High Salt Intake Induces Active Coping Behaviors by Enhancing the Resilience against Psychological Stress in Mice.

BACKGROUND: High salt intake increases the active coping behavior during psychological stress. Acute fear-related severe stress enhances passive coping behavior during subsequent inescapable stress. METHODS: We investigated the effect of high salt intake (2%) for 5 consecutive days on the coping behavior in C57BL6 mice which employing the tail suspension test (TST) at 1 h after the exposure to inescapable innate fear using 2,5-dihydro-2,4,5-trimethylthiazoline (TMT), a synthetic component of fox feces. By using a different mouse group, to investigated whether anxiety-like behavior was correlated with coping behavior during the TST, we performed the elevated-plus maze (EPM) test at 1 h before the TST without TMT. RESULTS: Both the distance traveled and the number of entries in the central zone of test box during TMT were negatively correlated with freezing time in both sodium- and water-intake mice. Sodium-intake increased the preference for central zone during TMT exposure, but did not change fear sensitivity and locomotor activity. Sodium-intake also prevented that TMT-induced increase in the immobility time during TST. The immobility time during TST was positively correlated with freezing time during TMT exposure in sodium-intake, but not in water-intake mice. Furthermore, the immobility time during TST in sodium-intake mice correlated with the distance traveled and with the number of entries in the central zone during TMT. Sodium intake also increased the number of entries and the time spent in the open arm of the EPM, indicating that high salt intake had an anxiolytic effect. However, neither the number of entries nor the time spent in the open arm of the EPM were correlated with immobility time during TST in sodium-intake mice. CONCLUSIONS: We conclude that a high salt intake induces active coping behavior after experiencing fear stress by enhancing stress resilience rather than by reducing the anxiety level.

Formation of False Context Fear Memory Is Regulated by Hypothalamic Corticotropin-Releasing Factor in Mice.

Traumatic events frequently produce false fear memories. We investigated the effect of hypothalamic corticotropin-releasing factor (CRF) knockdown (Hy-Crf-KD) or overexpression (Hy-CRF-OE) on contextual fear memory, as fear stress-released CRF and hypothalamic-pituitary-adrenal axis activation affects the memory system. Mice were placed in a chamber with an electric footshock as a conditioning stimulus (CS) in Context A, then exposed to a novel chamber without CS, as Context B, at 3 h (B-3h) or 24 h (B-24h). The freezing response in B-3h was intensified in the experimental mice, compared to control mice not exposed to CS, indicating that a false fear memory was formed at 3 h. The within-group freezing level at B-24h was higher than that at B-3h, indicating that false context fear memory was enhanced at B-24h. The difference in freezing levels between B-3h and B-24h in Hy-Crf-KD mice was larger than that of controls. In Hy-CRF-OE mice, the freezing level at B-3h was higher than that of control and Hy-Crf-KD mice, while the freezing level in B-24h was similar to that in B-3h. Locomotor activity before CS and freezing level during CS were similar among the groups. Therefore, we hypothesized that Hy-Crf-KD potentiates the induction of false context fear memory, while Hy-CRF-OE enhances the onset of false fear memory formation.

The α1-adrenergic receptors in the amygdala regulate the induction of learned despair through protein kinase C-beta signaling.

Hyperactivity of amygdala is observed in patients with major depressive disorder. Although the role of α1-adrenoceptor in amygdala on fear memory has been well studied, the role of α1-adrenoceptor in amygdala on depression-like behaviors remains unclear. Therefore, we investigated the effect of α1A-adrenoreceptor in amygdala on despair behavior, evaluated by the immobility time during tail suspension test (TST), pharmacological intervention, and immunohistological methods. C57BL6/J mice given a bilateral intra-amygdala injection of artificial cerebrospinal fluid exhibited an increased duration of immobility in the latter half of both trials of TST with a 24-h interval, a phenomenon known as learned despair. Intra-amygdala injection of WB4101 (1.7 nmol/0.1 µl), an α1 adrenoreceptor antagonist, but not propranolol (250 pmol/0.1 µl), a ß-adrenoreceptor antagonist, blocked the induction of learned despair during TST. Immunostaining experiments revealed that ~61-75% of α1A-adrenoreceptor-positive neurons were colocalized with GAD65/67 in amygdala, implying that the α1-adrenoceptors in amygdala may enormously regulate the GABA release. Protein kinase C-beta (PKCß) was predominantly expressed in the α1A-adrenoreceptor-positive neurons in the BLA, whereas protein kinase C-epsilon (PKCε) was highly expressed with the α1A-adrenoreceptor in the Central nucleus of amygdala. Intra-amygdala injection of ruboxistaurin (10 pmol/0.1 µl), a PKCß inhibitor, blocked the induction of learned despair during TST, whereas neither TAT-εV1-2 (500 ng/0.1 µl), a cell-permeant PKCε inhibitory peptide, nor HBDDE (50 pmol/0.1 µl), an inhibitor of PKCα and -γ, affected the duration of immobility during TST. These data suggest that the α1-adrenoreceptor in amygdala regulates the induction of learned despair via PKCß.

