereas the systemic arterial Pco2 was set by the level of PIco2 ventilating the denervated left or gas exchange lung (GEL). The following results were obtained: 1) Increasing the PIco2 to the VIL from 0 to 35 torr and maintaining Paco2 constant at 2. torr increased RA from apnea to 76% of the animals' maximal hypercapnic response and decreased f: further increases in PIco2 to VIL had only minimal effects on RA and f. 2) increasing Paco2 from 19 to 61 torr and maintaining pulmonary Pco2 constant increased RA and decreased further increases in Paco2 had only slight effects on RA ulmonary chemoreflex and can dominate the control of RA during hypocapnic conditions, and (2) systemic CO2-sensitive chemoreceptors dominate the control of RA during hypercapnic conditions. It is suggested that the intrapulmonary chemoreceptors may act as a sensory system which plays a pertinent role in the regulation of parabronchial ventilation.

Animals↗
PubMed1977

Chemoreceptor influence on pulmonary blood flow during unilateral hypoxia in dogs.

Dogs anesthetized with 30 mg/kg pentobarbital were artificially respired after differential cannulation of the main stem bronchi. Following median sternotomy, blood flow was monitored by electromagnetic flow probes on the left pulmonary artery (QL) and on the pulmonary trunk or aorta, QT. Following 10 min of bilateral 100% O2, QL was 42.5 +/- 7% of QT. When 6% O2, was substituted as the gas mixture inspired by the left lung while the right lung remained on 100% O2, PaO2 was above 70 mm Hg and QL fell to 24.5 +/- 5% of QT. Room air was then used to ventilate the right lung while the left lung remained on 6% O2. This caused PaO2 to fall to 42.3 +/- 3 MM Hg and QL to rise to 38.3 +/- 6% QT. This increase in blood flow to the unilaterally hypoxic lung during systemic hypoxemia did not occur in dogs after peripheral chemoreceptor denervation. Therefore, interference with the local response to alveolar hypoxia during systemic hypoxemia appears to be mediated by the arterial chemoreceptors.

Animals↗
PubMed1978

Effect of chemoreceptor denervation on the pulmonary vascular response to atelectasis.

Six dogs anesthetized with 30 mg/kg pentobarbital were ventilated after differential cannulation of the main stem bronchi. Following sternotomy, blood flow was monitored by electromagnetic flow probes on the left pulmonary artery (QL) and on the pulmonary trunk or aorta (QT). Following 10 min of bilateral 100% O2, QL was 37.4 +/- 5.8% of QT. When left lung atelectasis was induced while the right lung remained on 100% O2, PaO2 remained above 75 mm Hg and QL fell to 26.1 +/- 5.0% of QT. However, when the right lung was ventilated with room air while the left lung remained atelectatic, PaO2 fell to 50.0 +/- 2.6 mm Hg and QL rose to 36.7 +/- 6.2% of QT. Six dogs which had undergone peripheral chemoreceptor denervation prior to these experiments showed a similar decrease in perfusion of the atelectatic left lung when the right lung was ventilated with 100% O2, but did not increase blood flow to the atelectatic lung during systemic hypoxemia. Thus, the increased blood flow to the atelectatic lung which occurs during systemic hypoxemia appears to be mediated by the arterial chemoreceptors.

Animals↗
PubMed1978

A study of the effect of SO2 on pacing and intrapulmonary chemoreceptor discharge in the domestic fowl.

Kunz and Miller )1974) described a phenomenon called pacing in which FCO2 oscillations forced in the lungs of unanesthetized unidirectionally ventilated chickens cause one ventilatory movement per ECO2 oscillation. In the present study SO2 (0.08--0.32 vol%) added to the ventilating gas stream caused a loss of pacing in 11 of 12 birds. In 7 of the 11 birds in which SO2 was effective, pacing returned 3.2--7.0 min after removal of SO2. Intravenous infusion of a similar quantity of SO2 (dissolved in saline) did not block pacing. In a second series of experiments chickens were again unidirectionally ventilated and single nerve fiber recording was used to investigate the effect of SO2 on individual intrapulmonary chemoreceptors (IPC). Of necessity, this work was done on birds which were anesthetized and paralyzed. Discharge was abolished in 10 of 12 IPC by doses of SO2 similar to those which blocked pacing. In 6 of the 10 fibers in which SO2 was effective, discharge resumed after a mean period of quiescence lasting 7 min. It is concluded that pacing is mediated by intrapulmonary rather than systemic chemoreceptors.

