Haloperidol potentiation of latent inhibition in rats: evidence for a critical role at conditioning rather than pre-exposure.

Latent inhibition (LI) reflects a cognitive process whereby repeated pre-exposure of a to-be-conditioned stimulus impairs subsequent conditioning. Since it is believed to reflect the ability of an organism to screen out irrelevant stimuli, disrupted LI has been suggested as a model for a cognitive deficit in schizophrenia. Animal studies have previously shown that indirect dopamine (DA) agonists can disrupt LI, an effect which is reversed by neuroleptics. Conversely, neuroleptics given alone potentiate LI. In this study, using pre-exposure to a tone stimulus which is subsequently paired with mild footshock, we have demonstrated that haloperidol given before conditioning only is equally as effective as haloperidol given twice, before pre-exposure and conditioning, in potentiating LI after 10 pre-exposures. This supports our earlier results with nicotine, pointing to conditioning as the critical time for the action of dopaminergic manipulations on LI. The implications for the use of potentiated LI as a screening test for neuroleptic action are discussed.