Answer:
Opioids are currently the most effective pain relieving pharmaceuticals. However, they are also rewarding and their repeated use can lead to dependence and addiction. In fact, addiction to opioid analgesics is a growing socioeconomic and health problem with potentially serious consequences documented by a rise in deaths due to overdose [1, 2]. A critical CNS locus for opioid reward is the ventral tegmental area (VTA, glossary, vide infra). Recent work indicates that there is great anatomical and pharmacological heterogeneity in VTA neurons and that there are numerous opioid