Ca2+ entry via AMPA-type glutamate receptors triggers Ca2+-induced Ca2+ release from ryanodine receptors in rat spiral ganglion neurons

NADPH Oxidase 3 Deficiency Protects From Noise-Induced Sensorineural Hearing Loss

The reactive oxygen species (ROS)-generating NADPH oxidase NOX3 isoform is highly and specifically expressed in the inner ear. NOX3 is needed for normal vestibular development but NOX-derived ROS have also been implicated in the pathophysiology of sensorineural hearing loss. The role of NOX-derived ROS in noise-induced hearing loss, however, remains unclear and was addressed with the present study. Two different mouse strains, deficient in NOX3 or its critical subunit p22phox, were subjected to a single noise exposure of 2 h using an 8-16 kHz band noise at an intensity of 116-120 decibel sound pressure level. In the hours following noise exposure, there was a significant increase in cochlear mRNA expression of NOX3 in wild type animals. By using RNAscope in situ hybridization, NOX3 expression was primarily found in the Rosenthal canal area, colocalizing with auditory neurons. One day after the noise trauma, we observed a high frequency hearing loss in both knock-out mice, as well as their wild type littermates. At day seven after noise trauma however, NOX3 and p22phox knockout mice showed a significantly improved hearing recovery and a marked preservation of neurosensory cochlear structures compared to their wild type littermates. Based on these findings, an active role of NOX3 in the pathophysiology of noise-induced hearing loss can be demonstrated, in line with recent evidence obtained in other forms of acquired hearing loss. The present data demonstrates that the absence of functional NOX3 enhances the hearing recovery phase following noise trauma. This opens an interesting clinical window for pharmacological or molecular intervention aiming at post prevention of noise-induced hearing loss.

Prenatal High-Sucrose Diet Induced Vascular Dysfunction in Thoracic Artery of Fetal Offspring

SCOPE

Maternal nutrition during pregnancy is related to intrauterine fetal development. The authors' previous work reports that prenatal high sucrose (HS) diet impaired micro-vascular functions in postnatal offspring. It is unclear whether/how prenatal HS causes vascular injury during fetal life.

METHODS AND RESULTS

Pregnant rats are fed with normal drinking water or 20% high-sucrose solution during the whole gestational period. Pregnant HS increases maternal weight before delivery. Fetal thoracic aorta is separated for experiments. Angiotensin II (AII)-stimulated vascular contraction of fetal thoracic arteries in HS group is greater, which mainly results from the enhanced AT1 receptor (AT1R) function and the downstream signaling. Nifedipine significantly increases vascular tension in HS group, indicating that the L-type calcium channels (LTCCs) function is strengthened. 2-Aminoethyl diphenylborinate (2-APB), inositol 1,4,5-trisphosphate receptors (IP3Rs) inhibitor, increases vascular tension induced by AII in HS group and ryanodine receptors-sensitive vascular tone shows no difference in the two groups, which suggested that the activity of IP3Rs-operated calcium channels is increased.

CONCLUSION

These findings suggest that prenatal HS induces vascular dysfunction of thoracic arteries in fetal offspring by enhancing AT1R, LTCCs function and IP3Rs-associated calcium channels, providing new information regarding the impact of prenatal HS on the functional development of fetal vascular systems.

Australian Scorpion Hormurus waigiensis Venom Fractions Show Broad Bioactivity Through Modulation of Bio-Impedance and Cytosolic Calcium

