HPC-1/syntaxin 1A gene knockout mice show abnormal behavior possibly related to a disruption in 5-HTergic systems

Activator of KAT3 histone acetyltransferase family ameliorates a neurodevelopmental disorder phenotype in the syntaxin 1A ablated mouse model

Syntaxin-1A (stx1a) repression causes a neurodevelopmental disorder phenotype, low latent inhibition (LI) behavior, by disrupting 5-hydroxytryptaminergic (5-HTergic) systems. Herein, we discovered that lysine acetyltransferase (KAT) 3B increases stx1a neuronal transcription and TTK21, a KAT3 activator, induces stx1a transcription and 5-HT release in vitro. Furthermore, glucose-derived CSP-TTK21 could restore decreased stx1a expression, 5-HTergic systems in the brain, and low LI in stx1a (+/-) mice by crossing the blood-brain barrier, whereas the KAT3 inhibitor suppresses stx1a expression, 5-HTergic systems, and LI behaviors in wild-type mice. Finally, in wild-type and stx1a (-/-) mice treated with IKK inhibitors and CSP-TTK21, respectively, we show that KAT3 activator-induced LI improvement is a direct consequence of KAT3B-stx1a pathway, not a side effect. In conclusion, KAT3B can positively regulate stx1a transcription in neurons, and increasing neuronal stx1a expression and 5-HTergic systems by a KAT3 activator consequently improves the low LI behavior in the stx1a ablation mouse model.

Molecular and in silico analyses of SYN III gene variants in autism spectrum disorder

BACKGROUND

Defects in neurotransmission and synaptogenesis are noteworthy in the pathogenesis of ASD. Synapsin III (SYN III) is defined as a synaptic vesicle protein that plays an important role in synaptogenesis and regulation of neurotransmitter release and neurite outgrowth. Therefore, SYN III may associate with many neurodevelopmental diseases, including ASD.

AIM

The aim of this study was to investigate whether the SYN III gene -631 C > G (rs133946) and -196 G > A (rs133945) polymorphisms are associated with susceptibility to ASD.

METHODS

SYN III variants and the risk of ASD were investigated in 26 healthy children and 24 ASD children. SYN III gene variants were genotyped by PCR-RFLP methods. The differences in genotype and allele frequencies between the ASD and control groups were calculated using the chi-square (χ2). We analysed the SYN III gene using web-based tools.

RESULTS

Our results suggest that the presence of the AA genotype of the SYN III -196 G > A (rs133945) polymorphism affects the characteristics and development of ASD in children (p = 0.012). SYN III -631 C > G (rs133946) polymorphism was not associated with ASD (p = 0.524). We have shown the prediction of gene-gene interaction that SYN III is co-expressed with 17 genes, physical interaction with 3 genes, and co-localization with 12 genes. The importance of different genes (SYN I, II, III, GABRD, NOS1AP, GNAO1) for ASD pathogenesis was revealed by GO analysis.

CONCLUSION

Considering the role of SYN III and related genes, especially in the synaptic vesicle pathway and neurotransmission, its effect on ASD can be further investigated.

Heterozygous and homozygous variants in STX1A cause a neurodevelopmental disorder with or without epilepsy

The neuronal SNARE complex drives synaptic vesicle exocytosis. Therefore, one of its core proteins syntaxin 1A (STX1A) has long been suspected to play a role in neurodevelopmental disorders. We assembled eight individuals harboring ultra rare variants in STX1A who present with a spectrum of intellectual disability, autism and epilepsy. Causative variants comprise a homozygous splice variant, three de novo missense variants and two inframe deletions of a single amino acid. We observed a phenotype mainly driven by epilepsy in the individuals with missense variants in contrast to intellectual disability and autistic behavior in individuals with single amino acid deletions and the splicing variant. In silico modeling of missense variants and single amino acid deletions show different impaired protein-protein interactions. We hypothesize the two phenotypic courses of affected individuals to be dependent on two different pathogenic mechanisms: (1) a weakened inhibitory STX1A-STXBP1 interaction due to missense variants results in an STX1A-related developmental epileptic encephalopathy and (2) a hampered SNARE complex formation due to inframe deletions causes an STX1A-related intellectual disability and autism phenotype. Our description of a STX1A-related neurodevelopmental disorder with or without epilepsy thus expands the group of rare diseases called SNAREopathies.

