Nanomolar oxytocin synergizes with weak electrical afferent stimulation to activate the locomotor CpG of the rat spinal cord in vitro.

Synergizing the effect of afferent fibre stimulation with pharmacological interventions is a desirable goal to trigger spinal locomotor activity, especially after injury. Thus, to better understand the mechanisms to optimize this process, we studied the role of the neuropeptide oxytocin (previously shown to stimulate locomotor networks) on network and motoneuron properties using the isolated neonatal rat spinal cord. On motoneurons oxytocin (1 nM-1 μM) generated sporadic bursts with superimposed firing and dose-dependent depolarization.

Modeling truncated hemoglobin vibrational dynamics.

We present a study on the near equilibrium dynamics of two small proteins in the family of truncated hemoglobins, developed under the framework of a Gaussian network approach. Effective beta carbon atoms are taken into account besides Calphas for all residues but glycines in the coarse-graining procedure, without leading to an increase in the degrees of freedom (beta Gaussian Model). Normalized covariance matrix and deformation along slowest modes with collective character are analyzed, pointing out anticorrelations between functionally relevant sites for the proteins under study.

Inferring the diameter of a biopolymer from its stretching response.

We investigate the stretching response of a thick polymer model by means of extensive stochastic simulations. The computational results are synthesized in an analytic expression that characterizes how the force versus elongation curve depends on the polymer structural parameters: its thickness and granularity (spacing of the monomers). The expression is used to analyze experimental data for the stretching of various different types of biopolymers: polypeptides, polysaccharides, and nucleic acids.

Apoptotic effect of caspase-3 cleaved tau in hippocampal neurons and its potentiation by tau FTDP-mutation N279K.

Pathological changes in the microtubule associated protein tau are a major hallmark of many human dementias collectively defined as tauopathies. In familiar frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), several mutations in the tau gene have been identified showing that primary malfunction of tau can lead to neurodegeneration. In addition to mutation at genetic level, a number of post-translational modifications of tau occur in tauopathies, including abnormal phosphorylation and aberrant proteolysis described in Alzheimer's Disease (AD).

Folding pathways of prion and doppel.

The relevance of various residue positions for the stability and the folding characteristics of the prion protein in its normal cellular form are investigated by using molecular dynamics simulations of models exploiting the topology of the native state. These models allow for reproducing the experimentally validated two-state behavior of the normal prion isoform. Highly significant correlations are found between the most topologically relevant sites in our analysis and the single point mutations known to be associated with the arousal of the genetic forms of prion disease.

TRKB signalling controls the expression of N-methyl-d-aspartate receptors in the visual cortex.

NMDA receptors (NMDARs) are multimeric proteins, the biological and functional characteristics of which depend on differential subunit assembly during postnatal development. In the present paper, we investigated whether the expression of NMDAR subunits NR1, NR2A, NR2B is influenced by neurotrophins in rat visual cortex. We used a soluble form of the TrkB receptor engineered as an immunoadhesin (TrkB-IgG) in order to block TrkB ligands.

Elastic properties of proteins: insight on the folding process and evolutionary selection of native structures.

We carry out a theoretical study of the vibrational and relaxation properties of naturally occurring proteins with the purpose of characterizing both the folding and equilibrium thermodynamics. By means of a suitable model, we provide a full characterization of the spectrum and eigenmodes of vibration at various temperatures by merely exploiting the knowledge of the protein native structure. It is shown that the rate at which perturbations decay at the folding transition correlates well with experimental folding rates.

Conformations of proteins in equilibrium.

We introduce a simple theoretical approach for an equilibrium study of proteins with known native-state structures. We test our approach with results on well-studied globular proteins, chymotrypsin inhibitor (2ci2), barnase, and the alpha spectrin SH3 domain, and present evidence for a hierarchical onset of order on lowering the temperature with significant organization at the local level even at high temperatures. A further application to the folding process of HIV-1 protease shows that the model can be reliably used to identify key folding sites that are responsible for the development of drug resistance.

Role of secondary motifs in fast folding polymers: a dynamical variational principle.

A fascinating and open question challenging biochemistry, physics, and even geometry is the presence of highly regular motifs such as alpha helices in the folded state of biopolymers and proteins. Stimulating explanations ranging from chemical propensity to simple geometrical reasoning have been invoked to rationalize the existence of such secondary structures. We formulate a dynamical variational principle for selection in conformation space based on the requirement that the backbone of the native state of biologically viable polymers be rapidly accessible from the denatured state.

