Altered hippocampal gene expression prior to the onset of spontaneous seizures in the rat post-status epilepticus model H. Hendriksen, 1 Nicole A. Datson, 3 Wim E. J. M. Ghijsen, 1 Erwin A. van Vliet, 1 Fernando H. Lopes da Silva, 1,2 Jan A. Gorter 1,2 and Erno Vreugdenhil 3 1 Swammerdam Institute for Life Sciences (SILS), Section Neurobiology, University of Amsterdam, Kruislaan 320, 1098 SM Amsterdam, The Netherlands 2 Stichting Epilepsie Instelling Nederland, 2100 AA Heemstede, The Netherlands 3 Division of Medical Pharmacology Leiden/Amsterdam Center for Drug Research, Leiden University, Medical Centre, P.O.Box 9503, 2300 RA Leiden, The Netherlands Keywords: epileptogenesis, hippocampus, latent period, mRNA, SAGE, tag Abstract Neuronal loss, gliosis and axonal sprouting in the hippocampal formation are characteristics of the syndrome of mesial temporal sclerosis (MTS). In the post-status epilepticus (SE) rat model of spontaneous seizures these features of the MTS syndrome can be reproduced. To get a global view of the changes in gene expression in the hippocampus we applied serial analysis of gene expression (SAGE) during the early phase of epileptogenesis (latent period), prior to the onset of the ®rst spontaneous seizure. A total of 10 000 SAGE tags were analyzed per experimental group, resulting in 5053 (SE) and 5918 (control group) unique tags (genes), each representing a speci®c mRNA transcript. Of these, 92 genes were differentially expressed in the hippocampus of post-SE rats in comparison to controls. These genes appeared to be mainly associated with ribosomal proteins, protein processing, axonal growth and glial proliferation proteins. Veri®cation of two of the differentially expressed genes by in situ hybridization con®rmed the changes found by SAGE. Histological analysis of hippocampal sections obtained 8 days after SE showed extensive cell loss, mossy ®bre sprouting and gliosis in hippocampal sub regions. This study identi®es new high-abundant genes that may play an important role in post-SE epileptogenesis. Introduction Among the different types of epilepsies, temporal lobe epilepsy (TLE) occupies a special position taking into consideration the seriousness of the clinical condition and the fact that a well-de®ned syndrome characterized by mesial temporal lobe sclerosis (MTS) appears to be associated with TLE. MTS consists of a number of neuropathological features affecting mainly the hippocampal forma- tion, namely neuronal loss, gliosis and axonal sprouting. There is evidence that cases of MTS, or at least some of them, may be preceded by a brain injury that is a consequence of repeated complex febrile convulsions. In some cases previous status epilepticus (SE) may have occurred in early childhood (Annegers et al., 1987; Fernandez et al., 1998; Sloviter & Pedley, 1998). The post-status epilepticus model, in which SE is induced by electrical stimulation of a limbic brain region, is a rat model that reproduces not only the neuropathological features but also the typical evolution of spontaneous seizure occurrence (Bertram & Cornett, 1993; Nissinen et al., 2000; Gorter et al., 2001a). One of the characteristics of this model is a latent period of approximately 1±2 weeks between the induced status epilepticus and the appearance of the ®rst spontaneous seizure. During this latent period, the brain undergoes several changes that ultimately lead to the occurrence of spontaneous seizures. Studying this particular period may provide a better understanding of the molecular and cellular basis of the process of epileptogenesis leading to MTS. There is a growing body of evidence from literature and from our own ®ndings that the processes associated with hippocampal epileptogenesis such as sprouting, gliosis and cell death but also changes in neurotransmitter and ion-channel functions may be the result of a cascade of changes in gene expression (Aronica et al., 2001b; Khrestchatisky et al., 1995; Lopes da Silva et al., 1995; Hendriksen et al., 1997; Hevroni et al., 1998). Therefore, we investigated the process of epileptogenesis at the molecular level using serial analysis of gene expression (SAGE). SAGE is a technique that allows the quantitative and simultaneous analysis of a large number of transcripts (Velculescu et al., 1995). We investigated differential gene expression of hippocampal tissue of animals killed at 8 days after induction of status epilepticus and just prior to the onset of spontaneous seizures. We compared the expression of more than 10 000 transcripts in the hippocampus of post-status epilepticus and control animals. This resulted in the identi®cation of 92 differentially expressed genes, the majority of which could be linked with changes in the biosynthesis of ribosomal proteins, protein processing, axonal growth and glial proliferation processes. Together, the differences in gene expression pro®les presented here are in agreement with our hypothesis that alterations in the expression of a cascade of multiple Correspondence: Dr J.A. Gorter, 1 as above. E-mail: gorter@science.uva.nl Received 12 June 2001, revised 16 September 2001, accepted 21 September 2001 European Journal of Neuroscience, Vol. 14, pp. 1475±1484, 2001 ã Federation of European Neuroscience Societies