Propofol acts at the sigma-1 receptor and inhibits pentazocine-induced c-Fos expression in the mouse posterior cingulate and retrosplenial cortices
The sigma-1 receptor is functionally linked with psychotomimetic effects of various drugs. A sigma-1 receptor agonist enhances bradykinin-induced intracellular Ca2+ concentration ([Ca2+]i) increase and induces c-Fos expression in a part of the brain. The aim of this study was to investigate the effects of several intravenous anaesthetics on the sigma-1 receptor. Methods:
First, using Wistar rat brains, (+)[3H]SKF-10,047, a selective sigma-1 receptor agonist was displaced by propofol, dexmedetomidine, droperidol, and thiopental. Second, Fura-2 loaded NG-108 cells were incubated with (+)pentazocine, a selective sigma-1 receptor agonist, and propofol and then its fluorescence was observed after stimulation with bradykinin. Third, male ICR mice received Intrafat® or propofol intraperitoneally (i.p.), followed by pentazocine i.p. Brain slices were prepared and Fos-like immunoreactivity was detected using an immunohistochemical method. Results:
Propofol, droperidol, and dexmedetomidine displaced (+)[3H]SKF-10,047 binding in a concentration-dependent manner with Ki50s of 10.2 ± 0.6, 0.17 ± 0.03, 5.73 ± 1.2 M, respectively. Thiopental sodium was practically ineffective. Propofol produced a statistically significant reduction in the maximal binding capacity (Bmax) but did not affect the dissociation constant (Kd). (+)Pentazocine significantly enhanced bradykinin-induced [Ca2+]i increases, but propofol did not affect it. Pentazocine induced marked Fos-LI positive cells in the posterior cingulate and retrosplenial cortices (PC/RS), which was significantly reduced by propofol. Conclusions:
These results suggest that propofol may be a sigma-1 receptor antagonist, and that various effects of propofol on the brain may be mediated, at least partly, by the sigma-1 receptor.