Francesca Stratta - Academia.edu (original) (raw)

Papers by Francesca Stratta

Functional neurology

ABSTRACT

The Journal of Neuroscience, Oct 15, 1998

Functional Neurology, 1992

Journal of Neural Transmission Supplementum, Feb 1, 1995

In the last decades, the contribution given by basic electrophysiology to the understanding of th... more In the last decades, the contribution given by basic electrophysiology to the understanding of the nigrostriatal pathway in mammals has been rather important. The main results obtained by our group will be revised in this short review. The most common responses produced by dopamine (DA) on the principal striatal cells (the medium spiny neurons) are the modulation of the corticostriatal synaptic transmission and the decrease of voltage-dependent inward conductances. After blockade of DA transmission, both spontaneous and cortically driven glutamatergic postsynaptic potentials were inhibited by the selective activation of DA D2 receptors. In naive animals, the DA-mediated inhibition of postsynaptic firing activity was mediated by D1 receptor activation. Nevertheless, the two main subclasses of DA receptors seemed to cooperate in the formation of the long-term depression (LTD) of excitatory synaptic transmission in the striatum. The excitotoxic hypothesis of neurodegeneration has further stimulated our interest towards the study of the interactions between DA and other neurotransmitters into the basal ganglia.

Pointing to a remembered visual target involves the transformation of binocular visual informatio... more Pointing to a remembered visual target involves the transformation of binocular visual information into an appropriate motor output. Errors generated during pointing tasks may indicate the reference frames used by the CNS for the transformation and storage of the target position. Previous studies have proposed eye-, shoulder-, or hand-centered reference frames for various pointing tasks, depending on visual conditions. We asked subjects to perform pointing movements to remembered three-dimensional targets after a fixed memory delay. Pointing movements were executed under dim lighting conditions, allowing vision of the fingertip against a uniform black background. Subjects performed repeated movements to targets distributed uniformly within a small (radius 25 mm) workspace volume. In separate blocks of trials, subjects pointed to different workspace regions that varied in terms of distance and direction from the head and shoulder. Additional blocks were performed that differed in terms of starting position, effector hand, head rotation, and memory delay duration. Final pointing positions were quantified in terms of the constant and variable errors in three dimensions. The orientation of these errors was examined as a function of workspace location to identify the underlying reference frames. Subjects produced anisotropic patterns of variable error, with greater variability for endpoint distances from the body. The major axes of the variable-error tolerance ellipsoids pointed toward the eyes of the subject, independent of workspace region, effector hand (left or right), initial hand position, and head rotations. Constant errors were less consistent across subjects, but also tended to point toward the head and body. Both overshoots and undershoots of the target position were observed. Increasing the duration of the memory delay period increased the size but did not alter the orientation of the variable-error ellipsoids. Variability of the endpoint positions increased equally in all three Cartesian directions as the memory delay increased from 0.5 to 8.0 s. The anisotropy of variable errors indicates a viewer-centered reference frame for pointing to remembered visual targets with vision of the finger. The anisotropy of pointing variability stems from variability in egocentric binocular cues as opposed to reliance on allocentric visual references or to specific approximations in the sensorimotor transformation. Nevertheless, observed increases in variability with longer memory delays indicate that the short-term storage of the target position does not simply mirror the retinal and ocular sensory signals of the visually acquired target location. Thus spatial memory is carried out in an internal representation that is viewer-centered but that may be isotropic with respect to Cartesian space.

Experimental Brain Research, 2002

Subjects reached in three-dimensional space to a set of remembered targets whose position was var... more Subjects reached in three-dimensional space to a set of remembered targets whose position was varied randomly from trial to trial, but always fell along a "virtual" line (line condition). Targets were presented briefly, one-by-one and in an empty visual field. After a short delay, subjects were required to point to the remembered target location. Under these conditions, the target was presented in the complete absence of allocentric visual cues as to its position in space. However, because the subjects were informed prior to the experiment that all targets would fall on a straight line, they could conceivably imagine each point target as belonging to a single rigid object with a particular geometry and orientation in space, although this virtual object was never explicitly shown to the subjects. We compared the responses to repeated measurements of each target with those measured for targets presented in a directionally neutral configuration (sphere condition), and used the variable errors to infer the putative reference frames underlying the corresponding sensorimotor transformation. Performance in the different tasks was compared under two different lighting conditions (dim light or total darkness) and two memory delays (0.5 or 5 s). The pattern of variable errors differed significantly between the sphere condition and the line condition. In the former case, the errors were always accounted for by egocentric reference frames. By contrast the errors in the line condition revealed both egocentric and allocentric components, consistent with the hypothesis that target information can be defined concurrently in both egocentric and allocentric frames of reference, resulting in two independent coexisting representations.

