A forward genetic screen identifies Dolk as a regulator of startle magnitude through the potassium channel subunit Kv1.1.

The acoustic startle response is an evolutionarily conserved avoidance behavior. Disruptions in startle behavior, particularly startle magnitude, are a hallmark of several human neurological disorders. While the neural circuitry underlying startle behavior has been studied extensively, the repertoire of genes and genetic pathways that regulate this locomotor behavior has not been explored using an unbiased genetic approach. To identify such genes, we took advantage of the stereotypic startle behavior in zebrafish larvae and performed a forward genetic screen coupled with whole genome analysis. We uncovered mutations in eight genes critical for startle behavior, including two genes encoding proteins associated with human neurological disorders, Dolichol kinase (Dolk), a broadly expressed regulator of the glycoprotein biosynthesis pathway, and the potassium Shaker-like channel subunit Kv1.1. We demonstrate that Kv1.1 and Dolk play critical roles in the spinal cord to regulate movement magnitude during the startle response and spontaneous swim movements. Moreover, we show that Kv1.1 protein is mislocalized in dolk mutants, suggesting they act in a common genetic pathway. Combined, our results identify a diverse set of eight genes, all associated with human disorders, that regulate zebrafish startle behavior and reveal a previously unappreciated role for Dolk and Kv1.1 in regulating movement magnitude via a common genetic pathway.

Properties of the Caudal Pontine Reticular Nucleus Neurons Determine the Acoustic Startle Response in Cntnap2 KO Rats.

BACKGROUND: Rats with a loss-of-function mutation in the contactin-associated protein-like 2 (Cntnap2) gene have been validated as an animal model of autism spectrum disorder (ASD). Similar to many autistic individuals, Cntnap2 knock-out rats (Cntnap2-⁣/-) are hyperreactive to sound as measured through the acoustic startle response. The brainstem region that mediates the acoustic startle response is the caudal pontine reticular nucleus (PnC), specifically giant neurons in the PnC. We previously reported a sex-dependent genotypic effect in the sound-evoked neuronal activity recorded from the PnC, whereby female Cntnap2-⁣/- rats had a dramatic increase in sound-evoked responses compared with wildtype counterparts, but male Cntnap2-⁣/- rats showed only a modest increase in PnC activity that cannot fully explain the largely increased startle in male Cntnap2-⁣/- rats. The present study therefore investigates activation and histological properties of PnC giant neurons in Cntnap2-⁣/- rats and wildtype littermates. METHODS: The acoustic startle response was elicited by presenting rats with 95 dB startle pulses before rats were euthanized. PnC brain sections were stained and analyzed for the total number of PnC giant neurons and the percentage of giant neurons that expressed phosphorylated cAMP response element binding protein (pCREB) in response to startle stimuli. Additionally, in vitro electrophysiology was conducted to assess the resting state activity and intrinsic properties of PnC giant neurons. RESULTS: Wildtype and Cntnap2-⁣/- rats had similar total numbers of PnC giant neurons and similar levels of baseline pCREB expression, as well as similar numbers of giant neurons that were firing at rest. Increased startle magnitudes in Cntnap2-⁣/- rats were associated with increased percentages of pCREB-expressing PnC giant neurons in response to startle stimuli. Male rats had increased pCREB-expressing PnC giant neurons compared with female rats, and the recruited giant neurons in males were also larger in soma size. CONCLUSIONS: Recruitment and size of PnC giant neurons are important factors for regulating the magnitude of the acoustic startle response in Cntnap2-⁣/- rats, particularly in males. These findings allow for a better understanding of increased reactivity to sound in Cntnap2-⁣/- rats and in CNTNAP2-associated disorders such as ASD.

Expanding the spectrum of KCNJ6-related disorders: Milder phenotype with pathological startle responses.

Keppen-Lubinsky syndrome is caused by pathogenic variants in KCNJ6, which encodes the inwardly rectifying channel subfamily J6. The four confirmed cases reported to date were characterized by severe intellectual disability, global developmental delay, feeding difficulties, and dysmorphic features. All but one of the cases also had a severe form of lipodystrophy, resulting in tightly adherent facial skin and appearance of premature aging. Here, we describe a 36-year-old female with a de novo pathogenic variant in KCNJ6 (NM_002240.5: c.460G>T; p.(Gly154Cys)) presenting with mild intellectual disability, subtle dysmorphic features, obsessive-compulsive disorder, and an exaggerated startle response. This case indicates that KCNJ6-related disorders should be considered in patients with less pronounced dysmorphic features and milder cognitive impairment, as well as in patients with startle disorders.

