Reprod. Nutr. Dev. 45 (2005) 647-662
DOI: 10.1051/rnd:2005051

Injury and recovery of pyramidal neurons in the rat hippocampus after a single episode of oxidative stress induced by intracerebroventricular injection of ferrous ammonium citrate

Wei-Yi Ong^a, Su-Fung Ling^b, Jin-Fei Yeo^b, Chuang-Chin Chiueh^c and Akhlaq A. Farooqui<sup>d

a</sup>  Department of Anatomy, National University of Singapore, Lower Kent Ridge Road, Singapore 119260, Singapore
^b  Department of Oral and Maxillofacial Surgery, National University of Singapore, Lower Kent Ridge Road, Singapore 119260, Singapore
^c  College of Pharmacy, Taipei Medical University, Taipei City 110, Taiwan (ROC)
^d  Department of Molecular and Cellular Biochemistry, The Ohio State University, Columbus, Ohio 43210, USA

(Received 7 December 2004; accepted 25 May 2005)

Abstract - The present study was carried out to elucidate the effect of a single episode of oxidative stress on pyramidal neurons of the rat hippocampus. A significant increase in the number of neurons that were immunolabeled for the toxic lipid peroxidation product, 4-hydroxynonenal (HNE) was observed in field CA3 of the hippocampus, at 1 day, 7 days and 14 days after intracerebroventricular injection of 1 L of 5mM ferrous ammonium citrate, compared to ammonium citrate injected controls at these time points. The number of HNE positive cells was fewer at 14 days, compared to 1 day, after ferrous ammonium citrate injection. The changes in HNE imunoreactivity were paralleled by changes in cytoplasmic phospholipase A₂ (cPLA₂) labeling in the pyramidal neurons in adjacent sections, suggesting that some of the HNE could have arisen as a result of peroxidation of arachidonic acid that was released by cPLA₂. Interestingly, despite the HNE and cPLA₂ labeling, no loss of neurons was observed in adjacent Nissl and Fluoro-Jade stained sections. Electron microscopy also showed that the HNE or cPLA₂ labeled cells had features of injured neurons, rather than necrotic neurons. The reduction of HNE immunoreactivity in neurons at 14 days after oxidative injury, and the absence of cell loss at any of the time intervals, shows that hippocampal pyramidal neurons have remarkable ability to recover from a single episode of oxidative stress, if repeated injury such as seizures / excitotoxicity could be avoided.

Key words: iron / neurodegeneration / 4-hydroxynonenal / cytosolic phospholipase A₂ / lipid peroxidation / antioxidant defenses

Corresponding author: Wei-Yi Ong ntongwy@nus.edu.sg

© INRA, EDP Sciences 2005