The amygdala differentially regulates defensive behaviors evoked by CO2.

CO2 inhalation can provoke panic attacks in humans, and the likelihood is increased in patients with panic disorder. Identifying brain sites involved could provide important mechanistic insight into the illness. In mice, the amygdala has been suggested to promote CO2 responses; however, recent studies in humans with amygdala damage indicate the amygdala is not required for CO2-induced fear and panic and might actually oppose these responses. To clarify the role of the amygdala, we produced lesions in mice paralleling the human lesions, and characterized behavioral responses to CO2. Compared to sham controls, we found that amygdala-lesioned mice froze less to 10% CO2, and unlike shams they also began to jump frenetically. At 20% CO2, controls also exhibited jumping, suggesting it is a normal response to more extreme CO2 concentrations. The effect of amygdala lesions was specific to CO2 as amygdala-lesioned mice did not jump in response to a predator odor or to an auditory conditioned stimulus. In amygdala-lesioned mice, jumping evoked by 10% CO2 was eliminated by co-lesioning the dorsal periaqueductal gray, a structure implicated in panic and escape-related behaviors. Together, these observations suggest a dual role for the amygdala in the CO2 response: promoting CO2-induced freezing, and opposing CO2-induced jumping, which may help explain the exaggerated CO2 responses in humans with amygdala lesions.

ASIC1A in neurons is critical for fear-related behaviors.

Acid-sensing ion channels (ASICs) have been implicated in fear-, addiction- and depression-related behaviors in mice. While these effects have been attributed to ASIC1A in neurons, it has been reported that ASICs may also function in nonneuronal cells. To determine if ASIC1A in neurons is indeed required, we generated neuron-specific knockout (KO) mice with floxed Asic1a alleles disrupted by Cre recombinase driven by the neuron-specific synapsin I promoter (SynAsic1a KO mice). We confirmed that Cre expression occurred in neurons, but not all neurons, and not in nonneuronal cells including astrocytes. Consequent loss of ASIC1A in some but not all neurons was verified by western blotting, immunohistochemistry and electrophysiology. We found ASIC1A was disrupted in fear circuit neurons, and SynAsic1a KO mice exhibited prominent deficits in multiple fear-related behaviors including Pavlovian fear conditioning to cue and context, predator odor-evoked freezing and freezing responses to carbon dioxide inhalation. In contrast, in the nucleus accumbens ASIC1A expression was relatively normal in SynAsic1a KO mice, and consistent with this observation, cocaine conditioned place preference (CPP) was normal. Interestingly, depression-related behavior in the forced swim test, which has been previously linked to ASIC1A in the amygdala, was also normal. Together, these data suggest neurons are an important site of ASIC1A action in fear-related behaviors, whereas other behaviors likely depend on ASIC1A in other neurons or cell types not targeted in SynAsic1a KO mice. These findings highlight the need for further work to discern the roles of ASICs in specific cell types and brain sites.

Brain abnormalities in bipolar disorder detected by quantitative T1ρ mapping.

Abnormal metabolism has been reported in bipolar disorder, however, these studies have been limited to specific regions of the brain. To investigate whole-brain changes potentially associated with these processes, we applied a magnetic resonance imaging technique novel to psychiatric research, quantitative mapping of T1 relaxation in the rotating frame (T1ρ). This method is sensitive to proton chemical exchange, which is affected by pH, metabolite concentrations and cellular density with high spatial resolution relative to alternative techniques such as magnetic resonance spectroscopy and positron emission tomography. Study participants included 15 patients with bipolar I disorder in the euthymic state and 25 normal controls balanced for age and gender. T1ρ maps were generated and compared between the bipolar and control groups using voxel-wise and regional analyses. T1ρ values were found to be elevated in the cerebral white matter and cerebellum in the bipolar group. However, volumes of these areas were normal as measured by high-resolution T1- and T2-weighted magnetic resonance imaging. Interestingly, the cerebellar T1ρ abnormalities were normalized in participants receiving lithium treatment. These findings are consistent with metabolic or microstructural abnormalities in bipolar disorder and draw attention to roles of the cerebral white matter and cerebellum. This study highlights the potential utility of high-resolution T1ρ mapping in psychiatric research.

Localization and behaviors in null mice suggest that ASIC1 and ASIC2 modulate responses to aversive stimuli.

