Genetic reduction of noradrenergic function alters social memory and reduces aggression in mice

Aberrant social behavior is a hallmark of many cognitive, mood, and neurological disorders, although the specific molecular mechanisms underlying the behavioral deficits are not well understood. The neurotransmitter noradrenaline (NA) has been implicated in some of these disorders, as well as in several aspects of social behavior in humans and animals. We tested dopamine beta-hydroxylase knockout (Dbh -/-) mice that lack NA in various social behavior paradigms. Dbh -/- mice have relatively normal performance in the elevated plus maze, light/dark box, and open field test - three measures of anxiety - and a social recognition test. In contrast, Dbh -/- mice displayed a specific deficit in a social discrimination task and had a nearly complete absence of resident-intruder aggression. These results indicate that intact NA signaling is required for some types of social memory and aggression, but that a lack of NA does not greatly affect anxiety in mice. Further exploration of NA deficits in neurological disease may reveal mechanisms of aberrant social behavior.     

Association between experience of aggression and anxiety in male mice

The sensory contact technique increases aggressiveness in male mice and allows an aggressive type of behavior to be formed as a result of repeated experience of social victories in daily agonistic confrontations. In the low aggressive and high emotional mice of CBA/Lac strain, repeated positive fighting experience leads to increased plus maze anxiety in the winners after 10 days of experience of victories and much more after 20 days. Behavioral reactivity to other conspecifics was significantly increased as revealed by the parameters of partition test, which measures aggressive motivation in the winners. Thus, anxiety as a consequence of repeated experience of aggression is associated with the increase of aggressive motivation in CBA/Lac mice. It is concluded, that: (1) Repeated experience of aggression provokes the development of anxiety in male mice. (2) The level of anxiety as well as its behavioral realization depends on the duration of aggressive experience and genetic strain. Genetically defined features of innate anxiety (trait or state) in individuals may determine the kind of association between aggressive experience, aggressive motivation and anxiety.     

Prenatal and postnatal exposure to bisphenol a induces anxiolytic behaviors and cognitive deficits in mice

Bisphenol A (BPA), an environmental endocrine‐disrupting chemical, has been extensively evaluated for reproductive toxicity and carcinogenicity. However, little is known about the behavioral and neurochemical effects of BPA exposure. This study examined whether chronic daily exposure to an environmental endocrine‐disrupting chemical, bisphenol A [(BPA); 100 μg/kg/day or 500 μg/kg/day, p.o.], from prenatal Day 7 to postnatal Day 36 would lead to changes in anxiety and memory in mice. First, we observed the behavioral alterations of BPA‐treated mice using two anxiety‐related models, the open field test and elevated plus maze (EPM) test. In the open field test, BPA treatment (100 μg/kg/day) increased movement in the central zone. BPA treatment (500 μg/kg/day) also increased the time spent in the open arms in the EPM test. Second, we measured cognitive ability in the Y‐maze test and novel object test. BPA‐treated mice showed decreased alternation behavior in the Y‐maze at both of doses, indicating working memory impairment. BPA‐treated mice (100 μg/kg/day) also showed decreased novel object recognition as expressed by central locomotion and frequency in the central zone, showing recognition memory impairment. Finally, to measure changes in the dopaminergic and NMDAergic systems in the brain, we performed autoradiographic receptor binding assays for dopamine D₁ and D₂ receptors, the NMDA receptor, and the dopamine transporter. BPA treatment increased D₂ receptor binding in the caudate putamen (CPu) but decreased DAT binding. BPA treatment also decreased NMDA receptor binding in the frontal cortex and CA1, CA3, and DG of the hippocampus. Taken together, our results suggest that long‐term BPA exposure in mice can induce anxiolytic behaviors, cognitive deficits and changes in the dopaminergic and NMDAergic systems. Synapse 64:432–439, 2010. © 2010 Wiley‐Liss, Inc.     