A novel role for the ADHD risk gene latrophilin-3 in learning and memory in Lphn3 knockout rats.

Latrophilins (LPHNs) are adhesion G protein-coupled receptors with three isoforms but only LPHN3 is brain specific (caudate, prefrontal cortex, dentate, amygdala, and cerebellum). Variants of LPHN3 are associated with ADHD. Null mutations of Lphn3 in rat, mouse, zebrafish, and Drosophila result in hyperactivity, but its role in learning and memory (L&M) is largely unknown. Using our Lphn3 knockout (KO) rats we examined the cognitive abilities, long-term potentiation (LTP) in CA1, NMDA receptor expression, and neurohistology from heterozygous breeding pairs. KO rats were impaired in egocentric L&M in the Cincinnati water maze, spatial L&M and cognitive flexibility in the Morris water maze (MWM), with no effects on conditioned freezing, novel object recognition, or temporal order recognition. KO-associated locomotor hyperactivity had no effect on swim speed. KO rats had reduced early-LTP but not late-LTP and had reduced hippocampal NMDA-NR1 expression. In a second experiment, KO rats responded to a light prepulse prior to an acoustic startle pulse, reflecting visual signal detection. In a third experiment, KO rats given extra MWM pretraining and hidden platform overtraining showed no evidence of reaching WT rats' levels of learning. Nissl histology revealed no structural abnormalities in KO rats. LPHN3 has a selective effect on egocentric and allocentric L&M without effects on conditioned freezing or recognition memory.

Advances in hyperekplexia and other startle syndromes.

Startle, a basic alerting reaction common to all mammals, is described as a sudden involuntary movement of the body evoked by all kinds of sudden and unexpected stimulus. Startle syndromes are heterogeneous groups of disorders with abnormal and exaggerated responses to startling events, including hyperekplexia, stimulus-induced disorders, and neuropsychiatric startle syndromes. Hyperekplexia can be attributed to a genetic, idiopathic, or symptomatic cause. Excluding secondary factors, hereditary hyperekplexia, a rare neurogenetic disorder with highly genetic heterogeneity, is characterized by neonatal hypertonia, exaggerated startle response provoked by the sudden external stimuli, and followed by a short period of general stiffness. It mainly arises from defects of inhibitory glycinergic neurotransmission. GLRA1 is the major pathogenic gene of hereditary hyperekplexia, along with many other genes involved in the function of glycinergic inhibitory synapses. While about 40% of patients remain negative genetic findings. Clonazepam, which can specifically upgrade the GABARA1 chloride channels, is the main and most effective administration for hereditary hyperekplexia patients. In this review, with the aim at enhancing the recognition and prompting potential treatment for hyperekplexia, we focused on discussing the advances in hereditary hyperekplexia genetics and the expound progress in pathogenic mechanisms of the glycinergic-synapse-related pathway and then followed by a brief overview of other common startle syndromes.

Neurod1 Is Essential for the Primary Tonotopic Organization and Related Auditory Information Processing in the Midbrain.

Hearing depends on extracting frequency, intensity, and temporal properties from sound to generate an auditory map for acoustical signal processing. How physiology intersects with molecular specification to fine tune the developing properties of the auditory system that enable these aspects remains unclear. We made a novel conditional deletion model that eliminates the transcription factor NEUROD1 exclusively in the ear. These mice (both sexes) develop a truncated frequency range with no neuroanatomically recognizable mapping of spiral ganglion neurons onto distinct locations in the cochlea nor a cochleotopic map presenting topographically discrete projections to the cochlear nuclei. The disorganized primary cochleotopic map alters tuning properties of the inferior colliculus units, which display abnormal frequency, intensity, and temporal sound coding. At the behavioral level, animals show alterations in the acoustic startle response, consistent with altered neuroanatomical and physiological properties. We demonstrate that absence of the primary afferent topology during embryonic development leads to dysfunctional tonotopy of the auditory system. Such effects have never been investigated in other sensory systems because of the lack of comparable single gene mutation models.SIGNIFICANCE STATEMENT All sensory systems form a topographical map of neuronal projections from peripheral sensory organs to the brain. Neuronal projections in the auditory pathway are cochleotopically organized, providing a tonotopic map of sound frequencies. Primary sensory maps typically arise by molecular cues, requiring physiological refinements. Past work has demonstrated physiologic plasticity in many senses without ever molecularly undoing the specific mapping of an entire primary sensory projection. We genetically manipulated primary auditory neurons to generate a scrambled cochleotopic projection. Eliminating tonotopic representation to auditory nuclei demonstrates the inability of physiological processes to restore a tonotopic presentation of sound in the midbrain. Our data provide the first insights into the limits of physiology-mediated brainstem plasticity during the development of the auditory system.

