Abstracts

Inducible cAMP early repressor (ICER), produced from an alternate promoter of the cyclic AMP Response Element Modulator (CREM) gene, is a member of the cAMP response element binding protein (CREB) transcription family, which primarily acts to inhibit CRE binding dependent transcription. In addition, ICER has been hypothesized to play a role in excitotoxic neuronal injury. Here we have studied the role of CREM/ICER in neuronal injury and epileptogenesis. ICER/CREM null and wild type (WT) control mice are F1 hybrids produced from crossing mice heterozygous for the CREM/ICER gene deletion from multiple generation backcrossing in parental strains F9 129SvEv and F11 C57BL6. Status Epilepticus (SE) was induced in adult male mice with 1mg/kg methyl-scopolamine followed 30 minutes later with 320mg/kg pilocarpine HCl. SE was also induced in Sprague Dawley adult male rats by injection of 1mg/kg methyl-scopolamine followed 30-40 minutes later with 385mg/kg pilocarpine HCl. RT-PCR for mRNA expression of CREM and ICER was performed on hippocampal tissue of rats and mice after SE induction. Behavioral analysis of seizure semiology and morbidity was recorded. Following SE induction, ICER/CREM KO and WT mice were examined for spontaneous seizure activity. TUNEL staining was examined in the dentate gyrus of mice 76 hours after SE. ICER mRNA as measured by RT-PCR, is increased in the hippocampus of rats (8.6 fold, p=0.001) and WT mice (5.5 fold, p= 0.016) 24 hours after SE induction. In contrast, CREM mRNA does not increase at 1 hour (1.4 fold p=0.2) or 24 hours (1.2 fold, p=0.1), as measured in the DG of rats.
CREM KO and WT mice do not differ in their seizure semiology after pilocarpine induced SE, measured by behavioral analysis of falls, limb clonus, wild running and turning. The rate of mortality did not differ between KO and WT animals. KO: 3/12 (23.25%), vs. WT 5/19 (22.00%) p=0.94. Cell death does not differ between KO and WT mice as measured by cell density counts of TUNEL stained CA3 neurons (KO: 0.0036, n=3; WT: 0.0035, n=3, p=0.83). CREM KO mice, however, have an increased frequency of spontaneous seizures (KO: 0.025/hour, n=4 vs. WT 0.11/hour, n=3; p=0.037) following SE. ICER is significantly upregulated in the hippocampus after pilocarpine induced SE in both WT mice and rats, while CREM RNA levels do not change after SE. Absence of CREM/ICER in KO mice does not alter the severity of pilocarpine induced SE. CREM/ICER deletion does not protect CA3 pyramidal neurons from cell death following SE, suggesting that CREM/ICER is not necessary for neuronal death following SE. Also, differences in cell death are not responsible for the increase in spontaneous seizures in CREM/ICER KO mice. (Supported by K08 NS044869 F31 NS51943-01.)