Scorpion venoms are a rich source of bioactive molecules, but characterisation of toxin peptides affecting cytosolic Ca2+, central to cell signalling and cell death, is limited. We undertook a functional screening of the venom of the Australian scorpion Hormurus waigiensis to determine the breadth of Ca2+ mobilisation. A human embryonic kidney (HEK293) cell line stably expressing the genetically encoded Ca2+ reporter GCaMP5G and the rabbit type 1 ryanodine receptor (RyR1) was developed as a biosensor. Size-exclusion Fast Protein Liquid Chromatography separated the venom into 53 fractions, constituting 12 chromatographic peaks. Liquid chromatography mass spectroscopy identified 182 distinct molecules with 3 to 63 components per peak. The molecular weights varied from 258 Da-13.6 kDa, with 53% under 1 kDa. The majority of the venom chromatographic peaks (tested as six venom pools) were found to reversibly modulate cell monolayer bioimpedance, detected using the xCELLigence platform (ACEA Biosciences). Confocal Ca2+ imaging showed 9/14 peak samples, with molecules spanning the molecular size range, increased cytosolic Ca2+ mobilization. H. waigiensis venom Ca2+ activity was correlated with changes in bio-impedance, reflecting multi-modal toxin actions on cell physiology across the venom proteome.

Redox activation of excitatory pathways in auditory neurons as mechanism of age-related hearing loss

Age-related hearing (ARHL) loss affects a large part of the human population with a major impact on our aging societies. Yet, underlying mechanisms are not understood, and no validated therapy or prevention exists. NADPH oxidases (NOX), are important sources of reactive oxygen species (ROS) in the cochlea and might therefore be involved in the pathogenesis of ARHL. Here we investigate ARHL in a mouse model. Wild type mice showed early loss of hearing and cochlear integrity, while animals deficient in the NOX subunit p22^phox remained unaffected up to six months. Genes of the excitatory pathway were down-regulated in p22^phox-deficient auditory neurons. Our results demonstrate that NOX activity leads to upregulation of genes of the excitatory pathway, to excitotoxic cochlear damage, and ultimately to ARHL. In the absence of functional NOXs, aging mice conserve hearing and cochlear morphology. Our study offers new insights into pathomechanisms and future therapeutic targets of ARHL.

•

Mice devoid of NADPH oxidase (NOX) activity are protected from age-related hearing loss.

•

Cochlear NOX expression shows a similar pattern in mouse and human.

•

NOX3, the predominant NOX isoform in the cochlea, is mostly expressed in auditory neurons.

•

NOX-deficient auditory neurons show decreased transcription of glutamatergic pathway and are protected from excitotoxicity.

•

NOX-mediated gene regulation within auditory neurons contributes to age-related hearing loss.

Targeted single-cell electroporation loading of Ca2+ indicators in the mature hemicochlea preparation

Ca²⁺ is an important intracellular messenger and regulator in both physiological and pathophysiological mechanisms in the hearing organ. Investigation of cellular Ca²⁺ homeostasis in the mature cochlea is hampered by the special anatomy and high vulnerability of the organ. A quick, straightforward and reliable Ca²⁺ imaging method with high spatial and temporal resolution in the mature organ of Corti is missing. Cell cultures or isolated cells do not preserve the special microenvironment and intercellular communication, while cochlear explants are excised from only a restricted portion of the organ of Corti and usually from neonatal pre-hearing murines. The hemicochlea, prepared from hearing mice allows tonotopic experimental approach on the radial perspective in the basal, middle and apical turns of the organ. We used the preparation recently for functional imaging in supporting cells of the organ of Corti after bulk loading of the Ca²⁺ indicator. However, bulk loading takes long time, is variable and non-selective, and causes the accumulation of the indicator in the extracellular space. In this study we show the improved labeling of supporting cells of the organ of Corti by targeted single-cell electroporation in mature mouse hemicochlea. Single-cell electroporation proved to be a reliable way of reducing the duration and variability of loading and allowed subcellular Ca²⁺ imaging by increasing the signal-to-noise ratio, while cell viability was retained during the experiments. We demonstrated the applicability of the method by measuring the effect of purinergic, TRPA1, TRPV1 and ACh receptor stimulation on intracellular Ca²⁺ concentration at the cellular and subcellular level. In agreement with previous results, ATP evoked reversible and repeatable Ca²⁺ transients in Deiters', Hensen's and Claudius' cells. TRPA1 and TRPV1 stimulation by AITC and capsaicin, respectively, failed to induce any Ca²⁺ response in the supporting cells, except in a single Hensen's cell in which AITC evoked transients with smaller amplitude. AITC also caused the displacement of the tissue. Carbachol, agonist of ACh receptors induced Ca²⁺ transients in about a third of Deiters' and fifth of Hensen's cells. Here we have presented a fast and cell-specific indicator loading method allowing subcellular functional Ca²⁺ imaging in supporting cells of the organ of Corti in the mature hemicochlea preparation, thus providing a straightforward tool for deciphering the poorly understood regulation of Ca²⁺ homeostasis in these cells.