Adolescent behavioral abnormalities in a Scn1a+/- mouse model of Dravet syndrome.

Dravet syndrome is an intractable pediatric epilepsy associated with SCN1A mutations. In addition to having a large seizure burden and a reduced lifespan, patients with Dravet syndrome also exhibit delays in reaching normal developmental milestones in attentional, emotional, and cognitive function. These developmental delays manifest in autistic-like social withdrawal and compulsive behavior. Additionally, cognitive impairments including deficits in sensorimotor processing and memory function are present. Several mouse models utilizing heterozygous deletion of Scn1a (Scn1a+/- mice) have been generated that recapitulate many aspects of Dravet syndrome. Studies in these mouse models of Dravet syndrome have characterized behavioral phenotypes in adult mice. In the present study, we characterized the behavioral phenotype of Scn1a+/- mice generated by targeted deletion of Scn1a exon 1 (Scn1atm1Kea) during adolescence. Identifying behavioral deficits in adolescent mice would more closely model the early onset of attentional, emotional, and cognitive delays observed in patients with Dravet syndrome. The behaviors of adolescent Scn1a+/- and wildtype (WT) mice were compared across several behavioral domains. We assessed motor function (open-field test), sociability and social recognition memory (three-chambered social preference and social interaction tests), memory function (novel object recognition, Barnes maze, fear conditioning paradigm), anxiety-related behavior (elevated plus maze and open-field thigmotaxis), startle reflex and sensorimotor gating (prepulse inhibition of startle (PPI) tests), and repetitive compulsive behavior (marble burying test). Adolescent Scn1a+/- mice exhibited normal locomotor activity, marble burying behavior, sociability, and sensorimotor gating. However, adolescent Scn1a+/- mice displayed increased anxiety-related thigmotactic behavior, atypical fear expression, blunted acoustic startle responses, and impaired social recognition and spatial memory. Our results show that Scn1a+/- mice display various behavioral impairments during adolescence, which provides a foundation for testing early intervention therapies targeting developmental delays modeled in Dravet syndrome mice.

Genetic Ablation of All Cerebellins Reveals Synapse Organizer Functions in Multiple Regions Throughout the Brain.

Cerebellins are synaptic organizer molecules that bind to presynaptic neurexins and postsynaptic receptors. They are well studied in the cerebellum, but three of the four cerebellins (Cbln1, Cbln2, and Cbln4) are also broadly expressed outside of the cerebellum, suggesting that they perform general functions throughout the brain. Here, we generated male and female constitutive single (KO), double KO (dKO), and triple KO (tKO) mice of Cbln1, Cbln2, and Cbln4. We found that all constitutive cerebellin-deficient mice were viable and fertile, suggesting that cerebellins are not essential for survival. Cbln1/2 dKO mice exhibited salience-induced seizures that were aggravated in Cbln1/2/4 tKO mice, suggesting that all cerebellins contribute to brain function. As described previously, Cbln1 KO mice displayed major motor impairments that were aggravated by additional KO of Cbln2. Strikingly, the Cbln1/2 dKO did not cause alterations in synapse density in the hippocampus of young adult (1- and 2-month-old) mice, but produced a selective ∼50% decrease in hippocampal synapse density in the stratum lacunosum moleculare of the CA1 region and in the dentate gyrus of aging, 6-month-old mice. A similar decrease in excitatory synapse density was observed in the striatum and retrosplenial cortex. Behaviorally, the Cbln1 KO produced dramatic changes in motor behaviors that were partly aggravated by additional deletion of Cbln2 and/or Cbln4. Our results show that cerebellins are not essential for survival and do not contribute to initial synapse formation, but perform multiple functions throughout the brain; as a consequence, their ablation results in a delayed loss of synapses and in behavioral impairments.SIGNIFICANCE STATEMENT Cerebellins (Cbln1-4) are trans-synaptic cell adhesion molecules. In the cerebellum, Cbln1 functions as a bidirectional organizer of parallel fiber-Purkinje cell synapses by binding to presynaptic neurexins and postsynaptic GluRδ2. Little is known about the function of cerebellins outside of the cerebellum; therefore, the present study used single, double, and triple constitutive KO mice of Cbln1, Cbln2, and Cbln4 to analyze the overall function of cerebellins. We show that cerebellins act as important synaptic organizers in specific subsets of neurons and likely contribute to many different brain functions. We also show that cerebellins are not initially required for synapse formation, but rather for specification and long-term synapse maintenance and demonstrate that all cerebellins, not just Cbln1, contribute to brain function.

