Sites of respiratory rhythmogenesis during development in the tadpole

2001 ◽  
Vol 280 (4) ◽  
pp. R913-R920 ◽  
Author(s):  
C. S. Torgerson ◽  
M. J. Gdovin ◽  
J. E. Remmers
Keyword(s):  
Brain Stem ◽  
Rana Catesbeiana ◽  
Lung Ventilation ◽  
Respiratory Rhythmogenesis ◽  
Amphibian Larvae ◽  
Before And After ◽  
Lung Ventilator ◽  
Necessary And Sufficient ◽  
Stem Segments

During ontogeny, amphibian larvae experience a dramatic alteration in the motor act of breathing as the premetamorphic gill breather develops into the postmetamorphic lung ventilator. We tested the hypothesis that the site of lung rhythmogenesis relocates during metamorphosis by recording fictive lung ventilation before and after transecting the in vitro brain stem of pre- and postmetamorphic Rana catesbeiana into four segments. In premetamorphic tadpoles, the two caudalmost brain stem segments combined proved to be the minimum brain stem configuration necessary and sufficient for lung burst generation. In the postmetamorphic counterpart, this function was supplied by the combination of the two rostralmost brain stem segments. In the postmetamorphic brain stem, a 500-μm segment lying just rostral to cranial nerve IX conveys rhythmogenic capability to neighboring rostral or caudal segments. We conclude that lung rhythmogenic capability translocates rostrally during development as the tadpole shifts from gill to lung ventilation.

Location of central respiratory chemoreceptors in the developing tadpole

2001 ◽  
Vol 280 (4) ◽  
pp. R921-R928 ◽  
Author(s):  
C. S. Torgerson ◽  
M. J. Gdovin ◽  
R. Brandt ◽  
J. E. Remmers
Keyword(s):  
Cerebrospinal Fluid ◽  
Brain Stem ◽  
Rana Catesbeiana ◽  
Lung Ventilation ◽  
Maximum Reduction ◽  
Amphibian Larvae ◽  
Artificial Cerebrospinal Fluid ◽  
Premetamorphic Tadpole

The location of central respiratory chemoreceptors in amphibian larvae may change as the central chemoreceptive function shifts from driving gill to driving lung ventilation during metamorphosis. We examined this possibility in the in vitro brain stem of the pre- and postmetamorphic Rana catesbeiana tadpole by microinjecting hypercapnic artificial cerebrospinal fluid (aCSF) while recording fictive lung ventilation. The rostral and caudal brain stem were separately explored systematically using injections of 11 nl of aCSF equilibrated with 100% CO2 that transiently acidified a 500-μm region, producing a maximum reduction in pH of 0.23 ± 0.06 at the site of injection. In postmetamorphic tadpoles, chemoreceptive sites were concentrated in the rostral compared with the caudal brain stem. No such segregation was observed in the premetamorphic tadpole. We conclude that, as in lung rhythmogenic function, respiratory chemosensitivity emerges rostrally in the amphibian brain stem during development.

Fictive Gill and Lung Ventilation in the Pre- and Postmetamorphic Tadpole Brain Stem

1998 ◽  
Vol 80 (4) ◽  
pp. 2015-2022 ◽  
Author(s):  
C. S. Torgerson ◽  
M. J. Gdovin ◽  
J. E. Remmers
Keyword(s):  
Brain Stem ◽  
Rana Catesbeiana ◽  
Low Frequency ◽  
Lung Ventilation ◽  
High Amplitude ◽  
Spinal Nerve ◽  
Gill Ventilation ◽  
Respiratory Behavior ◽  
Spontaneously Breathing

