Reinforcing properties of substance P in the lateral hypothalamus revealed by conditioned place preference.

Reinforcing properties of substance P (SP) were investigated in rats using a conditioned place preference paradigm. After three baseline trials one conditioning trial of 10 min duration was performed. Either SP (100 pg, 1 ng, 100 ng) or saline (SI) was injected unilaterally into the lateral hypothalamus or a sham injection (OC) was given. Pairing one compartment with SP (100 pg, 1 ng) significantly increased the time spent in this compartment. Microinjections of 100 ng SP, saline or sham injection had no effect. Locomotor activity was not influenced by either treatment. These data are discussed in terms of (a) the possibility that SP has a role in mediating reinforcement and (b) the relationship between reinforcing effects and post-trial effects on learning and memory of SP applied into the lateral hypothalamus.