Rationale: In addition to its rewarding actions, cocaine has profound negative effects that are unmasked as the rewarding impact of the drug fades. While much is known about the neurobiology of cocaine reward, the mechanisms underlying the negative actions of the drug remain unclear.
Objectives: The current study investigates the role of three brain regions each implicated in the modulation of negative affective states-the bed nucleus of the stria terminalis (BNST), the central (CeA), and the basolateral (BLA) nucleus of the amygdala.
Methods: The dual actions of cocaine were assessed using a runway self-administration procedure in which rats exhibit both approach to and avoidance of a goal box associated with cocaine administration (retreat behaviors). Here, rats ran a straight alley once/day for i.v. cocaine (1.0 mg/kg/injection) over 14 days during which the BNST, CeA, or BLA was inactivated via bilateral intracranial infusions of lidocaine (0 or 20 μg/0.5 μl/side) administered 15 min prior to testing. The impact of lidocaine on spontaneous locomotor activity was also assessed to rule out nonspecific actions of the treatments.
Results: Control animals running for cocaine developed the expected pattern of approach-avoidance retreat behavior. Inactivation of the BNST attenuated such behavior, BLA inactivation had no appreciable effects, and CeA inactivation produced intermediate and more variable results. Locomotor activity was unaffected by any of the treatments.
Conclusions: These data suggest that the BNST and to a lesser extent the CeA, but not the BLA, play a role in mediating the opponent-process actions of self-administered cocaine.