Induction and expression of GluA1 (GluR-A)-independent LTP in the hippocampus

Long-term potentiation (LTP) at hippocampal CA3–CA1 synapses is thought to be mediated, at least in part, by an increase in the postsynaptic surface expression of α-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) receptors induced by N -methyl- d -aspartate (NMDA) receptor activation. While this process was originally attributed to the regulated synaptic insertion of GluA1 (GluR-A) subunit-containing AMPA receptors, recent evidence suggests that regulated synaptic trafficking of GluA2 subunits might also contribute to one or several phases of potentiation. However, it has so far been difficult to separate these two mechanisms experimentally. Here we used genetically modified mice lacking the GluA1 subunit ( Gria1 ^−/− mice) to investigate GluA1-independent mechanisms of LTP at CA3–CA1 synapses in transverse hippocampal slices. An extracellular, paired theta-burst stimulation paradigm induced a robust GluA1-independent form of LTP lacking the early, rapidly decaying component characteristic of LTP in wild-type mice. This GluA1-independent form of LTP was attenuated by inhibitors of neuronal nitric oxide synthase and protein kinase C (PKC), two enzymes known to regulate GluA2 surface expression. Furthermore, the induction of GluA1-independent potentiation required the activation of GluN2B (NR2B) subunit-containing NMDA receptors. Our findings support and extend the evidence that LTP at hippocampal CA3–CA1 synapses comprises a rapidly decaying, GluA1-dependent component and a more sustained, GluA1-independent component, induced and expressed via a separate mechanism involving GluN2B-containing NMDA receptors, neuronal nitric oxide synthase and PKC.     

Decreased anxiety in mice lacking the organic cation transporter 3

The organic cation transporter 3 (OCT3; synonymous: extraneuronal monoamine transporter, EMT, Slc22a3) encodes an isoform of the organic cation transporters and is expressed widely across the whole brain. OCTs are a family of high-capacity, bidirectional, multispecific transporters of organic cations. These also include serotonin, dopamine and norepinephrine making OCTs attractive candidates for a variety of neuropsychiatric disorders including anxiety disorders. OCT3 has been implicated in termination of monoaminergic signalling in the central nervous system. Interestingly, OCT3 mRNA is however also significantly up-regulated in the hippocampus of serotonin transporter knockout mice where it might serve as an alternative reuptake mechanism for serotonin. The examination of the behavioural phenotype of OCT3 knockout mice thus is paramount to assess the role of OCT3. We have therefore subjected mice lacking the OCT3 gene to a comprehensive behavioural test battery. While cognitive functioning in the Morris water maze test and aggression levels measured with the resident–intruder paradigm were in the same range as the respective control animals, OCT3 knockout animals showed a tendency of increased activity and were significantly less anxious in the elevated plus-maze test and the open field test as compared to their respective wild-type controls arguing for a role of OCT3 in the regulation of fear and anxiety, probably by modulating the serotonergic tone in limbic circuitries.     

Intermale aggression in corticotropin-releasing factor receptor 1 deficient mice

The anxiogenic neuropeptide, corticotropin-releasing factor (CRF), has a complex effect on intermale aggression. CRF receptor 1 (CRFR1) is the primary receptor for CRF and in this study, we examined in detail isolation-induced intermale aggression in CRFR1 deficient mice. All mice contained a mixed 50:50 inbred/outbred background to improve aggressive performance. Mice were isolated for 4 weeks prior to 2 consecutive days of aggression testing using the resident-intruder paradigm. Mice were also tested for anxiety on the elevated plus maze. Relative to littermate wild-type (WT) controls, CRFR1-mutant mice exhibited normal levels of intermale aggression over the 2 test days in terms of percentage showing aggression, number of attacks, time aggressive, and latency to first attack. In terms of sites of attacks on intruders, CRFR1-deficient mice attacked the ventral portion of the mid-section (including belly) significantly less frequently than WT males on test day 1, but these differences did not reach significance on test day 2. No other differences in sites of attacks were observed. Tail rattling also did not differ between groups. Importantly, KO males showed decreased anxiety relative to WT mice (consistent with previous reports) as evidenced by spending significantly more time on the open arms and significantly less time on the closed arms of the elevated plus maze. Plus maze performance did not correlate with any measure of levels of aggression, suggesting a dissociation between altered levels of anxiety and aggressive performance. Taken together, the results suggest that the activation CRFR1 is not necessary for the normal production of isolation-induced intermale aggression.     

