Nicotinic receptor activation in perirhinal cortex and hippocampus enhances object memory in rats

The perirhinal cortex (PRh) and its cholinergic inputs are implicated in object recognition memory. Conversely, the hippocampus (HPC) may be involved in spatial recognition processes that are not essential to the recognition of objects per se. Systemic nicotine has been shown to facilitate both object and spatial memory. The current study compared the roles of perirhinal and hippocampal nicotinic acetylcholine receptors (nAChRs) in object and spatial recognition memory using spontaneous object recognition (SOR) and object-location (OL) tasks for rats. Systemic pre-sample (acquisition) nicotine administration dose-dependently facilitated SOR and OL performance compared to vehicle conditions in which performance was at chance with a 72-h retention delay between the sample and choice phases. Subsequently, pre-sample intra-PRh infusions of nicotine significantly facilitated SOR; somewhat surprisingly, pre-sample intra-HPC nicotine also enhanced object recognition memory. Further experiments indicated facilitative effects on OL performance caused by pre-sample intra-PRh or intra-HPC nicotine administration. These results not only demonstrate that nAChR activation facilitates performance on object recognition and object-location memory tasks, but suggest that these effects can be produced by nAChR action in either PRh or HPC. Thus, although PRh and HPC are not required for OL or SOR task performance, respectively, nAChR-mediated enhancement of neural function in either of these temporal lobe regions appears capable of promoting stronger memory encoding and/or consolidation in either task. These findings further support the supposed interactive relationship between the HPC and PRh in object information processing and highlight the potential therapeutic value of nicotinic receptor activation in amnesic disorders.