Cortical Release of Labeled Compounds during Arousal in the Cat: Correlations with Carbon Dioxide, Brain Temperature and EEG.

摘要

The release of Ca(2+), H2O, (C)-carboxyl-inulin, (H)-gamma-aminobutyric acid, (C)-taurine, (H)-5-hydroxytryptamine, (H)-norepinephrine and (H)-lysine from cerebral cortex into a superfusion medium was studied in vivo, using locally anesthetized, immobilized cats. Peaks in the rate of release of these compounds from the suprasylvian gyrus could be correlated with a diminished amplitude of the cortical EEG and with increases in brain temperature and levels of CO2 in alveolar air. Peaks correlated with pCO2 could still be observed after topical application of 0.0005 NaCN. Death, produced by an overdose of pentobarbital, resulted in a 45% drop in the release of Ca(2+) and H-GABA followed by irregular peaks in efflux. Superfusion of the cortical surface with a low Ca(2+) medium resulted in very regular oscillations in the efflux of a number of isotopes including Ca and H2O. These oscillations, which had a period of about 6 min, were best observed immediately before or after a train of seizures, while the efflux pattern during seizures was slightly more irregular; at each individual seizure, the Ca/H2O ratio fell to a minimum. On two occasions marked long term changes in the amplitude of the EEG were observed to correlate with a change in the amplitude of the oscillations. Hemodynamic factors are considered to affect the rate of release of isotopes into the superfusate but cortical metabolism is also likely to play a role in controlling the rate of release.