Human BDNF rs6265 polymorphism as a mediator for the generalization of contextual anxiety.

The Met allele of the human brain-derived neurotrophic factor (BDNF) gene might be a risk factor for anxiety disorders and is associated with reduced hippocampal volume. Notably, hippocampus plays a crucial role in contextual learning and generalization. The role of the BDNF gene variation in human context-conditioning and generalization is still unknown. We investigated 33 carriers of the Met allele (18 females) and 32 homozygous carriers of the Val allele (15 females) with a virtual-reality context-conditioning paradigm. Electric stimulations (unconditioned stimulus, US) were unpredictably delivered in one virtual office (CTX+), but never in another virtual office (CTX-). During generalization, participants revisited CTX+ and CTX- and a generalization office (G-CTX), which was a mix of the other two. Rating data indicated successful conditioning (more negative valence, higher arousal, anxiety and contingency ratings for CTX+ than CTX-), and generalization of conditioned anxiety by comparable ratings for G-CTX and CTX+. The startle data indicated discriminative learning for Met allele carriers, but not for Val homozygotes. Moreover, a trend effect suggests that startle responses of only the Met carriers were slightly potentiated in G-CTX versus CTX-. In sum, the BDNF polymorphism did not affect contextual learning and its generalization on a verbal level. However, the physiological data suggest that Met carriers are characterized by fast discriminative contextual learning and a tendency to generalize anxiety responses to ambiguous contexts. We propose that such learning may be related to reduced hippocampal functionality and the basis for the risk of Met carriers to develop anxiety disorders.

GLRB allelic variation associated with agoraphobic cognitions, increased startle response and fear network activation: a potential neurogenetic pathway to panic disorder.

The molecular genetics of panic disorder (PD) with and without agoraphobia (AG) are still largely unknown and progress is hampered by small sample sizes. We therefore performed a genome-wide association study with a dimensional, PD/AG-related anxiety phenotype based on the Agoraphobia Cognition Questionnaire (ACQ) in a sample of 1370 healthy German volunteers of the CRC TRR58 MEGA study wave 1. A genome-wide significant association was found between ACQ and single non-coding nucleotide variants of the GLRB gene (rs78726293, P=3.3 × 10-8; rs191260602, P=3.9 × 10-8). We followed up on this finding in a larger dimensional ACQ sample (N=2547) and in independent samples with a dichotomous AG phenotype based on the Symptoms Checklist (SCL-90; N=3845) and a case-control sample with the categorical phenotype PD/AG (Ncombined =1012) obtaining highly significant P-values also for GLRB single-nucleotide variants rs17035816 (P=3.8 × 10-4) and rs7688285 (P=7.6 × 10-5). GLRB gene expression was found to be modulated by rs7688285 in brain tissue, as well as cell culture. Analyses of intermediate PD/AG phenotypes demonstrated increased startle reflex and increased fear network, as well as general sensory activation by GLRB risk gene variants rs78726293, rs191260602, rs17035816 and rs7688285. Partial Glrb knockout mice demonstrated an agoraphobic phenotype. In conjunction with the clinical observation that rare coding GLRB gene mutations are associated with the neurological disorder hyperekplexia characterized by a generalized startle reaction and agoraphobic behavior, our data provide evidence that non-coding, although functional GLRB gene polymorphisms may predispose to PD by increasing startle response and agoraphobic cognitions.

