As Verified with the Aid of Biotinylated Spermine, the Brain Cannot Take up Polyamines from the Bloodstream Leaving It Solely Dependent on Local Biosynthesis.

The importance of polyamines (PAs) for the central nervous system (CNS) is well known. Less clear, however, is where PAs in the brain are derived from. Principally, there are three possibilities: (i) intake by nutrition, release into the bloodstream, and subsequent uptake from CNS capillaries, (ii) production by parenchymatous organs, such as the liver, and again uptake from CNS capillaries, and (iii) uptake of precursors, such as arginine, from the blood and subsequent local biosynthesis of PAs within the CNS. The present investigation aimed to unequivocally answer the question of whether PAs, especially the higher ones like spermidine (SPD) and spermine (SPM), can or cannot be taken up into the brain from the bloodstream. For this purpose, a biotin-labelled analogue of spermine (B-X-SPM) was synthesized, characterized, and used to visualize its uptake into brain cells following application to acute brain slices, to the intraventricular space, or to the bloodstream. In acute brain slices there is strong uptake of B-X-SPM into protoplasmic and none in fibrous-type astrocytes. It is also taken up by neurons but to a lesser degree. Under in vivo conditions, astrocyte uptake of B-X-SPM from the brain interstitial fluid is also intense after intraventricular application. In contrast, following intracardial injection, there is no uptake from the bloodstream, indicating that the brain is completely dependent on the local synthesis of polyamines.

The nuclear lamina is a hub for the nuclear function of Jacob.

Jacob is a synapto-nuclear messenger protein that couples NMDAR activity to CREB-dependent gene expression. In this study, we investigated the nuclear distribution of Jacob and report a prominent targeting to the nuclear envelope that requires NMDAR activity and nuclear import. Immunogold electron microscopy and proximity ligation assay combined with STED imaging revealed preferential association of Jacob with the inner nuclear membrane where it directly binds to LaminB1, an intermediate filament and core component of the inner nuclear membrane (INM). The association with the INM is transient; it involves a functional nuclear export signal in Jacob and a canonical CRM1-RanGTP-dependent export mechanism that defines the residing time of the protein at the INM. Taken together, the data suggest a stepwise redistribution of Jacob within the nucleus following nuclear import and prior to nuclear export.

Polyamines and polyamine-metabolizing enzymes in schizophrenia: Current knowledge and concepts of therapy.

Polyamines play preeminent roles in a variety of cellular functions in the central nervous system and other organs. A large body of evidence suggests that the polyamine pathway is prominently involved in the etiology and pathology of schizophrenia. Alterations in the expression and activity of polyamine metabolizing enzymes, as well as changes in the levels of the individual polyamines, their precursors and derivatives, have been measured in schizophrenia and animal models of the disease. Additionally, neuroleptic treatment has been shown to influence polyamine concentrations in brain and blood of individuals with schizophrenia. Thus, the polyamine system may appear to be a promising target for neuropharmacological treatment of schizophrenia. However, for a number of practical reasons there is currently only limited hope for a polyamine-based schizophrenia therapy.

Detailed morphological analysis of rat hippocampi treated with CSF autoantibodies from patients with anti-NMDAR encephalitis discloses two distinct types of immunostaining patterns.

Anti-NMDA receptor encephalitis was first described about thirteen years ago and has become one of the most important differential diagnoses for new-onset psychosis. The disease is mediated by autoantibodies against the subunit 1 of the N-methyl-D-aspartate receptor (NMDA-R1) in patients presenting with variable clinical symptoms. Patients often profit from immunmodulatory therapy, independent of their individual symptoms. In this study CSF samples as well as monoclonal antibodies derived from patients diagnosed with NMDA-R1 encephalitis were applied to rat hippocampus and visualized by immunocytochemistry. This reveals at least two distinct patterns of immunoreactivity. Antibodies from "pattern group 1" display the familiar pattern of NMDA-R1 distribution in the hippocampus reported in experiments with rabbit anti-NMDA-R1 antibodies. Neurons and primary dendrites in the CA1 and CA3 region show strongly stained cell bodies, in line with the predominant postsynaptic localization of the NMDA receptor in the brain. However, autoantibodies from "pattern group 2" show an inverse pattern, with no staining of the cell bodies and primary dendrites in CA1 and CA3 regions. Electron microscopic experiments disclose that autoantibodies of "pattern group 1 patients" bind to postsynaptic NMDA receptors, while those of "pattern group 2 patients" target presynaptic NMDA receptors. We describe one NMDA-receptor antibody giving staining comparable to rabbit anti-NMDA-R1 antibodies, raised against the C-terminus. In the highly heterogenous disease anti-NMDA-receptor 1 encephalitis we found evidence for at least two different subtypes. It will be very interesting to determine whether there also are two distinct clinical phenotypes.

