Extinction of conditioned fear is an important model both of inhibitory learning and of behavior therapy for human anxiety disorders. Like other forms of learning, extinction learning is long-lasting and depends on regulated gene expression. Epigenetic mechanisms make an important contribution to persistent changes in gene expression; therefore, in these studies, we have investigated whether epigenetic regulation of gene expression contributes to fear extinction. Since brain-derived neurotrophic factor (BDNF) is crucial for synaptic plasticity and for the maintenance of long-term memory, we examined histone modifications around two BDNF gene promoters after extinction of cued fear, as potential targets of learning-induced epigenetic regulation of gene expression. Valproic acid (VPA), used for some time as an anticonvulsant and a mood stabilizer, modulates the expression of BDNF, and is a histone deacetylase (HDAC) inhibitor. Here, we report that extinction of conditioned fear is accompanied by a significant increase in histone H4 acetylation around the BDNF P4 gene promoter and increases in BDNF exon I and IV mRNA expression in prefrontal cortex, that VPA enhances long-term memory for extinction because of its HDAC inhibitor effects, and that VPA potentiates the effect of weak extinction training on histone H4 acetylation around both the BDNF P1 and P4 gene promoters and on BDNF exon IV mRNA expression. These results suggest a relationship between histone H4 modification, epigenetic regulation of BDNF gene expression, and long-term memory for extinction of conditioned fear. In addition, they suggest that HDAC inhibitors may become a useful pharmacological adjunct to psychotherapy for human anxiety disorders.Substantial evidence indicates that extinction of conditioned fear, the reduction in responding to a feared cue when the cue is repeatedly presented without any adverse consequence, is new learning that inhibits the expression of a conditioned association rather than erasing it. For example, conditioned fear shows "spontaneous recovery" after the passage of time (Baum 1988), "reinstatement" after presentations of the unconditioned stimulus (US) alone (Rescorla and Heth 1975), and "renewal" when the feared cue is presented in a context different from that of extinction training (Bouton and King 1983). Efforts to understand the mechanisms of this form of learning have increased recently, particularly since it is an important model of anxiety disorder treatment.Many forms of learning, including extinction, are dependent on changes in gene expression ( . Dynamic changes in chromatin structure make an important contribution to the regulation of tissue-specific gene expression. In particular, histone acetylation/deacetylation and dimethylation of specific lysine residues on nucleosomal histone proteins (i.e., H3-K9) and DNA methylation of CpG dinucleotides within promoter regions are ways that chromatin remodeling can influence ongoing transcription and synaptic plasticity (Martinowich et al. 2003;Levenson et al. 2...

Schizophrenia (SZ) is a complex disease characterized by impaired neuronal functioning. Although defective alternative splicing has been linked to SZ, the molecular mechanisms responsible are unknown. Additionally, there is limited understanding of the early transcriptomic responses to neuronal activation. Here, we profile these transcriptomic responses and show that long non-coding RNAs (lncRNAs) are dynamically regulated by neuronal activation, including acute downregulation of the lncRNA Gomafu, previously implicated in brain and retinal development. Moreover, we demonstrate that Gomafu binds directly to the splicing factors QKI and SRSF1 (serine/arginine-rich splicing factor 1) and dysregulation of Gomafu leads to alternative splicing patterns that resemble those observed in SZ for the archetypal SZ-associated genes DISC1 and ERBB4. Finally, we show that Gomafu is downregulated in post-mortem cortical gray matter from the superior temporal gyrus in SZ. These results functionally link activity-regulated lncRNAs and alternative splicing in neuronal function and suggest that their dysregulation may contribute to neurological disorders.

Early life experiences shape an individual's physical and mental health across the lifespan. Not surprisingly, an upbringing that is associated with adversity can produce detrimental effects on health. A central theme that arises from studies in human and nonhuman species is that the effects of adversity are mediated by the interactions between a mother and her young. In this review we describe some of the long-term effects of maternal care on the offspring and we focus on the impact of naturally occurring variations in the behavior of female rats. Of particular interest are mothers that engage in high or low amounts of licking/grooming (LG) and arched-back nursing (ABN) of their pups, but do so within the normal range for this species. Such variations in LG-ABN can alter the function of the hypothalamic-pituitary-adrenal (HPA) axis, and cognitive and emotional development by directly affecting the underlying neural mechanisms. At the heart of these mechanisms is gene expression. By studying the hippocampal glucocorticoid receptor gene, we have identified that maternal care regulates its expression by changing two processes: the acetylation of histones H3-K9, and the methylation of the NGFI-A consensus sequence on the exon 1(7) promoter. Sustained "maternal effects" appear elsewhere in biology, including plants, insects, and lizards, and may have evolved to program advantages in the environments that the offspring will likely face as adults. Given the importance of early life and parent-child interactions to later behavior, prevention and intervention programs should target this critical phase of development.

