Early socio-emotional experience induces expression of the immediate-early gene Arc/arg3.1 (activity-regulated cytoskeleton-associated protein/activity-regulated gene) in learning-relevant brain regions of the newborn chick

Changes in the dopaminergic circuitry and adult neurogenesis linked to reinforcement learning in corvids

The caudolateral nidopallium (NCL, an analog of the prefrontal cortex) is known to be involved in learning, memory, and discrimination in corvids (a songbird), whereas the involvement of other brain regions in these phenomena is not well explored. We used house crows (Corvus splendens) to explore the neural correlates of learning and decision-making by initially training them on a shape discrimination task followed by immunohistochemistry to study the immediate early gene expression (Arc), a dopaminoceptive neuronal marker (DARPP-32, Dopamine- and cAMP-regulated phosphoprotein, Mr 32 kDa) to understand the involvement of the reward pathway and an immature neuronal marker (DCX, doublecortin) to detect learning-induced changes in adult neurogenesis. We performed neuronal counts and neuronal tracing, followed by morphometric analyses. Our present results have demonstrated that besides NCL, other parts of the caudal nidopallium (NC), avian basal ganglia, and intriguingly, vocal control regions in house crows are involved in visual discrimination. We have also found that training on the visual discrimination task can be correlated with neurite pruning in mature dopaminoceptive neurons and immature DCX-positive neurons in the NC of house crows. Furthermore, there is an increase in the incorporation of new neurons throughout NC and the medial striatum which can also be linked to learning. For the first time, our results demonstrate that a combination of structural changes in mature and immature neurons and adult neurogenesis are linked to learning in corvids.

The power of innate: Behavioural attachment and neural activity in responses to natural and artificial objects in filial imprinting in chicks

Newly hatched domestic chicks are known to orient preferentially toward naturalistic stimuli, resembling a conspecific. Here, we examined to what extent this behavioral preference can be transcended by an artificial imprinting stimulus in both short-term and long-term tests. We also compared the expression maps of the plasticity-associated c-fos gene in the brains of chicks imprinted to naturalistic (rotating stuffed jungle fowl) and artificial (rotating illuminated red box) stimuli. During training, the approach activity of chicks to a naturalistic object was always higher than that to an artificial object. However, the induction of c-fos mRNA was significantly higher in chicks imprinted to a box than to a fowl, especially in the intermediate medial mesopallium, hyperpallium apicale, arcopallium, and hippocampus. Initially, in the short-term test (10 min after the end of training), chicks had a higher preference for a red box than for a stuffed fowl. However, in the long-term test (24 h after imprinting), the response to an artificial object decreased to the level of preference for a naturalistic object. Our results thus show that despite the artificial object causing a stronger c-fos novelty response and higher behavioral attachment in the short term, this preference was less stable and fades away, being overtaken by a more stable innate predisposition to the naturalistic social object.

Mapping the Neural Substrates of Recent and Remote Visual Imprinting Memory in the Chick Brain

Social attachment formed by filial imprinting in newborn chicks undergoes a process of memory consolidation that involves rearrangement of its neural storage substrates. In the first 3 h after imprinting it depends on the integrity of the intermediate medial mesopallium (IMM) and beyond that time on unidentified memory storage structures dubbed S’. To search for the S’ memory system in the chick brain, we mapped and compared patterns of activity induced by retrieval of filial attachment memory before and after this critical transition. Chicks were trained in the visual imprinting task, and their memory was reactivated by imprinting stimulus either 1 h (recent memory retrieval) or 24 h (remote memory retrieval) after the completion of training. Patterns of brain activity were mapped by in situ hybridization to mRNA of an immediate early gene c-fos. We also mapped c-fos expression induced by the first presentation of the imprinting stimulus. Memory retrieval triggered massive c-fos expression in the chick brain both 1 and 24 h after the end of training. These activity patterns mostly coincided with the c-fos expression induced by the first presentation of imprinting stimulus. However, in the hippocampus c-fos induction was observed only after the first exposure to imprinting stimulus but not after memory retrieval. In the IMM, medio-rostral nidopallium/mesopallium, and hyperpallium densocellulare c-fos activation was induced by retrieval of only the remote but not of the recent memory. These c-fos mapping data point to the candidate brain structures for systems reorganization of imprinting memory in chicks.