Gαq protein signaling in the bed nucleus of the stria terminalis regulate the lipopolysaccharide-induced despair-like behavior in mice.

Major depressive disorder (MDD) is highly comorbid with anxiety disorders. It has been reported that the bed nucleus of the stria terminalis (BNST) is important for the induction of anxiety and MDD. Recently, the Gαq protein signaling within the BNST is involved in the induction of anxiety through Gαq protein signaling-mediated RNA-editing of GluR2 subunit, which produces the calcium (Ca2+)-impermeable α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor. On the other hand, the role of Gαq protein signaling within the BNST on the induction of MDD has never been reported yet. Therefore, we investigated whether Gαq protein signaling-producing the Ca2+-impermeable AMPA receptors in the BNST is involved in the lipopolysaccharide (LPS)-induced depressive-like behavior, particularly, despair-like behavior. When mice were systemically challenged with a single dose of LPS (1.2 mg/kg, i.p.), the immobility time during tail suspension test (TST) was increased 24 h after LPS injection. However, pretreatment with bilateral intra-BNST injection of neomycin (6.5 mM, 0.125 µL/side), an inhibitor of phospholipase C that is activated by Gαq protein-coupled receptor stimulation, extended the LPS-induced increase in the immobility time of TST. Furthermore, the co-pretreatment with bilateral intra-BNST injection of neomycin with 1-naphthylacetyl spermine (3 mM, 0.125 µL/side), an antagonist of Ca2+-permeable AMPA receptor, to mimic one of the final forms of Gαq protein activation, abolished the aggravated effect of neomycin and significantly shortened the immobility time compared with the control mice with an intra-BNST injection of artificial cerebrospinal fluid before LPS injection. However, pretreatment with bilateral intra-BNST injection of MDL-12,330A (10 µM, 0.125 µL/side), an inhibitor of adenylyl cyclase that is activated by Gαs protein-coupled receptor stimulation, did not affect the LPS-induced increase in the immobility time of TST. These results indicate that the Gαq protein signaling-mediated RNA-editing of GluR2, which produces the Ca2+-impermeable AMPA receptors within the BNST, regulates the LPS-induced despair-like behavior.

Molecular mechanism of noradrenaline during the stress-induced major depressive disorder.

Chronic stress-induced depression is a common hallmark of many psychiatric disorders with high morbidity rate. Stress-induced dysregulation of noradrenergic system has been implicated in the pathogenesis of depression. Lack of monoamine in the brain has been believed to be the main causative factor behind pathophysiology of major depressive disorder (MDD) and several antidepressants functions by increasing the monoamine level at the synapses in the brain. However, it is undetermined whether the noradrenergic receptor stimulation is critical for the therapeutic effect of antidepressant. Contrary to noradrenergic receptor stimulation, it has been suggested that the desensitization of ß-adrenoceptor is involved in the therapeutic effect of antidepressant. In addition, enhanced noradrenaline (NA) release is central response to stress and thought to be a risk factor for the development of MDD. Moreover, fast acting antidepressant suppresses the hyperactivation of noradrenergic neurons in locus coeruleus (LC). However, it is unclear how they alter the firing activity of LC neurons. These inconsistent reports about antidepressant effect of NA-reuptake inhibitors (NRIs) and enhanced release of NA as a stress response complicate our understanding about the pathophysiology of MDD. In this review, we will discuss the role of NA in pathophysiology of stress and the mechanism of therapeutic effect of NA in MDD. We will also discuss the possible contributions of each subtype of noradrenergic receptors on LC neurons, hypothalamic-pituitary-adrenal axis (HPA-axis) and brain derived neurotrophic factor-induced hippocampal neurogenesis during stress and therapeutic effect of NRIs in MDD.

