Differential expression of the immediate early genes c-Fos, Arc, Egr-1, and Npas4 during long-term memory formation in the context preexposure facilitation effect (CPFE)

Paternal ethanol exposure alters offspring motor skills and behavior in a sex-dependent manner and modifies early growth response 1 expression in the medial prefrontal cortex

BACKGROUND

Alcohol consumption is linked to various health issues exerting direct effects on the consumer and indirectly on offspring through both maternal and paternal transmission pathways. Our recent studies highlight the importance of paternal health before conception, showing that male ethanol consumption can alter epigenetic sperm marks and DNA integrity and testicular organization which led to adverse effects on embryonic development and induced alterations in testicular and sperm characteristics in the offspring.

METHODS

Based on these findings, this study explores the effects of paternal ethanol (15 % v/v) consumption for 12 days on motor development in mice offspring. We also analyzed different behavioral parameters and evaluated the expression of immediate early genes from the medial prefrontal cortex in the progeny during adulthood.

RESULTS

Paternal alcohol intake negatively affects the offspring, showing a delay in the acquisition of motor developmental skills at an early age and some modifications of behavior in a sex-dependent manner in adulthood. Furthermore, this consumption shows an increase in the expression of the Early Growth Response 1 gene in both males and females in the medial prefrontal cortex.

LIMITATIONS

In situ expression of the early growth response 1 gene was not measured. Hormonal fluctuations during the estrous cycle of the female offspring were not considered, these changes could interact with the observed outcomes.

CONCLUSIONS

This gene plays a key role in regulating cognition, emotion, and behavior. These findings highlight the importance of considering paternal health and alcohol consumption when assessing the risks to future generations.

Effect of Low-Dose-Rate Radiation on Cognition and Gene Expression Profiles in Type II Diabetes Mellitus Mouse Model

Diabetes, a chronic metabolic disorder that disrupts blood glucose regulation, often results in cognitive impairment, diminishing the quality of life of affected individuals. H owever, the effect of low-dose-rate radiation on the progression of type 2 diabetes mellitus (T2DM) remains largely unexplored. Therefore, this study aimed to investigate whether low-dose-rate radiation could affect diabetic cognitive function and elucidate the underlying mechanisms using a mouse model of T2DM. In this study, male db/db (DB) mice were exposed to low-dose-rate (LDR) radiation, and their locomotor activity and cognitive functions were evaluated using the open-field and object recognition memory tests, respectively. The DB group exhibited diminished activity compared to the C57BL/6 mice used for wild-type (WT) group. Although no significant change was evident in locomotor activity, exposure to 2 Gy attenuated cognitive dysfunction in the DB group, as determined by the object recognition memory test. Following LDR radiation exposure, a total of 32 differentially expressed genes were identified in the hippocampus of DB mice (p < 0.05, fold change > 1.5). Subsequent analyses using DAVID and STRING clustered these genes into pathways related to apoptotic process, transcription, cellular response, cell differentiation, and long-term memory. Real-time polymerase chain reaction analysis indicated that LDR radiation ameliorated the expression of genes, including Arc, Bcl6, Cpne1, Egr1, and Nr4a1 in the hippocampus of DB mice, which was consistent with the RNA-sequencing data. Therefore, this study suggests the potential of LDR radiation to ameliorate cognitive function in DB mice, possibly by regulating genes associated with transcription, neuronal differentiation, and long-term memory in the hippocampus. These findings identify candidate genes for further investigation regarding the role of radiation in the progression of T2DM.

Structural synaptic signatures of contextual memory retrieval-reactivated hippocampal engram cells

Learning enhances hippocampal engram cell synaptic connectivity which is crucial for engram reactivation and recall to natural cues. Memory retrieval engages only a subset of the learning-activated ensemble, indicating potential differences in synaptic connectivity signatures of reactivated and non-reactivated cells. We probed these differences in structural synaptic connectivity patterns after recent memory retrieval, 72 h after either neutral Context Exploration (CE) or aversive Contextual Fear Conditioning (CFC). Using a combination of eGRASP (enhanced green fluorescent protein (GFP) reconstitution across synaptic partners) and viral-TRAP (targeted recombination in activated populations) to label CA3 synapses onto CA1 engram cells, we investigated differences in spine density, clusters, and morphology between the reactivated and non-reactivated population of the learning ensemble. In doing so, we developed a pipeline for reconstruction and analysis of dendrites and spines, taking nested data structure into account. Our data demonstrate an interplay between reactivation status, context valence or both factors on the number, distribution, and morphology of CA1 engram cell synapses. Despite a lack of differences in spine density, reactivated engram cells encoding an aversive context were characterised by a higher probability of forming spine clusters and a more dynamic spine type signature compared to their non-reactivated counterparts or engram cells encoding a neutral context. Together, our data indicate that the learning-activated ensemble undergoes different trajectories in structural synaptic connectivity during engram refinement.

Multiomic Network Analysis Identifies Dysregulated Neurobiological Pathways in Opioid Addiction

BACKGROUND

Opioid addiction is a worldwide public health crisis. In the United States, for example, opioids cause more drug overdose deaths than any other substance. However, opioid addiction treatments have limited efficacy, meaning that additional treatments are needed.

METHODS

To help address this problem, we used network-based machine learning techniques to integrate results from genome-wide association studies of opioid use disorder and problematic prescription opioid misuse with transcriptomic, proteomic, and epigenetic data from the dorsolateral prefrontal cortex of people who died of opioid overdose and control individuals.

RESULTS

We identified 211 highly interrelated genes identified by genome-wide association studies or dysregulation in the dorsolateral prefrontal cortex of people who died of opioid overdose that implicated the Akt, BDNF (brain-derived neurotrophic factor), and ERK (extracellular signal-regulated kinase) pathways, identifying 414 drugs targeting 48 of these opioid addiction-associated genes. Some of the identified drugs are approved to treat other substance use disorders or depression.

CONCLUSIONS

Our synthesis of multiomics using a systems biology approach revealed key gene targets that could contribute to drug repurposing, genetics-informed addiction treatment, and future discovery.

Melatonin Regulates Neuronal Synaptic Plasticity in the Supramammillary Nucleus and Attenuates Methamphetamine-Induced Conditioned Place Preference and Sensitization in Mice

Methamphetamine (METH) is an addictive drug that threatens human health. The supramammillary nucleus (SuM) and its neural circuits play key roles in the regulation of spatial memory retrieval, and hippocampal contextual or social memory. Melatonin (MLT), a pineal hormone, can regulate hypothalamic-neurohypophysial activity. Our previous study showed that MLT attenuates METH-induced locomotor sensitization. However, whether MLT regulates SuM function and participates in METH-induced contextual memory retrieval remains unclear. Using a mouse model of METH-conditioned place preference (CPP) and sensitization, we found that METH activated c-Fos expression and elevated calcium (Ca²⁺) levels in SuM neurons. Chemogenetic inhibition of SuM attenuates CPP and sensitization. Pretreatment with MLT decreased c-Fos expression and Ca2+ levels in the SuM and reversed METH-induced addictive behavior, effects that were blocked with the selective MT2 receptors antagonist 4P-PDOT and the MT1 receptors antagonist S26131. Furthermore, MLT reduced SuM synaptic plasticity, glutamate (Glu) release, and neuronal oscillations caused by METH, which were blocked by 4P-PDOT. In conclusion, our data revealed that MLT regulates neuronal synaptic plasticity in the SuM, likely through the MLT receptors (MTs), and plays a role in modulating METH-addictive behavior.

