ONTOGENIC DIFFERENCES IN ENERGY-METABOLISM AND INHIBITION OF PROTEIN-SYNTHESIS IN HIPPOCAMPAL SLICES DURING IN-VITRO ISCHEMIA AND 24 H OF RECOVERY

The present study was designed to clarify whether ontogenetic differen ces in the vulnerability of the brain towards hypoxic-ischemic insults are only caused by the low cerebral energy demand of immature animals or whether there are additional mechanisms, such as protein synthesis (PSR), that may be involved in this phenomenon. We therefore measured tissue levels of adenylates and PSR in hippocampal slices from immatu re (E40) and mature (E60) guinea pigs fetuses and from adult guinea pi gs during in vitro ischemia and 24 h of recovery using a recently modi fied method. Hippocampal slices were incubated in a temperature contro lled flow-through chamber, gassed with 95% O-2/5% CO2. In vitro ischem ia was induced by transferring slices to a glucose-free artificial cer ebrospinal fluid (aCSF) equilibrated with 95% N-2/5% CO2. The duration of ischemia ranged from 10 to 40 min. Adenylates were measured by HPL C after extraction with perchloric acid. PSR was evaluated as the inco rporation rate of [C-14]leucine into proteins. Under control condition s, tissue levels in adenylates did not change, whereas PSR increased s lightly in hippocampal slices from mature fetuses and adult animals du ring a 24-h control incubation period. In slices from immature fetuses ATP levels were only maintained for 2 h. During in vitro ischemia the decline in ATP, total adenylate pool, and adenylate energy charge was much slower in slices from immature fetuses than in slices from matur e fetuses or adults. After in vitro ischemia, ATP and the total adenyl ate pool did not completely recover in mature fetuses and adults, wher eas adenylate energy charge almost returned to control values independ ently of the developmental stage. Two hours after in vitro ischemia PS R was undisturbed in slices from immature fetuses, but severely inhibi ted in slices from mature fetuses and adults. With ongoing recovery, P SR in mature fetuses returned to control values, while in adults it wa s still inhibited even 24 h after in vitro ischemia. From these result s we conclude that hippocampal slices prepared from mature guinea pig fetuses as well as from adult guinea pigs can be held metabolically st able during long-term incubation using a recently modified technique. However, in slices from immature fetuses a stable energy state could n ot be maintained for more than 2 h. We further conclude that postische mic disturbances in PSR closely reflect the ontogenetic changes in the vulnerability of the brain to ischemia and that low energy metabolism is certainly not the only cause of the increased vulnerability of the fetal brain to ischemia.