Correction: Synaptic phospholipids as a new target for cortical hyperexcitability and E/I balance in psychiatric disorders.

Following the publication of this article the authors noted that Torfi Sigurdsson's name was misspelled. Instead of Sigrudsson it should be Sigurdsson. The PDF and HTML versions of the paper have been modified accordingly. The authors would like to apologise for this error and the inconvenience this may have caused.

Agmatine modulates spontaneous activity in neurons of the rat medial habenular complex-a relevant mechanism in the pathophysiology and treatment of depression?

The dorsal diencephalic conduction system connects limbic forebrain structures to monaminergic mesencephalic nuclei via a distinct relay station, the habenular complexes. Both habenular nuclei, the lateral as well as the medial nucleus, are considered to play a prominent role in mental disorders like major depression. Herein, we investigate the effect of the polyamine agmatine on the electrical activity of neurons within the medial habenula in rat. We present evidence that agmatine strongly decreases spontaneous action potential firing of medial habenular neurons by activating I1-type imidazoline receptors. Additionally, we compare the expression patterns of agmatinase, an enzyme capable of inactivating agmatine, in rat and human habenula. In the medial habenula of both species, agmatinase is similarly distributed and observed in neurons and, in particular, in distinct neuropil areas. The putative relevance of these findings in the context of depression is discussed. It is concluded that increased activity of the agmatinergic system in the medial habenula may strengthen midbrain dopaminergic activity. Consequently, the habenular-interpeduncular axis may be dysregulated in patients with major depression.

Synaptic phospholipids as a new target for cortical hyperexcitability and E/I balance in psychiatric disorders.

Lysophosphatidic acid (LPA) is a synaptic phospholipid, which regulates cortical excitation/inhibition (E/I) balance and controls sensory information processing in mice and man. Altered synaptic LPA signaling was shown to be associated with psychiatric disorders. Here, we show that the LPA-synthesizing enzyme autotaxin (ATX) is expressed in the astrocytic compartment of excitatory synapses and modulates glutamatergic transmission. In astrocytes, ATX is sorted toward fine astrocytic processes and transported to excitatory but not inhibitory synapses. This ATX sorting, as well as the enzymatic activity of astrocyte-derived ATX are dynamically regulated by neuronal activity via astrocytic glutamate receptors. Pharmacological and genetic ATX inhibition both rescued schizophrenia-related hyperexcitability syndromes caused by altered bioactive lipid signaling in two genetic mouse models for psychiatric disorders. Interestingly, ATX inhibition did not affect naive animals. However, as our data suggested that pharmacological ATX inhibition is a general method to reverse cortical excitability, we applied ATX inhibition in a ketamine model of schizophrenia and rescued thereby the electrophysiological and behavioral schizophrenia-like phenotype. Our data show that astrocytic ATX is a novel modulator of glutamatergic transmission and that targeting ATX might be a versatile strategy for a novel drug therapy to treat cortical hyperexcitability in psychiatric disorders.

Agmatine: multifunctional arginine metabolite and magic bullet in clinical neuroscience?

Agmatine, the decarboxylation product of arginine, was largely neglected as an important player in mammalian metabolism until the mid-1990s, when it was re-discovered as an endogenous ligand of imidazoline and α2-adrenergic receptors. Since then, a wide variety of agmatine-mediated effects have been observed, and consequently agmatine has moved from a wallflower existence into the limelight of clinical neuroscience research. Despite this quantum jump in scientific interest, the understanding of the anabolism and catabolism of this amine is still vague. The purification and biochemical characterization of natural mammalian arginine decarboxylase and agmatinase still are open issues. Nevertheless, the agmatinergic system is currently one of the most promising candidates in order to pharmacologically interfere with some major diseases of the central nervous system, which are summarized in the present review. Particularly with respect to major depression, agmatine, its derivatives, and metabolizing enzymes show great promise for the development of an improved treatment of this common disease.

PRG-1 Regulates Synaptic Plasticity via Intracellular PP2A/ß1-Integrin Signaling.

