Anticipated Synchronization in a Biologically Plausible Model of Neuronal Motifs

Two identical autonomous dynamical systems coupled in a master-slave configuration can exhibit anticipated synchronization (AS) if the slave also receives a delayed negative self-feedback. Recently, AS was shown to occur in systems of simplified neuron models, requiring the coupling of the neuronal membrane potential with its delayed value. However, this coupling has no obvious biological correlate. Here we propose a canonical neuronal microcircuit with standard chemical synapses, where the delayed inhibition is provided by an interneuron. In this biologically plausible scenario, a smooth transition from delayed synchronization (DS) to AS typically occurs when the inhibitory synaptic conductance is increased. The phenomenon is shown to be robust when model parameters are varied within physiological range. Since the DS-AS transition amounts to an inversion in the timing of the pre- and post-synaptic spikes, our results could have a bearing on spike-timing-dependent-plasticity models

Absence of Magnetic Fluctuations in the Ferromagnetic/Topological Heterostructure EuS/Bi2_{2}Se3_{3}

Heterostructures of topological insulators and ferromagnets offer new opportunities in spintronics and a route to novel anomalous Hall states. In one such structure, EuS/Bi$_{2}$Se$_{3}$ a dramatic enhancement of the Curie temperature was recently observed. We performed Raman spectroscopy on a similar set of thin films to investigate the magnetic and lattice excitations. Interfacial strain was monitored through its effects on the Bi$_{2}$Se$_{3}$ phonon modes while the magnetic system was probed through the EuS Raman mode. Despite its appearance in bare EuS, the heterostructures lack the corresponding EuS Raman signal. Through numerical calculations we rule out the possibility of Fabry-Perot interference suppressing the mode. We attribute the absence of a magnetic signal in EuS to a large charge transfer with the Bi$_{2}$Se$_{3}$. This could provide an additional pathway for manipulating the magnetic, optical, or electronic response of topological heterostructures.Comment: 6 pages, 3 figure

A tunable rf SQUID manipulated as flux and phase qubit

We report on two different manipulation procedures of a tunable rf SQUID. First, we operate this system as a flux qubit, where the coherent evolution between the two flux states is induced by a rapid change of the energy potential, turning it from a double well into a single well. The measured coherent Larmor-like oscillation of the retrapping probability in one of the wells has a frequency ranging from 6 to 20 GHz, with a theoretically expected upper limit of 40 GHz. Furthermore, here we also report a manipulation of the same device as a phase qubit. In the phase regime, the manipulation of the energy states is realized by applying a resonant microwave drive. In spite of the conceptual difference between these two manipulation procedures, the measured decay times of Larmor oscillation and microwave-driven Rabi oscillation are rather similar. Due to the higher frequency of the Larmor oscillations, the microwave-free qubit manipulation allows for much faster coherent operations.Comment: Proceedings of Nobel Symposium "Qubits for future quantum computers", Goeteborg, Sweden, May 25-28, 2009; to appear in Physica Script

