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C Rapisarda

Publications and source records attributed to C Rapisarda.

At least 19 recordsLinked to original sources
PubMed2001

Structural compatibility between the putative voltage sensor of voltage-gated K+ channels and the prokaryotic KcsA channel.

Sequence similarity among and electrophysiological studies of known potassium channels, along with the three-dimensional structure of the Streptomyces lividans K(+) channel (KcsA), support the tenet that voltage-gated K(+) channels (Kv channels) consist of two distinct modules: the "voltage sensor" module comprising the N-terminal portion of the channel up to and including the S4 transmembrane segment and the "pore" module encompassing the C-terminal portion from the S5 transmembrane segment onward. To substantiate this modular design, we investigated whether the pore module of Kv channels may be replaced with the pore module of the prokaryotic KcsA channel. Biochemical and immunocytochemical studies showed that chimeric channels were expressed on the cell surface of Xenopus oocytes, demonstrating that they were properly synthesized, glycosylated, folded, assembled, and delivered to the plasma membrane. Unexpectedly, surface-expressed homomeric chimeras did not exhibit detectable voltage-dependent channel activity upon both hyperpolarization and depolarization regardless of the expression system used. Chimeras were, however, strongly dominant-negative when coexpressed with wild-type Kv channels, as evidenced by the complete suppression of wild-type channel activity. Notably, the dominant-negative phenotype correlated well with the formation of stable, glycosylated, nonfunctional, heteromeric channels. Collectively, these findings imply a structural compatibility between the prokaryotic pore module and the eukaryotic voltage sensor domain that leads to the biogenesis of non-responsive channels. Our results lend support to the notion that voltage-dependent channel gating depends on the precise coupling between both protein domains, probably through a localized interaction surface.

Animals↗
PubMed2000

Single-channel analysis of a ClC-2-like chloride conductance in cultured rat cortical astrocytes.

The single-channel behavior of the hyperpolarization-activated, ClC-2-like inwardly rectifying Cl- current (IClh), induced by long-term dibutyryl-cyclic-AMP-treated cultured cortical rat astrocytes, was analyzed with the patch-clamp technique. In outside-out patches in symmetrical 144 mM Cl-solutions, openings of hyperpolarization-activated small-conductance Cl channels revealed burst activity of two equidistant conductance levels of 3 and 6 pS. The unitary openings displayed slow activation kinetics. The probabilities of the closed and conducting states were consistent with a double-barrelled structure of the channel protein. These results suggest that the astrocytic ClC-2-like Cl- current Iclh is mediated by a small-conductance Cl channel, which has the same structural motif as the Cl- channel prototype CIC-0.

Animals↗
PubMed2000

pH modulation of an inward rectifier chloride current in cultured rat cortical astrocytes.

The effects of changes in extra- and intracellular pH in the pathophysiological range (6.0-8.0) on astroglial plasma membrane ionic currents were investigated with the whole-cell patch-clamp technique. In cultured rat neocortical type-1 astrocytes differentiated by a long-term treatment with dibutyryl cyclic-AMP, exposure to an extracellular pH of 6.4 induced, as compared with the control extracellular pH at 7.3, a sustained and reversible increase in the holding current at -60mV. The rise in current was accompanied by a decrease in the apparent input resistance. Ion substitution experiments indicated that extracellular pH 6.4 upregulated the resting Cl(-) conductance, whereas an opposite effect could be observed at extracellular pH 8.0. Recordings of isolated Cl(-) currents showed that this modulation occurred on the previously identified hyperpolarization-activated, inwardly rectifying Cl(-) current, I(Clh). Extracellular acidification to pH 6.4 shifted the voltage dependence of I(Clh) activation by approximately 20mV towards more positive potentials, whereas a approximately 20mV opposite shift was observed upon exposure to extracellular pH 8.0. These effects were paralleled by an increase (extracellular pH 6.4) or decrease (extracellular pH 8.0) in the maximal conductance. Decreasing (6.0) or increasing (8.0) the intracellular pH shifted the steady-state activation of I(Clh) towards more negative or positive potentials, respectively, leaving unchanged the current sensitivity to extracellular pH modifications. The modulation of the inward rectifier Cl(-) current expressed by differentiated cultured neocortical astrocytes indicates that extra- and intracellular changes in pH occurring in a pathophysiological range may contribute to regulating Cl(-) accumulation in astroglial cells.

Animals↗
PubMed2000

The whiteflies (Hemiptera: Aleyrodidae) of Europe and the Mediterranean Basin.