The Arc gene: Retroviral heritage in cognitive functions

Stabilization of neuronal plastic changes is mediated by transient gene expression, including transcription of the activity-regulated cytoskeleton-associated gene (Arc), also known as Arg 3.1. Arc is implicated in several types of synaptic plasticity, including synaptic scaling, long-term potentiation, and long-term depression. However, the precise mechanisms by which Arc mediates these forms of long-term plasticity are unclear. It was recently found that Arc protein is capable of forming capsid-like structures and of transferring its own mRNA to neighboring cells. Moreover, Arc mRNA undergoes activity-dependent translation in these "transfected" cells. These new data raise unexpected possibilities for the mechanisms of the Arc action, and many intriguing questions concerning the role of Arc transcellular traffic in neuronal plasticity. In this mini-review, we discuss a possible link between the role of Arc in learning and memory and the virus-like properties of this protein. Additionally, we highlight some of the emerging questions for future neurobiological studies and translational applications of Arc transsynaptic effects.

Postnatal exposure to poly (I:C) impairs learning and memory through changes in synaptic plasticity gene expression in developing rat brain

Viral infection during early stage of life influences brain development and results in several neurodevelopmental disorders such as schizophrenia, autism and behavioral abnormalities. However, the mechanism through which infection causes long-term behavioral defects is not well known. To elucidate this, we have used synthetic polyinosinic-polycytidylic acid [poly (I:C)] which acts as a dsRNA molecule and interacts with toll-like receptor-3 (TLR-3) of microglia cells to evoke the immune system, thus mimicking the viral infection. Rat pups of postnatal day (PND) 7 were infused with a single dose of poly (I:C) (5 mg/kg BW) and vehicle alone to controls. When these pups grew to 3, 6 and 12 weeks, their spatial and fear conditioning memory were impaired as assessed by Morris water maze and passive avoidance test, respectively. We checked the immune activation by staining of TNF-α in the hippocampus and observed that poly (I:C) exposure elevated the number of TNF-α positive cells immediately after 12 h of infusion in one week rat and it persisted up to postnatal age of 3 and 12 weeks. Moreover, poly (I:C) significantly decreased the binding of ³H-QNB to the cholinergic receptors in the frontal cortex and hippocampus of 3 and 6 weeks rats as compared to control but did not change significantly in 12 weeks rats. RT-PCR and immunoblotting results showed that poly (I:C) exposure upregulated the expression of memory associated genes (BDNF, Arc, EGR1) at mRNA and protein level in frontal cortex and hippocampus of 3 weeks rats as compared to control. However, long-time persistence of poly (I:C) effects significantly decreased the expression of these genes in both brain regions of 12 weeks rats. Taken together, it is evident that early life exposure to poly (I:C) has a long-term effect and impairs learning and memory, probably through TNF-α mediated neuroinflammation and alteration in the expression of memory associated genes in frontal cortex and hippocampus of rats.

Regulation of filial imprinting and structural plasticity by mTORC1 in newborn chickens

Dysregulation of the mechanistic target of rapamycin complex 1 (mTORC1) signaling leads to memory deficits and abnormal social behaviors in adults. However, whether mTORC1 is involved in critical periods of early learning remains largely unexplored. Our study addressed this question by investigating imprinting, a form of learning constrained to a sensitive period that supports filial attachment, in newborn chickens. Imprinting to virtual objects and sounds was assessed after acute manipulations of mTORC1. To further understand the role of mTORC1 during the critical period, structural plasticity was analyzed using DiOlistic labeling of dendritic spines. We found that mTORC1 is required for the emergence of experience-dependent preferences and structural plasticity within brain regions controlling behavior. Furthermore, upon critical period closure, pharmacological activation of the AKT/mTORC1 pathway was sufficient to rescue imprinting across sensory modalities. Thus, our results uncover a novel role of mTORC1 in the formation of imprinted memories and experience-dependent reorganization of neural circuits during a critical period.

