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At least 1,153 records · Page 64Linked to original sources
PubMed1977

Role of Pco2 oscillations and chemoreceptors in ventilatory response to inhaled and infused CO2.

We have previously shown in the anaesthetized rabbit that the ventilatory response to an increase in Paco2 is greater if that increase is produced by intravenous infusion of hypercapnic blood than by inhalation of CO2 (Linton et al., 1976). The present set of experiments was designed to investigate the reason for this. It was found that the difference in ventilatory response observed in the intact rabbit was abolished by cutting the carotid sinus nerves or by eliminating the pH/Paco2 oscillations in the carotid blood flow. It is concluded that the normally greater ventilatory response to intravenous infusion of hypercapnic blood compared with inhalation of CO2 is due to a respiratory signal derived from Paco2 oscillations and carried in the carotid sinus nerves.

Animals↗
PubMed1979

Relative contribution of central and peripheral chemoreceptors to the ventilatory response to CO2 during hyperoxia.

Using the technique of artificial ponto-medullary perfusion, the steady state ventilation during hyperoxia was measured in 15 anaesthetized cats as a function of the central PaCO2 (PaCO2) and peripheral PaCO2 (PapCO2). To a first approximation the ventilatory response was linearly related to both the central and peripheral arterial carbon dioxide pressures, viz. VE=SC . PacCO2 + Sp . PapCO2 - K where Sc and Sp represent the overall central and peripheral sensitivity to carbon dioxide. The mean ratio Sp/Sc was 0.48 (range 0.21 to 1.08). In carotid sinus denervated cats Sp was zero, while the values of Sc in these cats were in the range of Sc of cats with intact carotid sinus nerves. It is concluded that the peripse to CO2 under steady-state conditions. Chemodenervation experiments revealed that the carotid bodies play an essential role in this contribution.

Animals↗
PubMed1990

The influence of carotid body chemoreceptors on expiratory muscle activity.

Respiratory muscle EMG responses to transient, specific carotid body excitation (NaCN, hypoxia) and inhibition (dopamine, hyperoxia) were studied in 7 unanesthetized standing dogs while intact (N = 7) and during bilateral cold block of the vagi (N = 3). In all dogs carotid body excitation augmented the EMG activities of both expiratory muscles (triangularis sterni, TS; transversus abdominis, TA) and the (inspiratory) crural diaphragm (CR); carotid body inhibition significantly reduced phasic EMG activities in all muscles. With vagal blockade the response of the TS to carotid body stimulation was increased; that of the TA was essentially unchanged from the intact state. In all dogs expiratory muscle recruitment in response to carotid body excitation/inhibition could either precede or follow that of the CR. We conclude that in response to specific, transient carotid body excitation or inhibition: (1) Changes in CR, TS and TA EMGs are qualitatively similar. (2) Vagal feedback is strongly inhibitory to TS and excitatory to TA. (3) Changes in expiratory muscle EMGs do not require preceding changes in the CR. Carotid body stimulation contributes significantly to the generation of phasic expiratory activity during eupnea.

Animals↗
PubMed1991

Thermal effects on ventilation in cats: participation of carotid body chemoreceptors.

In pentobarbitone anesthetized cats, raising body temperature from 37 to 40 degrees C by external heat increased respiratory frequency, tidal volume, frequency of spontaneous gasps and mean inspiratory flow. It reduced end-tidal CO2 pressure, together with inspiratory and expiratory durations. After bilateral section of the carotid nerves, raising body temperature still induced hyperventilation, but the increase in gasp frequency was less pronounced and no significant change in tidal volume was observed. In comparison to steady ventilatory values in the intact condition, significant reductions in tidal volume at 38 degrees C and in gasp frequency at 37, 39 and 40 degrees C were observed after bilateral carotid neurotomy. Brief hyperoxic tests induced transient decreases in tidal volume and increases in end-tidal CO2 pressure which were significantly larger at 40 degrees C than at 37 degrees C. These changes disappeared after bilateral carotid neurotomy. Anesthetic block of both carotid nerves produced transient reductions in tidal volume at any given temperature. We conclude that carotid body afferents contribute to the hyperventilation evoked by hyperthermia. After their interruption, such contribution is replaceable from other thermal afferents.

