The long-term objective of this project is to understand the molecular mechanisms that contribute to the generation and spread of epileptiform activity in the brain. We will utilize the single-locus mutant mouse tottering (tg/tg) as a model for generalized epilepsy and petit mal seizures. Although the molecular lesion is unknown, a consistent finding is a noradrenergic (NE) axon-terminal hyper-innervation in the tg/tg forebrain. Development of this abnormality coincides with the onset of seizures. Recent data suggest that this NE hyperinnervation leads to elevated levels of cAMP in the cortex. Furthermore, functional alterations in GABAA receptors (GaRs) have been found in the cortex of tottering mice. Since cAMP is an important regulator of both protein phosphorylation and gene expression, this project focuses on related changes in cortical GaRs of tg/tg mice.
The specific aims are: (1) To test the hypothesis that GABA-gated 36Cl flux is reduced in tg/tg cortical microsacs compared to +/+ controls. The effects of NE agonists and antagonists on this process will be determined. (2) To test the hypothesis that NE hyperinnervation in tg/tg mice increases the phosphorylation of GaRs. This will involve incorporating 32P into cortical GaRs and studying the effects of NE agonists and antagonists. (3) To test the hypothesis that the tottering mutation results in alterations in the pharmacological properties of GaRs. We plan to determine binding parameters for GABA and benzodiazepine agonists and evaluate their specificity. (4) To test the hypothesis that aberrations in the expression of the GaR subunit gene family occur during the development of the tg/tg cortex. Abnormalities in tg/tg will initially be detected by polymerase chain reaction amplification of GaR subunit cDNAs and confirmed by Northern hybridization analysis of poly A+ RNA. During maturation of the cerebrum, the incidence of these alterations in GaRs will be compared to seizure onset. This information will be useful in understanding the induction and spread of epileptiform seizures.
