Effects of local application of dopaminergic drugs into the medial prefrontal cortex of rats on latent inhibition.

The involvement of the dopamine (DA) innervation of the medial prefrontal cortex (PFC) in attention was studied in a latent inhibition (LI) paradigm in rats. LI becomes evident by a retardation of conditioning to a stimulus after nonreinforced preexposure to that stimulus. LI is thought to reflect an animal's ability not to attend to irrelevant stimuli and is often used as an animal paradigm modeling schizophreniclike attentional deficits. In the present study the effects of bilateral infusions of the DA receptor agonist apomorphine (APO, 9.0 micrograms/side) and the DA receptor antagonist cis-flupenthixol (FLU, 12.0 micrograms/side) into the medial PFC on LI were assessed. Although in comparison with vehicle both APO and FLU infusions attenuated response suppression in nonpreexposed animals, the drugs differentially affected LI in preexposed animals. After infusions of APO animals failed to show conditioned suppression, whereas FLU-treated animals displayed as much suppression of responding as nonpreexposed animals. The abolition of LI induced by FLU infusions into the medial PFC suggests that prefrontal DA is involved in attentional processes in a way opposite to the established role of subcortical DA systems in these processes.