Optogenetic insights on the relationship between anxiety-related behaviors and social deficits

CAV-2 Vector Development and Gene Transfer in the Central and Peripheral Nervous Systems

The options available for genetic modification of cells of the central nervous system (CNS) have greatly increased in the last decade. The current panoply of viral and nonviral vectors provides multifunctional platforms to deliver expression cassettes to many structures and nuclei. These cassettes can replace defective genes, modify a given pathway perturbed by diseases, or express proteins that can be selectively activated by drugs or light to extinguish or excite neurons. This review focuses on the use of canine adenovirus type 2 (CAV-2) vectors for gene transfer to neurons in the brain, spinal cord, and peripheral nervous system. We discuss (1) recent advances in vector production, (2) why CAV-2 vectors preferentially transduce neurons, (3) the mechanism underlying their widespread distribution via retrograde axonal transport, (4) how CAV-2 vectors have been used to address structure/function, and (5) their therapeutic applications.

Neural mechanisms of social homeostasis

Social connections are vital to survival throughout the animal kingdom and are dynamic across the life span. There are debilitating consequences of social isolation and loneliness, and social support is increasingly a primary consideration in health care, disease prevention, and recovery. Considering social connection as an "innate need," it is hypothesized that evolutionarily conserved neural systems underlie the maintenance of social connections: alerting the individual to their absence and coordinating effector mechanisms to restore social contact. This is reminiscent of a homeostatic system designed to maintain social connection. Here, we explore the identity of neural systems regulating "social homeostasis." We review findings from rodent studies evaluating the rapid response to social deficit (in the form of acute social isolation) and propose that parallel, overlapping circuits are engaged to adapt to the vulnerabilities of isolation and restore social connection. By considering the neural systems regulating other homeostatic needs, such as energy and fluid balance, we discuss the potential attributes of social homeostatic circuitry. We reason that uncovering the identity of these circuits/mechanisms will facilitate our understanding of how loneliness perpetuates long-term disease states, which we speculate may result from sustained recruitment of social homeostatic circuits.

An Appraisal of the Influence of the Metabotropic Glutamate 5 (mGlu5) Receptor on Sociability and Anxiety

Amongst the many neurotransmitter systems causally linked to the expression of social behavior, glutamate appears to play a pivotal role. In particular, metabotropic glutamate 5 (mGlu5) receptors have received much attention as its altered function has been reported in several mouse models of autism spectrum disorders and mental retardation. Inhibition of the activity of mGlu5 receptors by means of genetic or pharmacological manipulations improved social deficits in some of these animal models. However, in normal wild-type (WT) mice, pharmacological blockade of mGlu5 receptors yielded inconsistent results. The aim of our study was to investigate the actual contribution of decreased or absent mGlu5 receptor function in sociability and anxiety-like behavior as well as to explore the impact of mGlu5 receptor ablation on the pattern of brain activation upon social exposure. Here we show that Grm5-/- mice display higher social preference indexes compared to age-matched WT mice in the three-chambered social task. However, this effect was accompanied by a decreased exploratory activity during the test and increased anxiety-like behavior. Contrary to mGlu5 receptor ablation, the mGlu5 receptor negative allosteric modulator 3-((2-methyl-1,4-thiazolyl)ethynyl)pyridine (MTEP) induced anxiolytic effects without affecting social preference in WT mice. By mapping c-Fos expression in 21 different brain regions known to be involved in social interaction, we detected a specific activation of the prefrontal cortex and dorsolateral septum in Grm5-/- mice following social interaction. C-Fos expression correlation-based network and graph theoretical analyses further suggested dysfunctional connectivity and disruption of the functional brain network generated during social interaction in Grm5-/- mice. The lack of mGlu5 receptors resulted in profound rearrangements of the functional impact of prefrontal and hippocampal regions in the social interaction network. In conclusion, this work reveals a complex contribution of mGlu5 receptors in sociability and anxiety and points to the importance of these receptors in regulating brain functional connectivity during social interaction.

Neuromodulation Strategies in Post-Traumatic Stress Disorder: From Preclinical Models to Clinical Applications

Post-traumatic stress disorder (PTSD) is an often debilitating disease with a lifetime prevalence rate between 5⁻8%. In war veterans, these numbers are even higher, reaching approximately 10% to 25%. Although most patients benefit from the use of medications and psychotherapy, approximately 20% to 30% do not have an adequate response to conventional treatments. Neuromodulation strategies have been investigated for various psychiatric disorders with promising results, and may represent an important treatment option for individuals with difficult-to-treat forms of PTSD. We review the relevant neurocircuitry and preclinical stimulation studies in models of fear and anxiety, as well as clinical data on the use of transcranial direct current stimulation (tDCS), repetitive transcranial magnetic stimulation (rTMS), and deep brain stimulation (DBS) for the treatment of PTSD.

Influence of pharmacological and epigenetic factors to suppress neurotrophic factors and enhance neural plasticity in stress and mood disorders

Stress-induced major depression and mood disorders are characterized by behavioural abnormalities and psychiatric illness, leading to disability and immature mortality worldwide. Neurobiological mechanisms of stress and mood disorders are discussed considering recent findings, and challenges to enhance pharmacological effects of antidepressant, and mood stabilizers. Pharmacological enhancement of ketamine and scopolamine regulates depression at the molecular level, increasing synaptic plasticity in prefrontal regions. Blood-derived neurotrophic factors facilitate mood-deficit symptoms. Epigenetic factors maintain stress-resilience in hippocampal region. Regulation of neurotrophic factors blockades stress, and enhances neuronal survival though it paralyzes limbic regions. Molecular agents and neurotrophic factors also control behavioral and synaptic plasticity in addiction and stress disorders. Future research on neuronal dynamics and cellular actions can be directed to obtain the etiology of synaptic dysregulation in mood disorder and stress. For the first time, the current review contributes to the literature of synaptic plasticity representing the role of epigenetic mechanisms and glucocorticoid receptors to predict depression and anxiety in clinical conditions.

Anxiety in Patients With Acute Ischemic Stroke: Risk Factors and Effects on Functional Status

Background: Anxiety is prevalent after a stroke. The pathophysiological mechanisms underlying the development of poststroke anxiety (PSA) remain unclear. The aim of this study was to investigate the clinical and neuroimaging risk factors for development of PSA and examine the effects of PSA on activities of daily living (ADL) and quality of life (QOL) in Chinese patients with ischemic stroke. Methods: Two hundred nineteen patients with acute ischemic stroke were recruited to the study. A series of comprehensive assessments, including Hamilton Anxiety Rating Scale (HARS), Hamilton Depression Rating Scale (HDRS), Lawton ADL Scale, and the Stroke-Specific Quality of Life (SSQOL) Scale, were conducted in the acute stage and 3 months after stroke. Magnetic resonance imaging assessment focused on evaluation of infarctions, white matter lesions, and brain atrophy. Results: In the acute stage and 3 months after stroke, 34 (16%) and 33 (15%) patients had PSA, respectively. Multiple logistic regression analysis indicated that HDRS (OR = 1.269, 95% CI = 1.182-1.364, P < 0.001) and acute infarcts in cerebral hemispheric white matter (CHWM; OR = 2.902, 95% CI = 1.052-8.007, P = 0.040) were significant correlates of PSA in the acute stage of stroke. Three months after stroke, these correlates remained significant predictors, along with male sex. Multiple linear regressions showed that age, NIHSS, HARS, and HDRS in the acute stage were significant predictors for both ADL and SSQOL at 3 months after stroke. Conclusion: Depressive symptoms are the major correlates of PSA while more severe PSA is associated with poorer ADL and health-related QOL. Acute lesions involving CHWM may correlate with PSA in ischemic stroke patients with mild-to-moderate neurologic deficits, supporting a lesion-location hypothesis in PSA.

