Activation-induced cytidine deaminase regulates activity-dependent BDNF expression in post-mitotic cortical neurons

Activity-dependent gene expression depends, in part, on transcriptional regulation that is coordinated by rapid changes in the chromatin landscape as well as the covalent modification of DNA. Here we demonstrate that the expression of brain-derived neurotrophic factor (BDNF), a gene that is critically involved in neural plasticity and subject to epigenetic regulation, is regulated by the RNA/DNA editing enzyme, activation-induced cytidine deaminase (AID). Similar to previous reports, we observed an activity-dependent induction of BDNF exon IV mRNA expression, which correlated with a reduction in DNA methylation within the BDNF P4 promoter. Lentiviral-mediated knockdown of AID disrupted these effects and inhibited BDNF exon IV mRNA expression, an effect that was associated with decreased cAMP response element-binding protein occupancy within the BDNF P4 promoter. Thus, together with other epigenetic mechanisms, AID plays a key role in regulating activity-dependent BDNF expression in post-mitotic cortical neurons

Sex differences in learned fear expression and extinction involve altered gamma oscillations in medial prefrontal cortex

Sex differences in learned fear expression and extinction involve the medial prefrontal cortex (mPFC). We recently demonstrated that enhanced learned fear expression during auditory fear extinction and its recall is linked to persistent theta activation in the prelimbic (PL) but not infralimbic (IL) cortex of female rats. Emerging evidence indicates that gamma oscillations in mPFC are also implicated in the expression and extinction of learned fear. Therefore we re-examined our in vivo electrophysiology data and found that females showed persistent PL gamma activation during extinction and a failure of IL gamma activation during extinction recall. Altered prefrontal gamma oscillations thus accompany sex differences in learned fear expression and its extinction. These findings are relevant for understanding the neural basis of post-traumatic stress disorder, which is more prevalent in women and involves impaired extinction and mPFC dysfunction

Persistent prelimbic cortex activity contributes to enhanced learned fear expression in females

Anxiety disorders, such as post-traumatic stress, are more prevalent in women and are characterized by impaired inhibition of learned fear and medial prefrontal cortex (mPFC) dysfunction. Here we examined sex differences in fear extinction and mPFC activity in rats. Females showed more learned fear expression during extinction and its recall, but not fear conditioning. They also showed more spontaneous fear recovery and more contextual fear before extinction and its recall. Moreover, enhanced learned fear expression in females was associated with sustained prelimbic (PL) cortex activity. These results suggest that sex differences in learned fear expression may involve persistent PL activation

Paternal environmental enrichment transgenerationally alters affective behavioral and neuroendocrine phenotypes

Recent studies have demonstrated that paternal stress in rodents can result in modification of offspring behavior. Environmental enrichment, which enhances cognitive stimulation and physical activity, modifies various behaviors and reduces stress responses in adult rodents. We investigated the transgenerational influence of paternal environmental enrichment on offspring behavior and physiological stress response. Adult C57BL/6J male mice (F0) were exposed to either environmental enrichment or standard housing for four weeks and then pair-mated with naïve females. The F2 generation was generated using F1 male offspring. Male and female F1 and F2 offspring were tested for anxiety using the elevated-plus maze and large open field at 8 weeks of age. Depression-related behavior was assessed using the forced-swim test. Hypothalamic-pituitary-adrenal (HPA) axis function was determined by quantification of serum corticosterone and adrenocorticotropic hormone (ACTH) levels at baseline and after forced-swim stress. Paternal environmental enrichment was associated with increased body weights of male F1 and F2 offspring. There was no significant effect on F1 offspring anxiety and depression-related behaviors. There were no changes in anxiety-related behaviors in the F2 offspring, however these mice displayed a reduced latency to immobility in the forced-swim test. Furthermore, F2 females had significantly higher serum corticosterone levels post-stress, but not ACTH. These results show that paternal environmental enrichment exerts a sex-specific transgenerational impact on the behavioral and physiological response to stress. Our findings have implications for the modelling of psychiatric disorders in rodents

Paradoxical enhancement of fear extinction memory and synaptic plasticity by inhibition of the histone acetyltransferase p300

