Biomedical subjects

Annie Schweitzer

Publications and source records attributed to Annie Schweitzer.

6 recordsLinked to original sources

PubMed2006

Microtubule stabilizer ameliorates synaptic function and behavior in a mouse model for schizophrenia.

BACKGROUND: Recent data suggest that cytoskeletal defects may play a role in schizophrenia. We previously imitated features of schizophrenia in an animal model by disrupting gene coding for a microtubule-associated protein called STOP. STOP-null mice display synaptic defects in glutamatergic neurons, hyper-dopaminergy, and severe behavioral disorders. Synaptic and behavioral deficits are amended by neuroleptic treatment in STOP-null mice, providing an attractive model to test new antipsychotic agents. We examined the effects of a taxol-related microtubule stabilizer, epothilone D. METHODS: Mice were treated either with vehicle alone or with epothilone D. Treatment effects on synaptic function were assessed using electron-microscopy quantification of synaptic vesicle pools and electrophysiology in the CA1 region of the hippocampus. Dopamine transmission was investigated using electrochemical assays. Behavior was principally assessed using tests of maternal skills. RESULTS: In STOP-null mice, treatment with epothilone D increased synaptic vesicle pools, ameliorated both short- and long-term forms of synaptic plasticity in glutamatergic neurons, and had a dramatic beneficial effect on mouse behavior. CONCLUSIONS: A microtubule stabilizer can have a beneficial effect on synaptic function and behavior, suggesting new possibilities for treatment of schizophrenia.

Animals↗

PubMed2005

A vital role of tubulin-tyrosine-ligase for neuronal organization.

Tubulin is subject to a special cycle of detyrosination/tyrosination in which the C-terminal tyrosine of alpha-tubulin is cyclically removed by a carboxypeptidase and readded by a tubulin-tyrosine-ligase (TTL). This tyrosination cycle is conserved in evolution, yet its physiological importance is unknown. Here, we find that TTL suppression in mice causes perinatal death. A minor pool of tyrosinated (Tyr-)tubulin persists in TTL null tissues, being present mainly in dividing TTL null cells where it originates from tubulin synthesis, but it is lacking in postmitotic TTL null cells such as neurons, which is apparently deleterious because early death in TTL null mice is, at least in part, accounted for by a disorganization of neuronal networks, including a disruption of the cortico-thalamic loop. Correlatively, cultured TTL null neurons display morphogenetic anomalies including an accelerated and erratic time course of neurite outgrowth and a premature axonal differentiation. These anomalies may involve a mislocalization of CLIP170, which we find lacking in neurite extensions and growth cones of TTL null neurons. Our results demonstrate a vital role of TTL for neuronal organization and suggest a requirement of Tyr-tubulin for proper control of neurite extensions.

Animals↗

PubMed2005

Cellular disorders induced by high magnetic fields.

PURPOSE: To evaluate whether static high magnetic fields (HMFs), in the range of 10-17 T, affect the cytoskeleton and cell organization in different types of mammalian cells, including fibroblasts, epithelial cells, and differentiating neurons. MATERIALS AND METHODS: Cells were exposed to HMF for 30 or 60 minutes and subsequently assessed for viability. Cytoskeleton arrays and focal adhesions were visualized using immunofluorescence microscopy. RESULTS: Cell exposure to HMF over 10 T in the case of cycling cells, and over 15 T in the case of neurons, affected cell viability, apparently because of cell detachment from culture dishes. In the remaining adherent cells, the organization of actin assemblies was perturbed, and both cell adhesion and spreading were impaired. Moreover, in the case of neurons, exposure to HMF induced growth cone retraction and delayed cell differentiation. CONCLUSION: Cell exposure to HMF (over 10T and 15 T in the case of cycling cells and neurons, respectively) affects the cell cytoskeleton, with deleterious effects on cell viability, organization, and differentiation. Further studies are needed to determine whether such perturbations, as observed here in cultured cells, have consequences in whole animals.

Animals↗

PubMed2005

Dopaminergic transmission in STOP null mice.