Social behavior, neuroimmune markers and glutamic acid decarboxylase levels in a rat model of valproic acid-induced autism

Autism is a complex neurodevelopmental disorder characterized by impaired social communication and social interactions, and repetitive behaviors. The etiology of autism remains unknown and its molecular basis is not yet well understood. Pregnant Sprague-Dawley (SD) rats were administered 600 mg/kg of valproic acid (VPA) by intraperitoneal injection on day 12.5 of gestation. Both 11- to 13-week-old male and female rat models of VPA-induced autism showed impaired sociability and impaired preference for social novelty as compared to the corresponding control SD rats. Significantly reduced mRNA expressions of social behavior-related genes, such as those encoding the serotonin receptor, brain-derived neurotrophic factor and neuroligin3, and significantly increased expression levels of proinflammatory cytokines, such as interleukin-1 β and tumor necrosis factor-α, were noted in the hippocampi of both male and female rats exposed to VPA in utero. The hippocampal expression level of gamma amino butyric acid (GABA) enzyme glutamic acid decarboxylase (GAD) 67 protein was reduced in both male and female VPA-exposed rats as compared to the corresponding control animals. Our results indicate that developmental exposure to VPA affects the social behavior in rats by modulating the expression levels of social behavior-related genes and inflammatory mediators accompanied with changes in GABA enzyme in the hippocampus.

Diazepam reverses increased anxiety-like behavior, social behavior deficit, and dopamine dysregulation following withdrawal from acute amphetamine

Psychostimulants such as amphetamine (AMPH) increase dopamine (DA) release from ventral tegmental area (VTA) neurons, which is associated with their acute reinforcing actions. This positive state is followed by a negative affective state during the withdrawal period each time the drug is taken (i.e., opponent process theory). AMPH withdrawal is accompanied by symptoms of anxiety and depression, which are associated with DA system dysfunction in humans and animal models. Most studies have focused on the negative affective state after withdrawal from chronic drug administration; yet, this negative state appears even after a drug is taken for the first time in both humans and rodents. In rats, withdrawal from a single dose of AMPH (2 mg/kg) increases forced swim test immobility and decreases the number of spontaneously active VTA DA neurons up to 48 h post-withdrawal. In the current study, acute AMPH withdrawal was found to increase anxiety-like behavior in the elevated plus maze (EPM), reduce social cage time in the three-chambered social approach test (SAT), and attenuate VTA population activity. The effects of diazepam, a drug commonly used to treat anxiety disorders, were tested on anxiety-like and social behavior as well as VTA DA neuron activity following acute AMPH withdrawal. A single (5 mg/kg) dose of diazepam circumvented the neurobehavioral effects induced by acute AMPH withdrawal, as demonstrated by increased open arm time and social cage time as well as normalized VTA DA activity comparable to controls, suggesting that these neurobehavioral effects of acute AMPH withdrawal reflect an anxiety-like state.

Female mice are protected from space radiation-induced maladaptive responses

Interplanetary exploration will be humankind's most ambitious expedition and the journey required to do so, is as intimidating as it is intrepid. One major obstacle for successful deep space travel is the possible negative effects of galactic cosmic radiation (GCR) exposure. Here, we investigate for the first time how combined GCR impacts long-term behavioral and cellular responses in male and female mice. We find that a single exposure to simulated GCR induces long-term cognitive and behavioral deficits only in the male cohorts. GCR exposed male animals have diminished social interaction, increased anxiety-like phenotype and impaired recognition memory. Remarkably, we find that the female cohorts did not display any cognitive or behavioral deficits after GCR exposure. Mechanistically, the maladaptive behavioral responses observed only in the male cohorts correspond with microglia activation and synaptic loss in the hippocampus, a brain region involved in the cognitive domains reported here. Furthermore, we measured reductions in AMPA expressing synaptic terminals in the hippocampus. No changes in any of the molecular markers measured here are observed in the females. Taken together these findings suggest that GCR exposure can regulate microglia activity and alter synaptic architecture, which in turn leads to a range of cognitive alterations in a sex dependent manner. These results identify sex-dependent differences in behavioral and cognitive domains revealing promising cellular and molecular intervention targets to reduce GCR-induced chronic cognitive deficits thereby boosting chances of success for humans in deep space missions such as the upcoming Mars voyage.

Specificity of Primate Amygdalar Pathways to Hippocampus

The amygdala projects to hippocampus in pathways through which affective or social stimuli may influence learning and memory. We investigated the still unknown amygdalar termination patterns and their postsynaptic targets in hippocampus from system to synapse in rhesus monkeys of both sexes. The amygdala robustly innervated the stratum lacunosum-moleculare layer of cornu ammonis fields and uncus anteriorly. Sparser terminations in posterior hippocampus innervated the radiatum and pyramidal layers at the prosubicular/CA1 juncture. The terminations, which were larger than other afferents in the surrounding neuropil, position the amygdala to influence hippocampal input anteriorly, and its output posteriorly. Most amygdalar boutons (76-80%) innervated spines of excitatory hippocampal neurons, and most of the remaining innervated presumed inhibitory neurons, identified by morphology and label with parvalbumin or calretinin, which distinguished nonoverlapping neurochemical classes of hippocampal inhibitory neurons. In CA1, amygdalar axons innervated some calretinin neurons, which disinhibit pyramidal neurons. By contrast, in CA3 the amygdala innervated both calretinin and parvalbumin neurons; the latter strongly inhibit nearby excitatory neurons. In CA3, amygdalar pathways also made closely spaced dual synapses on excitatory neurons. The strong excitatory synapses in CA3 may facilitate affective context representations and trigger sharp-wave ripples associated with memory consolidation. When the amygdala is excessively activated during traumatic events, the specialized innervation of excitatory neurons and the powerful parvalbumin inhibitory neurons in CA3 may allow the suppression of activity of nearby neurons that receive weaker nonamygdalar input, leading to biased passage of highly charged affective stimuli and generalized fear.SIGNIFICANCE STATEMENT Strong pathways from the amygdala targeted the anterior hippocampus, and more weakly its posterior sectors, positioned to influence a variety of emotional and cognitive functions. In hippocampal field CA1, the amygdala innervated some calretinin neurons, which disinhibit excitatory neurons. By contrast, in CA3 the amygdala innervated calretinin as well as some of the powerful parvalbumin inhibitory neurons and may help balance the activity of neural ensembles to allow social interactions, learning, and memory. These results suggest that when the amygdala is hyperactive during emotional upheaval, it strongly activates excitatory hippocampal neurons and parvalbumin inhibitory neurons in CA3, which can suppress nearby neurons that receive weaker input from other sources, biasing the passage of stimuli with high emotional import and leading to generalized fear.

Design and manufacturing challenges of optogenetic neural interfaces: a review

Optogenetics is a relatively new technology to achieve cell-type specific neuromodulation with millisecond-scale temporal precision. Optogenetic tools are being developed to address neuroscience challenges, and to improve the knowledge about brain networks, with the ultimate aim of catalyzing new treatments for brain disorders and diseases. To reach this ambitious goal the implementation of mature and reliable engineered tools is required. The success of optogenetics relies on optical tools that can deliver light into the neural tissue. Objective/Approach: Here, the design and manufacturing approaches available to the scientific community are reviewed, and current challenges to accomplish appropriate scalable, multimodal and wireless optical devices are discussed.

SIGNIFICANCE

Overall, this review aims at presenting a helpful guidance to the engineering and design of optical microsystems for optogenetic applications.

