DTI-identified microstructural changes in the gray matter of mice overexpressing CRF in the forebrain.

Increased corticotroping releasing factor (CRF) contributes to brain circuit abnormalities associated with stress-related disorders including posttraumatic stress disorder. However, the causal relationship between CRF hypersignaling and circuit abnormalities associated with stress disorders is unclear. We hypothesized that increased CRF exposure induces changes in limbic circuit morphology and functions. An inducible, forebrain-specific overexpression of CRF (CRFOE) transgenic mouse line was used to longitudinally investigate its chronic effects on behaviors and microstructural integrity of several brain regions. Behavioral and diffusion tensor imaging studies were performed before treatment, after 3-4 wks of treatment, and again 3 mo after treatment ended to assess recovery. CRFOE was associated with increased perseverative movements only after 3 wks of treatment, as well as reduced fractional anisotropy at 3 wks in the medial prefrontal cortex and increased fractional anisotropy in the ventral hippocampus at 3 mo compared to the control group. In the dorsal hippocampus, mean diffusivity was lower in CRFOE mice both during and after treatment ended. Our data suggest differential response and recovery patterns of cortical and hippocampal subregions in response to CRFOE. Overall these findings support a causal relationship between CRF hypersignaling and microstructural changes in brain regions relevant to stress disorders.

AP-1 controls the p11-dependent antidepressant response.

Selective serotonin reuptake inhibitors (SSRIs) are the most widely prescribed drugs for mood disorders. While the mechanism of SSRI action is still unknown, SSRIs are thought to exert therapeutic effects by elevating extracellular serotonin levels in the brain, and remodel the structural and functional alterations dysregulated during depression. To determine their precise mode of action, we tested whether such neuroadaptive processes are modulated by regulation of specific gene expression programs. Here we identify a transcriptional program regulated by activator protein-1 (AP-1) complex, formed by c-Fos and c-Jun that is selectively activated prior to the onset of the chronic SSRI response. The AP-1 transcriptional program modulates the expression of key neuronal remodeling genes, including S100a10 (p11), linking neuronal plasticity to the antidepressant response. We find that AP-1 function is required for the antidepressant effect in vivo. Furthermore, we demonstrate how neurochemical pathways of BDNF and FGF2, through the MAPK, PI3K, and JNK cascades, regulate AP-1 function to mediate the beneficial effects of the antidepressant response. Here we put forth a sequential molecular network to track the antidepressant response and provide a new avenue that could be used to accelerate or potentiate antidepressant responses by triggering neuroplasticity.

Ahnak scaffolds p11/Anxa2 complex and L-type voltage-gated calcium channel and modulates depressive behavior.

Genetic polymorphisms of the L-type voltage-gated calcium channel (VGCC) are associated with psychiatric disorders including major depressive disorder. Alterations of S100A10 (p11) level are also implicated in the etiology of major depressive disorder. However, the existence of an endogenous regulator in the brain regulating p11, L-type VGCC, and depressive behavior has not been known. Here we report that Ahnak, whose function in the brain has been obscure, stabilizes p11 and Anxa2 proteins in the hippocampus and prefrontal cortex in the rodent brain. Protein levels of Ahnak, p11, and Anxa2 are highly and positively correlated in the brain. Together these data suggest the existence of an Ahnak/p11/Anxa2 protein complex. Ahnak is expressed in p11-positive as well as p11-negative neurons. Ahnak, through its N-terminal region, scaffolds the L-type pore-forming α1 subunit and, through its C-terminal region, scaffolds the ß subunit of VGCC and the p11/Anxa2 complex. Cell surface expression of the α1 subunits and L-type calcium current are significantly reduced in primary cultures of Ahnak knockout (KO) neurons compared to wild-type controls. A decrease in the L-type calcium influx is observed in both glutamatergic neurons and parvalbumin (PV) GABAergic interneurons of Ahnak KO mice. Constitutive Ahnak KO mice or forebrain glutamatergic neuron-selective Ahnak KO mice display a depression-like behavioral phenotype similar to that of constitutive p11 KO mice. In contrast, PV interneuron-selective Ahnak KO mice display an antidepressant-like behavioral phenotype. Our results demonstrate L-type VGCC as an effector of the Ahnak/p11/Anxa2 complex, revealing a novel molecular connection involved in the control of depressive behavior.

