Epigenetic Processes of DNA Methylation Are Selectively Involved in the Mechanisms of Retrograde and Anteograde Amnesia.

The participation of DNA methylation processes in the mechanisms of anterograde and retrograde amnesia caused by impaired reconsolidation of conditioned food aversion memory by NMDA glutamate receptor antagonists or serotonin receptor antagonists, respectively, were studied on grape snails. Anterograde amnesia was characterized by impaired formation of long-term memory during repeated learning. Administration of a DNA methyltransferase (DNMT) inhibitor to amnestic animals resulted in accelerated formation of long-term memory during 1 day of repetitive training vs 3 days during initial training. In serotonin-dependent retrograde amnesia, repeated learning without DNMT inhibitor administration or after inhibitor injections led to the formation of long-term memory. The dynamics of memory formation was similar in both cases and did not differ from that during the initial training: the memory was formed within 3 days of training. Thus, epigenetic processes of DNA methylation are selectively involved in the mechanisms of anterograde amnesia, but do not participate in the mechanisms of retrograde amnesia.

Comparative Study of the Effect of a DNA Methyltransferase Inhibitor and a Histone Deacetylase Inhibitor on Memory Formation Processes in Anterograde Amnesia.

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 Role of DNA Methylation and Activity of Neurotransmitter Receptors in the Mechanisms of Specific Anterograde Amnesia and Memory Recovery.

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.

Learning against the Background of DNA Methyltransferase Inhibition Leads to the Formation of Memory That Is Resistant to Reactivation and Impairment.

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.

Peculiarities in Synthesis of Proteins Implicated in Memory Reconsolidation and Induction of Amnesia.

The peculiarities of implication of NMDA glutamate receptors and protein synthesis into the mechanisms responsible for impairment of memory reconsolidation were studied in edible snails conditioned to food aversion. Injections of NMDA glutamate receptor antagonists or protein synthesis inhibitor prior to reminding with conditioned food stimulus provoked development of amnesia after different latent periods. NMDA glutamate receptor antagonists gradually weakened the aversive reactions to conditioned stimulus presented in parallel with reminder during 1 h. The protein synthesis inhibitor cycloheximide provoked the development of amnesia only 2.5 h after the onset of reminding procedure. Combined injections of protein synthesis inhibitor and NMDA glutamate receptor antagonist prior to reminding completely prevented the development of amnesia. The data agree with hypothesis that memory reconsolidation and amnesia are distinct processes, which need activation of synthesis of specific proteins.

A Study of the Participation of NMDA Glutamate Receptors in the Mechanisms of Specific Anterograde Amnesia Reversion.

We studied the involvement of NMDA glutamate receptors in the mechanisms of anterograde amnesia. It was found that repeated training of amnestic animals treated with D-cycloserine, a potent agonist of the glycine site of NMDA receptors, did not lead to consolidation of long-term memory, while expression of short-term memory was more pronounced in comparison with control animals that received saline before repeated training. It was shown that D-cycloserine in amnestic snails did not affect the food reactions caused by the presentation of a conditioned stimulus during the reminder (without combination with the unconditioned stimulus). It is assumed that NMDA glutamate receptors in amnestic animals are involved in the neural plasticity mechanisms that underlie short-term memory, but their activation does not influence the anterograde amnesia processes and does not lead to the formation or recovery of long-term memory.

Administration of Protein Synthesis Inhibitor before Reminder Reverses Amnesia Induced by Memory Reconsolidation Impairment with 5-HT Receptors Antagonist.

Administration of 5-HT receptor antagonist to snails trained in conditioned food aversion prior to reminding of the conditioning stimulus caused amnesia. At the early period of amnesia (day 3), injections of protein synthesis inhibitor cycloheximide without reminder or reminder alone were ineffective. At the same time, injections of the inhibitor combined with reminder led to memory recovery; this effect in most animals persisted for at least 10 days. In the rest snails, aversive responses to presentations of the conditioning stimulus persisted for 2 days. Cycloheximide injection and reminder in 10 days after induction of amnesia did not affect its development or caused a transient memory recovery (2 days). We hypothesized that amnesia is an active process unfolding in time. One of mechanism of this process is reminder-induced and protein synthesis-depended reactivation of amnesia. Inhibitor of protein synthesis disturbed this reactivation and led to recovery of the initial memory of conditioned food aversion.

Changes in Amnesia Parameters over Time after Long-Term Memory Disruption with Protein Kinase Mζ Inhibitor.

We studied the involvement of protein kinase Mζ (PKMζ) in the mechanisms of amnesia development within 10 days after disruption of conditioned food aversion memory with ZIP (a PKMζ inhibitor). Repeated training performed in 3 days after amnesia induction with ZIP, led to the formation of conditioned food aversion memory, but the number of combined presentations of food and reinforcer stimuli was lower than during the initial training. Repeated training performed in 10 days after amnesia induction also led to memory formation, but the number of combined presentations of the stimuli was similar to that during the initial training. It was hypothesized that at the early stages of ZIP-induced amnesia, residual memory trace can be restored and amplified during repeated training, which led to memory expression at the behavioral level. At the late stages of amnesia, this memory trace was completely erased and repeated training led to the formation of a new memory. Thus, PKMζ inhibition results in the relatively fast impairment of memory retrieval and induces long-term process of memory erasing.

