INDUCTION OF 72 KDA HEAT-SHOCK-PROTEIN FOLLOWING SUBLETHAL OXYGEN DEPRIVATION IN ORGANOTYPIC HIPPOCAMPAL SLICE CULTURES

The phenomenon of induced tolerance to a normally lethal episode of is chaemia by preconditioning with sub-lethal ischaemia has been linked t o induction of the 72 kDa heat-shock. protein (HSP72). However, a dire ct correlation between HSP72 expression and ischaemic preconditioning in vivo has not been proven, Using an in vitro model of ischaemia-rela ted neuronal damage we have investigated whether HSP72 protein express ion is temporally correlated with subsequent tolerance to a normally l ethal ischaemic episode, Organotypic hippocampal slice cultures were m aintained in vitro for 14 days before being exposed to hypoxia for 15- 180 min, Periods of hypoxia shorter than GO min did not produce neuron al damage. No HSP72 immunoreactivity was observed in either untreated cultures or in those exposed to hypoxia for 15 min, Following 30 and 4 5 min hypoxia a significant induction of HSP72 occurred in neurons of both the CA1 and CA3/4 regions of the pyramidal cell layer. A signific ant number of microglia were positively stained with HSP72. The peak o f HSP72 expression occurred 18 h after the induction of hypoxia hut re mained significantly elevated for 45 h post-hypoxia. Prolonged hypoxia (60 or 180 min) produced a selective lesion of the CA1 pyramidal cell layer which was not associated with an induction of HSP 72, Pre-condi tioning with 45 min hypoxia 18 h prior to 180 min hypoxia did not redu ce the neuronal damage associated with 180 min hypoxia alone, These da ta strongly suggest that HSP72 does not directly confer tolerance in t his in vitro model of ischaemia-related neuronal death.