Cellular and circuit features distinguish dentate gyrus semilunar granule cells and granule cells activated during contextual memory formation

The dentate gyrus is critical for spatial memory formation and shows task related activation of cellular ensembles considered as memory engrams. Semilunar granule cells (SGCs), a sparse dentate projection neuron subtype distinct from granule cells (GCs), were recently reported to be enriched among behaviorally activated neurons. However, the mechanisms governing SGC recruitment during memory formation and their role in engram refinement remains unresolved. By examining neurons labeled during contextual memory formation in TRAP2 mice, we empirically tested competing hypotheses for GC and SGC recruitment into memory ensembles. In support of the proposal that more excitable neurons are preferentially recruited into memory ensembles, SGCs showed greater sustained firing than GCs. Additionally, SGCs labeled during memory formation showed less adapting firing than unlabeled SGCs. Our recordings did not reveal glutamatergic connections between behaviorally labeled SGCs and GCs, providing evidence against SGCs driving local circuit feedforward excitation in ensemble recruitment. Contrary to a leading hypothesis, there was little evidence for individual SGCs or labeled neuronal ensembles supporting lateral inhibition of unlabeled neurons. Instead, pairs of GCs and SGCs within labeled neuronal cohorts received more temporally correlated spontaneous excitatory synaptic inputs than labeled-unlabeled neuronal pairs, validating a role for correlated afferent inputs in neuronal ensemble selection. These findings challenge the proposal that SGCs drive dentate GC ensemble refinement, while supporting a role for intrinsic active properties and correlated inputs in preferential SGC recruitment to contextual memory engrams.

Impact Statement

Evaluation of semilunar granule cell involvement in dentate gyrus contextual memory processing supports recruitment based on intrinsic and input characteristics while revealing limited contribution to ensemble refinement.

Functional network of contextual and temporal memory has increased amygdala centrality and connectivity with the retrosplenial cortex, thalamus, and hippocampus

In fear conditioning with time intervals between the conditioned (CS) and unconditioned (US) stimuli, a neural representation of the CS must be maintained over time to be associated with the later US. Usually, temporal associations are studied by investigating individual brain regions. It remains unknown, however, the effect of the interval at the network level, uncovering functional connections cooperating for the CS transient memory and its fear association. We investigated the functional network supporting temporal associations using a task in which a 5-s interval separates the contextual CS from the US (CFC-5s). We quantified c-Fos expression in forty-nine brain regions of male rats following the CFC-5s training, used c-Fos correlations to generate functional networks, and analyzed them by graph theory. Control groups were trained in contextual fear conditioning, in which CS and US overlap. The CFC-5s training additionally activated subdivisions of the basolateral, lateral, and medial amygdala; prelimbic, infralimbic, perirhinal, postrhinal, and intermediate entorhinal cortices; ventral CA1 and subiculum. The CFC-5s network had increased amygdala centrality and higher amygdala internal and external connectivity with the retrosplenial cortex, thalamus, and hippocampus. Amygdala and thalamic nuclei were network hubs. Functional connectivity among these brain regions could support CS transient memories and their association.

Social buffering reduces fear expression in Wistar rats when tested in pairs, but not when retested alone

Social buffering is a phenomenon in which the stress response of an individual can be reduced by the presence of another individual. However, little is known about the effect of social buffering on aversive after memory extinction, especially when animals are tested alone afterwards. The aim of this study was to verify the social buffering effect in rats during the extinction session of the contextual fear conditioning model and the fear response when animals are tested alone in the following day. Animals were divided into subjects and associates, with the subjects undergoing the fear conditioning protocol and the associates paired with the subjects during the fear extinction session. Across five different experiments, we tested moderate and high intensity contextual fear conditioning protocols, as well four variations of pairs: (i) two conditioned subjects, (ii) a conditioned subject and a non-conditioned associate, (iii) a conditioned subject and an associate who observed the conditioning of the partner and (iv) two conditioned subjects, with one treated with diazepam. The social buffering effect was found efficient to reduce the fear memory expression during the fear extinction session. In the moderate intensity protocol, the reduction in freezing time occurred only in subjects accompanied by non-conditioned associates and observer associates. In the high intensity protocol, the social buffering effect occurred in subjects accompanied by either conditioned or non-conditioned associates, although the effect was more evident in the presence of non-conditioned subjects. Treatment of the conditioned associates with diazepam did not improve the social buffering effect. Moreover, social buffering effects were not correlated with self-grooming or prosocial behaviors, which indicates that the presence of another animal might decrease freezing by promotion of exploratory activity. Finally, the social buffering effect was not observed in the extinction test, either because the extinction was too effective in the moderate intensity protocol or because the extinction was equally ineffective in the high intensity protocol. Our results suggest that social buffering does not improve fear extinction consolidation.

Empagliflozin enhances neuroplasticity in rotenone-induced parkinsonism: Role of BDNF, CREB and Npas4

AIMS

Parkinsonism is characterized by degeneration of dopaminergic neurons and impairment in neuroplasticity. Empagliflozin (EMPA) is an anti-diabetic drug that has been shown to improve cognitive dysfunctions and exerted antioxidant and anti-inflammatory effects in different models. This study aimed to determine the neuroprotective effects of EMPA against rotenone (ROT)-induced parkinsonism.

MAIN METHODS

ROT (1.5 mg/kg) was injected subcutaneously three times per week for two successive weeks. Mice were treated with EMPA (3 and 10 mg/kg, orally) for one week prior ROT administration and for another two weeks along with ROT. After that, motor functions and histopathological changes were assessed, and brains were isolated for biochemical analyses and immunohistochemical investigation.

KEY FINDINGS

Results indicated that, in a dose dependent manner, EMPA improved motor functions and histopathological changes induced by ROT, increased brain content of reduced glutathione (GSH), dopamine (DA), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), nuclear factor erythroid 2-related factor 2 (Nrf2), inositol trisphosphate (IP3), calcium (Ca²⁺), calcium/calmodulin-dependent protein kinase type IV (CaMKIV) and phospho-Protein kinase B (p-Akt) levels compared to ROT group. Additionally, EMPA decreased the levels of malondialdehyde (MDA), and tumor necrosis factor-α (TNF-α), and inactivated glycogen synthase kinase-3 beta (GSK-3β). Improvement in neuroplasticity was also observed indicated by elevation in brain derived neurotrophic factor (BDNF), cAMP response element-binding protein (CREB), and neuronal PAS domain Protein 4 (Npas4).

SIGNIFICANCE

EMPA improved motor functions possibly through improving neuroplasticity markers and antioxidant, anti-inflammatory, and neuroprotective effects in a dose dependent manner.

New Context Significantly Changes Expression of Irs2 Gene in Hippocampal Areas

Memory formation is a complex process involving changes in the synaptic activity and gene expression encoding the insulin-like growth factors. We analyzed changes in the expression of genes encoding the insulin/insulin-like growth factors' proteins at the early period of learning in the CA1 region and dentate gyrus of the dorsal and ventral hippocampus in mice 1 hour after presentation of a new context (contextual fear conditioning) with and without negative reinforcement. It was found that in addition to changes in the expression of immediate early genes c-Fos (in all studied hippocampal fields) and Arc (in dorsal and ventral CA1, as well as in dorsal dentate gyrus), exposure to a new context significantly altered expression of the insulin receptor substrate 2 gene (Irs2) in dorsal CA1 and ventral dentate gyrus irrespectively of the negative reinforcement, which suggests participation of the insulin/IGF system in the early stages of neural activation during learning.

Developmental differences in amygdala projection neuron activation associated with isolation-driven changes in social preference

Adolescence is a developmental period characterized by brain maturation and changes in social engagement. Changes in the social environment influence social behaviors. Memories of social events, including remembering familiar individuals, require social engagement during encoding. Therefore, existing differences in adult and adolescent social repertoires and environmentally-driven changes in social behavior may impact novel partner preference, associated with social recognition. Several amygdala subregions are sensitive to the social environment and can influence social behavior, which is crucial for novelty preference. Amygdala neurons project to the septum and nucleus accumbens (NAc), which are linked to social engagement. Here, we investigated how the social environment impacts age-specific social behaviors during social encoding and its subsequent impact on partner preference. We then examined changes in amygdala-septal and -NAc circuits that accompany these changes. Brief isolation can drive social behavior in both adults and adolescents and was used to increase social engagement during encoding. We found that brief isolation facilitates social interaction in adolescents and adults, and analysis across time revealed that partner discrimination was intact in all groups, but there was a shift in preference within isolated and non-isolated groups. We found that this same isolation preferentially increases basal amygdala (BA) activity relative to other amygdala subregions in adults, but activity among amygdala subregions was similar in adolescents, even when considering conditions (no isolation, isolation). Further, we identify isolation-driven increases in BA-NAc and BA-septal circuits in both adults and adolescents. Together, these results provide evidence for changes in neuronal populations within amygdala subregions and their projections that are sensitive to the social environment that may influence the pattern of social interaction within briefly isolated groups during development.

