Constitutive expression of zif268 in neocortex is regulated by synaptic activity

Exercise induction at expression immediate early gene (c-Fos, ARC, EGR-1) in the hippocampus: a systematic review

The immediate early gene exhibits activation markers in the nervous system consisting of ARC, EGR-1, and c-Fos and is related to synaptic plasticity, especially in the hippocampus. Immediate early gene expression is affected by physical exercise, which induces direct ARC, EGR-1, and c-Fos expression.

Objective

To assess the impact of exercise, we conducted a literature study to determine the expression levels of immediate early genes (ARC, c-Fos, and EGR-1).

Methods

The databases accessed for online literature included PubMed-Medline, Scopus, and ScienceDirect. The original English articles were selected using the following keywords in the title: (Exercise OR physical activity) AND (c-Fos) AND (Hippocampus), (Exercise OR physical activity) AND (ARC) AND (Hippocampus), (Exercise OR physical activity) AND (EGR-1 OR zif268) AND (Hippocampus).

Results

Physical exercise can affect the expression of EGR-1, c-Fos, and ARC in the hippocampus, an important part of the brain involved in learning and memory. High-intensity physical exercise can increase c-Fos expression, indicating neural activation. Furthermore, the expression of the ARC gene also increases due to physical exercise. ARC is a gene that plays a role in synaptic plasticity and regulation of learning and memory, changes in synaptic structure and increased synaptic connections, while EGR-1 also plays a role in synaptic plasticity, a genetic change that affects learning and memory. Overall, exercise or regular physical exercise can increase the expression of ARC, c-Fos, and EGR-1 in the hippocampus. This reflects the changes in neuroplasticity and synaptic plasticity that occur in response to physical activity. These changes can improve cognitive function, learning, and memory.

Conclusion

c-Fos, EGR-1, and ARC expression increases in hippocampal neurons after exercise, enhancing synaptic plasticity and neurogenesis associated with learning and memory.

Approaches and considerations of studying neuronal ensembles: a brief review

First theorized by Hebb, neuronal ensembles have provided a framework for understanding how the mammalian brain operates, especially regarding learning and memory. Neuronal ensembles are discrete, sparsely distributed groups of neurons that become activated in response to a specific stimulus and are thought to provide an internal representation of the world. Beyond the study of region-wide or projection-wide activation, the study of ensembles offers increased specificity and resolution to identify and target specific memories or associations. Neuroscientists interested in the neurobiology of learning, memory, and motivated behavior have used electrophysiological-, calcium-, and protein-based proxies of neuronal activity in preclinical models to better understand the neurobiology of learned and motivated behaviors. Although these three approaches may be used to pursue the same general goal of studying neuronal ensembles, technical differences lead to inconsistencies in the output and interpretation of data. This mini-review highlights some of the methodologies used in electrophysiological-, calcium-, and protein-based studies of neuronal ensembles and discusses their strengths and weaknesses.

Elevation of EGR1/zif268, a Neural Activity Marker, in the Auditory Cortex of Patients with Schizophrenia and its Animal Model

The family of epidermal growth factor (EGF) including neuregulin-1 are implicated in the neuropathology of schizophrenia. We established a rat model of schizophrenia by exposing perinatal rats to EGF and reported that the auditory pathophysiological traits of this model such as prepulse inhibition, auditory steady-state response, and mismatch negativity are relevant to those of schizophrenia. We assessed the activation status of the auditory cortex in this model, as well as that in patients with schizophrenia, by monitoring the three neural activity-induced proteins: EGR1 (zif268), c-fos, and Arc. Among the activity markers, protein levels of EGR1 were significantly higher at the adult stage in EGF model rats than those in control rats. The group difference was observed despite an EGF model rat and a control rat being housed together, ruling out the contribution of rat vocalization effects. These changes in EGR1 levels were seen to be specific to the auditory cortex of this model. The increase in EGR1 levels were detectable at the juvenile stage and continued until old ages but displayed a peak immediately after puberty, whereas c-fos and Arc levels were nearly indistinguishable between groups at all ages with an exception of Arc decrease at the juvenile stage. A similar increase in EGR1 levels was observed in the postmortem superior temporal cortex of patients with schizophrenia. The commonality of the EGR1 increase indicates that the EGR1 elevation in the auditory cortex might be one of the molecular signatures of this animal model and schizophrenia associating with hallucination.

The mouse brain after foot shock in four dimensions: Temporal dynamics at a single-cell resolution

Acute stress involves the majority of brain areas, which can be sequentially organized in functional brain networks as shown by our study with foot shock in mice. We used whole-brain microscopy to investigate different spatial resolutions over time. From mesoscale region–based analyses, we identified the order of activation of brain areas. With single-cell analyses, we analyzed shifts in activation over time within small nuclei—a result impossible to achieve with functional MRI’s resolution. These findings required the development of a four-dimensional (4D) analytical pipeline, which is made available as an R package. This “atlas” of foot shock can be visualized in 4D in our interactive web portal.

Acute stress leads to sequential activation of functional brain networks. A biologically relevant question is exactly which (single) cells belonging to brain networks are changed in activity over time after acute stress across the entire brain. We developed a preprocessing and analytical pipeline to chart whole-brain immediate early genes’ expression—as proxy for cellular activity—after a single stressful foot shock in four dimensions: that is, from functional networks up to three-dimensional (3D) single-cell resolution and over time. The pipeline is available as an R package. Most brain areas (96%) showed increased numbers of c-fos+ cells after foot shock, yet hypothalamic areas stood out as being most active and prompt in their activation, followed by amygdalar, prefrontal, hippocampal, and finally, thalamic areas. At the cellular level, c-fos+ density clearly shifted over time across subareas, as illustrated for the basolateral amygdala. Moreover, some brain areas showed increased numbers of c-fos+ cells, while others—like the dentate gyrus—dramatically increased c-fos intensity in just a subset of cells, reminiscent of engrams; importantly, this “strategy” changed after foot shock in half of the brain areas. One of the strengths of our approach is that single-cell data were simultaneously examined across all of the 90 brain areas and can be visualized in 3D in our interactive web portal.

Blockade of adenosine A2A receptors inhibits Tremulous Jaw Movements as well as expression of zif-268 and GAD65 mRNAs in brain motor structures

Tremor is one of the motor symptoms of Parkinson's disease (PD), present also in neuroleptic-induced parkinsonism. Tremulous Jaw Movements (TJMs) are suggested to be a well-validated rodent model of PD resting tremor. TJMs can be induced by typical antipsychotics and are known to be reduced by different drugs, including adenosine A_2A receptor antagonists. The aim of the present study was to search for brain structures involved in the tremorolytic action of SCH58261, a selective A_2A receptor antagonist, in TJMs induced by subchronic pimozide. Besides TJMs, we evaluated in the same animals the expression of zif-268 mRNA (neuronal responsiveness marker), and mRNA levels for glutamic acid decarboxylase 65-kDa isoform (GAD65) and vesicular glutamate transporters 1 and 2 (vGluT1/2) in selected brain structures, as markers of GABAergic and glutamatergic neurons, respectively. We found that SCH58261 reduced the pimozide-induced TJMs. Pimozide increased the zif-268 mRNA level in the striatum, nucleus accumbens (NAc) core, and substantia nigra pars reticulata (SNr). Additionally, it increased GAD65 mRNA in the striatum and SNr, and vGluT2 mRNA levels in the subthalamic nucleus (STN). A positive correlation between zif-268, GAD65 and vGluT2 mRNAs and TJMs was found. SCH58261 reversed the pimozide-increased zif-268 mRNA in the striatum and NAc core and GAD65 mRNA in the striatum and SNr. In contrast, SCH58261 did not influence vGluT2 mRNA in STN. The present study suggests an importance of the striato-subthalamo-nigro-thalamic circuit in neuroleptic-induced TJMs. The tremorolytic effect of A_2A receptor blockade seems to involve this circuit bypassing, however, STN.