Effects of the neuropeptide thyrotropin-releasing hormone on GABAergic synaptic transmission of CA1 neurons of the rat hippocampal slice during hypoxia.

Because thyrotropin-releasing hormone (TRH) has been suggested to improve recovery of brain neurons from hypoxia, which strongly impairs GABAergic synaptic transmission, the present electrophysiological study used intracellular recording from CA1 neurons of the rat hippocampal slice to examine the cellular mechanisms underlying this phenomenon. Hypoxia induced by superfusion with a medium devoid of oxygen evoked typical membrane hyperpolarization, fall in input resistance, and strong depression of monosynaptic, GABAA receptor-mediated fast inhibitory postsynaptic potentials (IPSPs). The depression of fast IPSPs during hypoxia was found to be due to a combination of factors such as shift in the IPSP reversal potential and membrane hyperpolarization.

Pharmacological block of the electrogenic sodium pump disrupts rhythmic bursting induced by strychnine and bicuculline in the neonatal rat spinal cord.

The cellular mechanisms underlying rhythmic bursts induced in the isolated neonatal rat spinal cord by bath application of strychnine and bicuculline (which block glycine- and gamma-aminobutyric acid-A-receptor-mediated inhibition, respectively) were probed with pharmacological tools. Such spontaneous bursts were recorded either intracellularly from lumbar motoneurons or extracellularly from ventral roots. As previously described, these network-driven events consisted of large-amplitude depolarizations arising abruptly from baseline with a highly regular period (on average 28 s).

Voltage-activated fast currents of frog optic tectum neurones are blocked by ouabain or K(+)-free solution.

Frog optic tectum neurones in vitro (under whole cell patch clamp with a Cs(+)-filled electrode) generated, in response to voltage steps negative to -80 mV from -60 mV holding potential, transient inward currents dependent on extracellular Na+ and blocked by tetrodotoxin (TTX). Depolarizing steps from the same holding potential induced conventional, fast Na+ currents followed by a transient outward cationic current (Icat). Voltage-activated Na+ currents (induced by negative or positive steps) and Icat were blocked by ouabain or K(+)-free solution with comparable timecourse.

A transient outward cationic current activated by Na+ influx into frog visual neurones in vitro.

Whole cell patch clamp recording from neurones of a slice preparation of the frog optic tectum showed that depolarizing step commands from -70 mV holding potential generated a fast inward current always followed by a fast outward current. The fast outward current was blocked by tetrodotoxin (TTX) or 4-aminopyridine (4-AP), or by replacing external Na+ with Li+. When the patch pipette contained Cs+ instead of K+ the outward current was fully preserved, suggesting that the membrane channels responsible for this response were relatively non-selective in their permeability properties.

The neuropeptide thyrotropin-releasing hormone modulates GABAergic synaptic transmission on pyramidal neurones of the rat hippocampal slice.

The modulatory action of thyrotropin-releasing hormone (TRH), an endogenously occurring neuropeptide, on synaptic potentials mediated by activation of GABAA or GABAB receptors was studied using intracellular recordings from CA1 pyramidal neurones of the rat hippocampal brain slice preparation. Bath-applied TRH (10 microM) produced a reversible depression of fast IPSPs (mediated by GABAA receptors) induced by electrical stimulation of the stratum lacunosum moleculare (LM) or stratum pyramidale (SP). This phenomenon was not associated with changes in the IPSP reversal potential, resting potential, or input resistance.

An NK1 receptor-dependent component of the slow excitation recorded intracellularly from rat motoneurons following dorsal root stimulation.

Intracellular recording from lumbar motoneurons of the neonatal rat spinal cord in vitro was used to study how recently developed non-peptide antagonists such as SR-140333 and SR-48698, known to block distinct subtypes of tachykinin receptors peripherally, might affect synaptic transmission elicited by electrical stimulation of dorsal root fibres. SR-140333 (1 microM) preferentially antagonized responses mediated by an exogenously applied agonist acting on the NK1 receptor subclass, while SR-48968 (0.5 microM) preferentially reduced responses mediated by an exogenously applied agonist acting on the NK2 receptor subclass.