Vesicle trafficking with snares: a perspective for autism

Vesicle-mediated membrane traffic is the mechanism fundamental to many biological events, especially the release of neurotransmitters. The main proteins of the mechanism that mediates membrane fusion in vesicle-mediated membrane traffic are N-ethylmaleimide sensitive factor (NSF) supplemental protein (SNAP) receptor (SNAREs) proteins. SNAREs are classified into vesicle-associated SNAREs (vesicle-SNAREs/v-SNAREs) and target membrane-associated SNAREs (target-SNARE/t-SNAREs). Autism spectrum disorders (ASD) are neurodevelopmental disorders characterized by many symptoms, especially complications in social communication and stereotypical behaviours. Defects in synaptogenesis and neurotransmission, oxidative stress, and developmental defects in the early stages of development are defined in the pathogenesis of the disease. SNARE proteins are on the basis of synaptogenesis and neurotransmission. Although the formation mechanisms and underlying causes of the SNARE complex are not fully understood, expression differences, polymorphisms, abnormal expressions or dysfunctions of the proteins that make up the SNARE complex have been associated with many neurodevelopmental diseases, including autism. Further understanding of SNARE mechanisms is crucial both for understanding ASD and for developing new treatments. In this review, the formation mechanisms of the SNARE complex and the roles of various factors involved in this process are explained. In addition, a brief evaluation of clinical and basic studies on the SNARE complex in autism spectrum disorders was made.

Disturbance of the reciprocal-interaction between the OXTergic and DAergic systems in the CNS causes atypical social behavior in syntaxin 1A knockout mice

Several studies have shown that oxytocin (OXT) modulates social behavior. Similarly, monoamines such as dopamine (DA) play a role in regulating social behavior. Previous studies have demonstrated that the soluble N-ethylmaleimide-sensitive fusion attachment protein receptor (SNARE) protein syntaxin 1A (STX1A) regulates the secretion of OXT and monoamines, and that STX1A gene knockout (STX1A KO) mice exhibit atypical social behavior, such as deficient social recognition, due to reduced OXT release. In this study, we analyzed the neural mechanism regulating social behavior by OXT and/or DA using STX1A KO mice as a model animal. We found that OXT directly induced DA release from cultured DA neurons through OXT and V1a receptors. In STX1A KO mice, the atypical social behavior was partially improved by OXT administration, which was inhibited by D1 receptor blockade. In addition, the atypical social behavior in STX1A KO mice was partially improved by facilitation of DAergic signaling with the DA reuptake inhibitor GBR12909. Moreover, the amelioration by GBR12909 was inhibited by OXTR blockade. These results suggest that the reciprocal interaction between the DAergic and OXTergic neuronal systems in the CNS may be important in regulating social behavior.

PLRP2 selectively localizes synaptic membrane proteins via acyl-chain remodeling of phospholipids

The plasma membrane of neurons consists of distinct domains, each of which carries specialized functions and a characteristic set of membrane proteins. While this compartmentalized membrane organization is essential for neuronal functions, it remains controversial how neurons establish these domains on the laterally fluid membrane. Here, using immunostaining, lipid-MS analysis and gene ablation with the CRISPR/Cas9 system, we report that the pancreatic lipase-related protein 2 (PLRP2), a phospholipase A1 (PLA1), is a key organizer of membrane protein localization at the neurite tips of PC12 cells. PLRP2 produced local distribution of 1-oleoyl-2-palmitoyl-PC at these sites through acyl-chain remodeling of membrane phospholipids. The resulting lipid domain assembled the syntaxin 4 (Stx4) protein within itself by selectively interacting with the transmembrane domain of Stx4. The localized Stx4, in turn, facilitated the fusion of transport vesicles that contained the dopamine transporter with the domain of the plasma membrane, which led to the localized distribution of the transporter to that domain. These results revealed the pivotal roles of PLA1, specifically PLRP2, in the formation of functional domains in the plasma membrane of neurons. In addition, our results suggest a mode of membrane organization in which the local acyl-chain remodeling of membrane phospholipids controls the selective localization of membrane proteins by regulating both lipid-protein interactions and the fusion of transport vesicles to the lipid domain.