Transcriptional and post-translational regulation of Arc in synaptic plasticity

One of the most interesting features of Arc-dependent synaptic plasticity is how multiple types of synaptic activity can converge to alter Arc transcription and then diverge to induce different plasticity outcomes, ranging from AMPA receptor internalisation that promotes long-term depression (LTD), to actin stabilisation that promotes long-term potentiation (LTP). This diversity suggests that there must be numerous levels of control to ensure the temporal profile, abundance, localisation and function of Arc are appropriately regulated to effect learning and memory in the correct contexts. The activity-dependent transcription and post-translational modification of Arc are crucial regulators of synaptic plasticity, fine-tuning the function of this key protein depending on the specific situation. The extensive cross-talk between signalling pathways and the numerous routes of Arc regulation provide a complex interplay of processes in which Arc-mediated plasticity can be broadly induced, but specifically tailored to synaptic activity. Here we provide an overview what is currently known about these processes and potential future directions.

Regulation of visual Wulst cell responsiveness by imprinting causes stimulus-specific activation of rostral cells

Imprinting behaviour in chicks can be induced exclusively during a short period after hatching. During this period, visual information on the imprinting stimulus is conveyed to the visual Wulst (VW) in the telencephalon, which corresponds to the visual cortex of mammals, and then to the memory-storing region known as the intermediate medial mesopallium. These two regions are indispensable for imprinting. We previously showed that imprinting training altered the response pattern of the VW to the imprinting stimulus; however, the precise distribution of cells and the mechanism involved with this altered response remains unclear. Here we showed that a specific population of rostral VW cells responded to the imprinting stimulus by analysing the subcellular localization of Arc/arg3.1 transcripts in VW cells. GABAergic parvalbumin (PV) cells are abundant in the dorsal region of this area, and imprinting training doubled the number of activated PV-positive neurons. An injection of bicuculline, a GABA(A) receptor antagonist, in the dorsal VW disturbed the rostral distribution of responsive cells and thus resulted in a lack of imprinting. These results suggest that activated PV cells restrict VW cells response to dorsal area to form a specific imprinting pathway.

Assessment of Cholinergic Properties of Ashwagandha Leaf-Extract in the Amnesic Mouse Brain

BACKGROUND

In our earlier study, we have shown the memory enhancing and scopolamine-induced amnesia recovery properties of Ashwagandha leaf extract using behavioral paradigm and expression analysis of synaptic plasticity genes.

PURPOSE

However, the exact mechanism through which Ashwagandha demonstrates these effects is still unknown.

METHODS

In the present study, we hypothesized that the alcoholic extract of Ashwagandha leaves (i-Extract) possesses cholinergic properties, which in turn inhibit the anti-cholinergic nature of scopolamine. Therefore, the potential of i-Extract to recover from the scopolamine-induced cholinergic deficits was assessed by measuring acetylcholine (neurotransmitter) and Arc (synaptic activity-related gene) expression level in the mouse brain.

RESULTS

The enzymatic activity of acetyl cholinesterase and choline acetyltransferase was assessed through colorimetric assays, and expression level of Arc protein was examined by Western blotting. Furthermore, mRNA level of these genes was examined by semi-quantitative reverse-transcriptase PCR. We observed that the treatment of i-Extract in scopolamine-induced amnesic mouse attenuates scopolamine-induced detrimental alterations in the cholinergic system.

CONCLUSION

Thus, our study provided biochemical and molecular evidence of cholinergic properties of Ashwagandha leaf extract during brain disorders associated with cholinergic dysfunction.

Glutaminase1 heterozygous mice show enhanced trace fear conditioning and Arc/Arg3.1 expression in hippocampus and cingulate cortex

Mice heterozygous for a mutation in the glutaminase (GLS1) gene (GLS1 HZ mice), with reduced glutamate recycling and release, display reduced hippocampal function as well as memory of contextual cues in a delay fear conditioning (FC) paradigm. Here, we asked whether this deficit reflects an inability to process contextual information or a selective alteration in salience attribution. In addition, we asked whether baseline and activity-induced hippocampal activity were diminished in GLS1 HZ mice. For this purpose, we manipulated the relative salience of the conditioned stimulus (CS) and contextual cues in FC tasks, and examined gene expression of the immediate early gene Arc (Arc/Arg3.1) in hippocampus and anterior cingulate cortex (ACC) following trace FC (tFC). The results indicate that GLS1 HZ mice succeed in processing contextual information when the salient CS is absent or less predictive. In addition, in the hippocampus-dependent tFC paradigm GLS1 HZ mice display enhanced CS learning. Furthermore, while baseline arc activation was reduced in GLS1 HZ mice in the hippocampus, in line with previous fMRI findings, it was enhanced in the hippocampus and anterior cingulate cortex following tFC. These findings suggest that GLS1 HZ mice have a pro-cognitive profile in the tFC paradigm, and this phenotype involves activation of both hippocampus and ACC. Taken together with previous work on the GLS1 HZ mouse, this study sheds light on the importance of glutamate transmission to memory processes that require the allocation of attentional resources, and extends our understanding of the underpinnings of attention deficits in SZ.

