Metabolic control of respiratory neuronal activity and the accompanying changes in breathing movements of the rabbit
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Expiratory-related neurons have been classified according to their phase relation within the respiratory cycle, their response to lung distension and collapse (α- and β-type), and to hyperventilation (tonic firing denoted by “+”, cessation of activity by “−”). The dorsal surface of the medulla oblongata was superfused with a metabolite-containing CSF solution and the activity of expiratory (E) and inspiratory-expiratory (IE) neurons was extracellularly recorded. The neuronal sub-types established by their functional behaviour could equally be distinguished by their differential response to one or several metabolites. In contrast to inspiratory (I) neurons, E − α , E + β , E − β and IE − β neurons are inhibited by 3.5 mM AMP, but are activated by 10 mM citrate (with the exception of E + β units). Furthermore I cells are activated by ATP, while Eα and Eβ units become inhibited. Vagotomy in some instances affected the response of some IEβ units. An increase in spike density of IE + β and E − α cells in paralleled by a reduction of both the respiratory rate and the tidal volume, while a lower spike density in IE + β , IE − β and E − α units is accompanied by increases in respiratory rate and tidal volume. In the case of E + β and E − β cells lower activity is associated with an increased tidal volume. No metabolite-induced changes could be obtained with cardiovascular or unspecific reticular neurons.
Key wordsBulbar respiratory centre Expiratory neurons Metabolic modifiers of neuronal activity Tidal volume Respiratory rate Stereotaxic mapping of respiratory neurons
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