Neuronal damage after repeated 5 minutes of ischemia in the gerbil is preceded by prolonged impairment of protein metabolism

Abstract

The effect of single or repeated episodes of cerebral ischemia on protein biosynthesis and neuronal injury was studied in halothane-anesthetized gerbils by autoradiography of [14C]leucine incorporation into brain proteins and light microscopy. For quantification of the protein synthesis rate, the steady-state precursor pool distribution space for labeled and unlabeled free leucine was determined by clamping the specific activity of [14C]leucine in plasma, and by measuring free tissue leucine in samples taken from various parts of the brain. Control values of protein synthesis were 14.6 +/- 2.2, 5.8 +/- 2.3, 14.2 +/- 3.1, and 10.0 +/- 3.8 nmol g-1 min-1 (means +/- SD) in the frontal cortex, striatum, CA1 sector, and thalamus, respectively. Following a single episode of 5 or 15 min of ischemia, protein synthesis recovered to normal in all brain regions except the CA1 sector, where it returned to only 50% of control after 6 h and to less than 20% after 3 days of recirculation. After three episodes of 5 min of ischemia spaced at 1 h intervals, protein synthesis remained severely suppressed in all brain regions after both 6 h and 3 days of recirculation. Inhibition of protein synthesis after 6 h predicted histological injury after 3 days of recirculation. In animals submitted to a single episode of 5 or 15 min of ischemia, histological damage was restricted to the CA1 sector but injury occurred throughout the brain after three episodes of 5 min of ischemia. These observations demonstrate that persisting inhibition of protein synthesis following cerebral ischemia is an early manifestation of neuronal injury. Prevention of neuronal injury requires restoration of a normal protein synthesis rate.