Peculiarities of Participation of DNA Methyltransferases in the Mechanisms of Storage, Impairment, and Recovery of Conditioned Food Aversion Memory.

We studied the participation of DNA-methylation processes in the mechanisms of memory storage and reconsolidation, amnesia induction, and in recovery of the conditioned food aversion memory in edible snails. It was found that daily injections of DNA methyltransferases inhibitor over 3 days combined with a reminder of a conditioned food stimulus did not affect memory storage. The administration of DNA methyltransferase inhibitors did not suppress induction of amnesia caused the NMDA receptor antagonist/reminder. Injections of DNA methyltransferase inhibitors combined with the reminder led to memory recovery in 3 days after amnesia induction. Thus, DNA methyltransferase inhibitors in the same doses did not affect storage and reconsolidation of memory, as well as the mechanisms of amnesia induction. At the same time, injections of inhibitors led to memory recovery, apparently, due to disruption of reactivation and amnesia development.

Involvement of Glycogen Synthase Kinase-3 in the Mechanisms of Conditioned Food Aversion Memory Reconsolidation.

Experiments were performed on the snails trained in conditioned food aversion for 3 days. Injection of TDZD-8 (glycogen synthase kinase-3 inhibitor, 2 mg/kg) in combination with reminder (presentation of a conditioned food stimulus) led to memory impairment developing 3 days after inhibitor/reminder exposure and followed by spontaneous recovery in 10 days. Injections of TDZD-8 in a dose of 4 or 20 mg/kg before reminder were shown to cause amnesia that persisted for more than 10 days. Memory recovery during repeated training was observed at the earlier period than after initial training. The impairment of memory reconsolidation by TDZD-8 after training of snails for 1 day was less pronounced than under standard training conditions (3 days). The effect of a glycogen synthase kinase-3 inhibitor during memory reconsolidation is probably followed by impairment of memory retrieval and/or partial loss, which can be compensated spontaneously or after repeated training.

Specificity of Mechanisms of Memory Reconsolidation in Snails Trained for Rejection of Two Types of Food.

Specificity of behavioral and neuronal mechanisms of impairment of long-term memory reconsolidation was studied in edible snails trained for associative skill of rejection of two types of food: raw carrots (conditioned stimulus 1) and apple (conditioned stimulus 2). In 2 days after training, the snails received protein synthesis inhibitor cycloheximide and a reminder (conditioned stimulus 1 or 2). In 3 and 14 days after cycloheximide/reminder, we observed the absence of aversive responses to the conditioned stimulus used as the reminder and preserved responses to the conditioned stimulus not used as the reminder. Moreover, we observed specific suppression of synaptic responses of command neurons of snail defensive behavior induced by the conditioned stimulus used as the reminder after cycloheximide injection and preserved synaptic responses of neurons to the other conditioned stimulus. It was hypothesized that protein synthesis-dependent synapse-specific plasticity of command neurons can be a mechanism of selective preservation of conditioned food aversion memory in snails.

Anterograde Amnesia Induced by Disruption of Consolidation or Reconsolidation of Long-Term Memory.

Mechanisms of amnesia caused by impairment of consolidation or reconsolidation of conditioned food aversion memory with protein synthesis inhibitor cycloheximide were studied in Helix lucorum. Cycloheximide injection during training or memory reconsolidation in trained snails produced amnesia. In both cases, repeated training 10 days after amnesia induction led to short-term memory formation, while long-term memory was not formed, despite the fact that the number of conditioned and reinforcing stimuli combinations was higher than during initial training. The possibility of formation of short-term memory not transforming into long-term memory is one of the key characteristics of anterograde amnesia. Our findings data and experimental model can be used for analysis of specific molecular mechanisms of anterograde amnesia.

Dynamics of the Development of Amnesia Caused by Disruption of Memory Reconsolidation by Neurotransmitter Receptors Antagonists.

The dynamics of amnesia development under conditions of memory reconsolidation disruption by serotonin receptor antagonist methiothepin or NMDA glutamate receptor antagonist MK-801 was studied in snails trained in conventional food aversion. In 2 days after training, injection of methiothepin or MK-801 before reminder induced amnesia development. During repeated training in 3 days after amnesia induction, the skill was formed more rapidly than during the initial training. During repeated training in 10 days after administration of methiothepin and reminder, the dynamics of habit formation was similar to that during initial learning. At the same time, repeated training in 10 days after MK-801 administration and reminder did not result in long-term memory formation. Disruption of reconsolidation of conditioned food aversion memory by antagonists of serotonin or NMDA glutamate receptors led to the development of different types of amnesia that had similar strengthening gradient at the early stages, but differed by the possibility of memory formation during re-training at the late stage.

Involvement of Mζ-Like Protein Kinase in the Mechanisms of Conditioned Food Aversion Memory Reconsolidation in the Helix lucorum.

