Impaired cognitive function and reduced anxiety‐related behavior in a promyelocytic leukemia (PML) tumor suppressor protein‐deficient mouse

The promyelocytic leukemia (PML) protein is a tumor suppressor factor mostly known by its involvement in acute promyelocytic leukemia (APL). Interestingly, recent studies have provided evidence that, in the central nervous system, PML is involved in neurogenesis. However, prospective studies of PML in brain are lacking. To further understand the role of PML in the mammalian brain, we studied plasticity and behavioral changes in PML knockout mice. If PML is involved in neurogenesis, and neurogenesis is an important process for proper brain development as well as learning and memory functions, we hypothesized that PML might have a role in plasticity and cognition. Behavioral studies demonstrated that PML knockout mice present abnormalities in conditioned learning and spatial memory, as determined by fear conditioning and Morris water maze tasks. Experiments to determine normal exploratory behavior interestingly revealed that PML knockout mice present reduced anxiety‐related responses as compared to control animals. This was confirmed when PML knockout mice spent more time in the open arms of an elevated plus‐maze, which is an indication of decreased anxiety. Additionally, impairments in hippocampus‐dependent learning were mirrored by altered long‐term plasticity at Schaffer collateral‐CA1 synapses. We now provide the first evidence for an important role of PML in the brain, indicating that PML might have a role in synaptic plasticity and associated behavioral processes.     

BDNF-restricted knockout mice as an animal model for aggression

Mice with global deletion of one brain-derived neurotrophic factor (BDNF) allele or with forebrain-restricted deletion of both alleles show elevated aggression, but this phenotype is accompanied by other behavioral changes, including increases in anxiety and deficits in cognition. Here we performed behavioral characterization of conditional BDNF knockout mice generated using a Cre recombinase driver line, KA1-Cre, which expresses Cre in few areas of brain: highly at hippocampal area CA3 and moderately in dentate gyrus, cerebellum and facial nerve nucleus. The mutant animals exhibited elevated conspecific aggression and social dominance, but did not show changes in anxiety-like behaviors assessed using the elevated plus maze and open field test. There were no changes in depression-like behaviors tested in the forced swim test, but small increase in immobility in the tail suspension test. In cognitive tasks, mutants showed normal social recognition and normal spatial and fear memory, but exhibited a deficit in object recognition. Thus, this knockout can serve as a robust model for BDNF-dependent aggression and object recognition deficiency.     

Motivational Disturbances and Effects of L-dopa Administration in Neurofibromatosis-1 Model Mice

Children with neurofibromatosis type 1 (NF1) frequently have cognitive and behavioral deficits. Some of these deficits have been successfully modeled in Nf1 genetically-engineered mice that develop optic gliomas (Nf1 OPG mice). In the current study, we show that abnormal motivational influences affect the behavior of Nf1 OPG mice, particularly with regard to their response to novel environmental stimuli. For example, Nf1 OPG mice made fewer spontaneous alternations in a Y-maze and fewer arm entries relative to WT controls. However, analysis of normalized alternation data demonstrated that these differences were not due to a spatial working memory deficit. Other reported behavioral results (e.g., open-field test, below) suggest that differential responses to novelty and/or other motivational influences may be more important determinants of these kinds of behavior than simple differences in locomotor activity/spontaneous movements. Importantly, normal long-term depression was observed in hippocampal slices from Nf1 OPG mice. Results from elevated plus maze testing showed that differences in exploratory activity between Nf1 OPG and WT control mice may be dependent on the environmental context (e.g., threatening or non-threatening) under which exploration is being measured. Nf1 OPG mice also exhibited decreased exploratory hole poking in a novel holeboard and showed abnormal olfactory preferences, although L-dopa (50 mg/kg) administration resolved the abnormal olfactory preference behaviors. Nf1 OPG mice displayed an attenuated response to a novel open field in terms of decreased ambulatory activity and rearing but only during the first 10 min of the session. Importantly, Nf1 OPG mice demonstrated investigative rearing deficits with regard to a novel hanging object suspended on one side of the field which were not rescued by L-dopa administration. Collectively, our results provide new data important for evaluating therapeutic treatments aimed at ameliorating NF1-associated cognitive/behavioral deficits.     

