Repetitive Self-Grooming Behavior in the BTBR Mouse Model of Autism is Blocked by the mGluR5 Antagonist MPEP

Autism is a neurodevelopmental disorder characterized by abnormal reciprocal social interactions, communication deficits, and repetitive behaviors with restricted interests. BTBR T+tf/J (BTBR) is an inbred mouse strain that shows robust behavioral phenotypes with analogies to all three of the diagnostic symptoms of autism, including well-replicated deficits in reciprocal social interactions and social approach, unusual patterns of ultrasonic vocalization, and high levels of repetitive self-grooming. These phenotypes offer straightforward behavioral assays for translational investigations of pharmacological compounds. Two suggested treatments for autism were evaluated in the BTBR mouse model. Methyl-6-phenylethynyl-pyridine (MPEP), an antagonist of the mGluR5 metabotropic glutamate receptor, blocks aberrant phenotypes in the Fmr1 mouse model of Fragile X, a comorbid neurodevelopmental disorder with autistic features. Risperidone has been approved by the United States Food and Drug Administration for the treatment of irritability, tantrums, and self-injurious behavior in autistic individuals. We evaluated the actions of MPEP and risperidone on two BTBR phenotypes, low sociability and high repetitive self-grooming. Open field activity served as an independent control for non-social exploratory activity and motor functions. C57BL/6J (B6), an inbred strain with high sociability and low self-grooming, served as the strain control. MPEP significantly reduced repetitive self-grooming in BTBR, at doses that had no sedating effects on open field activity. Risperidone reduced repetitive self-grooming in BTBR, but only at doses that induced sedation in both strains. No overall improvements in sociability were detected in BTBR after treatment with either MPEP or risperidone. Our findings suggest that antagonists of mGluR5 receptors may have selective therapeutic efficacy in treating repetitive behaviors in autism.     

GABAB Receptor Agonist R-Baclofen Reverses Social Deficits and Reduces Repetitive Behavior in Two Mouse Models of Autism

Autism spectrum disorder (ASD) is diagnosed by two core behavioral criteria, unusual reciprocal social interactions and communication, and stereotyped, repetitive behaviors with restricted interests. Excitatory/inhibitory imbalance is a prominent hypothesis for the etiology of autism. The selective GABA_B receptor agonist R-baclofen previously reversed social deficits and reduced repetitive behaviors in a mouse model of Fragile X syndrome, and Arbaclofen improved some clinical symptoms in some Fragile X and ASD patients. To evaluate R-baclofen in a broader range of mouse models of ASD, we tested both the R-baclofen enantiomer and the less potent S-baclofen enantiomer in two inbred strains of mice that display low sociability and/or high repetitive or stereotyped behaviors. R-baclofen treatment reversed social approach deficits in BTBR T+ Itpr3tf/J (BTBR), reduced repetitive self-grooming and high marble burying scores in BTBR, and reduced stereotyped jumping in C58/J (C58), at nonsedating doses. S-baclofen produced minimal effects at the same doses. These findings encourage investigations of R-baclofen in other preclinical model systems. Additional clinical studies may be warranted to further evaluate the hypothesis that the GABA_B receptor represents a promising pharmacological target for treating appropriately stratified subsets of individuals with ASD.     