CK1δ over-expressing mice display ADHD-like behaviors, frontostriatal neuronal abnormalities and altered expressions of ADHD-candidate genes.

The cognitive mechanisms underlying attention-deficit hyperactivity disorder (ADHD), a highly heritable disorder with an array of candidate genes and unclear genetic architecture, remain poorly understood. We previously demonstrated that mice overexpressing CK1δ (CK1δ OE) in the forebrain show hyperactivity and ADHD-like pharmacological responses to D-amphetamine. Here, we demonstrate that CK1δ OE mice exhibit impaired visual attention and a lack of D-amphetamine-induced place preference, indicating a disruption of the dopamine-dependent reward pathway. We also demonstrate the presence of abnormalities in the frontostriatal circuitry, differences in synaptic ultra-structures by electron microscopy, as well as electrophysiological perturbations of both glutamatergic and GABAergic transmission, as observed by altered frequency and amplitude of mEPSCs and mIPSCs. Furthermore, gene expression profiling by next-generation sequencing alone, or in combination with bacTRAP technology to study specifically Drd1a versus Drd2 medium spiny neurons, revealed that developmental CK1δ OE alters transcriptional homeostasis in the striatum, including specific alterations in Drd1a versus Drd2 neurons. These results led us to perform a fine molecular characterization of targeted gene networks and pathway analysis. Importantly, a large fraction of 92 genes identified by GWAS studies as associated with ADHD in humans are significantly altered in our mouse model. The multiple abnormalities described here might be responsible for synaptic alterations and lead to complex behavioral abnormalities. Collectively, CK1δ OE mice share characteristics typically associated with ADHD and should represent a valuable model to investigate the disease in vivo.

FMRP has a cell-type-specific role in CA1 pyramidal neurons to regulate autism-related transcripts and circadian memory.

Loss of the RNA binding protein FMRP causes Fragile X Syndrome (FXS), the most common cause of inherited intellectual disability, yet it is unknown how FMRP function varies across brain regions and cell types and how this contributes to disease pathophysiology. Here we use conditional tagging of FMRP and CLIP (FMRP cTag CLIP) to examine FMRP mRNA targets in hippocampal CA1 pyramidal neurons, a critical cell type for learning and memory relevant to FXS phenotypes. Integrating these data with analysis of ribosome-bound transcripts in these neurons revealed CA1-enriched binding of autism-relevant mRNAs, and CA1-specific regulation of transcripts encoding circadian proteins. This contrasted with different targets in cerebellar granule neurons, and was consistent with circadian defects in hippocampus-dependent memory in Fmr1 knockout mice. These findings demonstrate differential FMRP-dependent regulation of mRNAs across neuronal cell types that may contribute to phenotypes such as memory defects and sleep disturbance associated with FXS.

Excess Translation of Epigenetic Regulators Contributes to Fragile X Syndrome and Is Alleviated by Brd4 Inhibition.

Fragile X syndrome (FXS) is a leading genetic cause of intellectual disability and autism. FXS results from the loss of function of fragile X mental retardation protein (FMRP), which represses translation of target transcripts. Most of the well-characterized target transcripts of FMRP are synaptic proteins, yet targeting these proteins has not provided effective treatments. We examined a group of FMRP targets that encode transcriptional regulators, particularly chromatin-associated proteins. Loss of FMRP in mice results in widespread changes in chromatin regulation and aberrant gene expression. To determine if targeting epigenetic factors could reverse phenotypes associated with the disorder, we focused on Brd4, a BET protein and chromatin reader targeted by FMRP. Inhibition of Brd4 function alleviated many of the phenotypes associated with FXS. We conclude that loss of FMRP results in significant epigenetic misregulation and that targeting transcription via epigenetic regulators like Brd4 may provide new treatments for FXS.

Relevance of the COPI complex for Alzheimer's disease progression in vivo.

