Altered synaptic plasticity and behavioral abnormalities in CNGA3‐deficient mice

The role of the cyclic nucleotide‐gated (CNG) channel CNGA3 is well established in cone photoreceptors and guanylyl cyclase‐D‐expressing olfactory neurons. To assess a potential function of CNGA3 in the mouse amygdala and hippocampus, we examined synaptic plasticity and performed a comparative analysis of spatial learning, fear conditioning and step‐down avoidance in wild‐type mice and CNGA3 null mutants (CNGA3^?/?). CNGA3^?/? mice showed normal basal synaptic transmission in the amygdala and the hippocampus. However, cornu Ammonis (CA1) hippocampal long‐term potentiation (LTP) induced by a strong tetanus was significantly enhanced in CNGA3^?/? mice as compared with their wild‐type littermates. Unlike in the hippocampus, LTP was not significantly altered in the amygdala of CNGA3^?/? mice. Enhanced hippocampal LTP did not coincide with changes in hippocampus‐dependent learning, as both wild‐type and mutant mice showed a similar performance in water maze tasks and contextual fear conditioning, except for a trend toward higher step‐down latencies in a passive avoidance task. In contrast, CNGA3^?/? mice showed markedly reduced freezing to the conditioned tone in the amygdala‐dependent cued fear conditioning task. In conclusion, our study adds a new entry on the list of physiological functions of the CNGA3 channel. Despite the dissociation between physiological and behavioral parameters, our data describe a so far unrecognized role of CNGA3 in modulation of hippocampal plasticity and amydgala‐dependent fear memory.     

Human fear acquisition deficits in relation to genetic variants of the corticotropin‐releasing hormone receptor 1 and the serotonin transporter — revisited

We recently showed that a genetic polymorphism (rs878886) in the human corticotropin‐releasing hormone receptor 1 (CRHR1) is associated with reduced fear‐conditioned responses to a threat cue. This is a potentially important finding considering that the failure to acquire fear contingencies can leave an individual in a maladaptive state of more generalized anxiety. Consistent with that idea, the CRHR1‐dependent fear acquisition deficit translated into heightened contextual anxiety when taking genetic variability within the serotonin transporter long polymorphic region (5‐HTTLPR) into account. To replicate our previous findings, we conducted a replication study in 224 healthy medication‐free human subjects using the exact same cue and context virtual reality fear‐conditioning procedure as in study by Heitland et al. (2013). In the replication study, consistent with the original findings, CRHR1 rs878886 G‐allele carriers showed reduced acquisition of cue‐specific fear‐conditioned responses compared with C/C homozygotes. Also, in this larger sample the cue acquisition deficit of G‐allele carriers translated into heightened contextual anxiety, even independent of 5‐HTT gene variation. In contrast to our earlier findings, there was an additional interaction effect of CRHR1 rs878886 and the triallelic 5‐HTTLPR/rs25531 variant on cued fear acquisition. In summary, this study replicated the initially reported association of the CRHR1 rs878886 G‐allele with cued fear acquisition deficits, albeit with a different pattern of results regarding the interaction with 5‐HTT variation. This further supports the notion that the human corticotropin‐releasing hormone plays a role in the acquisition of fears.     

Localization and behaviors in null mice suggest that ASIC1 and ASIC2 modulate responses to aversive stimuli

Acid‐sensing ion channels (ASICs) generate H⁺‐gated Na⁺ currents that contribute to neuronal function and animal behavior. Like ASIC1, ASIC2 subunits are expressed in the brain and multimerize with ASIC1 to influence acid‐evoked currents and facilitate ASIC1 localization to dendritic spines. To better understand how ASIC2 contributes to brain function, we localized the protein and tested the behavioral consequences of ASIC2 gene disruption. For comparison, we also localized ASIC1 and studied ASIC1^?/? mice. ASIC2 was prominently expressed in areas of high synaptic density, and with a few exceptions, ASIC1 and ASIC2 localization exhibited substantial overlap. Loss of ASIC1 or ASIC2 decreased freezing behavior in contextual and auditory cue fear conditioning assays, in response to predator odor and in response to CO₂ inhalation. In addition, loss of ASIC1 or ASIC2 increased activity in a forced swim assay. These data suggest that ASIC2, like ASIC1, plays a key role in determining the defensive response to aversive stimuli. They also raise the question of whether gene variations in both ASIC1 and ASIC2 might affect fear and panic in humans .     