We studied the involvement of Mζ-like protein kinase (PKMζ) into mechanisms of conditioned food aversion memory reconsolidation in Helix lucorum. Injections PKMζ inhibitor ZIP in a dose of 5 mg/kg on day 2 or 10 after learning led to memory impairment and amnesia development. Injections of the inhibitor in doses of 1.5 or 2.5 mg/kg had no effect. Repeated training on day 11 after induction of amnesia resulted in the formation of memory on the same type of food aversion similar to first training. The number of combinations of conditional (food) and reinforcing (electrical shock) stimuli was similar during initial and repeated training. We hypothesize that the inhibition of Mζ-like protein kinase erases the memory trace and a new memory is formed during repeated training.

Reconsolidation of Reminder-Induced Amnesia: Role of NMDA and AMPA Glutamate Receptors.

We studied the role of glutamate receptors and reminder in the mechanisms of amnesia maintenance caused by disruption of conditioned food aversion reconsolidation with an antagonist of NMDA glutamate receptor in snails. At the early stage of amnesia (day 3 after induction), injection or NMDA of AMPA glutamate receptor antagonists prior to reminder (presentation of the conditioned food stimulus) led to memory recovery. Reminder alone or injection of antagonists without reminder or after reminder was ineffective. At the late stage of amnesia (day 10), antagonists/reminder had no effect on amnesia maintenance. It was hypothesized that reminder at the early stage of amnesia led to reactivation and reconsolidation of the molecular processes of amnesia including activation NMDA and AMPA glutamate receptors. Injection of antagonists of these receptors prior to reminder led to disruption of reactivation/reconsolidation of amnesia and recovery of the conditioned food aversion memory.

[Bisegmental anterior interbody spondylodesis, using rigid plates, in surgical treatment of cervical vertebral column traumas and diseases].

Results of surgical treatment of 34 patients, suffering cervical vertebral column traumas and diseases, are analyzed. In all the patients bisegmental anterior interbody spondylodesis was conducted, using cervical rigid plates and vertical cylindrical net implants. The existing and newly obtained information about changes in the radiological indices dynamics while the method application by its authors is presented. The interbody synostosis was achieved in 82.4% patients in 1 yr after the operation. The complications rate while the implants application have constituted 23.3%, and the total rate of complications--29.1%.

Long-term phase reorganization of conditioned food aversion memory in edible snail.

The specific features of memory reconsolidation in edible snails were studied over 30 days after learning of conditioned food aversion. Injections of a NMDA glutamate receptor antagonist MK-801 or protein synthesis inhibitor cycloheximide in combination with the conditioned food stimulus (reminder) on day 2 after learning were followed by the development of amnesia. Repeated training on day 10 after the induction of amnesia did not result in skill formation. Injections of MK-801 or cycloheximide and reminder by the 10th day after training had no effect on memory retention. Injections of MK-801 or cycloheximide and reminder by the 30th day after training were followed by the development of amnesia. In these experiments, memory was recovered after repeated training. Our results indicate that a complex phase reorganization of memory occurs over 30 days after learning. This process includes memory consolidation over the first days after training, stabilization and resistance to adverse factors after 10 days, and newly acquired ability for reconsolidation by the 30th day after training.

Processes of DNA methylation are involved in the mechanisms of amnesia induction and conditioned food aversion memory reconsolidation.

We studied the role of DNA methylation in the mechanisms of amnesia in edible snails, which was induced by impairment of conditioned food aversion memory reconsolidation with NMDA glutamate receptor antagonist. The effects of DNA methyltransferase inhibitors were shown to depend on the stage of amnesia. At the early stage of amnesia (day 3 after induction), injections of methyltransferase inhibitors in combination with conditioned food stimulus (reminder) were followed by memory recovery. Application of inhibitors in the absence of the reminder was ineffective. Methyltransferase inhibitors were ineffective at the late stage of amnesia (day 10). Our results suggest that the presentation of reminding conditioned stimuli is followed by reactivation of amnesia. Methylation or demethylation of DNA in nerve cells serves as one of the key mechanisms for amnesia.

Involvement of translation and transcription processes into neurophysiological mechanisms of long-term memory reconsolidation.

We studied the involvement of translation and transcription processes into behavioral and neuronal mechanisms of reconsolidation of the long-term memory of the conditioned taste aversion in edible snails. Injection of cycloheximide (an inhibitor of protein synthesis) to the snails in 48 h after training combined with subsequent reminder and presentation of the conditional stimulus resulted in the development of persistent amnesia and depression of the responses of the defensive behavior command neurons LPl1 and RPl1 to the conditional stimulus. Injection of mRNA synthesis inhibitors actinomycin D or DRB (5,6-dichloro-1-ß-D-ribofuranosylbenzimidasole) in 48 h after conditioning with subsequent reminding procedure produced no effects on memory retention and on the responses of the command neurons to the conditional stimulus. The study suggests that the proteins translated from previously synthesized and stored mRNA were involved in the mechanisms of reconsolidation of the memory responsible for conditioned taste aversion.

DNA methylation inhibition participates in the anterograde amnesia key mechanism through the suppression of the transcription of genes involved in memory formation in grape snails.

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.