Association of 24 h maternal deprivation with a saline injection in the neonatal period alters adult stress response and brain monoamines in a sex-dependent fashion

Maternal deprivation (MD) disinhibits the adrenal glands, rendering them responsive to various stressors, including saline injection, and this increased corticosterone (CORT) response can last for as long as 2 h. In the present study, we tested the hypothesis that association of MD on day 11 with a saline injection would alter emotional behavior, CORT response, and brain monoamine levels, in male and female adult rats. Rats were submitted to the novelty suppressed feeding (NSF), the sucrose negative contrast test (SNCT), social investigation test (SIT), and the elevated plus maze (EPM). One quarter of each group was not tested (providing basal values of CORT and brain monoamines) and the remainder was decapitated 15, 45, or 75 min after the EPM, to assess CORT reactivity. Monoamine levels were determined in the hypothalamus (HPT), frontal cortex (FC), amygdala (AMY), ventral, and dorsal hippocampus (vHPC, dHPC, respectively). MD reduced food intake, in the home-cage, and latency to eat in the NSF in both sexes; females explored less the target animal in the SIT and explored more the open arms of the EPM than males; the CORT response to the EPM was greater in maternally-deprived males and females than in their control counterparts, and this response was further elevated in maternally-deprived females injected with saline. Regarding monoamine levels, females were less affected, showing isolated effects of the stressors, while in males, MD increased 5-HT levels in the HPT and decreased this monoamine in the FC, MD associated with saline reduced dopamine levels in all brain regions, except the HPT. MD at 11 days did not alter emotional behaviors in adult rats, but had an impact in neurobiological parameters associated with this class of behaviors. The impact of MD associated with saline on dopamine levels suggests that males may be vulnerable to motivation-related disorders.

Social interaction-induced activation of RNA splicing in the amygdala of microbiome-deficient mice

Social behaviour is regulated by activity of host-associated microbiota across multiple species. However, the molecular mechanisms mediating this relationship remain elusive. We therefore determined the dynamic, stimulus-dependent transcriptional regulation of germ-free (GF) and GF mice colonised post weaning (exGF) in the amygdala, a brain region critically involved in regulating social interaction. In GF mice the dynamic response seen in controls was attenuated and replaced by a marked increase in expression of splicing factors and alternative exon usage in GF mice upon stimulation, which was even more pronounced in exGF mice. In conclusion, we demonstrate a molecular basis for how the host microbiome is crucial for a normal behavioural response during social interaction. Our data further suggest that social behaviour is correlated with the gene-expression response in the amygdala, established during neurodevelopment as a result of host-microbe interactions. Our findings may help toward understanding neurodevelopmental events leading to social behaviour dysregulation, such as those found in autism spectrum disorders (ASDs).

In our bodies, there are at least as many microbial cells as human cells. These microbes, known collectively as the microbiome, influence the activity of our brain and also our behaviour. Studies in species from insects to primates have shown that the microbiome affects social behaviour in particular. For example, germ-free mice, which grow up in a sterile environment and thus have no bacteria in or on their bodies, are less sociable than normal mice.

For animals to show behaviours such as social interaction, cells in specific regions of the brain must change the activity of their genes. These brain regions include the amygdala, which is part of the brain’s emotion processing network, and also contributes to fear and anxiety responses. Stilling et al. set out to determine whether gene activity in the amygdala during social interaction differs between germ-free mice and those with a normal microbiome.

Stilling et al. placed each mouse into a box with three chambers. One chamber contained an unfamiliar mouse while another contained an inanimate object. Germ-free mice were less sociable and spent less time than control animals interacting with the unfamiliar mouse. Before entering either test chamber, the germ-free animals showed signs of excessive activity in the amygdala. During social interaction, they displayed a strikingly different pattern of gene activity in this brain region compared to controls. In particular, they had increased levels of a process called alternative splicing. This process enables cells to produce many different proteins from a single gene.

These results reveal one of the steps leading from absence of bacteria during brain development to reduced sociability in adulthood in mice. Increases in gene activity in the amygdala may provide clues to the processes underlying reduced sociability in people with autism spectrum disorders. This new study thus deepens our understanding of the link between the microbiome and brain health.

Synaptic Regulation of a Thalamocortical Circuit Controls Depression-Related Behavior

The NMDA receptor (NMDAR) antagonist ketamine elicits a long-lasting antidepressant response in patients with treatment-resistant depression. Understanding how antagonism of NMDARs alters synapse and circuit function is pivotal to developing circuit-based therapies for depression. Using virally induced gene deletion, ex vivo optogenetic-assisted circuit analysis, and in vivo chemogenetics and fMRI, we assessed the role of NMDARs in the medial prefrontal cortex (mPFC) in controlling depression-related behavior in mice. We demonstrate that post-developmental genetic deletion of the NMDAR subunit GluN2B from pyramidal neurons in the mPFC enhances connectivity between the mPFC and limbic thalamus, but not the ventral hippocampus, and reduces depression-like behavior. Using intersectional chemogenetics, we show that activation of this thalamocortical circuit is sufficient to elicit a decrease in despair-like behavior. Our findings reveal that GluN2B exerts input-specific control of pyramidal neuron innervation and identify a medial dorsal thalamus (MDT)→mPFC circuit that controls depression-like behavior.

Brain region-specific disruption of Shank3 in mice reveals a dissociation for cortical and striatal circuits in autism-related behaviors

We previously reported a new line of Shank3 mutant mice which led to a complete loss of Shank3 by deleting exons 4-22 (Δe4-22) globally. Δe4-22 mice display robust ASD-like behaviors including impaired social interaction and communication, increased stereotypical behavior and excessive grooming, and a profound deficit in instrumental learning. However, the anatomical and neural circuitry underlying these behaviors are unknown. We generated mice with Shank3 selectively deleted in forebrain, striatum, and striatal D1 and D2 cells. These mice were used to interrogate the circuit/brain-region and cell-type specific role of Shank3 in the expression of autism-related behaviors. Whole-cell patch recording and biochemical analyses were used to study the synaptic function and molecular changes in specific brain regions. We found perseverative exploratory behaviors in mice with deletion of Shank3 in striatal inhibitory neurons. Conversely, self-grooming induced lesions were observed in mice with deletion of Shank3 in excitatory neurons of forebrain. However, social, communicative, and instrumental learning behaviors were largely unaffected in these mice, unlike what is seen in global Δe4-22 mice. We discovered unique patterns of change for the biochemical and electrophysiological findings in respective brain regions that reflect the complex nature of transcriptional regulation of Shank3. Reductions in Homer1b/c and membrane hyper-excitability were observed in striatal loss of Shank3. By comparison, Shank3 deletion in hippocampal neurons resulted in increased NMDAR-currents and GluN2B-containing NMDARs. These results together suggest that Shank3 may differentially regulate neural circuits that control behavior. Our study supports a dissociation of Shank3 functions in cortical and striatal neurons in ASD-related behaviors, and it illustrates the complexity of neural circuit mechanisms underlying these behaviors.

Using New Approaches in Neurobiology to Rethink Stress-Induced Amnesia

Purpose of Review

Psychological stress can impact memory systems in several different ways. In individuals with healthy defense and coping systems, stress results in the formation of negatively valenced memories whose ability to induce emotional and somatic distress subsides with time. Vulnerable individuals, however, go on to develop stress-related disorders such as post-traumatic stress disorder (PTSD) and suffer from significant memory abnormalities. Whether expressed as intrusive trauma memories, partial amnesia, or dissociative amnesia, such abnormalities are thought to be the core source of patients' symptoms, which are often debilitating and implicate an entire socio-cognitive-affective spectrum.

Recent Findings

With this in mind, and focusing on stress-responsive hippocampal microcircuits, this article highlights recent advances in the neurobiology of memory that allow us to (1) isolate and visualize memory circuits, (2) change their activity using genetic tools and state-dependent manipulations, and (3) directly examine their impact on socio-affective circuits and global network connectivity. By integrating these approaches, we are now in a position to address important questions that have troubled psychiatry for a long time-questions such as are traumatic memories special, and why are stress effects on memory diverse.

