Loss of glutamic acid decarboxylase (Gad67) in Gpr88-expressing neurons induces learning and social behavior deficits in mice

Orphan G Protein-Coupled Receptor GPR88: Mapping Its Significance in Central Nervous System Disorders

G protein-coupled receptors (GPCRs), comprising the largest family of membrane receptors in humans, play a crucial roles in various physiological and pathological processes. Although several drugs that target GPCRs have been discovered, the characterization of orphan GPCRs (oGPCRs) remains a significant challenge. Despite extensive research, knowledge on a significant portion of these receptors, along with their ligands and target sites, remains undefined. GPR88 belongs to the category of oGPCR that is expressed in various tissues and organs, with numerous studies indicating that it plays a regulatory role in cognitive processes, emotional responses, and motor control, thereby influencing various brain behaviors and functions associated with learning. Therefore, the purpose of this review was to thoroughly examine the role of GPR88 in various central nervous system diseases, with the ultimate aim of positioning it as a potential and promising target for drug development, particularly for the treatment of a broad spectrum of neurological disorders.

Action inflexibility and compulsive-like behavior accompany neurobiological alterations in the anterior orbitofrontal cortex and associated striatal nuclei

The orbitofrontal cortex (OFC) is a large cortical structure, expansive across anterior-posterior axes. It is essential for flexibly updating learned behaviors, and paradoxically, also implicated in inflexible and compulsive-like behaviors. Here, we investigated mice bred to display inflexible reward-seeking behaviors that are insensitive to action consequences. We found that these mice also demonstrate insensitivity to Pavlovian-to-instrumental transfer, as well as compulsive-like grooming behavior that is ameliorated by fluoxetine and inhibitory, but not excitatory, chemogenetic modulation of excitatory OFC neurons. Thus, these mice offer the opportunity to identify neurobiological factors associated with inflexible and compulsive-like behavior. Experimentally bred mice suffer excitatory dendritic spine attrition, as well as changes in inhibitory synapse-associated proteins, GAD67/GAD1 and SLITRK3, largely in the anterior and not posterior OFC (or medial frontal cortex). They also display higher levels of the excitatory synaptic marker striatin in the nucleus accumbens and lower levels of the excitatory synaptic marker SAPAP3 in the dorsal striatum, striatal nuclei that receive input from the anterior OFC. Together, our findings point to the anterior OFC as a potential locus controlling action flexibility and compulsive-like behavior alike.

Discovery of BI-9508, a Brain-Penetrant GPR88-Receptor-Agonist Tool Compound for In Vivo Mouse Studies

Decreased activity and expression of the G-protein coupled receptor GPR88 is linked to many behavior-linked neurological disorders. Published preclinical GPR88 allosteric agonists all have in vivo pharmacokinetic properties that preclude their progression to the clinic, including high lipophilicity and poor brain penetration. Here, we describe our attempts to improve GPR88 agonists' drug-like properties and our analysis of the trade-offs required to successfully target GPR88's allosteric pocket. We discovered two new GPR88 agonists: One that reduced morphine-induced locomotor activity in a murine proof-of-concept study, and the atropoisomeric BI-9508, which is a brain penetrant and has improved pharmacokinetic properties and dosing that recommend it for future in vivo studies in rodents. BI-9508 still suffers from high lipophilicity, and research on this series was halted. Because of its utility as a tool compound, we now offer researchers access to BI-9508 and a negative control free of charge via Boehringer Ingelheim's open innovation portal opnMe.com.

Neural substrates for regulating self-grooming behavior in rodents

Grooming, as an evolutionarily conserved repetitive behavior, is common in various animals, including humans, and serves essential functions including, but not limited to, hygiene maintenance, thermoregulation, de-arousal, stress reduction, and social behaviors. In rodents, grooming involves a patterned and sequenced structure, known as the syntactic chain with four phases that comprise repeated stereotyped movements happening in a cephalocaudal progression style, beginning from the nose to the face, to the head, and finally ending with body licking. The context-dependent occurrence of grooming behavior indicates its adaptive significance. This review briefly summarizes the neural substrates responsible for rodent grooming behavior and explores its relevance in rodent models of neuropsychiatric disorders and neurodegenerative diseases with aberrant grooming phenotypes. We further emphasize the utility of rodent grooming as a reliable measure of repetitive behavior in neuropsychiatric models, holding promise for translational psychiatry. Herein, we mainly focus on rodent self-grooming. Allogrooming (grooming being applied on one animal by its conspecifics via licking or carefully nibbling) and heterogrooming (a form of grooming behavior directing towards another animal, which occurs in other contexts, such as maternal, sexual, aggressive, or social behaviors) are not covered due to space constraints.

