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Anoxic disturbance of the isolated respiratory network of neonatal rats

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Abstract

Tissue oxygen (PO2), K+ (aKe), pH (pHe) and Ca2+ ([Ca2+]e) were measured in the region of the ventral respiratory group (VRG) in the in vitro brainstem-spinal cord preparation of neonatal rats. During tissue anoxia, elicited by superfusion of N2-gassed solutions, an initial increase in the frequency of respiratory activity, lasting between 2 and 12 min, turned into a frequency depression. During anoxia periods of up to 60 min, respiratory activity persisted in solutions containing CO2/bicarbonate, whereas a complete blockade was observed after 15–25 min in N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid- (Hepes)-buffered salines. After such anoxic apnea, respiratory rhythmicity could be reactivated by superfusion of hypoxic, CO2/bicarbonate-buffered solutions. In both types of hypoxic solutions, aKe increased by maximally 1.5mM, whereas an initial increase of pHe by up to 0.05 pH units turned, after 2–4 min, into an acidification which could exceed 0.5 pH units. In contrast, [Ca2+]e remained unaffected by anoxia. Addition of 2–5 mM cyanide (CN-) to oxygenated Hepes-buffered saline evoked an increase in PO2 in the VRG from 100 to more than 300 mmHg. The effects of CN- on respiratory activity, aKe and pHe were almost identical to those during anoxia. In oxygenated, CO2/bicarbonatefree solutions of different pH, however, an increase in pHe in the VRG led to a decrease in respiratory frequency, whereas a fall of pHe produced a frequency acceleration. A rise of aKe in the VRG by more than 2 mM as induced by superfusion of a 7 mM K+ solution led to a sustained increase of respiratory frequency. The results indicate that blockade of aerobic metabolism does not severely perturb K+ and Ca2+ homeostasis and that the biphasic response to anoxia is not directly related to the observed changes in PO2, aKe, pHe, or [Ca2+]e. In the respiratory network of neonatal mammals, CO2 might provide a stimulus for long-term maintenance of respiratory activity under oxygen depletion.

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Authors and Affiliations

  1. II. Physiologisches Institut, Universität Göttingen, Humboldtallee 23, D-37073, Göttingen, Germany

    A. Völker, Klaus Ballanyi & D. W. Richter

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  1. A. Völker
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  2. Klaus Ballanyi
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  3. D. W. Richter
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Völker, A., Ballanyi, K. & Richter, D.W. Anoxic disturbance of the isolated respiratory network of neonatal rats. Exp Brain Res 103, 9–19 (1995). https://doi.org/10.1007/BF00241960

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  • DOI: https://doi.org/10.1007/BF00241960

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