AMPAKINE enhancement of social interaction in the BTBR mouse model of autism

Autism is a neurodevelopmental disorder in which the first diagnostic symptom is unusual reciprocal social interactions. Approximately half of the children diagnosed with an autism spectrum disorder also have intellectual impairments. General cognitive abilities may be fundamental to many aspects of social cognition. Cognitive enhancers could conceivably be of significant benefit to children and adults with autism. AMPAKINE compounds are a novel class of pharmacological agents that act as positive modulators of AMPA receptors to enhance excitatory glutamatergic neurotransmission. This class of compounds was reported to improve learning and memory in several rodent and non-human primate tasks, and to normalize respiratory abnormalities in a mouse model of Rett syndrome. Here we evaluate the actions of AMPA compounds in adult male and female BTBR mice, a well characterized mouse model of autism. Acute treatment with CX1837 and CX1739 reversed the deficit in sociability in BTBR mice on the most sensitive parameter, time spent sniffing a novel mouse as compared to time spent sniffing a novel object. The less sensitive parameter, time in the chamber containing the novel mouse versus time in the chamber containing the novel object, was not rescued by CX1837 or CX1739 treatment. Preliminary data with CX546, in which β-cyclodextrin was the vehicle, revealed behavioral effects of the acute intraperitoneal and oral administration of vehicle alone. To circumvent the artifacts introduced by the vehicle administration, we employed a novel treatment regimen using pellets of peanut butter for drug delivery. Absence of vehicle treatment effects when CX1837 and CX1739 were given in the peanut butter pellets, to multiple cohorts of BTBR and B6 control mice, confirmed that the pharmacologically-induced improvements in sociability in BTBR were not confounded by the administration procedures. The highest dose of CX1837 improved the cognitive deficit in novel object recognition in BTBR. No drug effects were detected on the high levels of repetitive self-grooming in BTBR. In open field tests, CX1837 and CX1739 did not induce hyperactivity or sedation in either strain. It is interesting to speculate that the ability of CX1837 and CX1739 to restore aspects of sociability in BTBR mice could utilize synaptic mechanisms regulating social cognition, suggesting a potential pharmacological target for interventions to treat symptoms of autism. This article is part of a Special Issue entitled 'Cognitive Enhancers'.     

Effects of the Partial M1 Muscarinic Cholinergic Receptor Agonist CDD-0102A on Stereotyped Motor Behaviors and Reversal Learning in the BTBR Mouse Model of Autism

BackgroundAutism spectrum disorders (ASD) are a set of neurodevelopmental disorders marked by a lack of social interaction, restrictive interests, and repetitive behaviors. There is a paucity of pharmacological treatments to reduce core ASD symptoms. Various lines of evidence indicate that reduced brain muscarinic cholinergic receptor activity may contribute to an ASD phenotype.MethodsThe present experiments examined whether the partial M₁ muscarinic receptor agonist, 5-(3-ethyl-1,2,4-oxadiazol-5-yl)-1,4,5,6-tetrahydropyrimidine hydrochloride (CDD-0102A), alleviates behavioral flexibility deficits and/or stereotyped motor behaviors in the BTBR mouse model of autism. Behavioral flexibility was tested using a reversal learning test. Stereotyped motor behaviors were measured by eliciting digging behavior after removal of nesting material in a home cage and by measuring repetitive grooming.ResultsCDD-0102A (0.2 and 0.6 mg/kg but not 1.2 mg/kg) injected prior to reversal learning attenuated a deficit in BTBR mice but did not affect performance in B6 mice. Acute CDD-0102A treatment (1.2 and 3 mg/kg) reduced self-grooming in BTBR mice and reduced digging behavior in B6 and BTBR mice. The M₁ muscarinic receptor antagonist VU0255035 (3 mg/kg) blocked the effect of CDD-0102A on grooming behavior. Chronic treatment with CDD-0102A (1.2 mg/kg) attenuated self-grooming and digging behavior in BTBR mice. Direct CDD-0102A infusions (1 µg) into the dorsal striatum reduced elevated digging behavior in BTBR mice. In contrast, CDD-0102A injections in the frontal cortex were not effective.ConclusionsThe results suggest that treatment with a partial M₁ muscarinic receptor agonist may reduce repetitive behaviors and restricted interests in autism in part by stimulating striatal M₁ muscarinic receptors.     