Neural Computation, Dec 1, 2000

The execution of a simple pointing task invokes a chain of processing that includes visual acquis... more The execution of a simple pointing task invokes a chain of processing that includes visual acquisition of the target, coordination of multimodal proprioceptive signals, and ultimately the generation of a motor command that will drive the finger to the desired target location. These processes in the sensorimotor chain can be described in terms of internal representations of the target or limb positions and coordinate transformations between different internal reference frames. In this article we first describe how different types of error analysis can be used to identify properties of the internal representations and coordinate transformations within the central nervous system. We then describe a series of experiments in which subjects pointed to remembered 3D visual targets under two lighting conditions (dim light and total darkness) and after two different memory delays (0.5 and 5.0 s) and report results in terms of variable error, constant error, and local distortion. Finally, we present a set of simulations to help explain the patterns of errors produced in this pointing task. These analyses and experiments provide insight into the structure of the underlying sensorimotor processes employed by the central nervous system.

The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 15, 1998

Pointing to a remembered visual target involves the transformation of visual information into an ... more Pointing to a remembered visual target involves the transformation of visual information into an appropriate motor output, with a passage through short-term memory storage. In an attempt to identify the reference frames used to represent the target position during the memory period, we measured errors in pointing to remembered three-dimensional (3D) targets. Subjects pointed after a fixed delay to remembered targets distributed within a 22 mm radius volume. Conditions varied in terms of lighting (dim light or total darkness), delay duration (0.5, 5.0, and 8.0 sec), effector hand (left or right), and workspace location. Pointing errors were quantified by 3D constant and variable errors and by a novel measure of local distortion in the mapping from target to endpoint positions. The orientation of variable errors differed significantly between light and dark conditions. Increasing the memory delay in darkness evoked a reorientation of variable errors, whereas in the light, the viewer-c...

Journal of neurophysiology, 1997

Journal of neurophysiology, 1994

1. Dopamine-containing neurons of the rat midbrain were recorded intracellularly in vitro. Anoxia... more 1. Dopamine-containing neurons of the rat midbrain were recorded intracellularly in vitro. Anoxia (2-5 min) caused reversible membrane hyperpolarization (4-25 mV), which blocked spontaneous firing of action potentials. Under voltage clamp, anoxia produced an outward current (100-1,000 pA) associated with an increase in the apparent input conductance. 2. The mean reversal potential of the anoxia-induced response at 2.5 and 12.5 mM [K+] was -86 and -66 mV, respectively. 3. The effect of anoxia was not blocked by tetrodotoxin (TTX), saclofen, (-)sulpiride, or strychnine. Superfusate containing low calcium (0.5 mM CaCl2 and 10 mM MgCl2 or 0.5-1 mM CaCl2 and 1 mM CoCl2) or low sodium (25-40% of control) reduced the anoxia-induced outward current. 4. Extracellular barium (0.1-1 mM) blocked the anoxia-induced hyperpolarization/outward current. Other K+ channel blockers (tetraethylammonium, apamin, quinine, and glibenclamide) failed to reduce anoxia-induced current. 5. When the dopamine-con...

Neuroscience research, 1993

The responses of slice-cultured Purkinje cells to trans-DL-1-amino-1,3-cyclopentanedicarboxylic a... more The responses of slice-cultured Purkinje cells to trans-DL-1-amino-1,3-cyclopentanedicarboxylic acid (t-ACPD) were examined by intracellular recording techniques and fura-2 microfluorometry. Bath-application of t-ACPD (100 microM, 30 s), a selective agonist of metabotropic glutamate receptors (mGluRs), to Purkinje cells voltage-clamped near their resting potential -65 to -60 mV) consistently induced a transient inward current, followed by a slower outward current (Iout). This outward current was characterized by a linear current-voltage relationship in the range from -130 to -60 mV and accompanied by a significant decrease in membrane conductance. The extrapolated reversal potential of Iout was positive to 0 mV. When t-ACPD was applied for 60 s or more it became apparent that Iout emerged in parallel to the wash-out of t-ACPD. Microfluorometric fura-2 measurements in combination with electrophysiological recordings were used to assess the relation between Iout and intracellular free...