Mice lacking Asic3 show reduced anxiety‐like behavior on the elevated plus maze and reduced aggression

Sensing external stimulation is crucial for central processing in the brain and subsequent behavioral expression. Although sensory alteration or deprivation may result in behavioral changes, most studies related to the control of behavior have focused on central mechanisms. Here we created a sensory deficit model of mice lacking acid‐sensing ion channel 3 (Asic3^?/?) to probe behavioral alterations. ASIC3 is predominately distributed in the peripheral nervous system. RT‐PCR and immunohistochemistry used to examine the expression of Asic3 in the mouse brain showed near‐background mRNA and protein levels of ASIC3 throughout the whole brain, except for the sensory mesencephalic trigeminal nucleus. Consistent with the expression results, Asic3 knockout had no effect on synaptic plasticity of the hippocampus and the behavioral tasks of motor function, learning and memory. In anxiety behavior tasks, Asic3^?/? mice spent more time in the open arms of an elevated plus maze than did their wild‐type littermates. Asic3^?/? mice also displayed less aggressiveness toward intruders but more stereotypic repetitive behaviors during resident–intruder testing than did wild‐type littermates. Therefore, loss of ASIC3 produced behavioral changes in anxiety and aggression in mice, which suggests that ASIC3‐dependent sensory activities might relate to the central process of emotion modulation.     

Altered anxiety-related behavior in nociceptin/orphanin FQ receptor gene knockout mice

Studies showed that nociceptin/orphanin FQ (N/OFQ) peptide receptor (NOP) agonists produce anxiolytic-like actions, while little is known about the effects of blockade of NOP receptor signaling in anxiety. To this aim, we investigated the behavioral phenotype of NOP receptor gene knockout mice (NOP(-/-)) in different assays. In the elevated plus-maze and light-dark box, NOP(-/-) mice displayed increased anxiety-related behavior. In the novelty-suppressed feeding behavior and elevated T-maze, NOP(-/-) mice showed anxiolytic-like phenotype, while no differences were found in the open-field, hole-board, marble-burying, and stress-induced hyperthermia. Altogether, these findings suggest that the N/OFQ-NOP receptor system modulates anxiety-related behavior in a complex manner.     

Neuropsychological Deficits in Mice Depleted of the Schizophrenia Susceptibility Gene CSMD1

Recent meta-analyses of schizophrenia genome-wide association studies (GWASs) have identified the CUB and SUSHI multiple domains 1 (CSMD1) gene as a statistically strong risk factor. CSMD1 is a complement control-related protein suggested to inhibit the classical complement pathway, being expressed in developing neurons. However, expression of CSMD1 is largely uncharacterized and relevance for behavioral phenotypes is not previously demonstrated. Here, we assess neuropsychological behaviors of a Csmd1 knockout (KO) mouse in a selection of standard behavioral tests. Deregulation of neuropsychological responses were observed in both the open field and the elevated plus maze tests, in which KO mice spent 55% and 33% less time than WT littermate mice in open areas, respectively. Altered behaviors were also observed in tail suspension and to higher acoustic stimuli, for which Csmd1 KO mice showed helplessness and moderate increase in startle amplitude, respectively. Furthermore, Csmd1 KO mice also displayed increased weight-gain and glucose tolerance, similar to a major phenotype of the metabolic syndrome that also has been associated to the human CSMD1 locus. Consistent with a role in the control of behaviors, Csmd1 was found highly expressed in the central nervous system (CNS), and with some expression in visceral fat and ovary, under tissue-specific control by a novel promoter-associated lncRNA. In summary, disruption of Csmd1 induces behaviors reminiscent of blunted emotional responses, anxiety and depression. These observations suggest an influence of the CSMD1 schizophrenia susceptibility gene on psychopathology and endophenotypes of the negative symptom spectra.     