Pulsed infrared releases Ca2+ from the endoplasmic reticulum of cultured spiral ganglion neurons

Inner ear spiral ganglion neurons were cultured from day 4 postnatal mice and loaded with a fluorescent Ca²⁺ indicator (fluo-4, -5F, or -5N). Pulses of infrared radiation (IR; 1,863 nm, 200 µs, 200-250 Hz for 2-5 s, delivered via an optical fiber) produced a rapid, transient temperature increase of 6-12°C (above a baseline of 24-30°C). These IR pulse trains evoked transient increases in both nuclear and cytosolic Ca²⁺ concentration ([Ca²⁺]) of 0.20-1.4 µM, with a simultaneous reduction of [Ca²⁺] in regions containing endoplasmic reticulum (ER). IR-induced increases in cytosolic [Ca²⁺] continued in medium containing no added Ca²⁺ (±Ca²⁺ buffers) and low [Na⁺], indicating that the [Ca²⁺] increase was mediated by release from intracellular stores. Consistent with this hypothesis, the IR-induced [Ca²⁺] response was prolonged and eventually blocked by inhibition of ER Ca²⁺-ATPase with cyclopiazonic acid, and was also inhibited by a high concentration of ryanodine and by inhibitors of inositol (1,4,5)-trisphosphate (IP₃)-mediated Ca²⁺ release (xestospongin C and 2-aminoethoxydiphenyl borate). The thermal sensitivity of the response suggested involvement of warmth-sensitive transient receptor potential (TRP) channels. The IR-induced [Ca²⁺] increase was inhibited by TRPV4 inhibitors (HC-067047 and GSK-2193874), and immunostaining of spiral ganglion cultures demonstrated the presence of TRPV4 and TRPM2 that colocalized with ER marker GRP78. These results suggest that the temperature sensitivity of IR-induced [Ca²⁺] elevations is conferred by TRP channels on ER membranes, which facilitate Ca²⁺ efflux into the cytosol and thereby contribute to Ca²⁺-induced Ca²⁺-release via IP₃ and ryanodine receptors. NEW & NOTEWORTHY Infrared radiation-induced photothermal effects release Ca²⁺ from the endoplasmic reticulum of primary spiral ganglion neurons. This Ca²⁺ release is mediated by activation of transient receptor potential (TRPV4) channels and involves amplification by Ca²⁺-induced Ca²⁺-release. The neurons immunostained for warmth-sensitive channels, TRPV4 and TRPM2, which colocalize with endoplasmic reticulum. Pulsed infrared radiation provides a novel experimental tool for releasing intracellular Ca²⁺, studying Ca²⁺ regulatory mechanisms, and influencing neuronal excitability.

Glutamate‑mediated effects of caffeine and interferon‑γ on mercury-induced toxicity

The molecular mechanisms mediating mercury‑induced neurotoxicity are not yet completely understood. Thus, the aim of this study was to investigate whether the severity of MeHg‑ and HgCl2‑mediated cytotoxicity to SH‑SY5Y human dopaminergic neurons can be attenuated by regulating glutamate‑mediated signal‑transmission through caffeine and interferon‑γ (IFN‑γ). The SH‑SY5Y cells were exposed to 1, 2 and 5 µM of either MeHgCl2 or HgCl2 in the presence or absence of L‑glutamine. To examine the effect of adenosine receptor antagonist, the cells were treated with 10 and 20 µM caffeine. The total mitochondrial metabolic activity and oxidative stress intensity coefficient were determined in the 1 ng/ml IFN‑γ‑ and glutamate‑stimulated SH‑SY5Y cells. Following exposure to mercury, the concentration‑dependent decrease in mitochondrial metabolic activity inversely correlated with oxidative stress intensity. MeHg was more toxic than HgCl2. Mercury‑induced neuronal death was dependent on glutamate‑mediated excitotoxicity. Caffeine reduced the mercury‑induced oxidative stress in glutamine-containing medium. IFN‑γ treatment decreased cell viability and increased oxidative stress in glutamine‑free medium, despite caffeine supplementation. Although caffeine exerted a protective effect against MeHg-induced toxicity with glutamate transmission, under co‑stimulation with glutamine and IFN‑γ, caffeine decreased the MeHg‑induced average oxidative stress only by half. Thereby, our data indicate that the IFN‑γ stimulation of mercury‑exposed dopaminergic neurons in neuroinflammatory diseases may diminish the neuroprotective effects of caffeine.