The whitefly fauna of Europe and the Mediterranean Basin comprises 56 species that are considered to be native or naturalized, accommodated within 25 genera. Presented here are a check-list, an identification key to puparia, and a brief account of each species including its distribution and host-plant range. The puparium of each species is illustrated. One new nomenclatural combination (Aleuroclava similis, from Aleurotuberculatus) and two new synonymies (Parudamoselis kesselyaki with Ceraleurodicus varus, Asterobemisia nigrini with A. paveli) are proposed. Three nominal species (Aleurodes capreae, A. fraxini, and Aleyrodes campanulae) are here treated as nomina dubia. Species which, in the study area, have only been recorded from glasshouses are discussed. Four additional species, not yet recorded from the region, are included in the discussion, two of them because a particular quarantine risk is perceived and two because they are notifiable pests in European Union quarantine legislation.

Animals↗
PubMed1997

Characterization of an inwardly rectifying chloride conductance expressed by cultured rat cortical astrocytes.

The biophysical and pharmacological properties of the inwardly rectifying Cl- conductance (IClh), expressed in rat type-1 neocortical cultured astrocytes upon a long-term treatment (1-3 weeks) with dibutyryl-cyclic-AMP (dBcAMP), were investigated with the whole-cell patch-clamp technique. Using intra- and extra-cellular solutions with symmetrical high Cl- content and with the monovalent cations replaced with N-methyl-D-glucamine, time- and voltage-dependent Cl- currents were elicited in response to hyperpolarizing voltage steps from a holding potential of 0 mV. The inward currents activated slowly and did not display any time-dependent inactivation. The rising phase of the current traces was best fitted with two exponential components whose time constants decreased with larger hyperpolarization. The steady-state activation of IClh was well described by a single Boltzmann function with a half-maximal activation potential at - 62 mV and a slope of 19 mV that yields to an apparent gating charge of 1.3. The anion selectivity sequence was Cl- = Br- = I- > F- > cyclamate > or = gluconate. External application of the putative Cl- channel blockers 4,4 diisothiocyanatostilbene-2,2 disulphonic acid or 4-acetamido-4-isothiocyanatostilbene-2,2-disulphonic acid did not affect IClh. By contrast, anthracene-9-carboxylic acid, as well as Cd2+ and Zn2+, inhibited, albeit with different potencies, the Cl- current. Taken together, these results indicate that dBcAMP-treated cultured rat cortical astrocytes express a Cl- inward rectifier, which exhibits similar but not identical features compared with those of the cloned and heterologously expressed hyperpolarization-activated Cl- channel ClC-2.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1995

Two distinct inwardly rectifying conductances are expressed in long term dibutyryl-cyclic-AMP treated rat cultured cortical astrocytes.

Long term incubation (1-3 weeks) with 250 microM dibutyryl-cyclic-AMP (dBcAMP) of pure cultured cortical astrocytes from newborn rats leads to the expression of voltage-dependent, inward-rectifying potassium (K+) and chloride (Cl-) currents which are lacking in shortly treated (4-24 h) and in control cultured astrocytes. Both conductances are already activated at the holding potential of -60 mV and are distinguishable for their gating kinetics and pharmacological sensitivity. K+ currents have a fast activation kinetic and show a time- and voltage-dependent inactivation at potentials negative to -120 mV. The conductive property of the K+ currents increases upon elevation of the extracellular K+ concentration ([K+]o) and they are reversibly blocked by extracellular 0.1 mM barium ions (Ba2+). Cl- currents are activated only at negative membrane potentials; they display a slow activation kinetic, no time-dependent inactivation and are not affected by 0.1 mM Ba2+. In individual astrocyte the K+ and Cl- conductances can be expressed singularly or in combination. The results indicate that the expression of these two conductances is controlled by a cAMP-dependent molecular signalling, presumably by regulating a late gene activation. Thus, the strengthening of this signalling would contribute to promote the maturation of less differentiated astrocytes in culture, implicating the expression of K+ and Cl- membrane conductances which may operate together in the regulation of [K+]o homeostasis via the mechanism of the local accumulation.

Animals↗
PubMed1993

Excitatory amino acids as neurotransmitters of cortical and cerebellar projections to the red nucleus: an immunocytochemical study in the guinea pig.

We combined a retrograde labeling technique with peroxidase immunocytochemistry to verify whether cortical and cerebellar neurons projecting to the red nucleus (RN) contain high concentrations of glutamate and aspartate as possible neurotransmitters. Injections of a tracer, colloidal gold-labeled enzymatically inactive horseradish peroxidase conjugated to wheatgerm agglutinin, into the RN of adult guinea pigs produced retrograde labeling of layer V cortical neurons, with a large predominance in the ipsilateral hemisphere. Corticorubral neurons were located in the granular parietal cortex (Gr), agranular frontal cortex (Ag), agranular cingulate cortex (Cg), and retrobulbar cortex (Rb). Large numbers of retrogradely labeled neurons were concentrated in contralateral interpositus and dentate cerebellar nuclei. We found the majority of corticorubral neurons to be immunostained by antibodies raised in rabbits against glutamate or aspartate conjugated to invertebrate hemocyanin by glutaraldehyde, supporting the hypothesis that excitatory amino acids are neurotransmitters of corticorubral projections. With either antiserum, immunostaining was found in 58-72% of corticorubral neurons in Ag and Gr; higher percentages were observed in Rb (80-85%) and Cg (up to 96%). Cross-sectional area measurements indicated that the perikarya of corticorubral neurons were larger in Ag and Gr than in Rb and Cg; in each area, soma size values of immunopositive corticorubral neurons tended to be larger than those of immunonegative ones. In the cerebellar nuclei, virtually all retrogradely labeled neurons were immunostained by glutamate and aspartate antisera, suggesting that excitatory amino acids might also be considered as possible neurotransmitters for cerebellorubral projections.