Disorders of synaptic vesicle fusion machinery

The revolution in genetic technology has ushered in a new age for our understanding of the underlying causes of neurodevelopmental, neuromuscular and neurodegenerative disorders, revealing that the presynaptic machinery governing synaptic vesicle fusion is compromised in many of these neurological disorders. This builds upon decades of research showing that disturbance to neurotransmitter release via toxins can cause acute neurological dysfunction. In this review, we focus on disorders of synaptic vesicle fusion caused either by toxic insult to the presynapse or alterations to genes encoding the key proteins that control and regulate fusion: the SNARE proteins (synaptobrevin, syntaxin-1 and SNAP-25), Munc18, Munc13, synaptotagmin, complexin, CSPα, α-synuclein, PRRT2 and tomosyn. We discuss the roles of these proteins and the cellular and molecular mechanisms underpinning neurological deficits in these disorders.

Bisphenol a Exposure in Utero Disrupts Hypothalamic Gene Expression Particularly Genes Suspected in Autism Spectrum Disorders and Neuron and Hormone Signaling

Bisphenol A (BPA) is an endocrine-disrupting compound detected in the urine of more than 92% of humans, easily crosses the placental barrier, and has been shown to influence gene expression during fetal brain development. The purpose of this study was to investigate the effect of in utero BPA exposure on gene expression in the anterior hypothalamus, the basal nucleus of the stria terminalis (BNST), and hippocampus in C57BL/6 mice. Mice were exposed in utero to human-relevant doses of BPA, and then RNA sequencing was performed on male PND 28 tissue from whole hypothalamus (n = 3/group) that included the medial preoptic area (mPOA) and BNST to determine whether any genes were differentially expressed between BPA-exposed and control mice. A subset of genes was selected for further study using RT-qPCR on adult tissue from hippocampus to determine whether any differentially expressed genes (DEGs) persisted into adulthood. Two different RNA-Seq workflows indicated a total of 259 genes that were differentially expressed between BPA-exposed and control mice. Gene ontology analysis indicated that those DEGs were overrepresented in categories relating to mating, cell-cell signaling, behavior, neurodevelopment, neurogenesis, synapse formation, cognition, learning behaviors, hormone activity, and signaling receptor activity, among others. Ingenuity Pathway Analysis was used to interrogate novel gene networks and upstream regulators, indicating the top five upstream regulators as huntingtin, beta-estradiol, alpha-synuclein, Creb1, and estrogen receptor (ER)-alpha. In addition, 15 DE genes were identified that are suspected in autism spectrum disorders.

STX1A gene variations contribute to the susceptibility of children attention-deficit/hyperactivity disorder: a case-control association study

It was presumed syntaxin-1A (STX1A) might relate to the pathophysiology of attention-deficit/hyperactivity disorder (ADHD), but the results were inconsistent. The present study aims to confirm whether the STX1A gene is involved in the susceptibility of children ADHD. We genotyped three single nucleotide polymorphisms (SNPs) of STX1A gene using Sequenom MassARRAY technology. A case-control study was performed among Chinese Han population including 754 cases and 772 controls from two different provinces. The Conners Parent Symptom Questionnaire and Integrated Visual and Auditory Continuous Performance Test were used to assess ADHD clinical symptoms. We found for the first time that rs3793243 GG genotype carriers had a lower risk of ADHD compared with AA genotype (OR 0.564, 95% confidence interval (CI) 0.406-0.692, P = 0.001), and rs875342 was also associated with children ADHD (OR 1.806, 95% CI 1.349-2.591, P = 0.001). In addition, the two positive SNPs were also significantly associated with the clinical characteristics of ADHD. Expression quantitative trait loci analysis indicated that rs3793243 might mediate STX1A gene expression. Using a case-control study to explore the association between STX1A gene and children ADHD in Chinese Han population, our results suggest STX1A genetic variants might contribute to the susceptibility of children ADHD.