ATP-Evoked Intracellular Ca²⁺ Signaling of Different Supporting Cells in the Hearing Mouse Hemicochlea

Hearing and its protection is regulated by ATP-evoked Ca(2+) signaling in the supporting cells of the organ of Corti, however, the unique anatomy of the cochlea hampers observing these mechanisms. For the first time, we have performed functional ratiometric Ca(2+) imaging (fura-2) in three different supporting cell types in the hemicochlea preparation of hearing mice to measure purinergic receptor-mediated Ca(2+) signaling in pillar, Deiters' and Hensen's cells. Their resting [Ca(2+)]i was determined and compared in the same type of preparation. ATP evoked reversible, repeatable and dose-dependent Ca(2+) transients in all three cell types, showing desensitization. Inhibiting the Ca(2+) signaling of the ionotropic P2X (omission of extracellular Ca(2+)) and metabotropic P2Y purinergic receptors (depletion of intracellular Ca(2+) stores) revealed the involvement of both receptor types. Detection of P2X2,3,4,6,7 and P2Y1,2,6,12,14 receptor mRNAs by RT-PCR supported this finding and antagonism by PPADS suggested different functional purinergic receptor population in pillar versus Deiters' and Hensen's cells. The sum of the extra- and intracellular Ca(2+)-dependent components of the response was about equal with the control ATP response (linear additivity) in pillar cells, and showed supralinearity in Deiters' and Hensen's cells. Calcium-induced calcium release might explain this synergistic interaction. The more pronounced Ca(2+) leak from the endoplasmic reticulum in Deiters' and Hensen's cells, unmasked by cyclopiazonic acid, may also suggests the higher activity of the internal stores in Ca(2+) signaling in these cells. Differences in Ca(2+) homeostasis and ATP-induced Ca(2+) signaling might reflect the distinct roles these cells play in cochlear function and pathophysiology.

Caffeine Modulates Vesicle Release and Recovery at Cerebellar Parallel Fibre Terminals, Independently of Calcium and Cyclic AMP Signalling

Background

Cerebellar parallel fibres release glutamate at both the synaptic active zone and at extrasynaptic sites—a process known as ectopic release. These sites exhibit different short-term and long-term plasticity, the basis of which is incompletely understood but depends on the efficiency of vesicle release and recycling. To investigate whether release of calcium from internal stores contributes to these differences in plasticity, we tested the effects of the ryanodine receptor agonist caffeine on both synaptic and ectopic transmission.

Methods

Whole cell patch clamp recordings from Purkinje neurons and Bergmann glia were carried out in transverse cerebellar slices from juvenile (P16-20) Wistar rats.

Key Results

Caffeine caused complex changes in transmission at both synaptic and ectopic sites. The amplitude of postsynaptic currents in Purkinje neurons and extrasynaptic currents in Bergmann glia were increased 2-fold and 4-fold respectively, but paired pulse ratio was substantially reduced, reversing the short-term facilitation observed under control conditions. Caffeine treatment also caused synaptic sites to depress during 1 Hz stimulation, consistent with inhibition of the usual mechanisms for replenishing vesicles at the active zone. Unexpectedly, pharmacological intervention at known targets for caffeine—intracellular calcium release, and cAMP signalling—had no impact on these effects.