Mice lacking synapsin III show abnormalities in explicit memory and conditioned fear

Synapsin III is a neuron‐specific phosphoprotein that plays an important role in synaptic transmission and neural development. While synapsin III is abundant in embryonic brain, expression of the protein in adults is reduced and limited primarily to the hippocampus, olfactory bulb and cerebral cortex. Given the specificity of synapsin III to these brain areas and because it plays a role in neurogenesis in the dentate gyrus, we investigated whether it may affect learning and memory processes in mice. To address this point, synapsin III knockout mice were examined in a general behavioral screen, several tests to assess learning and memory function, and conditioned fear. Mutant animals displayed no anomalies in sensory and motor function or in anxiety‐ and depressive‐like behaviors. Although mutants showed minor alterations in the Morris water maze, they were deficient in object recognition 24 h and 10 days after training and in social transmission of food preference at 20 min and 24 h. In addition, mutants displayed abnormal responses in contextual and cued fear conditioning when tested 1 or 24 h after conditioning. The synapsin III knockout mice also showed aberrant responses in fear‐potentiated startle. As synapsin III protein is decreased in schizophrenic brain and because the mutant mice do not harbor obvious anatomical deficits or neurological disorders, these mutants may represent a unique neurodevelopmental model for dissecting the molecular pathways that are related to certain aspects of schizophrenia and related disorders.     

Behavioral characterization of striatal‐enriched protein tyrosine phosphatase (STEP) knockout mice

Striatal‐enriched protein tyrosine phosphatase (STEP) has been described as a regulator of multiple kinases and glutamate receptor subunits critical for synaptic plasticity. Published behavioral and biochemical characterization from the founder line of STEP knockout (KO) mice revealed superior cognitive performance, with enhanced phosphorylation of substrates such as ERK, Fyn and GluN2B; suggesting that inhibitors of STEP may have potential as therapeutic agents for the treatment of neuropsychiatric disorders. The objectives of this work aimed to replicate and extend the previously reported behavioral consequences of STEP knockout. Consistent with previous reported data, STEP KO mice demonstrated exploratory activity levels and similar motor coordination relative to WT littermate controls as well as intact memory in a Y‐maze spatial novelty test. Interestingly, KO mice demonstrated deficits in pre‐pulse inhibition as well as reduced seizure threshold relative to WT controls. Immunohistochemical staining of brains revealed the expected gene‐dependent reduction in STEP protein confirming knockout in the mice. The present data confirm expression and localization of STEP and the absence in KO mice, and describe functional downstream implications of reducing STEP levels in vivo.     

Behavioral characterization of mice lacking GIRK/Kir3 channel subunits

G protein-gated inwardly rectifying K(+) (GIRK/Kir3) channels mediate the postsynaptic inhibitory effects of many neurotransmitters and drugs of abuse. The lack of drugs selective for GIRK channels has hindered our ability to study their contributions to behavior. Here, we assessed the impact of GIRK subunit ablation on several behavioral endpoints. Mice were evaluated with respect to open-field motor activity and habituation, anxiety-related behavior, motor co-ordination and ataxia and operant performance. GIRK3 knockout ((-/-)) mice behaved indistinguishably from wild-type mice in this panel of tests. GIRK1(-/-) mice and GIRK2(-/-) mice, however, showed elevated motor activity and delayed habituation to an open field. GIRK2(-/-) mice, and to a lesser extent GIRK1(-/-) mice, also displayed reduced anxiety-related behavior in the elevated plus maze. Both GIRK1(-/-) mice and GIRK2(-/-) mice displayed marked resistance to the ataxic effects of the GABA(B) receptor agonist baclofen in the rotarod test. All GIRK(-/-) mice were able to learn an operant task using food as the reinforcing agent. Within-session progressive ratio scheduling, however, showed elevated lever press behavior in GIRK2(-/-) mice and, to a lesser extent, in GIRK1(-/-) mice. Phenotypic differences between mice lacking GIRK1, GIRK2 and GIRK3 correlate well with the known impact of GIRK subunit ablation on neurotransmitter-gated GIRK currents, arguing that most neuronal GIRK channels contain GIRK1 and/or GIRK2. Altogether, our data suggest that GIRK channels make important contribution to a range of behaviors and may represent points of therapeutic intervention in disorders of anxiety, spasticity and reward.     