Early life stress-induced histone acetylations correlate with activation of the synaptic plasticity genes Arc and Egr1 in the mouse hippocampus

Early life stress (ELS) programs the developing organism and influences the development of brain and behavior. We tested the hypothesis that ELS-induced histone acetylations might alter the expression of synaptic plasticity genes that are critically involved in the establishment of limbic brain circuits. Maternal separation (MS) from postnatal day 14-16 was applied as ELS and two immediate early genes underlying experience-induced synaptic plasticity, Arc and early growth response 1 (Egr1) were analyzed. We show here that repeated ELS induces a rapid increase of Arc and Egr1 in the mouse hippocampus. Furthermore, immunoblotting revealed that these changes are paralleled by histone modifications, reflected by increased acetylation levels of H3 and H4. Most importantly, using native Chromatin immunoprecipitation quantitative PCR (nChIP-qPCR), we show for the first time a correlation between elevated histone acetylation and increased Arc and Egr1 expression in response to ELS. These rapid epigenetic changes are paralleled by increases of dendritic complexity and spine number of hippocampal CA3 pyramidal neurons in ELS animals at weaning age. Our results are in line with our working hypothesis that ELS induces activation of synaptic plasticity genes, mediated by epigenetic mechanisms. These events are assumed to represent early steps in the adaption of neuronal networks to a stressful environment.

Two waves of transcription are required for long-term memory in the honeybee

Storage of information into long-term memory (LTM) usually requires at least two waves of transcription in many species. However, there is no clear evidence of this phenomenon in insects, which are influential models for memory studies. We measured retention in honeybees after injecting a transcription inhibitor at different times before and after conditioning. We identified two separate time windows during which the transcription blockade impairs memory quantitatively and qualitatively, suggesting the occurrence of an early transcription wave (triggered during conditioning) and a later one (starting several hours after learning). Hence insects, like other species, would require two transcription waves for LTM formation.

Hippocampal memory consolidation during sleep: a comparison of mammals and birds

The transition from wakefulness to sleep is marked by pronounced changes in brain activity. The brain rhythms that characterize the two main types of mammalian sleep, slow-wave sleep (SWS) and rapid eye movement (REM) sleep, are thought to be involved in the functions of sleep. In particular, recent theories suggest that the synchronous slow-oscillation of neocortical neuronal membrane potentials, the defining feature of SWS, is involved in processing information acquired during wakefulness. According to the Standard Model of memory consolidation, during wakefulness the hippocampus receives input from neocortical regions involved in the initial encoding of an experience and binds this information into a coherent memory trace that is then transferred to the neocortex during SWS where it is stored and integrated within preexisting memory traces. Evidence suggests that this process selectively involves direct connections from the hippocampus to the prefrontal cortex (PFC), a multimodal, high-order association region implicated in coordinating the storage and recall of remote memories in the neocortex. The slow-oscillation is thought to orchestrate the transfer of information from the hippocampus by temporally coupling hippocampal sharp-wave/ripples (SWRs) and thalamocortical spindles. SWRs are synchronous bursts of hippocampal activity, during which waking neuronal firing patterns are reactivated in the hippocampus and neocortex in a coordinated manner. Thalamocortical spindles are brief 7-14 Hz oscillations that may facilitate the encoding of information reactivated during SWRs. By temporally coupling the readout of information from the hippocampus with conditions conducive to encoding in the neocortex, the slow-oscillation is thought to mediate the transfer of information from the hippocampus to the neocortex. Although several lines of evidence are consistent with this function for mammalian SWS, it is unclear whether SWS serves a similar function in birds, the only taxonomic group other than mammals to exhibit SWS and REM sleep. Based on our review of research on avian sleep, neuroanatomy, and memory, although involved in some forms of memory consolidation, avian sleep does not appear to be involved in transferring hippocampal memories to other brain regions. Despite exhibiting the slow-oscillation, SWRs and spindles have not been found in birds. Moreover, although birds independently evolved a brain region--the caudolateral nidopallium (NCL)--involved in performing high-order cognitive functions similar to those performed by the PFC, direct connections between the NCL and hippocampus have not been found in birds, and evidence for the transfer of information from the hippocampus to the NCL or other extra-hippocampal regions is lacking. Although based on the absence of evidence for various traits, collectively, these findings suggest that unlike mammalian SWS, avian SWS may not be involved in transferring memories from the hippocampus. Furthermore, it suggests that the slow-oscillation, the defining feature of mammalian and avian SWS, may serve a more general function independent of that related to coordinating the transfer of information from the hippocampus to the PFC in mammals. Given that SWS is homeostatically regulated (a process intimately related to the slow-oscillation) in mammals and birds, functional hypotheses linked to this process may apply to both taxonomic groups.