Torgerson, C. S., M. J. Gdovin, and J. E. Remmers. Fictive gill and lung ventilation in the pre- and postmetamorphic tadpole brain stem. J. Neurophysiol. 80: 2015–2022, 1998. The pattern of efferent neural activity recorded from the isolated brain stem preparation of the tadpole Rana catesbeiana was examined to characterize fictive gill and lung ventilations during ontogeny. In vitro recordings from cranial nerve (CN) roots V, VII, and X and spinal nerve (SN) root II of premetamorphic tadpoles showed a coordinated sequence of rhythmic bursts occurring in one of two patterns, pattern1, high-frequency, low-amplitude bursts lacking corresponding activity in SN II and pattern 2, low-frequency, high-amplitude bursts with coincident bursts in SN II. These two patterns corresponded to gill and lung ventilatory burst patterns, respectively, recorded from nerve roots of decerebrate, spontaneously breathing tadpoles. Similar patterns were observed in brain stem preparations from postmetamorphic tadpoles except that they showed a greater frequency of lung bursts and they expressed fictive gill ventilation in SN II. The laryngeal branch of the vagus (Xl) displayed efferent bursts in phase with gill and lung activity, suggesting fictive glottal constriction during gill ventilation and glottal dilation during lung ventilation. The fictive gill ventilatory cycle of pre- and postmetamorphic tadpoles was characterized by a rostral to caudal sequence of CN bursts. The fictive lung ventilatory pattern in the premetamorphic animal was initiated by augmenting CN VII discharge followed by synchronous bursts in CN V, X, SN II, and Xl. By contrast, postmetamorphic patterns of fictive lung ventilation were characterized by lung burst activity in SN II that preceded burst onset in CN V and followed the lead burst in CN VII. We conclude that recruitment and timing of pattern 1 and pattern 2 rhythmic bursts recorded in vitro closely resemble that recorded during spontaneous respiratory behavior, indicating that the two patterns are the neural equivalent of gill and lung ventilation, respectively. Further, fictive gill and lung ventilatory patterns in postmetamorphic tadpoles differ in burst onset latency from premetamorphic tadpole patterns and resemble fictive oropharyngeal and pulmonary burst cycles in adult frogs.

Central respiratory activity of the tadpole in vitro brain stem is modulated diversely by nitric oxide

2002 ◽  
Vol 283 (2) ◽  
pp. R417-R428 ◽  
Author(s):  
Michael B. Harris ◽  
Richard J. A. Wilson ◽  
Konstantinon Vasilakos ◽  
Barbara E. Taylor ◽  
John E. Remmers
Keyword(s):  
Nitric Oxide ◽  
Rana Catesbeiana ◽  
Lung Ventilation ◽  
Central Chemosensitivity ◽  
Respiratory Rhythmogenesis ◽  
Specific Frequency ◽  
Central Respiratory Activity ◽  
Ph Conditions ◽  
Respiratory Rhythms

Nitric oxide (NO) is a potent central neuromodulator of respiration, yet its scope and site of action are unclear. We used 7-nitroindazole (7-NI), a selective inhibitor of endogenous neuronal NO synthesis, to investigate the neurogenesis of respiration in larval bullfrog ( Rana catesbeiana) isolated brain stems. 7-NI treatment (0.0625–0.75 mM) increased the specific frequency of buccal ventilation (BV) events, indicating influence on BV central rhythm generators (CRGs). The drug reduced occurrence, altered burst shape, and disrupted clustering of lung ventilation (LV) events, without altering their specific frequency. LV burst occurrence and clustering also differed between pH conditions. We conclude that NO has diverse effects on respiratory rhythmogenesis, being necessary for the expression of respiratory rhythms, inhibiting the frequency of BV CRG, and affecting both shape and clustering of LV bursts through conditional modulation of LV CRG. We confirm central chemosensitivity in these preparations and demonstrate chemomodulation of LV burst clustering and occurrence but not specific frequency. Results support distinct oscillators underlying LV and BV CRGs.

