Early postanoxic changes of polyphosphoinositides and bound Ca2+ content in relation to neuronal activity in brain...

We studied the changes in the content of membrane-bound calcium (Cab) and the polyphosphoinositides (poly-PI): bis- and trisphosphoinositide (PIP and PIP2) in the cat brain cortex during the early period (up to 30 min) of reoxygenation after 2.5 min and 5 min of anoxia. In vivo experiments were performed on a living cat cortical preparation. Studies included Cab estimation with clortetracycline, a calcium fluorescent chelate probe, and simultaneous registration of neuronal activity. Anoxia resulted in a significant drop of Cab and PIP2 in the cortex along with an absence of neuronal activity. During reoxygenation after 2.5 min of anoxia we observed an increase of Cab, however the Cab did not recover to the preanoxic level. An elevation of PIP and PIP2 content to 20% above the preanoxic level and recovery of neuronal activity with symptoms of hyperactivation were also observed. After 5 min of anoxia two qualitatively different types of changes were disclosed for the 30 min period of reoxygenation. In one half of the animals only slight symptoms of recovery in some of the indices were found. In the other group Cab and PIP2 content increased to a level significantly exceedingly the preanoxic one and abnormal spike activity appeared. Based on these results we suggest that disturbances in Ca- and poly-PI-related second messenger systems may significantly affect the recovery of neuronal function after anoxia.