Social Instability Stress in Adolescence and Social Interaction in Female Rats

Adolescence is a critical time of brain development for regions governing social behaviour and social learning. Social experiences influence the ongoing maturation of the neural structures and ultimately modify the social behaviour of adults in response to social cues. Social instability stress in adolescence (SS; daily 1-hour isolation + change of cage partner in postnatal days [PND] 30-45) leads to a long-lasting reduction in social interaction in SS rats compared with non-stressed (CTL) rats in males; here we investigate females. In a first experiment, we found that female rats exposed to adolescent SS also showed the decrement in social interaction irrespective of age at which tested, and replicated the effects previously found in males. In experiment 2, which involved females only, SS and CTL rats did not differ in anxiety-like behaviour in the elevated plus maze (EPM) and the reduction in social interaction was not significant. Nevertheless, when tested in adolescence at P47 (and not at P71), SS female rats had higher corticosterone release during the social interaction test than did CTL rats, and they exhibited a different pattern of neural activation as measured by immunoreactivity to the protein products of zif268 and c-fos (SS < CTL in medial prefrontal cortex and SS > CTL in hippocampus), and reduced oxytocin immunoreactivity in the paraventricular nucleus of the hypothalamus than did CTL rats. These results extend our previous findings of effects of SS in adolescent female rats on behavioural responses to psychostimulants to social behaviour, and point to directions for investigations of the neural mechanisms involved.

A transcriptome atlas of the mouse iris at single-cell resolution defines cell types and the genomic response to pupil dilation

The iris controls the level of retinal illumination by controlling pupil diameter. It is a site of diverse ophthalmologic diseases and it is a potential source of cells for ocular auto-transplantation. The present study provides foundational data on the mouse iris based on single nucleus RNA sequencing. More specifically, this work has (1) defined all of the major cell types in the mouse iris and ciliary body, (2) led to the discovery of two types of iris stromal cells and two types of iris sphincter cells, (3) revealed the differences in cell type-specific transcriptomes in the resting vs. dilated states, and (4) identified and validated antibody and in situ hybridization probes that can be used to visualize the major iris cell types. By immunostaining for specific iris cell types, we have observed and quantified distortions in nuclear morphology associated with iris dilation and clarified the neural crest contribution to the iris by showing that Wnt1-Cre-expressing progenitors contribute to nearly all iris cell types, whereas Sox10-Cre-expressing progenitors contribute only to stromal cells. This work should be useful as a point of reference for investigations of iris development, disease, and pharmacology, for the isolation and propagation of defined iris cell types, and for iris cell engineering and transplantation.

Neural substrates involved in the cognitive information processing in teleost fish

Over the last few decades, it has been shown that fish, comprising the largest group of vertebrates and in many respects one of the least well studied, possess many cognitive abilities comparable to those of birds and mammals. Despite a plethora of behavioural studies assessing cognition abilities and an abundance of neuroanatomical studies, only few studies have aimed to or in fact identified the neural substrates involved in the processing of cognitive information. In this review, an overview of the currently available studies addressing the joint research topics of cognitive behaviour and neuroscience in teleosts (and elasmobranchs wherever possible) is provided, primarily focusing on two fundamentally different but complementary approaches, i.e. ablation studies and Immediate Early Gene (IEG) analyses. More recently, the latter technique has become one of the most promising methods to visualize neuronal populations activated in specific brain areas, both during a variety of cognitive as well as non-cognition-related tasks. While IEG studies may be more elegant and potentially easier to conduct, only lesion studies can help researchers find out what information animals can learn or recall prior to and following ablation of a particular brain area.

Long-lasting tagging of neurons activated by seizures or cocaine administration in Egr1-CreERT2 transgenic mice

Permanent tagging of neuronal ensembles activated in specific experimental situations is an important objective to study their properties and adaptations. In the context of learning and memory, these neurons are referred to as engram neurons. Here, we describe and characterize a novel mouse line, Egr1-CreER^T2 , which carries a transgene in which the promoter of the immediate early gene Egr1 drives the expression of the CreER^T2 recombinase that is only active in the presence of tamoxifen metabolite, 4-hydroxy-tamoxifen (4-OHT). Egr1-CreER^T2 mice were crossed with various reporter mice, Cre-dependently expressing a fluorescent protein. Without tamoxifen or 4-OHT, no or few tagged neurons were observed. Epileptic seizures induced by pilocarpine or pentylenetetrazol in the presence of tamoxifen or 4-OHT elicited the persistent tagging of many neurons and some astrocytes in the dentate gyrus of hippocampus, where Egr1 is transiently induced by seizures. One week after cocaine and 4-OHT administration, these mice displayed a higher number of tagged neurons in the dorsal striatum than saline/4-OHT controls, with differences between reporter lines. Cocaine-induced tagging required ERK activation and tagged neurons were more likely than others to exhibit ERK phosphorylation or Fos induction after a second injection. Interestingly neurons tagged in saline-treated mice also had an increased propensity to express Fos, suggesting the existence of highly responsive striatal neurons susceptible to be re-activated by cocaine repeated administration, which may contribute to the behavioral adaptations. Our report validates a novel transgenic mouse model for permanently tagging activated neurons and studying long-term alterations of Egr1-expressing cells.

MEF2C and HDAC5 regulate Egr1 and Arc genes to increase dendritic spine density and complexity in early enriched environment

We investigated the effects of environmental enrichment during critical period of early postnatal life and how it interplays with the epigenome to affect experience-dependent visual cortical plasticity. Mice raised in an EE from birth to during CP have increased spine density and dendritic complexity in the visual cortex. EE upregulates synaptic plasticity genes, Arc and Egr1, and a transcription factor MEF2C. We also observed an increase in MEF2C binding to the promoters of Arc and Egr1. In addition, pups raised in EE show a reduction in HDAC5 and its binding to promoters of Mef2c, Arc and Egr1 genes. With an overexpression of Mef2c, neurite outgrowth increased in complexity. Our results suggest a possible underlying molecular mechanism of EE, acting through MEF2C and HDAC5, which drive Arc and Egr1. This could lead to the observed increased dendritic spine density and complexity induced by early EE.

