Recovery of monkey brain after prolonged ischemia. II. Protein synthesis and morphological alterations.

Recovery of protein synthesis following 1 h of complete ischemia of the monkey brain was assessed by 3H-labeled amino acid incorporation in vivo at various postischemic periods between 1.5 and 24 h. The regional autoradiographic patterns obtained were compared on the basis of precursor-product relationships determined biochemically at the end of the tracer incorporation studies. Shortly after ischemia, protein synthesis was severely inhibited, but it gradually recovered with increasing recirculation times. In the cerebellum it returned to almost normal levels within 3 h and in the cortex within 24 h. Hippocampal and thalamic regions, however, did not recover control levels of protein synthesis at 24 h. Histoautoradiographic evaluation of amino acid incorporation in individual neurons revealed recovery of pyramidal neurons in the CA1 and CA3 sectors of the hippocampus within 6 h of recirculation, which, however, was followed by secondary inhibition after longer recirculation. Neurons in cortical layer 5 steadily recovered to near control within 24 h, with the exception of those located in arterial border zones, which returned to only 50% of control at 24 h. Incomplete recovery was also observed in thalamic neurons and Purkinje cells. The regional and histoautoradiographic pattern of protein synthesis correlated with the morphological appearance of cells. Ischemic cell changes (mainly of the dark type with microvacuolization and perineuronal glial swelling) were marked after short recirculation times but gradually disappeared in parallel with the return of protein synthesis in most regions of the brain. Only in pyramidal cells of the hippocampus, thalamic neurons, and Purkinje cells were changes not reversed during the observation period. The results obtained corroborate the electrophysiological observations reported in the first part of this investigation and support the notion that the majority of the neurons of monkey brain survive complete cerebrocirculatory arrest of 1 h for at least 1 day.