Role of medial prefrontal NMDA receptors in spatial delayed alternation in 19-, 26-, and 33-day-old rats.

Long-Evans rats were trained on spatial delayed alteration (SDA) in a T-maze following medial prefrontal cortical (mPFC) infusions of different doses of the noncompetitive NMDA-receptor antagonist, MK-801 (.125 microl; .25 microl; or .25 microlsaline, bilaterally), on postnatal day (PND) 19, 26, or 33. Pups trained on PND 19 showed almost no learning of SDA, regardless of drug condition (including saline). On PND 26, both doses of MK-801 significantly and equivalently prevented SDA learning, with performance during the final three training blocks remaining near chance levels, in contrast with 85% correct performance in the saline control group. On PND 33, substantial SDA learning was evident regardless of dose, although a modest impairment appeared in mid-training at both doses. These findings confirm previous reports of mPFC involvement in the early postnatal ontogeny of SDA and suggest a developmentally transient role of mPFC NMDA-receptor function in this task.