Papers by Vanni Taglietti
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Analisi dei potenziali lenti e della frequenza di scarica derivabili dai canali semicircolari di rana
Trinker ha ampiamente descritto le vistose variazioni del campo elettrico che si possono misurare... more Trinker ha ampiamente descritto le vistose variazioni del campo elettrico che si possono misurare in prossimità dell'ampolla dei canali semicircolari in relazione agli spostamenti della cupola. Non è chiara tuttavia l'origine di tali segnali ne è nota la loro correlazione con la dinamica cupolare e la scarica afferente derivabile dai nervi ampollari. Le nostre ricerche sono state condotte su preparati di canale semicircolare isolato di Rana, derivando dal nervo ampollare dissezionato, mediante elettrodi fluidi, le risposte elettriche alle deflessioni della cupola, ottenute con un dispositivo meccanico di precisione. Il campo elettrico ampollare determina la frequenza di scarica delle fibre afferenti e, con ogni probabilità, ha origine nelle giunzioni citoneurali. Infatti i potenziali lenti in risposta agli usuali stimoli scompaiono in presenza di curaro, anche in piccole dosi. Per quanto riguarda la scarica afferente, in essa si possono riconoscere unità diverse, classificabili in base all'ampiezza dei rispettivi potenziali d'azione. L’attività spontanea è sostenuta esclusivamente da unità che conducono spikes a basso voltaggio; esse sono caratterizzate da una bassa soglia e la loro frequenza di scarica è strettamente correlata con la posizione della cupola. La frequenza di scarica di queste unità aumenta per deflessioni della cupola in senso eccitatorio e diminuisce per deflessioni in senso inibitorio in modo quasi simmetrico rispetto alla scarica di riposo. Le unità che conducono spikes ad alto voltaggio sono invece silenti quando la cupola è in riposo, e vengono attivate solo per ampie e rapide deflessioni cupolari in senso eccitatorio; la loro risposta, quindi, è praticamente unidirezionale e più strettamente correlata con la velocità della cupola che con la sua posizione
Proprietà funzionali delle diverse unità recettrici nei canali semicircolari isolati di rana
Notevoli differenze nell'adattamento allo stimolo tra le diverse unità recettrici della crest... more Notevoli differenze nell'adattamento allo stimolo tra le diverse unità recettrici della cresta ampollare sono state messe in evidenza derivando con tecnica microelettrodica i potenziali d'azione da singoli neuroni vestibolari del I ordine. Tuttavia non è stato finora possibile uno studio completo delle differenze tra le singole unità. Nella presente ricerca il problema è stato affrontato mediante l'analisi delle ampiezze dei potenziali d'azione derivati da fascetti di fibre del nervo ampollare. Le diverse unità sono infatti innervate da fibre di diverso diametro ed in queste l'ampiezza dei potenziali d'azione è correlata col diametro stesso. Sono stati utilizzati preparati costituiti dal canale verticale posteriore isolato di rana. La scarica è stata analizzata suddividendo i potenziali d'azione in due classi di ampiezza rispettivamente inferiore e superiore ai 150 microV. Gli stimoli erano costituiti da deflessioni cupolari di ampiezza e direzione predeterminate, ottenute con un dispositivo di microiniezione del liquido contenuto nel canale. Si è osservato che le unità caratterizzate da spikes a basso e medio voltaggio presentano attività spontanea e la loro frequenza di scarica può essere modulata in aumento ed in diminuzione dalle deflessioni cupolari rispettivamente in senso eccitatorio o inibitorio. Queste unità non presentano quindi una soglia ed inoltre sono caratterizzate da scarso adattamento. Le unità caratterizzate da spikes ad alto voltaggio invece non presentano attività spontanea e quindi non possono rivelare deflessioni inibitorie della cupola. Esse inoltre vengono attivate solo da rapide deflessioni cupolari e si adattano rapidamente. Il curaro alla concentrazione di 0,1 mM/1 abolisce selettivamente la risposta delle unità ad alto voltaggio, lasciando praticamente inalterata la risposta delle unità a basso e medio voltaggio. Un'analisi istologica del nervo ampollare ha dimostrato che le fibre di minor diametro (0,8-1 microm) si dividono in 3-4 rami prima di entrare nella cresta