Endogenous opioids and reward.

The discovery of endogenous opioids has markedly influenced the research on the biology of addiction and reward brain processes. Evidence has been presented that these brain substances modulate brain stimulation reward, self-administration of different drugs of abuse, sexual behaviour and social behaviour. There appears to be two different domains in which endogenous opioids, present in separate and distinct brain regions, are involved. One is related to the modulation of incentive motivational processes and the other to the performance of certain behaviours. It is concluded that endogenous opioids may play a role in the vulnerability to certain diseases, such as addiction and autism, but also when the disease is present, such as alcoholism.