NMDA and muscarinic blockade in the perirhinal cortex impairs object discrimination in rats

To determine the possible involvement of NMDA and muscarinic activation of the perirhinal cortex in object discrimination, an NMDA antagonist, D,L-2-amino-5-phosphonopentanoic acid (AP5), and a muscarinic antagonist, scopolamine (SCP) were injected into the perirhinal cortex of rats. Each drug at the higher dose (AP5 60 mM, SCP 80 mM) significantly decreased correct choices on the retention test of object discrimination. SCP, but not AP5, also significantly increased response latency, but this increase was not necessarily related to the time spent for a choice. These results suggest that activation of both NMDA and muscarinic receptors contributes to object discrimination.