Alcohol and substance dependence

: In this paper, we have outlined the neurobiological basis of alcohol and drug dependence. The prevalence of drug dependence is a serious social problem in many countries, including Japan. This problem involves many background factors, including those pertaining to medical sciences, socio economics, and politics. First, we briefly describe the findings pertaining to psychotomimetic drugs as a model of schizophrenia. The biological pathogenesis of schizophrenic disorders is still unknown. The symptoms of methamphetamine (MAP) and phencyclidine (PCP) psychoses are very similar to those of schizophrenic disorders involving hallucination or delusion. PCP causes not only positive symptoms but also negative symptoms. Therefore, it has been considered as a more comprehensive model of schizophrenia than other drugs. Furthermore, amotivational syndrome, which is observed in patients with chronic cannabis and organic solvent dependence, is similar to the negative symptoms of schizophrenia. Understanding the neurobiological basis of drug dependence by using the molecular biological approach will provide an important clue for elucidating the mechanisms underlying schizophrenia and endogenous psychiatric disorders. Next, we discuss account for the neurobiological mechanisms underlying drug dependence. The reward system in the brain, which is common for all dependent drugs, has been explained, and the stages of addiction corresponding to the development of drug dependence have been discussed followed. In addition, we have discussed the epigenetics aspects of substance dependence, which is one of the hottest topics in psychiatric genetics. We expect that further studies of the mechanisms underlying drug dependence will aid in elucidating of the pathophysiology of various psychiatric diseases.