Summary

Furthering our fundamental understanding of memory in the framework of adaptive and maladaptive stress responses has the potential to boost the development of new treatments that can benefit patients suffering from psychological trauma.

Cocaine-Induced Changes in Low-Dimensional Attractors of Local Field Potentials in Optogenetic Mice

Optogenetically evoked local field potential (LFP) recorded from the medial prefrontal cortex (mPFC) of mice during basal conditions and following a systemic cocaine administration were analyzed. Blue light stimuli were delivered to mPFC through a fiber optic every 2 s and each trial was repeated 100 times. As in the previous study, we used a surrogate data method to check that nonlinearity was present in the experimental LFPs and only used the last 1.5 s of steady activity to measure the LFPs phase resetting induced by the brief 10 ms light stimulus. We found that the steady dynamics of the mPFC in response to light stimuli could be reconstructed in a three-dimensional phase space with topologically similar "8"-shaped attractors across different animals. Therefore, cocaine did not change the complexity of the recorded nonlinear data compared to the control case. The phase space of the reconstructed attractor is determined by the LFP time series and its temporally shifted versions by a multiple of some lag time. We also compared the change in the attractor shape between cocaine-injected and control using (1) dendrogram clustering and (2) Frechet distance. We found about 20% overlap between control and cocaine trials when classified using dendrogram method, which suggest that it may be possible to describe mathematically both data sets with the same model and slightly different model parameters. We also found that the lag times are about three times shorter for cocaine trials compared to control. As a result, although the phase space trajectories for control and cocaine may look similar, their dynamics is significantly different.

Altered aspects of anxiety-related behavior in kisspeptin receptor-deleted male mice

The roles of kisspeptin signaling outside the hypothalamus in the brain are unknown. We examined here the impact of Kiss1r-deletion on hippocampus-related behaviors of anxiety and spatial learning in adult male mice using two mouse models. In the first, global Kiss1r-null and control mice were gonadectomized (GDX KISS1R-KO). In the second, KISS1R signalling was rescued selectively in gonadotropin-releasing hormone neurons to generate Kiss1r-null mice with normal testosterone levels (intact KISS1R-KO). Intact KISS1R-KO rescue mice were found to spend twice as much time in the open arms of the elevated plus maze (EPM) compared to controls (P < 0.01). GDX KISS1R-KO mice showed a similar but less pronounced trend. No differences were detected between intact KISS1R-KO mice and controls in the open field test (OFT), although a marked reduction in time spent in the centre quadrant was observed for all GDX mice (P < 0.001). No effects of KISS1R deletion or gonadectomy were detected in the Morris water maze. These observations demonstrate that KISS1R signalling impacts upon anxiogenic neural circuits operative in the EPM, while gonadal steroids appear important for anxiety behaviour observed in the OFT. The potential anxiogenic role of kisspeptin may need to be considered in the development of kisspeptin analogs for the clinic.

Morphological and functional changes in the preweaning basolateral amygdala induced by early chronic stress associate with anxiety and fear behavior in adult male, but not female rats

Suboptimal maternal care is a form of chronic early-life stress (ELS) and a risk factor for mental illness and behavioral impairments throughout the life span. The amygdala, particularly the basolateral amygdala (BLA), exhibits exquisite sensitivity to ELS and could promote dysregulation of stress reactivity and anxiety-related disorders. While ELS has profound impacts on the adult or adolescent amygdala, less is known regarding the sensitivity of the preweaning BLA to ELS. We employed a naturalistic rodent model of chronic ELS that limits the amount of bedding/nesting material (LB) available to the mother between postnatal day (PND) 1-9 and examined the morphological and functional effects in the preweaning BLA on PND10 and 18-22. BLA neurons displayed dendritic hypertrophy and increased spine numbers in male, but not female, LB pups already by PND10 and BLA volume tended to increase after LB exposure in preweaning rats, suggesting an accelerated and long-lasting recruitment of the amygdala. Morphological changes seen in male LB pups were paralleled with increased evoked synaptic responses recorded from BLA neurons in vitro, suggesting enhanced excitatory inputs to these neurons. Interestingly, morphological and functional changes in the preweaning BLA were not associated with basal hypercorticosteronemia or enhanced stress responsiveness in LB pups, perhaps due to a differential sensitivity of the neuroendocrine stress axis to the effects of LB exposure. Early changes in the synaptic organization and excitability of the neonatal amygdala might contribute to the increased anxiety-like and fear behavior observed in adulthood, specifically in male offspring.

Estimating a Separably Markov Random Field from Binary Observations

A fundamental problem in neuroscience is to characterize the dynamics of spiking from the neurons in a circuit that is involved in learning about a stimulus or a contingency. A key limitation of current methods to analyze neural spiking data is the need to collapse neural activity over time or trials, which may cause the loss of information pertinent to understanding the function of a neuron or circuit. We introduce a new method that can determine not only the trial-to-trial dynamics that accompany the learning of a contingency by a neuron, but also the latency of this learning with respect to the onset of a conditioned stimulus. The backbone of the method is a separable two-dimensional (2D) random field (RF) model of neural spike rasters, in which the joint conditional intensity function of a neuron over time and trials depends on two latent Markovian state sequences that evolve separately but in parallel. Classical tools to estimate state-space models cannot be applied readily to our 2D separable RF model. We develop efficient statistical and computational tools to estimate the parameters of the separable 2D RF model. We apply these to data collected from neurons in the prefrontal cortex in an experiment designed to characterize the neural underpinnings of the associative learning of fear in mice. Overall, the separable 2D RF model provides a detailed, interpretable characterization of the dynamics of neural spiking that accompany the learning of a contingency.

CD38 is Required for Dendritic Organization in Visual Cortex and Hippocampus

Morphological screening of mouse brains with known behavioral deficits can give great insight into the relationship between brain regions and their behavior. Oxytocin- and CD38-deficient mice have previously been shown to have behavioral phenotypes, such as restrictions in social memory, social interactions, and maternal behavior. CD38 is reported as an autism spectrum disorder (ASD) candidate gene and its behavioral phenotypes may be linked to ASD. To address whether these behavioral phenotypes relate to brain pathology and neuronal morphology, here we investigate the morphological changes in the CD38-deficient mice brains, with focus on the pathology and neuronal morphology of the cortex and hippocampus, using Nissl staining, immunohistochemistry, and Golgi staining. No difference was found in terms of cortical layer thickness. However, we found abnormalities in the number of neurons and neuronal morphology in the visual cortex and dentate gyrus (DG). In particular, there were arborisation differences between CD38^-/- and CD38^+/+ mice in the apical dendrites of the visual cortex and hippocampal CA1 pyramidal neurons. The data suggest that CD38 is implicated in appropriate development of brain regions important for social behavior.

Hippocampal oxytocin receptors are necessary for discrimination of social stimuli

Oxytocin receptor (Oxtr) signaling in neural circuits mediating discrimination of social stimuli and affiliation or avoidance behavior is thought to guide social recognition. Remarkably, the physiological functions of Oxtrs in the hippocampus are not known. Here we demonstrate using genetic and pharmacological approaches that Oxtrs in the anterior dentate gyrus (aDG) and anterior CA2/CA3 (aCA2/CA3) of mice are necessary for discrimination of social, but not non-social, stimuli. Further, Oxtrs in aCA2/CA3 neurons recruit a population-based coding mechanism to mediate social stimuli discrimination. Optogenetic terminal-specific attenuation revealed a critical role for aCA2/CA3 outputs to posterior CA1 for discrimination of social stimuli. In contrast, aCA2/CA3 projections to aCA1 mediate discrimination of non-social stimuli. These studies identify a role for an aDG-CA2/CA3 axis of Oxtr expressing cells in discrimination of social stimuli and delineate a pathway relaying social memory computations in the anterior hippocampus to the posterior hippocampus to guide social recognition.