Conclusions

We conclude that caffeine increases release probability and inhibits vesicle recovery at parallel fibre synapses, independently of known pharmacological targets. This complex effect would lead to potentiation of transmission at fibres firing at low frequencies, but depression of transmission at high frequency connections.

Epigallocatechin-3-gallate elicits Ca2+ spike in MCF-7 breast cancer cells: essential role of Cav3.2 channels

We used MCF-7 human breast cancer cells that endogenously express Cav3.1 and Cav3.2 T-type Ca(2+) channels toward a mechanistic study on the effect of EGCG on [Ca(2+)]i. Confocal Ca(2+) imaging showed that EGCG induces a [Ca(2+)]i spike which is due to extracellular Ca(2+) entry and is sensitive to catalase and to low-specificity (mibefradil) and high-specificity (Z944) T-type Ca(2+)channel blockers. siRNA knockdown of T-type Ca(2+) channels indicated the involvement of Cav3.2 but not Cav3.1. Application of EGCG to HEK cells expressing either Cav3.2 or Cav3.1 induced enhancement of Cav3.2 and inhibition of Cav3.1 channel activity. Measurements of K(+) currents in MCF-7 cells showed a reversible, catalase-sensitive inhibitory effect of EGCG, while siRNA for the Kv1.1 K(+) channel induced a reduction of the EGCG [Ca(2+)]i spike. siRNA for Cav3.2 reduced EGCG cytotoxicity to MCF-7 cells, as measured by calcein viability assay. Together, data suggest that EGCG promotes the activation of Cav3.2 channels through K(+) current inhibition leading to membrane depolarization, and in addition increases Cav3.2 currents. Cav3.2 channels are in part responsible for EGCG inhibition of MCF-7 viability, suggesting that deregulation of [Ca(2+)]i by EGCG may be relevant in breast cancer treatment.

Calcineurin mediates synaptic scaling via synaptic trafficking of Ca2+-permeable AMPA receptors

Kim and Ziff examine the molecular mechanism of synaptic scaling, showing that inhibition of neuronal excitability reduces calcium influx into neurons, resulting in decreased calcineurin activity. This leads to increased surface expression of calcium-permeable AMPA receptors as a homeostatic response.

Homeostatic synaptic plasticity is a negative-feedback mechanism for compensating excessive excitation or inhibition of neuronal activity. When neuronal activity is chronically suppressed, neurons increase synaptic strength across all affected synapses via synaptic scaling. One mechanism for this change is alteration of synaptic AMPA receptor (AMPAR) accumulation. Although decreased intracellular Ca²⁺ levels caused by chronic inhibition of neuronal activity are believed to be an important trigger of synaptic scaling, the mechanism of Ca²⁺-mediated AMPAR-dependent synaptic scaling is not yet understood. Here, we use dissociated mouse cortical neurons and employ Ca²⁺ imaging, electrophysiological, cell biological, and biochemical approaches to describe a novel mechanism in which homeostasis of Ca²⁺ signaling modulates activity deprivation-induced synaptic scaling by three steps: (1) suppression of neuronal activity decreases somatic Ca²⁺ signals; (2) reduced activity of calcineurin, a Ca²⁺-dependent serine/threonine phosphatase, increases synaptic expression of Ca²⁺-permeable AMPARs (CPARs) by stabilizing GluA1 phosphorylation; and (3) Ca²⁺ influx via CPARs restores CREB phosphorylation as a homeostatic response by Ca²⁺-induced Ca²⁺ release from the ER. Therefore, we suggest that synaptic scaling not only maintains neuronal stability by increasing postsynaptic strength but also maintains nuclear Ca²⁺ signaling by synaptic expression of CPARs and ER Ca²⁺ propagation.

