Molecular and Electrophysiological Analysis of Heterotopic Neurons in Rats Exposed to MAM In Utero
Abstract number :
1.008
Submission category :
Year :
2000
Submission ID :
2337
Source :
www.aesnet.org
Presentation date :
12/2/2000 12:00:00 AM
Published date :
Dec 1, 2000, 06:00 AM
Authors :
Peter A Castro, Edward C Cooper, Lily Y Jan, Jack M Parent, Samuel L Pleasure, Daniel H Lowenstein, Margaret L Sutherland, Scott C Baraban, UCSF, San Francisco, CA; UCSF, San Franscisco, CA; George Washington Univ, Washington, DC.
RATIONALE: Although brain malformations represent one of the major clinical findings in pediatric epilepsy, the cellular pathogenesis of these malformations remains unknown. To address this issue, we examined neuronal cell clusters (i.e., heterotopia) in a rodent model of dysplasia. METHODS: Pregnant Sprague-Dawley rats were injected with methylazoxymethanol (MAM; 25 mg/kg, i.p.) on E15. In situ hybridization was performed on 20 mm hippocampal sections using non-radiolabeled antisense riboprobes (P3-P20). Visualized whole-cell voltage-clamp recordings were performed on acute hippocampal slices (P10-P20). Slices were bathed in nACSF supplemented with TTX and CdCl2. RESULTS: In tissue sections from MAM rats (n = 45), hippocampal heterotopia expressed high levels of Id-2 mRNA (a cortical-specific marker), but lacked Math-2 mRNA (a hippocampal-specific marker). Normotopic and heterotopic pyramidal neurons expressed genes corresponding to the following potassium channels: Kv1.1-1.6, Kv2.1, Kvb1-b2,KvlQT1 and HERG1-3. Interestingly, the fast transient potassium channel gene (Kv4.2) was present only in normotopic pyramidal neurons. As expected, outward currents on normotopic pyramidal neurons were comprised of TEA-sensitive delayed rectifier and 4-AP-sensitive fast, transient K current components (n = 20). Tail current analysis of reversal potentials showed that outward currents were carried by K+ ions. Outward currents on heterotopic pyramidal neurons displayed a delayed rectifier current component with biophysical (and pharmacological) properties similar to those observed for normotopic pyramidal cells. However, a fast, transient outward current was not detected on any heterotopic neurons (n = 30). CONCLUSIONS: Our data suggest that i) heterotopic hippocampal neurons may be comprised of cortical cells, and ii) altered K channel expression contributes to the hyperexcitability of MAM hippocampi. Thus, animals with experimentally-induced malformations can provide valuable insights into mechanisms of epileptogenesis associated with dysplasia [Supported by March of Dimes and Sandler Family Supporting Foundations].