Hyperactivity, memory deficit and anxiety-related behaviors in mice lacking the p85alpha subunit of phosphoinositide-3 kinase

We previously reported that knockout mice lacking the p85alpha regulatory subunit of phosphoinositide-3 kinase (PI3K) (p85alpha(-/-) mice) significantly showed spatial learning-deficits, restlessness and motivation-deficit in water maze tests. It was also shown in the report that decline of PI3K activity in several brain areas related to losses of synapses and myelinated axons. However, any other behavioral patterns have not been elucidated, the aim of the present study was to observe behavioral natures of in p85alpha(-/-) mice using several behavioral tests. In order to examine behaviors, a novel object recognition test, an open field test, an object exploring test, a hole-board test and an elevated plus maze test were carried out in p85alpha(-/-) mice. The p85alpha(-/-) mice significantly showed a deficit in object recognition memory, less exploring novel objects, and anxiety. Hyperactivity was observed in p85alpha(-/-) mice in male-specific manner. The present results suggest that deficiencies in PI3K activity result in hyperactivity, memory deficit and an increase in anxiety. Therefore, these behavioral phenotypes can be analyzed in a relationship with losses of synapses and myelinated axons in the brain, which resulted from deficiencies in PI3K activity.     

Serotonin laterality in amygdala predicts performance in the elevated plus maze in rats

Behavior in the elevated plus maze was correlated with hemispheric asymmetries in neurotransmitter content in limbic brain regions assayed with HPLC-EC in adult rats. A strong (r=0.86, p < 0.003) correlation exists between increased anxiety (more time spent in the closed arm) and the lateralization of serotonin in the amygdala. Greater serotonin in the right versus left amygdala relates to greater anxiety. In addition, increased dopamine in right prefrontal cortex is strongly correlated with anxiety (r=0.84, p < 0.01). No such correlations were observed for accumbens, hippocampus, or striatum. These data support the hypothesis that the right hemisphere is involved in emotional states: increased serotonin in the right amygdala is related to anxiety, while cortical dopamine may be associated with attention to the environment.     

Kindling with the beta-carboline FG7142 suggests separation between changes in seizure threshold and anxiety-related behaviour

The aim of this paper was to determine whether the prolonged decrease in seizure threshold produced by chemical kindling was accompanied by behavioural changes in tests of anxiety and aggression. The responses of rats in five tests were examined after chronic treatment with the benzodiazepine inverse agonist FG7142. This treatment caused chemical kindling, so that the originally proconvulsant drug caused full seizures. This effect is very long-lasting, and our previous work with mice had suggested that it might be accompanied by an increase in anxiety-related behavior. In the present work no significant differences were found between the behaviour of FG7142-kindled rats and vehicle-treated controls in social interaction test, elevated plus maze, or the Vogel conflict test of anxiety or in tests of home cage aggression or startle responses. The results therefore show that prolonged changes in seizure threshold can occur without alterations in the apparent level of anxiety.     

Age-dependent measures of anxiety and cognition in male histidine decarboxylase knockout (Hdc-/-) mice

Histidine decarboxylase deficient (Hdc(-/-)) and wild-type male mice on the C57Bl6/J background were used to determine the role of histamine in brain function. 3-5 (Y) and 12-14 (MA) month-old Hdc(-/-) mice showed hypoactivity and increased measures of anxiety in the open field, light-dark, elevated plus-maze, and elevated zero maze tests. Y Hdc(-/-) mice showed superior performance in the hidden sessions of the water maze and passive avoidance memory retention. In contrast, Y Hdc(-/-) mice were impaired in novel location recognition, spent less time searching in the target quadrant and more time searching in the outer zone of the water maze during the probe trials. These behaviors are likely due to increased measures of anxiety and are not found in MA Hdc(-/-) mice. These data support a role for histamine in anxiety and cognition and underline the importance of considering age and potential effects on measures of anxiety in the interpretation of the role of histaminergic neurotransmission in cognitive function.     

