Changes in the cAMP-related signal transduction mechanism in postmortem human brains of heroin addicts

Immunoreactivities of adenylyl cyclase (AC) type I (AC-I), and basal, forskolin- and Mn2+-stimulated AC activities with or without calcium and calmodulin (Ca2+/CaM) were estimated in temporal cortex (TC)-and nucleus accumbens (NAc) membranes from brains of heroin addicts and controls. Immunoreactivity of AC-I was significantly decreased in TC from brains of heroin addicts, but that did not change in NAc. Ca2+/CaM-sensitive AC activity was significantly lower in TC from brains of heroin addicts, but that activity in NAc did not show significant difference compared with the control. Some previous reports demonstrated that Ca2+/CaM-sensitive AC activity in membranes from postmortem human brain reflected the function of AC-I. Therefore, the downregulation of AC-I in TC plays an important role in the molecular mechanism of chronic opiate addiction in human brain.