When microbes in the gut is altered by alcohol (downregulates the antimicrobial action by the gut), the microbes (toxic) then travels to the brain causing havoc.
See:
http://www.scientificamerican.com/article/drinking-causes-gut-microbe-imbalance-linked-to-liver-disease/

Heavy drinking and alcohol use suffered an intestinal dysbiosis

“We’ve known for a very long time that patients with heavy drinking and alcohol use suffered an intestinal dysbiosis, where bacteria in the gut increase and they suffer from liver disease,” says University of California, San Diego, research gastroenterologist Bernd Schnabl, who had seen similar outcomes in mouse models. “If we give rodents nonabsorbable antibiotics, get rid of the flora, they essentially are protected from liver disease. We started asking, what is going on?”

Genes generate are only produced in the gut and have broad-spectrum activity against gram-negative and gram-positive organisms

That curiosity led Schnabl and his research team to focus on antimicrobial molecules REG3B and REG3G and the genes (Reg3b and Reg3g) that produce them. The genes are only expressed in the intestines; the pair of peptides the genes generate are only produced in the gut and have broad-spectrum activity against gram-negative and gram-positive organisms, respectively.

More bacteria in their guts and more severe liver disease

Through a series of experiments, detailed in this week’s Cell Host & Microbe the researchers learned that administering alcohol downregulated the genes so that they produced significantly less of the antimicrobial molecules. Knockout mice lacking those genes developed more bacteria in their guts and more severe liver disease compared with normal wild-type mice.