ampollare; le fibre più grosse (5-10 microm) non presentano una evidente suddivisione. Se ne è dedotto che nelle unità a basso e medio voltaggio si ha una notevole convergenza degli impulsi da più cellule ciliate su ogni singola fibra, mentre per le unità ad alto voltaggio la convergenza è trascurabile. Questi risultati indicano che sebbene non siano state descritte differenze morfologiche fra le cellule sensoriali, nella cresta ampollare della rana sono presenti unità con caratteristiche di trasduzione molto diverse. Le diverse caratteristiche potrebbero essere dovute sia alla diversa innervazione delle cellule ciliate sia alle caratteristiche delle giunzioni cito- neurali. Si può concludere che i parametri del moto cupolare sono trasmessi ai centri tramite trasduttori di tipo diverso. Infatti le unità a basso voltaggio, scarsamente adattative, trasportano informazioni più strettamente correlate alla posizione della cupola, mentre le unità ad alto voltaggio, che si adattano prontamente, forniscono informazioni più strettamente correlate alla velocità della cupola
[Potassium concentration of frog endolymph]
Bollettino della Società italiana di biologia sperimentale, Jan 15, 1973
Pfl�gers Archiv European Journal of Physiology, 1968
The discharge of afferent impulses recorded from the vagus nerve in isolated frog's lung preparat... more The discharge of afferent impulses recorded from the vagus nerve in isolated frog's lung preparations showed a marked increase both during and after deflation of the lung. A quantitative analysis of the afferent discharge in slowed and sudden deflation experiments demonstrated that it cannot be related to deflation velocity of the lung and that it appears to be depending both on the air volume previously inflated and on the duration of previous inflation. The deflation discharge is interpreted as due to receptors responding to mechanical forces arising from the rearrangement taking place in the pulmonary structures during and after deflation and seem therefore to be anchored to "non-elastic" substructures present in the pulmonary network.
Brain Research, 1977
The generator potential in sensory afferents of frog crista ampullaris was extracellularly record... more The generator potential in sensory afferents of frog crista ampullaris was extracellularly recorded from the cut end of the posterior ampullary nerve by means of suction electrodes. A servocontrolled turntable allowed suitable rotatory stimulations. The analysis of the recorded generator potential revealed a different time course from that predicted on the basis of the pendulum model. Adaptation and undershoots in the responses to velocity ramps, steps and sinusoids, were mainly responsible for the deviations, which became very evident only when fairly high acceleration rates were applied. Both adaptation and undershoots were produced presumably by the activation of an electrogenic pump, probably located in nerve terminals contacting the hair cells. In fact, the time course of the generator potential became much more consistent with the predictions from the pendulum model under treatments capable of hindering the ion pump activity.
The Journal of Physiology, 1995
1. Current‐clamp recordings were made in whole‐cell patch‐clamp configuration from ninety‐one gra... more 1. Current‐clamp recordings were made in whole‐cell patch‐clamp configuration from ninety‐one granule cells in parasagittal cerebellar slices obtained from 21‐ to 31‐day‐old rats. Recordings were performed at 30 degrees C. 2. Resting membrane potential was ‐58 +/‐ 6 mV (n = 43). The membrane voltage response to step current injection showed inward rectification consistent with increasing input resistance during membrane depolarization. Over ‐35 +/‐ 7 mV (n = 14) repetitive firing with little or no adaptation was activated. Spike frequency increased nearly linearly with injected current. 3. Unitary EPSPs obtained by stimulating the mossy fibre bundle had an amplitude of 11.4 +/‐ 2.1 mV (n = 22, holding potential = ‐75 mV). Synchronous activation of greater than one to two mossy fibres was needed to elicit action potentials. Antidromic stimulation elicited antidromic spikes and also EPSPs, presumably through a mossy fibre ‘axon reflex’. 4. EPSPs were brought about by NMDA and non‐NMDA...
