Epileptiform activity in supragranular and infragranular blocks of mouse neocortex

Murine neocortical tissue blocks 450 microm in diameter displayed prolonged epileptiform bursts when exposed to magnesium-free medium in vitro; no evidence was found for a correlation between the ability to generate paroxysmal bursts and barrels, the specialized cortical modules or 'columns' found in rodent primary sensorimotor cortex. While previous reports suggested that preferential locations for the generation of epileptiform bursts exist within the six-layered structure of the neocortex, we find that cortical sections only containing either the supragranular or infragranular layers and an estimated 2000 neurones are capable of displaying epileptiform bursting. The subdivided blocks are markedly more sensitive to the inhibitory effects of bath-applied adenosine (100 microM) than intact blocks from the same animal. A similar enhancement of adenosine sensitivity is seen when the tissue is superfused with hypotonic ACSF (a model for injury-induced brain swelling), which by itself increases excitability. The increase in sensitivity to adenosine is a transient effect and may be related to its role as acute neuroprotective agent.