Expression of early growth responsive gene-1 in the lateral geniculate body of kittens with amblyopia caused by monocular form deprivation

OBJECTIVE

The expression of early growth responsive gene-1 (Egr-1) in the lateral geniculate body in the normal kittens and those affected with amblyopia caused by monocular visual deprivation was compared to explore the potential significance of Egr-1 in the pathogenesis of amblyopia.

METHODS

A total of 30 healthy kittens were equally and randomly divided into the control (n = 15) and the deprivation group (n = 15). The kittens were raised in natural light and the right eyes of the deprived kittens were covered with a black opaque covering. Pattern visual evoked potential (PVEP) was measured before and 1, 3, and 5 weeks after covering. Five kittens from each group were randomly selected and euthanized with 2% sodium pentobarbital (100 mg/kg) during the 1st, 3rd and 5th week after covering. The expression of Egr-1 in the lateral geniculate body in the two groups was compared by performing immunohistochemistry and in situ hybridization.

RESULTS

After three weeks of covering, PVEP detection indicated that the P100 wave latency in the deprivation group was significantly higher than that in the control group (P < 0.05), whereas the amplitude decreased markedly (P < 0.05). The number of the positive cells (P < 0.05) and mean optical density (P < 0.05) of Egr-1 protein expression in the lateral geniculate body of the deprivation group were found to be substantially lower in comparison to the normal group, as well as the number (P < 0.05) and mean optical density of Egr-1 mRNA-positive cells (P < 0.05). However, with increase of age, positive expression of Egr-1 in the control group showed an upward trend (P < 0.05), but this trend was not noted in the deprivation group (P > 0.05).

CONCLUSIONS

Monocular form deprivation can lead to substantially decreased expressions of Egr-1 protein and mRNA in the lateral geniculate body, which in turn can affect the normal expression of neuronal functions in the lateral geniculate body, thereby promoting the occurrence and development of amblyopia.

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.

Protein synthesis inhibitor administration before a reminder caused recovery from amnesia induced by memory reconsolidation impairment with NMDA glutamate receptor antagonist

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).