Acid-sensing ion channels (ASICs) generate H(+) -gated Na(+) currents that contribute to neuronal function and animal behavior. Like ASIC1, ASIC2 subunits are expressed in the brain and multimerize with ASIC1 to influence acid-evoked currents and facilitate ASIC1 localization to dendritic spines. To better understand how ASIC2 contributes to brain function, we localized the protein and tested the behavioral consequences of ASIC2 gene disruption. For comparison, we also localized ASIC1 and studied ASIC1(-/-) mice. ASIC2 was prominently expressed in areas of high synaptic density, and with a few exceptions, ASIC1 and ASIC2 localization exhibited substantial overlap. Loss of ASIC1 or ASIC2 decreased freezing behavior in contextual and auditory cue fear conditioning assays, in response to predator odor and in response to CO2 inhalation. In addition, loss of ASIC1 or ASIC2 increased activity in a forced swim assay. These data suggest that ASIC2, like ASIC1, plays a key role in determining the defensive response to aversive stimuli. They also raise the question of whether gene variations in both ASIC1 and ASIC2 might affect fear and panic in humans.

Disruption of the non-canonical Wnt gene PRICKLE2 leads to autism-like behaviors with evidence for hippocampal synaptic dysfunction.

Autism spectrum disorders (ASDs) have been suggested to arise from abnormalities in the canonical and non-canonical Wnt signaling pathways. However, a direct connection between a human variant in a Wnt pathway gene and ASD-relevant brain pathology has not been established. Prickle2 (Pk2) is a post-synaptic non-canonical Wnt signaling protein shown to interact with post-synaptic density 95 (PSD-95). Here, we show that mice with disruption in Prickle2 display behavioral abnormalities including altered social interaction, learning abnormalities and behavioral inflexibility. Prickle2 disruption in mouse hippocampal neurons led to reductions in dendrite branching, synapse number and PSD size. Consistent with these findings, Prickle2 null neurons show decreased frequency and size of spontaneous miniature synaptic currents. These behavioral and physiological abnormalities in Prickle2 disrupted mice are consistent with ASD-like phenotypes present in other mouse models of ASDs. In 384 individuals with autism, we identified two with distinct, heterozygous, rare, non-synonymous PRICKLE2 variants (p.E8Q and p.V153I) that were shared by their affected siblings and inherited paternally. Unlike wild-type PRICKLE2, the PRICKLE2 variants found in ASD patients exhibit deficits in morphological and electrophysiological assays. These data suggest that these PRICKLE2 variants cause a critical loss of PRICKLE2 function. The data presented here provide new insight into the biological roles of Prickle2, its behavioral importance, and suggest disruptions in non-canonical Wnt genes such as PRICKLE2 may contribute to synaptic abnormalities underlying ASDs.

Expressing acid-sensing ion channel 3 in the brain alters acid-evoked currents and impairs fear conditioning.

Previous studies on mice with a disruption of the gene encoding acid-sensing ion channel 1a (ASIC1a) suggest that ASIC1a is required for normal fear behavior. To investigate the effects of altering the subunit composition of brain ASICs on behavior, we developed transgenic mice expressing ASIC3 via the pan-neuronal synapsin I promoter. These mice express ASIC3 in the brain, where the endogenous ASIC3 protein is not detected. We found that in ASIC3 transgenic mice, ASIC3 co-immunoprecipitated with the endogenous ASIC1a protein and distributed in the same subcellular brain fractions as ASIC1a. In addition, ASIC3 significantly increased the rate of desensitization of acid-evoked currents in cultured cortical neurons. Importantly, ASIC3 reduced Pavlovian fear conditioning to both context and auditory cues. These observations suggest that ASIC3 can heteromultimerize with ASIC1a in the brain and alter the biophysical properties of the endogenous channel complex. Moreover, these data suggest that ASIC subunit composition and channel desensitization may be critical determinants for ASIC-dependent behavior.

Different contributions of ASIC channels 1a, 2, and 3 in gastrointestinal mechanosensory function.