Complex Environmental Rearing Enhances Social Salience and Affects Hippocampal Corticotropin Releasing Hormone Receptor Expression in a Sex-Specific Manner

Methods for understanding the neurocircuitry of ethologically relevant behaviors have advanced substantially; however renovations to standard animal laboratory housing, in the form of enhanced enrichment, have lagged behind. This is despite evidence that environmental enrichment (EE) reduces stress, stereotypy, and promotes healthy species typical behaviors. While many scientists express interest for increased EE as a standard for animal caging systems, there are concerns that its effects on brain, behavior, and cognition are not well characterized. In the present study, male and female Sprague-Dawley rats were housed for six weeks in either EE, Colony Nesting (CN), or Standard Housing (SD) conditions. We show that adolescent exposure to environmental complexity changed the dynamics of social interactions, sensory processing, and underlying basal stress neurocircuitry, in a sex- and enrichment-type-dependent manner. Specifically, EE and CN increased prosocial engagement and the social saliency of male and female rats while the profile of hippocampal Crhr2 expression was affected only in EE males. Hippocampal Crh was associated with anxiety-like behavior in SD males - this did not extend to EE or CN groups, nor to females. Observations such as these are an important consideration for the validity of translational research investigating the neurocircuitry of stress resiliency, and for understanding the mechanisms of psychiatric disorders. Future work must focus on characterizing how individual environmental enhancements (e.g. novelty, social enrichment, physical activity) shape phenotypic differences, how they vary as a function of species, strain and sex, and (if warranted) how to meaningfully implement this knowledge into biomedical research designs.

Early maternal separation promotes apoptosis in dentate gyrus and alters neurological behaviors in adolescent rats

Adverse early-life experience such as maternal separation (MS) affects the behavior of adult, and may also aggravate the outcome of neurological insults. In this study, we aimed to investigate the effects of early MS on hippocampus-related behaviors, and to assess the mechanisms. Newborn rats were randomly divided into normal control and MS groups. Our data showed that MS (P3-P21) impaired learning ability as well as memory retrieval, and caused depression-like activity, but decreased anxiety-like activity. Glutamate receptor 1 (GluR1) expression in the dentate gyrus (DG) region was significantly reduced in the adults (P60). Mechanically, MS promoted apoptosis, and reduced protein kinase B (AKT) phosphorylation in the DG region in the early phase (P21). By contrast, MS did not affect ERK phosphorylation. Our data implicate that the inactivation of AKT pathway and apoptosis of DG cells might contribute to MS-induced behavioral changes. This study would provide useful evidence implicating the pathological changes for MS.

Prenatal bisphenol A (BPA) exposure alters the transcriptome of the neonate rat amygdala in a sex-specific manner: a CLARITY-BPA consortium study

Bisphenol A (BPA) is a widely recognized endocrine disruptor prevalent in many household items. Because experimental and epidemiological data suggest links between prenatal BPA exposure and altered affective behaviors in children, even at levels below the current US FDA No Observed Adverse Effect Level (NOAEL) of 5mg/kg body weight (bw)/day, there is concern that early life exposure may alter neurodevelopment. The current study was conducted as part of the CLARITY-BPA (Consortium Linking Academic and Regulatory Insights on BPA Toxicity) program and examined the full amygdalar transcriptome on postnatal day (PND) 1, with the hypothesis that prenatal BPA exposure would alter the expression of genes and pathways fundamental to sex-specific affective behaviors. NCTR Sprague-Dawley dams were gavaged from gestational day 6 until parturition with BPA (2.5, 25, 250, 2500, or 25000μg/kg bw/day), a reference estrogen (0.05 or 0.5μg ethinyl estradiol (EE₂)/kg bw/day), or vehicle. PND 1 amygdalae were microdissected and gene expression was assessed with qRT-PCR (all exposure groups) and RNAseq (vehicle, 25 and 250μg BPA, and 0.5μg EE₂ groups only). Our results demonstrate that that prenatal BPA exposure can disrupt the transcriptome of the neonate amygdala, at doses below the FDA NOAEL, in a sex-specific manner and indicate that the female amygdala may be more sensitive to BPA exposure during fetal development. We also provide additional evidence that developmental BPA exposure can interfere with estrogen, oxytocin, and vasopressin signaling pathways in the developing brain and alter signaling pathways critical for synaptic organization and transmission.

Rescue of impaired sociability and anxiety-like behavior in adult cacna1c-deficient mice by pharmacologically targeting eIF2α

CACNA1C, encoding the Ca_v1.2 subunit of L-type Ca²⁺ channels, has emerged as one of the most prominent and highly replicable susceptibility genes for several neuropsychiatric disorders. Ca_v1.2 channels play a crucial role in calcium-mediated processes involved in brain development and neuronal function. Within the CACNA1C gene, disease-associated single-nucleotide polymorphisms have been associated with impaired social and cognitive processing and altered prefrontal cortical (PFC) structure and activity. These findings suggest that aberrant Ca_v1.2 signaling may contribute to neuropsychiatric-related disease symptoms via impaired PFC function. Here, we show that mice harboring loss of cacna1c in excitatory glutamatergic neurons of the forebrain (fbKO) that we have previously reported to exhibit anxiety-like behavior, displayed a social behavioral deficit and impaired learning and memory. Furthermore, focal knockdown of cacna1c in the adult PFC recapitulated the social deficit and elevated anxiety-like behavior, but not the deficits in learning and memory. Electrophysiological and molecular studies in the PFC of cacna1c fbKO mice revealed higher E/I ratio in layer 5 pyramidal neurons and lower general protein synthesis. This was concurrent with reduced activity of mTORC1 and its downstream mRNA translation initiation factors eIF4B and 4EBP1, as well as elevated phosphorylation of eIF2α, an inhibitor of mRNA translation. Remarkably, systemic treatment with ISRIB, a small molecule inhibitor that suppresses the effects of phosphorylated eIF2α on mRNA translation, was sufficient to reverse the social deficit and elevated anxiety-like behavior in adult cacna1c fbKO mice. ISRIB additionally normalized the lower protein synthesis and higher E/I ratio in the PFC. Thus this study identifies a novel Ca_v1.2 mechanism in neuropsychiatric-related endophenotypes and a potential future therapeutic target to explore.

Multisite Electrophysiology Recordings in Mice to Study Cross-Regional Communication During Anxiety

Recording neural activity in awake, freely moving mice is a powerful and flexible technique for dissecting the neural circuit mechanisms underlying pathological behavior. This unit describes protocols for designing a drive and recording single neurons and local field potentials during anxiety-related paradigms. We also include protocols for integrating pharmacologic and optogenetic means for circuit manipulations, which, when combined with electrophysiological recordings, demonstrate input-specific and cell-specific contributions to circuit-wide activity. We discuss the planning, execution, and troubleshooting of physiology experiments during anxiety-like behavior. © 2017 by John Wiley & Sons, Inc.

