Reversal of impaired hippocampal long-term potentiation and contextual fear memory deficits in Angelman syndrome model mice by ErbB inhibitors

BACKGROUND

Angelman syndrome (AS) is a human neuropsychiatric disorder associated with autism, mental retardation, motor abnormalities, and epilepsy. In most cases, AS is caused by the deletion of the maternal copy of UBE3A gene, which encodes the enzyme ubiquitin ligase E3A, also termed E6-AP. A mouse model of AS has been generated and these mice exhibit many of the observed neurological alterations in humans. Because of clinical and neuroanatomical similarities between AS and schizophrenia, we examined AS model mice for alterations in the neuregulin-ErbB4 pathway, which has been implicated in the pathophysiology of schizophrenia. We focused our studies on the hippocampus, one of the major brain loci impaired in AS mice.

METHODS

We determined the expression of neuregulin 1 and ErbB4 receptors in AS mice and wild-type littermates (ages 10-16 weeks) and studied the effects of ErbB inhibition on long-term potentiation in hippocampal area cornu ammonis 1 and on hippocampus-dependent contextual fear memory.

RESULTS

We observed enhanced neuregulin-ErbB4 signaling in the hippocampus of AS model mice and found that ErbB inhibitors could reverse deficits in long-term potentiation, a cellular substrate for learning and memory. In addition, we found that an ErbB inhibitor enhanced long-term contextual fear memory in AS model mice.

CONCLUSIONS

Our findings suggest that neuregulin-ErbB4 signaling is involved in synaptic plasticity and memory impairments in AS model mice, suggesting that ErbB inhibitors have therapeutic potential for the treatment of AS.

The impact of sleep deprivation on neuronal and glial signaling pathways important for memory and synaptic plasticity

Sleep deprivation is a common feature in modern society, and one of the consequences of sleep loss is the impairment of cognitive function. Although it has been widely accepted that sleep deprivation affects learning and memory, only recently has research begun to address which molecular signaling pathways are altered by sleep loss and, more importantly, which pathways can be targeted to reverse the memory impairments resulting from sleep deprivation. In this review, we discuss the different methods used to sleep deprive animals and the effects of different durations of sleep deprivation on learning and memory with an emphasis on hippocampus-dependent memory. We then review the molecular signaling pathways that are sensitive to sleep loss, with a focus on those thought to play a critical role in the memory and synaptic plasticity deficits observed after sleep deprivation. Finally, we highlight several recent attempts to reverse the effects of sleep deprivation on memory and synaptic plasticity. Future research building on these studies promises to contribute to the development of novel strategies to ameliorate the effects of sleep loss on cognition.

Association between sociability and diffusion tensor imaging in BALB/cJ mice

The purpose of this study was to use high-resolution diffusion tensor imaging (DTI) to investigate the association between DTI metrics and sociability in BALB/c inbred mice. The sociability of prepubescent (30-day-old) BALB/cJ mice was operationally defined as the time that the mice spent sniffing a stimulus mouse in a social choice test. High-resolution ex vivo DTI data on 12 BALB/cJ mouse brains were acquired using a 9.4-T vertical-bore magnet. Regression analysis was conducted to investigate the association between DTI metrics and sociability. Significant positive regression (p < 0.001) between social sniffing time and fractional anisotropy was found in 10 regions located in the thalamic nuclei, zona incerta/substantia nigra, visual/orbital/somatosensory cortices and entorhinal cortex. In addition, significant negative regression (p < 0.001) between social sniffing time and mean diffusivity was found in five areas located in the sensory cortex, motor cortex, external capsule and amygdaloid region. In all regions showing significant regression with either the mean diffusivity or fractional anisotropy, the tertiary eigenvalue correlated negatively with the social sniffing time. This study demonstrates the feasibility of using DTI to detect brain regions associated with sociability in a mouse model system.