AIMS: Members of the acid sensing ion channel (ASIC) family are strong candidates as mechanical transducers in sensory function. The authors have shown that ASIC1a has no role in skin but a clear influence in gastrointestinal mechanotransduction. Here they investigate further ASIC1a in gut mechanoreceptors, and compare its influence with ASIC2 and ASIC3. METHODS AND RESULTS: Expression of ASIC1a, 2, and 3 mRNA was found in vagal (nodose) and dorsal root ganglia (DRG), and was lost in mice lacking the respective genes. Recordings of different classes of splanchnic colonic afferents and vagal gastro-oesophageal afferents revealed that disruption of ASIC1a increased the mechanical sensitivity of all afferents in both locations. Disruption of ASIC2 had varied effects: increased mechanosensitivity in gastro-oesophageal mucosal endings, decreases in gastro-oesophageal tension receptors, increases in colonic serosal endings, and no change in colonic mesenteric endings. In ASIC3-/- mice, all afferent classes had markedly reduced mechanosensitivity except gastro-oesophageal mucosal receptors. Observations of gastric emptying and faecal output confirmed that increases in mechanosensitivity translate to changes in digestive function in conscious animals. CONCLUSIONS: These data show that ASIC3 makes a critical positive contribution to mechanosensitivity in three out of four classes of visceral afferents. The presence of ASIC1a appears to provide an inhibitory contribution to the ion channel complex, whereas the role of ASIC2 differs widely across subclasses of afferents. These findings contrast sharply with the effects of ASIC1, 2, and 3 in skin, suggesting that targeting these subunits with pharmacological agents may have different and more pronounced effects on mechanosensitivity in the viscera.

Mutational analysis of the Saccharomyces cerevisiae ATP-binding cassette transporter protein Ycf1p.

Ycf1p is a member of the ATP-binding cassette transporter family of membrane proteins. Strong sequence similarity has been observed between Ycf1p, the cystic fibrosis transmembrane conductance regulator (CFTR) and multidrug resistance protein (MRP). In this work, we have examined the functional significance of several of the conserved amino acid residues and the genetic requirements for Ycf1p subcellular localization. Biochemical fractionation experiments have established that Ycf1p, expressed at single-copy gene levels, co-fractionates with the vacuolar membrane and that this co-fractionation is independent of vps15, vps34 or end3 gene function. Several cystic fibrosis-associated alleles of the CFTR were introduced into Ycf1p and found to elicit defects analogous to those seen in the CFTR. An amino-terminal extension shared between Ycf1p and MRP, but absent from CFTR, was found to be required for Ycf1p function, but not its subcellular localization. Mutant forms of Ycf1p were also identified that exhibited enhanced biological function relative to the wild-type protein. These studies indicate that Ycf1p will provide a simple, genetically tractable model system for the study of the trafficking and function of ATP-binding cassette transporter proteins, such as the CFTR and MRP.

The Saccharomyces cerevisiae AP-1 protein discriminates between oxidative stress elicited by the oxidants H2O2 and diamide.

The Saccharomyces cerevisiae AP-1 protein (yAP-1) is a key mediator of oxidative stress tolerance. Transcriptional activation by yAP-1 has been shown to be inducible by exposure of cells to H2O2 and diamide, among other oxidative stress eliciting compounds. Here we define the segments of the yAP-1 protein that are required to respond to this environmental challenge. Western blotting analyses indicated that levels of yAP-1 do not change during oxidative stress. Deletion mutagenesis and gene fusion experiments indicate that two different segments of yAP-1 are required for oxidative stress inducibility. These two domains function differentially depending on the type of oxidant used to generate oxidative stress. Three repeated cysteine-serine-glutamate sequences located in the carboxyl terminus are required for normal regulation of yAP-1 function during oxidative stress. Replacement of these cysteine-serine-glutamate repeats by alanine residues does not similarly affect H2O2 and diamide regulation of yAP-1 function. While yAP-1 transactivation is enhanced by exposure to either H2O2 or diamide, the protein responds to the oxidative stress produced by these compounds in nonidentical ways.

Cadmium tolerance mediated by the yeast AP-1 protein requires the presence of an ATP-binding cassette transporter-encoding gene, YCF1.

