The roles of RNA synthesis and protein translation during reconsolidation of passive-avoidance learning in the day-old chick

Early memory consolidation window enables drug induced state-dependent memory

It is well established that newly acquired information is stabilized over time by processes underlying memory consolidation, these events can be impaired by many drug treatments administered shortly after learning. The consolidation hypothesis has been challenged by a memory integration hypothesis, which suggests that the processes underlying new memories are vulnerable to incorporation of the neurobiological alterations induced by amnesic drugs generating a state-dependent memory. The present experiments investigated the effects of amnesic drugs infused into the insular cortex of male Wistar rats on memory for object recognition training. The findings provide evidence that infusions of several amnesic agents including a protein synthesis inhibitor, an RNA synthesis inhibitor, or an NMDA receptor antagonist administered both after a specific period of time and before retrieval induce state-dependent recognition memory. Additionally, when amnesic drugs were infused outside the early consolidation window, there was amnesia, but the amnesia was not state-dependent. Data suggest that amnesic agents can induce state-dependent memory when administered during the early consolidation window and only if the duration of the drug effect is long enough to become integrated to the memory trace. In consequence, there are boundary conditions in order to induce state-dependent memory.

NMDA or 5-HT receptor antagonists impair memory reconsolidation and induce various types of amnesia

Elucidation of amnesia mechanisms is one of the central problems in neuroscience with immense practical application. Previously, we found that conditioned food presentation combined with injection of a neurotransmitter receptor antagonist or protein synthesis inhibitor led to amnesia induction. In the present study, we investigated the time course and features of two amnesias: induced by impairment of memory reconsolidation using an NMDA glutamate receptor antagonist (MK-801) and a serotonin receptor antagonist (methiothepin, MET) on snails trained with food aversion conditioning. During the early period of amnesia (<10th day), the unpaired presentation of conditioned stimuli (CS) or unconditioned stimuli (US) in the same training context did not have an effect on both types of amnesia. Retraining an on 1st or 3rd day of amnesia induction facilitated memory formation, i.e. the number of CS + US pairings was lower than at initial training. On the 10th or 30th day after the MET/reminder, the number of CS + US pairings did not change between initial training and retraining. Retraining on the 10th or 30th day following the MK-801/reminder in the same or a new context of learning resulted in short, but not long-term, memory, and the number of CS + US pairings was higher than at the initial training. This type of amnesia was specific to the CS we used at initial training, since long-term memory for another kind of CS could be formed in the same snails. The attained results suggest that disruption of memory reconsolidation using antagonists of serotonin or NMDA glutamate receptors induced amnesias with different abilities to form long-term memory during the late period of development.

Conditioned food aversion reconsolidation in snails is impaired by translation inhibitors but not by transcription inhibitors

Memory is destabilized during retrieval-induced reconsolidation and can therefore be disrupted or modified. In the present study, we examined the role of translation and transcription processes in long-term food aversion memory reconsolidation in the snail Helix lucorum. The administration of the protein synthesis inhibitor anisomycin followed by a reminding procedure (presentation of the conditioned stimulus) led to the development of amnesia that persist for 2 weeks or longer. Administration of the mRNA synthesis inhibitors actinomycin D, α-amanitin, or DRB (5,6-dichloro-1-β-D-ribofuranosylbenzimidasole) followed by a reminding procedure did not affect memory retrieval. Our present findings indicate that proteins synthesized from preexisting mRNA that is transcribed during learning and stored in a silent state may be involved in the mechanisms of conditioned food aversion reconsolidation.