Synaptic scaling is a form of homeostatic plasticity that normalizes the strength of synapses (the structure that allows nerve cells to communicate) and is triggered by chronic inhibition of neuronal activity. Although extensive studies have been conducted, the molecular mechanism of this synaptic adaptation is not understood. Using cultured cortical neurons, we show that chronic inhibition of neuronal activity reduces calcium influx into neurons, which, in turn, decreases the activity of the calcium-dependent phosphatase calcineurin. These changes lead to an increase in GluA1-containing, calcium-permeable AMPA receptors, which mediate communication at the synapse. Newly inserted calcium-permeable AMPA receptors restore calcium currents, which enhance synaptic strength and recover calcium signaling. We also show that inhibition or activation of calcineurin activity is sufficient to induce or block synaptic scaling, respectively, suggesting that calcineurin is an important mediator of homeostatic synaptic plasticity. Taken together, our findings show that synaptic scaling is a homeostatic process that not only enhances synaptic transmission but also maintains calcium signaling in neurons under activity deprivation.

Caffeine-induced Ca2+ oscillations in type I horizontal cells of the carp retina and the contribution of the store-operated Ca2+ entry pathway

The mechanisms of release, depletion, and refilling of endoplasmic reticulum (ER) Ca²⁺ were investigated in type I horizontal cells of the carp retina using a fluo-3-based Ca²⁺ imaging technique. Exogenous application of caffeine, a ryanodine receptor agonist, induced oscillatory intracellular free Ca²⁺ concentration ([Ca²⁺]_i) responses in a duration- and concentration-dependent manner. In Ca²⁺-free Ringer’s solution, [Ca²⁺]_i transients could also be induced by a brief caffeine application, whereas subsequent caffeine application induced no [Ca²⁺]_i increase, which implied that extracellular Ca²⁺ was required for ER refilling, confirming the necessity of a Ca²⁺ influx pathway for ER refilling. Depletion of ER Ca²⁺ by thapsigargin triggered a Ca²⁺ influx which could be blocked by the store-operated channel inhibitor 2-APB, which proved the existence of the store-operated Ca²⁺ entry pathway. Taken together, these results suggested that after being depleted by caffeine, the ER was replenished by Ca²⁺ influx via store-operated channels. These results reveal the fine modulation of ER Ca²⁺ signaling, and the activation of the store-operated Ca²⁺ entry pathway guarantees the replenishment of the ER so that the cell can be ready for response to the subsequent stimulus.

PCB-95 modulates the calcium-dependent signaling pathway responsible for activity-dependent dendritic growth

BACKGROUND

Non-dioxin-like (NDL) polychlorinated biphenyls (PCBs) promote dendritic growth in hippocampal neurons via ryanodine receptor (RyR)-dependent mechanisms; however, downstream signaling events that link enhanced RyR activity to dendritic growth are unknown. Activity-dependent dendritic growth, which is a critical determinant of neuronal connectivity in the developing brain, is mediated by calcium ion (Ca(2+))-dependent activation of Ca(2+)/calmodulin kinase-I (CaMKI), which triggers cAMP response element binding protein (CREB)-dependent Wnt2 transcription. RyRs regulate the spatiotemporal dynamics of intracellular Ca(2+) signals, but whether RyRs promote dendritic growth via modulation of this signaling pathway is not known.

OBJECTIVE

We tested the hypothesis that the CaMKI-CREB-Wnt2 signaling pathway couples NDL PCB-enhanced RyR activity to dendritic arborization.

METHODS AND RESULTS

Ca(2+) imaging of dissociated cultures of primary rat hippocampal neurons indicated that PCB-95 (2,2',3,5'6-pentachlorobiphenyl; a potent RyR potentiator), enhanced synchronized Ca(2+) oscillations in somata and dendrites that were blocked by ryanodine. As determined by Western blotting and quantitative polymerase chain reaction, PCB-95 also activated CREB and up-regulated Wnt2. Blocking CaMKK, CaMKIα/γ, MEK/ERK, CREB, or Wnt2 prevented PCB-95-induced dendritic growth. Antagonism of γ-aminobutyric acid (GABA) receptors with bicuculline (BIC) phenocopied the dendrite-promoting effects of PCB-95, and pharmacological antagonism or siRNA knockdown of RyR blocked BIC-induced dendritic growth in dissociated and slice cultures of hippocampal neurons.