Neuroleptics are thought to exert their anti-psychotic effects by counteracting a hyper-dopaminergic transmission. Here, we have examined the dopaminergic status of STOP (stable tubule only polypeptide) null mice, which lack a microtubule-stabilizing protein and which display neuroleptic-sensitive behavioural disorders. Dopamine transmission was investigated using both behavioural analysis and measurements of dopamine efflux in different conditions. Compared to wild-type mice in basal conditions or following mild stress, STOP null mice showed a hyper-locomotor activity, which was erased by neuroleptic treatment, and an increased locomotor reactivity to amphetamine. Such a behavioural profile is indicative of an increased dopaminergic transmission. In STOP null mice, the basal dopamine concentrations, measured by quantitative microdialysis, were normal in both the nucleus accumbens and the striatum. When measured by electrochemical techniques, the dopamine efflux evoked by electrical stimulations mimicking physiological stimuli was dramatically increased in the nucleus accumbens of STOP null mice, apparently due to an increased dopamine release, whereas dopaminergic uptake and auto-inhibition mechanisms were normal. In contrast, dopamine effluxes were slightly diminished in the striatum. Together with previous results, the present study indicates the association in STOP null mice of hippocampal hypo-glutamatergy and of limbic hyper-dopaminergy. Such neurotransmission defects are thought to be central to mental diseases such as schizophrenia.

Action Potentials↗

PubMed2003

Evidence for an intracellular ADP-ribosyl cyclase/NAD+-glycohydrolase in brain from CD38-deficient mice.

Cyclic ADP-ribose, a metabolite of NAD+, is known to modulate intracellular calcium levels and signaling in various cell types, including neural cells. The enzymes responsible for producing cyclic ADP-ribose in the cytoplasm of mammalian cells remain unknown; however, two mammalian enzymes that are capable of producing cyclic ADP-ribose extracellularly have been identified, CD38 and CD157. The present study investigated whether an ADP-ribosyl cyclase/NAD+-glycohydrolase independent of CD38 is present in brain tissue. To address this question, NAD+ metabolizing activities were accurately examined in developing and adult Cd38-/- mouse brain protein extracts and cells. Low ADP-ribosyl cyclase and NAD+-glycohydrolase activities (in the range of pmol of product formed/mg of protein/min) were detected in Cd38-/- brain at all developmental stages studied. Both activities were found to be associated with cell membranes. The activities were significantly higher in Triton X-100-treated neural cells compared with intact cells, suggesting an intracellular location of the novel cyclase. The cyclase and glycohydrolase activities were optimal at pH 6.0 and were inhibited by zinc, properties which are distinct from those of CD157. Both activities were enhanced by guanosine 5'-O-(3-thiotriphosphate), a result suggesting that the novel enzyme may be regulated by a G protein-dependent mechanism. Altogether our results indicate the presence of an intracellular membrane-bound ADP-ribosyl cyclase/NAD+-glycohydrolase distinct from CD38 and from CD157 in mouse brain. This novel enzyme, which is more active in the developing brain than in the adult tissue, may play an important role in cyclic ADP-ribose-mediated calcium signaling during brain development as well as in adult tissue.

ADP-ribosyl Cyclase↗

PubMed2002

The suppression of brain cold-stable microtubules in mice induces synaptic defects associated with neuroleptic-sensitive behavioral disorders.

Neurons contain abundant subsets of highly stable microtubules that resist depolymerizing conditions such as exposure to the cold. Stable microtubules are thought to be essential for neuronal development, maintenance, and function. Previous work has indicated an important role of the microtubule-associated protein STOP in the induction of microtubule cold stability. Here, we developed STOP null mice. These mice were devoid of cold-stable microtubules. In contrast to our expectations, STOP-/- mice had no detectable defects in brain anatomy but showed synaptic defects, with depleted synaptic vesicle pools and impaired synaptic plasticity, associated with severe behavioral disorders. A survey of the effects of psychotropic drugs on STOP-/- mice behavior showed a remarkable and specific effect of long-term administration of neuroleptics in alleviating these disorders. This study demonstrates that STOP is a major factor responsible for the intriguing stability properties of neuronal microtubules and is important for synaptic plasticity. Additionally, STOP-/- mice may yield a pertinent model for study of neuroleptics in illnesses such as schizophrenia, currently thought to result from synaptic defects.

Animals↗