Sociability and brain development in BALB/cJ and C57BL/6J mice

Sociability--the tendency to seek social interaction--propels the development of social cognition and social skills, but is disrupted in autism spectrum disorders (ASD). BALB/cJ and C57BL/6J inbred mouse strains are useful models of low and high levels of juvenile sociability, respectively, but the neurobiological and developmental factors that account for the strains' contrasting sociability levels are largely unknown. We hypothesized that BALB/cJ mice would show increasing sociability with age but that C57BL/6J mice would show high sociability throughout development. We also hypothesized that littermates would resemble one another in sociability more than non-littermates. Finally, we hypothesized that low sociability would be associated with low corpus callosum size and increased brain size in BALB/cJ mice. Separate cohorts of C57BL/6J and BALB/cJ mice were tested for sociability at 19-, 23-, 31-, 42-, or 70-days-of-age, and brain weights and mid-sagittal corpus callosum area were measured. BALB/cJ sociability increased with age, and a strain by age interaction in sociability between 31 and 42 days of age suggested strong effects of puberty on sociability development. Sociability scores clustered according to litter membership in both strains, and perinatal litter size and sex ratio were identified as factors that contributed to this clustering in C57BL/6J, but not BALB/cJ, litters. There was no association between corpus callosum size and sociability, but smaller brains were associated with lower sociability in BALB/cJ mice. The associations reported here will provide directions for future mechanistic studies of sociability development.

Aging impairs hippocampus-dependent long-term memory for object location in mice

The decline in cognitive function that accompanies normal aging has a negative impact on the quality of life of the elderly and their families. Studies in humans and rodents show that spatial navigation and other hippocampus-dependent functions are particularly vulnerable to the deleterious effects of aging. However, reduced motor activity and alterations in the stress response that accompany normal aging can hinder the ability to study certain cognitive behaviors in aged animals. In an attempt to circumvent these potential confounds, we used a hippocampus-dependent object-place recognition task to show that long-term spatial memory is impaired in aged mice. Aged animals performed similarly to young adult mice on an object recognition task that does not rely on hippocampal function.

Behavioral epigenetics

Sponsored by the New York Academy of Sciences, the Warren Alpert Medical School of Brown University and the University of Massachusetts Boston, "Behavioral Epigenetics" was held on October 29-30, 2010 at the University of Massachusetts Boston Campus Center, Boston, Massachusetts. This meeting featured speakers and panel discussions exploring the emerging field of behavioral epigenetics, from basic biochemical and cellular mechanisms to the epigenetic modulation of normative development, developmental disorders, and psychopathology. This report provides an overview of the research presented by leading scientists and lively discussion about the future of investigation at the behavioral epigenetic level.

Post-training intrahippocampal inhibition of class I histone deacetylases enhances long-term object-location memory

Long-term memory formation involves covalent modification of the histone proteins that package DNA. Reducing histone acetylation by mutating histone acetyltransferases impairs long-term memory, and enhancing histone acetylation by inhibiting histone deacetylases (HDACs) improves long-term memory. Previous studies using HDAC inhibitors to enhance long-term memory have focused on the fear-conditioning task using broad-spectrum HDAC inhibitors. We have found that post-training intrahippocampal administration of the broad-spectrum HDAC inhibitor trichostatin A (TSA) or the class I HDAC-selective inhibitor MS275 enhances long-term object-location memory, supporting a role for class I HDACs in the enhancement of hippocampus-dependent memory induced by HDAC inhibition.

Money is not enough: exploring the impact of social and cultural resources on youth health

BACKGROUND

Findings on socioeconomic health differentials in youth remain fragmented with the role of cumulative and interaction effects of different forms of health resources not well understood.

METHODS

European KIDSCREEN data were analysed to explore effects of material and non-material resources on subjective health in The Netherlands, Hungary, and the UK.

RESULTS

Regression analysis revealed significant main effects of economic, social, and cultural resources on youth health. In the UK an interaction effect between economic and cultural resources indicated a conditional relationship between material and non-material health resources.

CONCLUSIONS

Exploring the combined impact of economic, social, and cultural resources may contribute to our understanding of health differentials.

