•Memory reconsolidation impairment induces amnesia, developing over time.•Injections of protein synthesis inhibitors + reminder led to memory recovery.•Recovered memory can persist for more than 10 ...days.•Assumed that the reminder induces protein synthesis-dependent amnesia reactivation.•Suggested that amnesia, including its reactivation, is an active process.
Memory recovery in amnestic animals is one of the most poorly studied processes. In this paper, we examine the role of protein synthesis and a reminder in the mechanisms of amnesia and memory recovery in grape snails trained to conditioned food aversion. Amnesia was induced by the impairment of memory reconsolidation using NMDA (N-methyl d-aspartate) glutamate receptor antagonists. In an early stage of amnesia (day 3), injections of protein synthesis inhibitors into animals combined with a reminder by a conditioned stimulus (CS) led to the recovery of aversive reactions to its presentation. Two types of changes in reactions to CS were revealed. In most animals, a persistent recovery of memory retrieval was found that lasted for at least 10 days. In other snails, aversive responses to CS persisted for 24 h. Isolated injections of inhibitors, injections of inhibitors and a reminder by the learning environment (without presenting a CS), usage of a differentiating stimulus instead of a CS, or inhibitor injections after the reminder did not affect the development of amnesia. The administration of protein synthesis inhibitors and a reminder in the late period after amnesia induction (10 days) did not affect its development or caused a short-term memory recovery. We suggest that amnesia is an active process that develops over time. The reminder induces the reactivation of the amnesia process dependent on protein synthesis, while the administration of protein synthesis inhibitors leads to the impairment of amnesia reactivation and recovery of the state formed before amnesia induction (i.e., recovery of conditioned food aversion memory).
•NMDA or serotonin receptor antagonists paired with reminder-induced amnesia.•At an early (1 and 3 days) amnesia phase, the retraining was facilitated.•In the late phase (10 and 30 days), ...NMDA-dependent amnesia was resistant to retraining.•In the late phase, 5-HT-dependent amnesia retraining caused memory formation.
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.
•Protein and RNA syntheses are necessary for amnesia induction.•The sensitivity of amnesia to retraining and reminders is reorganized over time.•Amnesia can be reactivated by a reminder ...presentation.•Late-stage amnesia that is resistant to retraining can be defined as specific anterograde amnesia.•The key characteristics of amnesia and memory formation are similar.
According to a common perspective, amnesia is a passive consequence of memory consolidation or reconsolidation impairment. The results of our own study, as well as literature data, allowed us to offer an interpretation of amnesia. Amnesia is an active process whose key characteristics are similar to those of other long-term plastic rearrangements of the brain, including learning processes. In accordance with this hypothesis, the review considers the data we obtained on the mechanisms of amnesia induction and development caused by impairment of conditioned food aversion memory consolidation or reconsolidation. In particular, experimental data indicating the dependence of amnesia induction on protein and RNA syntheses are described. After amnesia induction, a time-dependent reorganization of its processes is shown to occur. In early amnesia stages (< 10 days), a gradual decrease in the possibility of memory formation during a second training was observed. In late stages of amnesia (10 days or more), an unusual physiological phenomenon was revealed—the second training did not lead to the formation of long-term memory. This effect was specific, as memory for a new type of food could possibly be formed in these animals. The described properties of amnesia facilitate its characterization as specific anterograde amnesia. In addition, at an early but not late amnesia stages, reminder presentation caused amnesia reactivation, impairment of which by DNA methyltransferase inhibitors caused memory recovery. The results obtained allow us to characterize amnesia as a specific, time-dependent, separate process. In conclusion, the potential biological significance of the described type of amnesia is considered, and we discuss the possible molecular mechanisms underlying it.
The participation of DNA methylation and histone acetylation in the mechanisms of anterograde amnesia and memory recovery was studied on grape snails trained in conditioned food aversion. Anterograde ...amnesia developed 10 days after memory reconsolidation impairment with an NMDA glutamate receptor antagonist and was characterized by long-term memory formation impairment upon repeated training. DNA methyltransferase inhibitor injections to snails 1 h before repeated training, as well as 15 min or 4 h after repeated training, caused rapid formation of memory that persisted for at least 10 days. Injections of histone deacetylase inhibitor before repeated training also induced the formation of a stable long-term memory. However, administration of histone deacetylase inhibitor 15 min after repeated training initiated a temporary memory recovery. Injections of the inhibitor 4 h after repeated training were ineffective. These results indicate that histone-dependent chromatin remodeling and DNA methylation are selectively involved in the mechanisms of anterograde amnesia and memory recovery.
The study of the amnesia mechanisms is of both theoretical and practical importance. The mechanisms of anterograde amnesia are the least studied, due to the lack of an experimental model that allows ...studying this amnesia type molecular and cellular mechanisms. Previously, we found that conditional food aversion memory reconsolidation impairment in snails by NMDA glutamate receptor antagonists led to the amnesia induction, in the late stages of which (>10 days) repeated training did not cause long-term memory formation. In the same animals, long-term memory aversion to a new food type was formed. We characterized this amnesia as specific anterograde amnesia. In the present work we studied the role of epigenetic DNA methylation processes as well as protein and mRNA synthesis in the mechanisms of anterograde amnesia and memory recovery. DNMT methyltransferase inhibitors (iDNMT: zebularine, RG108 (N-Phthalyl-1-tryptophan), and 5-AZA (5-Aza-2'-deoxycytidine)) were used to alter DNA methylation. It was found that in amnesic animals the iDNMT administration before or after shortened repeated training led to the rapid long-term conditional food aversion formation (Ebbinghaus saving effect). This result suggests that amnestic animals retain a latent memory, which is the basis for accelerated memory formation during repeated training. Protein synthesis inhibitors administration (cycloheximide) before or immediately after repeated training or administration of RNA synthesis inhibitor (actinomycin D) after repeated training prevented memory formation under iDNMT action. The earlier protein synthesis inhibitor effect suggests that the proteins required for memory formation are translated from the pre-existing, translationally repressed mRNAs. Thus, we have shown for the first time that the anterograde amnesia key mechanism is DNMT-dependent suppression of the transcription of genes involved in memory mechanisms. Inhibition of DNMT during repeated training reversed these genes expression blockade, opening access to them by transcription factors synthesized during training from the pre-existing mRNAs.
