Ž . Molecular Brain Research 56 1998 133–145 Research report Hippocampal Myc and p53 expression following transient global ischemia L. McGahan a , A.M. Hakim b , G.S. Robertson a, ) a Department of Pharmacology, Faculty of Medicine, UniÕersity of Ottawa, 451 Smyth Road, Ottawa, Ontario, Canada K1N 8M5 b Neuroscience Research Institute, Faculty of Medicine, UniÕersity of Ottawa, 451 Smyth Road, Ottawa, Ontario, Canada K1N 8M5 Accepted 3 February 1998 Abstract The proto-oncogene c-myc, and the tumor suppressor gene p53, encode proteins which function as transcriptional regulating factors governing cell proliferation, differentiation, and apoptosis. Recent evidence suggests that the delayed neuronal death which follows an episode of transient forebrain ischemia may involve apoptotic processes. We have therefore utilized immunohistochemistry to investigate the effects of transient global ischemia on neuronal expression of p53- and Myc-like immunoreactivities in the rodent forebrain 2, 12, 24, Ž . Ž . 48, and 72 h following reperfusion. Transient global ischemia 20 min , produced by four vessel occlusion 4-VO , initially elevated p53-like immunoreactivity in both CA1 and CA3 hippocampal subfields at 24 h of recirculation. However, distinct patterns of gene expression became evident in these regions at later time points. A pivotal difference was the persistence of ischemia-induced increases of p53- and Myc-like immunoreactivity in the CA1 region of the hippocampus. Unlike CA3 neurons where p53-like immunoreactivity subsided to basal levels by 48 h of survival, CA1 neurons continued to display increased p53-immunoreactivity 48 h post-ischemia, while Myc-like immunoreactivity was selectively elevated in CA1 neurons at this time point. Ischemia-induced increases in p53-like immunoreactivity were also detected in vulnerable regions of the amygdala, thalamus, and cortex 12 to 48 h after recirculation. Given that both p53 and Myc have been implicated in gene signalling pathways which mediate programmed cell death, our findings which demonstrate that 4-VO produces persistent elevations of p53- and Myc-like immunoreactivities in vulnerable neurons suggest that these proteins may also contribute to delayed neuronal death following an episode of transient forebrain ischemia. q 1998 Elsevier Science B.V. Keywords: Ischemia; Proto-oncogene; Tumor suppressor gene; Apoptosis; Selective vulnerability 1. Introduction Transient global ischemia produced by four-vessel oc- Ž . clusion 4-VO results in delayed neuronal loss in selected w x regions of the brain 42 . In the rat hippocampus, 20 min of 4-VO primarily damages CA1 pyramidal neurons w x 23,40,46 . These neurons degenerate slowly following reperfusion with death occurring 48–72 h after the is- w x chemic insult 42 . By comparison, CA3 pyramidal neu- Abbreviations: ANOVA, one-way analysis of variance; 4-VO, four- vessel occlusion; IEGs, immediate-early genes; PBS, phosphate buffered saline ) Corresponding author. Dept. of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, 451 Smyth Road, Ottawa, ON, Canada K1N 8M5. Fax: q1-613-562-5434; E-mail: grobert@labsun1.med.uottawa.ca rons are more resistant to ischemic stress. Despite intense investigations, the mechanisms by which CA1 neurons degenerate after transient global ischemia remains unclear. Several lines of evidence suggest that apoptotic mecha- nisms may contribute to the death of CA1 neurons follow- ing an episode of forebrain ischemia. Firstly, DNA frag- mentation, suggestive of apoptosis, has been demonstrated in CA1 neurons 48 h after transient global ischemia w x 20,24,30,48,51 . Secondly, morphological alterations char- acteristic of apoptotic death such as the appearance of dense chromatin masses and apoptotic bodies have been detected in the nuclei of degenerating CA1 neurons by w x electron microscopy 25,26,36 . Thirdly, ischemia rapidly enhances neuronal expression of immediate-early genes Ž . IEGs which encode transcriptional regulating factors known to participate in gene signalling pathways that w x mediate apoptosis 6,10,17,35,53 . 0169-328Xr98r$19.00 q 1998 Elsevier Science B.V. All rights reserved.