DEVELOPING A REGENERATIVE MEDICINE APPROACH FOR THE TREATMENT OF PARKINSON'S DISEASE

Parkinson\u2019s disease (PD) is the second most common neurodegenerative disease, after Alzheimer\u2019s disease, and the most common movement disorder. Drug treatment and deep brain stimulation can ameliorate symptoms, but the progressive degeneration of dopaminergic neurons in the substantia nigra eventually leads to severe motor dysfunction. While some effective treatments for patients with PD exist, these treatment strategies are mainly symptomatic and aimed at increasing dopamine levels in the degenerating nigrostriatal system. Existing drugs are limited in their relief and decrease in effectiveness as PD progresses.The transplantation of stem cells has emerged as a promising approach to replace lost neurons in order to restore dopamine levels in the striatum and reactivate functional circuits. Post mortem neural precursor cells (PM-NPCs) are a subclass of sub ventricular zone (SVZ)-derived neural progenitors, capable of surviving many hours (16 hours) after donor death. The in vitro differentiation yields more neurons (about 30-40%) compared to regular NPCs (Marfia et al., 2011). Recently from the SVZ of a transgenic mouse strain expressing green fluorescent protein (GFP) under the promoter C of the ubiquitin gene [(C57BL/6-Tg(UBC-GFP)30Scha/J)] we isolated GFP PM-NPCs, from mice at 6 hours after the donor death. These cells were characterized and their potential of in terms of replacement therapy was investigated in a mouse model of Parkinson disease. The degeneration of dopaminergic neurons was obtained through the administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) at the dosage of 36 mg/kg intraperiteoneally (i.p.). After 1 week the lesion was stabilized by a second administration (i.p.) of the neurotoxin at the dosage of 20 mg/kg. 1x 105 of PM-PCs-GFP were injected unilaterally into the striatum of C57/BL mice by using specific stereotaxic coordinates 3 days after the second MPTP administration. The effects of transplanted cells were determined by means of performance tests aimed at detecting behavioral improvements. Moreover, the neurochemical changes were also studied by high performance liquid chromatography (HPLC). In order to study the in vivo fate of grafted GFP PM-NPCs animals were perfused 2 weeks after transplantation and immunohistochemistry studies were performed. Our results show that animals grafted with GFP PM-NPCs determined a remarkable improvement of behavioral parameters measured by means of both horizontal and vertical grid tests (forepaw fault and time required to grab on the grids while turning and climbing down) since the third day after transplantation. These improvements were very significant and the average values were close to control animals. This was maintained during all the two weeks of experimental observation. By means of immunofluorescence staining we observed that the majority of transplanted GFP-PM-NPCs were vital and able to migrate ventrally and caudally from the injection site lengths as far as 1000 microns into the striatum, and could reach the ipsilateral and contralateral substantia nigra pars compacta. Moreover, morphological analyses revealed that transplanted cells in the striatum are able to differentiate into tyrosine hydroxylase (40%), cholinergic (40%), and gabaergic neurons (25%). This study provides new evidences that PM-NPCs will be useful for developing cellular PD therapies. Future studies should further explore the clinical potential role of the investigated post mortem neural precursors cells in order to provide new perspectives for PD treatment

Deep-well ultrafast manipulation of a SQUID flux qubit

Superconducting devices based on the Josephson effect are effectively used for the implementation of qubits and quantum gates. The manipulation of superconducting qubits is generally performed by using microwave pulses with frequencies from 5 to 15 GHz, obtaining a typical operating clock from 100MHz to 1GHz. A manipulation based on simple pulses in the absence of microwaves is also possible. In our system a magnetic flux pulse modifies the potential of a double SQUID qubit from a symmetric double well to a single deep well condition. By using this scheme with a Nb/AlOx/Nb system we obtained coherent oscillations with sub-nanosecond period (tunable from 50ps to 200ps), very fast with respect to other manipulating procedures, and with a coherence time up to 10ns, of the order of what obtained with similar devices and technologies but using microwave manipulation. We introduce the ultrafast manipulation presenting experimental results, new issues related to this approach (such as the use of a feedback procedure for cancelling the effect of "slow" fluctuations), and open perspectives, such as the possible use of RSFQ logic for the qubit control.Comment: 9 pages, 7 figure

Biomaterials in Neurodegenerative Disorders : A Promising Therapeutic Approach

Neurodegenerative disorders (i.e., Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and spinal cord injury) represent a great problem worldwide and are becoming prevalent because of the increasing average age of the population. Despite many studies having focused on their etiopathology, the exact cause of these diseases is still unknown and until now, there are only symptomatic treatments. Biomaterials have become important not only for the study of disease pathogenesis, but also for their application in regenerative medicine. The great advantages provided by biomaterials are their ability to mimic the environment of the extracellular matrix and to allow the growth of different types of cells. Biomaterials can be used as supporting material for cell proliferation to be transplanted and as vectors to deliver many active molecules for the treatments of neurodegenerative disorders. In this review, we aim to report the potentiality of biomaterials (i.e., hydrogels, nanoparticles, self-assembling peptides, nanofibers and carbon-based nanomaterials) by analyzing their use in the regeneration of neural and glial cells their role in axon outgrowth. Although further studies are needed for their use in humans, the promising results obtained by several groups leads us to suppose that biomaterials represent a potential therapeutic approach for the treatments of neurodegenerative disorders