Latent inhibition of fear potentiated startle in rats

Non-reinforced pre-exposure to a prospective conditioned stimulus impairs subsequent conditioning. This phenomenon is termed latent inhibition. In this report, we demonstrate latent inhibition in a classical conditioning procedure, the fear-potentiated startle reflex. Normally, the startle response is enhanced in the presence of a conditioned stimulus that has previously been paired with an aversive stimulus. We show that fear-potentiation of the startle response is significantly less pronounced in rats that have been repeatedly pre-exposed to a conditioned light stimulus. Similar to other procedures reported in the literature, the administration of the psychostimulant drug amphetamine (1.0 mg/kg) before pre-exposure and conditioning disrupts latent inhibition. A good deal is known about the neuronal mechanisms underlying the acquisition and expression of fear-potentiated startle, and therefore this new procedure could be a useful tool for investigating the neuronal basis of latent inhibition.