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At least 1,189 records · Page 66Linked to original sources
PubMed1998

Hans Loeschcke, Robert Mitchell and the medullary CO2 chemoreceptors: a brief historical review.

In the late 1950s, stimulated by reports from Leusen in Belgium and Winterstein in Germany on ventilatory responses to spinal fluid acid, Hans Loeschcke from Göttingen, and Robert Mitchell of the University of California in San Francisco were independently seeking the site of respiratory chemosensitivity to CO2 which they presumed to be mediated by cerebro-spinal fluid hydrogen ions. In 1960 Loeschcke came to San Francisco to join Mitchell for 3 months of intensive hunting for the site of action. This essay describes the events surrounding the localization of ventral medullary superficial (VMS) chemosensitivity to topical acidification, and some of their subsequent and largely independent work on the location, nature and function of this structure. The discovery led to a vast literature on all aspects of the regulation of respiration.

Carbon Dioxide↗
PubMedDate not supplied

Coding of periodic pulse stimulation in chemoreceptors.

In natural conditions odorants released continuously by animals and plants are broken in discontinuous clumps and filaments. In the case of flying insects these discontinuities are perceived as periodic variations in the concentration of the stimulus. This periodicity has been shown to be essential to orientation and location of mate and food. We study analytically and numerically a model of the receptor-ligand interaction that takes place in the receptor neurons. We show that this model can account quantitatively for the range of optimum stimulus frequencies measured experimentally in the sex-pheromone system of moths. The results obtained suggest that the rate constants characterising the pheromone-receptor interaction are optimally adapted to the temporal characteristics of the signal it perceives.

Chemoreceptor Cells↗
PubMed2000

Branchial chemoreceptors mediate ventilatory responses to hypercapnic acidosis in channel catfish.

The effects of hyperoxic hypercapnia on cardiovascular and ventilatory variables and blood gas and acid/base parameters were examined in conscious and anesthetized spontaneously breathing (ASB) channel catfish, Ictalurus punctatus. These separate experiments were designed to determine: (1) if channel catfish show a ventilatory response to hypercapnic acidosis when blood O(2) content is maintained in conscious animals; and (2) whether branchial receptors innervated by cranial nerves IX and X mediate this response. The combination of high O(2) and CO(2) tensions allowed the cardioventilatory effects of hypercapnic acidosis to be assessed independently of Root or Bohr mediated changes in blood O(2) content. In the absence of significant changes in dorsal or ventral aorta O(2) content, hyperoxic hypercapnia significantly stimulated ventilation, relative to hyperoxic exposure. Hypercapnic acidosis, however, had no significant effects on blood pressure or heart rate. Branchial denervation in ASB fish abolished the ventilatory response to hypercapnic acidosis. The results indicate that hypercapnic acidosis independently stimulates ventilation in channel catfish. This response is mediated by CO(2)/pH-sensitive branchial receptors innervated by cranial nerves IX and X.

Acidosis↗
PubMed2001

Regulation of oxygen sensing in peripheral arterial chemoreceptors.

The carotid bodies are a small pair of highly vascularized and well perfused organs located at each carotid artery bifurcation, strategically situated to sense oxygen in arterial blood as it leaves the heart. Carotid body glomus cells are identified as the primary oxygen sensors, which respond to changes in blood P(O(2)) within milliseconds. Acute hypoxia causes a rapid increase in carotid sinus nerve (CSN) activity, providing afferent signals to the respiratory center in the brainstem. Glomus cells secrete numerous neurotransmitters that modulate CSN firing rates. This review will discuss major hypotheses that have emerged regarding acute oxygen sensing by glomus cells. In contrast, chronic responses to hypoxia are much slower, involving cytosolic reactions that take place over several minutes and nuclear reactions which occur over several hours. Converging concepts from different areas of research in oxygen sensing cells and tissues (including the carotid body) have been combined to describe molecular and biochemical changes that take place in the carotid body with chronic hypoxia. These include oxygen dependent proteolytic processes in the cytosol and gene transcription in the nucleus. In addition, cellular and nuclear responses to chronic hypoxia will be discussed.

Animals↗
PubMed1998

Direct measurement of small ligand-induced conformational changes in the aspartate chemoreceptor using EPR.

Ligand-binding-induced conformational changes in the Salmonella typhimurium aspartate receptor were studied using spin-labeling electron paramagnetic resonance. Cysteine residues, introduced by site-directed mutagenesis at several positions in the aspartate receptor periplasmic domain, were used to attach covalently a thiol-specific spin label. The electron paramagnetic resonance spectra of these labeled proteins were obtained in the presence and absence of the ligand aspartate, and used to calculate the distance change between spin labels. The results support a model in which transmembrane signaling is executed by a combined movement of alpha helix 4 (which leads into transmembrane domain 2) relative to alpha helix 1 (connected to transmembrane domain 1), as well as a coming together of the two subunits. Ligand binding causes spin labels at position 39 and 179 (within one subunit) to move further from each other and spin labels at position 39 and 39' (between two subunits) to move closer to each other. Both of these changes are very small-less than 2.5 A. No similar changes were detected in any aspartate receptor samples solubilized in detergent, suggesting that the membrane is required for these conformational changes. This is the first case of physically measured ligand-induced changes in a full-length 1-2 transmembrane domain receptor, and the results suggest that very small ligand-induced movements can result in large effects on the activity of downstream proteins.