Transcriptomic Studies in Mouse Models of Rett Syndrome: A Review

Rett Syndrome (RTT) is a neurological disorder mainly associated with mutations in the X-linked gene coding for the methyl-CpG binding protein 2 (MECP2). To assist in studying MECP2's function, researchers have generated Mecp2 mouse mutants showing that MECP2's product (MeCP2) mostly functions as a transcriptional regulator. During the last two decades, these models have been used to determine the genes that are regulated by MeCP2, slowly dissecting the etiological mechanisms underlying RTT. In the present review, we describe the findings of these transcriptomic studies, and highlight differences between them, and discuss how studies on these genetic models can sharpen our understanding of the human disorder. We conclude that - while there's large variability regarding the number of differentially expressed genes identified - there are overlapping features that inform on the biology of RTT.

A Review of Oxytocin and Arginine-Vasopressin Receptors and Their Modulation of Autism Spectrum Disorder

Oxytocin (OXT) and arginine-vasopressin (AVP) play a key regulatory part in social and affiliative behaviors; two aspects highly compromised in Autism Spectrum Disorder (ASD). Furthermore, variants in the adjacent oxytocin-vasopressin gene regions have been found to be associated with ASD diagnosis and endophenotypes. This review focuses mainly on common OXTr single nucleotide polymorphisms (SNPs), AVPR1a microsatellites and AVPR1b polymorphisms in relation to the development of autism. Although these genes did not surface in genome-wide association studies, evidence supports the hypothesis that these receptors and their polymorphisms are widely involved in the regulation of social behavior, and in modulating neural and physiological pathways contributing to the etiology of ASD. With a specific focus on variants considered to be among the most prevalent in the development of ASD, these issues will be discussed in-depth and suggestions to approach inconsistencies in the present literature will be provided. Translational implications and future directions are deliberated from a short-term and a forward-looking perspective. While the scientific community has made significant progress in enhancing our understanding of ASD, more research is required for the ontology of this disorder to be fully elucidated. By supplementing information related to genetics, highlighting the differences across male and female sexes, this review provides a wider view of the current state of knowledge of OXTr and AVPr mechanisms of functioning, eventually addressing future research in the identification of further risk factors, to build new strategies for early interventions.

Syntaxin 1B contributes to regulation of the dopaminergic system through GABA transmission in the CNS

In neuronal plasma membrane, two syntaxin isoforms, HPC-1/syntaxin 1A (STX1A) and syntaxin 1B (STX1B), are predominantly expressed as soluble N-ethylmaleimide-sensitive fusion attachment protein receptors, also known as t-SNAREs. We previously reported that glutamatergic and GABAergic synaptic transmissions are impaired in Stx1b null mutant (Stx1b^-/- ) mice but are almost normal in Stx1a null mutant (Stx1a^-/- ) mice. These observations suggested that STX1A and STX1B have distinct functions in fast synaptic transmission in the central nervous system (CNS). Interestingly, recent studies indicated that Stx1a^-/- or Stx1a^+/- mice exhibit disruption in the monoaminergic system in the CNS, causing unusual behaviour that is similar to neuropsychological alterations observed in psychiatric patients. Here, we studied whether STX1B contributes to the regulation of monoaminergic system and if STX1B is related to neuropsychological properties in human neuropsychological disorders similar to STX1A. We found that monoamine release in vitro was normal in Stx1b^+/- mice unlike Stx1a^-/- or Stx1a^+/- mice, but the basal extracellular dopamine (DA) concentration in the ventral striatum was increased. DA secretion in the ventral striatum is regulated by GABAergic neurons, and Stx1b^+/- mice exhibited reduced GABA release both in vitro and in vivo, disrupting the DAergic system in the CNS of these mice. We also found that Stx1b^+/- mice exhibited reduced pre-pulse inhibition (PPI), which is believed to represent one of the prominent schizotypal behavioural profiles of human psychiatric patients. The reduction in PPI was rescued by DA receptor antagonists. These observations indicated that STX1B contributes to excess activity of the DAergic system through regulation of GABAergic transmission.