Animals↗
PubMed1979

Chemoreceptor stimulation and hypoxic pulmonary vasoconstriction in conscious dogs.

Dogs with electromagnetic flow probes implanted on their left (QL) and main (QT) pulmonary arteries, catheters in their left atria and external jugular veins, and chronic tracheostomies were trained to accept Carlens dual-lumen endotracheal tubes into their tracheostomies, thus allowing separate ventilation of the two lungs. Swan-Ganz catheters were inserted through the jugular vein catheters. Pneumotachographs measured air flow to each lung. During bilateral ventilation with room air or O2, QL was about 36% of QT. When the left lung was ventilated with N2 while the right remained on O2, PAO2 was above 90 mmHg and QL fell to about 25% of QT. When the left lung was ventilated with N2 and the right with room air, PAO2 fell below 40 mm Hg and QL increased to control levels. This increase in perfusion of the hypoxic lung during systemic hypoxemia was not seen in dogs after surgical deafferentation of the systemic arterial chemoreceptors, indicating that stimulation of the arterial chemoreceptors may interfere with the hypoxic pulmonary vasoconstriction.

Animals↗
PubMed1982

Effects of medullary area I(s) cooling on respiratory response to chemoreceptor inputs.

The effect on respiration, as measured by phrenic nerve activity, of bilateral graded cooling of the intermediate, or I(s), areas of the ventral medulla was determined in anesthetized, vagotomized, glomectomized and paralyzed cats. In addition the effect of cooling the I(s) areas on the responses to central and peripheral chemoreceptor afferent test stimuli were studied. When end-tidal PCO2 was kept constant, graded cooling of the I(s) areas led to graded reductions of phrenic activity and arterial pressure. Furthermore, the respiratory response to test stimuli (carotid sinus nerve or CO2) was decreased progressively during graded cooling of the I(s) areas from 40 degrees C to 20 degrees C. We conclude that area I(s) is part of a common pathway for afferent input from both the central and peripheral chemoreceptors and that it is involved in the initial integration of both inputs.

Animals↗
PubMed1983

Interaction of temperature with extra- and intrapulmonary chemoreceptor control of ventilatory movements in the awake chicken.

Several studies in artificially ventilated, anesthetized birds with opened thoracoabdominal cavities have shown that intrapulmonary chemoreceptors (IPC) sensitive to CO2 contribute to the control of ventilatory movements. Increasing colonic temperature (Tc) has been shown to increase depth and decrease frequency of ventilatory movements if PaCO2 is held constant at less than 35 torr in awake and anesthetized, artificially ventilated cockerels. The relative importances, though, of IPC and of extrapulmonary CO2-sensitive chemoreceptors (EPC) in controlling ventilation in the awake or hyperthermic bird is unknown. We dissociated the PCO2 affecting IPC and EPC in awake cockerels by ligating the left pulmonary artery, denervating the IPC in the right lung and artificially ventilating each lung separately. We found, that at constant PaCO2, ventilatory movements increased in depth and decreased in frequency with: (1) increasing PICO2 to the innervated, non-perfused lung (PipcCO2); and (2) increasing Tc. Similar responses were observed with increasing PaCO2 or Tc during constant PipcCO2. Multiple regression analyses show that IPC and EPC have about equal controlling influences on ventilatory movements in the awake and hyperthermic cockerel.

Alkalosis, Respiratory↗
PubMed1985

The effect of potassium on carotid chemoreceptor activity and ventilation in the cat.

Intravenous injections of potassium chloride were given to anaesthetised cats to produce rises in arterial plasma potassium within the range of those occurring in man during exercise. Carotid chemoreceptor activity was recorded as action potentials from a single or few fibre preparation of the right sinus nerve. Arterial potassium was recorded continuously using a potassium electrode placed in the abdominal aorta. In response to the potassium injections there was an increase in carotid chemoreceptor activity, which closely followed the arterial potassium concentration, and an increase in ventilation. It is suggested that potassium released from muscle may be an important drive to ventilation in exercise.

Animals↗