Positive reinforcing effects of substance P in the rat globus pallidus revealed by conditioned place preference

Substance P (SP) may have positive reinforcing effects when injected into different brain structures. Immunohistochemical experiments showed the presence of SP-immunoreactive fibers and also its receptors in the globus pallidus (GP). According to recent experimental data the GP may be involved in reward-related processes.The aim of our study was to test possible rewarding consequences of pallidal SP in conditioned place preference (CPP) paradigm. Male Wistar rats, microinjected with 10 ng SP, showed place preference, while 100 ng SP had no such positive reinforcing effect. The possible involvement of NK1 receptors was also studied. Prior treatment with the NK1 receptor antagonist WIN 51,708 could block the rewarding effects of SP, while the antagonist on its own did not influence CPP behavior. Our results show that SP and its NK1 receptors play important roles in pallidal positive reinforcing mechanisms.