Infusion of etoposide in the CA1 disrupts hippocampal immediate early gene expression and hippocampus-dependent learning

Tight regulation of immediate early gene (IEG) expression is important for synaptic plasticity, learning, and memory. Recent work has suggested that DNA double strand breaks (DSBs) may have an adaptive role in post-mitotic cells to induce IEG expression. Physiological activity in cultured neurons as well as behavioral training leads to increased DSBs and subsequent IEG expression. Additionally, infusion of etoposide-a common cancer treatment that induces DSBs-impairs trace fear memory. Here, we assessed the effects of hippocampal infusion of 60 ng of etoposide on IEG expression, learning, and memory in 3-4 month-old C57Bl/6J mice. Etoposide altered expression of the immediate early genes cFos and Arc in the hippocampus and impaired hippocampus-dependent contextual fear memory. These data add to the growing evidence that DSBs play an important role in IEG expression, learning, and memory, opening avenues for developing novel treatment strategies for memory-related disorders.

The Rab11-regulated endocytic pathway and BDNF/TrkB signaling: Roles in plasticity changes and neurodegenerative diseases

Neurons are highly polarized cells that rely on the intracellular transport of organelles. This process is regulated by molecular motors such as dynein and kinesins and the Rab family of monomeric GTPases that together help move cargo along microtubules in dendrites, somas, and axons. Rab5-Rab11 GTPases regulate receptor trafficking along early-recycling endosomes, which is a process that determines the intracellular signaling output of different signaling pathways, including those triggered by BDNF binding to its tyrosine kinase receptor TrkB. BDNF is a well-recognized neurotrophic factor that regulates experience-dependent plasticity in different circuits in the brain. The internalization of the BDNF/TrkB complex results in signaling endosomes that allow local signaling in dendrites and presynaptic terminals, nuclear signaling in somas and dynein-mediated long-distance signaling from axons to cell bodies. In this review, we briefly discuss the organization of the endocytic pathway and how Rab11-recycling endosomes interact with other endomembrane systems. We further expand upon the roles of the Rab11-recycling pathway in neuronal plasticity. Then, we discuss the BDNF/TrkB signaling pathways and their functional relationships with the postendocytic trafficking of BDNF, including axonal transport, emphasizing the role of BDNF signaling endosomes, particularly Rab5-Rab11 endosomes, in neuronal plasticity. Finally, we discuss the evidence indicating that the dysfunction of the early-recycling pathway impairs BDNF signaling, contributing to several neurodegenerative diseases.

Comprehensive Analysis of lncRNAs, miRNAs and mRNAs in Mouse Hippocampus With Hepatic Encephalopathy

Hepatic encephalopathy (HE) often presents with varying degrees of cognitive impairment. However, the molecular mechanism of its cognitive impairment has not been fully elucidated. Whole transcriptome analysis of hippocampus between normal and HE mice was performed by using RNA sequencing. 229 lncRNAs, 49 miRNAs and 363 mRNAs were differentially expressed in HE mice. The lncRNA-miRNA-mRNA interaction networks were established, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed. Dysregulated RNAs in interaction networks were mainly involved in synaptic plasticity and the regulation of learning and memory. In NH4Cl-treated hippocampal neurons, the dendritic spine density and maturity decreased significantly, the amplitude and frequency of mIPSC increased, while the amplitude and frequency of mEPSC decreased. These manifestations can be reversed by silencing SIX3OS1. Further research on these no-coding RNAs may lead to new therapies for the treatment and management of brain dysfunction caused by HE.

Plexin-A1 expression in the inhibitory neurons of infralimbic cortex regulates the specificity of fear memory in male mice

Maintaining appropriate levels of fear memory specificity is crucial for individual's survival and mental health, whereas overgeneralized fear commonly occurs in neuropsychiatric disorders, including posttraumatic stress disorder and generalized anxiety disorder. However, the molecular mechanisms regulating fear memory specificity remain poorly understood. The medial prefrontal cortex (mPFC) is considered as a key brain region in fear memory regulation. Previous transcriptomic studies have identified that plexin-A1, a transmembrane receptor critical for axon development, was downregulated in the mPFC after fear memory training. In this study, we identified that learning-induced downregulation of the mRNA and protein levels of plexin-A1 specifically occurred in the inhibitory but not excitatory neurons in the infralimbic cortex (IL) of mPFC. Further studies of plexin-A1 by virus-mediated over-expression of functional mutants selectively in the IL inhibitory neurons revealed the critical roles of plexin-A1 for regulating memory specificity and anxiety. Moreover, our findings revealed that plexin-A1 regulated the distribution of glutamic acid decarboxylase 67, a GABA synthetase, which in turn modulated the activity of IL and its downstream brain regions. Collectively, our findings elucidate the molecular modifier of IL inhibitory neurons in regulating memory specificity and anxiety, and provide candidates for developing therapeutic strategies for the prevention or treatment of a series of fear generalization-related neuropsychiatric disorders.

Basolateral amygdala stimulation plus water maze training restore dentate gyrus LTP and improve spatial learning and memory

Synaptic plasticity is a key mechanism of neural plasticity involved in learning and memory. A reduced or impaired synaptic plasticity could lead to a deficient learning and memory. On the other hand, besides reducing hipocampal dependent learning and memory, fimbria-fornix lesion affects LTP. However, we have consistently shown that stimulation of the basolateral amygdala (BLA) 15 min after water maze training is able to improve spatial learning and memory in fimbria fornix lesioned rats while also inducing changes in the expression of plasticity-related genes expression in memory associated brain regions like the hippocampus and prefrontal cortex. In this study we test that hypothesis: whether BLA stimulation 15 min after water maze training can improve LTP in the hippocampus of fimbria-fornix lesioned rats. To address this question, we trained fimbria-fornix lesioned rats in water maze for four consecutive days, and the BLA was bilaterally stimulated 15 min after each training session.Our data show that trained fimbria-fornix lesioned rats develop a partially improved LTP in dentated gyrus compared with the non-trained fimbria-fornix lesioned rats. In contrast, dentated gyrus LTP in trained and BLA stimulated fimbria-fornix lesioned rats improved significantly compared to the trained fimbria-fornix lesioned rats, but was not different from that shown by healthy animals. BLA stimulation in non-trained FF lesioned rats did not improve LTP; instead produces a transient synaptic depression. Restoration of the ability to develop LTP by the combination of training and BLA stimulation would be one of the mechanisms involved in ameliorating memory deficits in lesioned animals.

Expression of early growth responsive gene-1 in the visual cortex of monocular form deprivation amblyopic kittens

PURPOSE

The present study compared the expression of early growth responsive gene-1 (Egr-1) in visual cortex between amblyopia kittens and normal kittens, and to explore the role of Egr-1 in the pathogenesis of amblyopia.

METHODS

A total of 20 healthy kittens were randomly divided into deprivation group and control group with 10 kittens in each group. Raised in natural light, and covered the right eye of the deprived kittens with a black opaque covering cloth. Pattern visual evoked potentials (PVEP) were measured before and at the 1st, 3rd and 5th week after covering in all kittens. After the last PVEP test, all kittens were killed. The expression of Egr-1 in the visual cortex of the two groups was compared by immunohistochemistry and in situ hybridization.

RESULTS

PVEP detection showed that at the age of 6 and 8 weeks, the P100 wave latency in the right eye of deprivation group was higher than that in the left eye of deprivation group (P < 0.05) and the right eye of control group (P < 0.05), while the amplitude decreased (P < 0.05). The number of positive cells (P < 0.05) and mean optical density (P < 0.05) of Egr-1 protein expression in visual cortex of 8-week-old deprivation group were lower than those of normal group, as well as the number (P < 0.05) and mean optical density of Egr-1 mRNA-positive cells (P < 0.05).

CONCLUSIONS

Monocular form deprivation amblyopia can lead to the decrease of Egr-1 protein and mRNA expression in visual cortex, and then promote the occurrence and development of amblyopia.

