The mechanics of lung ventilation and the effects of hypercapnia on respiration in <i>Bufo marinus</i>

Macintyre, Doug; Toews, Daniel P.

doi:10.1139/z76-154

Cited by 73 publications

(14 citation statements)

References 9 publications

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“…The latency for induction of such responses was shortened with increasing stimulus frequencies. Most tachypneic patterns transiently observed were of breathing with progressively increasing buccal pressure , and were similar to those seen during hypoxic stimulation (in toads : BOUTILIER and TOEWS , 1977;in bullfrogs : in preliminary experiments), or in hypercapnia (MACINTYRE and TOEWS , 1976).…”

Section: Methodssupporting

confidence: 65%

Localization of CO2 Sensor Related to the Inhibition of the Bullfrog Respiration

Sakakibara

1978

Jpn.J.Physiol

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CO2 sensitivity in the airways and the general skin surface of the bullfrog under urethane anesthesia or without anesthesia was investigated. Pressure in the buccal cavity as well as blood pressure in the sciatic artery were measured with a differential or a straingauge transducer. Air containing 2-14 % CO2 was introduced into the regions as given below. (1) The nose and the body surface, both regions were separated from each other and independently exposed to CO2. (2) The larynx-lungs, the buccal cavity-lungs, the naso-buccal cavity separated from the airways at the glottis, and the internal or external nares, respectively. By analyzing the CO2 sensitivity of the respective regions mentioned above, both the nasal mucosa and the skin surface were found to be responsible for the respiratory inhibition by CO2. Sectioning both the olfactory and the trigeminal nerves abolished the CO2-induced inhibition mediated by the nasal mucosa and electrical stimulation of the proximal cut end of these nerves inhibited respiration. These findings suggested the existence of afferent reflex pathways from the nasal mucosa by these cranial nerves. Significance of this CO2-induced reflex was discussed.

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Section: Methodssupporting

confidence: 65%

Localization of CO2 Sensor Related to the Inhibition of the Bullfrog Respiration

Sakakibara

1978

Jpn.J.Physiol

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“…Mean subvertebral sac pressures were approximately 450-500·Pa and did not differ between the two species, but are comparable to lung pressures that have been measured in anurans. Lung pressures range from 200 to 600·Pa during episodic ventilation in Bufo (Chaunus) marinus (Wang, 1994;Macintyre and Toews, 1976). Similar pressures have also been measured in Rana (Lithobates) pipiens (West and Jones, 1975;Vitalis and Shelton, 1990) and Rana (Lithobates) catesbeiana (Kinkead and Milsom, 1994).…”

Section: Discussionmentioning

confidence: 64%

Lung ventilation contributes to vertical lymph movement in anurans

Hedrick

Drewes

Hillman

et al. 2007

Journal of Experimental Biology

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SUMMARY Anurans (frogs and toads) generate lymphatic fluid at 10 times the rate in mammals, largely as a consequence of their very `leaky' vasculature and high interstitial compliance. Lymph is ultimately pumped into the venous system by paired, dorsally located lymph hearts. At present, it is unclear how lymphatic fluid that accumulates in central body subcutaneous lymph sacs is moved to the anterior and posterior lymph hearts in the axillary regions and how lymph is moved, against gravity, to the dorsally located lymph hearts. In this study,we tested the hypothesis that lung ventilation, through its consequent effects on lymph sac pressure, contributes to the vertical movement of lymphatic fluid in the cane toad (Chaunus marinus) and the North American bullfrog(Lithobates catesbeiana). We measured pressure in the dorsal, lateral and subvertebral lymph sacs of anesthetized cane toads and bullfrogs during artificial lung inflation and deflation. We also measured pressure in the subvertebral lymph sac, which adheres to the dorsal surface of the lungs,simultaneously with brachial (forelimb) and pubic (posterior) sac pressure during ventilation in freely behaving animals. There were highly significant(P<0.001) relationships between lung pressure and lymph sac pressures (r2=0.19–0.72), indicating that pulmonary pressure is transmitted to the highly compliant lymph sacs that surround the lungs. Subvertebral sac pressure of resting animals was not significantly different between L. catesbeiana (518±282 Pa) and C. marinus (459±111 Pa). Brachial sac compliance (ml kPa–1 kg–1) also did not differ between the two species (33.6±5.0 in L. catesbeiana and 37.0±9.4 in C. marinus). During expiration (lung deflation), reductions in expanding subvertebral sac pressure are communicated to the brachial lymph sac. Changes in brachial and pubic lymph sac pressures were correlated almost entirely during expiration rather than inspiration. The change in brachial sac pressure during expiration was 235±43 Pa for C. marinus and 215±50 Pa for L. catesbeiana, which is of sufficient magnitude to move lymph the estimated 0.5–1.0 cm vertical distance from the forelimb to the vicinity of the anterior lymph hearts. We suggest that lymph is moved during expiration to the subvertebral sac from anterior and posterior lymph sacs. During lung inflation, increased lymph sac pressure moves lymph to axillary regions, where lymph hearts can return lymph to the vascular space. Consequently, pulmonary ventilation has an important role for lymph movement and, hence, blood volume regulation in anurans.