Food for song: expression of c-Fos and ZENK in the zebra finch song nuclei during food aversion learning

BACKGROUND

Specialized neural pathways, the song system, are required for acquiring, producing, and perceiving learned avian vocalizations. Birds that do not learn to produce their vocalizations lack telencephalic song system components. It is not known whether the song system forebrain regions are exclusively evolved for song or whether they also process information not related to song that might reflect their 'evolutionary history'.

METHODOLOGY/PRINCIPAL FINDINGS

To address this question we monitored the induction of two immediate-early genes (IEGs) c-Fos and ZENK in various regions of the song system in zebra finches (Taeniopygia guttata) in response to an aversive food learning paradigm; this involves the association of a food item with a noxious stimulus that affects the oropharyngeal-esophageal cavity and tongue, causing subsequent avoidance of that food item. The motor response results in beak and head movements but not vocalizations. IEGs have been extensively used to map neuro-molecular correlates of song motor production and auditory processing. As previously reported, neurons in two pallial vocal motor regions, HVC and RA, expressed IEGs after singing. Surprisingly, c-Fos was induced equivalently also after food aversion learning in the absence of singing. The density of c-Fos positive neurons was significantly higher than that of birds in control conditions. This was not the case in two other pallial song nuclei important for vocal plasticity, LMAN and Area X, although singing did induce IEGs in these structures, as reported previously.

CONCLUSIONS/SIGNIFICANCE

Our results are consistent with the possibility that some of the song nuclei may participate in non-vocal learning and the populations of neurons involved in the two tasks show partial overlap. These findings underscore the previously advanced notion that the specialized forebrain pre-motor nuclei controlling song evolved from circuits involved in behaviors related to feeding.

Characterization of the plasticity-related gene, Arc, in the frog brain

In mammals, expression of the immediate early gene Arc/Arg3.1 in the brain is induced by exposure to novel environments, reception of sensory stimuli, and production of learned behaviors, suggesting a potentially important role in neural and behavioral plasticity. To date, Arc has only been characterized in a few species of mammals and birds, which limits our ability to understand its role in modifying behavior. To begin to address this gap, we identified Arc in two frog species, Xenopus tropicalis and Physalaemus pustulosus, and characterized its expression in the brain of P. pustulosus. We found that the predicted protein for frog Arc shared 60% sequence similarity with Arc in other vertebrates, and we observed high Arc expression in the forebrain, but not the midbrain or hindbrain, of female túngara frogs sacrificed at breeding ponds. We also examined the time-course of Arc induction in the medial pallium, the homologue of the mammalian hippocampus, in response to a recording of a P. pustulosus mating chorus and found that accumulation of Arc mRNA peaked 0.75 h following stimulus onset. We found that the mating chorus also induced Arc expression in the lateral and ventral pallia and the medial septum, but not in the striatum, hypothalamus, or auditory midbrain. Finally, we examined acoustically induced Arc expression in response to different types of mating calls and found that Arc expression levels in the pallium and septum did not vary with the biological relevance or acoustic complexity of the signal.