Transcription regulation mechanism of the syntaxin 1A gene via protein kinase A

Syntaxin 1A (Stx1a) is primarily involved in the docking of synaptic vesicles at active zones in neurons. Its gene is a TATA-less gene, with several transcription initiation sites, which is activated by the binding of Sp1 and acetylated histone H3 (H3) in the core promoter region (CPR) through the derepression of class I histone deacetylase (HDAC). In the present study, to clarify the factor characterizing Stx1a gene expression via the protein kinase A (PKA) pathway inducing the Stx1a mRNA, we investigated whether the epigenetic process is involved in the Stx1a gene transcription induced by PKA signaling. We found that the PKA activator forskolin induced Stx1a expression in non-neuronal cells, FRSK and 3Y1, which do not endogenously express Stx1a, unlike PC12. HDAC8 inhibition by shRNA knockdown and specific inhibitors induced Stx1a expression in FRSK. The PKA inhibitor H89 suppressed HDAC8-Ser39 phosphorylation, H3 acetylation and Stx1a induction by forskolin in FRSK cells. Finally, we also found that forskolin led to the dissociation of HDAC8-CPR interaction and the association of Sp1 and Ac-H3 to CPR in FRSK. The results of the current study suggest that forskolin phosphorylates HDAC8-Ser39 via the PKA pathway and increases histone H3 acetylation in cells expressing HDAC8, resulting in the induction of the Stx1a gene.

The cell- and tissue-specific transcription mechanism of the TATA-less syntaxin 1A gene

Syntaxin 1A (Stx1a) plays an important role in regulation of neuronal synaptic function. To clarify the mechanism of basic transcriptional regulation and neuron-specific transcription of Stx1a we cloned the Stx1a gene from rat, in which knowledge of the expression profile was accumulated, and elucidated that Stx1a consisting of 10 exons, possesses multiple transcription initiation sites and a 204-bp core promoter region (CPR) essential for transcription in PC12 cells. The TATA-less, conserved, GC-rich CPR has 2 specific protein (SP) sites that bind SP1 and are responsible for 65% of promoter activity. The endogenous CPR, including 23 CpG sites, is not methylated in PC12 cells, which express Stx1a and fetal rat skin keratinocyte (FRSK) cells, which do not, although an exogenous methylated CPR suppresses reporter activity in both lines. Trichostatin A (TSA) and class I histone deacetylase (HDAC) inhibitors, but not 5-azacytidine, induce Stx1a in FRSK cells. Acetylated histone H3 only associates to the CPR in FRSK cells after TSA addition, whereas the high acetylated histone H3-CPR association in PC12 cells was unchanged following treatment. HDAC inhibitor induction of Stx1a was negated by mithramycin A and deletion/mutation of 2 SP sites. HDAC1, HDAC2, and HDAC8 detach from the CPR when treated with TSA in FRSK cells and are associated with the CPR in lungs, and acetylated histone H3 associates to this region in the brain. In the first study characterizing a syntaxin promoter, we show that association of SP1 and acetylated histone H3 to CPR is important for Stx1a transcription and that HDAC1, HDAC2, and HDAC8 decide cell/tissue specificity in a suppressive manner.

Regulation of munc18-1 and syntaxin-1A interactive partners in schizophrenia prefrontal cortex: down-regulation of munc18-1a isoform and 75 kDa SNARE complex after antipsychotic treatment

Munc18-1 and syntaxin-1 are crucial interacting molecules for synaptic membrane fusion and neurotransmitter release. Contrasting abnormalities of several proteins of the exocytotic machinery, including the formation of SNARE (synaptobrevin, SNAP-25 and syntaxin-1) complexes, have been reported in schizophrenia. This study quantified in the dorsolateral prefrontal cortex (PFC, Brodmann area 9) the immunocontent of munc18-1a/b isoforms, syntaxin-1A, other presynaptic proteins (synaptotagmin, synaptophysin), and SNARE complexes, as well as the effects of psychoactive drug exposure, in schizophrenia (SZ, n=24), non-schizophrenia suicide (SD, n=13) and major depression (MD, n=15) subjects compared to matched controls (n=39). SZ was associated with normal expression of munc18-1a/b and increased syntaxin-1A (+44%). The presence of antipsychotic drugs reduced the basal content of munc18-1a isoform (-23%) and synaptobrevin (-32%), and modestly reduced that of up-regulated syntaxin-1A (-16%). Munc18-1a and syntaxin-1A protein expression correlated positively in controls but showed a markedly opposite pattern in SZ, regardless of antipsychotic treatment. Thus, the ratio of syntaxin-1A to munc18-1a showed a net increase in SZ (+53/114%). The SNARE complex (75 kDa) was found unaltered in antipsychotic-free and reduced (-28%) in antipsychotic-treated SZ subjects. None of these abnormalities were observed in SD and MD subjects, unexposed or exposed to psychoactive drugs. The results reveal some exocytotic dysfunctions in SZ that are probably related to an imbalance of the interaction between munc18-1a and SNARE (mainly syntaxin-1A) complex. Moreover, antipsychotic drug treatment is associated with lower content of key proteins of the exocytotic machinery, which could result in a destabilization/impairment of neurosecretion.