Histone modifications contribute to the epigenetic regulation of gene expression, a process now recognized to be important for the consolidation of long-term memory. Valproic acid (VPA), used for many years as an anticonvulsant and a mood stabilizer, has effects on learning and memory and enhances the extinction of conditioned fear through its function as a histone deacetylase inhibitor (HDAC). Here we report that VPA enhances long-term memory for both acquisition and extinction of cued-fear. Interestingly, VPA enhances extinction, but also enhances renewal of the original conditioned fear when tested in a within-subjects design. This effect appears to be related to a reconsolidation-like process since a single CS reminder in the presence of VPA can enhance long-term memory for the original fear in the context in which fear conditioning takes place. We also show that by modifying the intertrial interval during extinction training, VPA can strengthen reconsolidation of the original fear memory or enhance long-term memory for extinction such that it becomes independent of context. These findings have important implications for the use of HDAC inhibitors as adjuncts to behavior therapy in the treatment of phobia and related anxiety disorders.Histone modification is a fundamental mechanism involved in epigenetic regulation of gene regulation, now recognized to contribute toward the consolidation of long-term memory. Histone modifications are mediated by direct enzymatic interactions with lysine residues on chromatin, and cause dynamic changes in chromatin structure that make an important contribution to the regulation of learning-induced gene expression (Levenson et al. 2004;Bredy et al. 2007). Among the superfamily of mammalian histone-modifying enzymes, prototypical compounds such as trichostatin (TSA), sodium valproate (VPA), and sodium butyrate (NaBt), which inhibit histone deacetylase (HDAC), have been shown to enhance long-term memory (Levenson et al. 2004;Yeh et al. 2004;Wood et al. 2006;Bredy et al. 2007;Lattal et al. 2007;Vecsey et al. 2007). The ability of HDAC inhibitors to modulate behavior makes them potential therapeutic targets for treating cognitive disorders, particularly disorders of fear-related learning including phobias and post-traumatic stress disorder (PTSD).The extinction of conditioned fear, the reduction in responding to a feared cue when the cue is repeatedly presented without any adverse consequence, is new learning that inhibits the expression of a conditioned association rather than erasing it. For example, conditioned fear shows "spontaneous recovery" after the passage of time (Baum 1988), "reinstatement" after presentations of the unconditioned stimulus (US) alone (Rescorla and Heth 1975), and "renewal" when the feared cue is presented in a context different from that of extinction training (Bouton and King 1983). Another important learning-related phenomenon is reconsolidation, in which memories become labile and sensitive to modification upon retrieval until restabilized over time ...

The RNA modification N 6 -methyladenosine (m 6 A) influences mRNA stability and cell-type-specific developmental programming, and is highly abundant in the adult brain. However, it has not been determined whether m 6 A is dynamically regulated by experience.

Fear conditioning and fear extinction are Pavlovian conditioning paradigms extensively used to study the mechanisms that underlie learning and memory formation. The neural circuits that mediate this learning are evolutionarily conserved, and seen in virtually all species from flies to humans. In mammals, the amygdala and medial prefrontal cortex are two structures that play a key role in the acquisition, consolidation and retrieval of fear memory, as well extinction of fear. These two regions have extensive bidirectional connections, and in recent years, the neural circuits that mediate fear learning and fear extinction are beginning to be elucidated. In this review, we provide an overview of our current understanding of the neural architecture within the amygdala and medial prefrontal cortex. We describe how sensory information is processed in these two structures and the neural circuits between them thought to mediate different aspects of fear learning. Finally, we discuss how changes in circuits within these structures may mediate fear responses following fear conditioning and extinction. Fear is an evolutionarily conserved behavioural response that is essential for survival. Studies of fear have used the paradigm of classical fear conditioning in which an emotionally neutral stimulus, the conditioned stimulus (CS), such as a light or tone, is temporally paired with an aversive stimulus, the unconditioned stimulus (US), typically a footshock. Following a small number of pairings, subjects form an association between the CS and US, and learn to respond to the CS with an avoidance response, the conditioned response (CR), which is rapidly acquired and long lasting. However, subsequent presentations of the CS that are not paired with the US Roger Marek (left), Cornelia Strobel, Tim Bredy and Pankaj Sah (right) all work at the Queensland Brain Institute in Brisbane, Australia. RM and CS have both just completed their PhD and TB and PS are group leaders in the institute. They share an interest in the mechanisms that underlie learning and memory formation in fear conditioning and extinction. Between the two labs they use a combination of electrophysiology, molecular and behavioural analysis. Their areas of interest are varied and this review comes from their common their interests in the roles of the prefrontal cortex and amygdala. break this association, and lead to a gradual reduction of the CR through a process known as extinction. Since the first studies of Pavlov, it has been appreciated that extinction does not result from erasure of previous memory associated with the CS but is due, at least in part, to new learning (Pavlov, 1927). This idea rests on three key observations. First, the learnt fear response to the CS can reappear with the passage of time (spontaneous recovery). Secondly, the CR returns when the CS is presented in a context different from the one in which extinction training originally took place (renewal). Finally, unexpected delivery of the US following extinction can