Cellular trafficking and recycling machineries belonging to late secretory compartments have been associated with increased Alzheimer's disease (AD) risk. We have shown that coat protein complex I (COPI)-dependent trafficking, an early step in Golgi-to-endoplasmic reticulum retrograde transport, affects amyloid precursor protein subcellular localization, cell-surface expression, as well as its metabolism. We present here a set of experiments demonstrating that, by targeting subunit δ-COP function, the moderation of the COPI-dependent trafficking in vivo leads to a significant decrease in amyloid plaques in the cortex and hippocampus of neurological 17 mice crossed with the 2xTg AD mouse model. Remarkably, an improvement of the memory impairments was also observed. Importantly, human genetic association studies of different AD cohorts led to the identification of 12 SNPs and 24 mutations located in COPI genes linked to an increased AD risk. These findings further demonstrate in vivo the importance of early trafficking steps in AD pathogenesis and open new clinical perspectives.

APP intracellular domain-WAVE1 pathway reduces amyloid-ß production.

An increase in amyloid-ß (Aß) production is a major pathogenic mechanism associated with Alzheimer's disease (AD), but little is known about possible homeostatic control of the amyloidogenic pathway. Here we report that the amyloid precursor protein (APP) intracellular domain (AICD) downregulates Wiskott-Aldrich syndrome protein (WASP)-family verprolin homologous protein 1 (WAVE1 or WASF1) as part of a negative feedback mechanism to limit Aß production. The AICD binds to the Wasf1 promoter, negatively regulates its transcription and downregulates Wasf1 mRNA and protein expression in Neuro 2a (N2a) cells. WAVE1 interacts and colocalizes with APP in the Golgi apparatus. Experimentally reducing WAVE1 in N2a cells decreased the budding of APP-containing vesicles and reduced cell-surface APP, thereby reducing the production of Aß. WAVE1 downregulation was observed in mouse models of AD. Reduction of Wasf1 gene expression dramatically reduced Aß levels and restored memory deficits in a mouse model of AD. A decrease in amounts of WASF1 mRNA was also observed in human AD brains, suggesting clinical relevance of the negative feedback circuit involved in homeostatic regulation of Aß production.

Inhibitor of the tyrosine phosphatase STEP reverses cognitive deficits in a mouse model of Alzheimer's disease.

STEP (STriatal-Enriched protein tyrosine Phosphatase) is a neuron-specific phosphatase that regulates N-methyl-D-aspartate receptor (NMDAR) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) trafficking, as well as ERK1/2, p38, Fyn, and Pyk2 activity. STEP is overactive in several neuropsychiatric and neurodegenerative disorders, including Alzheimer's disease (AD). The increase in STEP activity likely disrupts synaptic function and contributes to the cognitive deficits in AD. AD mice lacking STEP have restored levels of glutamate receptors on synaptosomal membranes and improved cognitive function, results that suggest STEP as a novel therapeutic target for AD. Here we describe the first large-scale effort to identify and characterize small-molecule STEP inhibitors. We identified the benzopentathiepin 8-(trifluoromethyl)-1,2,3,4,5-benzopentathiepin-6-amine hydrochloride (known as TC-2153) as an inhibitor of STEP with an IC50 of 24.6 nM. TC-2153 represents a novel class of PTP inhibitors based upon a cyclic polysulfide pharmacophore that forms a reversible covalent bond with the catalytic cysteine in STEP. In cell-based secondary assays, TC-2153 increased tyrosine phosphorylation of STEP substrates ERK1/2, Pyk2, and GluN2B, and exhibited no toxicity in cortical cultures. Validation and specificity experiments performed in wild-type (WT) and STEP knockout (KO) cortical cells and in vivo in WT and STEP KO mice suggest specificity of inhibitors towards STEP compared to highly homologous tyrosine phosphatases. Furthermore, TC-2153 improved cognitive function in several cognitive tasks in 6- and 12-mo-old triple transgenic AD (3xTg-AD) mice, with no change in beta amyloid and phospho-tau levels.

Forebrain-specific CRF overproduction during development is sufficient to induce enduring anxiety and startle abnormalities in adult mice.

