Effects of intra-accumbens focal administrations of glutamate antagonists on object recognition memory in mice

Generally recognition memory is distinguished into spatial and object memories that have been suggested to relay at a cortical level on different neural substrates. Recent studies point to a possible involvement of the nucleus accumbens (Nac) in spatial memory, demonstrating that blockade of glutamate antagonists within this structure impairs acquisition and consolidation of spatial information, while not many data are available on the potential role of this structure in object recognition. Thus in this study we wanted to investigate the effects of intra-accumbens focal administrations of NMDA antagonist, AP-5 (0.05, 0.1, 0.15 or 0.2 mug per side), and AMPA antagonist, DNQX (0.0005 or 0.001 mug per side), in object recognition memory. The spontaneous preference displayed by mice for novel objects was taken as an index for measuring object recognition. Pre-training focal administrations of both antagonists impaired the ability of mice to selectively explore the novel object in test session. However, the AMPA antagonist induced also a decrease in exploration and locomotion. In order to assess whether glutamate receptors located within the Nac were also involved in subsequent steps of object information processing, we performed additional experiments injecting AP-5 and DNQX immediately after training and testing the animals 24 h later. In this case, AP-5 but not the AMPA antagonist impaired exploration of the novel object. These results demonstrate that the Nac is involved in object recognition, and confirm that the different glutamate receptors mediate different component of information processing within the accumbens. (C) 2002 Elsevier Science B.V. All rights reserved.