Positive reinforcing effects of substance P in the rat central nucleus of amygdala.

Substance P (SP) can have positive reinforcing or aversive properties, depending on the dose used and the site of action in the brain. Experimental findings suggest that the amygdala is involved in reward-related processes. The presence of SP-immunoreactive fibers and cell bodies has been shown in the central nucleus (ACE) and neurokinin (NK)-1 and NK-3 receptors also could be found there. The rewarding or aversive effects of SP in the ACE were tested in conditioned place preference paradigm. 10 ng SP microinjections had positive reinforcing properties, while 100 ng SP had no effect. Prior treatment with NK-1 receptor antagonist could block the rewarding effects of SP, while the antagonist on its own did not influence place preference. Our results show that SP and NK-1 receptors play important roles in amygdaloid rewarding-reinforcing mechanisms.