Etiology and the pathology of addiction

What is the current thinking regarding the etiology and the pathology of addiction? Are there brain changes that occur with addiction? What about maternal use of substances; are there short and longterm fetal consequences?
• You may examine the information from links below
o Understanding Drug Use and Addiction
o Drugs, Brains, and Behavior: The Science of Addiction
o The Science of Drug Abuse and Addiction: The Basics