Green Tea Suppresses Brain Aging

Epidemiological studies have demonstrated that the intake of green tea is effective in reducing the risk of dementia. The most important component of green tea is epigallocatechin gallate (EGCG). Both EGCG and epigallocatechin (EGC) have been suggested to cross the blood–brain barrier to reach the brain parenchyma, but EGCG has been found to be more effective than EGC in promoting neuronal differentiation. It has also been suggested that the products of EGCG decomposition by the intestinal microbiota promote the differentiation of nerve cells and that both EGCG and its degradation products act on nerve cells with a time lag. On the other hand, the free amino acids theanine and arginine contained in green tea have stress-reducing effects. While long-term stress accelerates the aging of the brain, theanine and arginine suppress the aging of the brain due to their anti-stress effect. Since this effect is counteracted by EGCG and caffeine, the ratios between these green tea components are important for the anti-stress action. In this review, we describe how green tea suppresses brain aging, through the activation of nerve cells by both EGCG and its degradation products, and the reductions in stress achieved by theanine and arginine.

Npas4 regulates IQSEC3 expression in hippocampal somatostatin interneurons to mediate anxiety-like behavior

Activity-dependent GABAergic synapse plasticity is important for normal brain functions, but the underlying molecular mechanisms remain incompletely understood. Here, we show that Npas4 (neuronal PAS-domain protein 4) transcriptionally regulates the expression of IQSEC3, a GABAergic synapse-specific guanine nucleotide-exchange factor for ADP-ribosylation factor (ARF-GEF) that directly interacts with gephyrin. Neuronal activation by an enriched environment induces Npas4-mediated upregulation of IQSEC3 protein specifically in CA1 stratum oriens layer somatostatin (SST)-expressing GABAergic interneurons. SST+ interneuron-specific knockout (KO) of Npas4 compromises synaptic transmission in these GABAergic interneurons, increases neuronal activity in CA1 pyramidal neurons, and reduces anxiety behavior, all of which are normalized by the expression of wild-type IQSEC3, but not a dominant-negative ARF-GEF-inactive mutant, in SST+ interneurons of Npas4-KO mice. Our results suggest that IQSEC3 is a key GABAergic synapse component that is directed by Npas4 and ARF activity, specifically in SST+ interneurons, to orchestrate excitation-to-inhibition balance and control anxiety-like behavior.

ErbB4 mediates amyloid β-induced neurotoxicity through JNK/tau pathway activation: Implications for Alzheimer's disease

Accumulation of amyloid β (Aβ) in the brain is a hallmark of Alzheimer's disease (AD). We previously showed that ErbB4 in parvalbumin (PV)-positive interneurons was associated with Aβ-induced cognitive deficits; however, the underlying mechanism remains undetermined. Here we found that specific deletion of ErbB4 in PV neurons significantly attenuated oligomeric Aβ-induced neuronal toxicity and inhibited Aβ-induced decreases of PSD95 and synaptophysin. Moreover, specific ablation of ErbB4 in PV neurons altered activity-related protein c-Fos and decreased hippocampal PV neurons, especially in the dentate gyrus (DG) of hAPP-J20 mice. Furthermore, c-Jun N-terminal kinase (JNK), a protein downstream of ErbB4, was activated by Aβ but not ErbB4's ligand neuregulin 1 (NRG1) β1, suggesting different downstream pathways for Aβ and NRG1β1. JNK phosphorylation was inhibited by the ErbB4 inhibitor AG1478 and by pretreatment with NRG1β1. More importantly, siRNA knockdown of ErbB4 decreased JNK phosphorylation and expression, tau phosphorylation at Ser396 and Thr 205, and Bax expression. Therefore, ErbB4 might mediate Aβ-induced neuropathology through the JNK/tau pathway and represent a potential therapeutic target in patients with AD.

Limited contextual memory and transcriptional dysregulation in the medial prefrontal cortex of mice exposed to early protein malnutrition are intergenerationally transmitted

Memory contextualization is vital for the subsequent retrieval of relevant memories in specific situations and is a critical dimension of social cognition. The inability to properly contextualize information has been described as characteristic of psychiatric disorders like autism spectrum disorders, schizophrenia, and post-traumatic stress disorder. The exposure to early-life adversities, such as nutritional deficiency, increases the risk to trigger alterations in different domains of cognition related to those observed in mental diseases. In this work, we explored the consequences of exposure to perinatal protein malnutrition on contextual memory in a mouse model and assessed whether these consequences are transmitted to the next generation. Female mice were fed with a normal or hypoproteic diet during pregnancy and lactation. To evaluate contextual memory, the object-context mismatch test was performed in both sexes of F1 offspring and in the subsequent F2 generation. We observed that contextual memory was altered in mice of both sexes that had been subjected to maternal protein malnutrition and that the deficit in contextual memory was transmitted to the next generation. The basis of this alteration seems to be a transcriptional dysregulation of genes involved in the excitatory and inhibitory balance and immediate-early genes within the medial prefrontal cortex (mPFC) of both generations. The expression of genes encoding enzymes that regulate H3K27me3 levels was altered in the mPFC and partially in sperm of F1 malnourished mice. These results support the hypothesis that early nutritional deficiency represents a risk factor for the emergence of symptoms associated with mental disorders.

Neuroinflammation decreased hippocampal microtubule dynamics in the acute behavioral deficits induced by intracerebroventricular injection of lipopolysaccharide in male adult rats

Neuroinflammation plays a vital role in the pathology of depression. Microtubule dynamics produces an immediate response to stress, but the effect of microtubule dynamics in the rats with acute behavioral deficits following a central immune challenge remains elusive. Adult male Sprague-Dawley rats were subjected to the intracerebroventricular (icv) injection of lipopolysaccharide (. Behavioral tests, including bodyweight, sucrose preference test (SPT), forced swimming test (FST) and open field test (OFT), were performed to evaluate anxiety-like and depressive-like phenotypes at 24 h after injection, and some neuroinflammation biomarkers and microtubule dynamics in the hippocampus were detected. Lipopolysaccharide decreased the bodyweight, sucrose preference in SPT (depressive-like behavior), spontaneous activity in OFT (anxiety-like behavior) and increased the immobility time in FST (depressive-like behavior). Besides, lipopolysaccharide increased the mRNA levels of hippocampal CD11b and ionized calcium binding adaptor molecule (Iba1), which suggest microglial activation, and also upregulated hippocampal NLR Family Pyrin Domain Containing 3 inflammasome/interleukin-18/nuclear factor kappa-B mRNA. Lipopolysaccharide injection(icv) reduced the ratio of Tyr-/Acet-tubulin, an important marker of microtubule dynamics, in the acute behavioral deficit rats. Specifically, a decrease in Tyr-tubulin and an increase in the expression of Acet-tubulin were observed, indicating weakened microtubule dynamics. Pearson correlation analysis further showed that there was a significant negative correlation between hippocampal microtubule dynamics and neuroinflammatory activity. This study confirmed that hippocampal microtubule dynamics was decreased in the rats with acute behavioral deficits following a central immune challenge.

Functional genomics study of protein inhibitor of activated STAT1 in mouse hippocampal neuronal cells revealed by RNA sequencing

Protein inhibitor of activated STAT1 (PIAS1), a small ubiquitin-like modifier (SUMO) E3 ligase, was considered to be an inhibitor of STAT1 by inhibiting the DNA-binding activity of STAT1 and blocking STAT1-mediated gene transcription in response to cytokine stimulation. PIAS1 has been determined to be involved in modulating several biological processes such as cell proliferation, DNA damage responses, and inflammatory responses, both in vivo and in vitro. However, the role played by PIAS1 in regulating neurodegenerative diseases, including Alzheimer’s disease (AD), has not been determined. In our study, significantly different expression levels of PIAS1 between normal controls and AD patients were detected in four regions of the human brain. Based on a functional analysis of Pias1 in undifferentiated mouse hippocampal neuronal HT-22 cells, we observed that the expression levels of several AD marker genes could be inhibited by Pias1 overexpression. Moreover, the proliferation ability of HT-22 cells could be promoted by the overexpression of Pias1. Furthermore, we performed RNA sequencing (RNA-seq) to evaluate and quantify the gene expression profiles in response to Pias1 overexpression in HT-22 cells. As a result, 285 significantly dysregulated genes, including 79 upregulated genes and 206 downregulated genes, were identified by the comparison of Pias1/+ cells with WT cells. Among these genes, five overlapping genes, including early growth response 1 (Egr1), early growth response 2 (Egr2), early growth response 3 (Egr3), FBJ osteosarcoma oncogene (Fos) and fos-like antigen 1 (Fosl1), were identified by comparison of the transcription factor binding site (TFBS) prediction results for STAT1, whose expression was evaluated by qPCR. Three cell cycle inhibitors, p53, p18 and p21, were significantly downregulated with the overexpression of Pias1. Analysis of functional enrichment and expression levels showed that basic region leucine zipper domain-containing transcription factors including zinc finger C2H2 (zf-C2H2), homeobox and basic/helix-loop-helix (bHLH) in several signaling pathways were significantly involved in PIAS1 regulation in HT-22 cells. A reconstructed regulatory network under PIAS1 overexpression demonstrated that there were 43 related proteins, notably Nr3c2, that directly interacted with PIAS1.

