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P Calabresi

Publications and source records attributed to P Calabresi.

At least 127 records · Page 7Linked to original sources
PubMed1995

Transmitter release associated with long-term synaptic depression in rat corticostriatal slices.

Using a corticostriatal slice preparation, we have recently shown that tetanic stimulation of the corticostriatal pathway produces long-term depression (LTD) of striatal excitatory synaptic transmission. In the present study we have analysed the relationship between LTD and the striatal release of different endogenous transmitters. Samples of perfusate were collected via a small cannula placed just above the surface of the striatal slice close to the recording electrode, and were analysed by HPLC. The high-frequency stimulation (100 Hz, three trains, 3 s duration, 20 s interval) used to induce LTd caused a significant but transient increase in the release of both excitatory (aspartate and glutamate) and inhibitory (glycine and GABA) amino acid transmitters. Tetanic stimulation also produced a significant, but transient increase in the release of endogenous dopamine. We conclude that the tetanic stimulation of the corticostriatal pathway is able to induce a large but transient release of excitatory amino acids and of dopamine, whose participation in the induction of striatal LTD has been demonstrated previously. Moreover, the maintenance of this form of synaptic plasticity does not seem to require a sustained change in transmitter release.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1995

Vulnerability of medium spiny striatal neurons to glutamate: role of Na+/K+ ATPase.

In Huntington's disease neuronal degeneration mainly involves medium-sized spiny neurons. It has been postulated that both excitotoxic mechanisms and energy metabolism failure are implicated in the neuronal degeneration observed in Huntington's disease. In central neurons, > 40% of the energy released by respiration is used by Na+/K+ ATPase to maintain ionic gradients. Considering that impairment of Na+/K+ ATPase activity might alter postsynaptic responsivity to excitatory amino acids (EAAs), we investigated the effects of the Na+/K+ ATPase inhibitors, ouabain and strophanthidin, on the responses to different agonists of EAA receptors in identified medium-sized spiny neurons electrophysiologically recorded in the current- and voltage-clamp modes. In most of the cells both ouabain and strophanthidin (1-3 microM) did not cause significant change in the membrane properties of the recorded neurons. Higher doses of either ouabain (30 microM) or strophanthidin (30 microM) induced, per se, an irreversible inward current coupled to an increase in conductance, leading to cell deterioration. Moreover, both ouabain (1-10 microM) and strophanthidin (1-10 microM) dramatically increased the membrane depolarization and the inward current produced by subcritical concentrations of glutamate, AMPA and NMDA. These concentrations of Na+/K+ ATPase inhibitors also increased the membrane responses induced by repetitive cortical activation. In addition, since it had previously been proposed that dopamine mimics the effects of Na+/K+ ATPase inhibitors and that dopamine agonists differentially regulate the postsynaptic responses to EAAs, we tested the possible modulation of EAA-induced membrane depolarization and inward current by dopamine agonists. Neither dopamine nor selective dopamine agonists or antagonists affected the postsynaptic responses to EAAs. Our experiments show that impairment of the activity of Na+/K+ ATPase may render striatal neurons more sensitive to the action of glutamate, lowering the threshold for the excitotoxic events. Our data support neither the role of dopamine as an ouabain-like agent nor the differential modulatory action of dopamine receptors on the EAA-induced responses in the striatum.

Animals↗
PubMed1995

Paclitaxel disposition in plasma and central nervous systems of humans and rats with brain tumors.