Aspartic Acid↗
PubMedDate not supplied

Selective effects of an NMDA glutamate receptor antagonist on the sensory input from chemoreceptors in the snail's head during acquisition of nociceptive sensitization.

Experiments on semi-intact preparations from common snails were used to study the characteristics of the actions of MK-801, an antagonist of NMDA glutamate receptors, on the plasticity of various sensory inputs to defensive behavior command neurons LP11 and RP11 during acquisition of nociceptive sensitization. Application of sensitizing stimuli to the head or foot of control snails led to depression of neuron responses to tactile and chemical sensory stimulation during the short-term stage and marked facilitation of these responses during the long-term stage of sensitization. Application of sensitizing stimuli to the snail's head during administration of MK-801 led to marked depression of responses to chemical stimulation of the head in both the short-term and long-term stages of sensitization. In addition, blockade of NMDA receptors during application of sensitizing stimuli to the foot or head had no effect on changes in neuron responses elicited by chemical stimulation of the snail's foot and by tactile stimulation of the foot or head. It is suggested that NMDA-like glutamate receptors are selectively involved in the mechanism of induction of plasticity of synaptic inputs to command neurons LP11 and RP11, excited by chemical sensory stimulation of the head--a skin receptor zone specific for these neurons.

Animals↗
PubMed2001

Behavioural and chemoreceptor cell responses of the tick, Ixodes ricinus, to its own faeces and faecal constituents.

Ticks are ectoparasites of vertebrates and utilize a variety of infochemicals for host finding and acceptance as well as for intraspecific aggregation and mating responses. Individual male and female Ixodes ricinus. the vector of Lyme disease in Europe. readily arrest on filter paper strips contaminated with their own faeces. I. ricinus also responds, but to a lesser degree, to faeces-contaminated papers enclosed in metal mesh envelopes. i.e. without directly contacting the faeces, suggesting a role for volatiles in the arrestment response. The faccal constituents guanine. xanthine, uric acid and 8-azaguanine (a bacterial breakdown product of guanine) also caused arrestment of individual I. ricinus males and females. However, mixtures of these products induced arrestment of I. ricinus at doses one hundred fold lower than the lowest active dose of any of them tested singly. Saline extracts of faeces activated receptor cells in terminal pore sensilla on the first leg tarsi of I. ricinus. One cell in these sensilla responded in a similar dose dependent manner to guanine and 8-azaguanine, whereas a second cell was more sensitive to lower doses of 8-azaguanine. The response threshold approached 100 fM for both cells. These findings suggest that faeces and faecal breakdown products are implicated in aggregation responses of I. ricinus. This may account for the clumped distribution of this ectoparasite on the ground and contribute to the high proportion of mated individuals recorded prior to host colonization.

Animals↗
PubMed1997

Increased esophageal chemoreceptor sensitivity to acid in patients after successful reversal of Barrett's esophagus.

When compared to patients with erosive esophagitis, patients with Barrett's esophagus have demonstrated reduced chemo- and mechanoreceptor sensitivity to acid infusion and balloon distension, respectively. However, anecdotal clinical experience suggested an increase in symptom perception in patients after successful elimination of Barrett's epithelium, using multipolar electrocoagulation (MPEC) and high-dose proton pump inhibitor (PPI). To determine perception thresholds to acid infusion, we evaluated eight consecutive patients after a series of MPEC treatments resulted in complete elimination of Barrett's mucosa and compared them to 10 age-matched patients with nonreversed Barrett's esophagus and 10 patients with symptomatic, endoscopy-documented erosive esophagitis (Hetzel-Dent grade 2 or greater). Chemosensitivity was determined by a modified acid perfusion test, where acid perception thresholds were quantified by the lag time to initial typical symptom perception, sensory intensity rating, and an acid perfusion sensory score (APSS). While patients after successful elimination of Barrett's esophagus had similar sensory intensity ratings and APSS as patients with erosive esophagitis, the lag times differed significantly between the groups, and both groups had significantly higher sensory intensity ratings and APSS than patients with nonreversed Barrett's esophagus. In conclusion, patients after complete reversal of Barrett's mucosa are unexpectedly as sensitive to acid as symptomatic patients with erosive esophagitis.

Anti-Ulcer Agents↗