A molecular basis for interactions between sleep and memory

The electrophysiological properties of the sleeping brain profoundly influence memory function in various species, yet the molecular nature by which sleep and memory interact remains unclear. We summarize work that has established the cAMP-PKA-CREB intracellular signaling pathway as a major mechanism involved in the wakeful consolidation of memory in many organisms while highlighting newer evidence that this pathway has a role in sleep regulation, sleep deprivation and potentially sleep-memory interactions. We explore the possibility that sleep might influence memory processing by reactivating the same molecular cascades first recruited during learning during a sort of "molecular replay". Lastly, we discuss how new approaches together with established techniques will aid in our understanding of the nature of sleep-memory interactions.

Subregion-specific p300 conditional knock-out mice exhibit long-term memory impairments

Histone acetylation plays a critical role during long-term memory formation. Several studies have demonstrated that the histone acetyltransferase (HAT) CBP is required during long-term memory formation, but the involvement of other HAT proteins has not been extensively investigated. The HATs CBP and p300 have at least 400 described interacting proteins including transcription factors known to play a role in long-term memory formation. Thus, CBP and p300 constitute likely candidates for transcriptional coactivators in memory formation. In this study, we took a loss-of-function approach to evaluate the role of p300 in long-term memory formation. We used conditional knock-out mice in which the deletion of p300 is restricted to the postnatal phase and to subregions of the forebrain. We found that p300 is required for the formation of long-term recognition memory and long-term contextual fear memory in the CA1 area of the hippocampus and cortical areas.

The role of NR4A transcription factors in memory formation

In various physiological contexts, Nr4a genes are transcribed in response to external stimuli as part of an immediate early response that initiates a cascade of gene expression ultimately leading to distinct physiological outcomes in each of these contexts. The signaling pathway that initiates Nr4a gene expression in most of these contexts consists of elevated intracellular cAMP activating PKA, which in turn leads to phosphorylation of CREB and new gene synthesis. This cAMP-PKA-CREB pathway is a central molecular pathway in the formation of a long-term memory. Indeed, learning induces Nr4a family gene expression, and long-term memory formation requires at least two waves of transcription after learning, suggesting that NR4A nuclear receptors may contribute to the second of these waves of gene expression. In this article, we review insights gained in other physiological contexts regarding Nr4a function and regulation, and highlight how these lessons can be applied to the study of memory formation.

The cholinergic system and neostriatal memory functions

The striatum is one of the major forebrain regions that strongly expresses muscarinic and nicotinic cholinergic receptors. This article reviews the current knowledge and our new findings about the striatal cholinoceptive organization and its role in a variety of cognitive functions. Pharmacological and genetic manipulations have indicated that the cholinergic and dopaminergic system in the striatum modulate each other's function. In addition to modulating the dopaminergic system, nicotinic cholinergic receptors facilitate GABA release, whereas muscarinic receptors attenuate GABA release. The striatal cholinergic system has also been implicated in various cognitive functions including procedural learning and intradimensional set shifting. Together, these data indicate that the cholinergic system in the striatum is involved in a diverse set of cognitive functions through interactions with other neurotransmitter systems including the dopaminergic and GABAergic systems.

Days to criterion as an indicator of toxicity associated with human Alzheimer amyloid-beta oligomers

OBJECTIVE

Recent evidence suggests that high molecular weight soluble oligomeric Abeta (oAbeta) assemblies (also known as Abeta-derived diffusible ligands, or ADDLs) may represent a primary neurotoxic basis for cognitive failure in Alzheimer disease (AD). To date, most in vivo studies of oAbeta/ADDLs have involved injection of assemblies purified from the cerebrospinal fluid of human subjects with AD or from the conditioned media of Abeta-secreting cells into experimental animals. We sought to study the bioactivities of endogenously formed oAbeta/ADDLs generated in situ from the physiological processing of human amyloid precursor protein (APP) and presenitin1 (PS1) transgenes.

METHODS

We produced and histologically characterized single transgenic mice overexpressing APP(E693Q) or APP(E693Q) X PS1DeltaE9 bigenic mice. APP(E693Q) mice were studied in the Morris water maze (MWM) task at 6 and 12 months of age. Following the second MWM evaluation, mice were sacrificed, and brains were assayed for Abetatotal, Abeta40, Abeta42, and oAbeta/ADDLs by enzyme-linked immunosorbent assay (ELISA) and were also histologically examined. Based on results from the oAbeta/ADDL ELISA, we assigned individual APP(E693Q) mice to either an undetectable oAbeta/ADDLs group or a readily detectable oAbeta/ADDLs group. A days to criterion (DTC) analysis was used to determine delays in acquisition of the MWM task.