Corticotropin releasing factor (CRF) regulates physiological and behavioral responses to stress. Trauma in early life or adulthood is associated with increased CRF in the cerebrospinal fluid and heightened anxiety. Genetic variance in CRF receptors is linked to altered risk for stress disorders. Thus, both heritable differences and environmentally induced changes in CRF neurotransmission across the lifespan may modulate anxiety traits. To test the hypothesis that CRF hypersignaling is sufficient to modify anxiety-related phenotypes (avoidance, startle, and conditioned fear), we induced transient forebrain-specific overexpression of CRF (CRFOE) in mice (1) during development to model early-life stress, (2) in adulthood to model adult-onset stress, or (3) across the entire postnatal lifespan to model heritable increases in CRF signaling. The consequences of these manipulations on CRF peptide levels and behavioral responses were examined in adulthood. We found that transient CRFOE during development decreased startle habituation and prepulse inhibition, and increased avoidance (particularly in females) recapitulating the behavioral effects of lifetime CRFOE despite lower CRF peptide levels at testing. In contrast, CRFOE limited to adulthood reduced contextual fear learning in females and increased startle reactivity in males but did not change avoidance or startle plasticity. These findings suggest that forebrain CRFOE limited to development is sufficient to induce enduring alterations in startle plasticity and anxiety, while forebrain CRFOE during adulthood results in a different phenotype profile. These findings suggest that startle circuits are particularly sensitive to forebrain CRFOE, and that the impact of CRFOE may be dependent on the time of exposure.

Inhibition of phosphodiesterase 10A has differential effects on dopamine D1 and D2 receptor modulation of sensorimotor gating.

RATIONALE: Inhibitors of phosphodiesterase 10A (PDE10A), an enzyme highly expressed in medium spiny neurons of the mammalian striatum, enhance activity in direct (dopamine D1 receptor-expressing) and indirect (D2 receptor-expressing striatal output) pathways. The ability of such agents to act to potentiate D1 receptor signaling while inhibiting D2 receptor signaling suggest that PDE10A inhibitors may have a unique antipsychotic-like behavioral profile differentiated from the D2 receptor antagonist-specific antipsychotics currently used in the treatment of schizophrenia. OBJECTIVES: To evaluate the functional consequences of PDE10A inhibitor modulation of D1 and D2 receptor pathway signaling, we compared the effects of a PDE10A inhibitor (TP-10) on D1 and D2 receptor agonist-induced disruptions in prepulse inhibition (PPI), a measure of sensorimotor gating disrupted in patients with schizophrenia. RESULTS: Our results indicate that, in rats: (1) PDE10A inhibition (TP-10, 0.32-10.0 mg/kg) has no effect on PPI disruption resulting from the mixed D1/D2 receptor agonist apomorphine (0.5 mg/kg), confirming previous report; (2) Yet, TP-10 blocked the PPI disruption induced by the D2 receptor agonist quinpirole (0.5 mg/kg); and attenuated apomorphine-induced disruptions in PPI in the presence of the D1 receptor antagonist SCH23390 (0.005 mg/kg). CONCLUSIONS: These findings indicate that TP-10 cannot block dopamine agonist-induced deficits in PPI in the presence of D1 activation and suggest that the effect of PDE10A inhibition on D1 signaling may be counterproductive in some models of antipsychotic activity. These findings, and the contribution of TP-10 effects in the direct pathway on sensorimotor gating in particular, may have implications for the potential antipsychotic efficacy of PDE10A inhibitors.

Impaired conditioned fear response and startle reactivity in epinephrine-deficient mice.

Norepinephrine and epinephrine signaling is thought to facilitate cognitive processes related to emotional events and heightened arousal; however, the specific role of epinephrine in these processes is less known. To investigate the selective impact of epinephrine on arousal and fear-related memory retrieval, mice unable to synthesize epinephrine (phenylethanolamine N-methyltransferase knockout, PNMT-KO) were tested for contextual and cued-fear conditioning. To assess the role of epinephrine in other cognitive and arousal-based behaviors these mice were also tested for acoustic startle, prepulse inhibition, novel object recognition, and open-field activity. Our results show that compared with wild-type mice, PNMT-KO mice showed reduced contextual fear but normal cued fear. Mice exhibited normal memory performance in the short-term version of the novel object recognition task, suggesting that PNMT mice exhibit more selective memory effects on highly emotional and/or long-term memories. Similarly, open-field activity was unaffected by epinephrine deficiency, suggesting that differences in freezing are not related to changes in overall anxiety or exploratory drive. Startle reactivity to acoustic pulses was reduced in PNMT-KO mice, whereas prepulse inhibition was increased. These findings provide further evidence for a selective role of epinephrine in contextual-fear learning and support its potential role in acoustic startle.