Animals↗
PubMed1988

Transmembrane signaling by bacterial chemoreceptors: E. coli transducers with locked signal output.

Methyl-accepting chemotaxis proteins (MCPs) function as transmembrane signalers in bacteria. We isolated and characterized mutants of the E. coli Tsr protein that produce output signals in the absence of overt stimuli and that are refractory to sensory adaptation. The properties of these "locked" transducers indicate that MCP molecules are capable of generating signals that actively augment clockwise and counter-clockwise rotation of the flagellar motors. Transitions between MCP signaling states can be influenced by amino acid replacements in many parts of the molecule, including the methylation sites, at least one of the two membrane-spanning segments, and a linker region connecting the receptor and signaling domains. These findings suggest that transmembrane signaling may involve direct propagation of conformational changes between the periplasmic and cytoplasmic portions of the MCP molecule.

Amino Acid Sequence↗
PubMed1985

Cell and explant culture of olfactory chemoreceptor cells.

An in vitro system for the study of maturation of rat and chick embryonic olfactory receptor cells is presented. A variety of dissociating agents, culture media and substrata were tried in attempts to obtain a preparation of mature living olfactory receptor cells readily visible in the microscope. Maturation was judged by the development of axons greater than 1 mm long, by the presence of cilia at the end of the dendrites and, in the rat, by the presence of immunohistochemically demonstrable olfactory marker protein, a protein present only in olfactory receptor cells. By these criteria, dissociated cells did not mature in vitro, though occasional bipolar cells with relatively short axons were seen. In explant culture, small fragments of rat tissue were positive for all 3 criteria after 6 days. In 9-day cultures, the axons had grown up to 3 mm long in both rat and chick cultures. Olfactory bulb fragments co-cultured close to the olfactory epithelium had no influence on the direction of outgrowth of axons from the olfactory receptor cells. Preliminary experiments with intracellular electrodes on the fragment cultures suggest that there are two cell types in the epithelium; one with a potential of -25 to -30 mV and, the other, -12 to -15 mV.

Animals↗
PubMed1987

Study of possible transmitters in the solitary tract nucleus of the cat involved in the carotid sinus baro- and chemoreceptor reflex.

By using a multibarrelled microelectrode, the possibility that putative transmitters may influence on the field potential evoked in the solitary tract nucleus by electrical stimulation of the carotid sinus nerve (the NTS response) was examined electrophysiologically in the cat. After iontophoretic application of a selective antagonist to the putative transmitter, it was determined whether or not the NTS response was influenced. Both substance P antagonist and naloxone altered the NTS response recorded in the depressor and apneic (or hypopneic) response zone as well as in the pressor and apneustic (or inspiratory) response zone throughout the rostral, intermediate and commissure regions, suggesting that substance P and opioid peptide may play the role of excitatory transmitters. Under the polarizing cathodal current which may activate inhibitory inputs to the site of the NTS response, bicuculline and prazosin strongly enhanced the NTS response recorded in the pressor and apneustic zone, while naloxone weakly enhanced the NTS response recorded in the depressor and apneic zone. These results suggest that gamma-aminobutyric acid, alpha-adrenergic agonist and opioid peptide may have an inhibitory influence on the NTS response.

Animals↗
PubMed1987

Mechanisms for termination of the action of dopamine in carotid body chemoreceptors.

