Potentiation of d-amphetamine and L-dopa-induced acoustic startle activity after long-term exposure to amphetamine.

The startle response to an auditory stimulus was potentiated by treatment with d-amphetamine sulfate. Administration of L-dopa after pretreatment with the extracerebral decarboxylase inhibitor MK-486 also increased startle activity. After long-term exposure to amphetamine the startle response to L-dopa and d-amphetamine was enhanced. These findings are consistent with the consequences of long-term amphetamine administration on other amphetamine-induced behaviors (e.g. stereotype), and are discussed in terms of the effects of long-term amphetamine treatment on pre- and postsynaptic dopamine receptors and serotonin.