Pramipexole Reduces zif-268 mRNA Expression in Brain Structures involved in the Generation of Harmaline-Induced Tremor

Essential tremor is one of the most common neurological disorders, however, it is not sufficiently controlled with currently available pharmacotherapy. Our recent study has shown that pramipexole, a drug efficient in inhibiting parkinsonian tremor, reduced the harmaline-induced tremor in rats, generally accepted to be a model of essential tremor. The aim of the present study was to investigate brain targets for the tremorolytic effect of pramipexole by determination of the early activity-dependent gene zif-268 mRNA expression. Tremor in rats was induced by harmaline administered at a dose of 15 mg/kg ip. Pramipexole was administered at a low dose of 0.1 mg/kg sc. Tremor was measured by Force Plate Actimeters where four force transducers located below the corners of the plate tracked the animal's position on a Cartesian plane. The zif-268 mRNA expression was analyzed by in situ hybridization in brain slices. Harmaline induced tremor and increased zif-268 mRNA levels in the inferior olive, cerebellar cortex, ventroanterior/ventrolateral thalamic nuclei and motor cortex. Pramipexole reversed both the harmaline-induced tremor and the increase in zif-268 mRNA expression in the inferior olive, cerebellar cortex and motor cortex. Moreover, the tremor intensity correlated positively with zif-268 mRNA expression in the above structures. The present results seem to suggest that the tremorolytic effect of pramipexole is related to the modulation of the harmaline-increased neuronal activity in the tremor network which includes the inferior olive, cerebellar cortex and motor cortex. Potential mechanisms underlying the above pramipexole action are discussed.

Limitations of the GENSAT Egr1-EGFP transgenic mouse strain for neural circuit activity mapping

Transgenic immediate-early gene reporter mouse strains are valuable tools for studying activity-dependent neural cell populations in vivo. However, routine characterization of the Gene Expression Nervous System Atlas (GENSAT) "Egr1-EGFP" reporter mouse strain produced results that were highly inconsistent with endogenous Egr1 expression. Activity-dependent EGFP expression was not observed, and EGFP protein did not co-localize with native Egr1 protein. This precautionary study outlines the limitations of the Egr1-EGFP transgenic line as a tool to study the activity-dependent expression of Egr1 and emphasizes the necessity of taking into account the potential loss of regulatory elements, stability determinants, or translational modulation in transgenic reporter strains.

Sex differences in adult mood and in stress-induced transcriptional coherence across mesocorticolimbic circuitry

Women are approximately two times as likely to be diagnosed with major depressive disorder (MDD) compared to men. While sex differences in MDD might be driven by circulating gonadal hormones, we hypothesized that developmental hormone exposure and/or genetic sex might play a role. Mice were gonadectomized in adulthood to isolate the role of developmental hormones. We examined the effects of developmental gonadal and genetic sex on anhedonia-/depressive-like behaviors under non-stress and chronic stress conditions and performed RNA-sequencing in three mood-relevant brain regions. We used an integrative network approach to identify transcriptional modules and stress-specific hub genes regulating stress susceptibility, with a focus on whether these differed by sex. After identifying sex differences in anhedonia-/depressive-like behaviors (female > male), we show that both developmental hormone exposure (gonadal female > gonadal male) and genetic sex (XX > XY) contribute to the sex difference. The top biological pathways represented by differentially expressed genes were related to immune function; we identify which differentially expressed genes are driven by developmental gonadal or genetic sex. There was very little overlap in genes affected by chronic stress in males and females. We also identified highly co-expressed gene modules affected by stress, some of which were affected in opposite directions in males and females. Since all mice had equivalent hormone exposure in adulthood, these results suggest that sex differences in gonadal hormone exposure during sensitive developmental periods program adult sex differences in mood, and that these sex differences are independent of adult circulating gonadal hormones.

Recognition memory reconsolidation requires hippocampal Zif268

Object recognition memory (ORM) serves to distinguish familiar items from novel ones. Reconsolidation is the process by which active memories are updated. The hippocampus is engaged in ORM reconsolidation through a mechanism involving induction of long-term potentiation (LTP). The transcription factor Zif268 is essential for hippocampal LTP maintenance and has been frequently associated with memory processes. However, its possible involvement in ORM reconsolidation has not been determined conclusively. Using Zif268 antisense oligonucleotides in combination with behavioural, biochemical and electrophysiological tools in rats, we found that hippocampal Zif268 is necessary to update ORM through reconsolidation but not to retrieve it or keep it stored. Our results also suggest that knocking down hippocampal Zif268 during ORM reconsolidation deletes the active recognition memory trace.

Regionally selective knockdown of astroglial glutamate transporters in infralimbic cortex induces a depressive phenotype in mice

Elevation of energy metabolism and disturbance of astrocyte number/function in the ventral anterior cingulate cortex (vACC) contributes to the pathophysiology of major depressive disorder (MDD). Functional hyperactivity of vACC may result from reduced astrocytic glutamate uptake and increased neuronal excitation. Here we tested this hypothesis by knocking-down astrocytic glutamate transporter GLAST/GLT-1 expression in mouse infralimbic (IL, rodent equivalent of vACC) or prelimbic (PrL) cortices using RNAi strategies. Unilateral siRNA (small interfering RNA) microinfusion targeting GLAST or GLT-1 in mouse IL induced a moderate (20-30%) and long-lasting (7 days) decrease in their expression. Intra-IL GLAST-/GLT-1 siRNA microinfusion reduced the number of glial fibrillary acidic protein (GFAP)-positive and glutamine synthetase (GS)-positive astrocytes and evoked a depressive-like phenotype reversed by citalopram and ketamine. Intra-IL GLAST or GLT-1 knockdown markedly reduced serotonin (5-HT) release in the dorsal raphe nucleus (DR) and induced an overall reduction of brain-derived neurotrophic factor (BDNF) expression in ipsilateral and contralateral hemispheres. Egr-1 (early growth response protein-1) labeling suggests that both siRNAs enhance the GABAergic tone onto DR 5-HT neurons, leading to an overall decrease of 5-HT function, likely related to the widespread reduction on BDNF expression. Conversely, similar reductions of GLAST and GLT-1 expression in PrL did not induce a depressive-like phenotype. These results suggest that a focal glial change in IL translates into global change of brain activity by virtue of the descending projections from IL to DR and the subsequent attenuation of serotonergic function in forebrain, an effect perhaps related to the varied symptomatology of MDD.

Refining the nuclear localization signal within the Egr transcriptional coregulator NAB2

NAB1 and 2 are coregulators for early growth response (Egr) transcription factors. The NAB1 nuclear localization signal (NLS) was previously described as a bipartite NLS of sequence R(X₂ )K(X₁₁ )KRXK. The sequence is conserved in NAB2 as K(X₂ )R(X₁₁ )KKXK; however, whether it functions as the NAB2 NLS has not been tested. We show that the KKXK motif in NAB2 is necessary and sufficient to mediate nuclear localization. Mutation of the KKXK motif to AAXA causes cytoplasmic localization of NAB2, while Lys/Arg-to-Ala mutations of the upstream K(X₂ )R motif have no effect. Fusion of the KKXK motif to cytoplasmic protein eIF2Bε causes nuclear localization. Altogether, this study refines our knowledge of the NAB2 NLS, demonstrating that KKXK_343-346 is necessary and sufficient for nuclear localization.