Different attentional dysfunctions in eEF2K−/−, IL1RAPL1−/− and SHANK3Δ11−/− mice

A common feature of several psychiatric disorders is the attentional impairment. eEF2K ^?/?, IL1RAPL1 ^?/? and SHANK3Δ11 ^?/? mice were used as animal models consistently linked to changes in synaptic plasticity, learning and memory. All knockout (KO) mice and their corresponding littermates were submitted to the novel object recognition (NOR) and visual object recognition (VOR) tasks. In the NOR, eEF2K^?/? mice exhibited a normal performance in terms of mean discrimination index, while SHANK3Δ11^?/? and IL1RAPL1 ^?/? mice were impaired when a delay of 2 and 24 hours was introduced. Surprisingly, when submitted to VOR, where the two objects were replaced with two shapes delivered from two iPods, all the mutant mice performed worse than those in the NOR. In VOR, the application of motion to different shapes, to increase attention, improved performance in eEF2K ^?/? and IL1RAPL1 ^?/? but not in SHANK3Δ11 ^?/? mice. In SHANK3Δ11 ^?/? mice, attentional deficit was also present even if different motions were applied to the same shapes or when these mice were repeatedly exposed for 5 days to the context. Behavioral analysis showed that eEF2K^?/? and IL1RAPL1 ^?/? mice had a good flexibility tested in the T‐maze. eEF2K^?/? showed normal self‐grooming. On the basis of previous literature data indicating that SHANK3Δ11 ^?/? showed impaired flexibility and reduced sociability, we identified in this genotype the most exhaustive model showing all the core symptoms of autism spectrum disorder including a heavy visual attention deficit. These findings show the importance of VOR to identify mouse models of autism.     

Neuropeptide‐S‐receptor deficiency affects sex‐specific modulation of safety learning by pre‐exposure to electric stimuli

Neuropeptide S (NPS) is a neuropeptide involved in the regulation of fear. Because safety learning is impaired in patients suffering from anxiety‐related psychiatric disorders, and polymorphisms of the human neuropeptide S receptor (NPSR) gene have also been associated with anxiety disorders, we wanted to investigate whether NPSR‐deficiency interferes with safety learning, and how prior stress would affect this type of learning. We first investigated the effect of pre‐exposure to two different types of stressors (electric stimuli or immobilization) on safety learning in female and male C57Bl/6 mice, and found that while stress induced by electric stimuli enhanced safety learning in males, there were no differences in safety learning following immobilization stress. To further investigate the role of the NPS system in stress‐induced modulation of safety learning, we exposed NPSR‐deficient mice to stress induced by electric stimuli 10 days before safety learning. In nonstressed male mice, NPSR‐deficiency enhanced safety learning. As in male C57Bl/6 mice, pre‐exposure to electric stimuli increased safety learning in male NPSR +/+ mice. This pre‐exposure effect was blocked in NPSR‐deficient male mice showing impaired, but still intact, safety learning in comparison to their NPSR +/+ and NPSR +/? littermates. There was neither a pre‐exposure nor a genotype effect in female mice. Our findings provide evidence that pre‐exposure to stress induced by electric stimuli enhances safety learning in male mice, and that NPSR‐deficiency prevents the beneficial effect of stress exposure on safety learning. We propose an inverted U‐shape relationship between stress and safety learning.     