Advances in Behavioral Biology, 1994

Synapse, 1995

Voltage-dependent potassium currents play a key role in shaping the firing pattern of central neu... more Voltage-dependent potassium currents play a key role in shaping the firing pattern of central neurons. Their pharmacological and physiological identification is rather important in the structures which are involved in the filtering of input/output messages. In this regard, globus pallidus external segment (GPe) is indicated as a crucial station in the well-known indirect pathway of the basal ganglia. Among the potassium conductances which have been indicated to condition the firing behavior and the neuronal integrative properties in many central neurons, we analysed the depolarization-activated ones by means of patch-clamp recordings in the whole-cell configuration. Two main families of calcium-independent outward potassium currents are activated by depolarization in GPe neurons acutely isolated from the adult rat. From depolarized holding potentials (-50/-45 mV), a slowly-activating, sustained current is evoked; it manifests very little inactivation and it is available at rather depolarized potentials (-30 mV/-20 mV). This current is relatively resistant to 4-aminopyridine (4-AP) but it is blocked by tetraethilammonium ions (TEA) and consequently it resembles delayed rectifier current (Ik). From negative holding potentials (-80/-100 mV), on the other hand, A-like conductances are activated. Together with a fast-inactivating transient current, another component is observed in a significant proportion of recordings (45%). This current shows half-inactivation voltage around -90 mV, peculiar sensitivity to micromolar doses of 4-AP and a slow rate of recovery from inactivation. The presence and the modulation of these A-like currents may be a very critical aspect in the membrane physiology of pallidal neurons.

Synapse, 1991

GABA, applied by iontophoresis to striatal neurons of the rat in an in vivo preparation, depolari... more GABA, applied by iontophoresis to striatal neurons of the rat in an in vivo preparation, depolarized the membrane potential and decreased the input resistance in a dose-dependent manner. The null potential of the GABA depolarization was about -50 mV. In addition, a fading of the GABA-induced response was observed for prolonged and relatively high amino acid application. We conclude that GABA has a depolarizing effect on striatal cells. This is in line with recent in vitro works describing a depolarizing effect of GABA in the rat neostriatum.

Progress in Neuro-Psychopharmacology and Biological Psychiatry, 1995

A. Stefani et al. striatal Dl receptors were studied by extracellular single unit recordings in t... more A. Stefani et al. striatal Dl receptors were studied by extracellular single unit recordings in the intact animal as well as by intracellular recordings in rat brain slice preparation. More recently, whole-cell recordings on isolated striatal neurons have further addressed this issue and confirmed the inhibitory modulatory role of Dl receptor on the electrical activity of striatal neurons.

Neuroscience Letters, 1991

Responses of substantia nigra zona compacta neurons to nomifensine and amantadine were studied wi... more Responses of substantia nigra zona compacta neurons to nomifensine and amantadine were studied with intracellular recording techniques (current and voltage clamp) in in vitro slice preparation of rat mesencephalon. The application of nomifensine (1-10 microM) slightly hyperpolarized the cells and inhibited action potential discharge that occurs spontaneously. In voltage-clamp experiments (-50, -60 mV, holding potential) an outward current was observed. The membrane responses to exogenously-applied dopamine were potentiated by the concomitant superfusion of nomifensine. The effects of nomifensine were antagonized by (-)-sulpiride (1 microM), a D2 receptor antagonist. By contrast, the superfusion of amantadine (1-30 microM) on substantia nigra zona compacta cells was ineffective on firing rate, membrane potential or on sensitivity to exogenous dopamine. In the presence of high doses (300 microM to 1 mM) of amantadine a depolarization and an increase in firing activity was observed. While our results provide electrophysiological evidence for an inhibition of the dopamine uptake system by nomifensine, they do not support a dopaminergic mechanism for the actions of amantadine in the substantia nigra zona compacta.