Impairment of catecholamine systems during induction of long-term potentiation at hippocampal CA1 synapses in HPC-1/syntaxin 1A knock-out mice

The membrane protein HPC-1/syntaxin 1A is believed to play a key role in synaptic vesicle exocytosis, and it was recently suggested to be required for synaptic plasticity. Despite evidence for the function of HPC-1/syntaxin 1A in synaptic plasticity, the underlying cellular mechanism is unclear. We found that although fast synaptic transmission and long-term depression were unaffected, HPC-1/syntaxin 1A knock-out (STX1A(-/-)) mice showed impaired long-term potentiation (LTP) in response to theta-burst stimulation in CA1 hippocampal slices. The impairment in LTP was rescued by the application of forskolin, an adenylyl cyclase activator, or more robust stimulation, suggesting that cAMP/protein kinase A signaling was suppressed in these mice. In addition, catecholamine release from the hippocampus was significantly reduced in STX1A(-/-) mice. Because HPC-1/syntaxin 1A regulates exocytosis of dense-core synaptic vesicles, which contain neuromodulatory transmitters such as noradrenaline, dopamine and 5-HT, we examined the effect of neuromodulatory transmitters on LTP induction. Noradrenaline and dopamine enhanced LTP induction in STX1A(-/-) mice, whereas catecholamine depletion reduced LTP induction in wild-type mice. Theses results suggest that HPC-1/syntaxin 1A regulates catecholaminergic systems via exocytosis of dense-core synaptic vesicles, and that deletion of HPC-1/syntaxin 1A causes impairment of LTP induction.

The shortest isoform of dystrophin (Dp40) interacts with a group of presynaptic proteins to form a presumptive novel complex in the mouse brain

Duchenne muscular dystrophy (DMD) causes cognitive impairment in one third of the patients, although the underlying mechanisms remain to be elucidated. Recent studies showed that mutations in the distal part of the dystrophin gene correlate well with the cognitive impairment in DMD patients, which is attributed to Dp71. The study on the expression of the shortest isoform, Dp40, has not been possible due to the lack of an isoform specific antibody. Dp40 has the same promoter as that found in Dp71 and lacks the normal C-terminal end of Dp427. In the present study, we have raised polyclonal antibody against the N-terminal sequence common to short isoforms of dystrophin, including Dp40, and investigated the expression pattern of Dp40 in the mouse brain. Affinity chromatography with this antibody and the consecutive LC-MS/MS analysis on the interacting proteins revealed that Dp40 was abundantly expressed in synaptic vesicles and interacted with a group of presynaptic proteins, including syntaxin1A and SNAP25, which are involved in exocytosis of synaptic vesicles in neurons. We thus suggest that Dp40 may form a novel protein complex and play a crucial role in presynaptic function. Further studies on these aspects of Dp40 function might provide more insight into the molecular mechanisms of cognitive impairment found in patients with DMD.

