AMPA receptor phosphorylation and recognition memory: learning-related, time-dependent changes in the chick brain following filial imprinting

Src-NADH dehydrogenase subunit 2 complex and recognition memory of imprinting in domestic chicks

Src is a non-receptor tyrosine kinase participating in a range of neuronal processes, including synaptic plasticity. We have recently shown that the amounts of total Src and its two phosphorylated forms, at tyrosine-416 (activated) and tyrosine-527 (inhibited), undergoes time-dependent, region-specific learning-related changes in the domestic chick forebrain after visual imprinting. These changes occur in the intermediate medial mesopallium (IMM), a site of memory formation for visual imprinting, but not the posterior pole of the nidopallium (PPN), a control brain region not involved in imprinting. Src interacts with mitochondrial genome-coded NADH dehydrogenase subunit 2 (NADH2), a component of mitochondrial respiratory complex I. This interaction occurs at brain excitatory synapses bearing NMDA glutamate receptors. The involvement of Src-NADH2 complexes in learning and memory is not yet explored. We show for the first time that, independently of changes in total Src or total NADH2, NADH2 bound to Src immunoprecipitated from the P2 plasma membrane-mitochondrial fraction: (i) is increased in a learning-related manner in the left IMM 1 h after the end of training; (ii), is decreased in the right IMM in a learning-related way 24 h after training. These changes occurred in the IMM but not the PPN. They are attributable to learning occurring during training rather than a predisposition to learn. Learning-related changes in Src-bound NADH2 are thus time- and region-dependent.

Filial imprinting in domestic chicks; cytoplasmic polyadenylation element binding protein 3, predispositions and learning

Visual imprinting is a learning process, whereby young animals come to prefer a visual stimulus after exposure to it (training). Available evidence indicates that the intermediate medial mesopallium (IMM) in the domestic chick forebrain is a site of memory formation during visual imprinting. We have found previously that cytoplasmic polyadenylation element binding protein 3 in the P2 plasma membrane-mitochondrial fraction (CPEB3-P2) is upregulated in a learning-dependent way in the left IMM 24 h after training. CPEB3 has two forms, soluble and aggregated. Soluble CPEB3 represses translation; the aggregated form (CPEB3-AF) is amyloid-like and can promote translation. Our previous study did not show which of these two forms is increased after imprinting. We have now resolved this matter by measuring, 24 h after training, CPEB3-P2 and CPEB3-AF in the IMM and a control brain region, the posterior pole of nidopallium (PPN). The methods include imprinting training with a visual stimulus, behavioral measurement of preference, preparation of aggregated CPEB3, western immunoblotting, quantitation of proteins, statistical linear modeling. Only in the left IMM were the level of CPEB3-AF and learning strength correlated, increased CPEB3-AF level reflecting a predisposition to learn readily. CPEB3-P2 level also increased with learning strength in the left IMM, but as a result of learning. No correlations were detected in the right IMM or PPN. We propose two separate systems, both modulating synaptic strength through control of local translation. They are represented by CPEB3-AF (associated with a predisposition to learn) and soluble CPEB3 (associated with learning itself).

Src and Memory: A Study of Filial Imprinting and Predispositions in the Domestic Chick

Visual imprinting is a learning process whereby young animals come to prefer a visual stimulus after exposure to it (training). The available evidence indicates that the intermediate medial mesopallium (IMM) in the domestic chick forebrain is a site of memory formation during visual imprinting. We have studied the role of Src, an important non-receptor tyrosine kinase, in memory formation. Amounts of total Src (Total-Src) and its two phosphorylated forms, tyrosine-416 (activated, 416P-Src) and tyrosine-527 (inhibited, 527P-Src), were measured 1 and 24 h after training in the IMM and in a control brain region, the posterior pole of nidopallium (PPN). One hour after training, in the left IMM, we observed a positive correlation between the amount of 527P-Src and learning strength that was attributable to learning, and there was also a positive correlation between 416P-Src and learning strength that was attributable to a predisposition to learn readily. Twenty-four hours after training, the amount of Total-Src increased with learning strength in both the left and right IMM, and amount of 527P-Src increased with learning strength only in the left IMM; both correlations were attributable to learning. A further, negative, correlation between learning strength and 416P-Src/Total-Src in the left IMM reflected a predisposition to learn. No learning-related changes were found in the PPN control region. We suggest that there are two pools of Src; one of them in an active state and reflecting a predisposition to learn, and the second one in an inhibited condition, which increases as a result of learning. These two pools may represent two or more signaling pathways, namely, one pathway downstream of Src activated by tyrosine-416 phosphorylation and another upstream of Src, keeping the enzyme in an inactivated state via phosphorylation of tyrosine-527.