Association of social defeat stress-induced anhedonia-like symptoms with mGluR1-dependent decrease in membrane-bound AMPA-GluR1 in the mouse ventral midbrain.

Anhedonia is a core symptom of social defeat stress (SDS)-induced depression associated with the reward system. We previously reported that decreased membrane-bound AMPA-GluR1 in the reward system is associated with lipopolysaccharide-induced anhedonia-like symptoms. Since group I metabotropic glutamate receptor (mGluR) activation reduces the surface density of GluR1, we examined whether group I mGluR-dependent decrease in membrane-bound GluR1 in the reward system is involved in SDS-induced anhedonia-like symptoms. Mice exposed to SDS for 4 consecutive days had markedly decreased membrane-bound GluR1 and GluR2 in the prefrontal cortex (PFC) and membrane-bound GluR1 in the ventral midbrain (VM) along with lower sucrose preference (SP). Intra-PFC injection of the group I mGluR agonist (S)-3,5-dihydroxyphenylglycine (DHPG; 100 µmol) demonstrated decrease in membrane-bound GluR1 and GluR2 in the PFC 2 and 24 h and membrane-bound GluR1 in the VM 24 h after injection. Moreover, intra-PFC injection of DHPG decreased SP only in the second 24-h (24-48 h) period. Conversely, intra-VM injection of DHPG decreased SP in both the first and second 24-h period and decreased membrane-bound GluR1 in the VM 2 and 24 h after injection. Pre-treatment with the mGluR1 antagonist JNJ16259685 (30 mg/kg, subcutaneous) prevented SDS-decreased SP and membrane-bound GluR1 in the VM. The mGluR5 antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP; 10 mg/kg, subcutaneous) prevented SDS-induced decrease in membrane-bound GluR1 and GluR2 in the PFC, whereas MPEP did not affect SDS-induced decrease in SP and membrane-bound GluR1 in the VM. These results suggest that mGluR1-mediated decrease in membrane-bound GluR1 in VM is involved in SDS-induced anhedonia-like symptoms.

The role of the AMPA receptor and 5-HT(3) receptor on aggressive behavior and depressive-like symptoms in chronic social isolation-reared mice.

Chronic social isolation (SI)-reared mice exhibit aggressive and depressive-like behaviors. However, the pathophysiological changes caused by chronic SI remain unclear. The hypothalamus and amygdala have been suggested to be associated with the stress of SI. In addition to serotonin 3 (5-HT3) receptors, AMPA receptors have also been suggested to be involved in aggressive behavior and depressive-like symptoms in animals. Therefore, we examined whether chronic SI affects AMPA and 5-HT3 receptor expression levels in these regions. A Western blot analysis revealed that after four weeks of SI, mice exhibited up-regulated AMPA receptor subunit (GluR1, GluR2) protein levels in the amygdala and down-regulated hypothalamic 5-HT3 receptor protein levels. The AMPA/kainate receptor antagonist NBQX (10 mg/kg; i.p.) attenuated SI-induced depressive-like symptoms but not aggressive behavior. Intra-amygdalar infusions of the selective AMPA receptor agonist (S)-AMPA (10 µM) induced despair-like behavior, but not sucrose preference or aggressive behavior, in mice not reared in SI (naïve mice). Alternatively, treatment with the 5-HT3 receptor agonist SR57227A (3.0 mg/kg; i.p.) decreased aggression levels. In addition, intra-hypothalamic infusions of the 5-HT3 receptor antagonist ondansetron (3 µM) did not trigger aggressive behavior in naïve mice; however, the administration of ondansetron (0.3 mg/kg; i.p.) increased aggression levels in two-week SI mice, which rarely exhibited the aggressive behavior. Moreover, ondansetron did not affect the depressive-like symptoms of the SI mice. These results suggest that SI-induced up-regulation of GluR1 and GluR2 subunits protein levels in the amygdalar region and down-regulation of 5-HT3 receptor proteins level in the hypothalamic region are associated with the effect of AMPA receptor agonist and 5-HT3 receptor antagonist -induced aggressive behavior and depressive-like symptoms.

The development of depression-like behavior is consolidated by IL-6-induced activation of locus coeruleus neurons and IL-1ß-induced elevated leptin levels in mice.