Molecular insights into orphan G protein-coupled receptors relevant to schizophrenia

Schizophrenia remains a sizable socio-economic burden that continues to be treated with therapeutics based on 70-year old science. All currently approved therapeutics primarily target the dopamine D2 receptor to achieve their efficacy. Whilst dopaminergic dysregulation is a key feature in this disorder, the targeting of dopaminergic machinery has yielded limited efficacy and an appreciable side effect burden. Over the recent decades, numerous drugs that engage non-dopaminergic G protein-coupled receptors (GPCRs) have yielded a promise of efficacy without the deleterious side effect profile, yet none have successfully completed clinical studies and progressed to the market. More recently, there has been increased attention around non-dopaminergic GPCR-targeting drugs, which demonstrated efficacy in some schizophrenia symptom domains. This provides renewed hope that effective schizophrenia treatment may lie outside of the dopaminergic space. Despite the potential for muscarinic receptor- (and other well-characterised GPCR families) targeting drugs to treat schizophrenia, they are often plagued with complications such as lack of receptor subtype selectivity and peripheral on-target side effects. Orphan GPCR studies have opened a new avenue of exploration with many demonstrating schizophrenia-relevant mechanisms and a favourable expression profile, thus offering potential for novel drug development. This review discusses centrally expressed orphan GPCRs: GPR3, GPR6, GPR12, GPR52, GPR85, GPR88 and GPR139 and their relationship to schizophrenia. We review their expression, signalling mechanisms and cellular function, in conjunction with small molecule development and structural insights. We seek to provide a snapshot of the growing evidence and development potential of new classes of schizophrenia therapeutics. LINKED ARTICLES: This article is part of a themed issue Therapeutic Targeting of G Protein-Coupled Receptors: hot topics from the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists 2021 Virtual Annual Scientific Meeting. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.14/issuetoc.

The cortico-striatal circuitry in autism-spectrum disorders: a balancing act

The basal ganglia are major targets of cortical inputs and, in turn, modulate cortical function via their projections to the motor and prefrontal cortices. The role of the basal ganglia in motor control and reward is well documented and there is also extensive evidence that they play a key role in social and repetitive behaviors. The basal ganglia influence the activity of the cerebral cortex via two major projections from the striatum to the output nuclei, the globus pallidus internus and the substantia nigra, pars reticulata. This modulation involves a direct projection known as the direct pathway and an indirect projection via the globus pallidus externus and the subthalamic nucleus, known as the indirect pathway. This review discusses the respective contribution of the direct and indirect pathways to social and repetitive behaviors in neurotypical conditions and in autism spectrum disorders.

Caspase-1 affects chronic restraint stress-induced depression-like behaviors by modifying GABAergic dysfunction in the hippocampus

Major depression disorder (MDD) is one of the most common psychiatric disorders and one of the leading causes of disability in worldwide. Both inflammation and GABAergic dysfunction have been implicated in the pathophysiology of MDD. Caspase-1, a classic inflammatory caspase, regulates AMPARs-mediated glutamatergic neurotransmission. However, the role of caspase-1 in chronic stress-induced GABAergic dysfunction remains largely unknown. In this study, we found that serum and hippocampal caspase-1-IL-1β levels increased significantly in chronic restraint stress (CRS) mice, and a significant negative correlation occurred between levels of caspase-1 and depression-like behaviors. Furthermore, CRS significantly decreased GAD67 mRNA levels and GABAergic neurotransmission accompanied by the reduction of GABA concentration, reduced the amplitude and frequency of mIPSCs inhibitory postsynaptic currents (mIPSCs) and the decreased surface expression of GABA_ARs γ2 subunit in the hippocampus. Genetic deficiency of caspase-1 not only blocked CRS-induced depression-like behaviors, but also alleviated CRS-induced impairments in GABAergic neurotransmission. Finally, reexpression of caspase-1 in the hippocampus of Caspase-1^-/- mice increased susceptibility to stress-induced anxiety- and depression-like behaviors through inhibiting GAD67 expression and GABA_ARs-mediated synaptic transmission. Our study suggests that CRS dysregulates GABAergic neurotransmission via increasing the levels of caspase-1-mediated neuroinflammation in the hippocampus, ultimately leading to depression-like behaviors. This work illustrates that targeting caspase-1 may provide potential therapeutic benefits to stress-related GABAergic dysfunction in the pathogenesis of MDD.

Maternal immune activation affects socio-communicative behavior in adult rats

A wide body of evidence suggests a relationship between maternal immune activation (MIA) and neurodevelopmental disorders such as autism spectrum disorder (ASD). Since social and communicative deficits are included in the first diagnostic criterion of ASD, we aimed to characterize socio-communicative behaviors in the MIA model based on prenatal exposure to poly(I:C). Our previous studies demonstrated impaired socio-communicative functioning in poly(I:C)-exposed adolescent rats. Therefore, the current study sought to clarify whether these changes would persist beyond adolescence. For this purpose, we analyzed behavior during the social interaction test and recorded ultrasonic vocalizations (USVs) accompanying interactions between adult poly(I:C) rats. The results demonstrated that the altered pattern of social behavior in poly(I:C) males was accompanied by the changes in acoustic parameters of emitted USVs. Poly(I:C) males also demonstrated an impaired olfactory preference for social stimuli. While poly(I:C) females did not differ from controls in socio-positive behaviors, they displayed aggression during the social encounter and were more reactive to somatosensory stimulation. Furthermore, the locomotor pattern of poly(I:C) animals were characterized by repetitive behaviors. Finally, poly(I:C) reduced parvalbumin and GAD67 expression in the cerebellum. The results showed that prenatal poly(I:C) exposure altered the pattern of socio-communicative behaviors of adult rats in a sex-specific manner.