Influence of nitric oxide agents in the dorsal hippocampus of mice on anxiogenic-like effect induced by histamine

Histaminergic receptors and neuronal nitric oxide synthase (nNOS) are co-expressed at high levels in the hippocampal neurons and alter anxiety-like behaviors in rodents. Since the dorsal hippocampus may be involved in modulation of anxiety-like behaviors, the aim of the present study was to assess whether the nitric oxide (NO) system in the dorsal hippocampus affects anxiety-like behaviors induced by histaminergic agents in mice. The effects of the NO precursor, L-arginine and NOS inhibitor, L-nitro-amino-methyl-ester (L-NAME) on histamine, pyrilamine and ranitidine responses in elevated plus maze (E.P.M.) in mice were investigated. Intra-CA1 microinjection of histamine (9 μg/mouse) or H1 receptor antagonist, pyrilamine (3, 6 and 9 μg/mouse), but not H2 receptor antagonist, ranitidine decreased the percentage of open arm time (%OAT) and open arm entries (%OAE), without affecting locomotor activity, suggesting an anxiogenic-like response. Both L-arginine (0.4 and 0.8 μg/mouse) and L-NAME (40 ng/mouse) when injected into the dorsal hippocampus induced anxiety-like behaviors, but the drugs reversed the anxiogenic response induced by the effective dose of histamine (9 μg/mouse) or pyrilamine (9 μg/mouse). Our results also indicated that intra-CA1 administration of L-arginine and L-NAME, in the presence or absence of ranitidine, exerted an anxiogenic effect. The results may indicate a modulatory role for NO in the dorsal hippocampus in the anxiogenic-like response induced by histamine or pyrilamine.     

Post-weaning environmental enrichment alters affective responses and interacts with behavioral testing to alter nNOS immunoreactivity

Challenging early life events can dramatically affect mental health and wellbeing. Childhood trauma and neglect can increase the risk for developing depressive, anxiety, and substance abuse disorders. Early maternal separation in rodents has been extensively studied and induces long-lasting alterations in affective and stress responses. However, other developmental periods (e.g., the pubertal period) comprise a critical window whereby social and environmental complexity can exert lasting changes on the brain and behavior. In this study, we tested whether early life environmental complexity impacts affective responses, aggressive behaviors, and expression of neuronal nitric oxide synthase (nNOS), the synthetic enzyme for nitric oxide, in adulthood. Mice were weaned into social + nonsocial enrichment, social only enrichment, or standard (isolated) laboratory environments and were tested in open field, elevated plus maze, forced swim, and resident-intruder aggression tests 60 days later. Social + nonsocial enrichment reduced locomotor behavior and anxiety-like responses in the open field and reduced depressive-like responses in the forced swim test. Social housing increased open arm exploration in the elevated plus maze. Both social + nonsocial enrichment and social housing only reduced aggressive behaviors compared with isolation. Social + nonsocial enrichment also increased body mass gain throughout the study. Finally, socially-housed mice had reduced corticosterone concentrations compared with social + nonsocial-enriched mice. Behavioral testing reduced nNOS-positive neurons in the basolateral amygdala and the ventral lateral septum, but not in the social + nonsocial-enriched mice, suggesting that environmental complexity may buffer the brain against some environmental perturbations.     

Mice lacking the serotonin transporter exhibit 5-HT(1A) receptor-mediated abnormalities in tests for anxiety-like behavior.

The serotonin transporter (5-HTT) regulates serotonergic neurotransmission via clearance of extracellular serotonin. Abnormalities in 5-HTT expression or function are found in mood and anxiety disorders, and the 5-HTT is a major target for antidepressants and anxiolytics. The 5-HTT is further implicated in the pathophysiology of these disorders by evidence that genetic variation in the promoter region of the HTT (SLC6A4) is associated with individual differences in anxiety and neural responses to fear. To further evaluate the role of the 5-HTT in anxiety, we employed a mouse model in which the 5-HTT gene (htt) was constitutively inactivated. 5-HTT -/- mice were characterized for anxiety-related behaviors using a battery of tests (elevated plus maze, light<-->dark exploration test, emergence test, and open field test). Male and female 5-HTT -/- mice showed robust phenotypic abnormalities as compared to +/+ littermates, suggestive of increased anxiety-like behavior and inhibited exploratory locomotion. The selective 5-HT(1A) receptor antagonist, WAY 100635 (0.05-0.3 mg/kg), produced a significant anxiolytic-like effect in the elevated plus maze in 5-HTT -/- mice, but not +/+ controls. The present findings demonstrate abnormal behavioral phenotypes in 5-HTT null mutant mice in tests for anxiety-like and exploratory behavior, and suggest a role for the 5-HT(1A) receptor in mediating these abnormalities. 5-HTT null mutant mice provide a model to investigate the role of the 5-HTT in mood and anxiety disorders.     