5-HTR2A and 5-HTR3A but not 5-HTR1A antagonism impairs the cross-modal reactivation of deprived visual cortex in adulthood

Visual cortical areas show enhanced tactile responses in blind individuals, resulting in improved behavioral performance. Induction of unilateral vision loss in adult mice, by monocular enucleation (ME), is a validated model for such cross-modal brain plasticity. A delayed whisker-driven take-over of the medial monocular zone of the visual cortex is preceded by so-called unimodal plasticity, involving the potentiation of the spared-eye inputs in the binocular cortical territory. Full reactivation of the sensory-deprived contralateral visual cortex is accomplished by 7 weeks post-injury. Serotonin (5-HT) is known to modulate sensory information processing and integration, but its impact on cortical reorganization after sensory loss, remains largely unexplored. To address this issue, we assessed the involvement of 5-HT in ME-induced cross-modal plasticity and the 5-HT receptor (5-HTR) subtype used. We first focused on establishing the impact of ME on the total 5-HT concentration measured in the visual cortex and in the somatosensory barrel field. Next, the changes in expression as a function of post-ME recovery time of the monoamine transporter 2 (vMAT2), which loads 5-HT into presynaptic vesicles, and of the 5-HTR_1A and 5-HTR_3A were assessed, in order to link these temporal expression profiles to the different types of cortical plasticity induced by ME. In order to accurately pinpoint which 5-HTR exactly mediates ME-induced cross-modal plasticity, we pharmacologically antagonized the 5-HTR_1A, 5-HTR_2A and 5-HTR_3A subtypes. This study reveals brain region-specific alterations in total 5-HT concentration, time-dependent modulations in vMAT2, 5-HTR_1A and 5-HTR_3A protein expression and 5-HTR antagonist-specific effects on the post-ME plasticity phenomena. Together, our results confirm a role for 5-HTR_1A in the early phase of binocular visual cortex plasticity and suggest an involvement of 5-HTR_2A and 5-HTR_3A but not 5-HTR_1A during the late cross-modal recruitment of the medial monocular visual cortex. These insights contribute to the general understanding of 5-HT function in cortical plasticity and may encourage the search for improved rehabilitation strategies to compensate for sensory loss.

Immediate Early Genes, Memory and Psychiatric Disorders: Focus on c-Fos, Egr1 and Arc

Many psychiatric disorders, despite their specific characteristics, share deficits in the cognitive domain including executive functions, emotional control and memory. However, memory deficits have been in many cases undervalued compared with other characteristics. The expression of Immediate Early Genes (IEGs) such as, c-fos, Egr1 and arc are selectively and promptly upregulated in learning and memory among neuronal subpopulations in regions associated with these processes. Changes in expression in these genes have been observed in recognition, working and fear related memories across the brain. Despite the enormous amount of data supporting changes in their expression during learning and memory and the importance of those cognitive processes in psychiatric conditions, there are very few studies analyzing the direct implication of the IEGs in mental illnesses. In this review, we discuss the role of some of the most relevant IEGs in relation with memory processes affected in psychiatric conditions.

Memory Function in Feeding Habit Transformation of Mandarin Fish (Siniperca chuatsi)

Mandarin fish refuse dead prey fish or artificial diets and can be trained to transform their inborn feeding habit. To investigate the effect of memory on feeding habit transformation, we compared the reaction time to dead prey fish and the success rate of feeding habit transformation to dead prey fish with training of mandarin fish in the 1st experimental group (trained once) and the 2nd experimental group (trained twice). The mandarin fish in the 2nd group had higher success rate of feeding habit transformation (100%) than those in the 1st group (67%), and shorter reaction time to dead prey fish (<1 s) than those in the 1st group (>1 s). Gene expression of cAMP responsive element binding protein I (Creb I), brain-derived neurotrophic factor (Bdnf), CCAAT enhancer binding protein delta (C/EBPD), fos-related antigen 2 (Fra2), and proto-oncogenes c-fos (c-fos) involved in long-term memory formation were significantly increased in the 2nd group after repeated training, and taste 1 receptor member 1 (T1R1), involved in feeding habit formation, was significantly increased in brains of the 2nd group after repeated training. DNA methylation levels at five candidate CpG (cytosine–guanine) sites contained in the predicted CpG island in the 5′-flanking region of T1R1 were significantly decreased in brains of the 2nd group compared with that of the 1st group. These results indicated that the repeated training can improve the feeding habit transformation through the memory formation of accepting dead prey fish. DNA methylation of the T1R1 might be a regulatory factor for feeding habit transformation from live prey fish to dead prey fish in mandarin fish.

Transient and localized optogenetic activation of somatostatin-interneurons in mouse visual cortex abolishes long-term cortical plasticity due to vision loss

Unilateral vision loss through monocular enucleation (ME) results in partial reallocation of visual cortical territory to another sense in adult mice. The functional recovery of the visual cortex occurs through a combination of spared-eye potentiation and cross-modal reactivation driven by whisker-related, somatosensory inputs. Brain region-specific intracortical inhibition was recently recognized as a crucial regulator of the cross-modal component, yet the contribution of specific inhibitory neuron subpopulations remains poorly understood. Somatostatin (SST)-interneurons are ideally located within the cortical circuit to modulate sensory integration. Here we demonstrate that optogenetic stimulation of visual cortex SST-interneurons prior to eye removal decreases ME-induced cross-modal recovery at the stimulation site. Our results suggest that SST-interneurons act as local hubs, which are able to control the influx and extent of cortical cross-modal inputs into the deprived cortex. These insights critically expand our understanding of SST-interneuron-specific regulation of cortical plasticity induced by sensory loss.

Use of TAI-FISH to visualize neural ensembles activated by multiple stimuli

Researchers in behavioral neuroscience have long sought imaging techniques that can identify and distinguish neural ensembles that are activated by sequentially applied stimuli at single-cell resolution across the whole brain. Taking advantage of the different kinetics of immediate-early genes' mRNA and protein expression, we addressed this problem by developing tyramide-amplified immunohistochemistry-fluorescence in situ hybridization (TAI-FISH), a dual-epoch neural-activity-dependent labeling protocol. Here we describe the step-by-step procedures for TAI-FISH on brain sections from mice that were sequentially stimulated by morphine (appetitive first stimulus) and foot shock (aversive second stimulus). We exemplify our approach by FISH-labeling the neural ensembles that were activated by the second stimulus for the mRNA expression of c-fos, a well-established marker of neural activation. We labeled neuronal ensembles activated by the first stimulus using fluorescence immunohistochemistry (IHC) for the c-fos protein. To further improve the temporal separation of the c-fos mRNA and protein signals, we provide instructions on how to enhance the protein signals using tyramide signal amplification (TSA). Compared with other dual-epoch labeling techniques, TAI-FISH provides better temporal separation of the activated neural ensembles and is better suited to investigation of whole-brain responses. TAI-FISH has been used to investigate neural activation patterns in response to appetitive and aversive stimuli, and we expect it to be more broadly utilized for visualizing brain responses to other types of stimuli, such as sensory stimuli or psychiatric drugs. From first stimulation to image analysis, TAI-FISH takes ∼9 d to complete.