Hippocampal dysfunction effects on context memory: possible etiology for posttraumatic stress disorder.

Hippocampal volume reductions and functional impairments are reliable findings in posttraumatic stress disorder (PTSD) imaging studies. However, it is not clear if and how hippocampal dysfunction contributes to the etiology and maintenance of PTSD. Individuals with PTSD are often described as showing fear responses to trauma reminders outside of contexts in which these cues would reasonably predict danger. Animal studies suggest that the hippocampus is required to form and recall associations between contextual stimuli and aversive events. For example, the hippocampus is critical for encoding memories in which a complex configuration of multiple cues is associated with the aversive event. Conversely, the hippocampus is not required for associations with discrete cues. In animal studies, if configural memory is disrupted, learning strategies using discrete cue associations predominate. These data suggest poor hippocampal function could bias the organism toward forming multiple simple cue associations during trauma, thus increasing the chances of fear responses in multiple environments (or contexts) in which these cues may be present. Here we will examine clinical and preclinical literature to support a theory of hippocampal dysfunction as a primary contributory factor to the etiology of PTSD, and discuss future research required to test these hypotheses. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

Factor analysis of attentional set-shifting performance in young and aged mice.

BACKGROUND: Executive dysfunction may play a major role in cognitive decline with aging because frontal lobe structures are particularly vulnerable to advancing age. Lesion studies in rats and mice have suggested that intradimensional shifts (IDSs), extradimensional shifts (EDSs), and reversal learning are mediated by the anterior cingulate cortex, the medial prefrontal cortex, and the orbitofrontal cortex, respectively. We hypothesized that the latent structure of cognitive performance would reflect functional localization in the brain and would be altered by aging. METHODS: Young (4 months, n = 16) and aged (23 months, n = 18) C57BL/6N mice performed an attentional set-shifting task (ASST) that evaluates simple discrimination (SD), compound discrimination (CD), IDS, EDS, and reversal learning. The performance data were subjected to an exploratory factor analysis to extract the latent structures of ASST performance in young and aged mice. RESULTS: The factor analysis extracted two- and three-factor models. In the two-factor model, the factor associated with SD and CD was clearly separated from the factor associated with the rest of the ASST stages in the young mice only. In the three-factor model, the SD and CD loaded on distinct factors. The three-factor model also showed a separation of factors associated with IDS, EDS, and CD reversal. However, the other reversal learning variables, ID reversal and ED reversal, had somewhat inconsistent factor loadings. CONCLUSIONS: The separation of performance factors in aged mice was less clear than in young mice, which suggests that aged mice utilize neuronal networks more broadly for specific cognitive functions. The result that the factors associated with SD and CD were separated in the three-factor model may suggest that the introduction of an irrelevant or distracting dimension results in the use of a new/orthogonal strategy for better discrimination.

Corticotropin-releasing factor and noradrenergic signalling exert reciprocal control over startle reactivity.

