BRIEF COMMUNICATION Expression of Neuron-Specific Enolase in Adult Rat Brain Following Status Epilepticus Steven S. Schreiber,* , † ,1 Ning Sun,* Georges Tocco,‡ Michel Baudry,‡ and Christopher M. DeGiorgio* , § *Departments of Neurology, †Department of Cell and Neurobiology, §Department of Neurosurgery, University of Southern California School of Medicine, Los Angeles, California 90033; and ‡Neuroscience Program, University of Southern California, Los Angeles, California 90089-0191 Received January 18, 1999; accepted May 15, 1999 Increased levels of neuron-specific enolase (NSE), a key glycolytic enzyme, in either the cerebrospinal fluid or the serum is correlated with both the duration and the outcome of status epilepticus. To further under- stand the molecular basis of seizure-induced eleva- tions in NSE protein, we investigated NSE mRNA expression in the adult rat brain following systemic administration of kainic acid. The findings demon- strated either no change or a decrease in NSE gene expression during, and following, status epilepticus, suggesting that posttranscriptional mechanisms are responsible for seizure-induced increases in NSE protein.  1999 Academic Press Key Words: neuron-specific enolase; status epilepti- cus; brain damage Neuron-specific enolase (NSE) is a key enzyme in- volved in the conversion of 2-phospho-D-glycerate to phosphoenolpyruvate during glycolysis (6). The NSE isoform is brain-specific but can also be detected in serum and cerebrospinal fluid (CSF) (6, 7). Recent evidence has demonstrated that NSE is a marker of neuronal damage following cerebral ischemia (3, 4). Elevated serum and CSF NSE levels have also been shown to vary directly with the duration of status epilepticus (SE) and are also predictive of outcome (2, 8). While increased NSE protein may be a marker of neuronal injury, whether there is a corresponding increase in NSE mRNA and/or protein synthesis follow- ing central nervous system (CNS) injury is currently unknown. Preexisting cytoplasmic NSE protein may be released into the extracellular space, diffuse across the blood–brain barrier, and directly reflect the magnitude of neuronal injury. Alternatively, neuronal injury may stimulate new NSE mRNA and/or protein synthesis. Answers to these questions are critical to understand- ing the role of NSE as a marker of neuronal damage. Since SE results in a significant increase in NSE protein levels in rodents (9), the present study investi- gated whether seizure-induced alterations in NSE pro- tein are accompanied by corresponding changes in NSE mRNA. SE was induced in adult male Sprague–Dawley rats (200–250 g) by systemic administration of the excito- toxin, kainic acid (KA, 10 mg/kg, sc) (10). Rats were decapitated under methoxyflurane anesthesia at 1 h, 8 h, 16 h and 5 days after the onset of KA-induced seizures (N = 3 or 4 rats per group). Untreated rats were used as controls. The brain was rapidly removed and frozen at -70°C. In situ hybridization and film autoradiography were performed on 10-μm frozen coro- nal sections at the level of the dorsal hippocampus as previously described (10). NSE sense or antisense complementary RNA probes were transcribed from a linearized plasmid containing the rat NSE gene (11). Duplicate sections were probed simultaneously each time and experiments were repeated twice. Hybridiza- tion with the sense probe revealed a low level of background signal (data not shown). Film autoradio- graphs were analyzed by optical densitometry using the BRAIN image analysis system as described (5). In brain sections from untreated control rats NSE mRNA was present in multiple regions including the hippocampus, striatum, thalamus, and neocortex, con- sistent with widespread neuronal expression (Fig. 1A). Up to 16 h following seizure onset, KA-vulnerable regions including the hippocampal CA1 and CA3 pyra- midal cell layers, piriform cortex, and thalamus exhib- ited either no change or a small decrease in NSE gene expression (Fig. 1B). A small increase in NSE mRNA 1 To whom correspondence should be addressed at Department of Neurology, USC School of Medicine, 1333 San Pablo Street, MCH 142, Los Angeles, CA 90033. Fax: (323) 225-2369. E-mail: sschreib@hsc.usc.edu. Experimental Neurology 159, 329–331 (1999) Article ID exnr.1999.7147, available online at http://www.idealibrary.com on 329 0014-4886/99 $30.00 Copyright  1999 by Academic Press All rights of reproduction in any form reserved.