Association between genetic variability of neuronal nitric oxide synthase and sensorimotor gating in humans.

Research increasingly suggests that nitric oxide (NO) plays a role in the pathogenesis of schizophrenia. One important line of evidence comes from genetic studies, which have repeatedly detected an association between the neuronal isoform of nitric oxide synthase (nNOS or NOS1) and schizophrenia. However, the pathogenetic pathways linking nNOS, NO, and the disorder remain poorly understood. A deficit in sensorimotor gating is considered to importantly contribute to core schizophrenia symptoms such as psychotic disorganization and thought disturbance. We selected three candidate nNOS polymorphisms (Ex1f-VNTR, rs6490121 and rs41279104), associated with schizophrenia and cognition in previous studies, and tested their association with the efficiency of sensorimotor gating in healthy human adults. We found that risk variants of Ex1f-VNTR and rs6490121 (but not rs41279104) were associated with a weaker prepulse inhibition (PPI) of the acoustic startle reflex, a standard measure of sensorimotor gating. Furthermore, the effect of presence of risk variants in Ex1f-VNTR and rs6490121 was additive: PPI linearly decreased with increasing number of risk alleles, being highest in participants with no risk allele, while lowest in individuals who carry three risk alleles. Our findings indicate that NO is involved in the regulation of sensorimotor gating, and highlight one possible pathogenetic mechanism for NO playing a role in the development of schizophrenia psychosis.

A novel nonsense autosomal dominant mutation in the GLRA1 gene causing hyperekplexia.

We present a family with two members affected by hyperekplexia and two unaffected members. All exons in the glycine receptor alpha 1 subunit gene (GLRA1) were sequenced in all four family members. Our index patient harbored a novel nonsense mutation (p.Trp314*; rs867618642) in the transmembrane domain three of the GLRA1 and a novel missense variant in the NH2-terminal part (p.Val67Met; rs142888296). After development of tolerance for the effective treatment with clobazam a drug holiday led to a sustained restoration of the treatment response.

Dorsal Forebrain-Specific Deficiency of Reelin-Dab1 Signal Causes Behavioral Abnormalities Related to Psychiatric Disorders.

Reelin-Dab1 signaling is involved in brain development and neuronal functions. The abnormalities in the signaling through either reduction of Reelin and Dab1 gene expressions or the genomic mutations in the brain have been reported to be associated with psychiatric disorders. However, it has not been clear if the deficiency in Reelin-Dab1 signaling is responsible for symptoms of the disorders. Here, to examine the function of Reelin-Dab1 signaling in the forebrain, we generated dorsal forebrain-specific Dab1 conditional knockout mouse (Dab1 cKO) and performed a behavioral test battery on the Dab1 cKO mice. Although conventional Dab1 null mutant mice exhibit cerebellar atrophy and cerebellar ataxia, the Dab1 cKO mice had normal cerebellum and showed no motor dysfunction. Dab1 cKO mice exhibited behavioral abnormalities, including hyperactivity, decreased anxiety-like behavior, and impairment of working memory, which are reminiscent of symptoms observed in patients with psychiatric disorders such as schizophrenia and bipolar disorder. These results suggest that deficiency of Reelin-Dab1 signal in the dorsal forebrain is involved in the pathogenesis of some symptoms of human psychiatric disorders.

Impaired Dendritic Development and Memory in Sorbs2 Knock-Out Mice.

