Downregulation of the dynorphin/κ-opioid receptor system, which activation is generally characterized by inhibitory influences on glutamate release and neuronal excitability (Madamba et al., 1999) is consistent with this statement, and changes in dynorphins further supports the hypothesis that alcohol abuse may engage molecular mechanisms of synaptic plasticity in the dorsal striatal sub-region responsible for habit formation. This evidence concerns the gene PDYN and alcohol abuse.