Abstracts

Many new genetic models of epilepsy have been developed in mice over the past several years. In many cases, targeted disruption, modification, or over-expression of a gene has resulted in an epileptic phenotype that was not anticipated. The current study was initiated when an outbred, transgenic mouse strain, originally designed to cause a tissue-specific increase in polyamine levels, was observed having occasional spontaneous seizures. Tests were conducted to determine if the observed seizures correlated with the insertion of the transgene.
Male and female mice, age 10 weeks, were used. The mice were generated from a colony that had been started with the F1 generation of a C57B1 / CBA crossing. Of the 30 mice tested in this pilot study, 17 carried a transgene that linked the Beta-4 Galactosyltransferase-I promoter with the antizyme inhibitor gene. The other 13 mice evaluated were littermates that tested negative for the transgene insertion.
To determine if a difference in seizure thresholds existed between the two groups, a heparinized Metrazol solution, (0.5%) was infused at a constant rate of 0.34 ml/min into a lateral tail vein of an unrestrained mouse. Infusion was by means of a Sage syringe pump (model 341A) and a 10 ml B-D plastic syringe connected to a length of No 20 P.E. tubing. A 27 gauge stainless steel needle with the hub removed was connected to the tubing and inserted into a vein and secured to the tail by a piece of adhesive tape. At the start of the infusion a hemostat clamped to the tubing to prevent backflow was removed, the infusion started, and two stopwatches started. The time in seconds from the start of the infusion to the appearance of the [quot]first twitch[quot] and the onset of sustained clonus were recorded. The times to each endpoint were converted to mg/kg of Metrazol for each mouse.
A two-sample test of means, using Smith[rsquo]s Statistical Package for the Macintosh, was used to determine statistical significance between the two groups.
The following table demonstrates the calculated differences between the control group of mice, and those carrying the transgene.[table1]The dose of Metrazol necessary to induce both the first twitch and clonus was reduced by nearly 30% in the carrier group.
These data show a significant decrease in the seizure threshold of the transgene carrier mice in our colony. Further investigations are currently underway to determine if this difference in response is a result of an increased level of polyamines in sensitive regions of the brain, or the inadvertent disruption of another gene. Regardless of the cause, the mice show potential as a new model for the study of epilepsy.
[Supported by: Internal sources]