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“…Hypercarbia is a powerful stimulus for the anuran respiratory control system (8,9,26,31,46,50,54). In intact unanesthetized toads, the central chemoreceptors contribute about 80% of the hypercarbic drive to ventilation (8).…”

Section: Discussionmentioning

confidence: 99%

Locus coeruleus is a central chemoreceptive site in toads

Noronha-de-Souza¹,

Bícego²,

Michel³

et al. 2006

American Journal of Physiology-Regulatory, Integrative and Comp

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The locus coeruleus (LC) has been suggested as a CO2 chemoreceptor site in mammals. This nucleus is a mesencephalic structure of the amphibian brain and is probably homologous to the LC in mammals. There are no data available for the role of LC in the central chemoreception of amphibians. Thus the present study was designed to investigate whether LC of toads (Bufo schneideri) is a CO 2/H ϩ chemoreceptor site. Fos immunoreactivity was used to verify whether the nucleus is activated by hypercarbia (5% CO2 in air). In addition, we assessed the role of noradrenergic LC neurons on respiratory and cardiovascular responses to hypercarbia by using 6-hydroxydopamine lesion. To further explore the role of LC in central chemosensitivity, we examined the effects of microinjection of solutions with different pH values (7.2, 7.4, 7.6, 7.8, and 8.0) into the nucleus. Our main findings were that 1) a marked increase in c-fos-positive cells in the LC was induced after 3 h of breathing a hypercarbic gas mixture; 2) chemical lesions in the LC attenuated the increase of the ventilatory response to hypercarbia but did not affect ventilation under resting conditions; and 3) microinjection with acid solutions (pH ϭ 7.2, 7.4, and 7.6) into the LC elicited an increased ventilation, indicating that the LC of toads participates in the central chemoreception.ventilation; midbrain; brain stem; amphibian; isthmus; bufo; hypercarbia IT IS WELL ESTABLISHED THAT vertebrates display respiratory responses to changes in the arterial blood gases, and the underlying control mechanisms are very similar among different taxa. The transition of amphibians to air breathing was accompanied by an increase in the sensitivity to CO 2 /H ϩ (45). Interestingly, the ontogenetic changes of anuran amphibians involve modifications of the control system from being almost entirely oxygen driven to a combination of acid-base and oxygen driven (11).Central respiratory CO 2 chemoreceptors have been clearly established in adult anuran amphibians (8,46), and these receptors are probably distributed throughout the rostral medulla, surrounding the fourth ventricle (50). In mammals, these receptors were once thought to be located only close to the surface of the ventral medulla, but it is now clear that they are widespread within the brainstem (12). Recently, sites have been identified in the ventrolateral medulla, nucleus of the solitary tract, ventral respiratory group, locus coeruleus (LC), caudal medullary raphe, and fastigial nucleus of the cerebellum (for a review, see Ref. 35). However, it remains unclear whether chemoreceptors are also widely distributed in amphibians. An evaluation of specific contributions of these chemosensitive sites can be achieved by CO 2 challenge, focal stimulation, or focal disruption. Focal acidification of a single central chemosensitive site increases ventilation, whereas disruption decreases ventilation (3,28,37,47). According to Nattie (35), the presence of widespread central chemoreceptors may be related to the increased demands of a...

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The mechanics of lung ventilation and the effects of hypercapnia on respiration in Bufo marinus

Cited by 73 publications

References 9 publications

Localization of CO2 Sensor Related to the Inhibition of the Bullfrog Respiration

Localization of CO2 Sensor Related to the Inhibition of the Bullfrog Respiration

Lung ventilation contributes to vertical lymph movement in anurans

Locus coeruleus is a central chemoreceptive site in toads

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