Vesicular monoamine transporter 2 mediates fear behavior in mice

A subset of people exposed to a traumatic event develops post‐traumatic stress disorder (PTSD), which is associated with dysregulated fear behavior. Genetic variation in SLC18A2, the gene that encodes vesicular monoamine transporter 2 (VMAT2), has been reported to affect risk for the development of PTSD in humans. Here, we use transgenic mice that express either 5% (VMAT2‐LO mice) or 200% (VMAT2‐HI mice) of wild‐type levels of VMAT2 protein. We report that VMAT2‐LO mice have reduced VMAT2 protein in the hippocampus and amygdala, impaired monoaminergic vesicular storage capacity in both the striatum and frontal cortex, decreased monoamine metabolite abundance and a greatly reduced capacity to release dopamine upon stimulation. Furthermore, VMAT2‐LO mice showed exaggerated cued and contextual fear expression, altered fear habituation, inability to discriminate threat from safety cues, altered startle response compared with wild‐type mice and an anxiogenic‐like phenotype, but displayed no deficits in social function. By contrast, VMAT2‐HI mice exhibited increased VMAT2 protein throughout the brain, higher vesicular storage capacity and greater dopamine release upon stimulation compared with wild‐type controls. Behaviorally, VMAT2‐HI mice were similar to wild‐type mice in most assays, with some evidence of a reduced anxiety‐like responses. Together, these data show that presynaptic monoamine function mediates PTSD‐like outcomes in our mouse model, and suggest a causal link between reduced VMAT2 expression and fear behavior, consistent with the correlational relationship between VMAT2 genotype and PTSD risk in humans. Targeting this system is a potential strategy for the development of pharmacotherapies for disorders like PTSD.     

Variability in empathic fear response among 11 inbred strains of mice

Empathy is an important emotional process that involves the ability to recognize and share emotions with others. We have previously developed an observational fear learning (OFL) behavioral assay to measure empathic fear in mice. In the OFL task, a mouse is conditioned for context‐dependent fear when it observes a conspecific demonstrator receiving aversive stimuli. In the present study, by comparing 11 different inbred mouse strains that are commonly used in the laboratory, we found that empathic fear response was highly variable between different strains. Five strains – C57BL/6J, C57BL/6NTac, 129S1/SvImJ, 129S4/SvJae and BTBR T⁺ Itpr3^tf/J – showed observational fear (OF) responses, whereas AKR/J, BALB/cByJ, C3H/HeJ, DBA/2J, FVB/NJ and NOD/ShiLtJ mice exhibited low empathic fear response. Importantly, day 2 OF memory was significantly correlated with contextual memory in the classical fear conditioning among the 11 strains. Innate differences in anxiety, locomotor activity, sociability and preference for social novelty were not significantly correlated with OFL. Interestingly, early adolescent C57BL/6J mice exhibited an increase in acquisition of OF. The level of OFL in C57BL/6J strain was not affected by sex or strains of the demonstrator. Taken together, these data strongly suggest that there are naturally occurring OFL‐specific genetic variations modulating empathic fear behaviors in mice. The identification of causal genes may uncover novel genetic pathways and underlying neural mechanisms that modulate empathic fear and, ultimately, provide new targets for therapeutic intervention in human mental disorders associated with impaired empathy.     

Hippocampal knockdown of α2 nicotinic or M1 muscarinic acetylcholine receptors in C57BL/6J male mice impairs cued fear conditioning

Acetylcholine (ACh) signaling in the hippocampus is important for behaviors related to learning, memory and stress. In this study, we investigated the role of two ACh receptor subtypes previously shown to be involved in fear and anxiety, the M1 mAChR and the α2 nAChR, in mediating the effects of hippocampal ACh on stress‐related behaviors. Adeno‐associated viral vectors containing short‐hairpin RNAs targeting M1 or α2 were infused into the hippocampus of male C57BL/6J mice, and behavior in a number of paradigms related to stress responses and fear learning was evaluated. There were no robust effects of hippocampal M1 mAChR or α2 nAChR knockdown (KD) in the light/dark box, tail suspension, forced swim or novelty‐suppressed feeding tests. However, effects on fear learning were observed in both KD groups. Short term learning was intact immediately after training in all groups of mice, but both the M1 and α2 hippocampal knock down resulted in impaired cued fear conditioning 24 h after training. In addition, there was a trend for a deficit in contextual memory the M1 mAChR KD group 24 h after training. These results suggest that α2 nicotinic and M1 muscarinic ACh receptors in the hippocampus contribute to fear learning and could be relevant targets to modify brain circuits involved in stress‐induced reactivity to associated cues.     

