Summary
In anesthetized rabbits spirogram and diaphragmatic activity were examined during electrical stimulation, of regions of the medulla oblongata. One volley of repetitive stimuli per breath was applied. The volleys were triggered by the animal's own respiration.
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1.
Volleys of 120 msec duration, applied during inspiration, caused an immediate and transient inhibition of the diaphragmatic activity. After the end of the volley, the inspiration continued. An inspiratory rebound appeared: the tidal volume was increased; the inspiration was prolonged up to 124 msec. The respiratory rate decreased.
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2.
Stimulation with 100–150 pulses p.s. and 0.5 msec pulse duration was optimal. With lower frequencies or shorter pulses the threshold was higher.
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3.
The stimulation effects were still present after bilateral cervical vagotomy. Respiration was partially inactivated by artificial hyperventilation or by inducing a metabolic alkalosis, and was activated by an additional dead space. Neither of these manoeuvres abolished or enhanced the stimulation effects.
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4.
The histological verification showed that inhibition and rebound activation could be elicited from a relatively widespread area in the medulla oblongata.
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5.
With afferent vagal stimulation with similar volleys, the same effects were observed.
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6.
Results suggest that the stimulus-induced inhibition either corresponds to the expiratory component of the Hering-Breuer reflex, or is caused by direct stimulation of inhibitory interneurones The inspiratory rebound may be due to a delay in the activation by the respiratory centre of the central inhibitory feedback mechanism.
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This work was supported by the “Freiwillige Akademische Gesellschaft der Stadt Basel” and the “Sandoz-Stiftung zur Förderung der medizinisch-biologischen Forschung”. We are indebted to Mr. W. Mehlhose for his help in the development of the electronic device and to Prof. H. Herzog. Kantonsspital Basle, for the blood gas analyses.
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Fallert, M. Inspiratory inhibition and rebound activation caused by intermittent bulbar and afferent vagal stimulation in the rabbit. Pflugers Arch. 348, 167–184 (1974). https://doi.org/10.1007/BF00586478
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DOI: https://doi.org/10.1007/BF00586478