Alterations in dendritic spine numbers are linked to deficits in learning and memory. While we previously revealed that postsynaptic plasticity-related gene 1 (PRG-1) controls lysophosphatidic acid (LPA) signaling at glutamatergic synapses via presynaptic LPA receptors, we now show that PRG-1 also affects spine density and synaptic plasticity in a cell-autonomous fashion via protein phosphatase 2A (PP2A)/ß1-integrin activation. PRG-1 deficiency reduces spine numbers and ß1-integrin activation, alters long-term potentiation (LTP), and impairs spatial memory. The intracellular PRG-1 C terminus interacts in an LPA-dependent fashion with PP2A, thus modulating its phosphatase activity at the postsynaptic density. This results in recruitment of adhesome components src, paxillin, and talin to lipid rafts and ultimately in activation of ß1-integrins. Consistent with these findings, activation of PP2A with FTY720 rescues defects in spine density and LTP of PRG-1-deficient animals. These results disclose a mechanism by which bioactive lipid signaling via PRG-1 could affect synaptic plasticity and memory formation.

Possible sources and functions of L-homoarginine in the brain: review of the literature and own findings.

L-Homoarginine is a cationic amino acid derivative, which is structurally related to L-arginine and lysine. Several lines of evidence point to nervous tissue as an important target of homoarginine action. In the mammalian brain homoarginine can be detected in noticeable quantities, but its origin is currently poorly explored. In part I of this review we try to show that both uptake and transport into brain (carried out by cationic amino acid transporters) and local synthesis in the brain (carried out by the homoarginine-synthesizing enzymes L-arginine:glycine amidinotransferase and ornithine transcarbamylse) might contribute to homoarginine brain content. We then give a brief overview about the multiple effects of homoarginine on the healthy brain and show that both homoarginine excess and deficiency are potentially harmful to the central nervous system. In part II, we shortly report about own experiments with regard to the cellular localization of cationic amino acid transporters, as well the enzymes L-arginine:glycine amidinotransferase and ornithine transcarbamylse, in human and rat brains.

Downregulation of neuregulin 1-ErbB4 signaling and antidepressant properties of ketamine: ErbB4 expressing pyramidal neurons may play a role.

We comment on a recent paper of Wang et al. (J Mol Neurosci, 2014), who have shown that ketamine reduces neuregulin1-ErbB4 signaling in interneurons.

Specific biomolecule corona is associated with ring-shaped organization of silver nanoparticles in cells.

We correlate the localization of silver nanoparticles inside cells with respect to the cellular architecture with the molecular information in the vicinity of the particle surface by combining nanoscale 3D cryo-soft X-ray tomography (cryo-SXT) with surface-enhanced Raman scattering (SERS). The interaction of the silver nanoparticle surface with small molecules and biopolymers was monitored by SERS in vitro over time in living cells. The spectra indicate a stable, time-independent surface composition of silver nanoparticles, despite the changing environment in the endosomal structure. Cryo-SXT reveals a characteristic ring-shaped organization of the silver nanoparticles in endosomes of different cell types. The ring-like structures inside the endosomes suggest a strong association among silver particles and with membrane structures. The comparison of the data with those obtained with gold nanoparticles suggests that the interactions between the nanoparticles and with the endosomal component are influenced by the molecular composition of the corona.

Arginase and Arginine Decarboxylase - Where Do the Putative Gate Keepers of Polyamine Synthesis Reside in Rat Brain?

Polyamines are important regulators of basal cellular functions but also subserve highly specific tasks in the mammalian brain. With this respect, polyamines and the synthesizing and degrading enzymes are clearly differentially distributed in neurons versus glial cells and also in different brain areas. The synthesis of the diamine putrescine may be driven via two different pathways. In the "classical" pathway urea and carbon dioxide are removed from arginine by arginase and ornithine decarboxylase. The alternative pathway, first removing carbon dioxide by arginine decarboxlyase and then urea by agmatinase, may serve the same purpose. Furthermore, the intermediate product of the alternative pathway, agmatine, is an endogenous ligand for imidazoline receptors and may serve as a neurotransmitter. In order to evaluate and compare the expression patterns of the two gate keeper enzymes arginase and arginine decarboxylase, we generated polyclonal, monospecific antibodies against arginase-1 and arginine decarboxylase. Using these tools, we immunocytochemically screened the rat brain and compared the expression patterns of both enzymes in several brain areas on the regional, cellular and subcellular level. In contrast to other enzymes of the polyamine pathway, arginine decarboxylase and arginase are both constitutively and widely expressed in rat brain neurons. In cerebral cortex and hippocampus, principal neurons and putative interneurons were clearly labeled for both enzymes. Labeling, however, was strikingly different in these neurons with respect to the subcellular localization of the enzymes. While with antibodies against arginine decarboxylase the immunosignal was distributed throughout the cytoplasm, arginase-like immunoreactivity was preferentially localized to Golgi stacks. Given the apparent congruence of arginase and arginine decarboxylase distribution with respect to certain cell populations, it seems likely that the synthesis of agmatine rather than putrescine may be the main purpose of the alternative pathway of polyamine synthesis, while the classical pathway supplies putrescine and spermidine/spermine in these neurons.