Excitatory and inhibitory neuron imbalance in the intrauterine growth restricted fetal guinea pig brain: Relevance to the developmental origins of schizophrenia and autism

Neurodevelopmental disorders such as schizophrenia and autism are thought to involve an imbalance of excitatory and inhibitory signaling in the brain. Intrauterine growth restriction (IUGR) is a risk factor for these disorders, with IUGR onset occurring during critical periods of neurodevelopment. The aim of this study was to determine the impact of IUGR on excitatory and inhibitory neurons of the fetal neocortex and hippocampus. Fetal brains (n = 2) were first collected from an unoperated pregnant guinea pig at mid-gestation (32 days of gestation [dg]; term ∼67 dg) to visualize excitatory (Ctip2) and inhibitory (calretinin [CR] and somatostatin [SST]) neurons via immunohistochemistry. Chronic placental insufficiency (CPI) was then induced via radial artery ablation at 30 dg in another cohort of pregnant guinea pigs (n = 8) to generate IUGR fetuses (52 dg; n = 8); control fetuses (52 dg; n = 7) were from sham surgeries with no radial artery ablation. At 32 dg, Ctip2- and CR-immunoreactive (IR) cells had populated the cerebral cortex, whereas SST-IR cells had not, suggesting these neurons were yet to complete migration. At 52 dg, in IUGR versus control fetuses, there was a reduction in SST-IR cell density in the cerebral cortex (p = .0175) and hilus of the dentate gyrus (p = .0035) but not the striatum (p > .05). There was no difference between groups in the density of Ctip2-IR (cortex) or CR-IR (cortex, hippocampus) neurons (p > 0.05). Thus, we propose that an imbalance in inhibitory (SST-IR) and excitatory (Ctip2-IR) neurons in the IUGR fetal guinea pig brain could lead to excitatory/inhibitory dysfunction commonly seen in neurodevelopmental disorders such as autism and schizophrenia.

Autism Spectrum Disorder: Focus on Glutamatergic Neurotransmission

Disturbances in the glutamatergic system have been increasingly documented in several neuropsychiatric disorders, including autism spectrum disorder (ASD). Glutamate-centered theories of ASD are based on evidence from patient samples and postmortem studies, as well as from studies documenting abnormalities in glutamatergic gene expression and metabolic pathways, including changes in the gut microbiota glutamate metabolism in patients with ASD. In addition, preclinical studies on animal models have demonstrated glutamatergic neurotransmission deficits and altered expression of glutamate synaptic proteins. At present, there are no approved glutamatergic drugs for ASD, but several ongoing clinical trials are currently focusing on evaluating in autistic patients glutamatergic pharmaceuticals already approved for other conditions. In this review, we provide an overview of the literature concerning the role of glutamatergic neurotransmission in the pathophysiology of ASD and as a potential target for novel treatments.

Spontaneous seizure and memory loss in mice expressing an epileptic encephalopathy variant in the calmodulin-binding domain of Kv7.2

Epileptic encephalopathy (EE) is characterized by seizures that respond poorly to antiseizure drugs, psychomotor delay, and cognitive and behavioral impairments. One of the frequently mutated genes in EE is KCNQ2, which encodes the Kv7.2 subunit of voltage-gated Kv7 potassium channels. Kv7 channels composed of Kv7.2 and Kv7.3 are enriched at the axonal surface, where they potently suppress neuronal excitability. Previously, we reported that the de novo dominant EE mutation M546V in human Kv7.2 blocks calmodulin binding to Kv7.2 and axonal surface expression of Kv7 channels via their intracellular retention. However, whether these pathogenic mechanisms underlie epileptic seizures and behavioral comorbidities remains unknown. Here, we report conditional transgenic cKcnq2+/M547V mice, in which expression of mouse Kv7.2-M547V (equivalent to human Kv7.2-M546V) is induced in forebrain excitatory pyramidal neurons and astrocytes. These mice display early mortality, spontaneous seizures, enhanced seizure susceptibility, memory impairment, and repetitive behaviors. Furthermore, hippocampal pathology shows widespread neurodegeneration and reactive astrocytes. This study demonstrates that the impairment in axonal surface expression of Kv7 channels is associated with epileptic seizures, cognitive and behavioral deficits, and neuronal loss in KCNQ2-related EE.

