Central chemoreceptor drive to breathing in unanesthetized toads, Bufo paracnemis

Branco, Luiz G.S.; Glass, Mogens L.; Hoffmann, Anette

doi:10.1016/0034-5687(92)90059-6

Cited by 67 publications

(34 citation statements)

References 20 publications

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“…Am-phibians have been shown to possess central CO 2 chemoreceptors (e.g. Smatresk and Smits, 1991;Branco et al, 1992) and, despite attempts to superfuse these preparations with hyperoxic solutions, it is likely that some regions exhibit progressive degrees of hypoxia and acidosis at increasing depth from the brain surface. While Torgerson et al (1997b) have demonstrated that no such hypoxic regions are present in an in vitro brainstem preparation from the Rana catesbieana tadpole, the brainstem was moderately acidic throughout.…”

Section: Preparations Producing Episodic and Non-episodic Patterns Ofmentioning

confidence: 99%

Respiratory pattern formation in the isolated bullfrog (Rana catesbeiana) brainstem-spinal cord

Reid

Milsom

1998

Respiration Physiology

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This study characterizes various patterns of motor output obtained from cranial nerves V, VII, X, and XII of in vitro, saline-perfused, brainstem-spinal cord preparations of the American bullfrog (Rana catesbeiana). Motor output indicative of fictive breathing was present in all preparations. In 17 of 26 preparations, fictive breaths were either evenly spaced or randomly distributed, while in the remaining nine preparations fictive breaths occurred in episodes separated by relatively long periods of quiescence. With the exception of fictive breath duration in the non-episodic preparations and the instantaneous frequency of fictive breaths within episodes, all variables associated with fictive breathing were insensitive to changes in perfusion saline pH. In addition to fictive breathing, a large number of other forms of motor output were observed arising from these nerves. While the data suggest that the in vitro preparation is capable of producing a wide repertoire of motor patterns, similar to those seen in vivo, it was difficult, with the current protocol, to reliably produce any single pattern in spite of carefully regulated conditions.

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Section: Preparations Producing Episodic and Non-episodic Patterns Ofmentioning

confidence: 99%

Respiratory pattern formation in the isolated bullfrog (Rana catesbeiana) brainstem-spinal cord

Reid

Milsom

1998

Respiration Physiology

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“…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).…”

mentioning

confidence: 99%

“…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).…”

mentioning

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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“…Figure 1B shows the effects of L-NAME microinjection on BF during normocapnia and hypercapnia. Under normocapnia, no difference in BF was observed between control and L-NAME-treated animals, whereas well as the central acid-base receptors of Bufo paracnemis (18,19). The respiratory control of ectotherms resembles the mammalian control system; the rhythmogenic and pattern-forming elements in each are adapted to meet the demands determined by the environment, behavior, metabolic needs, and breathing mechanisms.…”

Section: Discussionmentioning

confidence: 97%

Participation of nitric oxide in the nucleus isthmi in CO2-drive to breathing in toads

Gargaglioni

Branco

1999

Braz J Med Biol Res

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The nucleus isthmi (NI) is a mesencephalic structure of the amphibian brain. It has been reported that NI plays an important role in integration of CO 2 chemoreceptor information and glutamate is probably involved in this function. However, very little is known about the mechanisms involved. Recently, it has been shown that nitric oxide synthase (NOS) is expressed in the brain of the frog. Thus the gas nitric oxide (NO) may be involved in different functions in the brain of amphibians and may act as a neurotransmitter or neuromodulator. We tested the hypothesis that NO plays a role in CO 2 -drive to breathing, specifically in the NI comparing pulmonary ventilation, breathing frequency and tidal volume, after microinjecting 100 nmol/0.5 µl of L-NAME (a nonselective NO synthase inhibitor) into the NI of toads (Bufo paracnemis) exposed to normocapnia and hypercapnia. Control animals received microinjections of vehicle of the same volume. Under normocapnia no significant changes were observed between control and L-NAME-treated toads. Hypercapnia caused a significant (P<0.01) increase in ventilation only after intracerebral microinjection of L-NAME. Exposure to hypercapnia caused a significant increase in breathing frequency both in control and L-NAME-treated toads (P<0.01 for the control group and P<0.001 for the L-NAME group). The tidal volume of the L-NAME group tended to be higher than in the control group under hypercapnia, but the increase was not statistically significant. The data indicate that NO in the NI has an inhibitory effect only when the respiratory drive is high (hypercapnia), probably acting on tidal volume. The observations reported in the present investigation, together with other studies on the presence of NOS in amphibians, indicate a considerable degree of phylogenetic conservation of the NO pathway amongst vertebrates.

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Central chemoreceptor drive to breathing in unanesthetized toads, Bufo paracnemis

Cited by 67 publications

References 20 publications

Respiratory pattern formation in the isolated bullfrog (Rana catesbeiana) brainstem-spinal cord

Respiratory pattern formation in the isolated bullfrog (Rana catesbeiana) brainstem-spinal cord

Locus coeruleus is a central chemoreceptive site in toads

Participation of nitric oxide in the nucleus isthmi in CO2-drive to breathing in toads

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