Cocaine enhances the expression of fear-potentiated startle: evaluation of state-dependent extinction and the shock-sensitization of acoustic startle.

Cocaine's effects on fear extinction and on the shock-sensitization of acoustic startle were examined. Following fear acquisition, rats exposed to the nonreinforced conditioned stimulus (CS) after cocaine administration demonstrated significant levels of fear-potentiated startle when evaluated in the drug-free state. The CS also increased startle amplitudes in subjects extinguished and tested with cocaine, indicating that mechanisms other than state-dependent learning are involved in the extinction deficit. The presentation of 10 footshocks augmented acoustic startle, and the shock enhancement was unaffected by cocaine preexposure. These data indicate that the aversive consequences of footshock relevant to the acquisition of conditional fear are not sensitized by the drug. It was suggested that cocaine reinforces fear responding to a threatening stimulus.