Elevations in gene dosage of the transcriptional regulatory protein yAP-1 in Saccharomyces cerevisiae can elicit pronounced phenotypic increases in tolerance of a variety of drugs including the toxic heavy metal cadmium. While a large elevation in cadmium tolerance occurs in response to overproduction of yAP-1, the target genes under yAP-1 control have not yet been identified that are responsible for this increase. We show here that the YCF1 gene, encoding a likely integral membrane protein, is required for yAP-1 to exert its normal effects on cadmium tolerance. Mutant strains of yeast that lack the YCF1 gene are hypersensitive to cadmium and this hypersensitivity is epistatic to yAP-1 overexpression. YCF1 mRNA levels and the expression of a YCF1-lacZ reporter construct positively correlates with changes in YAP1 gene dosage. A set of 5' truncation derivatives of the YCF1-lacZ fusion gene identified the region from -201 to +47 as being sufficient for the yAP-1-dependent increase in expression. DNase I footprinting using a probe from this segment of the YCF1 promoter showed that bacterially-produced yAP-1 protein was capable of binding a novel DNA element we have designated the yAP-1 response element. Insertion of the yAP-1 response element upstream of a CYC1-lacZ gene fusion led to the production of beta-galactosidase in a yAP-1-dependent fashion. These data establish that an important physiological target of yAP-1 transcriptional regulation is the YCF1 structural gene.

A yeast metal resistance protein similar to human cystic fibrosis transmembrane conductance regulator (CFTR) and multidrug resistance-associated protein.

Members of the ATP binding cassette (ABC) protein superfamily transport a variety of substances across biological membranes, including drugs, ions, and peptides. The yeast cadmium factor (YCF1) gene from Saccharomyces cerevisiae is required for cadmium resistance and encodes a 1,515 amino acid protein with extensive homology to both the human multidrug resistance-associated protein (MRP1) and the cystic fibrosis transmembrane conductance regulator (hCFTR). S. cerevisiae cells harboring a deletion of the YCF1 gene are hypersensitive to cadmium compared with wild type cells. Mutagenesis experiments demonstrate that conserved amino acid residues, functionally critical in hCFTR, play a vital role in YCF1-mediated cadmium resistance. Mutagenesis of phenylalanine 713 in the YCF1 nucleotide binding fold 1, which correlates with the delta F508 mutation found in the most common form of cystic fibrosis, completely abolished YCF1 function in cadmium detoxification. Furthermore, substitution of a serine to alanine residue in a potential protein kinase A phosphorylation site in a central region of YCF1, which displays sequence similarity to the central regulatory domain of hCFTR, also rendered YCF1 nonfunctional. These results suggest that YCF1 is composed of modular domains found in human proteins which function in drug and ion transport.

Transcriptional activation mediated by the yeast AP-1 protein is required for normal cadmium tolerance.

The yeast YAP1 gene encodes a transcriptional regulatory protein that utilizes a basic region-leucine zipper (bZip) DNA-binding domain to recognize its cognate DNA element. A synthetic reporter gene containing a SV40 AP-1 response element (ARE) cloned upstream of a TRP5 promoter-lacZ gene fusion shows yAP-1-dependent transactivation in vivo. Recent work has shown that changes in the gene dosage of this factor can dramatically alter the ability of a cell to tolerate a host of toxic agents including cadmium, cycloheximide, and sulfometuron methyl. We have focused on the YAP1-dependent cadmium resistance as cells that lack a functional YAP1 gene are hypersensitive to this metal. Deletion mapping experiments define two domains in the carboxyl-terminal region of the yAP-1 protein that are required for normal cadmium tolerance and ARE-TRP5-lacZ expression. Single amino acid substitutions in the bZip domain of yAP-1 indicate that this region is required for normal DNA binding and in vivo function of the protein. Replacement of a non-canonical asparagine with leucine in the yAP-1 leucine zipper leads to production of a defective protein. A substitution mutation in the basic domain converts this mutant protein into a dominant negative factor. The ability of yAP-1 to act as a positive regulator of transcription is required for its biological action.

Yeast bZip proteins mediate pleiotropic drug and metal resistance.

Saccharomyces cerevisiae contains a group of transcription factors related to mammalian c-Jun. This yeast Jun-family of proteins consists of GCN4, a regulator of genes involved in amino acid biosynthesis, and yAP-1, a factor conferring pleiotropic drug resistance when overexpressed. In the work described here, we show that a third member of the yeast Jun-family exists. This protein has been designated CAD1 and provides resistance to cadmium when present on a high-copy plasmid. CAD1 and yAP-1 are related in their amino-terminal DNA binding domains and can recognize the same DNA target site in vitro. Overproduction of CAD1 leads to transcriptional activation of an artificial reporter gene in delta yap1 cells. High level production of either CAD1 or yAP-1 causes cells to acquire a pleiotropic drug-resistant phenotype and to be able to tolerate normally toxic levels of iron chelators and zinc. Surprisingly, disruption of the CAD1 gene has no effect on the normal cellular resistance to cadmium but delta yap1 mutants are hypersensitive to this cytotoxic metal. The cadmium hypersensitivity of the delta yap1 mutant described here indicates that one major role of YAP1 in the yeast cell is to mediate resistance to this metal.

