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At least 955 records · Page 53Linked to original sources
PubMed1982

[Impulse activity of the rat medulla oblongata in response to stimulation of taste receptors and visceral chemoreceptors].

The unit activity from the medulla oblongata was extracellularly recorded during stimulation of taste receptors and visceral chemoreceptors of small intestine with the solutions of hydrochloric acid and sodium chloride. Neurons responding to the chemical stimulation are at the caudal part of nucleus tractus solitarius. Responses of taste, viscerochemical and convergence units are tonic and their discharge rates are low. The ability for chemical stimulus graduation analysis characterizes each group of units. Increased concentration of the solutions in intestine brings about the increase in the number of viscerochemical neurons with inhibited background activity. This may be the index of satiation and serve as a starting link in the mechanism of food rejection.

Animals↗
PubMed1981

Effects of carotid body chemoreceptor stimulation by norepinephrine, epinephrine and tyramine on ventilation in the rabbit.

Effects of norepinephrine, epinephrine and tyramine on the carotid body chemoreceptor in the rabbit were studied by measuring reflex ventilatory responses. The basic pattern of the responses was transient inhibition with a decrease in tidal volume followed by sustained excitation, even though the predominant feature was excitation in the epinephrine-induced response. The initial inhibition which was either unaffected or slightly potentiated after phenoxybenzamine was completely blocked by haloperidol. The late excitation was enhanced after mecamylamine and haloperidol treatments and was abolished following administration of phenoxybenzamine. The results indicated possible participation of inhibitory dopamine receptors for the induction of the initial depression and reduction of blood flow in the vessels of the carotid body by vasoconstriction for the excitatory response.

Animals↗
PubMed1980

[Preliminary data on intestinal chemoreceptor responses to amino acids].

Intestinal chemoreceptor responses to amino acids in the small intestine were investigated in anaesthetized cats with a microelectrophysiological technique, i.e. vagal units in the nodose ganglion were recorded by extracellular glass microelectrodes. About 400 neurons were tested by infusing the small intestine with a mixture of several amino acids at 38 degrees C. Fifty neurons, which were generally silent before the first infusion, were activated by amino acid solutions with a short latency of a few seconds. Their discharge frequency was always low (less than 10 Hz). The corresponding fibres were non-medullated (conduction velocity: 0.8-1.4 m/s). These receptors did not respond to osmotic or mechanical stimuli. Moreover, some of them were not activated by glucose infusion and must thus be considered as specific amino acid receptors. The others which responded to both amino acids and glucose infusions were non-specific receptors. The properties of these two types of amino receptors and their roles in the nervous regulations of feeding behaviour, in particular protein satiety, are discussed.

Amino Acids↗
PubMed1980

[Chemoreceptor organs of the antennae and maxillary palps of fleas (Siphonaptera)].

Ultrastructure of chemoreceptor sensillae on antennae and maxillary palps of fleas of Ceratophyllus sciurorum is described. On antennae of fleas are the following types of sensillae: trichoid cuspidate and obtusate, fungoid, basiconical sensillae in olfactory fossae and on the surface of antennae. On maxillary palps there are trichoid cuspidate, basiconical and campaniform sensillae. A comparison was made of the composition and number of chemo- and mechanoreceptor sensillae in 14 species of fleas differing in the type of parasitism. It has been established that "nest" fleas have the greatest number of sensillae.

Animals↗
PubMed1980

Effects of carotid body chemoreceptor stimulation by dopamine on ventilation.

Effects of carotid body chemoreceptor stimulation by dopamine (DA) on ventilation were studied by injecting it into the external carotid artery of rabbits. DA (3 micrograms--300 micrograms) induced dose-dependent ventilatory depression which was preceded by a transient increase in ventilatory rate in 65% of the experiments at higher doses. The DA-induced depression remained unaffected by prior administration of atropine, mecamylamine or phenoxybenzamine, while it was blocked or suppressed after haloperidol or reserpinization, indicating that the DA-induced ventilatory depression was due to its direct action on DA receptors in the carotid body. No response to adenosine triphosphate (ATP) was seen after the above treatments. The excitatory response to DA seemed to be mediated by a mechanism other than vasoconstriction, since it was not blocked by phenoxybenzamine and the pattern of the response was different from that of norepinephrine (NA).