RATIONALE: Many studies have supported the cytokine hypothesis as the underlying pathophysiology of depressive disorder. OBJECTIVES: We previously reported that lipopolysaccharide (LPS)-induced depression-like behavior is abrogated by the α1-adrenoceptor antagonist prazosin. Since cytokines are involved in LPS effects on the brain, we investigated the effects of cytokines on noradrenergic neurons in the locus coeruleus (LC) and whether central α1-adrenoceptors can cause the development of depression-like behavior. METHODS: Adult male CD1 mice were treated with LPS (1 mg/kg, i.p.) or saline and sacrificed 2 h later for immunofluorescence studies of c-fos and tyrosine hydroxylase (TH) expression in LC neurons. Serum cytokines were measured using enzyme-linked immunosorbent assay (ELISA). Another group of mice were implanted with intracerebroventricular (i.c.v.) cannulae and given artificial cerebrospinal fluid (CSF) (control), interleukin (IL)-1ß (0.5 µg), IL-6 (1 µg), or tumor necrosis factor (TNF)-α (1 µg), and sacrificed 2 h later for c-fos and TH immunofluorescence analysis. Serum samples were analyzed for leptin levels. In addition, tail suspension test (TST), forced swimming test (FST), and sucrose preference (SP) test were conducted in a separate group of mice treated i.c.v. with cytokines, recombinant mouse leptin (5 µg) or phenylephrine (40 µg). These effects were countered by i.c.v. administration of prazosin and a leptin antagonist. RESULTS: LPS increased c-fos expression in TH-positive neurons. Central administration of IL-6 and IL-1ß increased c-fos immunoreactivity and serum leptin levels. Phenylephrine, an α1-adrenoceptor agonist, given i.c.v., increased the immobility time during FST and decreased SP, but had no effect on TST. Central leptin administration increased immobility time during FST but did not affect TST or SP. The combination of phenylephrine and leptin increased immobility time during FST and TST, and decreased SP. Induction of depression-like behavior by co-administration of IL-1ß and IL-6 was prevented by pretreatment with prazosin alone. CONCLUSION: These results suggest that IL-6-dependent LC neuronal activation induced depression-like behavior and IL-1ß-induced increase in leptin levels enhanced α1-adrenoceptor-mediated depression-like behavior.

Lipopolysaccharide-induced depressive-like behavior is associated with α1-adrenoceptor dependent downregulation of the membrane GluR1 subunit in the mouse medial prefrontal cortex and ventral tegmental area.

BACKGROUND: Chronic stress-induced depressive-like behavior is relevant to inflammatory immune activation. However, the neurobiological alterations in the brain following the central inflammatory immune activation remain elusive. METHODS: Therefore, we investigated the neurobiological alterations during depressive-like behavior induced in mice by systemic administration of lipopolysaccharide (LPS; 1.2 mg/kg administered twice at a 30-min interval via intraperitoneal injection). RESULTS: At 24 h after the second administration of LPS, an increased immobility time in the tail suspension test and the forced swimming test were observed, as well as reduced sucrose preference. Protein levels of the AMPA receptor GluR1 were significantly decreased at the plasma membrane in the medial prefrontal cortex (mPFC) and ventral tegmental area (VTA), while levels of the GluR2 were increased at the plasma membrane in the nucleus accumbens (NAc) at 24h after LPS. However, total GluR1 and GluR2 protein levels in the mPFC, VTA, and NAc were not affected by LPS. Moreover, LPS facilitated release of noradrenaline in the mPFC and VTA, but not in the NAc. Consistently, systemic administration of prazosin, an α1-adrenoceptor antagonist, blocked the LPS-induced downregulation of the membrane GluR1 subunit in both the mPFC and VTA and also blocked the upregulation of the membrane GluR2 subunit in the NAc. Intracerebroventricular administration of prazosin 30 min before LPS injection abrogated the LPS-induced depressive-like behaviors. In opposition, administration of propranolol, a ß-adrenoceptor antagonist, did not affect the LPS-induced downregulation of GluR1, the upregulation of GluR2, or the depressive-like behavior. CONCLUSIONS: These results suggest that LPS-activated α1-adrenoceptor-induced downregulation of membrane GluR1 in the mPFC and VTA is associated with inflammation-induced depressive-like behavior.

Exendin-4 promotes the membrane trafficking of the AMPA receptor GluR1 subunit and ADAM10 in the mouse neocortex.