CONCLUSIONS

RyR activity contributes to dynamic remodeling of dendritic architecture in response to NDL PCBs via CaMKI-CREB-Wnt2 signaling in rats. Our findings identify PCBs as candidate environmental risk factors for neurodevelopmental disorders, especially in children with heritable deficits in calcium signaling associated with autism.

Differential expression of ryanodine receptor in the developing rat cochlea

Ryanodine receptors (RyRs) are one of the intracellular calcium channels involved in regulation of intracellular free calcium concentration ([Ca²⁺]i). The immunolocalization of RyRs was investigated in the developing rat cochlea at different postnatal days (PND). The change of [Ca²⁺]i in isolated outer hair cells (OHCs) was determined. Morphological results showed low expression of RyRs in the Kolliker’s organ from the PND 5 group. RyR expression in inner hair cells (IHCs) increased as the rats aged, and was mature after PND 14. RyRs in OHCs were expressed near the synaptic area of afferent and efferent nerves. RyRs in supporting cells were expressed widely and strongly. The application of ACh, ryanodine + ACh, and thapsigargin + ACh could induce a significant increase in [Ca²⁺]i in OHCs in the presence of extracellular calcium. This increase of [Ca²⁺]i induced by ACh was caused by not only the calcium influx through surface calcium channels, but also the calciuminduced calcium release (CICR) from intracellular RyR-sensitive calcium stores. Morphological and Ca imaging results suggested that RyRs expression is related to cochlear maturity, and may play an important role in its function.

Genomewide linkage analysis in Costa Rican families implicates chromosome 15q14 as a candidate region for OCD

Obsessive compulsive disorder (OCD) has a complex etiology that encompasses both genetic and environmental factors. However, to date, despite the identification of several promising candidate genes and linkage regions, the genetic causes of OCD are largely unknown. The objective of this study was to conduct linkage studies of childhood-onset OCD, which is thought to have the strongest genetic etiology, in several OCD-affected families from the genetically isolated population of the Central Valley of Costa Rica (CVCR). The authors used parametric and non-parametric approaches to conduct genome-wide linkage analyses using 5,786 single nucleotide repeat polymorphisms (SNPs) in three CVCR families with multiple childhood-onset OCD-affected individuals. We identified areas of suggestive linkage (LOD score ≥ 2) on chromosomes 1p21, 15q14, 16q24, and 17p12. The strongest evidence for linkage was on chromosome 15q14 (LOD = 3.13), identified using parametric linkage analysis with a recessive model, and overlapping a region identified in a prior linkage study using a Caucasian population. Each CVCR family had a haplotype that co-segregated with OCD across a ~7 Mbp interval within this region, which contains 18 identified brain expressed genes, several of which are potentially relevant to OCD. Exonic sequencing of the strongest candidate gene in this region, the ryanodine receptor 3 (RYR3), identified several genetic variants of potential interest, although none co-segregated with OCD in all three families. These findings provide evidence that chromosome 15q14 is linked to OCD in families from the CVCR, and supports previous findings to suggest that this region may contain one or more OCD susceptibility loci.

Minding the calcium store: Ryanodine receptor activation as a convergent mechanism of PCB toxicity

Chronic low-level polychlorinated biphenyl (PCB) exposures remain a significant public health concern since results from epidemiological studies indicate that PCB burden is associated with immune system dysfunction, cardiovascular disease, and impairment of the developing nervous system. Of these various adverse health effects, developmental neurotoxicity has emerged as a particularly vulnerable endpoint in PCB toxicity. Arguably the most pervasive biological effects of PCBs could be mediated by their ability to alter the spatial and temporal fidelity of Ca2+ signals through one or more receptor-mediated processes. This review will focus on our current knowledge of the structure and function of ryanodine receptors (RyRs) in muscle and nerve cells and how PCBs and related non-coplanar structures alter these functions. The molecular and cellular mechanisms by which non-coplanar PCBs and related structures alter local and global Ca2+ signaling properties and the possible short and long-term consequences of these perturbations on neurodevelopment and neurodegeneration are reviewed.