From Gene to Behavior: L-Type Calcium Channel Mechanisms Underlying Neuropsychiatric Symptoms

The L-type calcium channels (LTCCs) Cav1.2 and Cav1.3, encoded by the CACNA1C and CACNA1D genes, respectively, are important regulators of calcium influx into cells and are critical for normal brain development and plasticity. In humans, CACNA1C has emerged as one of the most widely reproduced and prominent candidate risk genes for a range of neuropsychiatric disorders, including bipolar disorder (BD), schizophrenia (SCZ), major depressive disorder, autism spectrum disorder, and attention deficit hyperactivity disorder. Separately, CACNA1D has been found to be associated with BD and autism spectrum disorder, as well as cocaine dependence, a comorbid feature associated with psychiatric disorders. Despite growing evidence of a significant link between CACNA1C and CACNA1D and psychiatric disorders, our understanding of the biological mechanisms by which these LTCCs mediate neuropsychiatric-associated endophenotypes, many of which are shared across the different disorders, remains rudimentary. Clinical studies with LTCC blockers testing their efficacy to alleviate symptoms associated with BD, SCZ, and drug dependence have provided mixed results, underscoring the importance of further exploring the neurobiological consequences of dysregulated Cav1.2 and Cav1.3. Here, we provide a review of clinical studies that have evaluated LTCC blockers for BD, SCZ, and drug dependence-associated symptoms, as well as rodent studies that have identified Cav1.2- and Cav1.3-specific molecular and cellular cascades that underlie mood (anxiety, depression), social behavior, cognition, and addiction.

Neuroanatomical Substrates of Rodent Social Behavior: The Medial Prefrontal Cortex and Its Projection Patterns

Social behavior encompasses a number of distinctive and complex constructs that form the core elements of human imitative culture, mainly represented as either affiliative or antagonistic interactions with conspecifics. Traditionally considered in the realm of psychology, social behavior research has benefited from recent advancements in neuroscience that have accelerated identification of the neural systems, circuits, causative genes and molecular mechanisms that underlie distinct social cognitive traits. In this review article, I summarize recent findings regarding the neuroanatomical substrates of key social behaviors, focusing on results from experiments conducted in rodent models. In particular, I will review the role of the medial prefrontal cortex (mPFC) and downstream subcortical structures in controlling social behavior, and discuss pertinent future research perspectives.

Endocannabinoid Signaling in the Control of Social Behavior

Many mammalian species, including humans, exhibit social behavior and form complex social groups. Mechanistic studies in animal models have revealed important roles for the endocannabinoid signaling system, comprising G protein-coupled cannabinoid receptors and their endogenous lipid-derived agonists, in the control of neural processes that underpin social anxiety and social reward, two key aspects of social behavior. An emergent insight from these studies is that endocannabinoid signaling in specific circuits of the brain is context dependent and selectively recruited. These insights open new vistas on the neural basis of social behavior and social impairment.

Amygdala-hippocampal dynamics during salient information processing

Recognizing motivationally salient information is critical to guiding behaviour. The amygdala and hippocampus are thought to support this operation, but the circuit-level mechanism of this interaction is unclear. We used direct recordings in the amygdala and hippocampus from human epilepsy patients to examine oscillatory activity during processing of fearful faces compared with neutral landscapes. We report high gamma (70–180 Hz) activation for fearful faces with earlier stimulus evoked onset in the amygdala compared with the hippocampus. Attending to fearful faces compared with neutral landscape stimuli enhances low-frequency coupling between the amygdala and the hippocampus. The interaction between the amygdala and hippocampus is largely unidirectional, with theta/alpha oscillations in the amygdala modulating hippocampal gamma activity. Granger prediction, phase slope index and phase lag analysis corroborate this directional coupling. These results demonstrate that processing emotionally salient events in humans engages an amygdala-hippocampal network, with the amygdala influencing hippocampal dynamics during fear processing.

Amygdala and hippocampus are involved in processing motivationally salient stimuli but the precise circuit dynamics of the interaction is not understood. Here the authors show that in response to fearful faces in humans, theta/alpha oscillations in the amygdala modulate hippocampal activity dynamics.

Intracellular signalling and plasma hormone profiles associated with the expression of unconditioned and conditioned fear and anxiety in female rats

There is considerable overlap in the neural regions and intracellular signalling pathways implicated in anxiety and fear, although less is known in females. Here, we investigated whether unconditioned and conditioned fear are associated with distinct patterns of expression of extracellular signal-regulated kinase-1 and -2 (ERK1/2), protein kinase B (Akt), and calcineurin (CaN) (proteins that are key regulators of the expression of and/or memory processes of fear and anxiety) in the dorsal and ventral hippocampus, medial prefrontal cortex, and amygdala (important regions in neural fear circuitry) of adult female rats, and used a multivariate approach to find patterns of signalling that might discriminate between the different states of fear. To isolate fear to the conditioned cue from generalized fear to the test context, rats were conditioned to an auditory tone (i.e. tone paired with footshock) and twenty-four hours later exposed to a novel context in the presence or absence of the conditioned cue. A third group that was exposed to the conditioning context without undergoing fear conditioning was included to control for unconditioned responses to the testing procedures, which are anxiogenic. A discriminate function analysis and MANOVA determined that hippocampal signalling best discriminated the three groups from each other. The addition of values for plasma concentrations of corticosterone and progesterone (as indices of activation of the hypothalamic-pituitary-adrenal stress axis) to statistical analyses increased the separation of the three groups. There was high degree of association among the three signalling molecules in the four brain regions within each group. There was an absence of the associations between the medial prefrontal cortex and the amygdala in the cued fear recall group that were strong for the non-conditioned group. These results demonstrated unique neuronal and hormonal signalling profiles associated with unconditioned, generalized, and conditioned fear expression in females and highlight the importance of including appropriate comparisons to best discriminate between these different emotional states.

Adult microbiota-deficient mice have distinct dendritic morphological changes: differential effects in the amygdala and hippocampus

Increasing evidence implicates the microbiota in the regulation of brain and behaviour. Germ-free mice (GF; microbiota deficient from birth) exhibit altered stress hormone signalling and anxiety-like behaviours as well as deficits in social cognition. Although the mechanisms underlying the ability of the gut microbiota to influence stress responsivity and behaviour remain unknown, many lines of evidence point to the amygdala and hippocampus as likely targets. Thus, the aim of this study was to determine if the volume and dendritic morphology of the amygdala and hippocampus differ in GF versus conventionally colonized (CC) mice. Volumetric estimates revealed significant amygdalar and hippocampal expansion in GF compared to CC mice. We also studied the effect of GF status on the level of single neurons in the basolateral amygdala (BLA) and ventral hippocampus. In the BLA, the aspiny interneurons and pyramidal neurons of GF mice exhibited dendritic hypertrophy. The BLA pyramidal neurons of GF mice had more thin, stubby and mushroom spines. In contrast, the ventral hippocampal pyramidal neurons of GF mice were shorter, less branched and had less stubby and mushroom spines. When compared to controls, dentate granule cells of GF mice were less branched but did not differ in spine density. These findings suggest that the microbiota is required for the normal gross morphology and ultrastructure of the amygdala and hippocampus and that this neural remodelling may contribute to the maladaptive stress responsivity and behavioural profile observed in GF mice.

Emergence of social behavior deficit, blunted corticolimbic activity and adult depression-like behavior in a rodent model of maternal maltreatment

Disrupted social behavior is a core symptom of multiple psychiatric and neurodevelopmental disorders. Many of these disorders are exacerbated by adverse infant experiences, including maltreatment and abuse, which negatively affect amygdala development. Although a link between impaired social behavior, abnormal amygdala function and depressive-like behavior following early adversity has been demonstrated in humans and animal models, the developmental emergence of maltreatment-related social deficits and associated amygdala neural activity are unknown. We used a naturalistic rodent model of maternal maltreatment during a sensitive period, postnatal days 8-12 (PN8-12), which produces social behavior deficits that precede adolescent depressive-like behavior and amygdala dysfunction, to examine social behavior in infancy, periweaning and adolescence. Neural activity in response to the social behavior test was assessed via c-Fos immunohistochemistry at these ages. A separate group of animals was tested for adult depressive-like behavior in the forced swim test. Maltreatment spared infant (PN16-18) social behavior but disrupted periweaning (PN20-22) and adolescent (PN42-48) social behavior. Maltreated rats exhibited blunted neural activation in the amygdala and other areas implicated in social functioning, including the medial prefrontal cortex and nucleus accumbens, at these ages and increased adult depressive-like behavior. These findings may suggest corticolimbic involvement in the emergence of maltreatment-induced social deficits that are linked to adult depressive-like behavior, thereby highlighting potential targets for therapeutic intervention. Understanding how infant experiences influence social behavior and age-specific expression across development may provide insights into basic neural mechanisms of social behaviors and disease-relevant social dysfunction exacerbated by early-life stress.