The endogenous functional turkey erythrocyte and rat liver insulin receptor is an alpha 2 beta 2 heterotetrameric complex.

Previous studies have indicated that turkey erythrocyte and rat liver membranes contain endogenous alpha beta heterodimeric insulin receptors in addition to the disulphide-linked alpha 2 beta 2 heterotetrameric complexes characteristic of most cell types. We utilized 125I-insulin affinity cross-linking to examine the structural properties of insulin receptors from rat liver and turkey erythrocyte membranes prepared in the absence and presence of sulphydryl alkylating agents. Rat liver membranes prepared in the absence of sulphydryl alkylating agents displayed specific labelling of Mr 400,000 and 200,000 bands, corresponding to the alpha 2 beta 2 heterotetrameric and alpha beta heterodimeric insulin receptor complexes respectively. In contrast, affinity cross-linking of membranes prepared with iodoacetamide (IAN) or N-ethylmaleimide identified predominantly the alpha 2 beta 2 heterotetrameric insulin receptor complex. Similarly, affinity cross-linking and solubilization of intact turkey erythrocytes in the presence of IAN resulted in exclusive labelling of the alpha 2 beta 2 heterotetrameric insulin receptor complex, whereas in the absence of IAN both alpha 2 beta 2 and alpha beta species were observed. Turkey erythrocyte alpha 2 beta 2 heterotetrameric insulin receptors from IAN-protected membranes displayed a 3-4-fold stimulation of beta subunit autophosphorylation and substrate phosphorylation by insulin, equivalent to that observed in intact human placenta insulin receptors. Turkey erythrocyte alpha beta heterodimeric insulin receptors, prepared by defined pH/dithiothreitol treatment of IAN-protected membranes, were also fully competent in insulin-stimulated protein kinase activity compared with alpha beta heterodimeric human placenta receptors. In contrast, endogenous turkey erythrocyte alpha beta heterodimeric insulin receptors displayed basal protein kinase activity which was insulin-insensitive. These data indicate that native turkey erythrocyte and rat liver insulin receptors are structurally and functionally similar to alpha 2 beta 2 heterotetrameric human placenta insulin receptors. The alpha beta heterodimeric insulin receptors previously identified in these tissues most likely resulted from disulphide bond reduction and denaturation of the alpha 2 beta 2 holoreceptor complexes during membrane preparation.

Functional properties of an isolated alpha beta heterodimeric human placenta insulin-like growth factor 1 receptor complex.

Treatment of human placenta membranes at pH 8.5 in the presence of 2.0 mM dithiothreitol (DTT) for 5 min, followed by the simultaneous removal of the DTT and pH adjustment to pH 7.6, resulted in the formation of a functional alpha beta heterodimeric insulin-like growth factor 1 (IGF-1) receptor complex from the native alpha 2 beta 2 heterotetrameric disulfide-linked state. The membrane-bound alpha beta heterodimeric complex displayed similar curvilinear 125I-IGF-1 equilibrium binding compared to the alpha 2 beta 2 heterotetrameric complex. Triton X-100 solubilization of the alkaline pH and DTT-pretreated placenta membranes, followed by Bio-Gel A-1.5m gel filtration chromatography, was found to effectively separate the alpha 2 beta 2 heterotetrameric and alpha beta heterodimeric IGF-1 receptor species, 125I-IGF-1 binding to both the isolated alpha 2 beta 2 heterotetrameric and alpha beta heterodimeric complexes demonstrated a marked straightening of the Scatchard plots, compared to the placenta membrane-bound IGF-1 receptors, with a 2-fold increase in the high-affinity binding component. Similar to the membrane-bound IGF-1 receptor species, the 125I-IGF-1 binding properties between the alpha 2 beta 2 heterotetrameric and alpha beta heterodimeric complexes were not significantly different. IGF-1 stimulation of IGF-1 receptor autophosphorylation indicated that the ligand-dependent activation of alpha beta heterodimeric protein kinase activity occurred concomitant with the reassociation into a covalent alpha 2 beta 2 heterotetrameric state.(ABSTRACT TRUNCATED AT 250 WORDS)