a role for enkephalin in the mediation of behavioral reinforcement is supported by several lines of evidence : i ) central injections of enkephalin serve as reinforcement for self-administration behavior , ii ) electrical stimulation of many enkephalin-rich regions serves as reinforcement for self-stimulation behavior , which is blocked by moderate doses of naloxone , and iii ) long-term retention of a passive avoidance response is facilitated by immediate post-learning injections of methionine-enkephalin and morphine .
C0014298
enkephalin
C0014295
methionine-enkephalin