CHANGES IN C-FOS MESSENGER-RNA IN THE NEONATAL RAT-BRAIN FOLLOWING HYPOXIC ISCHEMIA

We used quantitative in situ hybridization to study changes in the exp ression of c-fos following hypoxic-ischemia (H-I) in the neonatal rat brain. 7-day-old rat pups were subjected to a unilateral ligation of t he common carotid artery followed by a 2 h 15 min hypoxic period (7.7% O-2 in N-2). This resulted in the expected ipsilateral infarction of cortex, lateral hippocampus, lateral-superior aspects of the striatum and the white matter of the corpus callosum. Brain damage was not seen in the contralateral hemisphere subjected only to hypoxia. c-fos mRNA levels increased in the contralateral hemisphere immediately after th e hypoxia and had returned towards normal levels 2 h thereafter. In th e ipsilateral hemisphere, the expression of c-fos was delayed but very marked at 2 h. Animals subjected only to hypoxia showed little or no increase in c-fos mRNA. Thus the earliest recorded increase in c-fos a fter hypoxic ischemia, which occurred on the non-ischemic, contralater al side, may represent a generalized response to a more localized insu lt.