Methamphetamine-induced deficits in social interaction are not observed following abstinence from single or repeated exposures

The purpose of the current study was to assess social interaction (SI) following acute and repeated methamphetamine (MA) administration. Rats were injected with 5.0 mg/kg of MA and SI was tested 30 min or 24 h later. In another group of animals, MA sensitization was induced using 5.0 mg/kg of MA, and SI was assessed after 1 or 30 days of abstinence. SI was reduced in rats injected with MA 30 min, but not 24 h, before testing, compared with saline controls. Impaired SI was observed in combination with active avoidance of the conspecific animal. Repeated injections of MA progressively reduced locomotor activity and increased stereotypy, indicating that animals were sensitized. However, no differences in SI were observed 24 h or 30 days following the induction of sensitization. The absence of detectable differences in SI following MA sensitization may be attributable to the relatively short regimen used to induce sensitization. However, the current series of experiments provides evidence that an acute injection of MA decreases SI and simultaneously increases avoidance behavior, which supports a link between psychostimulant use and impaired social functioning. These data suggest that the acute injection model may provide a useful model to explore the neural basis of impaired social functioning and antisocial behavior.

Major neurotransmitter systems in dorsal hippocampus and basolateral amygdala control social recognition memory

Social recognition memory (SRM) is crucial for reproduction, forming social groups, and species survival. Despite its importance, SRM is still relatively little studied. Here we examine the participation of the CA1 region of the dorsal hippocampus (CA1) and the basolateral amygdala (BLA) and that of dopaminergic, noradrenergic, and histaminergic systems in both structures in the consolidation of SRM. Male Wistar rats received intra-CA1 or intra-BLA infusions of different drugs immediately after the sample phase of a social discrimination task and 24-h later were subjected to a 5-min retention test. Animals treated with the protein synthesis inhibitor, anisomycin, into either the CA1 or BLA were unable to recognize the previously exposed juvenile (familiar) during the retention test. When infused into the CA1, the β-adrenoreceptor agonist, isoproterenol, the D1/D5 dopaminergic receptor antagonist, SCH23390, and the H2 histaminergic receptor antagonist, ranitidine, also hindered the recognition of the familiar juvenile 24-h later. The latter drug effects were more intense in the CA1 than in the BLA. When infused into the BLA, the β-adrenoreceptor antagonist, timolol, the D1/D5 dopamine receptor agonist, SKF38393, and the H2 histaminergic receptor agonist, ranitidine, also hindered recognition of the familiar juvenile 24-h later. In all cases, the impairment to recognize the familiar juvenile was abolished by the coinfusion of agonist plus antagonist. Clearly, both the CA1 and BLA, probably in that order, play major roles in the consolidation of SRM, but these roles are different in each structure vis-à-vis the involvement of the β-noradrenergic, D1/D5-dopaminergic, and H2-histaminergic receptors therein.

Activation of basolateral amygdala in juvenile C57BL/6J mice during social approach behavior

There is a strong need to better understand the neurobiology of juvenile sociability (tendency to seek social interaction), a phenotype of central relevance to autism spectrum disorders (ASD). Although numerous genetic mouse models of ASD showing reduced sociability have been reported, and certain brain regions, such as the amygdala, have been implicated in sociability, there has been little emphasis on delineating brain structures and circuits activated during social interactions in the critical juvenile period of the mouse strain that serves as the most common genetic background for these models-the highly sociable C57BL/6J (B6) strain. We measured expression of the immediate early genes Fos and Egr-1 to map activation of brain regions following the Social Approach Test (SAT) in juvenile male B6 mice. We hypothesized that juvenile B6 mice would show activation of the amygdala during social interactions. The basolateral amygdala (BLA) was activated by social exposure in highly sociable, 4-week-old B6 mice. In light of these data, and the many lines of evidence indicating alteration of amygdala circuits in human ASD, future studies are warranted to assess structural and functional alterations in the BLA, particularly at BLA synapses, in various mouse models of ASD.

Netrin-G1 regulates fear-like and anxiety-like behaviors in dissociable neural circuits

In vertebrate mammals, distributed neural circuits in the brain are involved in emotion-related behavior. Netrin-G1 is a glycosyl-phosphatidylinositol-anchored synaptic adhesion molecule whose deficiency results in impaired fear-like and anxiety-like behaviors under specific circumstances. To understand the cell type and circuit specificity of these responses, we generated netrin-G1 conditional knockout mice with loss of expression in cortical excitatory neurons, inhibitory neurons, or thalamic neurons. Genetic deletion of netrin-G1 in cortical excitatory neurons resulted in altered anxiety-like behavior, but intact fear-like behavior, whereas loss of netrin-G1 in inhibitory neurons resulted in attenuated fear-like behavior, but intact anxiety-like behavior. These data indicate a remarkable double dissociation of fear-like and anxiety-like behaviors involving netrin-G1 in excitatory and inhibitory neurons, respectively. Our findings support a crucial role for netrin-G1 in dissociable neural circuits for the modulation of emotion-related behaviors, and provide genetic models for investigating the mechanisms underlying the dissociation. The results also suggest the involvement of glycosyl-phosphatidylinositol-anchored synaptic adhesion molecules in the development and pathogenesis of emotion-related behavior.

Vicarious trial and error

When rats come to a decision point, they sometimes pause and look back and forth as if deliberating over the choice; at other times, they proceed as if they have already made their decision. In the 1930s, this pause-and-look behaviour was termed 'vicarious trial and error' (VTE), with the implication that the rat was 'thinking about the future'. The discovery in 2007 that the firing of hippocampal place cells gives rise to alternating representations of each of the potential path options in a serial manner during VTE suggested a possible neural mechanism that could underlie the representations of future outcomes. More-recent experiments examining VTE in rats suggest that there are direct parallels to human processes of deliberative decision making, working memory and mental time travel.

Amygdala-Hippocampal Phospholipase D (PLD) Signaling As Novel Mechanism of Cocaine-Environment Maladaptive Conditioned Responses

BACKGROUND

Drug-environment associative memory mechanisms and the resulting conditioned behaviors are key contributors in relapse to cocaine dependence. Recently, we reported rat amygdala phospholipase D as a key convergent downstream signaling partner in the expression of cocaine-conditioned behaviors mediated by glutamatergic and dopaminergic pathways. In the present study, 1 of the 2 known upstream serotonergic targets of phospholipase D, the serotonin (5-hydroxytryptamine) 2C receptor, was investigated for its role in recruiting phospholipase D signaling in cocaine-conditioned behaviors altered in the rat amygdala and dorsal hippocampus.

METHODS

Using Western-blot analysis, amygdala phospholipase D phosphorylation and total expression of phospholipase D/5-hydroxytryptamine 2C receptor were observed in early (Day-1) and late (Day-14) withdrawal (cocaine-free) states among male Sprague-Dawley rats subjected to 7-day cocaine-conditioned hyperactivity training. Functional studies were conducted using Chinese Hamster Ovary cells with stably transfected human unedited isoform of 5-hydroxytryptamine 2C receptor.