Current Sodium Granule Cells Implicates the Action of a Persistent Ionic Mechanism of Electroresponsiveness in Cerebellar
Eccitamento e memoria nelle sinapsi centrali
CAPITOLO 6: Flussi ionici e potenziali transmembranari
The Journal of Neuroscience, 2002
The C-terminal domain of NMDA receptor 2 (NR2) subunits has been proposed to play a critical role... more The C-terminal domain of NMDA receptor 2 (NR2) subunits has been proposed to play a critical role in regulating NMDA receptor localization and function in postsynaptic densities. However, the mechanism of this regulation is not completely understood. In this paper we show that C-terminal truncation of NR2A and NR2C subunits in mice (NR2A/C ⌬C/⌬C) impairs synaptic transmission and plasticity at the cerebellar mossy fiber-granule cell relay. Activation of synaptic NMDA receptors could be distinguished from that of extrasynaptic receptors by using the glutamate scavenger glutamate pyruvate transaminase and the open channel blocker MK801. NR2A/C ⌬C/⌬C mice exhibited a specific reduction in synaptic NMDA receptor activation attributable to a severalfold decrease in channel open probability but not channel conductance. Immunodetection revealed normal developmental expression of NR subunit proteins. Quantitative immunogold analyses with an antibody to NR1 indicated that the reduction in receptor activation is not attributed to a reduced number of NR1-containing receptors in postsynaptic densities. Thus, NR2A/NR2C subunits and particularly their C termini regulate synaptic NMDA receptor activation and function by enhancing channel open probability, which is critical for long-term potentiation induction.
Journal of Neurophysiology, 1998
D'Angelo, Egidio, Giovanna De Filippi, Paola Rossi, and Vanni Taglietti. Ionic mechanism of e... more D'Angelo, Egidio, Giovanna De Filippi, Paola Rossi, and Vanni Taglietti. Ionic mechanism of electroresponsiveness in cerebellar granule cells implicates the action of a persistent sodium current. J. Neurophysiol. 80: 493–503, 1998. Although substantial knowledge has been accumulated on cerebellar granule cell voltage-dependent currents, their role in regulating electroresponsiveness has remained speculative. In this paper, we have used patch-clamp recording techniques in acute slice preparations to investigate the ionic basis of electroresponsiveness of rat cerebellar granule cells at a mature developmental stage. The granule cell generated a Na+-dependent spike discharge resistant to voltage and time inactivation, showing a linear frequency increase with injected currents. Action potentials arose when subthreshold depolarizing potentials, which were driven by a persistent Na+ current, reached a critical threshold. The stability and linearity of the repetitive discharge was base...
Journal of Neurophysiology, 1999
D'Angelo, Egidio, Paola Rossi, Simona Armano, and Vanni Taglietti. Evidence for NMDA and mGlu... more D'Angelo, Egidio, Paola Rossi, Simona Armano, and Vanni Taglietti. Evidence for NMDA and mGlu receptor-dependent long-term potentiation of mossy fiber–granule cell transmission in rat cerebellum. J. Neurophysiol. 81: 277–287, 1999. Long-term potentiation (LTP) is a form of synaptic plasticity that can be revealed at numerous hippocampal and neocortical synapses following high-frequency activation of N-methyl-d-aspartate (NMDA) receptors. However, it was not known whether LTP could be induced at the mossy fiber–granule cell relay of cerebellum. This is a particularly interesting issue because theories of the cerebellum do not consider or even explicitly negate the existence of mossy fiber–granule cell synaptic plasticity. Here we show that high-frequency mossy fiber stimulation paired with granule cell membrane depolarization (−40 mV) leads to LTP of granule cell excitatory postsynaptic currents (EPSCs). Pairing with a relatively hyperpolarized potential (−60 mV) or in the presen...
The Journal of Neuroscience, 2001
Neurons process information in a highly nonlinear manner, generating oscillations, bursting, and ... more Neurons process information in a highly nonlinear manner, generating oscillations, bursting, and resonance, enhancing responsiveness at preferential frequencies. It has been proposed that slow repolarizing currents could be responsible for both oscillation/burst termination and for high-pass filtering that causes resonance (Hutcheon and Yarom, 2000). However, different mechanisms, including electrotonic effects (Mainen and Sejinowski, 1996), the expression of resurgent currents (Raman and Bean, 1997), and network feedback, may also be important. In this study we report theta-frequency (3-12 Hz) bursting and resonance in rat cerebellar granule cells and show that these neurons express a previously unidentified slow re-polarizing K ϩ current (I K-slow). Our experimental and modeling results indicate that I K-slow was necessary for both bursting and resonance. A persistent (and potentially a resurgent) Na ϩ current exerted complex amplifying actions on bursting and resonance, whereas electrotonic effects were excluded by the compact structure of the granule cell. Theta-frequency bursting and resonance in granule cells may play an important role in determining synchronization, rhythmicity, and learning in the cerebellum.