Social impairments in mice lacking the voltage-gated potassium channel Kv3.1

Parvalbumin (PV)-expressing neurons have been implicated in the pathology of autism spectrum disorders (ASD). Loss of PV expression and/or reduced number of PV-expressing neurons have been reported not only in genetic and environmental rodent models of ASD, but also in post-mortem analyses of brain tissues from ASD vs. healthy control human subjects. PV-expressing neurons play a pivotal role in the maintenance of the balance between excitation and inhibition within neural circuits in part because of their fast-spiking properties. Their high firing rate is mostly regulated by the voltage-gated potassium channel Kv3.1. It is yet unknown whether disturbances in the electrophysiological properties of PV-expressing neurons per se can lead to behavioral disturbances. We assessed locomotor activity, social interaction, recognition and memory, and stereotypic behaviors in Kv3.1 wild-type (WT) and knockout (KO) mice. We then used Western Blot analyses to measure the impact of Kv3.1 deficiency on markers of GABA transmission (PV and GAD67) and neural circuit activity (Egr1). Deficiency in Kv3.1 channel is sufficient to induce social deficits, hyperactivity and stereotypic behaviors. These behavioral changes were independent of changes in GAD67 levels and associated with increased levels of PV protein in the prefrontal cortex and striatum. These findings reveal that a loss of PV expression is not a necessary factor to induce an ASD-like phenotype in mice and support the need for further investigation to fully understand the contribution of PV-expressing neurons to ASD pathology.

Excitation/inhibition imbalance and impaired neurogenesis in neurodevelopmental and neurodegenerative disorders

The excitation/inhibition (E/I) balance controls the synaptic inputs to prevent the inappropriate responses of neurons to input strength, and is required to restore the initial pattern of network activity. Various neurotransmitters affect synaptic plasticity within neural networks via the modulation of neuronal E/I balance in the developing and adult brain. Less is known about the role of E/I balance in the control of the development of the neural stem and progenitor cells in the course of neurogenesis and gliogenesis. Recent findings suggest that neural stem and progenitor cells appear to be the target for the action of GABA within the neurogenic or oligovascular niches. The same might be true for the role of neuropeptides (i.e. oxytocin) in neurogenic niches. This review covers current understanding of the role of E/I balance in the regulation of neuroplasticity associated with social behavior in normal brain, and in neurodevelopmental and neurodegenerative diseases. Further studies are required to decipher the GABA-mediated regulation of postnatal neurogenesis and synaptic integration of newly-born neurons as a potential target for the treatment of brain diseases.

Neuromedin U induces self-grooming in socially-stimulated mice

Emerging evidence suggest that appetite-regulating peptides modulate social behaviors. We here investigate whether the anorexigenic peptide neuromedin U (NMU) modulates sexual behavior in male mice. However, instead of modulating sexual behaviors, NMU administered into the third ventricle increased self-grooming behavior. In addition, NMU-treatment increased self-grooming behavior when exposed to other mice or olfactory social-cues, but not when exposed to non-social environments. As the neuropeptide oxytocin is released during social investigation and exogenous oxytocin induces self-grooming, its role in NMU-induced self-grooming behavior was investigated. In line with our hypothesis, the oxytocin receptor antagonist inhibited NMU-induced self-grooming behavior in mice exposed to olfactory social-cues. Moreover, dopamine in the mesocorticolimbic system is known to be a key regulator of self-grooming behavior. In line with this, we proved that infusion of NMU into nucleus accumbens increased self-grooming behavior in mice confronted with an olfactory social-cue and that this behavior was inhibited by antagonism of dopamine D2, but not D1/D5, receptors. Moreover repeated NMU treatment enhanced ex vivo dopamine levels and decreased the expression of dopamine D2 receptors in nucleus accumbens in socially housed mice. On the other hand, the olfactory stimuli-dependent NMU-induced self-grooming was not affected by a corticotrophin-releasing hormone antagonist, and NMU-treatment did not influence repetitive behaviors in the marble burying test. In conclusion, our results suggest that NMU treatment and, social cues - potentially triggering oxytocin release - together induce excessive grooming behavior in male mice. The mesolimbic dopamine system, including accumbal dopamine D2 receptors, was identified as a crucial downstream mechanism.

Heterozygous loss of epilepsy gene KCNQ2 alters social, repetitive and exploratory behaviors