Early survival and delayed death of developmentally-born dentate gyrus neurons

The storage and persistence of memories depends on plasticity in the hippocampus. Adult neurogenesis produces new neurons that mature through critical periods for plasticity and cellular survival, which determine their contributions to learning and memory. However, most granule neurons are generated prior to adulthood; the maturational timecourse of these neurons is poorly understood compared to adult-born neurons but is essential to identify how the dentate gyrus (DG), as a whole, contributes to behavior. To characterize neurons born in the early postnatal period, we labeled DG neurons born on postnatal day 6 (P6) with BrdU and quantified maturation and survival across early (1 hr to 8 weeks old) and late (2-6 months old) cell ages. We find that the dynamics of developmentally-born neuron survival is essentially the opposite of neurons born in adulthood: P6-born neurons did not go through a period of cell death during their immature stages (from 1 to 8 weeks). In contrast, 17% of P6-born neurons died after reaching maturity, between 2 and 6 months of age. Delayed death was evident from the loss of BrdU⁺ cells as well as pyknotic BrdU⁺ caspase3⁺ neurons within the superficial granule cell layer. Patterns of DCX, NeuN, and activity-dependent Fos expression indicate that developmentally-born neurons mature over several weeks and a sharp peak in zif268 expression at 2 weeks suggests that developmentally-born neurons mature faster than adult-born neurons (which peak at 3 weeks). Collectively, our findings are relevant for understanding how developmentally-born DG neurons contribute to memory and disorders throughout the lifespan. High levels of early survival and zif268 expression may promote learning, while also rendering neurons sensitive to insults at defined stages. Late neuronal death in young adulthood may result in the loss of hundreds of thousands of DG neurons, which could impact memory persistence and contribute to hippocampal/DG atrophy in disorders such as depression.

Tremorolytic effect of 5'-chloro-5'-deoxy-(±)-ENBA, a potent and selective adenosine A1 receptor agonist, evaluated in the harmaline-induced model in rats

AIM

The aim of this study was to examine the role of adenosine A₁ receptors in the harmaline-induced tremor in rats using 5'-chloro-5'-deoxy-(±)-ENBA (5'Cl5'd-(±)-ENBA), a brain-penetrant, potent, and selective adenosine A₁ receptor agonist.

METHODS

Harmaline was injected at a dose of 15 mg/kg ip and tremor was measured automatically in force-plate actimeters by an increased averaged power in the frequency band of 9-15 Hz (AP2) and by tremor index (a difference in power between AP2 and averaged power in the frequency band of 0-8 Hz). The zif-268 mRNA expression was additionally analyzed by in situ hybridization in several brain structures.

RESULTS

5'Cl5'd-(±)-ENBA (0.05-0.5 mg/kg ip) dose dependently reduced the harmaline-induced tremor and this effect was reversed by 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), a selective antagonist of adenosine A₁ receptors (1 mg/kg ip). Harmaline increased the zif-268 mRNA expression in the inferior olive, cerebellar cortex, ventroanterior/ventrolateral thalamic nuclei, and motor cortex. 5'Cl5'd-(±)-ENBA reversed these increases in all the above structures. DPCPX reduced the effect of 5'Cl5'd-(±)-ENBA on zif-268 mRNA in the motor cortex.

CONCLUSION

This study suggests that adenosine A₁ receptors may be a potential target for the treatment of essential tremor.

Widespread promoter methylation of synaptic plasticity genes in long-term potentiation in the adult brain in vivo

Background

DNA methylation is a key modulator of gene expression in mammalian development and cellular differentiation, including neurons. To date, the role of DNA modifications in long-term potentiation (LTP) has not been explored.

Results

To investigate the occurrence of DNA methylation changes in LTP, we undertook the first detailed study to describe the methylation status of all known LTP-associated genes during LTP induction in the dentate gyrus of live rats. Using a methylated DNA immunoprecipitation (MeDIP)-array, together with previously published matched RNA-seq and public histone modification data, we discover widespread changes in methylation status of LTP-genes. We further show that the expression of many LTP-genes is correlated with their methylation status. We show that these correlated genes are enriched for RNA-processing, active histone marks, and specific transcription factors. These data reveal that the synaptic activity-evoked methylation changes correlates with pre-existing activation of the chromatin landscape. Finally, we show that methylation of Brain-derived neurotrophic factor (Bdnf) CpG-islands correlates with isoform switching from transcripts containing exon IV to exon I.

Conclusions

Together, these data provide the first evidence of widespread regulation of methylation status in LTP-associated genes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3621-x) contains supplementary material, which is available to authorized users.

Role for Egr1 in the Transcriptional Program Associated with Neuronal Differentiation of PC12 Cells

PC12 cells are a well-established model to study how differences in signal transduction duration can elicit distinct cell behaviors. Epidermal growth factor (EGF) activates transient ERK signaling in PC12 cells that lasts 30–60 min, which in turn promotes proliferation; nerve growth factor (NGF) activates more sustained ERK signaling that lasts 4–6 h, which in turns induces neuronal differentiation. Data presented here extend a previous study by Mullenbrock et al. (2011) that demonstrated that sustained ERK signaling in response to NGF induces preferential expression of a 69-member gene set compared to transient ERK signaling in response to EGF and that the transcription factors AP-1 and CREB play a major role in the preferential expression of several genes within the set. Here, we examined whether the Egr family of transcription factors also contributes to the preferential expression of the gene set in response to NGF. Our data demonstrate that NGF causes transient induction of all Egr family member transcripts, but a corresponding induction of protein was detected for only Egr1 and 2. Chromatin immunoprecipitation experiments provided clearest evidence that, after induction, Egr1 binds 12 of the 69 genes that are preferentially expressed during sustained ERK signaling. In addition, Egr1 expression and binding upstream of its target genes were both sustained in response to NGF versus EGF within the same timeframe that its targets are preferentially expressed. These data thus provide evidence that Egr1 contributes to the transcriptional program activated by sustained ERK signaling in response to NGF, specifically by contributing to the preferential expression of its target genes identified here.

Synaptic activation of ribosomal protein S6 phosphorylation occurs locally in activated dendritic domains

Previous studies have shown that induction of long-term potentiation (LTP) induces phosphorylation of ribosomal protein S6 (rpS6) in postsynaptic neurons, but the functional significance of rpS6 phosphorylation is poorly understood. Here, we show that synaptic stimulation that induces perforant path LTP triggers phosphorylation of rpS6 (p-rpS6) locally near active synapses. Using antibodies specific for phosphorylation at different sites (ser235/236 versus ser240/244), we show that strong synaptic activation led to dramatic increases in immunostaining throughout postsynaptic neurons with selectively higher staining for p-ser235/236 in the activated dendritic lamina. Following LTP induction, phosphorylation at ser235/236 was detectable by 5 min, peaked at 30 min, and was maintained for hours. Phosphorylation at both sites was completely blocked by local infusion of the NMDA receptor antagonist, APV. Despite robust induction of p-rpS6 following high frequency stimulation, assessment of protein synthesis by autoradiography revealed no detectable increases. Exploration of a novel environment led to increases in the number of p-rpS6-positive neurons throughout the forebrain in a pattern reminiscent of immediate early gene induction and many individual neurons that were p-rpS6-positive coexpressed Arc protein. Our results constrain hypotheses about the possible role of rpS6 phosphorylation in regulating postsynaptic protein synthesis during induction of synaptic plasticity.

Nuclear RNA-seq of single neurons reveals molecular signatures of activation

Single-cell sequencing methods have emerged as powerful tools for identification of heterogeneous cell types within defined brain regions. Application of single-cell techniques to study the transcriptome of activated neurons can offer insight into molecular dynamics associated with differential neuronal responses to a given experience. Through evaluation of common whole-cell and single-nuclei RNA-sequencing (snRNA-seq) methods, here we show that snRNA-seq faithfully recapitulates transcriptional patterns associated with experience-driven induction of activity, including immediate early genes (IEGs) such as Fos, Arc and Egr1. SnRNA-seq of mouse dentate granule cells reveals large-scale changes in the activated neuronal transcriptome after brief novel environment exposure, including induction of MAPK pathway genes. In addition, we observe a continuum of activation states, revealing a pseudotemporal pattern of activation from gene expression alone. In summary, snRNA-seq of activated neurons enables the examination of gene expression beyond IEGs, allowing for novel insights into neuronal activation patterns in vivo.