Withdrawal from repeated treatment with amphetamine reduces novelty-seeking behavior and enhances environmental habituation in mice

Anhedonia associated with a dysphoric state is an important feature of amphetamine withdrawal in humans. We aimed to investigate the effects of amphetamine withdrawal on two motivation-related behaviors in mice: novelty seeking and environmental habituation. Because anxiety can interfere with the behavioral outcome of other tasks, amphetamine-withdrawn mice were also evaluated in the elevated plus maze. Swiss male mice (three months old) were treated with 2.0 mg/kg amphetamine for 13 days, every other day, in their home cages (a total of seven injections). Twenty-four hours after withdrawal from drug treatment, mice were tested in a free-choice novelty apparatus containing one familiar and one novel compartment or in the elevated plus maze. Novelty-seeking behavior was assessed by comparing the time spent in the novel compartment vs. the familiar compartment, whereas environmental habituation was concomitantly evaluated by the time-response curve of total locomotion (novel + familiar). Novelty seeking was decreased during amphetamine withdrawal, and this result was not associated with changes in the anxiety-like behavior of mice. Additionally, amphetamine withdrawal enhanced environmental habituation. The concomitant decrease in novelty seeking and the increase in environmental habituation seem to be related to amphetamine withdrawal-induced anhedonia. Thus, the model proposed here could be used as a tool for the study of mechanisms and potential treatment of the anhedonic behavioral consequences of psychostimulant withdrawal.     

Blockade of CRF1 and CCK2 receptors attenuated the elevated anxiety-like behavior induced by immobilization stress

Two highly co-localized neurotransmitters: corticotropin-releasing factor (CRF) and cholecystokinin (CCK), have been implicated in the development of stress-related anxiety disorders. This study was designed to examine the role of CRF1 and CCK2 receptors on the anxiety-like behavior induced by immobilization stress. Our results showed that 30-min immobilization enhanced the anxiety-like behavior in C57BL/6J mice examined in the elevated plus maze (EPM). The combined pretreatment of CR2945 (a CCK2 receptor antagonist) and antalarmin (a CRF1 receptor antagonist) fully blocked this elevated anxiety-like behavior, while the application of CR2945 or antalarmin alone showed only partial effects. The increased expression of CRF1 and CCK2 receptors at protein levels in three anxiety-related brain regions: cortex, hippocampus and hypothalamus, was detected by Western blot. The increased mRNA expression of CCK, CRF, CCK2 and CRF1 receptors was also examined by real-time RT-PCR. Our study demonstrated that the blockade of CRF1 and CCK2 receptors attenuated the elevated anxiety-like behavior induced by immobilization stress, suggestive of the CRF and CCK systems contributing to the development of stress-related anxiety behavior.     

Co-learning facilitates memory in mice: A new avenue in social neuroscience

Social context affects brain function but our understanding of its neurobiology is at an early stage. The mere presence of one individual can alter the cognitive capacities of another and social learning has been demonstrated in many species, including the mouse. We asked several questions: 1. How can active engagement of two familiar mice in the same learning activity (co-learning) alter their memory? 2. Under which environmental conditions (aversive vs non-aversive) can we expect the memory to be enhanced, impaired, or not affected? 3. Can a genetic factor modify the co-learning effect on memory? More specifically, can co-learning correct memory deficits in autistic-like BTBR inbred mice with deficient sociability? We demonstrated that pairs of familiar inbred mice of the same or different genotypes (C57BL/6J and BTBR) that were habituated to new objects and their spatial location, had enhanced episodic memory in the spatial object recognition test, whereas individually-trained animals failed to solve this task. Notably, the co-learning effect was genotype-dependent. BTBR mice paired with BTBR cage-mates in the habituation session modestly ameliorated their performance in the object recognition test but co-learning with a familiar C57BL/6J mouse completely normalized episodic memory deficit. Next, we explored the co-learning effect on fear memory in these inbred strains. Interestingly, mice of both genotypes displayed significantly enhanced contextual fear memory once they had been conditioned together with BTBR animals. The same influence of BTBR presence was observed on cued fear memory in C57BL/6J mice, whereas a modest co-learning effect was found on cued fear conditioning in the BTBR strain. Taken together, we demonstrated for the first time the co-learning effect on cognitive capacities in mice, which can be modified by genetic background and environmental conditions. The possible implications of this methodological approach in social neuroscience are discussed. This article is part of a Special Issue entitled 'Cognitive Enhancers'.     

