Proteinase-activated receptor-2 expression on cerebral neurones after radiation damage: Immunohistochemical observation in wistar rats

Radiation damage results in blood-brain barrier damage followed by blood plasma transfer into the neuropil. The transferred liquid contains high amounts of biologically active substances/proteinases including factor Xa and a free pool of serum trypsin, which is not bound to antiproteases (α 1 AT α 2 -macroglobulin). The aim of this study was to follow up expression of proteinase-activated receptor-2 (PAR-2) in the brains of Wistar rats after single exposure to radiation at 26 Gy ( 6 0 Co, 23 min, 15 sec). After irradiation, the animals were sacrificed on days 10, 20, 30 and 40. Control rat brains served as negative control. Coronal sections of caudal diencephalons were investigated using histology and immunohistochemistry. Polyclonal goat specified antibody against the NH-end of murine and rat PAR-2. Significant PAR-2 membrane positivity of scattered swollen neurons in deeper cortical layers was found in irradiated animals compared with controls. Although this membrane positivity was noticed in all irradiated animals, the most prominent occurred on day 30. Diffuse cytoplasmic positivity was also demonstrated on shrunken neurons in the cortex and hippocampus. Increased cytoplasmic and polarized membrane positivity was also noticed on the neurons of hypothalamic nuclei. The causal relationship between blood-brain barrier damage, PAR-2 activation and neurodegeneration has not yet been verified. However, the present findings indicate that PAR-2 mediates a certain cellular response. It remains to be demonstrated whether this is a response to higher concentrations of factor Xa, a free pool of trypsin or other unknown possible proteinases in brain tissue; whether changes in PAR-2 expression are consequences of direct radiation damage to neuronal cells; whether this reaction is protective; and whether primary PAR-2 activation results in neuronal damage.