Expression of the GABA(A) receptor gamma4-subunit gene in discrete nuclei within the zebra finch song system

The acquisition, production and maintenance of song by oscine birds is a form of audition-dependent learning that, in many ways, resembles the process by which humans learn to speak. In songbirds, the generation of structured song is determined by the activity of two interconnected neuronal pathways (the anterior forebrain pathway and the vocal motor pathway), each of which contains a number of discrete nuclei that together form the song system. It is becoming increasingly evident that inhibitory GABAergic mechanisms are indispensable in counterbalancing the excitatory actions of glutamate and, thus, likely shape the neuronal firing patterns of neurons within this network. Furthermore, there is compelling evidence for the involvement of GABA(A) receptors, although the molecular composition of these has, to date, remained elusive. Here we describe the isolation of a complementary DNA for the zebra finch GABA(A) receptor gamma4 subunit, and map the expression pattern of the corresponding gene within the zebra finch (Taeniopygia guttata) brain. Our findings show, remarkably, that the gamma4-subunit transcript is highly enriched in the major nuclei of the song system, including the lateral magnocellular nucleus of the anterior nidopallium (LMAN), the medial magnocellular nucleus of the anterior nidopallium (MMAN), Area X, the robust nucleus of the arcopallium (RA) and the HVC (used as the proper name), as well as Field L, which innervates the area surrounding HVC. In summary, we have demonstrated the presence of the mRNA for the gamma4 subunit of the GABA(A) receptor, the major inhibitory receptor in brain, in most of the nuclei of the two neural circuits that mediate song production in the zebra finch. This not only marks the beginning of the characterization of the GABA(A) receptor subtype(s) that mediates the actions of GABA in the song system but it also provides a robust molecular marker with which to distinguish song system-specific brain structures.

Arc/Arg3.1 translation is controlled by convergent N-methyl-D-aspartate and Gs-coupled receptor signaling pathways

Arc/Arg3.1 is an immediate early gene whose expression is necessary for the late-phase of long-term potentiation (LTP) and memory consolidation. Whereas pathways regulating Arc transcription have been extensively investigated, less is known about the role of post-transcriptional mechanisms in Arc expression. Fluorescence microscopy experiments in cultured hippocampal neurons revealed that Arc protein level was dramatically increased by activation of the cAMP-dependent protein kinase (PKA) pathway, which is implicated in long-term memory. A PKA-dependent increase in Arc protein level was observed after pharmacological or synaptic activation of N-methyl-D-aspartate (NMDA) receptors, which play a critical role in both LTP induction and learning. Arc protein was also up-regulated by activation of PKA through G(s)-coupled dopamine and beta-adrenergic receptors, which regulate the late-phase of LTP and memory. When agonists for the NMDA and G(s)-coupled receptors were co-applied, they had an additive effect on Arc protein expression. Interestingly, G(s)-coupled receptor stimulation was ineffective in the presence of an NMDA receptor antagonist, suggesting calcium influx through the NMDA receptor plays a gating role in this pathway. Stimulation of the cAMP/PKA pathway did not affect Arc mRNA level or protein stability, identifying translational efficacy as the main determinant of Arc protein expression level. It is concluded that efficient Arc translation requires NMDA receptor activity, whereas a further enhancement can be achieved with activation of G(s)-coupled receptors. These experiments have, therefore, revealed remarkable similarities in the signaling pathways that control Arc expression and those that regulate LTP, learning, and memory.

Activity-regulated cytoskeleton-associated protein Arc/Arg3.1 binds to spectrin and associates with nuclear promyelocytic leukemia (PML) bodies

Activity-regulated cytoskeleton-associated protein (Arc/Arg3.1) is an immediate early gene, whose expression in the central nervous system is induced by specific patterns of synaptic activity. Arc is required for the late-phase of long-term potentiation (LTP) and memory consolidation, and has been implicated in AMPA receptor trafficking. Since Arc's molecular function remains incompletely understood, we have determined its subcellular localization in cultured hippocampal neurons and HEK 293T cells. Fluorescence microscopy experiments revealed that both endogenous and exogenous Arc protein was primarily found in the nucleus, where it concentrated in puncta associated with promyelocytic leukemia (PML) bodies, proposed sites of transcriptional regulation. Arc co-localized and interacted with the betaIV spectrin splice variant betaSpIVSigma5, a nuclear spectrin isoform associated with PML bodies and the nuclear matrix. A small region of Arc containing the coiled-coil domain is also restricted to beta-spectrin-positive puncta, while the isolated spectrin homology domain is diffusely localized. Finally, Arc and betaSpIVSigma5 synergistically increased the number of PML bodies. These results suggest that Arc functions as a spectrin-binding protein, forming a complex that may provide a role at sites of transcriptional regulation within the nucleus.