It is well established that the coordinated regulation of activity-dependent gene expression by the histone acetyltransferase (HAT) family of transcriptional coactivators is crucial for the formation of contextual fear and spatial memory, and for hippocampal synaptic plasticity. However, no studies have examined the role of this epigenetic mechanism within the infralimbic prefrontal cortex (ILPFC), an area of the brain that is essential for the formation and consolidation of fear extinction memory. Here we report that a postextinction training infusion of a combined p300/CBP inhibitor (Lys-CoA-Tat), directly into the ILPFC, enhances fear extinction memory in mice. Our results also demonstrate that the HAT p300 is highly expressed within pyramidal neurons of the ILPFC and that the small-molecule p300-specific inhibitor (C646) infused into the ILPFC immediately after weak extinction training enhances the consolidation of fear extinction memory. C646 infused 6 h after extinction had no effect on fear extinction memory, nor did an immediate postextinction training infusion into the prelimbic prefrontal cortex. Consistent with the behavioral findings, inhibition of p300 activity within the ILPFC facilitated long-term potentiation (LTP) under stimulation conditions that do not evoke long-lasting LTP. These data suggest that one function of p300 activity within the ILPFC is to constrain synaptic plasticity, and that a reduction in the function of this HAT is required for the formation of fear extinction memory

p300/CBP-associated factor selectively regulates the extinction of conditioned fear

It is well established that the activity of chromatin-modifying enzymes is crucial for regulating gene expression associated with hippocampal-dependent memories. However, very little is known about how these epigenetic mechanisms influence the formation of cortically dependent memory, particularly when there is competition between opposing memory traces, such as that which occurs during the acquisition and extinction of conditioned fear. Here we demonstrate, in C57BL/6mice, that the activityofp300/CBP-associated factor (PCAF) within the infralimbic prefrontal cortex is required for long-term potentiation and is necessary for the formation of memory associated with fear extinction, but not for fear acquisition. Further, systemic administration of the PCAF activator SPV106 enhances memory for fear extinction and prevents fear renewal. The selective influence of PCAF on fear extinction is mediated, in part, by a transient recruitment of the repressive transcription factor ATF4tothe promoter of the immediate early genezif268, which competitively inhibits its expression. Thus, within the context of fear extinction, PCAF functions as a transcriptional coactivator, which may facilitate the formation of memory for fear extinction by interfering with reconsolidation of the original memory trace

MicroRNA-mediated rescue of fear extinction memory by miR-144-3p in extinction-impaired mice

Background MicroRNA (miRNA)-mediated control of gene expression suggests that miRNAs are interesting targets and/or biomarkers in the treatment of anxiety- and trauma-related disorders, where often memory-associated gene expression is adversely affected. Methods The role of miRNAs in the rescue of impaired fear extinction was assessed using the 129S1/SvlmJ (S1) mouse model of impaired fear extinction. miRNA microarray analysis, reverse transcription polymerase chain reaction, fluorescent in situ hybridization, lentiviral overexpression, and Luciferase reporter assays were used to gain insight into the mechanisms underlying miRNA-mediated normalization of deficient fear extinction. Results Rescuing impaired fear extinction via dietary zinc restriction was associated with differential expression of miRNAs in the amygdala. One candidate, miR-144-3p, robustly expressed in the basolateral amygdala, showed specific extinction-induced, but not fear-induced, increased expression in both extinction-rescued S1 mice and extinction-intact C57BL/6 (BL6) mice. miR-144-3p upregulation and effects on subsequent behavioral adaption was assessed in S1 and BL6 mice. miR-144-3p overexpression in the basolateral amygdala rescued impaired fear extinction in S1 mice, led to enhanced fear extinction acquisition in BL6 mice, and furthermore protected against fear renewal in BL6 mice. miR-144-3p targets a number of genes implicated in the control of plasticity-associated signaling cascades, including Pten, Spred1, and Notch1. In functional interaction studies, we revealed that the miR-144-3p target, PTEN, colocalized with miR-144-3p in the basolateral amygdala and showed functional downregulation following successful fear extinction in S1 mice. Conclusions These findings identify a fundamental role of miR-144-3p in the rescue of impaired fear extinction and suggest this miRNA as a viable target in developing novel treatments for posttraumatic stress disorder and related disorders