Prefrontal NMDA-receptor antagonism disrupts encoding or consolidation but not retrieval of incidental context learning

The Context Preexposure Facilitation Effect (CPFE) is a variant of contextual fear conditioning in which learning about the context, acquiring a context-shock association, and retrieval of this association occur separately across three phases (context preexposure, immediate-shock training, and retention). We have shown that prefrontal inactivation or muscarinic-receptor antagonism prior to any phase disrupts retention test freezing during the CPFE in adolescent rats (Heroux et al., 2017; Robinson-Drummer et al., 2017). Furthermore, the medial prefrontal cortex (mPFC) is the only region in which robust learning-related expression of the immediate early genes c-Fos, Arc, Egr-1 and Npas4 is observed during immediate-shock training in the CPFE (Asok et al., 2013; Heroux et al., 2018; Schreiber et al., 2014). However, the role of prefrontal NMDA-receptor plasticity in supporting preexposure- and training-day processes of the CPFE is not known. Therefore, the current study examined the effects of intra-mPFC infusion of the NMDA-receptor antagonist MK-801 or saline vehicle prior to context preexposure (Experiment 1) or immediate-shock training (Experiment 2) in adolescent Long-Evans male and female rats. This infusion given prior to context preexposure but not training abolished retention test freezing, with no difference between MK-801-infused rats and non-associative controls preexposed to an alternative context (pooled across drug). These results demonstrate a role of prefrontal NMDA-receptor plasticity in the acquisition and/or consolidation of incidental context learning (i.e., encoded in the absence of reinforcement). In contrast, this plasticity is not required for context retrieval, or acquisition, expression, or consolidation of a context-shock association during immediate-shock training in the CPFE. These experiments add to a growing body of work implicating the mPFC in Pavlovian contextual fear conditioning processes in rodents.

Mechanisms of context conditioning in the developing rat

The article reviews our studies of contextual fear conditioning (CFC) in rats during a period of development---Postnatal Day (PND) 17-33---that represents the late-infant, juvenile, and early-adolescent stages. These studies seek to acquire 'systems level' knowledge of brain and memory development and apply it to a rodent model of Fetal Alcohol Spectrum Disorder (FASD). This rodent model focuses on alcohol exposure from PND4-9, a period of brain development equivalent to the human third trimester, when neocortex, hippocampus, and cerebellum are especially vulnerable to adverse effects of alcohol. Our research emphasizes a variant of CFC, termed the Context Preexposure Facilitation Effect (CPFE, Fanselow, 1990), in which context representations incidentally learned on one occasion are retrieved and associated with immediate shock on a subsequent occasion. These representations can be encoded at the earliest developmental stage but seem not to be retained or retrieved until the juvenile period. This is associated with developmental differences in context-elicited expression, in prefrontal cortex, hippocampus, and amygdala, of immediate early genes (IEGs) that are implicated in long-term memory. Loss-of-function studies establish a functional role for these regions as soon as the CPFE emerges during ontogeny. In our rodent model of FASD, the CPFE is much more sensitive to alcohol dose than other commonly used cognitive tasks. This impairment can be reversed by acute administration during behavioral testing of drugs that enhance cholinergic function. This effect is associated with normalized IEG expression in prefrontal cortex during incidental context learning. In summary, our findings suggest that long-term memory of incidentally-learned context representations depends on prefrontal-hippocampal circuitry that is important both for the normative development of context conditioning and for its disruption by developmental alcohol exposure.

Applications of the SR4G Transgenic Zebrafish Line for Biomonitoring of Stress-Disrupting Compounds: A Proof-of-Concept Study

Transgenic zebrafish models have been successfully used in biomonitoring and risk assessment studies of environmental pollutants, including xenoestrogens, pesticides, and heavy metals. We employed zebrafish larva (transgenic SR4G line) with a cortisol-inducible green fluorescence protein reporter (eGFP) as a model to detect stress responses upon exposure to compounds with environmental impact, including bisphenol A (BPA), vinclozolin (VIN), and fluoxetine (FLX). Cortisol, fluorescence signal, and mRNA levels of eGFP and 11 targeted genes were measured in a homogenized pool of zebrafish larvae, with six experimental replicates for each endpoint. Eleven targeted genes were selected according to their association with stress-axis and immediate early response class of genes. Hydrocortisone (CORT)and dexamethasone (DEX) were used as positive and negative controls, respectively. All measurements were done in two unstressed and stressed condition using standardized net handling as the stressor. A significant positive linear correlation between cortisol levels and eGFP mRNA levels was observed (r> 0.9). Based on eGFP mRNA levels in unstressed and stressed larvae two predictive models were trained (Random Forest and Logistic Regression). Both these models could correctly predict the blunted stress response upon exposure to BPA, VIN, FLX and the negative control, DEX. The negative predictive value (NPV) of these models were 100%. Similar NPV was observed when the predictive models trained based on the mRNA levels of the eleven assessed genes. Measurement of whole-body fluorescence intensity signal was not significant to detect blunted stress response. Our findings support the use of SR4G transgenic larvae as an in vivo biomonitoring model to screen chemicals for their stress-disrupting potentials. This is important because there is increasing evidence that brief exposures to environmental pollutants modify the stress response and critical coping behaviors for several generations.

Essential Functions of the Transcription Factor Npas4 in Neural Circuit Development, Plasticity, and Diseases

Signaling from the synapse to nucleus is mediated by the integration and propagation of both membrane potential changes (postsynaptic potentials) and intracellular second messenger cascades. The electrical propagation of postsynaptic potentials allows for rapid neural information processing, while propagating second messenger pathways link synaptic activity to the transcription of genes required for neuronal survival and adaptive changes (plasticity) underlying circuit formation and learning. The propagation of activity-induced calcium signals to the cell nucleus is a major synapse-to-nucleus communication pathway. Neuronal PAS domain protein 4 (Npas4) is a recently discovered calcium-dependent transcription factor that regulates the activation of genes involved in the homeostatic regulation of excitatory–inhibitory balance, which is critical for neural circuit formation, function, and ongoing plasticity, as well as for defense against diseases such as epilepsy. Here, we summarize recent findings on the neuroprotective functions of Npas4 and the potential of Npas4 as a therapeutic target for the treatment of acute and chronic diseases of the central nervous system.

The Rab5-Rab11 Endosomal Pathway is Required for BDNF-Induced CREB Transcriptional Regulation in Hippocampal Neurons

Brain-derived neurotrophic factor (BDNF) is a key regulator of the morphology and connectivity of central neurons. We have previously shown that BDNF/TrkB signaling regulates the activity and mobility of the GTPases Rab5 and Rab11, which in turn determine the postendocytic sorting of signaling TrkB receptors. Moreover, decreased Rab5 or Rab11 activity inhibits BDNF-induced dendritic branching. Whether Rab5 or Rab11 activity is important for local events only or for regulating nuclear signaling and gene expression is unknown. Here, we investigated, in rat hippocampal neuronal cultures derived from embryos of unknown sex, whether BDNF-induced signaling cascades are altered when early and recycling endosomes are disrupted by the expression of dominant-negative mutants of Rab5 and Rab11. The activity of both Rab5 and Rab11 was required for sustained activity of Erk1/2 and nuclear CREB phosphorylation, and increased transcription of a BDNF-dependent program of gene expression containing CRE binding sites, which includes activity-regulated genes such as Arc, Dusp1, c-fos, Egr1, and Egr2, and growth and survival genes such as Atf3 and Gem Based on our results, we propose that early and recycling endosomes provide a platform for the integration of neurotrophic signaling from the plasma membrane to the nucleus in neurons, and that this mechanism is likely to regulate neuronal plasticity and survival.SIGNIFICANCE STATEMENT BDNF is a neurotrophic factor that regulates plastic changes in the brain, including dendritic growth. The cellular and molecular mechanisms underlying this process are not completely understood. Our results uncover the cellular requirements that central neurons possess to integrate the plasma membrane into nuclear signaling in neurons. Our results indicate that the endosomal pathway is required for the signaling cascade initiated by BDNF and its receptors at the plasma membrane to modulate BDNF-dependent gene expression and neuronal dendritic growth mediated by the CREB transcription factor. CREB is a key transcription factor regulating circuit development and learning and memory.

