CO2 transduction mechanisms in avian intrapulmonary chemoreceptors: experiments and models

Hempleman, Steven C.; Posner, Richard G.

doi:10.1016/j.resp.2004.02.013

Cited by 27 publications

(18 citation statements)

References 51 publications

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“…Denervating the IPCs in this study appeared to increase overall total ventilation by 25%, probably because tonic inhibitory afferent activity from these receptors was eliminated. An additional mechanism through which the IPCs regulate CO 2 exchange is likely through the control of breathing pattern (Hempleman and Posner, 2004;Milsom et al, 2004); indeed, in this study IPC denervation also altered breathing pattern, such that breaths became deeper and slower.…”

Section: Intrapulmonary Chemoreceptor Control Of Ventilatory Adjustmentsmentioning

confidence: 58%

“…The IPC are believed to have an analogous function in birds to that of the mammalian pulmonary stretch receptors, which are involved in terminating the inspiratory cycle (Hempleman and Posner, 2004;Milsom et al, 2004). IPC firing rate is inversely proportional to inspired P CO 2 , unlike most CO 2 -sensitive chemoreceptors, and activity by IPC afferents is known to inhibit breathing (Peterson and Fedde, 1968;Scheid et al, 1978).…”

Section: Intrapulmonary Chemoreceptor Control Of Ventilatory Adjustmentsmentioning

confidence: 99%

“…Stimulation of central chemoreceptors appears to be the most effective at increasing ventilation in response to hypercapnia, while the carotid body chemoreceptors also contribute substantially to ventilatory drive during hypercapnia (Milsom et al, 1981). Intrapulmonary chemoreceptors (IPCs), which are unique amongst birds and diapsid reptiles, are also CO 2 sensitive (Hempleman and Posner, 2004;Milsom et al, 2004), but the role of this chemoreceptor group is unclear: IPCs are definitely known to regulate breathing pattern, and may also influence total ventilation. In addition to the contributions of central and peripheral chemoreceptors, the ventilatory response to hypercapnia can be modulated by mechanisms of central integration, depending on the pattern and time course of the CO 2 exposure (Baker et al, 2001).…”

Section: Introductionmentioning

confidence: 99%

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Ventilatory roll off during sustained hypercapnia is gender specific in pekin ducks

Dodd

Scott

Milsom

2007

Respiratory Physiology & Neurobiology

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The objective of the present study was to examine the relative roles of peripheral versus central mechanisms in producing ventilatory adjustments in pekin ducks during prolonged (5 h) hypercapnia (5% inspired CO 2 ), and to determine whether these adjustments differed between male and female ducks. After 20 min of CO 2 exposure, intact ducks increased total ventilation (V E ) 2.5-3-fold above control values, due to large increases (∼200%) in tidal volume (V T ) and slightly smaller increases (∼140%) in breathing frequency (f R ). This response was accompanied by respiratory acidosis (pHa fell from ∼7.46 to ∼7.41) and hypercapnia (Pa CO 2 increased from ∼35 to ∼40 Torr). In males,V E fell progressively thereafter due exclusively to a fall in f R , in parallel with a rapid partial recovery of pH (to 7.44) while Pa CO 2 continued to climb (to ∼42 Torr). In females,V E remained elevated during hypercapnia, and no pH recovery occurred. This suggests that a respiratory decline resulting from acid-base compensation (probably due to HCO 3 − mobilization) occurred in males but not in females. Bicarbonate mobilization, and thus pH compensation, may have been reduced in females due to the CaCO 3 requirements of eggshell formation. In males, the acute ventilatory response was reduced slightly by denervation of the carotid bodies or intrapulmonary chemoreceptors, but there was no effect of denervation of either receptor group on the responses to prolonged CO 2 . We conclude that pH compensation triggered by constant or increasing Pa CO 2 , acting at central chemoreceptors, likely mediates the respiratory adjustments seen in male pekin ducks during hypercapnia. Furthermore, we suggest that this ventilatory response be considered a gender-specific hypercapnic ventilatory roll off, in the context of the various time domains of the hypercapnic ventilatory response.