Mx1‐Cre mediated Rgs12 conditional knockout mice exhibit increased bone mass phenotype

Regulators of G‐protein Signaling (Rgs) proteins are the members of a multigene family of GTPase‐accelerating proteins (GAP) for the Galpha subunit of heterotrimeric G‐proteins. Rgs proteins play critical roles in the regulation of G protein couple receptor (GPCR) signaling in normal physiology and human diseases such as cancer, heart diseases, and inflammation. Rgs12 is the largest protein of the Rgs protein family. Some in vitro studies have demonstrated that Rgs12 plays a critical role in regulating cell differentiation and migration; however its function and mechanism in vivo is largely unknown. Here, we generated a floxed Rgs12 allele (Rgs12^flox/flox) in which the exon 2, containing both PDZ and PTB_PID domains of Rgs12, was flanked with two loxp sites. By using the inducible Mx1‐cre and Poly I:C system to specifically delete Rgs12 at postnatal 10 days in interferon‐responsive cells including monocyte and macrophage cells, we found that Rgs12 mutant mice had growth retardation with the phenotype of increased bone mass. We further found that deletion of Rgs12 reduced osteoclast numbers and had no significant effect on osteoblast formation. Thus, Rgs12^flox/flox conditional mice provide a valuable tool for in vivo analysis of Rgs12 function and mechanism through time‐ and cell‐specific deletion of Rgs12. genesis 51:201–209, 2013. © 2013 Wiley Periodicals, Inc.     

Physiological and behavioral effects of amphetamine in BACE1−/− mice

β‐Site APP‐cleaving Enzyme 1 (BACE1) is a protease that has been linked to schizophrenia, a severe mental illness that is potentially characterized by enhanced dopamine (DA) release in the striatum. Here, we used acute amphetamine administration to stimulate neuronal activity and investigated the neurophysiological and locomotor‐activity response in BACE1‐deficient (BACE1^?/?) mice. We measured locomotor activity at baseline and after treatment with amphetamine (3.2 and 10 mg/kg). While baseline locomotor activity did not vary between groups, BACE1^?/? mice exhibited reduced sensitivity to the locomotor‐enhancing effects of amphetamine. Using high‐performance liquid chromatography (HPLC) to measure DA and DA metabolites in the striatum, we found no significant differences in BACE1^?/? compared with wild‐type mice. To determine if DA neuron excitability is altered in BACE1^?/? mice, we performed patch‐clamp electrophysiology in putative DA neurons from brain slices that contained the substantia nigra. Pacemaker firing rate was slightly increased in slices from BACE1^?/? mice. We next measured G protein‐coupled potassium currents produced by activation of D2 autoreceptors, which strongly inhibit firing of these neurons. The maximal amplitude and decay times of D2 autoreceptor currents were not altered in BACE1^?/? mice, indicating no change in D2 autoreceptor‐sensitivity and DA transporter‐mediated reuptake. However, amphetamine (30 µm )‐induced potassium currents produced by efflux of DA were enhanced in BACE1^?/? mice, perhaps indicating increased vesicular DA content in the midbrain. This suggests a plausible mechanism to explain the decreased sensitivity to amphetamine‐induced locomotion, and provides evidence that decreased availability of BACE1 can produce persistent adaptations in the dopaminergic system.     

Behavioral flexibility in a mouse model for obsessive‐compulsive disorder: Impaired Pavlovian reversal learning in SAPAP3 mutants

Obsessive‐compulsive disorder (OCD) is characterized by obsessive thinking, compulsive behavior and anxiety, and is often accompanied by cognitive deficits. The neuropathology of OCD involves dysregulation of cortical‐striatal circuits. Similar to OCD patients, SAPAP3 knockout mice 3 (SAPAP3^?/?) exhibit compulsive behavior (grooming), anxiety and dysregulated cortical‐striatal function. However, it is unknown whether SAPAP3^?/? display cognitive deficits and how these different behavioral traits relate to one another. SAPAP3^?/? and wild‐type (WT) littermates were trained in a Pavlovian conditioning task pairing visual cues with the delivery of sucrose solution. After mice learned to discriminate between a reward‐predicting conditioned stimulus (CS+) and a non‐reward stimulus (CS?), contingencies were reversed (CS+ became CS? and vice versa). Additionally, we assessed grooming, anxiety and general activity. SAPAP3^?/? acquired Pavlovian approach behavior similarly to WT, albeit less vigorously and with a different strategy. However, unlike WT, SAPAP3^?/? were unable to adapt their behavior after contingency reversal, exemplified by a lack of re‐establishing CS+ approach behavior (sign tracking). Surprisingly, such behavioral inflexibility, decreased vigor, compulsive grooming and anxiety were unrelated. This study shows that SAPAP3^?/? are capable of Pavlovian learning, but lack flexibility to adapt associated conditioned approach behavior. Thus, SAPAP3^?/? not only display compulsive‐like behavior and anxiety, but also cognitive deficits, confirming and extending the validity of SAPAP3^?/? as a suitable model for the study of OCD. The observation that compulsive‐like behavior, anxiety and behavioral inflexibility were unrelated suggests a non‐causal relationship between these traits and may be of clinical relevance for the treatment of OCD.     