Biochemical Journal, 2002
In non-excitable cells, many agonists increase the intracellular Ca2+ concentration ([Ca2+]i) by ... more In non-excitable cells, many agonists increase the intracellular Ca2+ concentration ([Ca2+]i) by inducing an inositol 1,4,5-trisphosphate (IP3)-mediated Ca2+ release from the intracellular stores. Ca2+ influx from the extracellular medium may then sustain the Ca2+ signal. [Ca2+]i recovers its resting level as a consequence of Ca2+-removing mechanisms, i.e. plasma-membrane Ca2+-ATPase (PMCA) pump, Na+/Ca2+ exchanger (NCX) and sarco-endoplasmic reticulum Ca2+-ATPase (SERCA) pump. In a study performed in pancreatic acinar cells, evidence has been provided suggesting that, during the decay phase of the agonist-evoked Ca2+ transients, the Ca2+ concentration within the intracellular stores remains essentially constant [Mogami, Tepikin and Petersen (1998) EMBO J. 17, 435–442]. It was therefore hypothesized that, in such a situation, intracellular Ca2+ is not only picked up by the SERCA pump, but is also newly released through IP3-sensitive Ca2+ channels, with the balance between these two ...
The Journal of Physiology, 1988
1. We have carried out patch-clamp measurements on a cationic channel in the plasma membrane of t... more 1. We have carried out patch-clamp measurements on a cationic channel in the plasma membrane of the frog oocyte, which can be specifically activated by membrane stretch. The kinetics of this channel also display a distinct dependence upon membrane potential, the probability of the channel being open increasing with membrane depolarization. 2. When the patch-clamp pipette filling solution was standard Ringer solution, the single-channel current-voltage (I-V) relationship was linear, the elementary conductance being 38 pS and the reversal potential + 7 mV, suggesting very poor selectivity of the channel for the various cations. 3. The I-V relationship was highly non-linear having a strong inward-going rectification when Ca2+-free solutions were used to fill the patch pipette. These solutions also resulted in a selective, inward cationic permeability through the membrane, with K+ being more permeable than Na+ > Li+ > Ba2+ > Ca2. 4. Though permeant through the stretch-activated channel, Ca2+ inhibited in a concentration-dependent manner the currents carried by other cations. La3(0-1 mM) was also an effective channel blocker. 5. The inward current carried by individual cations at a given membrane potential increased with increasing external cation concentration up to a saturating level, this level being maximal for K+ and minimal for Ca2+. Also the half-saturating concentration was maximal for K+ and minimal for Ca2+ at all membrane potentials. 6. In the presence of a constant Ca2+ concentration (50 AM) increasing [K+] did not change the absolute level at which the current saturated; however the halfsaturating K+ concentration was greatly increased, indicating competitive inhibition between Ca2+ and K+ for the same site. 7. The data are consistent with a model based on Eyring rate theory for current conduction through ionic channels, in which we assume that the ions capable of entering the channel compete for a binding site that they must first occupy before proceeding on. The possible energy profile of the stretch-activated channel was defined by optimizing the model parameters to obtain the best fit of the experimental data. Ca2+ was found to have a smaller dissociation constant and much longer Authors' names are in alphabetical order. 2V. TAGLIETTI AND M. TOSELLI occupancy time than Na+ or K+, thus accounting for its lower permeability and inhibitory effect on current conduction by other cations through the stretchactivatable channel.
The Journal of physiology, Jan 15, 2004
During long-term potentiation (LTP) at mossy fibre-granule cell synapses in rat cerebellum synapt... more During long-term potentiation (LTP) at mossy fibre-granule cell synapses in rat cerebellum synaptic transmission and granule cell intrinsic excitability are enhanced. Although it is clear that changes in granule cell excitability are mediated postsynaptically, there is as yet no direct evidence for the site and mechanism of changes in transmission. To approach this problem, evoked postsynaptic currents (EPSCs) and miniature synaptic currents (mEPSCs) were recorded by patch-clamp in cerebellar slices obtained from P17-P23 rats. LTP was induced by theta-burst stimulation paired with depolarization. During LTP, the EPSCs showed a significant decrease in the coefficient of variation (CV; 28.9 +/- 5.2%, n= 8; P < 0.002), the number of failures (87.1 +/- 41.9%, n= 8; P < 0.04), and the paired-pulse ratio (PPR; 25.5 +/- 4.1% n= 5; P < 0.02). Similar changes were observed by increasing neurotransmitter release (extracellular solutions with high Ca(2+)/Mg(2+) ratio), whereas increas...