Serotonergic modulation of respiratory motor output during tadpole development

2002 ◽  
Vol 93 (3) ◽  
pp. 936-946 ◽  
Author(s):  
Richard Kinkead ◽  
Olivier Belzile ◽  
Roumiana Gulemetova
Keyword(s):  
Brain Stem ◽  
Lung Ventilation ◽  
Receptor Activation ◽  
Motor Output ◽  
Burst Frequency ◽  
Bath Application ◽  
Age Dependent ◽  
Dose Dependent ◽  
Serotonergic Modulation

To test the hypothesis that serotonin (5-hydroxytryptamine; 5-HT)-receptor activation elicits age-dependent changes in respiratory motor output, we compared the effects of 5-HT bath application (5-HT concentration = 0.5–25 μM) onto in vitro brain stem preparations from pre- and postmetamorphic bullfrog tadpoles. Recording of motor output related to gill and lung ventilation showed that 5-HT elicits a dose-dependent depression of gill burst frequency in both groups. In contrast, the lung burst frequency response was stage dependent; an increase in lung burst frequency at low 5-HT concentration (≤0.5 μM) was observed only in the postmetamorphic group. Higher 5-HT concentrations decreased lung burst frequency in all preparations. Gill burst frequency attenuation is mediated (at least in part) by 5-HT1A-receptor activation in an age-dependent fashion. We conclude that serotonergic modulation of respiratory motor output 1) changes during tadpole development and 2) is distinct for gill and lung ventilation.

Central CO2 chemoreception in developing bullfrogs: anomalous response to acetazolamide

2003 ◽  
Vol 94 (3) ◽  
pp. 1204-1212 ◽  
Author(s):  
Barbara E. Taylor ◽  
Michael B. Harris ◽  
E. Lee Coates ◽  
Matthew J. Gdovin ◽  
J. C. Leiter
Keyword(s):  
Carbonic Anhydrase ◽  
Late Stage ◽  
Rana Catesbeiana ◽  
Early Stage ◽  
Lung Ventilation ◽  
Carbonic Anhydrase Activity ◽  
Spinal Nerve ◽  
Before And After ◽  
Hypercapnic Response

Central CO2 chemoreception and the role of carbonic anhydrase were assessed in brain stems from Rana catesbeiana tadpoles and frogs. Buccal and lung rhythms were recorded from cranial nerve VII and spinal nerve II during normocapnia and hypercapnia before and after treatment with 25 μM acetazolamide. The lung response to acetazolamide mimicked the hypercapnic response in early-stage and midstage metamorphic tadpoles and frogs. In late-stage tadpoles, acetazolamide actually inhibited hypercapnic responses. Acetazolamide and hypercapnia decreased the buccal frequency but had no effect on the buccal duty cycle. Carbonic anhydrase activity was present in the brain stem in every developmental stage. Thus more frequent lung ventilation and concomitantly less frequent buccal ventilation comprised the hypercapnic response, but the response to acetazolamide was not consistent during metamorphosis. Therefore, acetazolamide is not a useful tool for central CO2 chemoreceptor studies in this species. The reversal of the effect of acetazolamide in late-stage metamorphosis may reflect reorganization of central chemosensory processes during the final transition from aquatic to aerial respiration.

Excitatory and inhibitory effects of tricaine (MS-222) on fictive breathing in isolated bullfrog brain stem

2003 ◽  
Vol 284 (2) ◽  
pp. R405-R412 ◽  
Author(s):  
Michael S. Hedrick ◽  
Rachel E. Winmill
Keyword(s):  
Brain Stem ◽  
Rana Catesbeiana ◽  
Motor Output ◽  
Inhibitory Effects ◽  
Low Concentrations ◽  
Artificial Cerebrospinal Fluid ◽  
Channel Blocking ◽  
The Central Nervous System ◽  
Excitatory Neurotransmission