Uncovering memory-related gene expression in contextual fear conditioning using ribosome profiling

Contextual fear conditioning (CFC) in rodents is the most widely used behavioural paradigm in neuroscience research to elucidate the neurobiological mechanisms underlying learning and memory. It is based on the pairing of an aversive unconditioned stimulus (US; e.g. mild footshock) with a neutral conditioned stimulus (CS; e.g. context of the test chamber) in order to acquire associative long-term memory (LTM), which persists for days and even months. Using genome-wide analysis, several studies have generated lists of genes modulated in response to CFC in an attempt to identify the “memory genes”, which orchestrate memory formation. Yet, most studies use naïve animals as a baseline for assessing gene-expression changes, while only few studies have examined the effect of the US alone, without pairing to context, using genome-wide analysis of gene-expression. Herein, using the ribosome profiling methodology, we show that in male mice an immediate shock, which does not lead to LTM formation, elicits pervasive translational and transcriptional changes in the expression of Immediate Early Genes (IEGs) in dorsal hippocampus (such as Fos and Arc), a fact which has been disregarded by the majority of CFC studies. By removing the effect of the immediate shock, we identify and validate a new set of genes, which are translationally and transcriptionally responsive to the association of context-to-footshock in CFC, and thus constitute salient “memory genes”.

The endoplasmic reticulum acetyltransferases ATase1/NAT8B and ATase2/NAT8 are differentially regulated to adjust engagement of the secretory pathway

Nε-lysine acetylation of nascent glycoproteins within the endoplasmic reticulum (ER) lumen regulates the efficiency of the secretory pathway. The ER acetylation machinery consists of the membrane transporter, acetyl-CoA transporter 1 (AT-1/SLC33A1), and two acetyltransferases, ATase1/NAT8B and ATase2/NAT8. Dysfunctional ER acetylation is associated with severe neurological diseases with duplication of AT-1/SLC33A1 being associated with autism spectrum disorder, intellectual disability, and dysmorphism. Neuron-specific AT-1 over-expression in the mouse alters neuron morphology and function, causing an autism-like phenotype, indicating that ER acetylation plays a key role in neurophysiology. As such, characterizing the molecular mechanisms that regulate the acetylation machinery could reveal critical information about its biology. By using structure-biochemistry approaches, we discovered that ATase1 and ATase2 share enzymatic properties but differ in that ATase1 is post-translationally regulated via acetylation. Furthermore, gene expression studies revealed that the promoters of AT-1, ATase1, and ATase2 contain functional binding sites for the neuron-related transcription factors cAMP response element-binding protein and the immediate-early genes c-FOS and c-JUN, and that ATase1 and ATase2 exhibit additional modes of transcriptional regulation relevant to aging and Alzheimer's disease. In vivo rodent gene expression experiments revealed that Atase2 is specifically induced following activity-dependent events. Finally, over-expression of either ATase1 or ATase2 was sufficient to increase the engagement of the secretory pathway in PC12 cells. Our results indicate important regulatory roles for ATase1 and ATase2 in neuron function with induction of ATase2 expression potentially serving as a critical event that adjusts the efficiency of the secretory pathway for activity-dependent neuronal functions.

Amygdala stimulation ameliorates memory impairments and promotes c-Fos activity in fimbria-fornix-lesioned rats

Recently we provided data showing that amygdala stimulation can ameliorate spatial memory impairments in rats with lesion in the fimbria-fornix (FF). The mechanisms for this improvement involve early gene expression and synthesis of BDNF, MAP-2, and GAP43 in the hippocampus and prefrontal cortex. Now we have studied which brain structures are activated by the amygdala using c-Fos as a marker of neural activation. First, we studied neuronal activation after tetanic stimulation to the amygdala in intact rats. We then carried out a second study in FF-lesioned rats in which the amygdala was stimulated 15 min after daily spatial memory training in the water maze. Our results showed that amygdala stimulation produces widespread brain activation, that includes cortical, thalamic, and brain stem structures. Activation was particularly intense in the dentate gyrus and the prefrontal cortex. Training in the water maze increased c-Fos positive nuclei in the dentate gyrus of the hippocampus and in medial prefrontal cortex. Amygdala stimulation to trained FF-lesioned rats induced an increase of neural activity in the dentate gyrus and medial prefrontal cortex relative to the FF-lesioned, but not stimulated group, like the c-Fos activity seen in trained control rats. Based on these and previous results we explain the mechanisms of amygdala reinforcement of neural plasticity and the partial recovery of spatial memory deficits.

Green Tea Catechins Trigger Immediate-Early Genes in the Hippocampus and Prevent Cognitive Decline and Lifespan Shortening

Senescence-accelerated mouse prone 10 (SAMP10) mice, after ingesting green tea catechins (GT-catechin, 60 mg/kg), were found to have suppressed aging-related decline in brain function. The dose dependence of brain function on GT-catechin indicated that intake of 1 mg/kg or more suppressed cognitive decline and a shortened lifespan. Mice that ingested 1 mg/kg GT-catechin had the longest median survival, but the dose was less effective at suppressing cognitive decline. The optimal dose for improving memory acquisition was 60 mg/kg, and memory retention was higher in mice that ingested 30 mg/kg or more. To elucidate the mechanism by which cognitive decline is suppressed by GT-catechin, changes in gene expression in the hippocampus of SAMP10 mice one month after ingesting GT-catechin were analyzed. The results show that the expression of immediate-early genes such as nuclear receptor subfamily 4 (Nr4a), FBJ osteosarcoma oncogene (Fos), early growth response 1 (Egr1), neuronal PAS domain protein 4 (Npas4), and cysteine-rich protein 61 (Cyr61) was significantly increased. These results suggest that GT-catechin suppresses age-related cognitive decline via increased expression of immediate-early genes that are involved in long-term changes in plasticity of synapses and neuronal circuits.

Role of prelimbic cortex PKC and PKMζ in fear memory reconsolidation and persistence following reactivation

The persistence of newly acquired memories is supported by the activity of PKMζ, an atypical isoform of protein kinase C (PKC). Whether the activity of conventional and atypical PKC isoforms contributes to reactivated memories to persist is still unknown. Similarly, whether memory reactivation is a prerequisite for interventions to be able to change memory persistence is scarcely investigated. Based on the above, we examined the role of conventional and atypical PKC isoforms in the prelimbic cortex in reconsolidation and persistence of a reactivated contextual fear memory in male Wistar rats. It is shown that (i) inhibiting the PKC activity with chelerythrine or the PKMζ activity with ZIP impaired the persistence of a reactivated memory for at least 21 days; (ii) ZIP given immediately after memory reactivation affected neither the reconsolidation nor the persistence process. In contrast, when given 1 h later, it impaired the memory persistence; (iii) chelerythrine given immediately after memory reactivation impaired the reconsolidation; (iv) omitting memory reactivation prevented the chelerythrine- and ZIP-induced effects: (v) the ZIP action is independent of the time elapsed between its administration and the initial memory test. The results indicate that prelimbic cortex PKC and PKMζ are involved in memory reconsolidation and persistence.

Fluoxetine exposure for more than 2 days decreases the neuronal plasticity mediated by CRMP2 in differentiated PC12 cells

BACKGROUND

Recent studies indicate that antidepressants treatment restores neuronal plasticity. In contrast, some researchers claim that serotonergic antidepressants, including fluoxetine (FLU), may exacerbate neuronal plasticity, which is contradictory and rarely studied. Since almost those studies exposed cells with drugs for 1-2 days as treatment models of antidepressants, it is possible that FLU exposure for longer periods would have opposite effects on neuronal plasticity.