RESULTS

Both single transgenic and bigenic mice developed intraneuronal accumulation of APP/Abeta, although only APP(E693Q) X PS1Delta9 bigenic mice developed amyloid plaques. The APP(E693Q) mice did not develop amyloid plaques at any age studied, up to 30 months. APP(E693Q) mice were tested for spatial learning and memory, and only 12-month-old APP(E693Q) mice with readily detectable oAbeta/ADDLs displayed a significant delay in acquisition of the MWM task when compared to nontransgenic littermates.

INTERPRETATION

These data suggest that cerebral oAbeta/ADDL assemblies generated in brain in situ from human APP transgenes may be associated with cognitive impairment. We propose that a DTC analysis may be a sensitive method for assessing the cognitive impact in mice of endogenously generated oligomeric human Abeta assemblies. ANN NEUROL 2010.

Genetic evidence for a role for protein kinase A in the maintenance of sleep and thalamocortical oscillations

STUDY OBJECTIVES

Genetic manipulation of cAMP-dependent protein kinase A (PKA) in Drosophila has implicated an important role for PKA in sleeplwake state regulation. Here, we characterize the role of this signaling pathway in the regulation of sleep using electroencephalographic (EEG) and electromyographic (EMG) recordings in R(AB) transgenic mice that express a dominant negative form of the regulatory subunit of PKA in neurons within cortex and hippocampus. Previous studies have revealed that these mutant mice have reduced PKA activity that results in the impairment of hippocampus-dependent long-term memory and long-lasting forms of hippocampal synaptic plasticity.

DESIGN

PKA assays, in situ hybridization, immunoblots, and sleep studies were performed in R(AB) transgenic mice and wild-type control mice.

MEASUREMENTS AND RESULTS

We have found that R(AB) transgenic mice have reduced PKA activity within cortex and reduced Ser845 phosphorylation of the glutamate receptor subunit GluR1. R(AB) transgenic mice exhibit non-rapid eye movement (NREM) sleep fragmentation and increased amounts of rapid eye movement (REM) sleep relative to wild-type mice. Further, R(AB) transgenic mice have more delta power but less sigma power during NREM sleep relative to wild-type mice. After sleep deprivation, the amounts of NREM and REM sleep were comparable between wild-type and R(AB) transgenic mice. However, the homeostatic rebound of sigma power in R(AB) transgenic mice was reduced.

CONCLUSIONS

Alterations in cortical synaptic receptors, impairments in sleep continuity, and alterations in sleep oscillations in R(AB) mice imply that PKA is involved not only in synaptic plasticity and memory storage but also in the regulation of sleep/wake states.

Pathology associated memory deficits in Swedish mutant genome-based amyloid precursor protein transgenic mice

To gain insight into the relationship between pathological alterations and memory deficits observed in Alzheimer's disease (AD), a number of amyloid precursor protein (APP) transgenic animal models have been generated containing familial AD mutations. The most commonly utilized method involves a cDNA-based approach, utilizing heterologous promoters to drive expression of specific APP isoforms. As a result of the assumptions inherent in the design of each model, the different cDNA-based transgenic mouse models have revealed different relationships between the biochemical, pathological and behavioral alterations observed in these models. Here we provide further characterization of a genomic-based, amyloid precursor protein yeast artificial chromosome transgenic mouse model of AD, R1.40, that makes few assumptions regarding disease pathogenesis to study the relationship between brain pathology and altered behavior. Aged R1.40 transgenic and control mice were tested for learning and memory in the Morris water maze and for working memory in the Y maze. Results from the water maze demonstrated intact learning in the both control and R1.40 mice, but impairments in the long-term retention of this information in the transgenic mice, but not controls. Interestingly, however, long-term memory deficits did not correlate with the presence of Abeta deposits within the group of animals examined. By contrast, age-related working memory impairments were also observed in the Y maze in the R1.40 mice, and these deficits correlated with the presence of Abeta deposits. Our results demonstrate unique behavioral alterations in the R1.40 mouse model of AD that are likely both dependent and independent of Abeta deposition.