Adenosine Triphosphate↗
PubMedDate not supplied

[Effect of radiofrequency range electromagnetic radiation on chemoreceptor structure].

The data concerning the effects of radio frequency electromagnetic radiation on chemoreceptor systems available in current literature were reviewed. These effects were systematized by the level of organization of the systems including organisms, cell and subcell preparations and membrane structures. The different mechanisms which could underlie electromagnetic radiation effects were analyzed.

Animals↗
PubMed1995

Regulation of respiratory muscle activities during chemoreceptor stimulation in adult horses.

We examined the electromyographic activity of the costal portion of the diaphragm and the transverse abdominal and external oblique muscles in 6 chronically instrumented awake adult horses during eupneic breathing, during 2 levels of hypercapnia (fractional concentration of inspired CO2; FICO2 = 0.4 and 0.6), and during 2 levels of hypocapnic hypoxia (FIO2 = 0.15 and 0.12). Using the inert gas technique, we also measured the end-expiratory lung volumes of the 6 horses during eupnea, 6% CO2 challenge, and 12% O2 breathing. During eupneic breathing, phasic electrical activity of these 3 muscles was always present and was preceded by the onset of mechanical flow. At progressive levels of hypercapnia, the magnitude of inspiratory and expiratory electrical activity increased, and for the expiratory muscles, this recruitment coincided with significant (P < 0.05) increases in peak expiratory gastric pressure. However, during hypocapnic hypoxia, differential recruitment patterns of the respiratory muscles were found. The electrical activity of the diaphragm increased in magnitude and occurred sooner relative to the onset of mechanical flow. The magnitude and onset of abdominal expiratory activity failed to increase significantly during these episodes of hyperpnea and this pattern of activity coincided with decrements in peak expiratory gastric pressure. Despite alterations in muscle recruitment patterns during these hyperpneic episodes, end-expiratory lung volume remained unchanged. Thus, we conclude that adult horses respond similarly to awake dogs during peripheral and central chemoreceptor stimulation.

Animals↗
PubMed1975

[Control of respiration in teleostean fishes: existence of chemoreceptors, physiologically analogous to those of higher vertebrates].

Injection of NaCN or lobeline into the ventral aorta of the trout or carp provokes hyperventilation and bradycardia within 5 seconds, responses which are the weaker the higher the oxygen tension of the ambient water. The reactions, precisely similar to the chemoreflexes of higher vertebrates, suggest that these fish also possess arterial chemoreceptors.

Animals↗
PubMed1994

The role of the carotid chemoreceptors in the control of breathing during exercise.

Our objective was to gain insight into the role of the carotid chemoreceptors (CC) in the exercise hyperpnea. Humans and ponies were studied at rest and during submaximal exercise breathing room air. In healthy humans, alveolar ventilation (VA) was tightly matched to CO2 production (CO2) resulting in PaCO2 deviating during exercise less than 1-2 mm Hg from rest. In contrast, ponies' VA increased proportionately more than VCO2 during exercise resulting in a workload dependent hypocapnia. Attenuating CC activity through hyperoxia had no effect on exercise PaCO2 of humans but hyperoxia accentuated the exercise hypocapnia of ponies. Similarly, CC denervation accentuated the exercise hypocapnia of ponies. Healthy humans were also studied while external airway resistance was increased, which, while breathing room air, resulted in a workload dependent hypercapnia, and this hypercapnia was accentuated by hyperoxia. Finally, a majority of asthmatic humans studied were hypercapnic during exercise while breathing room air and the hypercapnia was accentuated by hyperoxia. We conclude that the CC do not provide a primary drive for the exercise hyperpnea but they "fine tune" VA to minimize disruptions of arterial blood gases. In healthy humans, attenuating CC activity has no effect on PaCO2 because the primary VA drive is closely matched to VCO2.

Animals↗
PubMedDate not supplied

The role of CO2/pH chemoreceptors in ventilatory control.