Acetylcholine Elevation Relieves Cognitive Rigidity and Social Deficiency in a Mouse Model of Autism

Autism spectrum disorders (ASD) are defined by behavioral deficits in social interaction and communication, repetitive stereotyped behaviors, and restricted interests/cognitive rigidity. Recent studies in humans and animal-models suggest that dysfunction of the cholinergic system may underlie autism-related behavioral symptoms. Here we tested the hypothesis that augmentation of acetylcholine (ACh) in the synaptic cleft by inhibiting acetylcholinesterase may ameliorate autistic phenotypes. We first administered the acetylcholinesterase inhibitor (AChEI) Donepezil systemically by intraperitoneal (i.p.) injections. Second, the drug was injected directly into the rodent homolog of the caudate nucleus, the dorsomedial striatum (DMS), of the inbred mouse strain BTBR T+tf/J (BTBR), a commonly-used model presenting all core autism-related phenotypes and expressing low brain ACh levels. We found that i.p. injection of AChEI to BTBR mice significantly relieved autism-relevant phenotypes, including decreasing cognitive rigidity, improving social preference, and enhancing social interaction, in a dose-dependent manner. Microinjection of the drug directly into the DMS, but not into the ventromedial striatum, led to significant amelioration of the cognitive-rigidity and social-deficiency phenotypes. Taken together, these findings provide evidence of the key role of the cholinergic system and the DMS in the etiology of ASD, and suggest that elevated cognitive flexibility may result in enhanced social attention. The potential therapeutic effect of AChEIs in ASD patients is discussed.     

Enhancing the value of psychiatric mouse models; differential expression of developmental behavioral and cognitive profiles in four inbred strains of mice

The behavioral characterization of animal models of psychiatric disorders is often based upon independent traits measured at adult age. To model the neurodevelopmental aspects of psychiatric pathogenesis, we introduce a novel approach for a developmental behavioral analysis in mice. C57BL/6J (C57) mice were used as a reference strain and compared with 129S1/SvImJ (129Sv), BTBR T+tf/J (BTBR) and A/J (AJ) strains as marker strains for aberrant development. Mice were assessed at pre-adolescence (4 weeks), adolescence (6 weeks), early adulthood (8 weeks) and in adulthood (10–12 weeks) on a series of behavioral tasks measuring general health, neurological reflexes, locomotor activity, anxiety, short- and long-term memory and cognitive flexibility. Developmental delays in short-term object memory were associated with either a hypo-reactive profile in 129Sv mice or a hyper-reactive profile in BTBR mice. Furthermore, BTBR mice showed persistent high levels of repetitive grooming behavior during all developmental stages that was associated with the adult expression of cognitive rigidity. In addition, strain differences in development were observed in puberty onset, touch escape, and body position. These data showed that this longitudinal testing battery provides sufficient behavioral and cognitive resolution during different development stages and offers the opportunity to address the behavioral developmental trajectory in genetic mouse models for neurodevelopmental disorders. Furthermore, the data revealed that the assessment of multiple behavioral and cognitive domains at different developmental stages is critical to determine confounding factors (e.g., impaired motor behavior) that may interfere with the behavioral testing performance in mouse models for brain disorders.     