BACKGROUND: Paclitaxel (Taxol) has been shown to sensitize some malignant cells to the effects of radiation. A number of clinical protocols, combining paclitaxel with radiation therapy, have been designed to exploit this phenomenon. The radiation-potentiating effect of paclitaxel is likely dependent on the ability of the drug to penetrate the tissue being radiated. Paclitaxel is known to have limited access to the central nervous system (CNS) of rats and mice, but its ability to penetrate malignant tissue in the CNS is inadequately documented. PURPOSE: Our purpose was to examine the concentrations of paclitaxel in the cerebrospinal fluid (CSF) of patients with CNS malignancies and in normal and malignant tissues from the brains of Fischer rats bearing the C6 rat glioma and then to compare those paclitaxel concentrations with concomitant paclitaxel concentrations in the plasma of those same patients and animals. METHODS: Four patients were treated with 3-hour infusions of paclitaxel at doses between 90 and 200 mg/m2. Plasma and CSF were sampled at 0.33, 1.5, 3.25, 5, 6, and 24 hours after initiation of the paclitaxel infusion. Four Fischer rats had 20,000 C6 glioma cells stereotactically implanted into their right frontal lobes; 28 days later, they were given 3-hour infusions of paclitaxel at 10 mg/kg. Plasma was sampled during the paclitaxel infusion. At the completion of the infusion, rats were killed, and portions of their normal and malignant CNS tissues were removed for histologic assessment. Concentrations of paclitaxel in plasma, CSF, and brain tissue were determined with high-pressure liquid chromatography. RESULTS: Plasma pharmacokinetics of paclitaxel in patients with brain tumors were comparable to those previously described in patients with other malignancies. Paclitaxel could be measured in CSF of all patients, but concentrations were very low. Peak paclitaxel concentrations in CSF ranged between 5 and 83 nM and occurred between 3.25 and 5 hours after initiation of the paclitaxel infusion. Peak paclitaxel concentrations in CSF were between 0.12% and 8.3% of those present in concomitant plasma samples. Paclitaxel was not detectable in the normal or malignant CNS tissue of any rat, despite the fact that plasma concentrations of paclitaxel at the time of tissue acquisition ranged from 0.62 to 153 microM. CONCLUSIONS: Paclitaxel has only limited access to the CSF of patients with CNS malignancies and to normal and malignant CNS tissues of rats bearing brain tumors. IMPLICATIONS: The utility of combining paclitaxel with radiation therapy to treat CNS malignancies should be considered in light of the documented limited access of paclitaxel to the CNS.

Adult↗
PubMed1995

Properties of the hyperpolarization-activated cation current Ih in rat midbrain dopaminergic neurons.

Intracellular electrophysiological recordings in current- and voltage-clamp mode were obtained from dopaminergic neurons of the rat mesencephalon in an in vitro slice preparation. In current-clamp mode, a time-dependent anomalous rectification (TDR) of the membrane was observed in response to hyperpolarizing current pulses. In single-electrode voltage-clamp mode, a slowly developing inward current (Ih) underlying the TDR was studied by hyperpolarizing voltage commands from a holding potential of -50 to -60 mV. Ih started to be activated at approximately -69 mV, was fully activated at -129 to -141 mV, with half-maximal activation at -87 mV, and showed no inactivation with time. The time course of development of Ih followed a single exponential, and its time constant was voltage-dependent. At -81 mV, Ih activated with a time constant of 379 +/- 47.6 ms, whereas at -129 mV Ih activated with a time constant of 65 +/- 2.2 ms. Its estimated reversal potential was -35 +/- 4 mV. Raising the extracellular concentration of K+ from 2.5 to 6.5 and to 12.5 mM increased the amplitude of Ih while reducing the extracellular concentration of Na+ from 153.2 to 27.2 mM caused a reduction in amplitude of Ih. Bath application of caesium (1-5 mM) reversibly reduced or blocked the TDR/Ih. Perfusion of tetrodotoxin (0.5-1 microM), tetraethylammonium (10-20 mM) or barium (0.3-2 mM) did not significantly affect Ih. Ih was also present in cells impaled with CsCl-filled electrodes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Tumor angiogenesis as a prognostic factor in cervical carcinoma.

Angiogenesis, the induction of new capillaries and venules, has been associated with tumor growth. Increased tumor size and new vessel growth may further the opportunity for tumor cells to enter the circulation and potentiate metastatic disease. To investigate if tumor angiogenesis could serve as a prognostic factor in cervical carcinoma, we counted microvessels (capillaries and venules) in 29 patients with squamous cell carcinoma of the cervix. Surgical specimens were stained for endothelial cells specifically with Factor VIII to identify all vessels. The microvessels were counted by light microscopy (per 200 x field) in tumor sections with the highest population of microvessels. This was performed by two investigators without knowledge of patient outcome or extent of disease. Microvessel counts in patients with squamous cell carcinoma were significantly different from those of control subjects: 56 +/- 28.9 and 16.3 +/- 3.3 (P = 0.013). There was no correlation between microvessel count and node status, parametrial involvement, depth of invasion, or gross disease. Microvessel count was significantly correlated with vascular space involvement (P = 0.017). Four patients who developed recurrent disease within 1 year had high microvessel counts and yet were node negative and VSI negative at surgery. As shown by Folkman in breast cancer, angiogenesis may also be an independent predictor for recurrent disease in squamous cell carcinoma of the cervix. Microvessel counts could be of prognostic value in patients who do not have other risk factors for disease recurrence.

Adult↗
PubMed1995

Gene-modified cells for the treatment of cancer.