Intellectual disability is a common neurodevelopmental disorder characterized by impaired intellectual and adaptive functioning. Both environmental insults and genetic defects contribute to the etiology of intellectual disability. Copy number variations of SORBS2 have been linked to intellectual disability. However, the neurobiological function of SORBS2 in the brain is unknown. The SORBS2 gene encodes ArgBP2 (Arg/c-Abl kinase binding protein 2) protein in non-neuronal tissues and is alternatively spliced in the brain to encode nArgBP2 protein. We found nArgBP2 colocalized with F-actin at dendritic spines and growth cones in cultured hippocampal neurons. In the mouse brain, nArgBP2 was highly expressed in the cortex, amygdala, and hippocampus, and enriched in the outer one-third of the molecular layer in dentate gyrus. Genetic deletion of Sorbs2 in mice led to reduced dendritic complexity and decreased frequency of AMPAR-miniature spontaneous EPSCs in dentate gyrus granule cells. Behavioral characterization revealed that Sorbs2 deletion led to a reduced acoustic startle response, and defective long-term object recognition memory and contextual fear memory. Together, our findings demonstrate, for the first time, an important role for nArgBP2 in neuronal dendritic development and excitatory synaptic transmission, which may thus inform exploration of neurobiological basis of SORBS2 deficiency in intellectual disability. SIGNIFICANCE STATEMENT: Copy number variations of the SORBS2 gene are linked to intellectual disability, but the neurobiological mechanisms are unknown. We found that nArgBP2, the only neuronal isoform encoded by SORBS2, colocalizes with F-actin at neuronal dendritic growth cones and spines. nArgBP2 is highly expressed in the cortex, amygdala, and dentate gyrus in the mouse brain. Genetic deletion of Sorbs2 in mice leads to impaired dendritic complexity and reduced excitatory synaptic transmission in dentate gyrus granule cells, accompanied by behavioral deficits in acoustic startle response and long-term memory. This is the first study of Sorbs2 function in the brain, and our findings may facilitate the study of neurobiological mechanisms underlying SORBS2 deficiency in the development of intellectual disability.

Behavioral abnormalities and reduced norepinephrine in EP4 receptor-associated protein (EPRAP)-deficient mice.

EP4 receptor-associated protein (EPRAP) is a newly identified molecule that regulates macrophage activation. We recently demonstrated the presence of EPRAP in the mice brain; however, little is known about the function of EPRAP in this tissue. Therefore, we investigated the role of EPRAP in behavior and emotion using behavioral analysis in mice. In this study, we subjected EPRAP-deficient (KO) mice and wild-type C57BL/6 (WT) mice to a battery of behavioral tests. EPRAP-KO mice tended to have shorter latencies to fall in the wire hang test, but had normal neuromuscular strength. EPRAP-KO mice exhibited elevated startle responses and reduced pre-pulse inhibition. Compared with WT mice, EPRAP-KO mice increased depression-like behavior in the forced swim test. These abnormal behaviors partially mimic symptoms of depression, attention deficit hyperactivity disorder (ADHD) and schizophrenia. Methylphenidate administration increased locomotor activity less in EPRAP-KO mice than in WT mice. Finally, levels of norepinephrine were reduced in the EPRAP-KO mouse brain. These behavioral abnormalities in EPRAP-KO mice may result from the dysfunction of monoamines, in particular, norepinephrine. Our results suggest that EPRAP participates in the pathogenesis of various behavioral disorders.

Clinical and genetic features of 13 Spanish patients with KCNQ2 mutations.

The KCNQ2 gene codifies a subunit of the voltage-gated potassium M channel underlying the neuronal M-current. Classically, mutations in this gene have been associated with benign familial neonatal seizures, however, in recent years KCNQ2 mutations have been reported associated to early-onset epileptic encephalopathy. In this work, detailed familiar, clinical and genetic data were collected for 13 KCNQ2-positive patients revealed among a cohort of 80 epileptic pediatric probands from Spain who were analyzed through a targeted next-generation sequencing assay for 155 epilepsy-associated genes. This work shows for the first time the association between KCNQ2 mutations and startle attacks in 38% of patients, which opens the possibility to define electroclinical phenotypes associated to KCNQ2 mutations. It also demonstrates that KCNQ2 mutations contribute to an important percentage of Spanish patients with epilepsy. The study confirm the high genetic heterogeneity of this gene with 13 different mutations found, 10 of them novel and the better outcome of patients treated with sodium channel blockers.

Cortical network dysfunction caused by a subtle defect of myelination.

Subtle white matter abnormalities have emerged as a hallmark of brain alterations in magnetic resonance imaging or upon autopsy of mentally ill subjects. However, it is unknown whether such reduction of white matter and myelin contributes to any disease-relevant phenotype or simply constitutes an epiphenomenon, possibly even treatment-related. Here, we have re-analyzed Mbp heterozygous mice, the unaffected parental strain of shiverer, a classical neurological mutant. Between 2 and 20 months of age, Mbp(+/-) versus Mbp(+/+) littermates were deeply phenotyped by combining extensive behavioral/cognitive testing with MRI, 1H-MR spectroscopy, electron microscopy, and molecular techniques. Surprisingly, Mbp-dependent myelination was significantly reduced in the prefrontal cortex. We also noticed a mild but progressive hypomyelination of the prefrontal corpus callosum and low-grade inflammation. While most behavioral functions were preserved, Mbp(+/-) mice exhibited defects of sensorimotor gating, as evidenced by reduced prepulse-inhibition, and a late-onset catatonia phenotype. Thus, subtle but primary abnormalities of CNS myelin can be the cause of a persistent cortical network dysfunction including catatonia, features typical of neuropsychiatric conditions. GLIA 2016;64:2025-2040.

