Latent inhibition in rats neonatally treated chronically with MK-801: differential effects on conditioned taste aversion and conditioned emotional response.

Chronic neonatal blockade of N-methyl-d-aspartate (NMDA) receptors produces various abnormal behaviors in adulthood animals. This study investigated the effects of neonatal treatment chronically with MK-801 in rats on the preexposure-induced retardation of CS-US association, i.e. latent inhibition (LI), of two aversive classical conditioning tasks in adulthood. In conditioned taste aversion (CTA) using sucrose taste and LiCl, neonatal chronic MK-801 (0.4 mg/kg twice/day) treatment attenuated the inhibitory effect of sucrose preexposure on the aversive conditioning, although the treatment did not affect CTA conditioning itself. On the other hand, in conditioned emotional response (CER) using tone and electrical foot shock, rats neonatally treated with MK-801 showed the same degree of inhibitory effect of tone preexposure on the aversive conditioning compared with neonatally vehicle-treated rats, and also showed the same level of CER conditioning itself. Thus, the effect of chronic neonatal blockade of NMDA receptors on the LI of classical conditioning in adulthood was differentiated by the task employed. Results suggest that LI of CTA paradigm compared with that of CER is more sensitive to abnormal development after chronic neonatal blockade of NMDA receptors as an index of cognitive/attentional deficits caused by the treatment.