Effect of focal low-frequency stimulation on amygdala-kindled afterdischarge thresholds and seizure profiles in fast- and slow-kindling rat strains.

PURPOSE

To determine whether low-frequency, 1-Hz sine-wave stimulation (LFS) applied to a fully kindled amygdala focus would show antiepileptic properties in rats that were either naturally seizure prone (Fast) or seizure resistant (Slow).

METHODS

Normal twisted and/or "spanning" bipolar electrode configurations were implanted in the amygdalae of adult male Fast and Slow rats. In experiment one, rats were kindled daily to stage-5 levels through one electrode type until stable afterdischarge thresholds (ADTs) were obtained. Next, LFS was applied through the kindled electrode, and ADTs were redetermined 1 min later, and daily for a week, without reapplying the LFS. In experiment two, a single, normal bipolar kindling electrode was implanted in the amygdala and centered between two poles of a spanning electrode. After stable kindled ADTs were obtained, LFS was applied to the amygdala "area" through the spanning electrode. ADTs were redetermined at the kindled electrode as earlier.

RESULTS

LFS through the kindling electrode had no effect on ADTs 1 min later, but the ADTs increased dramatically 24 h later and then slowly returned to baseline over days. In experiment two, LFS applied through the nonkindled spanning electrode also showed a small but significant threshold elevation at the interposing kindled electrode. Importantly, no obvious neuropathology was associated with these LFS treatments.

CONCLUSIONS

LFS applied directly to the kindled network has significant threshold-elevating properties that are less evident when applied to the "general area"; here LFS must be delivered through a larger surface area and/or at higher intensity.