RESULTS

In the present study, we examined the effects of FLU exposure (up to 3 days) on the neuronal plasticity in differentiated PC12 cells. The cell viability shown a slight decrease at day 2 (93.5 ± 3.5 %), followed by a highly significant decrease at day 3(71.4 ± 4.4 %). As previously reported, neuronal plasticity was significantly upregulated by FLU exposure at day 1. However, the neurite length, activity-regulated cytoskeleton-associated protein (Arc) and c-Fos mRNA were inhibited with FLU exposure at day 3. Similarly, the expression of tubulin, which play important roles in the neuronal plasticity, was the same result. Furthermore, we found α-tubulin interacted with collapsing response mediator protein 2(CRMP2), which is related to neuronal plasticity, and the regulation of CRMP2 activity influenced the neurite length, Arc, c-Fos and tubulin expression.

CONCLUSIONS

The results demonstrated that neuronal plasticity was increased by FLU exposure at day 1, but exposure with FLU for more than 2 days had opposite effect on it. The reduction in neuronal plasticity with FLU exposure for more than 2 days might be involved in some aspects of the therapeutic effect of antidepressant on depression.

Cholinergic rescue of neurocognitive insult following third-trimester equivalent alcohol exposure in rats

Neonatal ethanol exposure during the third trimester equivalent of human pregnancy in the rat significantly impairs hippocampal and prefrontal neurobehavioral functioning. Postnatal day [PD] 4-9 ethanol exposure in rats disrupts long-term context memory formation, resulting in abolished post-shock and retention test freezing in a variant of contextual fear conditioning called the Context Preexposure Facilitation Effect (CPFE). This behavioral impairment is accompanied by disrupted medial prefrontal, but not dorsal hippocampal expression of the immediate early genes (IEGs) c-Fos, Arc, Egr-1, and Npas4 (Heroux, Robinson-Drummer, Kawan, Rosen, & Stanton, 2019). The current experiment examined if systemic administration of the acetylcholinesterase inhibitor physostigmine (PHY) prior to context learning would rescue prefrontal IEG expression and freezing in the CPFE. From PD4-9, Long-Evans rats received oral intubation of ethanol (EtOH; 5.25 g/kg/day) or sham-intubation (SI). Rats received a systemic injection of saline (SAL) or PHY (0.01 mg/kg) prior to all three phases (Experiment 1) or just context exposure (Experiment 2) in the CPFE from PD31-33. A subset of rats were sacrificed 30 min after context learning to assay changes in IEG expression in the medial prefrontal cortex (mPFC), dorsal hippocampus (dHPC), and ventral hippocampus (vHPC). Administration of PHY prior to all three phases or just context learning rescued both post-shock and retention test freezing in the CPFE in EtOH rats without altering performance in SI rats. EtOH-SAL rats had significantly reduced mPFC but not dHPC expression of c-Fos, Arc, Egr-1, and Npas4. EtOH-PHY treatment rescued mPFC expression of c-Fos in ethanol-exposed rats and increased Arc and Npas4 regardless of dosing condition. While there was no effect of PHY on dHPC or vHPC expression of Arc, Egr-1, or Npas4, this treatment significantly boosted hippocampal expression of c-Fos regardless of ethanol treatment. These findings implicate impaired cholinergic and prefrontal function in cognitive deficits arising from 3rd-trimester equivalent alcohol exposure.

Future considerations for pediatric cancer survivorship: Translational perspectives from developmental neuroscience

Breakthroughs in modern medicine have increased pediatric cancer survival rates throughout the last several decades. Despite enhanced cure rates, a subset of pediatric cancer survivors exhibit life-long psychological side effects. A large body of work has addressed potential mechanisms for secondary symptoms of anxiety, post-traumatic stress, impaired emotion regulation and cognitive deficits in adults. Yet, absent from many studies are the ways in which cancer treatment can impact the developing brain. Additionally, it remains less known whether typical neurobiological changes during adolescence and early adulthood may potentially buffer or exacerbate some of the known negative cancer survivorship outcomes. This review highlights genetic, animal, and human neuroimaging research across development. We focus on the neural circuitry associated with aversive learning, which matures throughout childhood, adolescence and early adulthood. We argue that along with other individual differences, the precise timing of oncological treatment insults on such neural circuitry may expose particular vulnerabilities for pediatric cancer patients. We also explore other moderators of treatment outcomes, including genetic polymorphisms and neural mechanisms underlying memory and cognitive control. We discuss how neural maturation extending into young adulthood may also provide a sensitive period for intervention to improve psychological and cognitive outcomes in pediatric cancer survivors.

Spatial exploration induced expression of immediate early genes Fos and Zif268 in adult-born neurons Is reduced after pentylenetetrazole kindling

Seizure activity stimulates adult neurogenesis, the birth of new neurons, in the hippocampus. Many new neurons that develop in the presence of repeatedly induced seizures acquire abnormal morphological and functional characteristics that can promote network hyperexcitability and hippocampal dysfunction. However, the impact of seizure induced neurogenesis on behaviour remains poorly understood. In this study, we investigated whether adult-born neurons generated immediately before and during chronic seizures were capable of integration into behaviorally relevant hippocampal networks. Adult rats underwent pentylenetetrazole (PTZ) kindling for either 1 or 2 weeks. Proliferating cells were labelled with BrdU immediately before kindling commenced. Twenty-four hours after receiving their last kindling treatment, rats were placed in a novel environment and allowed to freely explore for 30 min. The rats were euthanized 90 min later to examine for behaviourally-induced immediate early gene expression (c-fos, Zif268). Using this approach, we found that PTZ kindled rats did not differ from control rats in regards to exploratory behaviour, but there was a marked attenuation in behaviour-induced expression of Fos and Zif268 for rats that received 2 weeks of PTZ kindling. Further examination revealed that PTZ kindled rats showed reduced colocalization of Fos and Zif268 in 2.5 week old BrdU + cells. The proportion of immature granule cells (doublecortin-positive) expressing behaviorally induced Zif268 was also significantly lower for PTZ kindled rats than control rats. These results suggest that chronic seizures can potentially disrupt the ability of adult-born cells to functionally integrate into hippocampal circuits important for the processing of spatial information.

Synaptic and memory dysfunction induced by tau oligomers is rescued by up-regulation of the nitric oxide cascade

BACKGROUND

Soluble aggregates of oligomeric forms of tau protein (oTau) have been associated with impairment of synaptic plasticity and memory in Alzheimer's disease. However, the molecular mechanisms underlying the synaptic and memory dysfunction induced by elevation of oTau are still unknown.

METHODS

This work used a combination of biochemical, electrophysiological and behavioral techniques. Biochemical methods included analysis of phosphorylation of the cAMP-responsive element binding (CREB) protein, a transcriptional factor involved in memory, histone acetylation, and expression immediate early genes c-Fos and Arc. Electrophysiological methods included assessment of long-term potentiation (LTP), a type of synaptic plasticity thought to underlie memory formation. Behavioral studies investigated both short-term spatial memory and associative memory. These phenomena were examined following oTau elevation.

RESULTS

Levels of phospho-CREB, histone 3 acetylation at lysine 27, and immediate early genes c-Fos and Arc, were found to be reduced after oTau elevation during memory formation. These findings led us to explore whether up-regulation of various components of the nitric oxide (NO) signaling pathway impinging onto CREB is capable of rescuing oTau-induced impairment of plasticity, memory, and CREB phosphorylation. The increase of NO levels protected against oTau-induced impairment of LTP through activation of soluble guanylyl cyclase. Similarly, the elevation of cGMP levels and stimulation of the cGMP-dependent protein kinases (PKG) re-established normal LTP after exposure to oTau. Pharmacological inhibition of cGMP degradation through inhibition of phosphodiesterase 5 (PDE5), rescued oTau-induced LTP reduction. These findings could be extrapolated to memory because PKG activation and PDE5 inhibition rescued oTau-induced memory impairment. Finally, PDE5 inhibition re-established normal elevation of CREB phosphorylation and cGMP levels after memory induction in the presence of oTau.

CONCLUSIONS

Up-regulation of CREB activation through agents acting on the NO cascade might be beneficial against tau-induced synaptic and memory dysfunctions.

