CORTICAL DC SHIFTS ASSOCIATED WITH CHANGES OF VENTILATION RATE

The shifts of the cortical steady potential (DC-component) associated with changes of the ventilation rate (VR) were studied in anesthetized rats. The following results have been obtained: 1. A decrease of VR releases a surface-positive DC displacement, and vice versa. The voltage of the evoked DC shifts is linearly related to the pH and to the log pCO2. Within a medium range, simultaneously occuring fluctuations of the cortical pO2 prove ineffective. However, if they exceed a critical lower and upper level they give rise to surface-negative DC responses which interfere with the actions of the pCO2 and pH, respectively. 2. The induced DC shifts are associated with typical alterations of both spontaneous and evoked EEG waves. They coincide, furthermore, with changes of the membrane potential and of excitatory postsynaptic potentials (EPSP) in single spinal and cortical neurons. Thus, the positive DC deflection during hypoventilation is accompanied by a moderate hyperpolarisation and by a depression of both mono- and polysynaptic EPSPs in the majority of cortical and lumbar units. 3. The present findings allow to conclude that neuronal membrane potentials may contribute, in principal, to the observed DC shifts. The possible participation of other generator structures is discussed. © 1969 Springer-Verlag.