Afferent Pathways↗
PubMed1992

Cortical modulation of thalamo-cortical neurons relaying exteroceptive information: a microstimulation study in the guinea pig.

The nature and organization of cortical influences on somatosensory thalamic neurons were investigated in the guinea pig in order to ascertain if mechanisms subserving sensory-motor integration in the thalamus are as precise as has previously been demonstrated in the agranular frontal cortex (AGr) and granular parietal cortex (Gr). The study was carried out on 14 chronically-implanted awake animals. In each experiment one or two motor foci within AGr and Gr were identified according to the region of the movement evoked by intracortical microstimulation at the lowest threshold stimulation (usually 5-15 microA). Spontaneous activity of 182 thalamo-cortical single neurons was recorded in the nucleus ventralis thalami (VT). The neurons were also identified by their response to activation of cutaneous receptive fields (RFs) located in regions of vibrissae or limbs, and then tested for cortical stimulation with a pulse intensity equal to the threshold for evoking motor effects. During the cortico-thalamic tests, the duration of stimulating trains was reduced in order to avoid the appearance of limb or vibrissa movements which could activate somatosensory ascending pathways forwarding peripheral messages to VT. The cortical control on VT neurons appears to be organized in a very precise manner. It was seen that: 1) The influences on these neurons relaying exteroceptive signals specifically emanated from AGr and Gr areas which in turn received exteroceptive input. 2) The vibrissa units responded to stimulation of foci in either AGr or Gr but the reactivity was greater upon stimulation of Gr than AGr. The incidence of responses was very high when the vibrissa RF was overlapping or adjacent to the region of the cortically-evoked vibrissa movement. The response pattern was mostly excitatory. Responses were rarely observed when vibrissa RF lay distant from the vibrissa moved by cortical stimulation. 3) Neurons with limb RFs responded constantly to stimulation of Gr foci only when the RF was overlapping or adjacent to the region of the cortical motor target; in these two conditions the response pattern was excitatory and inhibitory, respectively. Inhibitions only concerned neurons with forelimb RFs. Responses to stimulation of AGr were rarely obtained. From a functional point of view, the excitatory nature of the cortical control on thalamo-cortical VT neurons suggests that a cortical signal inducing movement of a given body part is able to enhance the afferent transmission of somatosensory messages arising in the same body part.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Multiple representations of the body and input-output relationships in the agranular and granular cortex of the chronic awake guinea pig.

The organization of somatosensory input and the input-output relationships in regions of the agranular frontal cortex (AGr) and granular parietal cortex (Gr) were examined in the chronic awake guinea pig, using the combined technique of single-unit recording and intracortical microstimulation (ICMS). AGr, which was cytoarchitectonically subdivided into medial (AGrm) and lateral (AGrl) parts, also can be characterized on a functional basis. AGrl contains the head, forelimb, and most hindlimb representations; only a small number of hindlimb neurons are confined in AGrm. Different distributions of submodalities exist in AGr and Gr: AGr receives predominantly deep input (with the exception of the vibrissa region, which receives cutaneous input), whereas neurons of Gr respond almost exclusively to cutaneous input. The cutaneous or deep receptive field (RF) of each neuron was determined by natural peripheral stimulation. All studied neurons were activated by small RFs, with the exception of lip, nose, pinna, and limb units of lateral Gr (Grl), for which the RFs were larger. Microelectrode mapping experiments revealed the existence of three spatially separate, incomplete body maps in which somatosensory and motor representations overlap. One body map, with limbs medially and head rostrolaterally, is contained in AGr. A second map, comparable to the first somatosensory cortex (SI) of other mammals, is found in Gr, with hindlimb, trunk, forelimb, and head representations in an orderly mediolateral sequence. An unresponsive zone separates the head area from the forelimb region. A third map, with the forelimb rostrally and the hindlimb caudally, lies adjacent and lateral to the SI head area. This limb representation, which is characterized by an upright and small size compared to that found in SI, can be considered to be part of the second somatosensory cortex (SII). A distinct head representation was not recognized as properly belonging to SII, but the evidence that neurons of the SI head region respond to stimulation of large RFs located in lips, nose, and pinna leads us to hypothesize that the SII face area overlaps that of SI to some extent, or, alternatively, that the two areas strictly contiguous and the limits are ambiguous, making them difficult to distinguish. The input-output relationships were based on the results of RF mapping and ICMS in the same electrode penetration. The intrinsic specific interconnections of cortical neurons whose afferent input and motor output is related to identical body regions show a considerable degree of refinement.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

[Evaluation of the risk of hepatitis delta virus (HDV) infection in a population of hemodialyzed patients: significance of the determination of anti-delta antibodies in the blood].

