Protease-activated receptor-1 mediates protection elicited by thrombin preconditioning in a rat 6-hydroxydopamine model of Parkinson's disease

The etiology of Parkinson's disease remains poorly understood, and current treatment options do not slow disease progression. Recently, chemical (thrombin) preconditioning (TPC) was found to be protective in a 6-hydroxydopamine (6-OHDA) model of the disease. It is important to understand the mechanisms behind these thrombin-induced protective effects. The current study was conducted in the rat to determine whether the protective effects of TPC are mediated via activation of protease-activated receptors (PARs). Preconditioning with specific local infusion of agonist peptides for PAR-1 and PAR-4 3 days before unilateral 6-OHDA administration (10 μg into the medial forebrain bundle) was tested. In addition, co-administration of a PAR-1 antagonist with TPC was examined. In a neurobehavioral assessment battery, PAR-1 agonist preconditioning provided protection in a vibrissae-elicited forelimb placing test, a forelimb-use asymmetry test, and a corner turn test. In addition, inclusion of a PAR-1 antagonist prevented the protective effects elicited by TPC. In contrast to the effects of the PAR-1 agonist, PAR-4 agonist preconditioning afforded no such protection. Indeed, in a lower-dose model of 6-OHDA (5 μg), PAR-4 preconditioning significantly increased behavioral deficits. These results indicate that the protective effects of TPC in this model are mediated through PAR-1 activation. Neither the effects of PAR-1 nor TPC on later 6-OHDA-induced behavioral deficits appeared to be mediated through (DA) content sparing. Further mechanistic studies on the actions of PAR-1 and PAR-4 as detrimental in experimental models of Parkinson's disease are warranted.