RESULTS

Phosphorylation of phospholipase D isoforms was altered in the Day-1 group of cocaine-conditioned animals, while increased amygdala and decreased dorsal hippocampus phospholipase D/5-hydroxytryptamine 2C receptor protein expression were observed in the Day-14 cocaine-conditioned rats. Functional cellular studies established that increased p phospholipase D is a mechanistic response to 5-HT2CR activation and provided the first evidence of a biased agonism by specific 5-hydroxytryptamine 2C receptor agonist, WAY163909 in phospholipase D phosphorylation 2, but not phospholipase D phosphorylation 1 activation.

CONCLUSIONS

Phospholipase D signaling, activated by dopaminergic, glutamatergic, and serotonergic signaling, can be a common downstream element recruited in associative memory mechanisms altered by cocaine, where increased expression in amygdala and decreased expression in dorsal hippocampus may result in altered anxiety states and increased locomotor responses, respectively.

Deletion of CTNNB1 in inhibitory circuitry contributes to autism-associated behavioral defects

Mutations in β-catenin (CTNNB1) have been implicated in cancer and mental disorders. Recently, loss-of-function mutations of CTNNB1 were linked to intellectual disability (ID), and rare mutations were identified in patients with autism spectrum disorder (ASD). As a key regulator of the canonical Wnt pathway, CTNNB1 plays an essential role in neurodevelopment. However, the function of CTNNB1 in specific neuronal subtypes is unclear. To understand how CTNNB1 deficiency contributes to ASD, we generated CTNNB1 conditional knockout (cKO) mice in parvalbumin interneurons. The cKO mice had increased anxiety, but had no overall change in motor function. Interestingly, CTNNB1 cKO in PV-interneurons significantly impaired object recognition and social interactions and elevated repetitive behaviors, which mimic the core symptoms of patients with ASD. Surprisingly, deleting CTNNB1 in parvalbumin-interneurons enhanced spatial memory. To determine the effect of CTNNB1 KO in overall neuronal activity, we found that c-Fos was significantly reduced in the cortex, but not in the dentate gyrus and the amygdala. Our findings revealed a cell type-specific role of CTNNB1 gene in regulation of cognitive and autistic-like behaviors. Thus, this study has important implications for development of therapies for ASDs carrying the CTNNB1 mutation or other ASDs that are associated with mutations in the Wnt pathway. In addition, our study contributes to a broader understanding of the regulation of the inhibitory circuitry.

Divergent Routing of Positive and Negative Information from the Amygdala during Memory Retrieval

Although the basolateral amygdala (BLA) is known to play a critical role in the formation of memories of both positive and negative valence, the coding and routing of valence-related information is poorly understood. Here, we recorded BLA neurons during the retrieval of associative memories and used optogenetic-mediated phototagging to identify populations of neurons that synapse in the nucleus accumbens (NAc), the central amygdala (CeA), or ventral hippocampus (vHPC). We found that despite heterogeneous neural responses within each population, the proportions of BLA-NAc neurons excited by reward predictive cues and of BLA-CeA neurons excited by aversion predictive cues were higher than within the entire BLA. Although the BLA-vHPC projection is known to drive behaviors of innate negative valence, these neurons did not preferentially code for learned negative valence. Together, these findings suggest that valence encoding in the BLA is at least partially mediated via divergent activity of anatomically defined neural populations.

Frontal Lobe Contusion in Mice Chronically Impairs Prefrontal-Dependent Behavior

Traumatic brain injury (TBI) is a major cause of chronic disability in the world. Moderate to severe TBI often results in damage to the frontal lobe region and leads to cognitive, emotional, and social behavioral sequelae that negatively affect quality of life. More specifically, TBI patients often develop persistent deficits in social behavior, anxiety, and executive functions such as attention, mental flexibility, and task switching. These deficits are intrinsically associated with prefrontal cortex (PFC) functionality. Currently, there is a lack of analogous, behaviorally characterized TBI models for investigating frontal lobe injuries despite the prevalence of focal contusions to the frontal lobe in TBI patients. We used the controlled cortical impact (CCI) model in mice to generate a frontal lobe contusion and studied behavioral changes associated with PFC function. We found that unilateral frontal lobe contusion in mice produced long-term impairments to social recognition and reversal learning while having only a minor effect on anxiety and completely sparing rule shifting and hippocampal-dependent behavior.

Ethological Evaluation of the Effects of Social Defeat Stress in Mice: Beyond the Social Interaction Ratio

In rodents, repeated exposure to unavoidable aggression followed by sustained sensory treat can lead to prolonged social aversion. The chronic social defeat stress model explores that phenomenon and it has been used as an animal model for human depression. However, some authors have questioned whether confounding effects may arise as the model also boosts anxiety-related behaviors. Despite its wide acceptance, most studies extract limited information from the behavior of the defeated animal. Often, the normalized occupancy around the social stimulus, the interaction zone, is taken as an index of depression. We hypothesized that this parameter is insufficient to fully characterize the behavioral consequences of this form of stress. Using an ethological approach, we showed that repeated social defeat delayed the expression of social investigation in long (10 min) sessions of social interaction. Also, the incidence of defensive behaviors, including stretched-attend posture and high speed retreats, was significantly higher in defeated mice in comparison to controls. Interestingly, a subpopulation of defeated mice showed recurrent and non-habituating stretched-attend posture and persistent flights during the entire session. Two indexes were created based on defensive behaviors to show that only recurrent flights correlates with sucrose intake. Together, the present study corroborates the idea that this model of social stress can precipitate a myriad of behaviors not readily disentangled. We propose that long sessions (>150 s) and detailed ethological evaluation during social interaction tests are necessary to provide enough information to correctly classify defeated animals in terms of resilience and susceptibility to social defeat stress.

Caution When Diagnosing Your Mouse With Schizophrenia: The Use and Misuse of Model Animals for Understanding Psychiatric Disorders

Animal models are widely used in biomedical research, but their applicability to psychiatric disorders is less clear. There are several reasons for this, including 1) emergent features of psychiatric illness that are not captured by the sum of individual symptoms, 2) a lack of equivalency between model animal behavior and human psychiatric symptoms, and 3) the possibility that model organisms do not have (and may not be capable of having) the same illnesses as humans. Here, we discuss the effective use, and inherent limitations, of model animals for psychiatric research. As disrupted-in-schizophrenia 1 (DISC1) is a genetic risk factor across a spectrum of psychiatric disorders, we focus on the results of studies using mice with various mutations of DISC1. The data from a broad range of studies show remarkable consistency with the effects of DISC1 mutation on developmental/anatomical endophenotypes. However, when one expands the phenotype to include behavioral correlates of human psychiatric diseases, much of this consistency ends. Despite these challenges, model animals remain valuable for understanding the basic brain processes that underlie psychiatric diseases. We argue that model animals have great potential to help us understand the core neurobiological dysfunction underlying psychiatric disorders and that marrying genetics and brain circuits with behavior is a good way forward.

Neighborhood matters: divergent patterns of stress-induced plasticity across the brain

The fact that exposure to severe stress leads to the development of psychiatric disorders serves as the basic rationale for animal models of stress disorders. Clinical and neuroimaging studies have shown that three brain areas involved in learning and memory--the hippocampus, amygdala and prefrontal cortex--undergo distinct structural and functional changes in individuals with stress disorders. These findings from patient studies pose several challenges for animal models of stress disorders. For instance, why does stress impair cognitive function, yet enhance fear and anxiety? Can the same stressful experience elicit contrasting patterns of plasticity in the hippocampus, amygdala and prefrontal cortex? How does even a brief exposure to traumatic stress lead to long-lasting behavioral abnormalities? Thus, animal models of stress disorders must not only capture the unique spatio-temporal features of structural and functional alterations in these brain areas, but must also provide insights into the underlying neuronal plasticity mechanisms. This Review will address some of these key questions by describing findings from animal models on how stress-induced plasticity varies across different brain regions and thereby gives rise to the debilitating emotional and cognitive symptoms of stress-related psychiatric disorders.