The possible presence of a high affinity uptake mechanism for dopamine and the metabolism of this amine was investigated in the rabbit carotid body. The type I cells of this sensory organ contain high levels of dopamine and share with sympathetic nerve endings (which possess a high affinity uptake mechanism for catecholamines) the properties of being presynaptic catecholaminergic elements, but also have in common with chromaffin cells from intact adrenal medulla (which lack a high affinity catecholamine uptake) a similar embryological origin and ultrastructural appearance. Our experiments revealed only a low affinity uptake process (Km = 6.76 X 10(-4) M [3H]dopamine; Vmax = 1.84 X 10(-9) mol [3H]dopamine/mg protein/min) in the rabbit carotid body. In agreement with our kinetic findings, the uptake of [3H]dopamine was found to be independent of the Na+ concentration in the incubation media. The efflux from the tissue of incorporated [3H]dopamine was very fast (88% wash-out with a half-time of 4 min). DOPAC was the principal catabolite of dopamine in the carotid body, and the organ exhibited a very low capacity for norepinephrine synthesis. Neither chronic carotid sinus nerve section nor chronic sympathectomy modified the uptake of [3H]dopamine, suggesting that the lack of expression of a high affinity uptake was not a consequence of trophic suppression by the neural innervation of the organ. We conclude that overflow, or wash-out, of released dopamine may be quantitatively the most important mechanism for the inactivation of this putative neurotransmitter in the rabbit carotid body.

Animals↗
PubMed1994

Adrenergic cell group in rostral ventrolateral medulla of cat: its correlation with central chemoreceptors.

We have proposed a hypothesis that secondary neurons mediating central respiratory chemoreception are not restricted to the medullary superficial layer. This idea was further examined in the present physiological and morphological studies. We identified the 'S' area, i.e. the medullary surface area where cold blockade produced apnea, in anesthetized, spontaneously breathing cat. We then evaluated how the apnea was modified by injection of CO2-saturated saline into the vertebral-basilar artery. The CO2 injection caused immediate reappearance of respiratory rhythm, although intensity of inspiratory activity was smaller than in the control. This incomplete recovery suggests that the responsive structure extends deeply below the surface. The extent of the cell group underlying the 'S' area was evaluated by morphological study. Medullary transverse sections including the 'S' area were treated with three distinct antisera against phenylethanolamine N-methyltransferase (PNMT), dopamine-beta-hydroxylase (DBH), and 5-hydroxytryptamine (5-HT). The PNMT-labelled cell group was found to exactly underlie the 'S' area, although the DBH- and the 5-HT-labelled cell groups did not show close topographic correlation with the 'S' area. PNMT cells were located in the region ventral to retrofacial nucleus within 0.5-1.5 mm depth beneath the surface. These results suggest that adrenergic cells in the rostral ventrolateral medulla are important candidates for secondary neurons mediating central respiratory chemoreception.

Animals↗
PubMed1995

Activation of peripheral and/or central chemoreceptors changes retching activities of Bötzinger complex neurons and induces expulsion in decerebrate dogs.

Fictive expulsion can be induced by electrical stimulation of the carotid sinus nerve during fictive retching or by discontinuing artificial ventilation in decerebrate paralyzed dogs. Both the phrenic and abdominal muscle nerves discharge during the early phase of fictive expulsion, but only the abdominal muscle nerve continues to discharge during the late phase. To determine whether Bötzinger complex (BOT) neurons participate in expulsion, responses to sinus nerve stimulation were examined in 47 non-respiratory (N-RES), 15 inspiratory (INS) and 12 expiratory (EXP) BOT neurons during eupnea. About 80% of the neurons produced excitatory or inhibitory responses. FIring patterns were observed in 61 N-RES, 39 INS and 56 EXP BOT neurons during expulsion induced by sinus nerve stimulation or by discontinuation of artificial ventilation. An activity pattern similar to that of the phrenic nerve was exhibited during fictive retching and expulsions by 13 N-RES< 3 INS and 8 EXP neurons, and a firing pattern like that of the abdominal muscle nerve was produced by 11 N-RES, 6 INS and 5 EXP neurons. Bursts were limited to the late phase of expulsion and to the period just after expulsion in 5 N-RES, 3 INS and 3 EXP neurons, and in 8 N-RES and 21 EXP neurons, respectively. Firings of the two latter groups of neurons decreased concomitantly with each retch or during retching. These results suggest that neurons of the two latter groups play crucial roles in the central patterning of neuronal expulsion activities.

Animals↗