Gabrb3 gene deficient mice exhibit increased risk assessment behavior, hypotonia and expansion of the plexus of locus coeruleus dendrites

Gabrb3 gene deficient (gabrb3(-/-)) mice, control littermates (gabrb3(+/+)) and their progenitor strains C57Bl/6J and 129/SvJ were assessed for changes in the morphology of the main noradrenergic nuclei, the locus coeruleus (LC) and LC-associated behaviors including anxiety and muscle tone. While the area defined by the cell bodies of the LC was found not to differ between gabrb3(-/-) mice and controls, the pericoerulear dendritic zone of the LC was found to be significantly enlarged in gabrb3(-/-) mice. Relative to controls, gabrb3(-/-) mice were also found to be hypotonic, as was indicated by poor performance on the wire hanging task. Gabrb3(-/-) mice also exhibited a significant increase in stretch-attend posturing, a form of risk assessment behavior associated with anxiety. However, in the plus maze, a commonly used behavioral test for assessing anxiety, no significant difference was observed between gabrb3(-/-) and control mice. Lastly, relative to controls, gabrb3(-/-) mice exhibited significantly less marble burying behavior, a method commonly used to assess obsessive-compulsive behavior. However, the poor marble burying performance of the gabrb3(-/-) mice could be associated with the hypotonic condition exhibited by these mice. In conclusion, the results of this study indicate that the gabrb3 gene contributes to LC noradrenergic dendrite development with the disruption of this gene in mice resulting in an enlarged plexus of LC dendrites with a concurrent reduction in muscle tone and marble burying behavior, an increase in risk assessment behavior but no change in the plus maze parameters that are commonly used for assessing anxiety.     

Excessive novelty-induced c-Fos expression and altered neurogenesis in the hippocampus of GluA1 knockout mice

α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor GluA1 subunit-deficient (GluA1-/-) mice display novelty-induced hyperactivity, cognitive and social defects and may model psychiatric disorders, such as schizophrenia and depression/mania. We used c-Fos expression in GluA1-/- mice to identify brain regions responsible for novelty-induced hyperlocomotion. Exposure to a novel cage for 2 h significantly increased c-Fos expression in many brain regions in both wild-type and knockout mice. Interestingly, the clearest genotype effect was observed in the hippocampus and its main input region, the entorhinal cortex, where the novelty-induced c-Fos expression was more strongly enhanced in GluA1-/- mice. Their novelty-induced hyperlocomotion partly depended on the activity of AMPA receptors, as it was diminished by the AMPA receptor antagonist 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulphonamide (NBQX) and unaffected by the AMPA receptor potentiator 2,3-dihydro-1,4-benzodioxin-6-yl-1-piperidinylmethanone (CX546). The hyperlocomotion of GluA1-/- mice was normalised to the level of wild-type mice within 5-6 h, after which their locomotion followed normal circadian rhythm and was not affected by acute or chronic treatments with the selective serotonin reuptake inhibitor escitalopram. We propose that hippocampal dysfunction, as evidenced by the excessive c-Fos response to novelty, is the major contributor to novelty-induced hyperlocomotion in GluA1-/- mice. Hippocampal dysfunction was also indicated by changes in proliferation and survival of adult-born dentate gyrus cells in the knockout mice. These results suggest focusing on the functions of hippocampal formation, such as novelty detection, when using the GluA1-/- mouse line as a model for neuropsychiatric and cognitive disorders.     

Neurobehavioral alterations in mice with a targeted deletion of the tumor necrosis factor-alpha gene: implications for emotional behavior

Tumor necrosis factor-alpha (TNF-alpha) is emerging as an important modulator of the function of the central nervous system. In the present study, we investigated a role of endogenous TNF-alpha in cognitive and emotional function using mice with targeted deletions of the TNF-alpha gene. TNF-alpha-(-/-) mice showed normal diurnal rhythms of spontaneous locomotor activity and cognitive functions. Emotional behavior in the mutant mice, however, was significantly altered, which manifested in the performance in the open-field, elevated plus maze, and forced swimming tests. The altered performance in the elevated plus maze test was significantly alleviated by treatment with diazepam. Postmortem brain analysis of TNF-alpha-(-/-) mice revealed a significant increase in serotonin metabolism in the brain. These findings suggest a role for endogenous TNF-alpha in emotional behavior, which may possibly be related to alterations of serotonine metabolism.     