KCNQ/K_v7 channels conduct voltage‐dependent outward potassium currents that potently decrease neuronal excitability. Heterozygous inherited mutations in their principle subunits K_v7.2/KCNQ2 and K_v7.3/KCNQ3 cause benign familial neonatal epilepsy whereas patients with de novo heterozygous K_v7.2 mutations are associated with early‐onset epileptic encephalopathy and neurodevelopmental disorders characterized by intellectual disability, developmental delay and autism. However, the role of K_v7.2‐containing K_v7 channels in behaviors especially autism‐associated behaviors has not been described. Because pathogenic K_v7.2 mutations in patients are typically heterozygous loss‐of‐function mutations, we investigated the contributions of K_v7.2 to exploratory, social, repetitive and compulsive‐like behaviors by behavioral phenotyping of both male and female KCNQ2^+/− mice that were heterozygous null for the KCNQ2 gene. Compared with their wild‐type littermates, male and female KCNQ2^+/− mice displayed increased locomotor activity in their home cage during the light phase but not the dark phase and showed no difference in motor coordination, suggesting hyperactivity during the inactive light phase. In the dark phase, KCNQ2^+/− group showed enhanced exploratory behaviors, and repetitive grooming but decreased sociability with sex differences in the degree of these behaviors. While male KCNQ2^+/− mice displayed enhanced compulsive‐like behavior and social dominance, female KCNQ2^+/− mice did not. In addition to elevated seizure susceptibility, our findings together indicate that heterozygous loss of K_v7.2 induces behavioral abnormalities including autism‐associated behaviors such as reduced sociability and enhanced repetitive behaviors. Therefore, our study is the first to provide a tangible link between loss‐of‐function K_v7.2 mutations and the behavioral comorbidities of K_v7.2‐associated epilepsy.

Changes in GABAergic markers accompany degradation of neuronal function in the primary visual cortex of senescent rats

Numerous studies have reported age-dependent degradation of neuronal function in the visual cortex and have attributed this functional decline to weakened intracortical inhibition, especially GABAergic inhibition. However, whether this type of functional decline is linked to compromised GABAergic inhibition has not been fully confirmed. Here, we compared the neuronal response properties and markers of GABAergic inhibition in the primary visual cortex (V1) of young adult and senescent rats. Compared with those of young adult rats, old rats’ V1 neurons exhibited significantly increased visually evoked responses and spontaneous activity, a decreased signal-to-noise ratio and reduced response selectivity for the stimulus orientation and motion direction. Additionally, the ratio of GABA-positive neurons to total cortical neurons in old rats was significantly decreased compared with that in young rats. Expression of the key GABA-synthesizing enzyme GAD67 was significantly lower in old rats than in young rats, although GAD65 expression showed a marginal difference between the two age groups. Further, expression of an important GABA_A receptor subunit, GABA_AR α₁, was significantly attenuated in old rats relative to young ones. These results demonstrate that ageing may result in decreased GABAergic inhibition in the visual cortex and that this decrease in GABAergic inhibition accompanies neuronal function degradation.

INTERNEURONOPATHIES AND THEIR ROLE IN EARLY LIFE EPILEPSIES AND NEURODEVELOPMENTAL DISORDERS

GABAergic interneurons control the neural circuitry and network activity in the brain. The advances in genetics have identified genes that control the development, maturation and integration of GABAergic interneurons and implicated them in the pathogenesis of epileptic encephalopathies or neurodevelopmental disorders. For example, mutations of the Aristaless-Related homeobox X-linked gene (ARX) may result in defective GABAergic interneuronal migration in infants with epileptic encephalopathies like West syndrome (WS), Ohtahara syndrome or X-linked lissencephaly with abnormal genitalia (XLAG). The concept of "interneuronopathy", i.e. impaired development, migration or function of interneurons, has emerged as a possible etiopathogenic mechanism for epileptic encephalopathies. Treatments that enhance GABA levels, may help seizure control but do not necessarily show disease modifying effect. On the other hand, interneuronopathies can be seen in other conditions in which epilepsy may not be the primary manifestation, such as autism. In this review, we plan to outline briefly the current state of knowledge on the origin, development, and migration and integration of GABAergic interneurons, present neurodevelopmental conditions, with or without epilepsy, that have been associated with interneuronopathies and discuss the evidence linking certain types of interneuronal dysfunction with epilepsy and/or cognitive or behavioral deficits.

GPR88 is a critical regulator of feeding and body composition in mice

GPR88 is an orphan G-protein-coupled receptor with predominant expression in reward-related areas in the brain. While the lack of GPR88 has been demonstrated to induce behavioral deficits, the potential function of the receptor in the control of food intake and energy balance remains unexplored. In this work, the role of GPR88 in energy homeostasis was investigated in Gpr88^−/− mice fed either standard chow or high fat diet (HFD). Gpr88^−/− mice showed significantly reduced adiposity accompanied with suppressed spontaneous food intake, particularly pronounced under HFD treatment. While energy expenditure was likewise lower in Gpr88^−/− mice, body weight gain remained unchanged. Furthermore, deregulation in glucose tolerance and insulin responsiveness in response to HFD was attenuated in Gpr88^−/− mice. On the molecular level, distinct changes in the hypothalamic mRNA levels of cocaine-and amphetamine-regulated transcript (Cartpt), a neuropeptide involved in the control of feeding and reward, were observed in Gpr88^−/− mice. In addition, GPR88 deficiency was associated with altered expressions of the anorectic Pomc and the orexigenic Npy in the arcuate nucleus, especially under HFD condition. Together, our results indicate that GPR88 signalling is not only important for reward processes, but also plays a role in the central regulatory circuits for energy homeostasis.

