Study of the effect of post-ischaemic mild hypothermia after transient focal cerebral ischaemia on apoptosis and inflammation

Stroke is an important cause of death in industrialized countries and few therapeutic compounds are effective to ameliorate the outcome of stroke. Only hypothermia has proven to be a robust neuroprotectant in experimental stroke models. In our laboratory, the endothelin-1 (Et-1) rat model, in which Et-1 is infused adjacent to the middle cerebral artery to induce a transient focal cerebral ischaemia, is used to study the effects of hypothermia. In this model, the core and the penumbra of the insult are respectively represented by the striatum and the cortex. Anaesthetized rats (with sevoflurane) are kept either under normothermic (37°C) or post-ischaemic mild hypothermic (34°C for 2 h) conditions. In previous research, our laboratory correlated the volume of ischaemic damage and the degree of apoptosis 24 h after the insult. Hypothermia reduced apoptosis (by a reduction in caspase-3 stained cells) and infarct size in the cortex, but it had little effect on the striatum. Further investigations on possible pathways by which this occurred suggested that post-ischaemic mild hypothermia inhibited apoptosis in the penumbra by reducing neuronal nitric oxide synthase activity (nNOS). The aim of the present study is to look at these effects not only after 24 h, but after 72 h and one week as well. Besides, it is believed that hypothermia has an effect on inflammation too, so we will determine pro- and anti-inflammatory markers at the same time points. By immunohistochemistry on paraffin embedded coupes and by ELISA, it should be possible to quantitatively determine respectively interleukin-1 _, tumor necrosis factor _ and transforming growth factor _. Using behavioural experiments (cylinder test, neurological deficit score), we will investigate if there is an amelioration on motorological impairment as well. Our final objective is to determine the optimal time of onset and duration, i.e. best therapeutic window of hypothermia in the Et-1 rat model for focal cerebral ischaemia.