Post-training reversible inactivation of the hippocampus enhances novel object recognition memory

Research on the role of the hippocampus in object recognition memory has produced conflicting results. Previous studies have used permanent hippocampal lesions to assess the requirement for the hippocampus in the object recognition task. However, permanent hippocampal lesions may impact performance through effects on processes besides memory consolidation including acquisition, retrieval, and performance. To overcome this limitation, we used an intrahippocampal injection of the GABA agonist muscimol to reversibly inactivate the hippocampus immediately after training mice in two versions of an object recognition task. We found that the inactivation of the dorsal hippocampus after training impairs object-place recognition memory but enhances novel object recognition (NOR) memory. However, inactivation of the dorsal hippocampus after repeated exposure to the training context did not affect object recognition memory. Our findings suggest that object recognition memory formation does not require the hippocampus and, moreover, that activity in the hippocampus can interfere with the consolidation of object recognition memory when object information encoding occurs in an unfamiliar environment.

Involvement of hippocampal jun-N terminal kinase pathway in the enhancement of learning and memory by nicotine

Despite intense scrutiny over the past 20 years, the reasons for the high addictive liability of nicotine and extreme rates of relapse in smokers have remained elusive. One factor that contributes to the development and maintenance of nicotine addiction is the ability of nicotine to produce long-lasting modifications of behavior, yet little is known about the mechanisms by which nicotine alters the underlying synaptic plasticity responsible for behavioral changes. This study is the first to explore how nicotine interacts with learning to alter gene transcription, which is a process necessary for long-term memory consolidation. Transcriptional upregulation of hippocampal jun-N terminal kinase 1 (JNK1) mRNA was found in mice that learned contextual fear conditioning (FC) in the presence of nicotine, whereas neither learning alone nor nicotine administration alone exerted an effect. Furthermore, the upregulation of JNK1 was absent in beta2 nicotinic receptor subunit knockout mice, which are mice that do not show enhanced learning by nicotine. Finally, hippocampal JNK activation was increased in mice that were administered nicotine before conditioning, and the inhibition of JNK during consolidation prevented the nicotine-induced enhancement of contextual FC. These data suggest that nicotine and learning interact to alter hippocampal JNK1 gene expression and related signaling processes, thus resulting in strengthened contextual memories.

Sleep deprivation impairs cAMP signalling in the hippocampus

Millions of people regularly obtain insufficient sleep1. Given the impact of sleep deprivation on our lives, understanding the cellular and molecular pathways affected by sleep deprivation is clearly of social and clinical importance. One of the major effects of sleep deprivation on the brain is to produce memory deficits in learning paradigms that are dependent on the hippocampus2–5. In this study, we have identified a molecular mechanism by which brief sleep deprivation alters hippocampal function. Sleep deprivation selectively impaired cAMP/PKA-dependent forms of synaptic plasticity6 in the hippocampus, reduced cAMP signaling, and increased activity and protein levels of phosphodiesterase-4 (PDE4), an enzyme that degrades cAMP. Treatment with PDE inhibitors rescued the sleep deprivation-induced deficits in cAMP signaling, synaptic plasticity, and hippocampus-dependent memory. These findings demonstrate that brief sleep deprivation disrupts hippocampal function by interfering with cAMP signaling through increased PDE4 activity. Thus drugs that enhance cAMP signaling may provide a novel therapeutic approach to counteract the cognitive effects of sleep deprivation.

Chronic ketamine impairs fear conditioning and produces long-lasting reductions in auditory evoked potentials

Ketamine is an NMDA receptor antagonist with a variety of uses, ranging from recreational drug to pediatric anesthetic and chronic pain reliever. Despite its value in the clinical setting, little is known about the immediate and long-lasting effects of repeated ketamine treatment. We assessed the effects of chronic administration of a subanesthetic dose of ketamine on contextual fear conditioning, detection of pitch deviants and auditory gating. After four, but not two, weeks of daily ketamine injections, mice exhibited decreased freezing in the fear conditioning paradigm. Gating of the P80 component of auditory evoked potentials was also significantly altered by treatment condition, as ketamine caused a significant decrease in S1 amplitude. Additionally, P20 latency was significantly increased as a result of ketamine treatment. Though no interactions were found involving test week, stimulus and treatment condition, these results suggest that repeated ketamine administration impairs fear memory and has lasting effects on encoding of sensory stimuli.