Intracellular- and extracellular-derived Ca(2+) influence phospholipase A(2)-mediated fatty acid release from brain phospholipids

Docosahexaenoic acid (DHA) and arachidonic acid (AA) are found in high concentrations in brain cell membranes and are important for brain function and structure. Studies suggest that AA and DHA are hydrolyzed selectively from the sn-2 position of synaptic membrane phospholipids by Ca(2+)-dependent cytosolic phospholipase A(2) (cPLA(2)) and Ca(2+)-independent phospholipase A(2) (iPLA(2)), respectively, resulting in increased levels of the unesterified fatty acids and lysophospholipids. Cell studies also suggest that AA and DHA release depend on increased concentrations of Ca(2+), even though iPLA(2) has been thought to be Ca(2+)-independent. The source of Ca(2+) for activation of cPLA(2) is largely extracellular, whereas Ca(2+) released from the endoplasmic reticulum can activate iPLA(2) by a number of mechanisms. This review focuses on the role of Ca(2+) in modulating cPLA(2) and iPLA(2) activities in different conditions. Furthermore, a model is suggested in which neurotransmitters regulate the activity of these enzymes and thus the balanced and localized release of AA and DHA from phospholipid in the brain, depending on the primary source of the Ca(2+) signal.

Mechanisms underlying cognitive enhancement and reversal of cognitive deficits in nonhuman primates by the ampakine CX717

RATIONALE

Performance of cognitive tasks in nonhuman primates (NHPs) requires specific brain regions to make decisions under different degrees of difficulty or "cognitive load."

OBJECTIVE

Local cerebral metabolic activity ([18F]FDG PET imaging) in dorsolateral prefrontal cortex (DLPFC), medial temporal lobe (MTL), and dorsal striatum (DStr) is examined in NHPs performing a delayed-match-to-sample (DMS) task with variable degrees of cognitive load.

MATERIALS AND METHODS

Correlations between cognitive load and degree of brain metabolic activity were obtained with respect to the influence of the ampakine CX717 (Cortex Pharmaceuticals), using brain imaging and recordings of neuronal activity in NHPs and measures of intracellular calcium release in rat hippocampal slices.

RESULTS

Activation of DLPFC, MTL, and DStr reflected changes in performance related to cognitive load within the DMS task and were engaged primarily on high load trials. Similar increased activation patterns and improved performance were also observed following administration of CX717. Sleep deprivation in NHPs produced impaired performance and reductions in brain activation which was reversed by CX717. One potential basis for this facilitation of cognition by CX717 was increased firing of task-specific hippocampal cells. Synaptic mechanisms affected by CX717 were examined in rat hippocampal slices which showed that N-methyl-D-aspartic acid-mediated release of intracellular calcium was reduced in slices from sleep-deprived rats and reversed by application of CX717 to the bathing medium.

CONCLUSIONS

The findings provide insight into how cognition is enhanced by CX717 in terms of brain, and underlying neural, processes that are activated on high vs. low cognitive load trials.

Fast inhibition of glutamate-activated currents by caffeine

BACKGROUND

Caffeine stimulates calcium-induced calcium release (CICR) in many cell types. In neurons, caffeine stimulates CICR presynaptically and thus modulates neurotransmitter release.

METHODOLOGY/PRINCIPAL FINDINGS

Using the whole-cell patch-clamp technique we found that caffeine (20 mM) reversibly increased the frequency and decreased the amplitude of miniature excitatory postsynaptic currents (mEPSCs) in neocortical neurons. The increase in mEPSC frequency is consistent with a presynaptic mechanism. Caffeine also reduced exogenously applied glutamate-activated currents, confirming a separate postsynaptic action. This inhibition developed in tens of milliseconds, consistent with block of channel currents. Caffeine (20 mM) did not reduce currents activated by exogenous NMDA, indicating that caffeine block is specific to non-NMDA type glutamate receptors.

CONCLUSIONS/SIGNIFICANCE

Caffeine-induced inhibition of mEPSC amplitude occurs through postsynaptic block of non-NMDA type ionotropic glutamate receptors. Caffeine thus has both pre and postsynaptic sites of action at excitatory synapses.