The molecular dynamics associated with neuronal activation patterns in vivo are unclear. Lacar et al. perform single-nuclei RNA-sequencing of hippocampal neurons from mice exposed to a novel environment, and identify large-scale transcriptome changes in individual neurons associated with the experience.

Retinal lesions induce fast intrinsic cortical plasticity in adult mouse visual system

Neuronal activity plays an important role in the development and structural-functional maintenance of the brain as well as in its life-long plastic response to changes in sensory stimulation. We characterized the impact of unilateral 15° laser lesions in the temporal lower visual field of the retina, on visually driven neuronal activity in the afferent visual pathway of adult mice using in situ hybridization for the activity reporter gene zif268. In the first days post-lesion, we detected a discrete zone of reduced zif268 expression in the contralateral hemisphere, spanning the border between the monocular segment of the primary visual cortex (V1) with extrastriate visual area V2M. We could not detect a clear lesion projection zone (LPZ) in areas lateral to V1 whereas medial to V2M, agranular and granular retrosplenial cortex showed decreased zif268 levels over their full extent. All affected areas displayed a return to normal zif268 levels, and this was faster in higher order visual areas than in V1. The lesion did, however, induce a permanent LPZ in the retinorecipient layers of the superior colliculus. We identified a retinotopy-based intrinsic capacity of adult mouse visual cortex to recover from restricted vision loss, with recovery speed reflecting the areal cortical magnification factor. Our observations predict incomplete visual field representations for areas lateral to V1 vs. lack of retinotopic organization for areas medial to V2M. The validation of this mouse model paves the way for future interrogations of cortical region- and cell-type-specific contributions to functional recovery, up to microcircuit level.

Exploring Memory Representations with Activity-Based Genetics

The brain is thought to represent specific memories through the activity of sparse and distributed neural ensembles. In this review, we examine the use of immediate early genes (IEGs), genes that are induced by neural activity, to specifically identify and genetically modify neurons activated naturally by environmental experience. Recent studies using this approach have identified cellular and molecular changes specific to neurons activated during learning relative to their inactive neighbors. By using opto- and chemogenetic regulators of neural activity, the neurons naturally recruited during learning can be artificially reactivated to directly test their role in coding external information. In contextual fear conditioning, artificial reactivation of learning-induced neural ensembles in the hippocampus or neocortex can substitute for the context itself. That is, artificial stimulation of these neurons can apparently cause the animals to "think" they are in the context. This represents a powerful approach to testing the principles by which the brain codes for the external world and how these circuits are modified with learning.

The modulation of BDNF expression and signalling dissects the antidepressant from the reinforcing properties of ketamine: Effects of single infusion vs. chronic self-administration in rats

Ketamine is a drug of abuse with a unique profile, which besides its inherent mechanism of action as a non-competitive antagonist of the NMDA glutamate receptor, displays both antidepressant and reinforcing properties. The major aim of our study was to find a molecular signature of ketamine that may help in discriminating between its reinforcing and antidepressant effects. To this end, we focused our attention on BDNF, a neurotrophin that has been shown to play a role in both antidepressant and reinforcing properties of several drugs. Rats were exposed to self-administer intravenous (IV) ketamine (S/A) for 43 days or to receive a single IV ketamine 0.5mg/kg, or vehicle infusion. Although the dose we employed is lower than that reported by the literature, it however yields Cmax values that correspond to those achieved in humans after antidepressant treatment. Our results show that while the single infusion of ketamine increased the neurotrophin expression in the hippocampus while reducing it in the ventral striatum, a feature shared with other antidepressants, the repeated self-administration reduced mBDNF expression and its downstream signalling in both ventral striatum and hippocampus. Further, we here show that phosphorylation of Akt is oppositely regulated by ketamine, pointing to this pathway as central to the different actions of the drug. Taken together, we here point to BDNF and its downstream signalling pathway as a finely tuned mechanism whose modulation might subserve the different features of ketamine.

Regional Specificity of GABAergic Regulation of Cross-Modal Plasticity in Mouse Visual Cortex after Unilateral Enucleation

In adult mice, monocular enucleation (ME) results in an immediate deactivation of the contralateral medial monocular visual cortex. An early restricted reactivation by open eye potentiation is followed by a late overt cross-modal reactivation by whiskers (Van Brussel et al., 2011). In adolescence (P45), extensive recovery of cortical activity after ME fails as a result of suppression or functional immaturity of the cross-modal mechanisms (Nys et al., 2014). Here, we show that dark exposure before ME in adulthood also prevents the late cross-modal reactivation component, thereby converting the outcome of long-term ME into a more P45-like response. Because dark exposure affects GABAergic synaptic transmission in binocular V1 and the plastic immunity observed at P45 is reminiscent of the refractory period for inhibitory plasticity reported by Huang et al. (2010), we molecularly examined whether GABAergic inhibition also regulates ME-induced cross-modal plasticity. Comparison of the adaptation of the medial monocular and binocular cortices to long-term ME or dark exposure or a combinatorial deprivation revealed striking differences. In the medial monocular cortex, cortical inhibition via the GABAA receptor α1 subunit restricts cross-modal plasticity in P45 mice but is relaxed in adults to allow the whisker-mediated reactivation. In line, in vivo pharmacological activation of α1 subunit-containing GABAA receptors in adult ME mice specifically reduces the cross-modal aspect of reactivation. Together with region-specific changes in glutamate acid decarboxylase (GAD) and vesicular GABA transporter expression, these findings put intracortical inhibition forward as an important regulator of the age-, experience-, and cortical region-dependent cross-modal response to unilateral visual deprivation.

SIGNIFICANCE STATEMENT

In adult mice, vision loss through one eye instantly reduces neuronal activity in the visual cortex. Strengthening of remaining eye inputs in the binocular cortex is followed by cross-modal adaptations in the monocular cortex, in which whiskers become a dominant nonvisual input source to attain extensive cortical reactivation. We show that the cross-modal component does not occur in adolescence because of increased intracortical inhibition, a phenotype that was mimicked in adult enucleated mice when treated with indiplon, a GABAA receptor α1 agonist. The cross-modal versus unimodal responses of the adult monocular and binocular cortices also mirror regional specificity in inhibitory alterations after visual deprivation. Understanding cross-modal plasticity in response to sensory loss is essential to maximize patient susceptibility to sensory prosthetics.