Gene therapy involves the insertion of a gene into an organism to treat a disease. Since its early development in the 1970s, gene therapy has expanded rapidly both in terms of the methods available and the number of candidate diseases for treatment. This report reviews gene therapy for cancer, including methodology, pre-clinical studies and experimental clinical trials.

Clinical Trials as Topic↗
PubMed1995

Electrophysiology of dopamine D-1 receptors in the basal ganglia: old facts and new perspectives.

1. The dopamine (DA) D1-receptor family is highly represented in the mammalian brain and particularly in the nigrostriatal system, whose integrity is crucial for the execution of motor performances. 2. In the last decade, our understanding of the electrophysiology of D1 receptors on caudate-putamen neurons has greatly improved. The effects of the activation of striatal D1 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 D1 receptor on the electrical activity of striatal neurons. 3. Several important questions, however, concerning the functional effects of D1 receptor activation in the basal ganglia are still debated: the cellular segregation of the distribution of D1-D2-like receptors, their synergistic or opposite functional roles at the second messenger level, the effects of D1 receptor activation on the transmitter release and the modifications of D1 receptor pharmacology in dopamine-denervated striata. 4. A different perspective will also be discussed: the involvement of D1 receptors in long-term changes of synaptic efficacy in the striatum as a possible correlate of motor learning.

Animals↗
PubMed1995

Hypoxia-induced electrical changes in striatal neurons.

We have studied the effects of hypoxia on the membrane properties of striatal neurons intracellularly recorded from a corticostriatal slice preparation. Brief (2-10 min) periods of hypoxia produced reversible membrane depolarizations. Longer periods of hypoxia (12-20 min) produced irreversible membrane depolarizations. In voltage-clamp experiments, hypoxia caused an inward current coupled with an increased membrane conductance. Tetrodotoxin or low calcium (Ca2+)-high magnesium-containing solutions blocked synaptic transmission, but they did not reduce the hypoxia-induced electrical changes. Antagonists of excitatory amino acid (EAA) receptors failed to affect the electrical effects caused by oxygen (O2) deprivation. In low sodium (Na+)-containing solutions the hypoxia-induced inward current was largely reduced. Blockade of ATP-dependent Na(+)-potassium (K+) pump by ouabain enhanced hypoxia-induced membrane depolarizations and/or inward currents. Our findings indicate that, at least for in vitro experiments, the release of EAAs is not required for the acute hypoxia-induced electrical changes in striatal neurons.

Animals↗
PubMed1995

Sex-hormone-related events in migrainous females. A clinical comparative study between migraine with aura and migraine without aura.

In this study, the relationship between hormonal-related events and migraine with aura (MA) and without aura (MO) was investigated. Subjects included 268 women suffering from MA (88) and MO (180). Data were collected on the relationship between sex-hormone-related events and migraine. Migraine during menses was observed in a significantly higher percentage of MO than MA patients (p < 0.03). Menstrual migraine was significantly more common in MO than in MA patients (p < 0.01). Migraine began during pregnancy in a significantly higher percentage of MA than of MO patients (p < 0.01). No significant difference was observed between the two groups of patients regarding the onset of migraine at menarche, after menopause, in the postpartum period or during the early cycles of oral contraceptives. Also, both groups of patients showed a similar migraine course during pregnancy, oral contraceptive use and menopause. Eight patients with coexisting migraine with aura and migraine without aura attacks reported the appearance of the aura symptom for the first time in the early cycles of oral contraceptive intake. These findings suggest that gonadal hormone fluctuation may influence both types of migraine.

Adult↗
PubMed1995

On the mechanisms underlying hypoxia-induced membrane depolarization in striatal neurons.

Clinical and experimental evidence has shown that the striatal neurons are particularly vulnerable to hypoxia and ischaemia. An excessive excitatory action of glutamate, released by the corticostriatal terminals, has been implicated in this peculiar vulnerability of striatal neurons. We have studied the effects of hypoxia on the membrane properties of striatal neurons intracellularly recorded from a corticostriatal slice preparation. Brief (2-10 min) periods of hypoxia produced reversible membrane depolarizations. During the initial phase of the hypoxia-induced depolarization the frequency of action potential discharge was transiently increased; 2-3 min after the onset of hypoxia the firing activity was fully abolished. Brief periods of hypoxia also caused a reversible reduction of the amplitude of the excitatory postsynaptic potentials (EPSPs) evoked by cortical stimulation. Longer period of hypoxia (12-20 min) produced irreversible membrane depolarizations. In voltage-clamp experiments hypoxia caused an inward current coupled with an increased membrane conductance. Tetrodotoxin (TTX) or low calcium (Ca2+)-high magnesium containing solutions blocked synaptic transmission, but they did not reduce the hypoxia-induced electrical changes. Antagonists of excitatory amino acid receptors failed to affect the electrical effects caused by oxygen deprivation. Hypoxia-induced inward currents were reduced either by the potassium (K+) channel blockers, barium and tetraethyl ammonium (TEA) cations, or by lowering external sodium (Na+) concentration. Blockade of ATP-dependent Na(+)-K+ pump by both ouabain and strophanthidin enhanced hypoxia-induced membrane depolarization/inward current. Our findings indicate that the release of excitatory amino acids does not seem to be required for the acute hypoxia-induced electrical changes in striatal neurons. Moreover, TTX-resistant Na+ influx and K+ currents seem to play an important role in the generation of hypoxia-induced electrical changes. These data also suggest that the selective vulnerability of striatal neurons to oxygen deprivation may be caused by their peculiar sensitivity to energy metabolism failure.