Consequences of cannabinoid and monoaminergic system disruption in a mouse model of autism spectrum disorders

Autism spectrum disorders (ASDs) are heterogenous neurodevelopmental disorders characterized by impairment in social, communication skills and stereotype behaviors. While autism may be uniquely human, there are behavioral characteristics in ASDs that can be mimicked using animal models. We used the BTBR T+tf/J mice that have been shown to exhibit autism-like behavioral phenotypes to 1). Evaluate cannabinoid-induced behavioral changes using forced swim test (FST) and spontaneous wheel running (SWR) activity and 2). Determine the behavioral and neurochemical changes after the administration of MDMA (20 mg/kg), methamphetamine (10 mg/kg) or MPTP (20 mg/kg). We found that the BTBR mice exhibited an enhanced basal spontaneous locomotor behavior in the SWR test and a reduced depressogenic profile. These responses appeared to be enhanced by the prototypic cannabinoid, Δ(9)-THC. MDMA and MPTP at the doses used did not modify SWR behavior in the BTBR mice whereas MPTP reduced SWR activity in the control CB57BL/6J mice. In the hippocampus, striatum and frontal cortex, the levels of DA and 5-HT and their metabolites were differentially altered in the BTBR and C57BL/6J mice. Our data provides a basis for further studies in evaluating the role of the cannabinoid and monoaminergic systems in the etiology of ASDs.     

The effects of phencyclidine (PCP) on anxiety-like behavior in the elevated plus maze and the light-dark exploration test are age dependent, sexually dimorphic, and task dependent

Previous research in our laboratory revealed sexually dimorphic effects of prior exposure to phencyclidine (PCP) on elevated plus maze behavior. In an attempt to examine the developmental time course of this effect and determine the extent to which it generalizes to other anxiety paradigms, young adult (61-64 days old) and adult (96-107 days old) male and female rats were treated with PCP (15 mg/kg) or saline. Following a two week withdrawal period, animals were tested in either the elevated plus maze (EPM) or a light-dark exploration (LD) test. In adults, both tests revealed a sexually dimorphic effect driven by PCP-induced decreases in anxiety in females as indicated by increased time spent in the open arms of the EPM and in the lit compartment of the LD test and increased anxiety in males as indicated by decreased time spent in the lit compartment of the LD. In young animals, PCP pretreatment decreased open arm exploration in the elevated plus maze, indicating increased anxiety. However, PCP increased time spent in the light compartment in the light-dark exploration test, indicating decreased anxiety. Corticosterone levels measured 15 min after the onset of the EPM failed to reveal an association between the behavioral effects of PCP and corticosterone levels. The results in adults substantiate the previously observed sexually dimorphic effect of PCP on elevated plus maze behavior in adults and indicate that the effect generalizes to another anxiety paradigm. The results in the younger animals suggest an age dependent effect of PCP on anxiety in general and indicate that behaviors in the elevated plus maze and the light-dark exploration test reflect dissociable psychobiological states.     

Relationship between Rgs2 gene expression level and anxiety and depression-like behaviour in a mutant mouse model: serotonergic involvement

RGS2 is a member of a family of proteins that negatively modulate G-protein coupled receptor transmission. Variations in the RGS2 gene were found to be associated in humans with anxious and depressive phenotypes. We sought to study the relationship of Rgs2 expression level to depression and anxiety-like behavioural features, sociability and brain 5-HT1A and 5-HT1B receptor expression. We studied male mice carrying a mutation that causes lower Rgs2 gene expression, employing mice heterozygous (Het) or homozygous (Hom) for this mutation, or wild-type (WT). Mice were subjected to behavioural tests reflecting depressive-like behaviour [forced swim test (FST), novelty suppressed feeding test (NSFT)], elevated plus maze (EPM) for evaluation of anxiety levels and the three-chamber sociability test. The possible involvement of raphe nucleus 5-HT1A receptors in these behavioural features was examined by 8-OH-DPAT-induced hypothermia. Expression levels of 5-HT1A and 5-HT1B receptors in the cortex, raphe nucleus and hypothalamus were compared among mice of the different Rgs2 genotype groups. NSFT results demonstrated that Hom mice showed more depressive-like features than Rgs2 Het and WT mice. A trend for such a relationship was also suggested by the FST results. EPM and sociability test results showed Hom and Het mice to be more anxious and less sociable than WT mice. In addition Hom and Het mice were characterized by lower basal body temperature and demonstrated less 8-OH-DPAT-induced hypothermia than WT mice. Finally, Hom and Het mice had significantly lower 5-HT1A and 5-HT1B receptor expression levels in the raphe than WT mice. Our findings demonstrate a relationship between Rgs2 gene expression level and a propensity for anxious and depressive-like behaviour and reduced social interaction that may involve changes in serotonergic receptor expression.     