Neonatal ethanol exposure impairs long-term context memory formation and prefrontal immediate early gene expression in adolescent rats

Fetal alcohol exposure leads to severe disruptions in learning and memory involving the hippocampus and prefrontal cortex in humans. Animal model research on FASD has documented impairment of hippocampal neuroanatomy and function but animal studies of cognition involving the prefrontal cortex are sparse. We have found that a variant of contextual fear conditioning in which both the hippocampus and prefrontal cortex is required, the Context Preexposure Facilitation Effect (CPFE), is particularly sensitive to neurobehavioral disruption caused by neonatal ethanol exposure during the third trimester equivalent of human pregnancy in the rat (i.e., PD4-9). In the CPFE, learning about the context, acquiring a context-shock association, and retrieving contextual fear are temporally separated across three days. The current study asked whether neonatal alcohol exposure impairs context learning, consolidation, or retrieval and examined prefrontal and hippocampal molecular signaling as correlates of this impairment. Long-Evans rats that received oral intubation of ethanol (AE; 5.25 g/kg/day, split into two doses) or underwent sham-intubation (SI) from PND4-9 were tested on the CPFE on PD31-33. Extending our previous reports, ethanol abolished both post-shock and retention test freezing in the CPFE. Assays (qPCR) of immediate early gene expression revealed that ethanol disrupted prefrontal but not hippocampal expression of c-Fos, Arc, Egr-1, and Npas4 during context learning. Finally, ethanol-exposed animals were unimpaired in a standard contextual fear conditioning procedure in which learning about the context and acquiring a context-shock association occurs concurrently. These findings implicate impaired prefrontal function in cognitive deficits arising from 3rd-trimester equivalent alcohol exposure in the rat.

Norepinephrine triggers an immediate-early regulatory network response in primary human white adipocytes

BACKGROUND

Norepinephrine (NE) signaling has a key role in white adipose tissue (WAT) functions, including lipolysis, free fatty acid liberation and, under certain conditions, conversion of white into brite (brown-in-white) adipocytes. However, acute effects of NE stimulation have not been described at the transcriptional network level.

RESULTS

We used RNA-seq to uncover a broad transcriptional response. The inference of protein-protein and protein-DNA interaction networks allowed us to identify a set of immediate-early genes (IEGs) with high betweenness, validating our approach and suggesting a hierarchical control of transcriptional regulation. In addition, we identified a transcriptional regulatory network with IEGs as master regulators, including HSF1 and NFIL3 as novel NE-induced IEG candidates. Moreover, a functional enrichment analysis and gene clustering into functional modules suggest a crosstalk between metabolic, signaling, and immune responses.

CONCLUSIONS

Altogether, our network biology approach explores for the first time the immediate-early systems level response of human adipocytes to acute sympathetic activation, thereby providing a first network basis of early cell fate programs and crosstalks between metabolic and transcriptional networks required for proper WAT function.

Nucleus incertus ablation disrupted conspecific recognition and modified immediate early gene expression patterns in 'social brain' circuits of rats

Social interaction involves neural activity in prefrontal cortex, septum, hippocampus, amygdala and hypothalamus. Notably, these areas all receive projections from the nucleus incertus (NI) in the pontine tegmentum. Therefore, we investigated the effect of excitotoxic lesions of NI neurons in adult male, Wistar rats on performance in a social discrimination test, and associated changes in immediate-early gene protein levels. NI was lesioned with quinolinic acid, and after recovery, rats underwent two trials in the 3-chamber test. In the first trial, NI-lesioned and sham-lesioned rats spent longer exploring a conspecific than an inanimate object. By contrast, in the second trial, NI-lesioned rats visited the familiar and novel conspecific chambers equally, whereas sham-lesioned rats spent longer engaging with the novel rat. Quantification of Fos- and Egr-1-immunoreactivity (IR) levels in brain areas implicated in social behaviour, revealed that social encounter and NI lesion produced complex, differential changes. For example, Egr-1-IR was broadly decreased in several amygdala nuclei in NI-lesioned rats relative to sham, but Fos-IR levels were unaltered. In hippocampus, NI-lesioned rats displayed decreased Fos-IR in CA2 and CA3, while Egr-1-IR was increased in the polymorphic dentate gyrus, CA1, CA2 and subiculum of NI-lesioned rats, relative to sham. Social encounter-related Egr-1-IR was also decreased in septum and anterior and lateral hypothalamus of NI-lesioned rats. Overall, these data suggest NI networks can modulate the activity of sensory, emotional and executive brain areas involved in social recognition, with a likely involvement of neuronal Egr-1 activation in amygdala, septum and hypothalamus, and Erg-1 inhibition in hippocampus.

Contextual fear retrieval-induced Fos expression across early development in the rat: An analysis using established nervous system nomenclature ontology

The neural circuits underlying the acquisition, retention and retrieval of contextual fear conditioning have been well characterized in the adult animal. A growing body of work in younger rodents indicates that context-mediated fear expression may vary across development. However, it remains unclear how this expression may be defined across the full range of key developmental ages. Nor is it fully clear whether the structure of the adult context fear network generalizes to earlier ages. In this study, we compared context fear retrieval-induced behavior and neuroanatomically constrained immediate early-gene expression across infant (P19), early and late juvenile (P24 and P35), and adult (P90) male Long-Evans rats. We focused our analysis on neuroanatomically defined subregions and nuclei of the basolateral complex of the amygdala (BLA complex), dorsal and ventral portions of the hippocampus and the subregions of the medial prefrontal cortex as defined by the nomenclature of the Swanson (2004) adult rat brain atlas. Relative to controls and across all ages tested, there were greater numbers of Fos immunoreactive (Fos-ir) neurons in the posterior part of the basolateral amygdalar nuclei (BLAp) following context fear retrieval that correlated statistically with the expression of freezing. However, Fos-ir within regions having known connections with the BLA complex was differentially constrained by developmental age: early juvenile, but not adult rats exhibited an increase of context fear-dependent Fos-ir neurons in prelimbic and infralimbic areas, while adult, but not juvenile rats displayed increases in Fos-ir neurons within the ventral CA1 hippocampus. These results suggest that juvenile and adult rodents may recruit developmentally unique pathways in the acquisition and retrieval of contextual fear. This study extends prior work by providing a broader set of developmental ages and a rigorously defined neuroanatomical ontology within which the contextual fear network can be studied further.

Age and experience dependent changes in Egr-1 expression during the ontogeny of the context preexposure facilitation effect (CPFE)

The context preexposure facilitation effect (CPFE) is a variant of contextual fear conditioning in which acquisition of the contextual representation and association of the retrieved contextual memory with an immediate foot-shock are separated by 24 h. During the CPFE, learning- related expression patterns of the early growth response-1 gene (Egr-1) vary based on training phase and brain sub-region in adult and adolescent rats (Asok, Schreiber, Jablonski, Rosen, & Stanton, 2013; Schreiber, Asok, Jablonski, Rosen, & Stanton, 2014; Chakraborty, Asok, Stanton, & Rosen, 2016). The current experiments extended our previous findings by examining Egr-1 expression in infant (PD17) and juvenile (PD24) rats during the CPFE using preexposure protocols involving single-exposure (SE) or multiple-exposure (ME) to context. Following a 5 min preexposure to the training context (i.e. the SE protocol), Egr-1 expression in the medial prefrontal cortex (mPFC), dorsal hippocampus (dHPC) and lateral nucleus of the amygdala (LA) was differentially increased in PD24 rats relative to PD17 rats. In contrast, increased Egr-1 expression following an immediate foot-shock (2s, 1.5 mA) did not differ between PD17 and PD24 rats, and was not learning-related. Interestingly, increasing the number of exposures to the training chamber on the preexposure day (i.e. ME protocol) altered training-day expression such that a learning-related increase in expression was observed in the mPFC in PD24 but not PD17 rats. Together, these results illustrate a clear maturation of Egr-1 expression that is both age- and experience-dependent. In addition, the data suggest that regional activity and plasticity within the mPFC on the preexposure but not the training day may contribute to the ontogenetic profile of the effect. Further studies are necessary to elucidate the causal role of sub-region-specific neuroplasticity in the ontogeny of the CPFE.