Protocadherin 10 alters γ oscillations, amino acid levels, and their coupling; baclofen partially restores these oscillatory deficits

Approximately one in 45 children have been diagnosed with Autism Spectrum Disorder (ASD), which is characterized by social/communication impairments. Recent studies have linked a subset of familial ASD to mutations in the Protocadherin 10 (Pcdh10) gene. Additionally, Pcdh10's expression pattern, as well as its known role within protein networks, implicates the gene in ASD. Subsequently, the neurobiology of mice heterozygous for Pcdh10 (Pcdh10^+/-) has been investigated as a proxy for ASD. Male Pcdh10^+/- mice have demonstrated sex-specific deficits in social behavior, recapitulating the gender bias observed in ASD. Furthermore, in vitro slice preparations of these Pcdh10^+/- mice demonstrate selective decreases to high frequency electrophysiological responses, mimicking clinical observations. The direct in vivo ramifications of such decreased in vitro high frequency responses are unclear. As such, Pcdh10^+/- mice and their wild-type (WT) littermates underwent in vivo electrocorticography (ECoG), as well as ex vivo amino acid concentration quantification using High Performance Liquid Chromatography (HPLC). Similar to the previously observed reductions to in vitro high frequency electrophysiological responses in Pcdh10^+/- mice, male Pcdh10^+/- mice exhibited reduced gamma-band (30-80Hz), but not lower frequency (10 and 20Hz), auditory steady state responses (ASSR). In addition, male Pcdh10^+/- mice exhibited decreased signal-to-noise-ratio (SNR) for high gamma-band (60-100Hz) activity. These gamma-band perturbations for both ASSR and SNR were not observed in females. Administration of a GABA_B agonist remediated these electrophysiological alterations among male Pcdh10^+/-mice. Pcdh10^+/- mice demonstrated increased concentrations of GABA and glutamine. Of note, a correlation of auditory gamma-band responses with underlying GABA concentrations was observed in WT mice. This correlation was not present in Pcdh10^+/- mice. This study demonstrates the role of Pcdh10 in the regulation of excitatory-inhibitory balance as a function of GABA in ASD.

Basal ganglia and autism - a translational perspective

The basal ganglia are a collection of nuclei below the cortical surface that are involved in both motor and non-motor functions, including higher order cognition, social interactions, speech, and repetitive behaviors. Motor development milestones that are delayed in autism such as gross motor, fine motor and walking can aid in early diagnosis of autism. Neuropathology and neuroimaging findings in autism cases revealed volumetric changes and altered cell density in select basal ganglia nuclei. Interestingly, in autism, both the basal ganglia and the cerebellum are impacted both in their motor and non-motor domains and recently, found to be connected via the pons through a short disynaptic pathway. In typically developing individuals, the basal ganglia plays an important role in: eye movement, movement coordination, sensory modulation and processing, eye-hand coordination, action chaining, and inhibition control. Genetic models have proved to be useful toward understanding cellular and molecular changes at the synaptic level in the basal ganglia that may in part contribute to these autism-related behaviors. In autism, basal ganglia functions in motor skill acquisition and development are altered, thus disrupting the normal flow of feedback to the cortex. Taken together, there is an abundance of emerging evidence that the basal ganglia likely plays critical roles in maintaining an inhibitory balance between cortical and subcortical structures, critical for normal motor actions and cognitive functions. In autism, this inhibitory balance is disturbed thus impacting key pathways that affect normal cortical network activity. Autism Res 2017, 10: 1751-1775. © 2017 International Society for Autism Research, Wiley Periodicals, Inc.

LAY SUMMARY

Habit learning, action selection and performance are modulated by the basal ganglia, a collection of groups of neurons located below the cerebral cortex in the brain. In autism, there is emerging evidence that parts of the basal ganglia are structurally and functionally altered disrupting normal information flow. The basal ganglia through its interconnected circuits with the cerebral cortex and the cerebellum can potentially impact various motor and cognitive functions in the autism brain.

Decreasing GABA function within the medial prefrontal cortex or basolateral amygdala decreases sociability

INTRODUCTION

Decreased sociability is a symptom of psychiatric conditions including autism-spectrum disorder and schizophrenia. Both of these conditions are associated with decreases in GABA function, particularly in the medial prefrontal cortex (PFC) and the basolateral amygdala (BLA); structures that are components of the social brain. Here, we determined if decreasing GABA transmission within either the PFC or the BLA decreases social behavior.

METHODS

Rats were implanted with cannulae aimed at either the medial PFC or the BLA and then were tested on up to 4 behavioral tests following bilateral infusions of 0.5μl bicuculline methiodide (BMI, a GABA_A receptor antagonist) at doses of 0, 25, or 50ng/μl. Rats were tested in the social interaction test, the social preference test, the sucrose preference test and for locomotor activity (BLA infusions only).

RESULTS

Intra-BLA or PFC BMI infusions decreased the amount of time and the number of social interactions in the social interaction test. Further, in the social preference test, rats infused with 50ng BMI no longer exhibited a preference to explore a social over a non-social stimulus. The change in sociability was not due to a change in reward processing or locomotor behavior.