It now appears that at least some members of all classes of vertebrates exhibit ventilatory responses to changes in CO2/pH per se, including fishes. With the transition from aquatic to aerial respiration, there is an increase in the sensitivity of animals to this complex of stimuli, an increase in the variety of putative receptors possibly involved in eliciting ventilatory responses and an increase in the relative importance of this complex of stimuli in the genesis of resting ventilation. The variety of CO2-sensitive chemoreceptors present in air-breathing lower vertebrates adds considerable complexity to experimental studies of ventilatory responses to CO2/pH. Because of the locations, discharge characteristics and reflex effects of the different receptor groups, most air-breathing lower vertebrates show different responses to increases in CO2/[H+] due to cerebral ischemia, anoxia, metabolic acidosis and environmental hypercarbia. In some cases the differences are only quantitative, while in other cases the responses are qualitatively very different. These differences appear to reflect differences in the relative strength of the reflexes elicited by the various receptor groups and the net sum of their modulating influences when CO2/pH are altered via different routes. Although the situation is simpler in the higher vertebrates, in all cases the input from all of the CO2/[H+]-sensitive receptors appears to act as a biasing input which summates with other afferent information to modulate respiratory motor output, even in those species that breathe intermittently.

Acidosis, Respiratory↗
PubMed1997

Reduced chemoreceptor sensitivity in patients with Barrett's esophagus may be related to age and not to the presence of Barrett's epithelium.

BACKGROUND: Patients with Barrett's esophagus have demonstrated reduced chemo- and mechanoreceptor sensitivity to acid infusion and balloon distension, respectively. However, Barrett's esophagus is mainly a disease of the elderly, making age the possible underlying mechanism for altered pain perception in this patient population. OBJECTIVES: To determine perception thresholds to acid infusion in elderly (>65 yr) versus younger (< or =50 yr) patients with Barrett's esophagus. METHODS: Twelve elderly and 10 younger patients, matched by length of Barrett's mucosa, were recruited into the study. All patients participated in our Barrett's esophagus surveillance program. The patients were treated with omeprazole 20 to 60 mg/day and were symptom free. Chemosensitivity was determined by a modified acid perfusion test, in which acid perception thresholds were quantified by the lag time to initial typical symptom perception, sensory intensity rating, and an acid perfusion sensory score. RESULTS: Five of the elderly patients with Barrett's esophagus had a negative test, whereas all younger patients with Barrett's esophagus experienced typical symptom perception during acid infusion. Elderly patients with Barrett's esophagus had significantly longer lag time to initial perception, lower acid perfusion sensory score, and sensory intensity rating in comparison with the younger patients. CONCLUSIONS: Reduced chemoreceptor sensitivity to acid perfusion that has previously been demonstrated in patients with Barrett's esophagus may be related to age and not to the presence of Barrett's epithelium.

Adult↗
PubMed1996

Mechanisms of carotid chemoreceptor resetting after birth. In vitro studies.

The results of these studies are consistent with the hypothesis that carotid chemoreceptor type-I cell resetting occurs, at least in part, at the level of the type-I cell. Furthermore, we have developed an in vitro model of newborn type-I cell resetting, in which freshly isolated glomus cells from newborns exhibit small, immature [Ca2+]i response to anoxia, but-after 72 hours in culture-[Ca2+]i responses convert to adult magnitude and profile. Finally, work so far suggests that glomus cell resetting in this model is modulated by oxygen tension. The mechanisms of glomus cell resetting remain unknown. Resetting of O2 sensitivity could result from withdrawal of tonic inhibitory influences present in vivo, changes in the oxygen sensor itself, changes in ion channel expression, modulation, and function, or other mechanisms occurring around the time of birth. Additional work is needed to determine the mechanisms of glomus cell resetting at the cellular level, and the role of O2 tension and other potential modulators of resetting.

Animals↗
PubMed1982

The chemoreceptor surface of the taste organ in the frog Rana esculenta. A freeze-fracture analysis.

The epithelial surface of the taste disc on the fungiform papillae of the frog was studied by means of freeze-fracture and conventional electron microscopy. The plasma membrane of the apical process of taste receptor cells was found to exhibit a uniform population of 10-nm intramembrane particles on its fracture face P in a density of 1,000-1,800/micrometers2. In contrast to intramembrane particles in mucous cells or in other regions of the plasma membrane, these particles were observed to protrude approximately twice as high from the fracture face. Not more than 1-2% of the particles were found on fracture face E of the apical process of the taste cell. The apical regions of satellite and mucous secretory cells are also described. The occurrence of relatively large intramembrane particles in a membrane region presumed to function as the chemoreceptor area of taste cells suggests that the particles may be involved in chemoreception.