Glucagon-like peptide-1 (GLP-1) is a novel treatment modality for type 2 diabetes mellitus. However, GLP-1 has been suggested as a therapeutic target for Alzheimer's disease (AD). In rodent studies, GLP-1 reduces amyloid beta (Aß) and facilitates synaptic plasticity. Therefore, in the present study, we investigated how GLP-1 facilitates synaptic plasticity and reduces the Aß in vivo. Exendin-4, a GLP-1 receptor agonist that can cross the blood brain barrier, was subcutaneously administered to adult mice. We then extracted the total and the plasma membrane proteins from the mouse neocortex. Exendin-4 significantly increased the phosphorylation level of cAMP response element-binding protein (CREB). Consistently, the expression level of brain-derived neurotrophic factor (BDNF), a transcriptional target of CREB, was increased. Furthermore, exendin-4 increased the membrane protein level of the AMPA receptor GluR1 subunit and postsynaptic density protein-95 (PSD-95), whereas GluR2 was unaffected. These exendin-4-dependent increases in membrane GluR1, total PSD-95 and BDNF were abrogated by pretreatment with temozolomide (TMZ), a DNA-alkylating agent, indicating that these alterations were dependent on exendin-4-induced transcriptional activity. In addition, we found that exendin-4 increased the level of the α-C terminal fragment (α-CTF) of amyloid precursor protein (APP). Furthermore, protein levels of both mature and immature ADAM10, the α-secretase of APP in the plasma membrane, were increased, whereas the total mature and immature ADAM10 levels were unchanged. These exendin-4-dependent increases in α-CTF and ADAM10 were not affected by TMZ. These findings suggested that GLP-1 facilitates the GluR1 membrane insertion through CREB activation and increases α-secretase activity through ADAM10 membrane trafficking. Upregulation of GluR1 and ADAM10 at the plasma membrane were also observed in mice with intracerebroventricular administration of Aß oligomer, indicating that a part of benefit of exendin-4 against AD may depend on the GluR1 and ADAM10 membrane trafficking.

Sensory Experience in Development Balances Excitation and Inhibition to Stabilize Frequency Tuning in Central Auditory Neurons.

The balance between excitation and inhibition is critical in shaping receptive field tuning properties in sensory neurons and, ultimately, in determining how sensory cues are extracted, transformed and interpreted by brain circuits. New findings suggest that developmentally-regulated, experience-dependent changes in intracortical inhibitory networks are key to defining receptive field tuning properties of auditory cortical neurons.

Synovial fibroblasts promote the expression and granule accumulation of tryptase via interleukin-33 and its receptor ST-2 (IL1RL1).

A characteristic feature of tissue resident human mast cells (MCs) is their hTryptase-beta-rich cytoplasmic granules. Mouse MC protease-6 (mMCP-6) is the ortholog of hTryptase-beta, and we have shown that this tetramer-forming tryptase has beneficial roles in innate immunity but adverse roles in inflammatory disorders like experimental arthritis. Because the key tissue factors that control tryptase expression in MCs have not been identified, we investigated the mechanisms by which fibroblasts mediate the expression and granule accumulation of mMCP-6. Immature mouse bone marrow-derived MCs (mBMMCs) co-cultured with fibroblast-like synoviocytes (FLS) or mouse 3T3 fibroblasts markedly increased their levels of mMCP-6. This effect was caused by an undefined soluble factor whose levels could be increased by exposing FLS to tumor necrosis factor-alpha or interleukin (IL)-1beta. Gene expression profiling of mBMMCs and FLS for receptor.ligand pairs of potential relevance raised the possibility that IL-33 was a sought after fibroblast-derived factor that promotes tryptase expression and granule maturation via its receptor IL1RL1/ST2. MCs lacking IL1RL1 exhibited defective fibroblast-driven tryptase accumulation, whereas recombinant IL-33 induced mMCP-6 mRNA and protein accumulation in wild-type mBMMCs. In agreement with these data, synovial MCs from IL1RL1-null mice exhibited a marked reduction in mMCP-6 expression. IL-33 is the first factor shown to modulate tryptase expression in MCs at the mRNA and protein levels. We therefore have identified a novel pathway by which mesenchymal cells exposed to inflammatory cytokines modulate the phenotype of local MCs to shape their immune responses.

Interleukin-33 prevents apoptosis and improves survival after experimental myocardial infarction through ST2 signaling.