Oxytocin receptor activation does not mediate associative fear deficits in a Williams Syndrome model

Williams Syndrome results in distinct behavioral phenotypes, which include learning deficits, anxiety, increased phobias and hypersociability. While the underlying mechanisms driving this subset of phenotypes is unknown, oxytocin (OT) dysregulation is hypothesized to be involved as some studies have shown elevated blood OT and altered OT receptor expression in patients. A “Complete Deletion” (CD) mouse, modeling the hemizygous deletion in Williams Syndrome, recapitulates many of the phenotypes present in humans. These CD mice also exhibit impaired fear responses in the conditioned fear task. Here, we address whether OT dysregulation is responsible for this impaired associative fear memory response. We show direct delivery of an OT receptor antagonist to the central nervous system did not rescue the attenuated contextual or cued fear memory responses in CD mice. Thus, increased OT signaling is not acutely responsible for this phenotype. We also evaluated OT receptor and serotonin transporter availability in regions related to fear learning, memory and sociability using autoradiography in wild type and CD mice. While no differences withstood correction, we identified regions that may warrant further investigation. There was a nonsignificant decrease in OT receptor expression in the lateral septal nucleus and nonsignificant lowered serotonin transporter availability in the striatum and orbitofrontal cortex. Together, these data suggest the fear conditioning anomalies in the Williams Syndrome mouse model are independent of any alterations in the oxytocinergic system caused by deletion of the Williams locus.     

Endocannabinoids mediate acute fear adaptation via glutamatergic neurons independently of corticotropin-releasing hormone signaling

Recent evidence showed that the endocannabinoid system plays an important role in the behavioral adaptation of stress and fear responses. In this study, we chose a behavioral paradigm that includes criteria of both fear and stress responses to assess whether the involvement of endocannabinoids in these two processes rely on common mechanisms. To this end, we delivered a footshock and measured the fear response to a subsequently presented novel tone stimulus. First, we exposed different groups of cannabinoid receptor type 1 (CB₁)‐deficient mice (CB₁^?/?) and their wild‐type littermates (CB₁^+/+) to footshocks of different intensities. Only application of an intense footshock resulted in a sustained fear response to the tone in CB₁^?/?. Using the intense protocol, we next investigated whether endocannabinoids mediate their effects via an interplay with corticotropin‐releasing hormone (CRH) signaling. Pharmacological blockade of CB₁ receptors by rimonabant in mice deficient for the CRH receptor type 1 (CRHR1^?/?) or type 2 (CRHR2^?/?), and in respective wild‐type littermates, resulted in a sustained fear response in all genotypes. This suggests that CRH is not involved in the fear‐alleviating effects of CB₁. As CRHR1^?/? are known to be severely impaired in stress‐induced corticosterone secretion, our observation also implicates that corticosterone is dispensable for CB₁‐mediated acute fear adaptation. Instead, conditional mutants with a specific deletion of CB₁ in principal neurons of the forebrain (CaMK‐CB₁^?/?), or in cortical glutamatergic neurons (Glu‐CB₁^?/?), showed a similar phenotype as CB₁^?/?, thus indicating that endocannabinoid‐controlled glutamatergic transmission plays an essential role in acute fear adaptation.     

