Central GPR55 may prevent nicotine reinforcing actions: a preliminary study.

GPR55 is an orphan receptor whose endogenous agonists include lysophosphatidylinositol (LPI) and N­acetylethanolamides (NAEs), such as palmitoylethanolamide (PEA) and anandamide. Furthermore, its physiology in the central nervous system involves motor coordination, procedural and spatial memory, pain, and anxiety, among others. Recent reports indicate that systemic injections of O­1602 (a GPR55 and GPR18 agonist) blocked the reinforcing effects of morphine and nicotine in the conditioned place preference (CPP) paradigm, suggesting a possible participation of peripheral and/or central GPR55/GPR18 in brain reward/anti­reward systems. In this pilot study, the endogenous GPR55 agonists LPI and PEA, the highly selective GPR55 synthetic agonist ML184 or the selective GPR55 antagonist ML193 were injected to examine their pharmacological effects on the reinforcing actions of nicotine in the CPP paradigm. Our preliminary study shows that injections of LPI, PEA, ML184 and ML193 interfered with the change in place preference induced by nicotine via mechanisms that remain to be identified (which probably include central GPR55).