Membrane potential oscillations of neonatal rat spinal motoneurons evoked by electrical stimulation of dorsal root fibres.

Intracellular recording from lumbar motoneurons of the neonatal rat isolated spinal cord bathed in standard saline solution was used to study membrane potential oscillations which accompanied the decay phase of excitatory postsynaptic potentials (EPSP) induced by single electrical pulses to an adjacent dorsal root. About 60% of motoneurons displayed rhythmic oscillations of 10 +/- 2 mV maximal amplitude and 7 +/- 0.5 Hz frequency.

Desensitization of AMPA receptors limits the amplitude of EPSPs and the excitability of motoneurons of the rat isolated spinal cord.

Intracellular recording was used to study the effect of cyclothiazide, a selective blocker of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor desensitization, on lumbar motoneurons of the rat isolated spinal cord. Cyclothiazide (25 microM) enhanced the responses to AMPA in a tetrodotoxin-insensitive fashion, without affecting those produced by N-methyl-D-aspartate or gamma-aminobutyric acid. Excitatory postsynaptic potentials (EPSPs) evoked by dorsal root stimulation were strongly potentiated in amplitude while paired-pulse depression (produced by applying pairs of pulses at 2 s interval) of the EPSP was decreased.

Enhancement of NMDA receptor mediated synaptic potentials of rat hippocampal neurones in vitro by thyrotropin releasing hormone.

The effects of thyrotropin releasing hormone (TRH) on excitatory postsynaptic potentials (EPSPs) evoked by electrical stimulation of Schaffer collaterals on CA1 neurones of the adult rat hippocampal slice preparation were investigated using intracellular recording under current clamp conditions. At resting membrane potential and in the presence of extracellular Mg2+, TRH (10-20 microM) largely potentiated NMDA receptor-mediated EPSPs while leaving those mediated by non-NMDA receptors unaffected. This phenomenon had a brief duration (approximately 2 min) and was not accompanied by changes in resting membrane potential or input conductance.

Effects of RP 67580 on substance P-elicited responses and postsynaptic potentials of motoneurones of the rat isolated spinal cord.

The effect of RP 67580, a recently developed antagonist selective for the NK1 tachykinin receptors of peripheral tissues, was studied with intracellular recording from motoneurones of the rat isolated spinal cord. In the presence of RP 67580 (1-2 microM), membrane depolarization induced by the putative transmitter substance P (SP) was either unchanged or enhanced (an effect prevented by tetrodotoxin; TTX). Neither short nor long excitatory synaptic potentials (EPSPs) were antagonized by RP 67580.

Serum fractions from amyotrophic lateral sclerosis patients depress voltage-activated Ca2+ currents of rat cerebellar granule cells in culture.

Whole-cell patch clamp recording from rat cerebellar granule cells in culture was used to study the effect of immune protein fractions extracted from the serum of amyotrophic lateral sclerosis (ALS) patients on voltage-activated Ca2+ currents. The inward currents, carried by Ba2+, were induced by depolarizing step commands positive to -50 mV and showed typical voltage-dependent inactivation. Application of immunoprotein fractions obtained from the serum of ALS patients produced a strong depression of the inward current amplitude without changing its threshold potential at which the maximum was attained, or its time course.

Non-monotonic decay of excitatory synaptic transmission in the frog optic tectum following repetitive stimulation of the optic nerve in vitro.

The monosynaptic field excitatory postsynaptic potentials (EPSPs) evoked in the optic tectum of the frog (Rana remporaria) in vitro by different patterns of stimulation of the contralateral optic nerve were studied using extracellular recording. Pulse trains at frequencies of less than or equal to 0.033 Hz elicited field potentials of stable amplitude, whereas in the range 0.

A study of the barium-sensitive and -insensitive components of the action of thyrotropin-releasing hormone on lumbar motoneurons of the rat isolated spinal cord.

The electrophysiological action of thyrotropin-releasing hormone (TRH) on rat spinal motoneurons was studied in vitro using single-electrode voltage- and current-clamp techniques. In current-clamp conditions TRH elicited a slowly developing depolarization, associated with a large input resistance increase and sustained neuronal firing; the primary metabolites of TRH were ineffective. Under voltage-clamp conditions in the presence of tetrodotoxin, TRH evoked a large inward current (ITRH; peaking at approximately -40 mV) associated with a large input conductance fall.