Animals↗
PubMed1995

Electrophysiological actions of felbamate on rat striatal neurones.

1. We have investigated the effects of the anticonvulsant drug, felbamate (FBM), on striatal neurones, recorded in vitro by using both intracellular and extracellular conventional recordings in slices and whole-cell recordings in acutely isolated neurones. 2. FBM, at therapeutically relevant concentrations (30-300 microM) showed multiple mechanisms of action. Like other antiepileptic drugs, FBM (30-300 microM) showed a direct inhibitory action on current-evoked firing discharge of striatal neurones. A patch-clamp analysis of this effect revealed a dose-related reduction of voltage-dependent sodium (Na+) currents (10-100 microM), with a half inhibiton dose (IC50) value of 28 microM. 3. We also tested whether FBM affected corticostriatal glutamate transmission. In control medium (1.2 mM external magnesium), both extracellularly recorded field potentials and intracellularly recorded excitatory postsynaptic potentials (e.p.s.ps) evoked by cortical stimulation were no affected by bath application of 30-300 microM FBM. 4. When magnesium was removed from the perfusing solution, a procedure which reveals a N-methyl-D-aspartate (NMDA)-mediated component in the corticostriatal synaptic potential, FBM (30-300 microM) produced a dose-dependent reduction of the amplitude of both the field potential and the e.p.s.p. 5. FBM reduced the inward currents produced either by bath or by focal applications of 30 microM NMDA, finding consistent with the hypothesis that the observed reduction of the NMDA-mediated component of the synaptic potentials may be caused at postsynaptic level. 6. The reduction of the NMDA-mediated component of the synaptic transmission by FBM and its depressant effect on the voltage-dependent Na+ channels, may account for the antiepileptic action of this drug. Moreover, the pharmacological properties of FBM might render this drug interesting as a neuroprotectant agent.

Action Potentials↗
PubMed1995

Action of GP 47779, the active metabolite of oxcarbazepine, on the corticostriatal system. I. Modulation of corticostriatal synaptic transmission.

Oxcarbazepine (OCBZ) is the keto-analogue of carbamazepine (CBZ). In humans, OCBZ is rapidly and almost completely metabolized to 10, 11-dihydro-10-hydroxy-CBZ (GP 47779), the main metabolite responsible for the drug's antiepileptic activity. The corticostriatal pathway is involved in the propagation of epileptic discharges. We characterized the electrophysiological effects of GP 47779 on striatal neurons by making intracellular recordings from corticostriatal slices. GP 47779 (3-100 microM) produced a dose-dependent inhibition of glutamatergic excitatory postsynaptic potentials (EPSPs). This effect was not coupled either with changes of the membrane potential of these cells or with alterations of their postsynaptic sensitivity to excitatory amino acids (EAA) suggesting a presynaptic site of action. GP 47779 reduced the current-evoked firing discharge only at concentrations > 100 microM. GP 47779 did not affect the presynaptic inhibitory action of adenosine, showing that presynaptic adenosine receptors were not implicated in the GP 47779-mediated reduction of corticostriatal EPSPs. Our data indicate that GP 47779 apparently acts directly on corticostriatal terminals to reduce the release of EAA, probably by inhibiting high-voltage-activated (HVA) calcium (Ca2+) currents (described in the accompanying article). The inhibitory action of GP 47779 on corticostriatal transmission may contribute to the antiepileptic effects of this drug.

Adenosine↗
PubMed1995

Action of GP 47779, the active metabolite of oxcarbazepine, on the corticostriatal system. II. Modulation of high-voltage-activated calcium currents.