Long Noncoding RNA-Directed Epigenetic Regulation of Gene Expression Is Associated With Anxiety-like Behavior in Mice

Background RNA-directed regulation of epigenetic processes has recently emerged as an important feature of mammalian differentiation and development. Perturbation of this regulatory system in the brain may contribute to the development of neuropsychiatric disorders. Methods RNA sequencing was used to identify changes in the experience-dependent expression of long noncoding RNAs (lncRNAs) within the medial prefrontal cortex of adult mice. Transcripts were validated by real-time quantitative polymerase chain reaction and a candidate lncRNA, Gomafu, was selected for further investigation. The functional role of this schizophrenia-related lncRNA was explored in vivo by antisense oligonucleotide-mediated gene knockdown in the medial prefrontal cortex, followed by behavioral training and assessment of fear-related anxiety. Long noncoding RNA-directed epigenetic regulation of gene expression was investigated by chromatin and RNA immunoprecipitation assays. Results RNA sequencing analysis revealed changes in the expression of a significant number of genes related to neural plasticity and stress, as well as the dynamic regulation of lncRNAs. In particular, we detected a significant downregulation of Gomafu lncRNA. Our results revealed that Gomafu plays a role in mediating anxiety-like behavior and suggest that this may occur through an interaction with a key member of the polycomb repressive complex 1, BMI1, which regulates the expression of the schizophrenia-related gene beta crystallin (Crybb1). We also demonstrated a novel role for Crybb1 in mediating fear-induced anxiety-like behavior. Conclusions Experience-dependent expression of lncRNAs plays an important role in the epigenetic regulation of adaptive behavior, and the perturbation of Gomafu may be related to anxiety and the development of neuropsychiatric disorders

Parental care, environmental enrichment, and hippocampal development and function in the adult rodent

This thesis examines the effect of early parental care and environmental experience on hippocampal development and cognitive function in the adult rodent. Maternal care in the rat contributes to cognitive function through effects on neural systems known to mediate certain forms of learning and memory. The offspring of mothers that exhibit a low frequency of licking/grooming (Low-LG mothers) over the first week of life show decreased hippocampal synaptogenesis and N-Methyl-D-aspartate (NMDA) receptor mRNA expression, and poor spatial learning; relative to the offspring of mothers that exhibit high levels of maternal care. The results of cross-fostering studies provide evidence for a direct relationship between maternal behaviour and hippocampal development in the offspring of Low-LG mothers (Liu et al., 1997; 2000).Indeed, peripubertal environmental enrichment reversed the effect of reduced maternal care on hippocampal-dependent learning and memory, synaptic density, and several genes encoding for glutamate receptor subunits. For example, hippocampal NR2A, NR2B, GluR1 and GluR3 mRNA expression was reversed, with the strongest effects occurring in area CA1 of the hippocampal formation. Interestingly, the effect of enrichment on GluR1 and GluR3 mRNA expression was lateralized to the right hippocampus. Environmental enrichment did not reverse the effect of reduced maternal care on NMDA receptor binding or long-term potentiation in the dentate gyrus. In every instance where reversal occurred after exposure to enrichment during adolescence, the effect was specific to the offspring of Low-LG mothers, with little or no effect on the offspring of High-LG mothers. It is suggested that an increased level of astrocyte expression in the hippocampus of Low-LG offspring at the time of weaning could account for the individual differences in sensitivity to environmental enrichment. The findings are extended with the presentation of a new model where the issue of a paternal contribution towards offspring cognitive development is addressed in the monogamous California mouse (Peromyscus californicus)

Social modulation of associative fear learning by pheromone communication

Mice communicate through visual, vocal, and olfactory cues that influence innate, nonassociative behavior. We here report that exposure to a recently fear-conditioned familiar mouse impairs acquisition of conditioned fear and facilitates fear extinction, effects mimicked by both an olfactory chemosignal emitted by a recently fear-conditioned familiar mouse and by the putative stress-related anxiogenic pheromone β-phenylethylamine (β-PEA). Together, these findings suggest social modulation of higher-order cognitive processing through pheromone communication and support the concurrent excitor hypothesis of extinction learning