NRC-interacting factor directs neurite outgrowth in an activity-dependent manner

Nuclear hormone receptor coregulator-interacting factor 1 (NIF-1) is a zinc finger nuclear protein that was initially identified to enhance nuclear hormone receptor transcription via its interaction with nuclear hormone receptor coregulator (NRC). NIF-1 may regulate gene transcription either by modulating general transcriptional machinery or remodeling chromatin structure through interactions with specific protein partners. We previously reported that the cytoplasmic/nuclear localization of NIF-1 is regulated by the neuronal Cdk5 activator p35, suggesting potential neuronal functions for NIF-1. The present study reveals that NIF-1 plays critical roles in regulating neuronal morphogenesis at early stages. NIF-1 was prominently expressed in the nuclei of developing rat cortical neurons. Knockdown of NIF-1 expression attenuated both neurite outgrowth in cultured cortical neurons and retinoic acid (RA)-treated Neuro-2a neuroblastoma cells. Furthermore, activity-induced Ca(2+) influx, which is critical for neuronal morphogenesis, stimulated the nuclear localization of NIF-1 in cortical neurons. Suppression of NIF-1 expression reduced the up-regulation of neuronal activity-dependent gene transcription. These findings collectively suggest that NIF-1 directs neuronal morphogenesis during early developmental stages through modulating activity-dependent gene transcription.

Chronic stress enhanced fear memories are associated with increased amygdala zif268 mRNA expression and are resistant to reconsolidation

The chronically stressed brain may present a vulnerability to develop maladaptive fear-related behaviors in response to a traumatic event. In rodents, chronic stress leads to amygdala hyperresponsivity and dendritic hypertrophy and produces a post traumatic stress disorder (PTSD)-like phenotype that includes exaggerated fear learning following Pavlovian fear conditioning and resistance to extinction. It is unknown whether chronic stress-induced enhanced fear memories are vulnerable to disruption via reconsolidation blockade, as a novel therapeutic approach for attenuating exaggerated fear memories. We used a chronic stress procedure in a rat model (wire mesh restraint for 6h/d/21d) to create a vulnerable brain that leads to a PTSD-like phenotype. We then examined freezing behavior during acquisition, reactivation and after post-reactivation rapamycin administration (i.p., 40mg/kg) in a Pavlovian fear conditioning paradigm to determine its effects on reconsolidation as well as the subsequent functional activation of limbic structures using zif268 mRNA. Chronic stress increased amygdala zif268 mRNA during fear memory retrieval at reactivation. Moreover, these enhanced fear memories were unaffected by post reactivation rapamycin to disrupt long-term fear memory. Also, post-reactivation long term memory processing was also associated with increased amygdala (LA and BA), and decreased hippocampal CA1 zif268 mRNA expression. These results suggest potential challenges for reconsolidation blockade as an effective approach in treating exaggerated fear memories, as in PTSD. Our findings also support chronic stress manipulations combined with fear conditioning as a useful preclinical approach to study a PTSD-like phenotype.

Ocular hypertension results in retinotopic alterations in the visual cortex of adult mice

PURPOSE

Glaucoma is a group of optic neuropathies characterized by the loss of retinal ganglion cells (RGCs). Since ocular hypertension (OHT) is a main risk factor, current therapies are predominantly based on lowering eye pressure. However, a subset of treated patients continues to lose vision. More research into pathological mechanisms underlying glaucoma is therefore warranted in order to develop novel therapeutic strategies. In this study we investigated the impact of OHT from eye to brain in mice.

METHODS

Monocular hypertension (mOHT) was induced in CD-1 mice by laser photocoagulation (LP) of the perilimbal and episcleral veins. The impact on the retina and its main direct target area, the superficial superior colliculus (sSC), was examined via immunostainings for Brn3a, VGluT2 and GFAP. Alterations in neuronal activity in V1 and extrastriate areas V2L and V2M were assessed using in situ hybridization for the activity reporter gene zif268.

RESULTS

Transient mOHT resulted in diffuse and sectorial RGC degeneration. In the sSC contralateral to the OHT eye, a decrease in VGluT2 immunopositive synaptic connections was detected one week post LP, which appeared to be retinotopically linked to the sectorial RGC degeneration patterns. In parallel, hypoactivity was discerned in contralateral retinotopic projection zones in V1 and V2. Despite complete cortical reactivation 4 weeks post LP, in the sSC no evidence for recovery of RGC synapse density was found and also the concomitant inflammation was not completely resolved. Nevertheless, sSC neurons appeared healthy upon histological inspection and subsequent analysis of cell density revealed no differences between the ipsi- and contralateral sSC.

CONCLUSION

In addition to RGC death, OHT induces loss of synaptic connections and neuronal activity in the visual pathway and is accompanied by an extensive immune response. Our findings stress the importance of looking beyond the eye and including the whole visual system in glaucoma research.

Zif268 mRNA Expression Patterns Reveal a Distinct Impact of Early Pattern Vision Deprivation on the Development of Primary Visual Cortical Areas in the Cat

Pattern vision deprivation (BD) can induce permanent deficits in global motion perception. The impact of timing and duration of BD on the maturation of the central and peripheral visual field representations in cat primary visual areas 17 and 18 remains unknown. We compared early BD, from eye opening for 2, 4, or 6 months, with late onset BD, after 2 months of normal vision, using the expression pattern of the visually driven activity reporter gene zif268 as readout. Decreasing zif268 mRNA levels between months 2 and 4 characterized the normal maturation of the (supra)granular layers of the central and peripheral visual field representations in areas 17 and 18. In general, all BD conditions had higher than normal zif268 levels. In area 17, early BD induced a delayed decrease, beginning later in peripheral than in central area 17. In contrast, the decrease occurred between months 2 and 4 throughout area 18. Lack of pattern vision stimulation during the first 4 months of life therefore has a different impact on the development of areas 17 and 18. A high zif268 expression level at a time when normal vision is restored seems to predict the capacity of a visual area to compensate for BD.

Lower expression of glutamic acid decarboxylase 67 in the prefrontal cortex in schizophrenia: contribution of altered regulation by Zif268

OBJECTIVE

Cognitive deficits of schizophrenia may be due at least in part to lower expression of the 67-kDa isoform of glutamic acid decarboxylase (GAD67), a key enzyme for GABA synthesis, in the dorsolateral prefrontal cortex of individuals with schizophrenia. However, little is known about the molecular regulation of lower cortical GAD67 levels in schizophrenia. The GAD67 promoter region contains a conserved Zif268 binding site, and Zif268 activation is accompanied by increased GAD67 expression. Thus, altered expression of the immediate early gene Zif268 may contribute to lower levels of GAD67 mRNA in the dorsolateral prefrontal cortex in schizophrenia.

METHOD

The authors used polymerase chain reaction to quantify GAD67 and Zif268 mRNA levels in dorsolateral prefrontal cortex area 9 from 62 matched pairs of schizophrenia and healthy comparison subjects, and in situ hybridization to assess Zif268 expression at laminar and cellular levels of resolution. The effects of potentially confounding variables were assessed in human subjects, and the effects of antipsychotic treatments were tested in antipsychotic-exposed monkeys. The specificity of the Zif268 findings was assessed by quantifying mRNA levels for other immediate early genes.

RESULTS

GAD67 and Zif268 mRNA levels were significantly lower and were positively correlated in the schizophrenia subjects. Both Zif268 mRNA-positive neuron density and Zif268 mRNA levels per neuron were significantly lower in the schizophrenia subjects. These findings were robust to the effects of the confounding variables examined and differed from other immediate early genes.

CONCLUSIONS

Deficient Zif268 mRNA expression may contribute to lower cortical GAD67 levels in schizophrenia, suggesting a potential mechanistic basis for altered cortical GABA synthesis and impaired cognition in schizophrenia.