Environmental enrichment reverses behavioral alterations in rats prenatally exposed to valproic acid: issues for a therapeutic approach in autism.

Environmental enrichment has been repeatedly shown to affect multiple aspects of brain function, and is known to improve cognitive, behavioral, and histopathological outcome after brain injuries. The purpose of the present experiments was to determine the effect of an enriched environment on behavioral aberrations observed in male rats exposed to valproic acid on day 12.5 of gestation (VPA rats), and proposed on the basis of etiological, anatomical, and behavioral data as an animal model of autism. Environmental enrichment reversed almost all behavioral alterations observed in the model. VPA rats after environmental enrichment (VPA-E) compared to VPA rats reared in standard conditions have higher sensitivity to pain and lower sensitivity to nonpainful stimuli; stronger acoustic prepulse inhibition; lower locomotor, repetitive/stereotypic-like activity, and enhanced exploratory activity; decreased anxiety; increased number of social behaviors; and shorter latency to social explorations. In comparison with control animals (Con), VPA-E rats exhibited increased number of pinnings in adolescence and social explorations in adulthood, and were less anxious in the elevated plus maze. Similar differences in social behavior and anxiety were observed between control rats exposed to environmental enrichment (Con-E) and control group reared in standard conditions. These results suggest that postnatal environmental manipulations can counteract the behavioral alterations in VPA rats. We propose environmental enrichment as an important tool for the treatment of autism spectrum disorders.     

Galanin GAL-R1 receptor null mutant mice display increased anxiety-like behavior specific to the elevated plus-maze.

The neuropeptide galanin coexists with norepinephrine and serotonin in neural systems mediating emotion. Previous findings suggested that galanin modulates anxiety-related behaviors in rodents. Three galanin receptor subtypes have been cloned; however, understanding their functions has been limited by the lack of galanin receptor subtype-selective ligands. To study the role of the galanin GAL-R1 receptor subtype in mediating anxiety-related behavior, we generated mice with a null mutation in the Galr1 gene. GAL-R1 -/- are viable and show no abnormalities in health, neurological reflexes, motoric functions, or sensory abilities. On a battery of tests for anxiety-like behavior, GAL-R1 -/- showed increased anxiety-like behavior on the elevated plus-maze test. Anxiety-related behaviors on the light/dark exploration, emergence, and open field tests were normal in GAL-R1 -/-. This test-specific anxiety-like phenotype was confirmed in a second, independent cohort of GAL-R1 null mutant mice and +/+ controls. Principal components factor analysis of behavioral scores from 279 mice suggested that anxiety-like behavior on the elevated plus-maze was qualitatively distinct from behavior on other tests in the battery. In addition, exposure to the elevated plus-maze produced a significantly greater neuroendocrine response than exposure to the light/dark exploration test, as analyzed in normal C57BL/6J mice. These behavioral findings in the first galanin receptor null mutant mouse are consistent with the hypothesis that galanin exerts anxiolytic actions via the GAL-R1 receptor under conditions of relatively high stress.     

A comparison between Dark Agouti and Sprague-Dawley rats in their behaviour on the elevated plus-maze, open-field apparatus and activity meters, and their response to diazepam