In-vivo gene transfer into newly hatched chick brain by electroporation

Newly hatched domestic chicks serve as ideal models for studies of the neural basis of behavioral plasticity, particularly for understanding the mechanisms of learning such as filial imprinting. To elucidate the molecular basis and gene functions involved in learning, we developed an in-vivo gene-transfer system in the brain of a living chick using electroporation. When green fluorescent protein-encoding plasmids were transfected to a chick brain, green fluorescence was clearly observed, and expression at the protein level was confirmed by immunoblotting. Most of the transfected brain cells were neuronal cells with dendrites. This neuron-selective electroporation system will facilitate the analysis of gene functions in the living chick brain and provide further clues as to the molecular mechanisms of avian learning.

Gene expression and plasticity in the rat auditory cortex after bilateral cochlear ablation

CONCLUSION

The plastic changes in the auditory cortex after bilateral cochlear ablation are related to the immediate early genes as well as the neural plasticity-related genes. In addition, cross-modal plasticity may play an important role in the early changes in the auditory cortex after bilateral cochlear ablation.

OBJECTIVES

The purpose of this study was to identify candidate genes involved in the normal development of primary auditory cortex during the critical period as well as those genes specifically modulated under conditions of sensory deafferentation by bilateral cochlear ablation.

MATERIALS AND METHODS

We produced a bilaterally deaf rat model and used DNA microarray technology to analyze differential gene expression in the primary auditory cortex of bilateral cochlear ablated and sham-operated age-matched control rats. Gene expression in the auditory cortex was compared at 2, 4, and 12 weeks after surgery. For selected genes, the changes in gene expression were confirmed by real-time polymerase chain reaction (PCR).

RESULTS

In the cochlear ablation groups, the expression of immediate early genes (Egr1, 2, 3, 4, c-fos, etc.) and neural plasticity-related genes (Arc, Syngr1, Bdnf, etc.) was decreased at 2 weeks and increased at 4 weeks. The expression of neurotransmission-related genes (Gabra5, Chrnb3, Chrne, etc.) was decreased at 12 weeks.

Arc/Arg3.1 interacts with the endocytic machinery to regulate AMPA receptor trafficking

Arc/Arg3.1 is an immediate-early gene whose mRNA is rapidly transcribed and targeted to dendrites of neurons as they engage in information processing and storage. Moreover, Arc/Arg3.1 is known to be required for durable forms of synaptic plasticity and learning. Despite these intriguing links to plasticity, Arc/Arg3.1's molecular function remains enigmatic. Here, we demonstrate that Arc/Arg3.1 protein interacts with dynamin and specific isoforms of endophilin to enhance receptor endocytosis. Arc/Arg3.1 selectively modulates trafficking of AMPA-type glutamate receptors (AMPARs) in neurons by accelerating endocytosis and reducing surface expression. The Arc/Arg3.1-endocytosis pathway appears to regulate basal AMPAR levels since Arc/Arg3.1 KO neurons exhibit markedly reduced endocytosis and increased steady-state surface levels. These findings reveal a novel molecular pathway that is regulated by Arc/Arg3.1 and likely contributes to late-phase synaptic plasticity and memory consolidation.

Arc/Arg3.1 is essential for the consolidation of synaptic plasticity and memories

Arc/Arg3.1 is robustly induced by plasticity-producing stimulation and specifically targeted to stimulated synaptic areas. To investigate the role of Arc/Arg3.1 in synaptic plasticity and learning and memory, we generated Arc/Arg3.1 knockout mice. These animals fail to form long-lasting memories for implicit and explicit learning tasks, despite intact short-term memory. Moreover, they exhibit a biphasic alteration of hippocampal long-term potentiation in the dentate gyrus and area CA1 with an enhanced early and absent late phase. In addition, long-term depression is significantly impaired. Together, these results demonstrate a critical role for Arc/Arg3.1 in the consolidation of enduring synaptic plasticity and memory storage.