Experiments were performed on intact and chronically undercut cat suprasylvian gyrus attempting to determine a critical minimum size of cortical aggregate for acetylcholine (Ach) induced epileptiform activity. Cortical seizure foci of different sizes, 4 × 4 mm, 2 × 2 mm, and 1 × 1 mm were made with filter papers wetted to contain equal fluid volumes with equimolar amounts of Ach per unit area for each experiment. Concentrations of Ach varied from 0.5% (3.4 nmoles/mm2) to 4% (28 nmoles/mm2). The following results were obtained: The probability of seizure increased with increasing focus size and with increasing amount of Ach per mm2 of filter paper. Seizure occurred reliably with small (1 × 1 mm) foci in intact animals with 28 nmoles of Ach, whereas only 6.8 nmoles was required in chronically undercut preparations of 31 days or more. Average time to seizure onset was 8.75 min and was not statistically different for different size foci. No minimum cortical aggregate size necessary for Ach induced seizure could be established with this method. The size may vary under differing stimulus conditions but the results suggest that a volume with linear dimensions of 1 mm or less would be large enough.
ASJC Scopus subject areas
- Developmental Neuroscience