Neonatal infection modulates behavioral flexibility and hippocampal activation on a Morris Water Maze task

Neonatal infection has enduring effects on the brain, both at the cellular and behavioral levels. We determined the effects of peripheral infection with Escherichia coli at postnatal day (P) 4 in rats on a water maze task in adulthood, and assessed neuronal activation in the dentate gyrus (DG) following the memory test. Rats were trained and tested on one of 3 distinct water maze task paradigms: 1) minimal training (18 trials/3days), 2) extended training (50 trials/10days) or 3) reversal training (extended training followed by 30 trials/3days with a new platform location). Following a 48h memory test, brains were harvested to assess neuronal activation using activity-regulated cytoskeleton-associated (Arc) protein in the DG. Following minimal training, rats treated neonatally with E. coli had improved performance and paradoxically reduced Arc expression during the memory test compared to control rats treated with PBS early in life. However, neonatally-infected rats did not differ from control rats in behavior or neuronal activation during the memory test following extended training. Furthermore, rats treated neonatally with E. coli were significantly impaired during the 48h memory test for a reversal platform location, unlike controls. Specifically, whereas neonatally-infected rats were able to acquire the new location at the same rate as controls, they spent significantly less time in the target quadrant for the reversal platform during a memory test. However, neonatally-infected and control rats had similar levels of Arc expression following the 48h memory test for reversal. Together, these data indicate that neonatal infection may improve the rate of acquisition on hippocampal-dependent tasks while impairing flexibility on the same tasks; in addition, network activation in the DG during learning may be predictive of future cognitive flexibility on a hippocampal-dependent task.

The transcription factor Zif268/Egr1, brain plasticity, and memory

The capacity to remember our past experiences and organize our future draws on a number of cognitive processes that allow our brain to form and store neural representations that can be recalled and updated at will. In the brain, these processes require mechanisms of neural plasticity in the activated circuits, brought about by cellular and molecular changes within the neurons activated during learning. At the cellular level, a wealth of experimental data accumulated in recent years provides evidence that signaling from synapses to nucleus and the rapid regulation of the expression of immediate early genes encoding inducible, regulatory transcription factors is a key step in the mechanisms underlying synaptic plasticity and the modification of neural networks required for the laying down of memories. In the activated neurons, these transcriptional events are thought to mediate the activation of selective gene programs and subsequent synthesis of proteins, leading to stable functional and structural remodeling of the activated networks, so that the memory can later be reactivated upon recall. Over the past few decades, novel insights have been gained in identifying key transcriptional regulators that can control the genomic response of synaptically activated neurons. Here, as an example of this approach, we focus on one such activity-dependent transcription factor, Zif268, known to be implicated in neuronal plasticity and memory formation. We summarize current knowledge about the regulation and function of Zif268 in different types of brain plasticity and memory processes.

Role of movement in long-term basal ganglia changes: implications for abnormal motor responses

Abnormal involuntary movements (AIMs) and dyskinesias elicited by drugs that stimulate dopamine receptors in the basal ganglia are a major issue in the management of Parkinson’s disease (PD). Preclinical studies in dopamine-denervated animals have contributed to the modeling of these abnormal movements, but the precise neurochemical and functional mechanisms underlying these untoward effects are still elusive. It has recently been suggested that the performance of movement may itself promote the later emergence of drug-induced motor complications, by favoring the generation of aberrant motor memories in the dopamine-denervated basal ganglia. Our recent results from hemiparkinsonian rats subjected to the priming model of dopaminergic stimulation are in agreement with this. These results demonstrate that early performance of movement is crucial for the manifestation of sensitized rotational behavior, indicative of an abnormal motor response, and neurochemical modifications in selected striatal neurons following a dopaminergic challenge. Building on this evidence, this paper discusses the possible role of movement performance in drug-induced motor complications, with a look at the implications for PD management.

Cognitive and cerebrovascular improvements following kinin B1 receptor blockade in Alzheimer's disease mice

Background

Recent evidence suggests that the inducible kinin B₁ receptor (B₁R) contributes to pathogenic neuroinflammation induced by amyloid-beta (Aβ) peptide. The present study aims at identifying the cellular distribution and potentially detrimental role of B₁R on cognitive and cerebrovascular functions in a mouse model of Alzheimer’s disease (AD).

Methods

Transgenic mice overexpressing a mutated form of the human amyloid precursor protein (APP_Swe,Ind, line J20) were treated with a selective and brain penetrant B₁R antagonist (SSR240612, 10 mg/kg/day for 5 or 10 weeks) or vehicle. The impact of B₁R blockade was measured on i) spatial learning and memory performance in the Morris water maze, ii) cerebral blood flow (CBF) responses to sensory stimulation using laser Doppler flowmetry, and iii) reactivity of isolated cerebral arteries using online videomicroscopy. Aβ burden was quantified by ELISA and immunostaining, while other AD landmarks were measured by western blot and immunohistochemistry.

Results

B₁R protein levels were increased in APP mouse hippocampus and, prominently, in reactive astrocytes surrounding Aβ plaques. In APP mice, B₁R antagonism with SSR240612 improved spatial learning, memory and normalized protein levels of the memory-related early gene Egr-1 in the dentate gyrus of the hippocampus. B₁R antagonism restored sensory-evoked CBF responses, endothelium-dependent dilations, and normalized cerebrovascular protein levels of endothelial nitric oxide synthase and B₂R. In addition, SSR240612 reduced (approximately 50%) microglial, but not astroglial, activation, brain levels of soluble Aβ_1-42, diffuse and dense-core Aβ plaques, and it increased protein levels of the Aβ brain efflux transporter lipoprotein receptor-related protein-1 in cerebral microvessels.

Conclusion

These findings show a selective upregulation of astroglial B₁R in the APP mouse brain, and the capacity of the B₁R antagonist to abrogate amyloidosis, cerebrovascular and memory deficits. Collectively, these findings provide convincing evidence for a role of B₁R in AD pathogenesis.

Monocular inhibition reveals temporal and spatial changes in gene expression in the primary visual cortex of marmoset

We investigated the time course of the expression of several activity-dependent genes evoked by visual inputs in the primary visual cortex (V1) in adult marmosets. In order to examine the rapid time course of activity-dependent gene expression, marmosets were first monocularly inactivated by tetrodotoxin (TTX), kept in darkness for two days, and then exposed to various length of light stimulation. Activity-dependent genes including HTR1B, HTR2A, whose activity-dependency were previously reported by us, and well-known immediate early genes (IEGs), c-FOS, ZIF268, and ARC, were examined by in situ hybridization. Using this system, first, we demonstrated the ocular dominance type of gene expression pattern in V1 under this condition. IEGs were expressed in columnar patterns throughout layers II–VI of all the tested monocular marmosets. Second, we showed the regulation of HTR1B and HTR2A expressions by retinal spontaneous activity, because HTR1B and HTR2A mRNA expressions sustained a certain level regardless of visual stimulation and were inhibited by a blockade of the retinal activity with TTX. Third, IEGs dynamically changed its laminar distribution from half an hour to several hours upon a stimulus onset with the unique time course for each gene. The expression patterns of these genes were different in neurons of each layer as well. These results suggest that the regulation of each neuron in the primary visual cortex of marmosets is subjected to different regulation upon the change of activities from retina. It should be related to a highly differentiated laminar structure of marmoset visual systems, reflecting the functions of the activity-dependent gene expression in marmoset V1.