To examine the effect of NIC on PARP expression, total protein extracts were prepared from either untreated control cultures or from extracts prepared 12 h after a 4 h period of anoxia with or without pretreatment of NIC (12.5 mM). For a positive control, lanes 1 and 2 employed 20 μl of protein extract from human HL60 leukemia cells uninduced (lane 1) or induced (lane 2) to undergo apoptosis by the agent etoposide. In lanes 3, 4, and 5, equal amounts of neuronal protein extracts (25 μg/lane) were separated by 7.5% SDS-PAGE and were then immunoblotted with polyclonal anti-PARP antibody. Detection was by enhanced chemiluminescence. In lanes 1 and 2, extracts of the human HL60 cells were analyzed to compare migration of PARP and its 85 kDa proteolytic fragment. Lane 3 contained an extract from untreated rat hippocampal cultures. A decrease in the amount of 116 kDa PARP occurred within 12 h following anoxia exposure (lane 4). In lane 5, pretreatment with NIC (12.5 mM) 1 h prior to anoxic exposure inhibited PARP cleavage.