Progesterone modulation of α5 nAChR subunits influences anxiety‐related behavior during estrus cycle

Smokers often report an anxiolytic effect of cigarettes. In addition, stress‐related disorders such as anxiety, post‐traumatic stress syndrome and depression are often associated with chronic nicotine use. To study the role of the α5 nicotinic acetylcholine receptor subunit in anxiety‐related responses, control and α5 subunit null mice (α5^?/?) were subjected to the open field activity (OFA), light–dark box (LDB) and elevated plus maze (EPM) tests. In the OFA and LDB, α5^?/? behaved like wild‐type controls. In the EPM, female α5^?/? mice displayed an anxiolytic‐like phenotype, while male α5^?/? mice were undistinguishable from littermate controls. We studied the hypothalamus–pituitary–adrenal axis by measuring plasma corticosterone and hypothalamic corticotropin‐releasing factor. Consistent with an anxiolytic‐like phenotype, female α5^?/? mice displayed lower basal corticosterone levels. To test whether gonadal steroids regulate the expression of α5, we treated cultured NTera 2 cells with progesterone and found that α5 protein levels were upregulated. In addition, brain levels of α5 mRNA increased upon progesterone injection into ovariectomized wild‐type females. Finally, we tested anxiety levels in the EPM during the estrous cycle. The estrus phase (when progesterone levels are low) is anxiolytic‐like in wild‐type mice, but no cycle‐dependent fluctuations in anxiety levels were found in α5^?/? females. Thus, α5‐containing neuronal nicotinic acetylcholine receptors may be mediators of anxiogenic responses, and progesterone‐dependent modulation of α5 expression may contribute to fluctuations in anxiety levels during the ovarian cycle.     

Lysosomal cholesterol accumulation in macrophages leading to coronary atherosclerosis in CD38−/− mice

The disruption in transportation of oxLDL‐derived cholesterol and the subsequent lipid accumulation in macrophages are the hallmark events in atherogenesis. Our recent studies demonstrated that lysosomal Ca²⁺ messenger of nicotinic acid adenine dinucleotide phosphate (NAADP), an enzymatic product of CD38 ADP‐ribosylcyclase (CD38), promoted lipid endocytic trafficking in human fibroblast cells. The current studies are designed to examine the functional role of CD38/NAADP pathway in the regulation of lysosomal cholesterol efflux in atherosclerosis. Oil red O staining showed that oxLDL concentration‐dependently increased lipid buildup in bone marrow‐derived macrophages from both wild type and CD38^?/?, but to a significant higher extent with CD38 gene deletion. Bodipy 493/503 fluorescence staining found that the deposited lipid in macrophages was mainly enclosed in lysosomal organelles and largely enhanced with the blockade of CD38/NAADP pathway. Filipin staining and direct measurement of lysosome fraction further revealed that the free cholesterol constituted a major portion of the total cholesterol segregated in lysosomes. Moreover, in situ assay disclosed that both lysosomal lumen acidity and the acid lipase activity were reduced upon cholesterol buildup in lysosomes. In CD38^?/? mice, treatment with Western diet (12 weeks) produced atherosclerotic damage in coronary artery with striking lysosomal cholesterol sequestration in macrophages. These data provide the first experimental evidence that the proper function of CD38/NAADP pathway plays an essential role in promoting free cholesterol efflux from lysosomes and that a defection of this signalling leads to lysosomal cholesterol accumulation in macrophages and results in coronary atherosclerosis in CD38^?/? mice.     

Distinct serum proteome profiles associated with collagen‐induced arthritis and complete Freund's adjuvant‐induced inflammation in CD38−/− mice: The discriminative power of protein species or proteoforms

Collagen‐type‐II‐induced arthritis (CIA) is an autoimmune disease, which involves a complex host systemic response including inflammatory and autoimmune reactions. CIA is milder in CD38^?/? than in wild‐type (WT) mice. ProteoMiner‐equalized serum samples were subjected to 2D‐DiGE and MS‐MALDI‐TOF/TOF analyses to identify proteins that changed in their relative abundances in CD38^?/? versus WT mice either with arthritis (CIA⁺), with no arthritis (CIA^?), or with inflammation (complete Freund's adjuvant (CFA)‐treated mice). Multivariate analyses revealed that a multiprotein signature (n = 28) was able to discriminate CIA⁺ from CIA^? mice, and WT from CD38^?/? mice within each condition. Likewise, a distinct multiprotein signature (n = 16) was identified which differentiated CIA⁺ CD38^?/? mice from CIA⁺ WT mice, and lastly, a third multiprotein signature (n = 18) indicated that CD38^?/? and WT mice could be segregated in response to CFA treatment. Further analyses showed that the discriminative power to distinguish these groups was reached at protein species level and not at the protein level. Hence, the need to identify and quantify proteins at protein species level to better correlate proteome changes with disease processes. It is crucial for plasma proteomics at the low‐abundance protein species level to apply the ProteoMiner enrichment. All MS data have been deposited in the ProteomeXchange with identifiers PXD001788, PXD001799 and PXD002071 ( http://proteomecentral.proteomexchange.org/dataset/PXD001788 , http://proteomecentral.proteomexchange.org/dataset/PXD001799 and http://proteomecentral.proteomexchange.org/dataset/PXD002071 ).     