The Journal of Physiology, 2003
In neuronal cells, the influx of Ca2+ ions through voltage‐dependent L‐type calcium (L) channels ... more In neuronal cells, the influx of Ca2+ ions through voltage‐dependent L‐type calcium (L) channels couples excitation to multiple cellular functions. In addition to voltage, several neurotransmitters, hormones and cytokines regulate L channel gating via binding to G‐protein‐coupled receptors. Intracellular molecules that modify G‐protein activity – such as regulator of G‐protein‐signalling (RGS) proteins – are therefore potential candidates for regulating Ca2+ influx through L channels. Here we show that a novel RGS2 splice variant from chick dorsal root ganglion (DRG) neurons, RGS2L, reduces bradykinin (BK)‐mediated inhibition of neuronal L channels and accelerates recovery from inhibition. Chick RGS2 reduces the inhibition mediated by both the pertussis toxin (PTX)‐sensitive (Gi/o‐coupled) and the PTX‐insensitive (presumably Gq/11‐coupled) pathways. However, we demonstrate for the first time in a living cell that the extent of coupling to each pathway varies with RGS2L concentration...
Pflügers Archiv European Journal of Physiology, 1994
Ca 2+ currents play a crucial role during neuronal growth. In this paper we describe the developm... more Ca 2+ currents play a crucial role during neuronal growth. In this paper we describe the development of Ca 2 § currents using whole-cell patch-clamp recordings in granule cells of cerebellar slices obtained from 7-to 24day-old rats. Granule cells expressed high-voltage-activated (HVA) Ca 2 § currents in different proportions. The percentage of cells with a measurable HVA current, and the size of HVA current increased in parallel with granule cell maturation. At less than 14 days HVA currents consisted of a fast-and slow-inactivating component, while at more than 19 days only the slow-inactivating component remained. The fast-inactivating component had faster activation and inactivation kinetics, a more negative threshold for activation, and steeper steady-state inactivation than the slow-inactivating component. Nifedipine (5 gM) partially blocked both components. co-Conotoxin (5 gM, co-CgTx) blocked the slow-inactivating component rather selectively. These results indicate that HVA currents change their gating and pharmacological properties during development. Although the mechanism at the molecular level remains speculative, the developmental changes of the HVA current are relevant to the processes of granule cell maturation and excitability.
Action-potential-like depolarizations relieve opioid inhibition of N-type Ca 2+ channels in NG108-15 cells
Pfl�gers Archiv European Journal of Physiology, 1999
The ability of action-potential-like waveforms (APWs) to attenuate opioid-induced inhibition of N... more The ability of action-potential-like waveforms (APWs) to attenuate opioid-induced inhibition of N-type Ca2+ channels was investigated in the neuroblastoma x glioma cell line NG108-15 using whole-cell voltage clamp methods. In in vitro differentiated NG108-15 cells, the opioid agonist [d-ala2]-methionine-enkephalin (DAME) reversibly decreased omega-conotoxin-GVIA-sensitive Ba2+ currents (N-type currents). Agonist-mediated inhibition of N-type currents could be transiently relieved by strong unphysiological depolarizing prepulses to +80 mV (facilitation). Significant facilitation was also achieved by conditioning the cell with a train of 15 APWs, which roughly mimicked physiological action potentials (1- to 6-ms-long depolarizations to +30 mV from a holding potential of -40 mV). The APW-induced facilitation depended on both conditioning pulse frequency and duration. Summation of the disinhibition produced by each APW was possible because reinhibition following repolarization to -40 mV was a much slower process (tau=88 ms) than the onset of facilitation at +80 mV (tau=7 ms). These results provide evidence that N-type Ca2+ channel facilitation may be a physiologically relevant process, and suggest that neuronal firing may relieve agonist-induced inhibition of N-type currents to an extent depending on both the shape of action potentials and the frequency of firing.
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Papers by Vanni Taglietti