The use of addictive substances is characterized by a positive emotional state
followed by drug withdrawal and a negative affective state. These highs and lows are caused by neuroadaptational changes in multiple brain structures when exposed to drugs of abuse. However, the neural events responsible for triggering the negative affective component of withdrawal during the early stages of morphine and nicotine dependence has yet to be definitively determined. By measuring the acoustic startle reflex in rats, we show that decreased dopaminergic activity causes the characteristic anxiety observed during
withdrawal from drugs of abuse. These results parallel the substantial research
showing the importance of the mesolimbic dopamine system in regulating the effects of drugs of abuse.