Corticotropin-releasing factor (CRF) and norepinephrine (NE) levels are altered in post-traumatic stress disorder and may be related to symptoms of hyperarousal, including exaggerated startle, in these patients. In animals, activation of both systems modulates anxiety behaviours including startle plasticity; however, it is unknown if they exert their actions orthogonally or dependently. We tested the hypothesis that NE receptor activation is required for CRF effects on startle and that CRF1 receptor activation is required for NE effects on startle. The study examined the effects of: (1) α2 agonist clonidine (0.18 mg/kg i.p.), α1 antagonist prazosin (0.8 mg/kg), and ß1/2 antagonist propranolol (0.8, 8.0 mg/kg) pretreatment on ovine-CRF (oCRF)- (0.6 nmol) induced increases in startle reactivity and disruption of prepulse inhibition (PPI); (2) α2 antagonist atipamezole (1-30 mg/kg) and α1 agonist cirazoline (0.025-1.0 mg/kg) treatment on startle; (3) CRF1 antagonist (antalarmin, 14 mg/kg) pretreatment on atipamezole- (10.0 mg/kg) induced increases in startle. oCRF robustly increased startle and reduced PPI. Pretreatment with clonidine or prazosin, but not propranolol, blocked oCRF-induced increases in startle but had no effect on oCRF-induced disruptions in PPI. Atipamezole treatment increased startle, which was partially attenuated by CRF1 antagonist pretreatment. Cirazoline treatment did not increase startle. These findings suggest that CRF modulation of startle, but not PPI, requires activation of α1 adrenergic receptors, while CRF1 activation also contributes to NE modulation of startle. These data support a bi-directional model of CRF-NE modulation of stress responses and suggest that both systems must be activated to induce stress effects on startle reactivity.

Initial evidence linking synaptic superoxide production with poor short-term memory in aged mice.

Unregulated production of reactive oxygen species (ROS) is a marker of cellular and organismal aging linked to cognitive decline in humans and rodents. The sources of elevated ROS contributing to cognitive decline are unknown. Because NADPH oxidase (Nox) inhibition may prevent memory decline with age, we hypothesized that Nox and not mitochondrial sources of synaptic ROS production are linked to individual variance in cognitive performance in aged mice. Young (8 months) and aged (26 months) mice were tested in the novel object recognition task (NORT). Mitochondrial and Nox ROS production was assayed in isolated synaptosomes using spin trapping electron paramagnetic resonance (EPR) spectroscopy. Aged mice exhibited variance in NORT performance, with some performing similar to young mice while others exhibited poorer short-term memory. EPR studies indicated that Nox rather than mitochondria was the major ROS source at the synapse, and Nox-induced but not mitochondrial-induced ROS levels correlated with NORT performance in aged mice. Our findings support the hypothesis that variance in Nox-specific synaptic ROS production may predict short-term memory deficits with age.

CRF2 null mutation increases sensitivity to isolation rearing effects on locomotor activity in mice.

BACKGROUND: Developmental stressors are consistently reported to increase risk for certain neuropsychiatric disorders including schizophrenia, depression, and post-traumatic stress disorder. Recent clinical evidence supports a "double-hit" hypothesis of genetic vulnerability interacting with developmental challenges to modulate this risk. Early life stressor effects on behavior may be modulated in part by alterations in corticotropin releasing factor (CRF) signaling via two known receptors, CRF(1) and CRF(2). One extant hypothesis is that CRF(2) activation may modulate long-term adaptive responses after homeostatic challenge. As such, loss of CRF(2) activity via genetic variance may increase sensitivity to the long-term effects of developmental stress. METHODS: We tested the hypothesis that CRF(2) function may mitigate the behavioral effects of isolation rearing, predicting that loss of CRF(2) function increases sensitivity to this developmental challenge. Using the behavioral pattern monitor (BPM), we examined exploratory behavior and locomotor patterns in adult CRF(2) wild-type (WT) and gene knockout (KO) mice reared socially or in isolation. RESULTS: Isolation housing produced robust increases in the amount of locomotor activity and investigatory holepoking, and altered the temporal distribution of activity in CRF(2) KO but not CRF(2) WT mice. Isolation housing significantly increased rearing behavior and altered spatial patterns of locomotor activity regardless of genotype. CONCLUSIONS: Loss of CRF(2) function increased sensitivity to the effects of chronic social isolation on exploratory locomotor behavior. Thus, CRF(2) activation appears to mitigate isolation rearing effects on exploratory behavior. Further research assessing the interaction between CRF(2) function and developmental challenges is warranted.

Isolation rearing-induced deficits in contextual fear learning do not require CRF(2) receptors.