Neuregulin 1 transgenic mice display reduced mismatch negativity, contextual fear conditioning and social interactions

INTRODUCTION

Neuregulin-1 (NRG1) is one of susceptibility genes for schizophrenia and plays critical roles in glutamatergic, dopaminergic and GABAergic signaling. Using mutant mice heterozygous for Nrg1 (Nrg1(+/-)) we studied the effects of Nrg1 signaling on behavioral and electrophysiological measures relevant to schizophrenia.

EXPERIMENTAL PROCEDURE

Behavior of Nrg1(+/-) mice and their wild type littermates was evaluated using pre-pulse inhibition, contextual fear conditioning, novel object recognition, locomotor, and social choice paradigms. Event-related potentials (ERPs) were recorded to assess auditory gating and novel stimulus detection.

RESULTS

Gating of ERPs was unaffected in Nrg1(+/-) mice, but mismatch negativity in response to novel stimuli was attenuated. The Nrg1(+/-) mice exhibited behavioral deficits in contextual fear conditioning and social interactions, while locomotor activity, pre-pulse inhibition and novel object recognition were not impaired.

SUMMARY

Nrg1(+/-) mice had impairments in a subset of behavioral and electrophysiological tasks relevant to the negative/cognitive symptom domains of schizophrenia that are thought to be influenced by glutamatergic and dopaminergic neurotransmission. These mice are a valuable tool for studying endophenotypes of schizophrenia, but highlight that single genes cannot account for the complex pathophysiology of the disorder.

Exchange protein activated by cAMP enhances long-term memory formation independent of protein kinase A

It is well established that cAMP signaling within neurons plays a major role in the formation of long-term memories--signaling thought to proceed through protein kinase A (PKA). However, here we show that exchange protein activated by cAMP (Epac) is able to enhance the formation of long-term memory in the hippocampus and appears to do so independent of PKA, thus demonstrating the importance of Epac-mediated signaling in memory consolidation.

Cultural capital and social inequality in health

Economic and social resources are known to contribute to the unequal distribution of health outcomes. Culture-related factors such as normative beliefs, knowledge and behaviours have also been shown to be associated with health status. The role and function of cultural resources in the unequal distribution of health is addressed. Drawing on the work of French Sociologist Pierre Bourdieu, the concept of cultural capital for its contribution to the current understanding of social inequalities in health is explored. It is suggested that class related cultural resources interact with economic and social capital in the social structuring of people's health chances and choices. It is concluded that cultural capital is a key element in the behavioural transformation of social inequality into health inequality. New directions for empirical research on the interplay between economic, social and cultural capital are outlined.

Genetic dissection of neural circuits and behavior in Mus musculus

One of the major challenges in the field of neurobiology is to elucidate the molecular machinery that underlies the formation and storage of memories. For many decades, genetic studies in the fruit fly (Drosophila melanogaster) have provided insight into the role of specific genes underlying memory storage. Although these pioneering studies were groundbreaking, a transition to a mammalian system more closely resembling the human brain is critical for the translation of basic research findings into therapeutic strategies in humans. Because the mouse (Mus musculus) shares the complex genomic and neuroanatomical organization of mammals and there is a wealth of molecular tools that are available to manipulate gene function in mice, the mouse has become the primary model for research into the genetic basis of mammalian memory. Another major advantage of mouse research is the ability to examine in vivo electrophysiological processes, such as synaptic plasticity and neuronal firing patterns during behavior (e.g., the analysis of place cell activity). The focus on mouse models for memory research has led to the development of sophisticated behavioral protocols capable of exploring the role of particular genes in distinct phases of learning and memory formation, which is one of the major accomplishments of the past decade. In this chapter, we will give an overview of several state of the art genetic approaches to study gene function in the mouse brain in a spatially and temporally restricted fashion.