Increased anxiety-like behavior during the post-stress period in mice exposed to repeated restraint stress

Mice exposed to repeated restraint (RR: 2 h of restraint on each of 3 consecutive days) lose weight and do not return to the weight of non-stressed controls after restraint ends. These mice also exhibit an exaggerated endocrine response to mild stressors in the post-stress period. To determine if other aspects of the stress response are altered, NIH Swiss mice were repeatedly restrained then evaluated for anxiety-like behavior in various behavioral tests. Twelve days after the end of RR half of the control and RR mice were subjected to the mild stress of an intraperitoneal injection of saline before placement in an elevated plus maze. RR mice not subjected to mild stress showed the same level of anxiety as the control and RR mice exposed to mild stress. Placement in a light-dark box 20 days after restraint also indicated an increase in anxiety-like behavior in RR mice that had not been exposed to mild stress. In contrast, RR mice displayed no increase in anxiety-like behavior in the defensive withdrawal apparatus and the marble burying test 6 and 17 days, respectively, after restraint. RR mice released more corticosterone than non-restrained controls exposed to defensive withdrawal or EPM apparatus although baseline corticosterone remained at control levels. These results suggest that RR induces an exaggeration of both endocrine and behavioral responses to subsequent mild stressors. This post-stress hypersensitivity to mild stress may contribute to the sustained reduction in the body weight of RR animals.     

Differences in anxiety-related behavior between apolipoprotein E-deficient C57BL/6 and wild type C57BL/6 mice

The influence of ApoE gene deletion on the anxiety state has not been previously investigated. The elevated plus maze was used in this study to determine differences in anxiety-related behavior between apoE-deficient and wild type C57BL/6 mice. The apoE-deficient mice demonstrated less anxiety on the elevated plus maze by spending more time in the open arms of the elevated plus maze compared to wild type mice (p<0.001). Additionally, female apoE-deficient mice visited the open arm of the maze more often than their apoE-deficient male counterpart (p<0.05). The anxiety state and/or sex are possible variables to be considered when designing physiological and/or behavioral studies involving mice that are apoE-deficient.     

Assessment of NMDA receptor NR1 subunit hypofunction in mice as a model for schizophrenia

N-methyl- D -aspartate receptors (NMDARs) play a pivotal role in excitatory neurotransmission, synaptic plasticity and brain development. Clinical and experimental evidence suggests a dysregulation of NMDAR function and glutamatergic pathways in the pathophysiology of schizophrenia. We evaluated electrophysiological and behavioral properties of NMDAR deficiency utilizing mice that express only 5–10% of the normal level of NMDAR NR1 subunit. Auditory and visual event related potentials yielded significantly increased amplitudes for the P20 and N40 components in NMDAR deficient (NR1^neo−/−) mice suggesting decreased inhibitory tone. Compared to wild types, NR1^neo−/− mice spent less time in social interactions and showed reduced nest building. NR1^neo−/− mice displayed a preference for open arms of a zero maze and central zone of an open field, possibly reflecting decreased anxiety-related behavioral inhibition. However, locomotor activity did not differ between groups in either home cage environment or during behavioral testing. NR1^neo−/− mice displayed hyperactivity only when placed in a large unfamiliar environment, suggesting that neither increased anxiety nor non-specific motor activation accounts for differential behavioral patterns. Data suggest that NMDAR NR1 deficiency causes disinhibition in sensory processing as well as reduced behavioral inhibition and impaired social interactions. The behavioral signature in NR1^neo−/− mice supports the impact of impaired NMDAR function in a mouse model with possible relevance to negative symptoms in schizophrenia.     

Neurabin contributes to hippocampal long-term potentiation and contextual fear memory

Neurabin is a scaffolding protein that interacts with actin and protein phosphatase-1. Highly enriched in the dendritic spine, neurabin is important for spine morphogenesis and synaptic formation. However, less is known about the role of neurabin in hippocampal plasticity and its possible effect on behavioral functions. Using neurabin knockout (KO) mice, here we studied the function of neurabin in hippocampal synaptic transmission, plasticity and behavioral memory. We demonstrated that neurabin KO mice showed a deficit in contextual fear memory but not auditory fear memory. Whole-cell patch clamp recordings in the hippocampal CA1 neurons showed that long-term potentiation (LTP) was significantly reduced, whereas long-term depression (LTD) was unaltered in neurabin KO mice. Moreover, increased AMPA receptor but not NMDA receptor-mediated synaptic transmission was found in neurabin KO mice, and is accompanied by decreased phosphorylation of GluR1 at the PKA site (Ser845) but no change at the CaMKII/PKC site (Ser831). Pre-conditioning with LTD induction rescued the following LTP in neurabin KO mice, suggesting the loss of LTP may be due to the saturated synaptic transmission. Our results indicate that neurabin regulates contextual fear memory and LTP in hippocampal CA1 pyramidal neurons.     

