Introduction
In addition to its role in the blood coagulation cascade, the serine protease thrombin has, depending on the specific conditions, either neuroprotective or neurotoxic effects on brain tissue during cerebral ischemia. Previous data suggest that thrombin-induced protection in vivo can be achieved by preconditioning rather than by acute treatment (Masada et al., 2000, Striggow et al., 2000). In the current approach we evaluated the regenerative potency of thrombin by injecting the protease repeatedly, starting from 1 week post ischaemia. As a parameter of neural damage we quantified the infarct areas.
Materials and methods
Male Sprague Dawley rats were used for all experiments. A guiding cannula was implanted under pentobarbitone anaesthesia 7 days before induction of ischaemia. We occluded the Middle Cerebral Artery by intracerebral injection of endothelin-1 (eMCAO) in freely moving animals. Thrombin (0.009 U/rat) was injected via the same guiding cannula intracerebrally on day 7, 8, 9 and 10 post ischaemia. Histological quantification of the infarct areas were performed 14 days post ischaemia.
Results
Control animals, which were injected with saline on day 7, 8, 9 and 10 post ischaemia developed an average infarct volume of 20.7±2.5 mm3. In rats which received 4 injections of thrombin we measured a damaged area of 12.6±1.9 mm3. Statistical analysis revealed a significant difference between both groups (Mann-Whitney, U-test; *p<0.05; N=12–15).
Conclusions
Data from literature indicate, that 7 days post eMCAO the ischaemic damage is fully developed. Therefore protection cannot be induced when we inject thrombin on day 7 post ischaemia. Also influences of thrombin on oedema are unlikely to be the cause of the reduced infarct volume, as there should be no pronounced oedema anymore on day of injection (7 d post ischaemia) or on day of decapitation (14 d post ischaemia). It has been shown that thrombin induces proliferation in astrocytes (Wang et al., 2002), but astrocytosis is defined as damaged area and therefore cannot account for the smaller infarct areas. Further studies are needed to examine the underlying mechanism of this reduction in infarct volume with late post-ischemic intracerebral injection of thrombin.