http://www.iflscience.com/brain/what-happens-alcoholics-brains-when-they-quit-drinking/

“The study’s authors also note that the brains of deceased alcoholics displayed no reduction in D2 receptor sites, which bind with dopamine in order to inhibit, rather than excite, neurons. All in all, this evidence explains how alcohol dampens the brain’s reward center, compelling alcohol-dependent individuals to continually seek stimulation through booze.

Next, the study authors sought to determine the sequence of events leading to this situation. To do so, they used radiography techniques to track dopamine levels in the brains of alcohol-dependent rats that were denied alcohol for several weeks.

They discovered that dopamine levels dropped during the first six days, confirming the existing theory that acute alcohol withdrawal is characterized by a hypodopaminergic state. Interestingly, during this initial period, the availability of dopamine receptor sites and transporter sites were found to be normal.“