Requirements of Postnatal proBDNF in the Hippocampus for Spatial Memory Consolidation and Neural Function

Mature brain-derived neurotrophic factor (BDNF) and its downstream signaling pathways have been implicated in regulating postnatal development and functioning of rodent brain. However, the biological role of its precursor pro-brain-derived neurotrophic factor (proBDNF) in the postnatal brain remains unknown. The expression of hippocampal proBDNF was blocked in postnatal weeks, and multiple behavioral tests, Western blot and morphological techniques, and neural recordings were employed to investigate how proBDNF played a role in spatial cognition in adults. The peak expression and its crucial effects were found in the fourth but not in the second or eighth postnatal week. Blocking proBDNF expression disrupted spatial memory consolidation rather than learning or memory retrieval. Structurally, blocking proBDNF led to the reduction in spine density and proportion of mature spines. Although blocking proBDNF did not affect N-methyl-D-aspartate (NMDA) receptor (NMDAR) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) subunits, the learning-induced phosphorylation of the GluN2B subunit level declined significantly. Functionally, paired-pulse facilitation, post-low-frequency stimulation (LFS) transiently enhanced depression, and GluN2B-dependent short-lasting long-term depression in the Schaffer collateral-CA1 pathway were weakened. The firing rate of pyramidal neurons was significantly suppressed around the target region during the memory test. Furthermore, the activation of GluN2B-mediated signaling could effectively facilitate neural function and mitigate memory impairment. The findings were consistent with the hypothesis that postnatal proBDNF played an essential role in synaptic and cognitive functions.

Chicken cognin interactome and the memory of filial imprinting

Visual imprinting is a learning process whereby young animals come to prefer a visual stimulus after exposure to it (training). The intermediate medial mesopallium in the domestic chick forebrain is critical for visual imprinting and contributes to molecular regulation of memory formation. Criteria used to infer that a change following training is learning-related have been formulated and published. Cognin (protein disulphide isomerase) is one of several identified plasma membrane and mitochondrial proteins that are upregulated in a learning-related way 24 hours after training. Since virtually nothing is known about the cognin interactome, we have used immunoaffinity chromatography and mass spectrometry to identify proteins that interact with cognin in the cytoplasmic and plasma membrane-mitochondrial fractions. As the learning-related upregulation of cognin has been shown to occur in the plasma membrane-mitochondrial fraction and not in the cytoplasmic fraction, we studied the effect of training on three cognin-interacting partners in the plasma membrane-mitochondrial fraction: the b5 subunit of mitochondrial ATP synthase and the alpha-2 and alpha-3 subunits of sodium-potassium ATPase. Learning-related upregulation was found in the left intermediate medial mesopallium 24 hours after training for the b5 subunit of mitochondrial ATP synthase and the alpha-2 subunit of sodium-potassium ATPase. The hemispheric asymmetry revealed here is consistent with the predominance of many other learning-related effects in the left intermediate medial mesopallium. The alpha-2 subunit of sodium-potassium ATPase is mainly expressed in astrocytes, supporting a role for these glial cells in memory.

Visual Imprinting in Birds: Behavior, Models, and Neural Mechanisms

Filial imprinting is a process, readily observed in precocial birds, whereby a social attachment is established between a young animal and an object that is typically (although not necessarily) a parent. During a perinatal sensitive period, the young animal learns characteristics of the object (the imprinting stimulus) simply by being exposed to it and will subsequently recognize and selectively approach this stimulus. Imprinting can thus establish a filial bond with an individual adult: a form of social cohesion that may be crucial for survival. Behavioral predispositions can act together with the learning process of imprinting in the formation, maintenance, and modification of the filial bond. Memory of the imprinting stimulus, as well as being necessary for social recognition, is also used adaptively in perceptual classification of sensory signals. Abstract features of an imprinting stimulus, such as similarity or difference between stimulus components, can also be recognized. Studies of domestic chicks have elucidated the neural basis of much of the above behavior. This article discusses (1) principal behavioral characteristics of filial imprinting and related predispositions, (2) theoretical models that have been developed to account for this behavior, and (3) physiological results elucidating the underlying neural mechanisms. Interactions between these different levels of analysis have resulted in advancement of all of them. Taken together, the different approaches have helped define strategies for investigating mechanisms of learning, memory, and perception.

