RESPONSES OF RAT HIPPOCAMPAL SLICES IN A HIGH-K-VIVO GLOBAL-ISCHEMIA(MEDIUM FOLLOWING IN)

1. We hypothesized that burst activity induced in rat hippocampal tiss ue by a high-K+ medium in vitro would be increased by a previous episo de of global ischaemia, severe enough to induce persistent neurologica l dysfunction. 2. Male Wistar rats that were subjected to 9 min of che st compression, sufficient to reduce blood pressure (BP) to zero, show ed evidence of neurological damage attributed to a global ischaemic in sult. Hindlimb function was impaired for 24-48 h and a susceptibility to sound-induced seizures was induced in 25 of 35 rats. The seizure su sceptibility cleared spontaneously within 2 weeks in 10 of 25 rats. 3. Hippocampal slices from postischaemic rats were prepared, tested for viability and were then exposed to an 8.0 mmol/L K+ artificial cerebro spinal fluid in vitro. Spontaneous epileptiform bursting activity in t he high-K+ medium was not increased. Instead, burst size decreased wit h time after ischaemia. 4. The decrement in bursting activity is attri buted to loss of cellular activity or integrity. These changes correla te with functional changes described by others, but not necessarily to histologically verifiable cell death. The time course of these change s was remarkably long, continuing for almost 3 weeks. Thus, a less-tha n-lethal ischaemia appears to induce neuronal changes, possibly revers ible, that continue for at least 20 days after the global ischaemic in sult.