RECOVERY OF PROTEIN-SYNTHESIS IN TOLERANCE-INDUCED HIPPOCAMPAL CA1 NEURONS AFTER TRANSIENT FOREBRAIN ISCHEMIA

Protein synthesis at various recirculation times after 5-min transient forebrain ischemia was evaluated in gerbil hippocampal CA1 pyramidal neurons that had acquired tolerance to delayed-type ischemic injury. E valuation was performed by observing polyribosomes under electron micr oscopy, and by [C-14] leucine autoradiography. Hippocampal CA1 pyramid al neurons in the gerbils acquired stable and reproducible tolerance t o delayed-type ischemic injury subsequent to a 5-min ischemia by pretr eatment that consisted of loading two 2-min ischemic periods at a 1-da y interval, followed by 48 h of recirculation. During the early phase following the 5-min ischemia, polyribosomal disaggregation, loss of de ndritic microtubules, and significant suppression of radiolabeled leuc ine incorporation were observed in the tolerance-induced CA1 neurons a s well as in the nontolerance-induced neurons. While these findings pe rsisted in the non-tolerance-induced neurons throughout the duration o f the experiment, most of the tolerance-induced neurons demonstrated r eaggregation of cytosomal ribosomes, increase in the number of dendrit ic microtubules, and restoration of impaired amino acid incorporation 24 h after the ischemia. These findings suggest that revovery of prote in synthesis during the early post ischemic phase is essential for CA1 neuron survival after ischemic injury.