Exaggerated aggression and decreased anxiety in mice deficient in brain serotonin

Serotonin is a major neurotransmitter in the central nervous system (CNS). Dysregulation of serotonin transmission in the CNS is reported to be related to different psychiatric disorders in humans including depression, impulsive aggression and anxiety disorders. The most frequently prescribed antidepressants and anxiolytics target the serotonergic system. However, these drugs are not effective in 20–30% of cases. The causes of this failure as well as the molecular mechanisms involved in the origin of psychological disorders are poorly understood. Biosynthesis of serotonin in the CNS is initiated by tryptophan hydroxylase 2 (TPH2). In this study, we used Tph2-deficient (Tph2^−/−) mice to evaluate the impact of serotonin depletion in the brain on mouse behavior. Tph2^−/− mice exhibited increased depression-like behavior in the forced swim test but not in the tail suspension test. In addition, they showed decreased anxiety-like behavior in three different paradigms: elevated plus maze, marble burying and novelty-suppressed feeding tests. These phenotypes were accompanied by strong aggressiveness observed in the resident–intruder paradigm. Despite carrying only one copy of the gene, heterozygous Tph2^+/− mice showed only 10% reduction in brain serotonin, which was not sufficient to modulate behavior in the tested paradigms. Our findings provide unequivocal evidence on the pivotal role of central serotonin in anxiety and aggression.     

The group II metabotropic glutamate receptor agonist LY354740 and the D2 receptor antagonist haloperidol reduce locomotor hyperactivity but fail to rescue spatial working memory in GluA1 knockout mice

Group II metabotropic glutamate receptor agonists have been suggested as potential anti‐psychotics, at least in part, based on the observation that the agonist LY354740 appeared to rescue the cognitive deficits caused by non‐competitive N‐methyl‐d ‐aspartate receptor (NMDAR) antagonists, including spatial working memory deficits in rodents. Here, we tested the ability of LY354740 to rescue spatial working memory performance in mice that lack the GluA1 subunit of the AMPA glutamate receptor, encoded by Gria1, a gene recently implicated in schizophrenia by genome‐wide association studies. We found that LY354740 failed to rescue the spatial working memory deficit in Gria1^?/? mice during rewarded alternation performance in the T‐maze. In contrast, LY354740 did reduce the locomotor hyperactivity in these animals to a level that was similar to controls. A similar pattern was found with the dopamine receptor antagonist haloperidol, with no amelioration of the spatial working memory deficit in Gria1^?/? mice, even though the same dose of haloperidol reduced their locomotor hyperactivity. These results with LY354740 contrast with the rescue of spatial working memory in models of glutamatergic hypofunction using non‐competitive NMDAR antagonists. Future studies should determine whether group II mGluR agonists can rescue spatial working memory deficits with other NMDAR manipulations, including genetic models and other pharmacological manipulations of NMDAR function.     

Mice expressing the A53T mutant form of human alpha‐synuclein exhibit hyperactivity and reduced anxiety‐like behavior