Post-weaning social isolation of rodents is used to model developmental stressors linked to neuropsychiatric disorders including schizophrenia as well as anxiety and mood disorders. Isolation rearing produces alterations in emotional memory and hippocampal neuropathology. Corticotropin releasing factor (CRF) signaling has recently been shown to be involved in behavioral effects of isolation rearing. Activation of the CRF(2) receptor is linked to stress-induced alterations in fear learning and may also be involved in long-term adaptation to stress. Here we tested the hypothesis that CRF(2) contributes to isolation rearing effects on emotional memory. At weaning, mice were housed either in groups of three or individually in standard mouse cages. In adulthood, isolation-reared mice exhibited significant reductions in context-specific, but not cue-specific, freezing. Isolation-reared mice exhibited no significant changes in locomotor exploration during brief exposure to a novel environment, suggesting that the reduced freezing in response to context cues was not due to activity confounds. Isolation rearing also disrupted context fear memory in mice with a CRF(2) gene null mutation, indicating that the CRF(2) receptor is not required for isolation effects on fear memory. Thus, isolation rearing disrupts hippocampal-dependent fear learning as indicated by consistent reductions in context-conditioned freezing in two separate cohorts of mice, and these effects are via a CRF(2)-independent mechanism. These findings may be clinically relevant because they suggest that isolation rearing in mice may be a useful model of developmental perturbations linked to disruptions in emotional memory in a variety of neuropsychiatric disorders.

Estradiol-induced enhancement of object memory consolidation involves hippocampal extracellular signal-regulated kinase activation and membrane-bound estrogen receptors.

The extracellular signal-regulated kinase (ERK) pathway is critical for various forms of learning and memory, and is activated by the potent estrogen 17beta-estradiol (E(2)). Here, we asked whether E(2) modulates memory via ERK activation and putative membrane-bound estrogen receptors (ERs). Using ovariectomized mice, we first demonstrate that intraperitoneal injection of 0.2 mg/kg E(2) significantly increases dorsal hippocampal levels of phosphorylated ERK protein 1 h after injection. Second, we show that E(2) administered intraperitoneally (0.2 mg/kg) or via intrahippocampal infusion (5.0 microg/side) immediately after training in an object recognition task significantly enhances memory retention, and that the beneficial effect of intraperitoneal E(2) is blocked by dorsal hippocampal inhibition of ERK activation. Third, using bovine serum albumin-conjugated 17beta-estradiol (BSA-E(2)), we demonstrate that E(2) binding at membrane-bound ERs can increase dorsal hippocampal ERK activation and enhance object memory consolidation in an ERK-dependent manner. Fourth, we show that this effect is independent of nuclear ERs, but is dependent on the dorsal hippocampus. By demonstrating that E(2) enhances memory consolidation via dorsal hippocampal ERK activation, this study is the first to identify a specific molecular pathway by which E(2) modulates memory and to demonstrate a novel role for membrane-bound ERs in mediating E(2)-induced improvements in hippocampal memory consolidation.

Life-long environmental enrichment differentially affects the mnemonic response to estrogen in young, middle-aged, and aged female mice.

The present study was designed to examine whether life-long exposure to standard or enriched housing affects the ability of estrogen to improve spatial and object memory throughout the lifespan. Three-week-old female mice were maintained in standard or enriched housing up to and through ovariectomy and behavioral testing at 5, 17, or 22 months of age. Spatial memory was tested in the Morris water maze and object memory was tested using an object recognition task. Immediately after training each day, mice were injected intraperitoneally with vehicle or 0.2 mg/kg 17beta-estradiol. Among young females, object recognition was enhanced by estradiol alone, an effect that was reduced by enrichment. In contrast, spatial water maze performance was impaired by estradiol alone, but improved by the combination of both estradiol and enrichment. At middle-age, object recognition was enhanced by estradiol or enrichment alone, and the combination of both treatments. Spatial memory in the water maze was also improved by both treatments at middle-age, but the beneficial effects of estradiol were limited to standard-housed females. Finally, whereas enrichment in aged females significantly enhanced performance in both tasks, estradiol had no effect at this age in either task. In total, the data indicate that life-long enrichment can significantly alter the extent to which estradiol affects memory in mice throughout the lifespan. Importantly, the interaction between these treatments is highly dependent on age and type of memory tested.