Protection Against Blood-Brain Barrier Permeability as a Possible Mechanism for Protective Effects of Thymoquinone Against Sickness Behaviors Induced by Lipopolysaccharide in Rats

Background: Blood-brain barrier (BBB), as well-known protection for the brain, plays an active role in normal homeostasis. It might be changed by a range of inflammatory mediators to have a role in sickness behaviors. Objectives: Regarding the anti-inflammatory effects of thymoquinone (TQ), its protection against BBB permeability, as a possible mechanism for protective effects against sickness behaviors elicited by lipopolysaccharide (LPS), was evaluated in rats. Methods: The animals were grouped as follows and treated (n = 10 in each): (1) control (saline); (2) LPS 1 mg/kg, was injected two hours before behavioral tests for two weeks; (3-5) 2, 5, and 10 mg/kg TQ, respectively was injected 30 min before LPS injection. Open-field (OF), elevated plus-maze (EPM) and Forced Swimming test (FST) were done. Finally, the animals were anesthetized to evaluate for BBB permeability using Evans blue (EB) dye method. Results: Compared with control, LPS decreased the peripheral distance and crossing and also total crossing and distance in OF, (P 0.01 - P 0.001). The central crossing and distance and central time in all three treatment groups were more than LPS (P 0.05 - P 0.001). LPS also reduced the entries and the time spent in the open arm while increased the time spent in the closed arm in EPM (P 0.05 - P 0.001). The effects of LPS were reversed by TQ (P 0.05 - P 0.001). In FST, the immobility time and active time were increased and decreased by LPS compared with control (P 0.001), respectively. In all three TQ-treated groups, the active and climbing times were more while the immobility time was fewer than the LPS (P 0.05 - P 0.001). The animals of the LPS group showed more EB dye content in their brain tissue than the control group (P 0.05 - P 0.001). TQ significantly reduced EB dye content of the brain tissues (P 0.05 - P 0.001). Conclusions: According to this study, protection against BBB permeability as a possible mechanism for the protective effects of TQ against sickness behaviors induced by LPS might be suggested.