Age-related sperm DNA methylation changes are transmitted to offspring and associated with abnormal behavior and dysregulated gene expression.

Advanced paternal age (APA) has been shown to be a significant risk factor in the offspring for neurodevelopmental psychiatric disorders, such as schizophrenia and autism spectrum disorders. During aging, de novo mutations accumulate in the male germline and are frequently transmitted to the offspring with deleterious effects. In addition, DNA methylation during spermatogenesis is an active process, which is susceptible to errors that can be propagated to subsequent generations. Here we test the hypothesis that the integrity of germline DNA methylation is compromised during the aging process. A genome-wide DNA methylation screen comparing sperm from young and old mice revealed a significant loss of methylation in the older mice in regions associated with transcriptional regulation. The offspring of older fathers had reduced exploratory and startle behaviors and exhibited similar brain DNA methylation abnormalities as observed in the paternal sperm. Offspring from old fathers also had transcriptional dysregulation of developmental genes implicated in autism and schizophrenia. Our findings demonstrate that DNA methylation abnormalities arising in the sperm of old fathers are a plausible mechanism to explain some of the risks that APA poses to resulting offspring.

Dysfunction in GABA signalling mediates autism-like stereotypies and Rett syndrome phenotypes.

Mutations in the X-linked MECP2 gene, which encodes the transcriptional regulator methyl-CpG-binding protein 2 (MeCP2), cause Rett syndrome and several neurodevelopmental disorders including cognitive disorders, autism, juvenile-onset schizophrenia and encephalopathy with early lethality. Rett syndrome is characterized by apparently normal early development followed by regression, motor abnormalities, seizures and features of autism, especially stereotyped behaviours. The mechanisms mediating these features are poorly understood. Here we show that mice lacking Mecp2 from GABA (γ-aminobutyric acid)-releasing neurons recapitulate numerous Rett syndrome and autistic features, including repetitive behaviours. Loss of MeCP2 from a subset of forebrain GABAergic neurons also recapitulates many features of Rett syndrome. MeCP2-deficient GABAergic neurons show reduced inhibitory quantal size, consistent with a presynaptic reduction in glutamic acid decarboxylase 1 (Gad1) and glutamic acid decarboxylase 2 (Gad2) levels, and GABA immunoreactivity. These data demonstrate that MeCP2 is critical for normal function of GABA-releasing neurons and that subtle dysfunction of GABAergic neurons contributes to numerous neuropsychiatric phenotypes.

CHRNA4 was associated with prepulse inhibition of schizophrenia in Chinese: a pilot study.

INTRODUCTION: Prepulse inhibition (PPI) of the auditory startle reflex, as an operational measurement used to evaluate the function of brain sensorimotor gating, appears to be a sensitive potential endophenotype for schizophrenia. CHRNA4 is highly expressed in the central nervous system and has been demonstrated to be significantly associated with schizophrenia by previous studies. The purpose of the current study was to evaluate the effect of CHRNA4 on PPI and acoustic startle parameters in schizophrenia. METHODS: 77 patients with schizophrenia and 62 controls were administered the test PPI, and 3 single nucleotide polymorphisms (SNPs) (rs3746372, rs1044396, and rs3787140) of CHRNA4 were genotyped in these subjects. RESULTS: Patients with schizophrenia showed significantly lower levels of PPI at the 120 ms prepulse intervals and longer peak latency than controls, and the GG genotype of rs3746372 and the TT genotype of rs1044396 were associated with decreased PPI levels in schizophrenia but not in controls. CONCLUSION: PPI may be influenced by the polymorphisms of the CHRNA4 in schizophrenia and it may be a potential endophenotype of schizophrenia. An independent replication would greatly increase the value of this study.