BACKGROUND: ST2 is an interleukin (IL)-1 receptor family member with membrane-bound (ST2L) and soluble (sST2) isoforms, and sST2 is a biomarker for poor outcome in patients with myocardial infarction (MI). IL-33, the recently discovered ligand for ST2, activates nuclear factor kappaB and thus may regulate apoptotic cell death. We tested the hypothesis that IL-33 is cardioprotective after MI through ST2 signaling. METHODS AND RESULTS: IL-33 protected cultured cardiomyocytes from hypoxia-induced apoptosis, and this cardioprotection was partially inhibited by sST2. IL-33 induced expression of the antiapoptotic factors XIAP, cIAP1, and survivin. To define the cardioprotective role of IL-33 in vivo, we performed a blinded and randomized study of ischemia/reperfusion in rats. IL-33 reduced cardiomyocyte apoptosis, suppressed caspase-3 activity, and increased expression of IAP family member proteins. IL-33 decreased both infarct and fibrosis volumes at 15 days; furthermore, both echocardiographic and hemodynamic studies revealed that IL-33 improved ventricular function. To determine whether cardioprotection by IL-33 is mediated through ST2 signaling, a randomized and blinded study of ST2(-/-) versus wild-type littermate mice was performed in 98 mice subjected to MI. At 4 weeks after MI, IL-33 reduced ventricular dilation and improved contractile function in wild-type mice but not in ST2(-/-) mice. Finally, IL-33 improved survival after MI in wild-type but not in ST2(-/-) mice. CONCLUSIONS: IL-33 prevents cardiomyocyte apoptosis and improves cardiac function and survival after MI through ST2 signaling.

Baroreflex increases correlation and coherence of muscle sympathetic nerve activity (SNA) with renal and cardiac SNAs.

Despite accumulating data of muscle sympathetic nerve activity (SNA) measured by human microneurography, whether neural discharges of muscle SNA correlates and coheres with those of other SNAs controlling visceral organs remains unclear. Further, how the baroreflex control of SNA affects the relations between these SNAs remains unknown. In urethane and alpha-chloralose anesthetized, vagotomized, and aortic-denervated rabbits, we recorded muscle SNA from the tibial nerve using microneurography and simultaneously recorded renal and cardiac SNAs. After isolating the carotid sinuses, we produced a baroreflex closed-loop condition by matching the isolated intracarotid sinus pressure (CSP) with systemic arterial pressure (CLOSE). We also fixed CSP at operating pressure (FIX) or altered CSP widely (WIDE: operating pressure +/- 40 mmHg). Under these conditions, we calculated time-domain and frequency-domain measures of the correlation between muscle SNA and renal or cardiac SNAs. At CLOSE, muscle SNA resampled at 1 Hz correlated with both renal (r(2) = 0.71 +/- 0.04, delay = 0.10 +/- 0.004 s) and cardiac SNAs (r(2) = 0.58 +/- 0.03, delay = 0.13 +/- 0.004 s) at optimal delays. Moreover,muscle SNA at CLOSE strongly cohered with renal and cardiac SNAs(coherence >0.8) at the autospectral peak frequencies, and weakly (0.4-0.5) at the remaining frequencies. Increasing the magnitude of CSP change from FIX to CLOSE and further to WIDE resulted in corresponding increases in correlation and coherence functions at nonpeak frequencies, and the coherence functions at peak frequencies remained high (>0.8). In conclusion, muscle SNA correlates and coheres approximately with renal and cardiac SNAs under closed-loop baroreflex conditions. The arterial baroreflex is capable of potently homogenizing neural discharges of these SNAs by modulating SNA at the nonpeak frequencies of SNA autospectra.

Loss of M5 muscarinic acetylcholine receptors leads to cerebrovascular and neuronal abnormalities and cognitive deficits in mice.

The M5 muscarinic acetylcholine receptor (M5R) has been shown to play a crucial role in mediating acetylcholine-dependent dilation of cerebral blood vessels. We show that male M5R-/- mice displayed constitutive constriction of cerebral arteries using magnetic resonance angiography in vivo. Male M5R-/- mice exhibited a significantly reduced cerebral blood flow (CBF) in the cerebral cortex, hippocampus, basal ganglia, and thalamus. Cortical and hippocampal pyramidal neurons from M5R-/- mice showed neuronal atrophy. Hippocampus-dependent spatial and nonspatial memory was also impaired in M5R-/- mice. In M5R-/- mice, CA3 pyramidal cells displayed a significantly attenuated frequency of the spontaneous postsynaptic current and long-term potentiation was significantly impaired at the mossy fiber-CA3 synapse. Our findings suggest that impaired M5R signaling may play a role in the pathophysiology of cerebrovascular deficits. The M5 receptor may represent an attractive novel therapeutic target to ameliorate memory deficits caused by impaired cerebrovascular function.