DISCUSSION

Decreasing GABA transmission in either the medial PFC or BLA decreased sociability. Thus, changes in GABA signaling observed in conditions such as autism or schizophrenia may mediate the social withdrawal characteristic of these conditions. Moreover, they suggest that social withdrawal may be treated by drugs that potentiate GABA transmission.

DNA Methylation Profiling at Single-Base Resolution Reveals Gestational Folic Acid Supplementation Influences the Epigenome of Mouse Offspring Cerebellum

It is becoming increasingly more evident that lifestyle, environmental factors, and maternal nutrition during gestation can influence the epigenome of the developing fetus and thus modulate the physiological outcome. Variations in the intake of maternal nutrients affecting one-carbon metabolism may influence brain development and exert long-term effects on the health of the progeny. In this study, we investigated whether supplementation with high maternal folic acid during gestation alters DNA methylation and gene expression in the cerebellum of mouse offspring. We used reduced representation bisulfite sequencing to analyze the DNA methylation profile at the single-base resolution level. The genome-wide DNA methylation analysis revealed that supplementation with higher maternal folic acid resulted in distinct methylation patterns (P < 0.05) of CpG and non-CpG sites in the cerebellum of offspring. Such variations of methylation and gene expression in the cerebellum of offspring were highly sex-specific, including several genes of the neuronal pathways. These findings demonstrate that alterations in the level of maternal folic acid during gestation can influence methylation and gene expression in the cerebellum of offspring. Such changes in the offspring epigenome may alter neurodevelopment and influence the functional outcome of neurologic and psychiatric diseases.

Calbindin Knockout Alters Sex-Specific Regulation of Behavior and Gene Expression in Amygdala and Prefrontal Cortex

Calbindin-D(28K) (Calb1), a high-affinity calcium buffer/sensor, shows abundant expression in neurons and has been associated with a number of neurobehavioral diseases, many of which are sexually dimorphic in incidence. Behavioral and physiological end points are affected by experimental manipulations of calbindin levels, including disruption of spatial learning, hippocampal long-term potentiation, and circadian rhythms. In this study, we investigated novel aspects of calbindin function on social behavior, anxiety-like behavior, and fear conditioning in adult mice of both sexes by comparing wild-type to littermate Calb1 KO mice. Because Calb1 mRNA and protein are sexually dimorphic in some areas of the brain, we hypothesized that sex differences in behavioral responses of these behaviors would be eliminated or revealed in Calb1 KO mice. We also examined gene expression in the amygdala and prefrontal cortex, two areas of the brain intimately connected with limbic system control of the behaviors tested, in response to sex and genotype. Our results demonstrate that fear memory and social behavior are altered in male knockout mice, and Calb1 KO mice of both sexes show less anxiety. Moreover, gene expression studies of the amygdala and prefrontal cortex revealed several significant genotype and sex effects in genes related to brain-derived neurotrophic factor signaling, hormone receptors, histone deacetylases, and γ-aminobutyric acid signaling. Our findings are the first to directly link calbindin with affective and social behaviors in rodents; moreover, the results suggest that sex differences in calbindin protein influence behavior.

Maturation of auditory neural processes in autism spectrum disorder - A longitudinal MEG study

BACKGROUND

Individuals with autism spectrum disorder (ASD) show atypical brain activity, perhaps due to delayed maturation. Previous studies examining the maturation of auditory electrophysiological activity have been limited due to their use of cross-sectional designs. The present study took a first step in examining magnetoencephalography (MEG) evidence of abnormal auditory response maturation in ASD via the use of a longitudinal design.

METHODS

Initially recruited for a previous study, 27 children with ASD and nine typically developing (TD) children, aged 6- to 11-years-old, were re-recruited two to five years later. At both timepoints, MEG data were obtained while participants passively listened to sinusoidal pure-tones. Bilateral primary/secondary auditory cortex time domain (100 ms evoked response latency (M100)) and spectrotemporal measures (gamma-band power and inter-trial coherence (ITC)) were examined. MEG measures were also qualitatively examined for five children who exhibited "optimal outcome", participants who were initially on spectrum, but no longer met diagnostic criteria at follow-up.

RESULTS

M100 latencies were delayed in ASD versus TD at the initial exam (~ 19 ms) and at follow-up (~ 18 ms). At both exams, M100 latencies were associated with clinical ASD severity. In addition, gamma-band evoked power and ITC were reduced in ASD versus TD. M100 latency and gamma-band maturation rates did not differ between ASD and TD. Of note, the cohort of five children that demonstrated "optimal outcome" additionally exhibited M100 latency and gamma-band activity mean values in-between TD and ASD at both timepoints. Though justifying only qualitative interpretation, these "optimal outcome" related data are presented here to motivate future studies.