A glutamatergic projection from the lateral hypothalamus targets VTA-projecting neurons in the lateral habenula of the rat.

Homeostasis describes the fundamental biological ability of individuals to maintain stable internal conditions in a changing environment. Homeostatic reactions include internal adjustments as well as behavioral responses. In vertebrates, behavioral responses are induced by the reward system. This system originates in the ventral tegmental area (VTA) and leads to increased dopamine levels in the forebrain whenever activated. A major inhibitor of VTA activity is the lateral habenula (LHb). This epithalamic structure is able to almost completely suppress dopamine release, either directly or via the rostromedial tegmental nucleus (RMTg), when rewarding expectations are not met. A major input to the LHb arises from the lateral hypothalamic area (LHA), an important regulator of the homeostatic system. Currently, little is known about the effects of the strong hypothalamic projection on the activity of LHb neurons. In the present study, we analyze neurotransmitters and cellular targets of the LHA-LHb projection in the rat. Therefore, anterograde tracing from the LHA was combined with the visualization of neurotransmitters in the LHb. These experiments revealed a mainly glutamatergic projection, probably exerting excitatory effects on the targeted LHb cells. These cellular targets were analyzed in a second step. Anterograde tracing from the LHA in combination with retrograde tracing from the VTA/RMTg region revealed that LHb neurons projecting to the VTA/RMTg region are densely targeted by the LHA projection. Visualization of synaptophysin at these contact sites indicates that the contact sites indeed are synapses. Taken together, the present study describes a strong mainly glutamatergic projection from the LHA that targets VTA/RMTg-projecting neurons in the LHb. These findings emphasize the potential role of the LHb as direct link between homeostatic areas and reward circuitries, which may be important for the control of homeostatic behaviors.

Agmatinase, an inactivator of the putative endogenous antidepressant agmatine, is strongly upregulated in hippocampal interneurons of subjects with mood disorders.

The diamine agmatine may serve as a precursor in polyamine synthesis. In addition, agmatine may also act as a neurotransmitter, binding to imidazoline receptors. Behaviorally, agmatine exerts antidepressant-like effects. The enzyme agmatinase degrades agmatine. The gene coding for human agmatinase is located on chromosome 1p36, a gene locus which has been linked to bipolar disorder and major depression, but the enzyme has not yet been studied in the context of neuropsychiatric diseases. We analyzed agmatinase protein expression in postmortem hippocampi of individuals with affective disorders. Data from eleven patients with mood disorders (unipolar and bipolar depression) and twelve matched control cases were compared by immunocytochemical and morphometrical analysis. Agmatinase protein was detected in a subset of hippocampal interneurons. The protein was localized to perikarya, neurites and putative nerve endings contacting hippocampal pyramidal neurons and dentate gyrus granule cells. The number and the numerical density of agmatinase-immunopositive cell bodies were strongly elevated in depressive patients. In addition, a significantly increased density of agmatinase-immunoreactive punctate profiles was observed in the CA(4) region in unipolar and bipolar depression. The reported increased expression of agmatinase suggests a functional relevance of the enzyme in the pathophysiology of human affective disorders. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Toxicity of amorphous silica nanoparticles on eukaryotic cell model is determined by particle agglomeration and serum protein adsorption effects.

Cell cultures form the basis of most biological assays conducted to assess the cytotoxicity of nanomaterials. Since the molecular environment of nanoparticles exerts influence on their physicochemical properties, it can have an impact on nanotoxicity. Here, toxicity of silica nanoparticles upon delivery by fluid-phase uptake is studied in a 3T3 fibroblast cell line. Based on XTT viability assay, cytotoxicity is shown to be a function of (1) particle concentration and (2) of fetal calf serum (FCS) content in the cell culture medium. Application of dynamic light scattering shows that both parameters affect particle agglomeration. The DLS experiments verify the stability of the nanoparticles in culture medium without FCS over a wide range of particle concentrations. The related toxicity can be mainly accounted for by single silica nanoparticles and small agglomerates. In contrast, agglomeration of silica nanoparticles in all FCS-containing media is observed, resulting in a decrease of the associated toxicity. This result has implications for the evaluation of the cytotoxic potential of silica nanoparticles and possibly also other nanomaterials in standard cell culture.