RATIONALE: Preliminary unpublished studies in our laboratory suggested that the behaviour of Sprague-Dawley (SD) and Dark Agouti (DA) rats was markedly different on both the elevated plus maze and in the open-field apparatus. We wished to confirm and extend this initial finding. OBJECTIVE: The study was designed to examine the behaviour of SD and DA rats in the elevated plus maze, open-field apparatus and automated activity meters. The response of both strains on the elevated plus maze following diazepam (1 mg/kg and 1.5 mg/kg) administration was subsequently investigated. RESULTS: DA rats showed markedly greater anxiety-like behaviour than SD rats in both the plus maze and open field, with fewer percentage open/total arm entries and percentage time spent on open/total arms in the plus maze and fewer crossings in the open field. Acute handling plus administration of vehicle abolished this difference in anxiety levels, with DA rats showing similar open-arm behaviour to that of SD rats. Both strains demonstrated a clear anxiolytic response to diazepam (1 mg/kg) in terms of percentage time spent on the open arms, but only SD rats had a statistically significant increase in percentage open-arm entries compared with vehicle-injected control animals. CONCLUSIONS: While the high level of anxiety-like behaviour of DA rats versus SD rats could prove useful in future ethological studies on anxiety, the fact that acute handling decreased the anxiety-like behaviour on the elevated plus maze may limit the value of this strain for the study of putative anxiolytic drugs.     

Elevated anxiety-like behavior following ethanol exposure in mutant mice lacking neuropeptide Y (NPY)

BACKGROUND: Neuropeptide Y (NPY) is a neuromodulator with anxiolytic properties. Recent evidence suggests that NPY modulates neurobiological responses to ethanol. Because withdrawal from ethanol is associated with elevated anxiety-like behavior, and because central NPY modulates anxiety, we assessed anxiety-like behavior in mutant mice lacking normal production of NPY (NPY-/-) and in normal wild-type mice (NPY+/+) 6h after removal of a liquid diet containing 4.5% ethanol. METHODS: NPY-/- and NPY+/+ mice on a pure 129/SvEv genetic background were given 6 days of access to a liquid ethanol diet (ED) or control diet (CD). Six hours before elevated plus maze (EPM) testing, ED was replaced with CD in the ethanol-withdrawn group. RESULTS: Ethanol-withdrawn NPY-/- mice showed significantly less open arm time and total proportion of time spent in the open arm of the EPM relative to ethanol-withdrawn NPY+/+ mice and when compared to NPY-/- and NPY+/+ mice that had access to the CD. On the other hand, ethanol-withdrawn NPY+/+ mice did not show altered EPM behavior relative to controls. CONCLUSIONS: Central NPY is protective against anxiety-like behavior stemming from exposure to and/or withdrawal from ethanol. Targets aimed at NPY receptors may be useful compounds for treating anxiety associated with ethanol dependence.     

Long-Term Memory Deficits are Associated with Elevated Synaptic ERK1/2 Activation and Reversed by mGluR5 Antagonism in an Animal Model of Autism

A significant proportion of patients with autism exhibit some degree of intellectual disability. The BTBR T⁺ Itpr3^tf/J mouse strain exhibits behaviors that align with the major diagnostic criteria of autism. To further evaluate the BTBR strain''s cognitive impairments, we quantified hippocampus-dependent object location memory (OLM) and found that one-third of the BTBR mice exhibited robust memory, whereas the remainder did not. Fluorescence deconvolution tomography was used to test whether synaptic levels of activated extracellular signal-regulated kinase 1/2 (ERK1/2), a protein that contributes importantly to plasticity, correlate with OLM scores in individual mice. In hippocampal field CA1, the BTBRs had fewer post-synaptic densities associated with high levels of phosphorylated (p-) ERK1/2 as compared with C57BL/6 mice. Although counts of p-ERK1/2 immunoreactive synapses did not correlate with OLM performance, the intensity of synaptic p-ERK1/2 immunolabeling was negatively correlated with OLM scores across BTBRs. Metabotropic glutamate receptor (mGluR) 5 signaling activates ERK1/2. Therefore, we tested whether treatment with the mGluR5 antagonist MPEP normalizes synaptic and learning measures in BTBR mice: MPEP facilitated OLM and decreased synaptic p-ERK1/2 immunolabeling intensity without affecting numbers of p-ERK1/2+ synapses. In contrast, semi-chronic ampakine treatment, which facilitates memory in other models of cognitive impairment, had no effect on OLM in BTBRs. These results suggest that intellectual disabilities associated with different neurodevelopmental disorders on the autism spectrum require distinct therapeutic strategies based on underlying synaptic pathology.