Oxygen supply and respiratory-like activity in the isolated perfused brainstem of the adult guinea pig.
In isolated brainstem preparations of mature guinea pigs the respiratory network remains functional only if perfused internally via the basilar artery with Krebs solution equilibrated with 95% O2/5% CO2. In order to determine the oxygen availability in this preparation, we measured tissue partial oxygen pressures at the level of respiratory-related neurons using oxygen-sensitive microelectrodes. To estimate oxygen consumption we studied the effects of ischemia and cyanide-induced blockade of oxidative metabolism in relation to the respiratory-like rhythmic activity recorded from the hypoglossal nerve. The pO2 profiles obtained from 9 stepwise measurements from the ventral to the dorsal surface decreased from 423 +/- 32 (SE) mmHg on the ventral surface to 219 +/- 64 mmHg at 1900 microns and stabilized near this value up to a depth of 5000 microns. In the superfused preparation without internal perfusion pO2 was 0 mmHg within the first 500 microns. An interruption of perfusion resulted in a rapid (less than 2 min) decrease of tissue pO2 to 0 mmHg. During the ischemic period, respiratory-like neural activity exhibited first an increase in frequency and tonic discharge, followed by a marked decrease in both parameters. Cyanide added to the perfusate caused an immediate increase of tissue pO2 and the drop of tissue pO2 associated with ischemia was abolished. We conclude that there is a considerable oxygen consumption but no hypoxic or anoxic core in the isolated perfused brainstem at the level of the respiratory-related neurons.
Department of Applied Physiology, Ruhr-University, Bochum, Germany.
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Schäfer
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Morin-Surun
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Denavit-Saubié
D000818:Animals; D001933:Brain Stem / Q000187:drug effects / Q000378:metabolism*; D006168:Guinea Pigs; D007002:Hypoglossal Nerve / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D008526:Medulla Oblongata / Q000378:metabolism; D008839:Microelectrodes; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology*; D010477:Perfusion; D012966:Sodium Cyanide / Q000494:pharmacology
D012966:Sodium Cyanide