Deletion of RAGE Causes Hyperactivity and Increased Sensitivity to Auditory Stimuli in Mice

The receptor for advanced glycation end-products (RAGE) is a multi-ligand receptor that belongs to the immunoglobulin superfamily of cell surface receptors. In diabetes and Alzheimer''s disease, pathological progression is accelerated by activation of RAGE. However, how RAGE influences gross behavioral activity patterns in basal condition has not been addressed to date. In search for a functional role of RAGE in normal mice, a series of standard behavioral tests were performed on adult RAGE knockout (KO) mice. We observed a solid increase of home cage activity in RAGE KO. In addition, auditory startle response assessment resulted in a higher sensitivity to auditory signal and increased prepulse inhibition in KO mice. There were no significant differences between KO and wild types in behavioral tests for spatial memory and anxiety, as tested by Morris water maze, classical fear conditioning, and elevated plus maze. Our results raise a possibility that systemic therapeutic treatments to occlude RAGE activation may have adverse effects on general activity levels or sensitivity to auditory stimuli.     

Magel2 knockout mice manifest altered social phenotypes and a deficit in preference for social novelty

MAGEL2 is one of five protein‐coding, maternally imprinted, paternally expressed genes in the Prader–Willi syndrome (PWS)‐critical domain on chromosome 15q11‐q13. Truncating pathogenic variants of MAGEL2 cause Schaaf‐Yang syndrome (SHFYNG) (OMIM #615547), a neurodevelopmental disorder related to PWS. Affected individuals manifest a spectrum of neurocognitive and behavioral phenotypes, including intellectual disability and autism spectrum disorder (ASD). Magel2 knockout mice carrying a maternally inherited, imprinted wild‐type (WT) allele and a paternally inherited Magel2‐lacZ knock‐in allele, which abolishes endogenous Magel2 gene function, exhibit several features reminiscent of the human Prader–Willi phenotypes, including neonatal growth retardation, excessive weight gain after weaning and increased adiposity in adulthood. They were shown to have altered circadian rhythm, reduced motor activity and reduced fertility. An extensive assessment for autism‐like behaviors in this mouse model was warranted, because of the high prevalence of ASD in human patients. The behavior of Magel2 knockout mice and their WT littermates were assayed via open field, elevated plus maze, tube, three‐chamber and partition tests. Our studies confirm decreased horizontal activity of male and female mice and increased vertical activity of females, in the open field. Both sexes spent more time in the open arm of the elevated plus maze, suggestive of reductions in anxiety. Both sexes displayed a lack of preference for social novelty, via a lack of discrimination between known and novel partners in the partition test. The in‐depth investigation of behavioral profiles caused by Magel2 loss‐of‐function helps to elucidate the etiology of behavioral phenotypes both for SHFYNG and PWS in general.     

Deficits in social behavior and sensorimotor gating in mice lacking phospholipase Cbeta1

Abnormal phospholipid metabolism has been implicated in the pathogenesis of schizophrenia, and it was reported that phospholipase C (PLC) β1 is reduced in specific brain areas of patients with schizophrenia. However, the causal relationship of the PLCβ1 gene with behavioral symptoms of schizophrenia remains unclear. To address this issue, we have examined the mutant mice lacking PLCβ1 for schizophrenia-related phenotypes by performing various behavioral tests, including general locomotor activity, sensorimotor gating, social behaviors, and learning and memory. Phospholipase C β1 knockout mice showed hyperactivities in an open field. They showed impaired prepulse inhibition of acoustic startle response, which was ameliorated by a systemic administration of an antipsychotic D2-receptor antagonist, haloperidol. In addition, they showed abnormal social behaviors, such as lack of barbering behavior, socially recessive trait and lack of nesting behavior. Furthermore, they showed impaired performance in the delayed-non-match-to-sample T-maze test. The present results show that the PLCβ1 mutant mice share some of the behavioral abnormalities that have been reported in patients with schizophrenia. Thus, the PLCβ1-linked signaling pathways may be involved in the neural system whose function is disrupted in the pathogenesis of schizophrenia.     