Hepatitis delta virus (HDV) is a defective virus which requires the helper function of hepatitis B virus (HBV) for replication. HDV infection occurs only during or after HDV infection. Viral infection spreads parenterally in both cases. However, it has been reported that the risk of HDV infection is limited to hemodialysed patients, unlike the risk of HBV infection. In order to verify these findings the Authors studied 108 patients undergoing periodical hemodialytic treatment in order to study the delta antibodies present in their blood. Sixty-one of these subjects had received previous blood transfusions, 15 were HBsAg positive and 7 positive for other serological markers of the hepatitis B virus. None of the subjects examined was positive for anti HDV. Our results agreed with the literature reporting an incidence of positive HDV serological markers limited to hemodialyzed patients. The Authors observed that the behaviour of the HDV serological markers can vary from patient to patient and that it is impossible to furnish diagnosis of HDV infection after HBV and HDV clearance. Since these factors can lead to underestimation of the real incidence of HDV infection in hemodialyzed patients, the Authors underline the need to perform long term epidemiological studies and to investigate all the HDV serological markers.

Antibodies, Viral↗
PubMed1985

Cells of origin and topographic organization of corticospinal neurons in the guinea pig by the retrograde HRP method.

In the guinea pig, horseradish peroxidase (HRP) was injected in the cervical or lumbar enlargements of the spinal cord in order to examine the origin and topographical organization of corticospinal (CS) neurons. The cortex was divided into granular and agranular regions to attempt correlations with the location of labeled CS neurons. These, of all sizes, are found only in pyramidal layer V of both kinds of cortical regions and could be seen as single, grouped or organized in clusters of 3-5 or more cells. The soma diameters of HRP CS neurons ranged from 13 to 49 microns. The largest labeled cells were present in the medial part of both agranular and granular cortices and included the giant pyramidal neurons which were found only in the rostromedial agranular cortex. The predominating intermediate-size cells were mostly present in lateral granular areas. The smaller cells were distributed in rostrolateral agranular and caudal granular regions. Morphological evidence suggests that an aggregation in clusters of labeled neurons and the different groups of CS neurons identified in different cortical areas may have additional differences in organization with respect to their precise topographical relations and functional properties. Neurons projecting to cervical levels were more abundant compared to projecting to the lumbar spinal cord, being distributed widely more lateral and anterior on the hemisphere to cortical neurons projecting to lumbar enlargement. These were located only medially on the dorsal surface of the brain. The two groups of labeled neurons were distributed in both agranular and granular cortices and occur adjacent to each other with only a narrow strip of overlap. The findings i.e. laminar organization, the pyramidal shape of CS neurons of all sizes, the presence of clusters and the somatotopic distribution of CS neurons seen in the guinea pig are discussed in comparison with equivalent findings on the corticospinal tract (CST) system of other species. The presence of labeled neurons within the cortex on both sides following unilateral HRP injections in the spinal cord points to a bilateral origin of the CST. This finding is discussed on the basis of the present study and previous autoradiographic findings.

Animals↗
PubMed1984

Single unit activity and visual perception of motion.

Extracellular recordings were carried out in the primary visual cortex of behaving macaque monkeys. Neurons were activated by moving a visual stimulus across their receptive fields during steady fixation and by moving their receptive fields (by visual tracking) at the same velocity across a stationary visual stimulus. Out of a total number of 123 cells studied, 111 were activated by the visual stimulation both during fixation and tracking. The remaining 12 cells showed good response during fixation and very weakened response during tracking. Our results show that a small percentage of striate neurons in macaque monkey could discriminate between the real motion of an object in the visual world and the self-induced displacement of its retinal image.

Animals↗
PubMed1981

The distribution of descending brain stem projections to spinal cord in the guinea pig. A horseradish peroxidase study.

In the guinea pig brain stem neurons projecting to the spinal cord were identified by the horseradish peroxidase (HRP) method. Following lumbar injection labelled neurons were found in the RF, VL, R, MNV, TMNV, RTP, NR, PVG, LH and DMH. The distribution of HRP-positive neurons following cervical injection was roughly the same as that observed after lumbar injection except for the presence of labelled cells in the NSNV and their absence in the MNV and TMNV.

Animals↗