Bacterial pore-forming cytolysins induce neuronal damage in a rat model of neonatal meningitis.

BACKGROUND: Group B Streptococcus (GBS) and Streptococcus pneumoniae (SP) are leading causes of bacterial meningitis in neonates and children. Each pathogen produces a pore-forming cytolytic toxin, ß-hemolysin/cytolysin (ß-h/c) by GBS and pneumolysin by SP. The aim of this study was to understand the role of these pore-forming cytotoxins, in particular of the GBS ß-h/c, as potential neurotoxins in experimental neonatal meningitis. METHODS: Meningitis was induced in 7- and 11-day-old rats by intracisternal injection of wild type (WT) GBS or SP and compared with isogenic ß-h/c- or pneumolysin-deficient mutants, or a double mutant of SP deficient in pneumolysin and hydrogen peroxide production. RESULTS: GBS ß-h/c and SP pneumolysin contributed to neuronal damage, worsened clinical outcome and weight loss, but had no influence on the early kinetics of leukocyte influx and bacterial growth in the cerebrospinal fluid. In vitro, ß-h/c-induced neuronal apoptosis occurred independently of caspase-activation and was not preventable by the broad spectrum caspase-inhibitor z-VAD-fmk. CONCLUSIONS: These data suggest that both cytolytic toxins, the GBS ß-h/c and SP pneumolysin, contribute to neuronal damage in meningitis and extend the concept of a key role for bacterial pore-forming cytolysins in the pathogenesis and sequelae of neonatal meningitis.

Different importance of the volatile and non-volatile fractions of an olfactory signature for individual social recognition in rats versus mice and short-term versus long-term memory.

When tested in the olfactory cued social recognition/discrimination test, rats and mice differ in their retention of a recognition memory for a previously encountered conspecific juvenile: Rats are able to recognize a given juvenile for approximately 45 min only whereas mice show not only short-term, but also long-term recognition memory (≥ 24 h). Here we modified the social recognition/social discrimination procedure to investigate the neurobiological mechanism(s) underlying the species differences. We presented a conspecific juvenile repeatedly to the experimental subjects and monitored the investigation duration as a measure for recognition. Presentation of only the volatile fraction of the juvenile olfactory signature was sufficient for both short- and long-term recognition in mice but not rats. Applying additional volatile, mono-molecular odours to the "to be recognized" juveniles failed to affect short-term memory in both species, but interfered with long-term recognition in mice. Finally immunocytochemical analysis of c-Fos as a marker for cellular activation, revealed that juvenile exposure stimulated areas involved in the processing of olfactory signals in both the main and the accessory olfactory bulb in mice. In rats, we measured an increased c-Fos synthesis almost exclusively in cells of the accessory olfactory bulb. Our data suggest that the species difference in the retention of social recognition memory is based on differences in the processing of the volatile versus non-volatile fraction of the individuals' olfactory signature. The non-volatile fraction is sufficient for retaining a short-term social memory only. Long-term social memory - as observed in mice - requires a processing of both the volatile and non-volatile fractions of the olfactory signature.

In vivo imaging of partially reversible th17 cell-induced neuronal dysfunction in the course of encephalomyelitis.

Neuronal damage in autoimmune neuroinflammation is the correlate for long-term disability in multiple sclerosis (MS) patients. Here, we investigated the role of immune cells in neuronal damage processes in animal models of MS by monitoring experimental autoimmune encephalomyelitis (EAE) by using two-photon microscopy of living anaesthetized mice. In the brainstem, we detected sustained interaction between immune and neuronal cells, particularly during disease peak. Direct interaction of myelin oligodendrocyte glycoprotein (MOG)-specific Th17 and neuronal cells in demyelinating lesions was associated with extensive axonal damage. By combining confocal, electron, and intravital microscopy, we showed that these contacts remarkably resembled immune synapses or kinapses, albeit with the absence of potential T cell receptor engagement. Th17 cells induced severe, localized, and partially reversible fluctuation in neuronal intracellular Ca(2+) concentration as an early sign of neuronal damage. These results highlight the central role of the Th17 cell effector phenotype for neuronal dysfunction in chronic neuroinflammation.