A family-based association study and gene expression analyses of netrin-G1 and -G2 genes in schizophrenia.

BACKGROUND: The netrin-G1 (NTNG1) and -G2 (NTNG2) genes, recently cloned from mouse, play a role in the formation and/or maintenance of glutamatergic neural circuitry. Accumulating evidence strongly suggests that disturbances of neuronal development and the N-methyl-d-aspartate receptor-mediated signaling system might represent a potential pathophysiology in schizophrenia. We therefore set out to examine the genetic contribution of human NTNG1 and NTNG2 to schizophrenia. METHODS: Twenty-one single nucleotide polymorphisms (SNPs) from NTNG1 and 10 SNPs from NTNG2 were analyzed in 124 schizophrenic pedigrees. All genotypes were determined with the TaqMan assay. The expression levels of NTNG1 and NTNG2 were examined in the frontal (Brodmann's Area [BA]11 and BA46) and temporal (BA22) cortices from schizophrenic and control postmortem brains. The isoform-specific expression of NTNG1 splice variants was assessed in these samples. RESULTS: Specific haplotypes encompassing alternatively spliced exons of NTNG1 were associated with schizophrenia, and concordantly, messenger ribonucleic acid isoform expression was significantly different between schizophrenic and control brains. An association between NTNG2 and schizophrenia was also observed with SNPs and haplotypes that clustered in the 5' region of the gene. CONCLUSIONS: The NTNG1 and NTNG2 genes might be relevant to the pathophysiology of schizophrenia.

Sound sequence discrimination learning is dependent on cholinergic inputs to the rat auditory cortex.

In rat auditory cortex (AC) slices, synaptic potentiation following heterosynaptic stimulation is affected by the stimulus sequence used for induction. It was hypothesized that this sequence-dependent plasticity might be partly involved in the cellular mechanisms underlying sound sequence discrimination. Sequence dependence is abolished by muscarinic receptor antagonists. Therefore, dependence of sound sequence discrimination learning on cholinergic inputs to the rat AC was investigated. Rats were trained to discriminate the sequences of two sound components and a licking behavior in response to one of two possible sequences was rewarded with water. Atropine, a muscarinic receptor antagonist, attenuated sound sequence discrimination learning. The acquired sound sequence discrimination was not affected by atropine. Injections of the cholinergic immunotoxin 192IgG-saporin into the AC suppressed sound sequence discrimination learning, while discrimination between the two sound components was not affected. An inhibitor of M-current, linopirdine, restores the sequence dependence of synaptic potentiation in the AC slices suppressed by atropine. In this study, sound sequence discrimination learning attenuated by 192IgG-saporin was also restored by linopirdine. These similarities between sequence dependent plasticity in the AC slices and sound sequence discrimination learning support the hypothesis that the former is involved in the cellular mechanisms underlying the latter.

Polysynaptic slow depolarization and spiking activity elicited after induction of long-term potentiation in rat auditory cortex.

Polysynaptic activity was recorded in supragranular pyramidal neurons before and after the induction of long-term potentiation (LTP) in slices obtained from rat auditory cortex. LTP was induced by tetanic stimulation of layer IV. In the pyramidal neurons exhibiting LTP, repetitive stimulation at 50 Hz with 15 pulses triggered a slow 15-35 mV depolarization lasting 0.5-2 s with two to five spike discharges. There was no such response before the induction of LTP or in the neurons that did not exhibit LTP. Slow depolarization with spike discharges was blocked by an NMDA receptor antagonist but not by a metabotropic glutamate receptor antagonist. The reversal potential of the slow depolarization was approximately -7 mV and the membrane resistance decreased during slow depolarization, suggesting that the slow depolarization was produced by polysynaptic excitatory post-synaptic potentials. LTP was also induced by low frequency stimulation paired with a depolarizing current injection. In the pyramidal neurons exhibiting LTP after the paired stimulation, the slow depolarization amplitude was small and repetitive stimulation did not trigger spike discharges. Tetanic stimulation is expected to induce LTP in the polysynaptic neural circuits connecting many pyramidal neurons. The present findings suggest that polysynaptic activity can be generated in the potentiated neural circuits. Such activity might serve to read out the memory stored in polysynaptic neural circuits in the cerebral cortex.