5-hydroxymethylcytosine (5-hmC) is a novel DNA modification that is highly enriched in the adult brain and dynamically regulated by neural activity. 5-hmC accumulates across the lifespan; however, the functional relevance of this change in 5-hmC and whether it is necessary for behavioral adaptation have not been fully elucidated. Moreover, although the ten-eleven translocation (Tet) family of enzymes is known to be essential for converting methylated DNA to 5-hmC, the role of individual Tet proteins in the adult cortex remains unclear. Using 5-hmC capture together with high-throughput DNA sequencing on individual mice, we show that fear extinction, an important form of reversal learning, leads to a dramatic genome-wide redistribution of 5-hmC within the infralimbic prefrontal cortex. Moreover, extinction learning-induced Tet3-mediated accumulation of 5-hmC is associated with the establishment of epigenetic states that promote gene expression and rapid behavioral adaptation.E pigenetic mechanisms are critically involved in the regulation of gene expression underlying learning and memory (1). Dynamic variation in the accumulation of a particular epigenetic mark, 5-methycytosine (5-mC), has emerged as a key factor in experience-dependent plasticity and the formation of fearrelated memory (2). However, 5-mC is not the only covalent modification of DNA in eukaryotes, as methylated cytosine guanine (CpG) dinucleotides can be successively oxidized and converted to 5-hydroxymethylcytosine (5-hmC), 5-formylcytosine (5-fC), and 5-carboxylcytosine by the Tet family of DNA dioxygenases (3, 4). Although little is known about the functional relevance of 5-fC and 5-carboxylcytosine (5, 6), an understanding of 5-hmC is starting to emerge. 5-hmC is highly enriched in the adult brain (7), dynamically regulated by neural activity (8), and accumulates across the lifespan (9). This epigenetic mark is critically involved in neuronal differentiation and in the reprogramming of pluripotent stem cells (10), and rather than being an intermediate state of active DNA demethylation, 5-hmC can be either dynamic or stable (8, 10). Unlike its repressive cousin, 5-mC, which is primarily found along CpG-rich gene promoters, 5-hmC is enriched within gene bodies and at intronexon boundaries of synaptic plasticity-related genes, as well as within distal cis-regulatory elements, which together point to an important role for 5-hmC in coordinating transcriptional activity (11-13). Thus, it is evident that the relationship between this particular covalent modification of DNA and gene expression is far more complex than currently realized.The inhibition of learned fear is an evolutionarily conserved behavioral adaptation that is essential for survival. This learning process, known as extinction, involves rapid reversal of previously learned contingencies, which depend on gene expression and protein synthesis. Impairments in the neural mechanisms that promote this beneficial response to threat can lead to the development of posttraumatic stress disorder ...

Recent studies have suggested that physiological and behavioral traits may be transgenerationally inherited through the paternal lineage, possibly via non-genomic signals derived from the sperm. To investigate how paternal stress might influence offspring behavioral phenotypes, a model of hypothalamic–pituitary–adrenal (HPA) axis dysregulation was used. Male breeders were administered water supplemented with corticosterone (CORT) for 4 weeks before mating with untreated female mice. Female, but not male, F1 offspring of CORT-treated fathers displayed altered fear extinction at 2 weeks of age. Only male F1 offspring exhibited altered patterns of ultrasonic vocalization at postnatal day 3 and, as adults, showed decreased time in open on the elevated-plus maze and time in light on the light–dark apparatus, suggesting a hyperanxiety-like behavioral phenotype due to paternal CORT treatment. Interestingly, expression of the paternally imprinted gene Igf2 was increased in the hippocampus of F1 male offspring but downregulated in female offspring. Male and female F2 offspring displayed increased time spent in the open arm of the elevated-plus maze, suggesting lower levels of anxiety compared with control animals. Only male F2 offspring showed increased immobility time on the forced-swim test and increased latency to feed on the novelty-supressed feeding test, suggesting a depression-like phenotype in these animals. Collectively, these data provide evidence that paternal CORT treatment alters anxiety and depression-related behaviors across multiple generations. Analysis of the small RNA profile in sperm from CORT-treated males revealed marked effects on the expression of small noncoding RNAs. Sperm from CORT-treated males contained elevated levels of three microRNAs, miR-98, miR-144 and miR-190b, which are predicted to interact with multiple growth factors, including Igf2 and Bdnf. Sustained elevation of glucocorticoids is therefore involved in the transmission of paternal stress-induced traits across generations in a process involving small noncoding RNA signals transmitted by the male germline.