Genetic mutations associated with α‐synuclein (α‐Syn) are implicated in the pathogenesis of Parkinson's disease (PD). PD is primarily a movement disorder, but patients are known to experience anxiety and other mood disorders. In this study, we examined the effect of the hA53T mutation during development by analyzing the protein expression of norepinephrine (NET), serotonin (SERT), and dopamine (DAT) transporters in addition to assessing locomotor and anxiety‐like behavior. We observed significant decreases in DAT expression at 8 months in transgenic animals compared with normal and younger mice. We used the elevated plus maze, open‐field test, and rotarod apparatus to evaluate wild‐type and hA53T hemizygous mice at 2, 8, and 12 months of age. Our results showed that 12‐month‐old transgenic mice spend more time in the open arms and display a greater number of open entries of the elevated plus maze compared with wild‐type controls and younger mice. Open‐field test results showed that 12‐month‐old mice travel a greater distance overall and travel more in the inner zone than either wild‐type or younger mice. Rotarod testing showed that 8‐ and 12‐month‐old transgenic mice perform better than either wild‐type controls or younger mice. Overall, 8–12‐month‐old transgenic mice showed a trend toward reduced anxiety‐like behavior and increased hyperactivity. These results indicate a possible role of the A53T α‐Syn mutation in anxiety‐like and hyperactive behaviors in a PD mouse model, suggesting that these behaviors might be comorbid with this disease. © 2010 Wiley‐Liss, Inc.     

Enhancement of Aggression Induced by Isolation Rearing is Associated with a Lack of Central Serotonin

Isolation rearing(IR) enhances aggressive behavior, and the central serotonin(5-hydroxytryptamine,5-HT) system has been linked to IR-induced aggression.However, whether the alteration of central serotonin is the cause or consequence of enhanced aggression is still unknown. In the present study, using mice deficient in central serotonin Tph2-/-and Lmx1 b-/-, we examined the association between central serotonin and aggression with or without social isolation. We demonstrated that central serotonergic neurons are critical for the enhanced aggression after IR. 5-HT depletion in wild-type mice increased aggression. On the other hand, application of 5-HT in Lmx1 b-/-mice inhibited the enhancement of aggression under social isolation conditions. Dopamine was downregulated in Lmx1 b-/-mice. Similar to 5-HT, L-DOPA decreased aggression in Lmx1 b-/-mice. Our results linkthe serotoninergic system directly to aggression and this may have clinical implications for aggression-related human conditions.     

Emotional behavior and expression patterns of tyrosine hydroxylase and tryptophan hydroxylase in senescence-accelerated mouse (SAM) P6 mice

Senescence-accelerated prone mouse 6 (SAMP6) is a model for senile osteoporosis. It was recently reported that SAMP6 has a memory deficit in the water maze test. Because emotion and cognition are thought to interact, in the present study to examine emotional behavior in SAMP6, we employed a battery of tasks (open field, elevated plus maze, light-dark exploration, marble-burying behavior, tail suspension), using three age groups (1, 4, and 8 months of age) of SAMP6 mice and age-matched control SAMR1 (senescence-accelerated resistant mouse 1) mice. All three age groups of SAMP6 showed higher activity than SAMR1 in the open field test and reduced anxiety as measured in terms of time spent on the open arms in the elevated plus maze, time spent in the light box in the light-dark exploration, and time spent in marble-burying behavior in the marble-burying test. All three age groups of SAMP6 showed reduced immobility time compared with SAMR1 in the tail suspension test. Western blot analyses showed increased expression levels of tyrosine hydroxylase phosphorylated at serine-40 in striatum and nucleus accumbens and of tryptophan hydroxylase phosphorylated at serine-58 in brain stem of 1-month-old SAMP6. These results suggest that one possible reason for the alterations of motor activity and emotional behavior of SAMP6, at least after 1 month of age, is increased dopamine and serotonin levels.     

Normal inhibitory avoidance learning and anxiety, but increased locomotor activity in mice devoid of PrP(C).

Prions are the causative agents of transmissible spongiform encephalopathies. The transmissible agent (PrP(Sc)) is an abnormal form of PrP(C), a normal neuronal protein. The physiological role of PrP(C) remains unclear. In the present report, we evaluated behavioral parameters in Prnp(0/0) mice devoid of PrP(C). Prnp(0/0) mice showed normal short- and long-term retention of a step-down inhibitory avoidance task and normal behavior in an elevated plus maze test of anxiety. During a 5-min exploration of an open field, Prnp(0/0) mice showed normal number of rearings, defecation, and latency to initiate locomotion, but a significant increase in the number of crossings. The results suggest that Prnp(0/0) mice show normal fear-motivated memory, anxiety and exploratory behavior, and a slight increase in locomotor activity during exploration of a novel environment.