Animals↗
PubMed1995

Distribution of OMP-, PGP 9.5- and CaBP-like immunoreactive chemoreceptor neurons in the developing human olfactory epithelium.

We have examined the distribution of olfactory marker protein (OMP), protein gene product 9.5 (PGP 9.5) and calcium-binding protein D-28k (CaBP) in the olfactory epithelium of mid- to late fetal and newborn humans using immunocytochemistry. Olfactory chemoreceptor neurons (ORNs) in a 24-week-old female fetus, a 31-week-old male fetus and a newborn male were examined. OMP-like immunoreactivity (-LI) and PGP 9.5-LI were distributed throughout ORNs at all ages. CaBP-like immunoreactivity, however, was found only in clustered or isolated fetal ORNs; in the newborn, CaBP-LI was seen only in isolated ORNs sparsely distributed throughout the OE. These findings demonstrate that human ORNs express OMP-LI nearly 4 weeks earlier in development than previously reported. PGP 9.5-LI is coincidentally abundant within these cells, suggesting it may have an important role in mature ORNs. Because the number of ORNs expressing CaBP-LI decreases during perinatal development, CaBP may be important in intracellular calcium regulation during ORN growth and maturation in the developing OE.

Calbindins↗
PubMed1976

Carotid chemoreceptor influence on the cardiac sympathetic nerve discharge.

Pure stimulation of carotid chemoreceptors induces, as a primary effect, the general spontaneous activation of both the cardioexcitatory and the cardioinhibitory medullary centres. These effects have been shown by keeping constant those parameters which, when modified, produced secondary effects hiding the investigated primary ones.

Animals↗
PubMed1983

Effects of temperature on the response of chemoreceptor fibers to chemical agents.

The effects of stimulating (NaCN, ACh, eserine and haloperidol) and depressant (zero [Ca2+]o, mecamylamine and dopamine) agents of carotid body chemoreceptors were tested at different temperatures. Temperature was varied between 29 and 39 degrees C and Arrhenius plots of the sensory discharge frequency against the reciprocal of absolute temperature were constructed before and during application of the chemicals. NaCN, ACh and zero [Ca2+]o did not change the apparent activation energy (mu) whereas eserine, haloperidol and probably mecamylamine depressed mu. Dopamine probably increased mu. Thus, there were no uniform effects of temperature on the action of different chemosensory stimulants or depressants, suggesting that these agents act on different steps of a chain reaction.

Acetylcholine↗
PubMed1986

A ventromedullary relay involved in the hypothalamic and chemoreceptor activation of sympathetic postganglionic neurones to skeletal muscle, kidney and splanchnic area.

Bilateral application of glycine to the ventral surface of the medulla produces a profound hypotension during which sympathetic vasoconstrictor activity to splanchnic, renal and skeletal muscle vascular beds is reduced. The pattern of activation of sympathetic vasoconstrictor fibres to kidney and skeletal muscle, during carotid chemoreceptor activation and hypothalamic stimulation, is attenuated as tonic sympathetic activity diminishes. Functioning ventromedullary neurones are thus necessary for maintaining tonic sympathetic nerve activity, and for reflex and brain evoked patterns of sympathetic nerve activity, in the anaesthetized cat.

Animals↗
PubMed1992

Time course of K+ current inhibition by low oxygen in chemoreceptor cells of adult rabbit carotid body. Effects of carbon monoxide.

K+ currents recorded from adult rabbit chemoreceptor cells are reversibly inhibited on lowering the pO2 in the bathing solution. Bath application of a hypoxic TTX-containing solution revealed that inhibition of K+ current by low pO2 proceeds faster than TTX inhibition of Na+ currents, the apparent t1/2 being 3.68 and 7.14 s, respectively. Addition of carbon monoxide to the hypoxic gas mixture used to equilibrate the bathing solution reversed the inhibition of K+ currents by approx. 70%.

Animals↗