CONCLUSIONS

Children with ASD showed perturbed auditory cortex neural activity, as evidenced by M100 latency delays as well as reduced transient gamma-band activity. Despite evidence for maturation of these responses in ASD, the neural abnormalities in ASD persisted across time. Of note, data from the five children whom demonstrated "optimal outcome" qualitatively suggest that such clinical improvements may be associated with auditory brain responses intermediate between TD and ASD. These "optimal outcome" related results are not statistically significant though, likely due to the low sample size of this cohort, and to be expected as a result of the relatively low proportion of "optimal outcome" in the ASD population. Thus, further investigations with larger cohorts are needed to determine if the above auditory response phenotypes have prognostic utility, predictive of clinical outcome.

Dietary Restriction Affects Neuronal Response Property and GABA Synthesis in the Primary Visual Cortex

Previous studies have reported inconsistent effects of dietary restriction (DR) on cortical inhibition. To clarify this issue, we examined the response properties of neurons in the primary visual cortex (V1) of DR and control groups of cats using in vivo extracellular single-unit recording techniques, and assessed the synthesis of inhibitory neurotransmitter GABA in the V1 of cats from both groups using immunohistochemical and Western blot techniques. Our results showed that the response of V1 neurons to visual stimuli was significantly modified by DR, as indicated by an enhanced selectivity for stimulus orientations and motion directions, decreased visually-evoked response, lowered spontaneous activity and increased signal-to-noise ratio in DR cats relative to control cats. Further, it was shown that, accompanied with these changes of neuronal responsiveness, GABA immunoreactivity and the expression of a key GABA-synthesizing enzyme GAD67 in the V1 were significantly increased by DR. These results demonstrate that DR may retard brain aging by increasing the intracortical inhibition effect and improve the function of visual cortical neurons in visual information processing. This DR-induced elevation of cortical inhibition may favor the brain in modulating energy expenditure based on food availability.

Neurobiology of rodent self-grooming and its value for translational neuroscience

Self-grooming is a complex innate behaviour with an evolutionarily conserved sequencing pattern and is one of the most frequently performed behavioural activities in rodents. In this Review, we discuss the neurobiology of rodent self-grooming, and we highlight studies of rodent models of neuropsychiatric disorders--including models of autism spectrum disorder and obsessive compulsive disorder--that have assessed self-grooming phenotypes. We suggest that rodent self-grooming may be a useful measure of repetitive behaviour in such models, and therefore of value to translational psychiatry. Assessment of rodent self-grooming may also be useful for understanding the neural circuits that are involved in complex sequential patterns of action.

The Role of Epigenetic Change in Autism Spectrum Disorders

Autism spectrum disorders (ASD) are a heterogeneous group of neurodevelopmental disorders characterized by problems with social communication, social interaction, and repetitive or restricted behaviors. ASD are comorbid with other disorders including attention deficit hyperactivity disorder, epilepsy, Rett syndrome, and Fragile X syndrome. Neither the genetic nor the environmental components have been characterized well enough to aid diagnosis or treatment of non-syndromic ASD. However, genome-wide association studies have amassed evidence suggesting involvement of hundreds of genes and a variety of associated genetic pathways. Recently, investigators have turned to epigenetics, a prime mediator of environmental effects on genomes and phenotype, to characterize changes in ASD that constitute a molecular level on top of DNA sequence. Though in their infancy, such studies have the potential to increase our understanding of the etiology of ASD and may assist in the development of biomarkers for its prediction, diagnosis, prognosis, and eventually in its prevention and intervention. This review focuses on the first few epigenome-wide association studies of ASD and discusses future directions.

Novel systems modeling methodology in comparative microbial metabolomics: identifying key enzymes and metabolites implicated in autism spectrum disorders

Autism spectrum disorders are a group of mental illnesses highly correlated with gastrointestinal dysfunction. Recent studies have shown that there may be one or more microbial “fingerprints” in terms of the composition characterizing individuals with autism, which could be used for diagnostic purposes. This paper proposes a computational approach whereby metagenomes characteristic of “healthy” and autistic individuals are artificially constructed via genomic information, analyzed for the enzymes coded within, and then these enzymes are compared in detail. This is a text mining application. A custom-designed online application was built and used for the comparative metabolomics study and made publically available. Several of the enzyme-catalyzing reactions involved with the amino acid glutamate were curiously missing from the “autism” microbiome and were coded within almost every organism included in the “control” microbiome. Interestingly, there exists a leading hypothesis regarding autism and glutamate involving a neurological excitation/inhibition imbalance; but the association with this study is unclear. The results included data on the transsulfuration and transmethylation pathways, involved with oxidative stress, also of importance to autism. The results from this study are in alignment with leading hypotheses in the field, which is impressive, considering the purely in silico nature of this study. The present study provides new insight into the complex metabolic interactions underlying autism, and this novel methodology has potential to be useful for developing new hypotheses. However, limitations include sparse genome data availability and conflicting literature experimental data. We believe our software tool and methodology has potential for having great utility as data become more available, comprehensive and reliable.