Fear-conditioning mechanisms associated with trait vulnerability to anxiety in humans

Investigations of fear conditioning in rodents and humans have illuminated the neural mechanisms underlying cued and contextual fear. A critical question is how personality dimensions such as trait anxiety act through these mechanisms to confer vulnerability to anxiety disorders, and whether humans' ability to overcome acquired fears depends on regulatory skills not characterized in animal models. In a neuroimaging study of fear conditioning in humans, we found evidence for two independent dimensions of neurocognitive function associated with trait vulnerability to anxiety. The first entailed increased amygdala responsivity to phasic fear cues. The second involved impoverished ventral prefrontal cortical (vPFC) recruitment to downregulate both cued and contextual fear prior to omission (extinction) of the aversive unconditioned stimulus. These two dimensions may contribute to symptomatology differences across anxiety disorders; the amygdala mechanism affecting the development of phobic fear and the frontal mechanism influencing the maintenance of both specific fears and generalized anxiety.     

Naloxone Facilitates Contextual Learning and Memory in a Receptor-Independent and Tet1-Dependent Manner

Opioids, like morphine and naloxone, regulate the proliferation and neuronal differentiation of neural stem cells (NSCs) in a receptor-independent and ten-eleven translocation methylcytosine dioxygenase (TET1)-dependent manner in vitro. Whether naloxone regulates hippocampal NSCs and contextual learning in vivo in a similar manner was determined. Naloxone infusion increased the Ki67 and Doublecortin positive cells in subgranular zone of wild type mice, which suggested the increased proliferation and differentiation of hippocampal NSCs in vivo and was consistent with the in vitro functions of naloxone. In addition, naloxone infusion also facilitated the contextual learning and memory of wild type mice. To determine the contribution of μ-opioid receptor (OPRM1) and TET1 to these functions of naloxone, several types of knockout mice were used. Since Tet1^?/? mice have high deficiency in contextual learning and memory, Tet1^+/? mice were used instead. The abilities of naloxone to regulate NSCs and to facilitate contextual learning were significantly impaired in Tet1^+/? mice. In addition, these abilities of naloxone were not affected in Oprm1^?/? mice. Therefore, naloxone facilitates contextual learning and memory in a receptor-independent and Tet1-dependent manner, which provides new understanding on the receptor-independent functions of opioids.

     

Systems genetic analysis of nicotine withdrawal deficits in hippocampus-dependent learning

Cognitive deficits, such as disrupted learning, are a major symptom of nicotine withdrawal. These deficits are heritable, yet their genetic basis is largely unknown. Our lab has developed a mouse model of nicotine withdrawal deficits in learning, using chronic nicotine exposure via osmotic minipumps and fear conditioning. Here, we utilized the BXD genetic reference panel to identify genetic variants underlying nicotine withdrawal deficits in learning. Male and female mice (n = 6–11 per sex per strain, 31 strains) received either chronic saline or nicotine (6.3 mg/kg per day for 12 days), and were then tested for hippocampus-dependent learning deficits using contextual fear conditioning. Quantitative trait locus (QTL) mapping analyses using GeneNetwork identified a significant QTL on Chromosome 4 (82.13 Mb, LRS = 20.03, p < 0.05). Publicly available hippocampal gene expression data were used to identify eight positional candidates (Snacpc3, Mysm1, Rps6, Plaa, Lurap1l, Slc24a2, Hacd4, Ptprd) that overlapped with our behavioral QTL and correlated with our behavioral data. Overall, this study demonstrates that genetic factors impact cognitive deficits during nicotine withdrawal in the BXD recombinant inbred panel and identifies candidate genes for future research.