Metabolic control of respiratory neuronal activity and the accompanying changey-expiratory neurons

Expiratory-related neurons have been classified according to their phase relation within the respiratory cycle, their response to lung distension and collapse (alpha- and beta-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 extracellulary 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, Ealpha- Ebeta-, Ebeta- and IEbeta- neurons are inhibited by 3.5 mM AMP, but are activated by 10 mM citrate (with the exception of Ebeta+ units). Furthermore I cells are activated by ATP, while Ealpha and Ebeta units become inhibited. Vagotomy in some instances affected the response of some IEbeta units. An increase in spike density of IEbeta+ and Ealpha- cells is paralleled by a reduction of both the respiratory rate and the tidal volume, while a lower spike density in IEbeta+, IEbeta- and Ealpha- units is accompanied by increases in respiratory rate and tidal volume. In the case of Ebeta+ and Ebeta- cells lower activity is associated with an increased tidal volume. No metabolite-induced changes could be obtained with cardiovascular or unspecific reticular neurons.