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Section: Intrapulmonary Chemoreceptor Control Of Ventilatory Adjustmentsmentioning

confidence: 58%

Section: Intrapulmonary Chemoreceptor Control Of Ventilatory Adjustmentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ventilatory roll off during sustained hypercapnia is gender specific in pekin ducks

Dodd

Scott

Milsom

2007

Respiratory Physiology & Neurobiology

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“…The average breathing rate for a 1.9·kg chicken is about 20·breaths·min -1 (Frappell et al, 2001). As shown in Fig.·6, decreasing lung CO 2 causes increases in IPC discharge rate (Hempleman and Posner, 2004;Molony, 1974). At 20·cycles·min -1 , changes in IPC spike frequency faithfully follow the sinusoidal variations of carbon dioxide, and there are ample numbers of spikes generated during the cyclic increases and decreases in CO 2 to encode the associated changes in CO 2 as changes in spike frequency (i.e.…”

Section: Matching Spike Code To Biological Timementioning

confidence: 94%

“…IPCs detect breath-by-breath fluctuations in lung CO 2 , and transmit spike-encoded feedback information to the brainstem to help match breathing pattern to metabolic demands (Hempleman and Posner, 2004). Because the frequency of CO 2 fluctuations sensed by IPC is set by the breathing rate (breaths·s -1 ), which scales to M b -1/4 , and this is matched by IPC peak discharge frequency (spikes·s ].…”

Section: Scaling Of Peak Discharge Frequency To Phasic Stimulationmentioning

confidence: 99%

Spike firing allometry in avian intrapulmonary chemoreceptors: matching neural code to body size

Hempleman

Kilgore

Colby

et al. 2005

Journal of Experimental Biology

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3065Biological rates, such as the frequencies of breathing, cardiac contraction, gait, and mass-specific metabolic rate, usually scale inversely to animal body mass M b . Accordingly, small animals like hummingbirds and shrews have intrinsically higher biological rates than ostriches and elephants (Calder, 1996;Lindstedt and Calder, 1981;Schmidt-Nielsen, 1984). This is often explained as biological time (as opposed to clock time) running faster for small animals and slower for large animals. When quantified using the allometric scaling model, ; that is, they scale to the negative 1/4 to 1/3 power of body mass (Brown and West, 2000;Calder, 1996;Frappell et al., 2001;Lindstedt and Calder, 1981;Schmidt-Nielsen, 1984). In the allometric model, y is a biological trait, M b is body mass, a is a constant associated with phylogenetic characteristics, and b is the mass exponent.An exception to frequency scaling occurs in the nervous systems of animals. Maximal action potential (spike) generation rate in neurons is relatively fixed in animals of varying size because of the highly conserved genetics and kinetics of voltage-gated ion channels. Ion channel kinetics and gating are key determinants of transmembrane ionic fluxes, and control the width, shape and refractory periods of action potentials. The interplay of expressed ion channels in axonal membranes sets a practical upper limit for spike frequency at approximately 300·s -1 in most neurons, but normal discharge rates are usually much slower even in very small animals (Hille, 1992).Action potential spike trains are the mechanism for long distance information transmission in the nervous system. In general, neural information may be 'rate coded,' with average spike rate over a time period encoding stimulus intensity, or 'time coded,' with the occurrence of a single spike (or spike burst) encoding the occurrence of a rapid stimulus transition (Rieke et al., 1999). Rate and time codes are not mutually exclusive: 'partially adapting' sensory neurons are common, and have both tonic (rate coded) and phasic (time coded) discharge responses (see below). , like breathing rate (P<0.05). Previously published values of peak discharge rate in IPC also fit this allometric relationship. We suggest that mass-dependent scaling of neural coding may be necessary for preserving information transmission with decreasing body size.

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Control of Breathing in Ectothermic Vertebrates

Milsom

Gilmour

Perry

et al. 2022

Comprehensive Physiology

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CO2 transduction mechanisms in avian intrapulmonary chemoreceptors: experiments and models

Cited by 27 publications

References 51 publications

Ventilatory roll off during sustained hypercapnia is gender specific in pekin ducks

Ventilatory roll off during sustained hypercapnia is gender specific in pekin ducks

Spike firing allometry in avian intrapulmonary chemoreceptors: matching neural code to body size

Control of Breathing in Ectothermic Vertebrates

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