Effects of acute stress and GluN2B-containing NMDA receptor antagonism on object and object-place recognition memory.

The mechanisms underlying the complex effects of acute stress on memory are incompletely understood. Previous work suggests that the activation of N-methyl-d-aspartate (NMDA) receptors specifically containing GluN2B subunits may underlie the disruptions in spatial memory retrieval caused by acute stress (Wong et al., 2007 PNAS 104:11471). The present experiments were designed to assess whether a similar mechanism is involved in recognition memory. Recognition memory retrieval was assessed in Sprague-Dawley rats using an object recognition test and an object-place recognition test, both of which rely on patterns of spontaneous exploration. Exposure to acute stress for 30 min immediately before the test phase of either test disrupted memory retrieval. Administration of the GluN2B-selective antagonist Ro25-6981 (6 mg/kg; i.p.) enhanced memory in the object recognition test regardless of whether animals were exposed to acute stress. In the object-place test, Ro25-6981 had no effect on memory retrieval in the absence of stress but promoted memory following acute stress. These data highlight the specific contributions made by GluN2B-containing NMDA receptors to recognition memory for different types of stimuli.