Pharmacological effects and behavioral interventions on memory consolidation and reconsolidation

In this article, we will review some behavioral, pharmacological and neurochemical studies from our laboratory on mice, which might contribute to our understanding of the complex processes of memory consolidation and reconsolidation. We discuss the post-training (memory consolidation) and post-reactivation (memory reconsolidation) effects of icv infusions of hemicholinium, a central inhibitor of acetylcholine synthesis, of intraperitoneal administration of L-NAME, a non-specific inhibitor of nitric oxide synthase, of intrahippocampal injections of an inhibitor of the transcription factor NF-κB, and the exposure of mice to a new learning situation on retention performance of an inhibitory avoidance response. All treatments impair long-term memory consolidation and retrieval-induced memory processes different from extinction, probably in accordance with the "reconsolidation hypothesis".

Effects of oxytocin and an oxytocin receptor antagonist on retention of a nose-poke habituation response in mice

The present study describes the use of nose-poke habituation as a memory task in mice and demonstrates that it is sensitive to oxytocin (OT) and an oxytocin receptor antagonist (AOT) administered after the learning trial. Habituation of nose-poke behavior of mice was defined as a reduction in number of nose-pokes compared to baseline, and was measured in a hole-board apparatus to which male Swiss mice were exposed on two consecutive days for 5 min, respectively. Immediate post-training subcutaneous administration of OT (2.00 mug/kg) impaired retention performance, whereas AOT (0.20 mug/kg) enhanced it. Neither the impairing effects of OT (2.00 mug/kg) nor the enhancing effects of AOT (0.20 mug/kg) were seen when the training treatment interval was 180 min, suggesting that both treatments influenced the storage of recently acquired information. The effects of OT (2.00 mug/kg) on retention were prevented by AOT (0.02 mug/kg) administered immediately after training but 10 min prior OT treatment. This dose of antagonist did not affect retention by itself which suggest that impairing effects of OT on retention are probably due to an interaction of the neuropeptide with specific receptors. The actions of OT and AOT on retention were not due to enduring proactive effects of the compounds on performance during the retention test, since when given to untrained mice did not modify their spontaneous activities in the hole-board when recorded 24 h later. We suggest that nose-poke habituation learning can be a suitable method to investigate the mnestic effects of drugs, and that oxytocin negatively modulates memory storage of this form of learning elicited by stimuli repeatedly presented without reinforcement.