This study examined the direct effects of tricaine methanesulfonate (MS-222), a sodium-channel blocking local anesthetic, on respiratory motor output using an in vitro brain stem preparation of adult North American bullfrogs ( Rana catesbeiana). Bullfrogs were anesthetized with halothane, and the brain stem was removed and superfused with artificial cerebrospinal fluid containing MS-222 at concentrations ranging from 0.1 to 1,000 μM. At the lowest concentration of MS-222, respiratory frequency ( f R) increased significantly ( P < 0.05), but at higher concentrations, f R progressively decreased and was abolished in all preparations at 1,000 μM ( P < 0.01). Respiratory burst amplitude and burst duration were not affected by MS-222. The frequency of nonrespiratory neural activity did not significantly change with the addition of MS-222 below 1,000 μM. These data indicate that MS-222 has a significant, direct effect on respiratory motor output from the central nervous system, producing both excitation and inhibition of fictive breathing. The results are consistent with other studies demonstrating that low concentrations of anesthetics generally cause excitation followed by depression at higher concentrations. Although the mechanisms underlying the excitatory effects of MS-222 in this study are unclear, they may include increased excitatory neurotransmission and/or disinhibition of inputs to the respiratory central pattern generator.

Thyrotropin-releasing hormone stimulates perinatal rat respiration in vitro

1996 ◽  
Vol 271 (5) ◽  
pp. R1160-R1164 ◽  
Author(s):  
J. J. Greer ◽  
Z. al-Zubaidy ◽  
J. E. Carter
Keyword(s):  
Spinal Cord ◽  
Brain Stem ◽  
Thyrotropin Releasing Hormone ◽  
Neonatal Rat ◽  
Discharge Frequency ◽  
Releasing Hormone ◽  
Respiratory Rhythmogenesis ◽  
Fetal Rat ◽  
Bötzinger Complex

In the present study, we test whether thyrotropin-releasing hormone (TRH) stimulates respiratory frequency in perinatal rats by acting at regions of the medulla responsible for respiratory rhythmogenesis, the pre-Botzinger complex. We also test whether TRH stimulates respiration in the fetal rat at a time shortly after the inception of respiratory rhythmogenesis [embryonic days (E) 17-18]. Two in vitro experimental models were utilized: the isolated brain stem-spinal cord preparation from fetal (E17-E18) and neonatal [postnatal days (P) 0-2] rats and the medullary slice preparation isolated from neonatal rats (P1-P2). Bath application of TRH caused a dose-dependent, reversible increase (maximum increase approximately 60%) in the frequency of respiratory rhythmic neural discharge generated by brain stem-spinal cord [half-maximal effective concentration (EC50) approximately 9 nM] and medullary slice (EC50 approximately 2.5 nM) neonatal rat preparations. Pressure injection of TRH unilaterally into the region of the pre-Botzinger complex of the neonatal medullary slice caused an approximately 28% increase in the frequency of respiratory discharge. Application of TRH to the medium bathing fetal rat brain stem-spinal cord preparations caused an approximately threefold increase in respiratory discharge frequency. We conclude that TRH stimulates respiratory discharge frequency from the time near inception of respiratory motor discharge and acts directly at the pre-Botzinger complex.

Intercostal and Abdominal Respiratory Motoneurons in the Neonatal Rat Spinal Cord: Spatiotemporal Organization and Responses to Limb Afferent Stimulation

2008 ◽  
Vol 99 (5) ◽  
pp. 2626-2640 ◽  
Author(s):  
Aurore Giraudin ◽  
Marie-Jeanne Cabirol-Pol ◽  
John Simmers ◽  
Didier Morin
Keyword(s):  
Spinal Cord ◽  
Brain Stem ◽  
Neonatal Rat ◽  
Descending Pathways ◽  
Respiratory Rhythmogenesis ◽  
Electrophysiological Procedures ◽  
Low Threshold ◽  
Rhythmic Contractions ◽  
First Time