•Memory reconsolidation impairment leads to anterograde amnesia development.•Retraining of amnestic grape snails did not induce long-term memory formation.•DNA methyltransferase inhibitor (iDNMT)+retraining induced memory formation.•The effect of iDNMT on memory formation depended on protein and RNA synthesis.•DNA methylation-dependent gene repression underlies the anterograde amnesia.
Impairment of reconsolidation of conditioned food aversion memory led to the development of a specific anterograde amnesia: repeated training of amnestic snails did not induce long-term memory ...formation. DNA demethylation caused by injections of DNA methyltransferase inhibitor (DNAMT) during repeated training led to long-term memory formation. Injections of an NMDA glutamate receptor antagonist or a serotonin receptor antagonist prevented memory formation induced by administration of DNAMT inhibitor and repeated training. We hypothesize that methylation-dependent repression of neuronal genes underlies anterograde amnesia. Demethylation eliminated the blockade of these genes and created conditions for long-term memory formation, the induction mechanisms of which involve neurotransmitter receptors.
The involvement of DNA methylation in the mechanisms of formation of conditioned food aversion memory was studied on
Helix lucorum
snails. The dynamics of aversion formation in snails injected with ...DNA methyltransferase inhibitor RG108 did not differ from that in control snails. The memory was retained for more than one month after training following RG108 injection and the duration of memory persistence did not differ from that in control animals. However, the characteristics of memory in control and experimental snails differed significantly. In control snails, injections of glutamate NMDA-receptor antagonist or protein synthesis inhibitor before memory retrieval caused disorders in the memory reconsolidation and development of amnesia 2 days after training. By contrast, injections of these substances before retrieval to snails trained against the background of RG108 treatment caused no memory disorders. We hypothesized that inhibition of DNA methylation processes led to the formation of strong memory, not reactivated after retrieval and not transformed into a labile state sensitive to amnesic agents.
•DNA methylation inhibitors do not influence memory reconsolidation.•MK-801/reminding cause memory reconsolidation impairment and amnesia development.•DNA methylation inhibitors/reminding caused ...amnesia impairment and memory recovery.•DNA methylation inhibitors in 3, but not in 9h after reminding impaired amnesia.•DNA methylation inhibitors/reminding don’t affect the late amnesia stage.
Current considerations suggest that the mechanisms of long term memory are based on the changes of the neuronal genetic algorithms. Process of the enzyme DNA methylation have great importance to the differential genes expression, and is likely to be one of the key mechanisms of the consolidation and memory storage. The present study aimed to investigate the DNA methylation processes role in the mechanisms of the conditioned food aversion memory reconsolidation and also in the amnesia development mechanisms, caused by disturbances of the reconsolidation in Helix lucorum. It was found that DNA–methyltransferase inhibitors zebularine and RG108 had no influence on the memory reconsolidation. We investigated the effects of the DNA–methyltransferase inhibitors on different amnesia stage. The amnesia was induced by NMDA glutamate receptors antagonists. At the early stage of amnesia (3rd day after its induction) injections of the DNA–methyltransferase inhibitors in combination with reminder by conditioned food stimuli led to memory recall. Memory was recovered by the DNA–methyltransferase inhibitors injections before the reminder and also 3h, but not 9h after the reminder. In case when enzyme inhibitors or reminders were applied separately, no effect on memory was revealed. At the late stage of amnesia (10th day) the DNA–methyltransferase inhibitors didn’t affects amnesia development. It might be hypothesized that presentation of reminding stimuli result in the reactivation/reconsolidation of molecular processes, involved in amnesia development, one of the key mechanisms of which could be the DNA methylation/demethylation of neural cells.
Direct laser deposition (DLD) technology was used to obtain magnesium (Mg) samples in this work. The morphology, composition, electrochemical and mechanical properties of the Mg specimens with and ...without protective layers were investigated using microhardness and scratch tests, SEM-EDX and XRD analysis, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), and immersion tests. The localized corrosion processes on the DLD Mg sample surface were studied using scanning vibrating electrode technique (SVET) and scanning ion-selective electrode technique (SIET). Plasma electrolytic oxidation (PEO) method was applied to modify the DLD Mg material intended to be used as bioresorbable implants for bone repair applications. Composite polymer-containing layers were designed to increase the corrosion resistance of the protected material. It was established that the use of additive technology for the formation of the material does not require correction of the electrical modes of PEO, developed for wrought magnesium alloys. The formed coatings possess high adhesive strength and sufficiently increase the protective properties of the DLD samples in a 3 wt% NaCl solution.
Display omitted
•Direct laser deposition (DLD) technology was used to obtain magnesium samples.•Properties of the DLD Mg sample with different surface layers were studied.•The localized corrosion processes on the DLD Mg surface were studied by SVET/SIET.•PEO method was applied to modify the DLD Mg to be used as bioresorbable implants.•Composite polymer-containing layer improved a corrosion resistance of PEO-coating.
PDF