Micro-RNAs, their target proteins, predispositions and the memory of filial imprinting

Visual imprinting is a learning process whereby young animals come to prefer a visual stimulus after exposure to it (training). The intermediate medial mesopallium (IMM) in the domestic chick forebrain is critical for visual imprinting and contributes to molecular regulation of memory formation. We investigated the role of micro-RNAs (miRNAs) in such regulation. Twenty-four hours after training, miRNA spectra in the left IMM were compared between chicks with high preference scores (strong memory for imprinting stimulus), and chicks with low preference scores (weak memory for imprinting stimulus). Using criteria of significance and expression level, we chose gga-miR-130b-3p for further study and found that down-regulation correlated with learning strength. No effect was detected in posterior nidopallium, a region not involved in imprinting. We studied two targets of gga-miR-130b-3p, cytoplasmic polyadenylation element binding proteins 1 (CPEB-1) and 3 (CPEB-3), in two subcellular fractions (P2 membrane-mitochondrial and cytoplasmic) of IMM and posterior nidopallium. Only in the left IMM was a learning-related effect observed, in membrane CPEB-3. Variances from the regression with preference score and untrained chicks suggest that, in the IMM, gga-miR-130b-3p level reflects a predisposition, i.e. capacity to learn, whereas P2 membrane-mitochondrial CPEB-3 is up-regulated in a learning-specific way.

A Proteomic Study of Memory After Imprinting in the Domestic Chick

The intermediate and medial mesopallium (IMM) of the domestic chick forebrain has previously been shown to be a memory system for visual imprinting. Learning-related changes occur in certain plasma membrane and mitochondrial proteins in the IMM. Two-dimensional gel electrophoresis/mass spectrometry has been employed to identify more comprehensively learning-related expression of proteins in the membrane-mitochondrial fraction of the IMM 24 h after training. We inquired whether amounts of these proteins in the IMM and a control region (posterior pole of the nidopallium, PPN) are correlated with a behavioral estimate of memory for the imprinting stimulus. Learning-related increases in amounts of the following proteins were found in the left IMM, but not the right IMM or the left or right PPN: (i) membrane cognin; (ii) a protein resembling the P32 subunit of splicing factor SF2; (iii) voltage-dependent anionic channel-1; (iv) dynamin-1; (v) heterogeneous nuclear ribonucleoprotein A2/B1. Learning-related increases in some transcription factors involved in mitochondrial biogenesis were also found, without significant change in mitochondrial DNA copy number. The results indicate that the molecular processes involved in learning and memory underlying imprinting include protein stabilization, increased mRNA trafficking, synaptic vesicle recycling, and specific changes in the mitochondrial proteome.

Calcium/Calmodulin-dependent Protein Kinase II is a Ubiquitous Molecule in Human Long-term Memory Synaptic Plasticity: A Systematic Review

BACKGROUND

Long-term memory is based on synaptic plasticity, a series of biochemical mechanisms include changes in structure and proteins of brain's neurons. In this article, we systematically reviewed the studies that indicate calcium/calmodulin kinase II (CaMKII) is a ubiquitous molecule among different enzymes involved in human long-term memory and the main downstream signaling pathway of long-term memory.

METHODS

All of the observational, case-control and review studies were considered and evaluated by the search engines PubMed, Cochrane Central Register of Controlled Trials and ScienceDirect Scopus between 1990 and February 2015. We did not carry out meta-analysis.

RESULTS

At the first search, it was fined 1015 articles which included "synaptic plasticity" OR "neuronal plasticity" OR "synaptic density" AND memory AND "molecular mechanism" AND "calcium/calmodulin-dependent protein kinase II" OR CaMKII as the keywords. A total of 335 articles were duplicates in the databases and eliminated. A total of 680 title articles were evaluated. Finally, 40 articles were selected as reference.

CONCLUSIONS

The studies have shown the most important intracellular signal of long-term memory is calcium-dependent signals. Calcium linked calmodulin can activate CaMKII. After receiving information for learning and memory, CaMKII is activated by Glutamate, the most important neurotransmitter for memory-related plasticity. Glutamate activates CaMKII and it plays some important roles in synaptic plasticity modification and long-term memory.

Molecular mechanisms of memory in imprinting

Converging evidence implicates the intermediate and medial mesopallium (IMM) of the domestic chick forebrain in memory for a visual imprinting stimulus. During and after imprinting training, neuronal responsiveness in the IMM to the familiar stimulus exhibits a distinct temporal profile, suggesting several memory phases. We discuss the temporal progression of learning-related biochemical changes in the IMM, relative to the start of this electrophysiological profile. c-fos gene expression increases <15 min after training onset, followed by a learning-related increase in Fos expression, in neurons immunopositive for GABA, taurine and parvalbumin (not calbindin). Approximately simultaneously or shortly after, there are increases in phosphorylation level of glutamate (AMPA) receptor subunits and in releasable neurotransmitter pools of GABA and taurine. Later, the mean area of spine synapse post-synaptic densities, N-methyl-D-aspartate receptor number and phosphorylation level of further synaptic proteins are elevated. After ∼ 15 h, learning-related changes in amounts of several synaptic proteins are observed. The results indicate progression from transient/labile to trophic synaptic modification, culminating in stable recognition memory.