Respiration requires the coordinated rhythmic contractions of diverse muscles to produce ventilatory movements adapted to organismal requirements. During fast locomotion, locomotory and respiratory movements are coordinated to reduce mechanical conflict between these functions. Using semi-isolated and isolated in vitro brain stem-spinal cord preparations from neonatal rats, we have characterized for the first time the respiratory patterns of all spinal intercostal and abdominal motoneurons and explored their functional relationship with limb sensory inputs. Neuroanatomical and electrophysiological procedures were initially used to locate intercostal and abdominal motoneurons in the cord. Intercostal motoneuron somata are distributed rostrocaudally from C7–T13 segments. Abdominal motoneuron somata lie between T8 and L2. In accordance with their soma distributions, inspiratory intercostal motoneurons are recruited in a rostrocaudal sequence during each respiratory cycle. Abdominal motoneurons express expiratory-related discharge that alternates with inspiration. Lesioning experiments confirmed the pontine origin of this expiratory activity, which was abolished by a brain stem transection at the rostral boundary of the VII nucleus, a critical area for respiratory rhythmogenesis. Entrainment of fictive respiratory rhythmicity in intercostal and abdominal motoneurons was elicited by periodic low-threshold dorsal root stimulation at lumbar (L2) or cervical (C7) levels. These effects are mediated by direct ascending fibers to the respiratory centers and a combination of long-projection and polysynaptic descending pathways. Therefore the isolated brain stem-spinal cord in vitro generates a complex pattern of respiratory activity in which alternating inspiratory and expiratory discharge occurs in functionally identified spinal motoneuron pools that are in turn targeted by both forelimb and hindlimb somatic afferents to promote locomotor-respiratory coupling.

Ontogeny of central chemoreception during fictive gill and lung ventilation in an in vitro brainstem preparation of Rana catesbeiana

1997 ◽  
Vol 200 (15) ◽  
pp. 2063-2072 ◽  
Author(s):  
C Torgerson ◽  
M Gdovin ◽  
J Remmers
Keyword(s):  
Rana Catesbeiana ◽  
Cranial Nerves ◽  
Lung Ventilation ◽  
Artificial Cerebrospinal Fluid ◽  
Gill Ventilation ◽  
Central Chemoreception ◽  
Bullfrog Tadpole ◽  
Spontaneously Breathing ◽  
Hypercapnic Response

An isolated brainstem preparation of the bullfrog tadpole, Rana catesbeiana, displays coordinated rhythmic bursting activities in cranial nerves V, VII and X in vitro. In decerebrate, spontaneously breathing tadpoles, we have previously shown that these bursts correspond to fluctuations in buccal and lung pressures and to bursts of activity in the buccal levator muscle H3a. This demonstrates that the rhythmic bursting activities recorded in vitro represent fictive gill and lung ventilation. To investigate the ontogeny of central respiratory chemoreception during the transition from gill to lung ventilation, we superfused the isolated brainstems of four larval stage groups with oxygenated artificial cerebrospinal fluid at various levels of PCO2. We measured shifts in the pattern of fictive respiratory output and the response to central hypercapnic stimulation throughout development. At normal PCO2 (2.3 kPa), stage 3&shy;9 tadpoles displayed rhythmic neural bursts associated with gill ventilation, while stages 10&shy;14 and 15&shy;19 tadpoles produced oscillating bursting activity associated with both gill and lung respiration, and tadpoles at stages 20&shy;25 displayed neural activity predominantly associated with lung ventilation. In stage 3&shy;9 tadpoles, variations in PCO2 of the superfusate (0.5&shy;6.0 kPa) caused almost no change in fictive gill or lung ventilation. By contrast, stage 10&shy;14 tadpoles showed a significant hypercapnic response (P&lt;0.05) in the amplitude and frequency of fictive gill ventilation, which was accompanied by a significant increase (P&lt;0.05) in the burst amplitude and respiratory output of cranial nerve X over that occurring at all other stages. The amplitude and frequency of fictive gill ventilation in stages 15&shy;19 increased significantly (P&lt;0.05) in response to pH reduction, but became insensitive to hypercapnia at stages 20&shy;25. The frequency of fictive lung ventilation was unresponsive to hypercapnia in stage 10&shy;14, increased significantly by stage 15&shy;19 (P&lt;0.05) and became maximal (P&lt;0.05) in stages 20&shy;25. Overall, we describe the ontological development of central respiratory chemoreceptors driving respiratory output in the larval amphibian, demonstrating transfer in central chemoreceptive influence from gill to lung regulation during metamorphic stages. In addition, we provide novel evidence for the stimulatory influence of central chemoreceptors on fictive gill ventilation in response to CO2.

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