Involvement of the insular nitric oxide signaling pathway in the expression of morphine-induced conditioned place preference in rats.

Nitric oxide (NO) has been recently reported to play an important role in the rewarding effects of addictive drugs. The regional NO signaling in the brain, however, is not completely clear. Here, we studied the effects of insular NO signaling on the expression of morphine-induced conditioned place preference (CPP). Insular microinjection of the NO inhibitors N-nitro L-arginine methyl ester (L-NAME) and 7-nitroindazole reduced the expression of morphine-induced CPP. The NO donor molsidomine, in contrast, reversed L-NAME-induced reduction of CPP expression. These results suggest that insular NO signaling is involved in the expression of morphine-CPP.