Poly(ADP-ribose) polymerase-1 (PARP-1) overactivation plays a significant role in hypoglycemia-induced brain injury in adult rats. To determine the influence of postnatal age on PARP-1 activation, developing and adult male rats were subjected to acute hypoglycemia of equivalent severity and duration. The expression of PARP-1 and its downstream effectors, apoptosis-inducing factor (Aifm1), caspase 3 (Casp3), NF-kappaB (Nfkb1) and bcl-2 (Bcl2), and cellular poly(ADP-ribose) (PAR) polymer expression were assessed in the cerebral cortex, hippocampus, striatum, and hypothalamus at 0 h and 24 h posthypoglycemia. Compared with the control group, PARP-1 expression increased in the cerebral cortex of adult rats 24 h posthypoglycemia, but not at 0 h, and it was accompanied by increased number of PAR-positive cells. The expression was not altered in other brain regions. Aifm1, Nfkb1, Casp3, and Bcl2 expressions also increased in the cerebral cortex of adult rats 24 h posthypoglycemia. Conversely, hypoglycemia did not alter PARP-1 expression and its downstream effectors in any brain region in developing rats. These data parallel the previously demonstrated pattern of hypoglycemia-induced brain injury and suggest that PARP-1 overactivation may determine age- and region-specific vulnerability during hypoglycemia.