Loss of EphA4 impairs short‐term spatial recognition memory performance and locomotor habituation

EphA4 receptor (EphA4) tyrosine kinase is an important regulator of central nervous system development and synaptic plasticity in the mature brain, but its relevance to the control of normal behavior remains largely unexplored. This study is the first attempt to obtain a behavioral profile of constitutive homozygous and heterozygous EphA4 knockout mice. A deficit in locomotor habituation in the open field, impairment in spatial recognition in the Y‐maze and reduced probability of spatial spontaneous alternation in the T‐maze were identified in homozygous EphA4^?/? mice, while heterozygo us EphA4^+/? mice appeared normal on these tests in comparison with wild‐type (WT) controls. The multiple phenotypes observed in EphA4^?/? mice might stem from an underlying deficit in habituation learning, reflecting an elementary form of nonassociative learning that is in contrast to Pavlovian associative learning, which appeared unaffected by EphA4 disruption. A deficit in motor coordination on the accelerating rotarod was also demonstrated only in EphA4^?/? mice – a finding in keeping with the presence of abnormal gait in EphA4^?/? mice – although they were able to improve performance over training. There was no evidence for substantial changes in major neurochemical markers in various brain regions rich in EphA4 as shown by post‐mortem analysis. This excludes the possibility of major neurochemical compensation in the brain of EphA4^?/? mice. In summary, we have demonstrated for the first time the behavioral significance of EphA4 disruption, supporting further investigation of EphA4 as a possible target for behavioral interventions where habituation deficits are prominent.     

Effects of the essential oil from Citrus aurantium L. in experimental anxiety models in mice

Citrus aurantium L. is popularly used to treat anxiety, among other indications suggesting central nervous system action. Previous studies showed anxiolytic effect in the essential oil from peel in mice evaluated on the elevated plus maze [Carvalho-Freitas, M.I.R., Costa, M., 2002. Anxiolytic and sedative effects of extracts and essential oil from Citrus aurantium L. Biological and Pharmaceutical Bulletin 25, 1629-1633.]. In order to better characterize the activity of the essential oil, it was evaluated in two other experimental models: the light-dark box and the marble-burying test, respectively related to generalized anxiety disorder and to obsessive compulsive disorder. Mice were treated acutely by oral route 30 min (single dose) or once a day for 15 days (repeated doses) before experimental procedures. In light-dark box test, single treatment with essential oil augmented the time spent by mice in the light chamber and the number of transitions between the two compartments. There were no observed alterations in the parameters evaluated in light-dark box after repeated treatment. Otherwise, single and repeated treatments with essential oil were able to suppress marble-burying behavior. At effective doses in the behavioral tests, mice showed no impairment on rotarod procedure after both single and repeated treatments with essential oil, denoting absence of motor deficit. Results observed in marble-burying test, related to obsessive compulsive disorder, appear more consistent than those observed in light-dark box.     

Comprehensive behavioural study of GluR4 knockout mice: implication in cognitive function

Fast excitatory transmission in the mammalian central nervous system is mediated by AMPA‐type glutamate receptors. The tetrameric AMPA receptor complexes are composed of four subunits, GluR1–4. The GluR4 subunit is highly expressed in the cerebellum and the early postnatal hippocampus and is thought to be involved in synaptic plasticity and the development of functional neural circuitry through the recruitment of other AMPA receptor subunits. Previously, we reported an association of the human GluR4 gene (GRIA4) with schizophrenia. To examine the role of the GluR4 subunit in the higher brain function, we generated GluR4 knockout mice and conducted electrophysiological and behavioural analyses. The mutant mice showed normal long‐term potentiation (LTP) in the CA1 region of the hippocampus. The GluR4 knockout mice showed mildly improved spatial working memory in the T‐maze test. Although the retention of spatial reference memory was intact in the mutant mice, the acquisition of spatial reference memory was impaired in the Barnes circular maze test. The GluR4 knockout mice showed impaired prepulse inhibition. These results suggest the involvement of the GluR4 subunit in cognitive function.