Dysfunction of the hypothalamic-pituitary-adrenal axis in STX1A knockout mice

HPC-1/syntaxin1A (STX1A) is considered to regulate exocytosis in neurones and endocrine cells. Previously, we reported that STX1A null mutant (STX1A KO) mice unexpectedly showed normal glutamatergic and GABAergic fast synaptic transmission but exhibited disturbances in monoaminergic transmission, such as serotonin, 5-hydroxytryptamine (5-HT), which may induce attenuation of latent inhibition. These results suggest that STX1A may contribute to dense-core vesicle exocytosis in vivo. Thus, we hypothesised that the lack of STX1A might affect the secretion of several hormones, as also mediated by dense-core vesicles exocytosis. In the present study, we focused on the hypothalamic-pituitary-adrenal (HPA) axis, which is a neuroendocrine system that regulates responses to stress stimuli and is considered to be associated with neuropsychiatric disorders. Specifically, we examined whether the HPA axis is impaired in STX1A KO mice. Interestingly, plasma concentrations of both corticosterone (CORT) and adrenocorticotrophin hormone (ACTH) during the resting condition decreased in STX1A KO mice compared to WT mice. Additionally, elevated plasma CORT, ACTH and corticotrophin-releasing hormone (CRH) which were usually observed after acute restraint stress, were also reduced in STX1A KO mice. We also observed the suppression of 5-HT-induced CRH release in STX1A KO mice in vitro. Furthermore, an in vivo microdialysis study revealed that the elevation of extracellular 5-HT in the hypothalamus, which was induced by the selective serotonin reuptake inhibitor, fluoxetine, was significantly reduced in STX1A KO mice compared to WT mice. 5-HT elevation in the hypothalamus, which was induced by acute restraint stress, was also reduced in STX1A KO mice. Finally, STX1A KO mice showed abnormal behavioural responses after mild restraint stress. These results indicate that the lack of STX1A could induce dysfunction of the HPA axis, and the deficit may result in abnormal behavioural properties, such as unusual responses to stress stimuli.

Raphe pallidus modulates Bötzinger complex-induced inhibition of the phrenic nerve activity in rats

The raphe pallidus (RPa) and Bötzinger complex (BötC) represent two important nuclei which project to spinal phrenic motor neurons. Stimulation of the RPa produces facilitative effects on respiratory activity, whereas stimulation of the BötC induces inhibitory effects on respiratory activity. In the present study, we examined the modulatory effects of serotonergic (5-hydroxytryptamine, 5-HT) RPa neurons on the inhibitory response of the phrenic nerve activity elicited from the BötC in rats. Experiments were performed on spontaneously breathing, urethane-anesthetized adult rats. Either high-frequency stimulation or glutamatergic chemical activation of the RPa region significantly attenuated the BötC-induced inhibition of the phrenic nerve. This attenuation showed a post-stimulation time and intensity dependency. Pharmacological experiments showed that intravenous injection of methysergide, a broad-spectrum antagonist of 5-HT receptors, markedly reduced the respiratory facilitation induced by electrical stimulation of the RPa. Furthermore, microinjections of methysergide into the cerebrospinal fluid around the phrenic motor nucleus (PMN) region at spinal cord segments C4 and C5 significantly decreased the RPa-related attenuation effects on BötC-evoked inhibition of phrenic nerve discharge. These results suggest that RPa serotonergic neurons could modulate the inhibition of phrenic nerve activity induced by BötC. Moreover, as the relevant 5-HT receptors for RPa's modulatory effects are located in the cervical spinal cord, 5-HT may, in part, function as a modulator to suppress the BötC neuronal activity via direct RPa-PMN and BötC-PMN convergent projection pathways to phrenic motoneurons.

Unusual retinal layer organization in HPC-1/syntaxin 1A knockout mice

HPC-1/syntaxin 1A (STX1A) is abundantly expressed in neurons. STX1A is believed to regulate exocytosis in synaptic vesicles. In our recent studies, STX1A knockout (KO) mice showed normal development, and basal synaptic transmission in cultured hippocampal neurons appeared to be normal. However, behavioral abnormalities were observed in STX1A KO mice. In the normal rodent retina, the STX1A protein is expressed in two synaptic layers (plexiform layers). Here, to evaluate the effects of the loss of STX1A on retinal structure, we examined the retinal layer structure in STX1A KO mice using hematoxylin staining and immunostaining. We found that the general layer structures in the retina were preserved in all genotypes. However, the outer plexiform layer (OPL) was significantly thicker in KO and heterozygous mutant (HT) mice compared with that in wild-type (WT) mice. No significant differences were observed in the thicknesses of the other layers. Immunostaining for protein kinase C α showed that the alignment of rod bipolar cell bodies in the inner nuclear layer (INL) was slightly disrupted in HT and KO retinas. Furthermore, the dendrites of these cells in the OPL of KO mice were sparse, compared to those in WT mice. Our results show that STX1A KO mice have increased thickness of the OPL and changes in the morphology of the INL that may contribute to the change in OPL thickness. We suggest that STX1A may play a role in the structural formation of the INL and OPL in the retina.