GP 47779, the active metabolite of oxcarbazepine (OCBZ) inhibits glutamatergic excitatory postsynaptic potentials (EPSPs) in rat striatum (described in the accompanying article). This effect was presumed to involve the modulation of the calcium (Ca2+) signals at either pre- or postsynaptic level. Therefore, we directly tested whether GP 47779 could modulate Ca2+ conductances in cortical as well as in striatal neurons. GP 47779 produced a reversible dose-dependent decrease in high-voltage-activated (HVA) Ca2+ currents evoked by membrane depolarization in isolated cortical pyramidal cells. GP 47779-mediated reduction in HVA Ca2+ currents, if occurring also at corticostriatal axon terminals, might explain the reduction of glutamate release in the striatum. An inhibitory action of GP 47779 on HVA Ca2+ currents was also observed in isolated striatal neurons. The effect of HVA Ca2+ currents in cortical and striatal neurons persisted in the presence of nifedipine, suggesting that dihydropyridine-sensitive channels were not involved in the GP 47779-mediated responses. We propose that the modulation of HVA Ca2+ channels by this carbamazepine (CBZ) analogue may account for its inhibitory action on transmitter release.

Animals↗
PubMed1995

The modulation of dopamine receptors in rat striatum.

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.

Animals↗
PubMed1994

Detection of elevated basic fibroblast growth factor during early hours of in vitro angiogenesis using a fast ELISA immunoassay.

Basic FGF (bFGF) is a growth factor that is thought to play an important role in angiogenesis. Available assays that are used to detect bFGF are long and cumbersome. Here, we present a fast, easy and sensitive sandwich-type enzyme immunoassay for bFGF detection. Our method is a modification of the method described by Watanabe et al (Biochem. Biophys. Res. Commun. 1991; 175, 229). Two monoclonal antibodies for antigen capture and one noncongugated polyclonal antibody for antigen detection are used instead of using three monoclonal antibodies with the congugation of one of them for detection. There is no change in the sensitivity of the assay with average detection limit of 1 pg/well. Acidic fibroblast growth factor does not interfere with the assay. Using this method, samples from conditioned media of capillary endothelial cell culture before and after angiogenesis were measured. Associated with detection of start of tube formation, basic FGF was elevated at 8 hours from angiogenic stimulation and peaked at 48 hour (4 times control), showing for the first time in an in vitro system that there is a transient increase in endogenous bFGF accompanying early steps of angiogenesis which in turn may be the trigger for new capillary formation.

Adrenal Glands↗
PubMed1994

Intrinsic and extrinsic characteristics of human tumors relevant to radiosurgery: comparative cellular radiosensitivity and hypoxic percentages.

UNLABELLED: We have collected the in vitro x-ray radiation survival characteristics of 181 lines from 12 different classes of exponentially growing human tumor cells (sarcomas, lung cancers, colo-rectal cancers, medulloblastomas, melanoma, breast cancers, prostate cancers, renal cell cancers, grades III and IV brain tumors, ovarian, and head and neck cancers). This information was used to intercompare survival after single high doses of 20-40 Gy for each tumor line. Radiosensitivities could roughly be divided into two groups. The more radiosensitive group included: sarcoma, small-cell lung cancer, non-small cell lung cancer, colorectal cancer, medulloblastoma and melanoma. The more radioresistant group included breast, prostate, renal cell, primary brain tumors, ovarian tumors, and head and neck cancers. Using a model of a 3 cm diameter brain lesion containing about 1.4 x 10(9) oxic cells, the single doses calculated to reduce survival to 1 cell were: sarcoma and small cell lung cancers-22-23 Gy; melanoma-25 Gy; non-small cell lung and colorectal cancer-26 Gy; medullo-blastoma-28 Gy; breast, prostate, renal cell, primary brain tumors, ovarian tumors, and head and neck cancers-30-36 Gy. If, however, tumors contained on average 20 percent hypoxic cells, the dose needed for equivalent cell killing increased by about a factor of 2.6-2.8. Also, there was no correlation between the ranking of relative radiosensitivities of the various classes of tumor cells at high doses (as in radiosurgery) to the sensitivity at low doses (as in conventional fractionated radiotherapy). CONCLUSION: available information on the intrinsic radiosensitivity of human tumor cells indicates that meaningful differences exist among different histological classes of neoplasm that are relevant to the single high doses used in radioneurosurgery, and which could constitute a basis for "tailoring" the administered dose to the particular neoplasm. However, if intracerebral lesions contain a large number of hypoxic cells (e.g., 20%), this may constitute a significant problem.

Cells, Cultured↗