Biomedical subjects

M Simonato

Publications and source records attributed to M Simonato.

49 records · Page 3Linked to original sources

PubMed1993

A pathogenetic hypothesis of temporal lobe epilepsy.

Temporal lobe epilepsy is the most common type of epilepsy in adults. It frequently develops in previously normal nervous tissue, secondary to trauma, tumour or stroke. The disease has a tendency to progress toward generalization and neurologic deficits. The pathogenesis of temporal lobe epilepsy is still unclear. In this article, a hypothesis is proposed suggesting that a cascade of biological events may underlie its development and progression. These include increased excitatory amino acid release, NMDA receptor activation, influx of calcium into neurones, activation of calcium-dependent enzymes (including phospholipase A2), immediate early gene expression, and synthesis of new proteins. Positive and negative feedback loops as well as other events, taking place in parallel, are also hypothesized. The clinical and pharmacological ramifications of this working hypothesis are discussed.

Epilepsy, Temporal Lobe↗

PubMed1993

Characterization of K(+)-evoked [3H]D-aspartate outflow in the rat hippocampus in vitro.

The characteristics of K(+)-evoked outflow of [3H]D-aspartate, a glutamate release marker, were systematically investigated in the rat hippocampus, using 35 mM K(+)-evoked [3H]noradrenaline outflow as a reference. Elevation of external K+ concentrations increased [3H]D-aspartate outflow in a concentration-dependent manner both in slices and synaptosomes. In the absence of external Ca2+, K(+)-evoked [3H]D-aspartate outflow was decreased by approx 60% in synaptosomes and 80% in slices. However, elimination of external Ca2+ in the presence of 2 mM EGTA significantly reduced only 100 mM K(+)-evoked outflow, both in slices and synaptosomes. In the absence of external Ca2+, 35 mM K(+)-evoked [3H]noradrenaline outflow was abolished even when EGTA was present in the solution. Furthermore, the Ca(2+)-channel blockers omega-conotoxin (10 nM) and nifedipine (0.5 microM) did not significantly reduce K(+)-evoked [3H]D-aspartate outflow; [3H]noradrenaline outflow, however, was reduced by more than one third by omega-conotoxin. Finally [3H]D-aspartate overflow was insensitive to tetrodotoxin (0.5 microM) both in synaptosomes and in slices, while that of [3H]noradrenaline was significantly reduced in slices. It is concluded that (1) [3H]D-aspartate outflow is partly Ca(2+)-dependent; (2) differences between K(+)-evoked [3H]D-aspartate and [3H]noradrenaline outflow include sensitivity to stimulation by EGTA, to Ca(2+)-channel blockers and to tetrodotoxin. Some of these discrepancies may be ascribed to the existence of a cytosolic, Ca(2+)-independent pool of releasable glutamate and [3H]D-aspartate. These observations pose some problems as to the experimental approach for the study of Ca(2+)-dependent [3H]D-aspartate release.

Animals↗

PubMed1992

Photobiological activity of certain new methylazapsoralens.

The photobiological activity of a series of psoralen isosters carrying a nitrogen atom at 8 position, new potential drugs for the photochemotherapy of hyperproliferative skin diseases, have been studied; the more active derivatives appeared to be 5,4'-dimethyl-8-azapsoralen and 3,4,4'-trimethyl-8-azapsoralen which induced a strong inhibition of DNA synthesis in Ehrlich ascites cells, very similar to that provoked by 8-methoxypsoralen, the furocoumarin at present used in photochemotherapy. Such compounds induced a small amount of inter-strand DNA cross-links and were non phototoxic when assayed on guinea-pig skin; however, both derivatives appeared to be highly mutagenic in E. coli WP2 TM6. This strain contains the plasmid R46 and it is proficient in DNA repair, and therefore monoadducts do not should be mutagenic in such a strain. Because the first steps of excision, which remove monoadducts, and of the main cross-link repair use the same enzymes (produced by the uvrABC complex), in the presence of a great number of monofunctional lesions, it is possible that there are not sufficient enzyme molecules for removing cross-links according this pathway, which could be repaired by a second one, uvrABC independent and based on glycosilase activity, which works at reduced levels and is much less accurate.

Animals↗

PubMed1991

Differential expression of immediate early genes in the hippocampus in the kindling model of epilepsy.

Kindling is a phenomenon in which brief afterdischarges (ADs) evoked by periodic electrical stimulation of the brain eventually result in generalized clonic motor seizures. Once present, the enhanced sensitivity to electrical stimulation is lifelong. The mechanism by which brief ADs produce this long-lasting effect may involve a change in gene expression. To begin to investigate changes in gene expression that occur during kindling, we used in situ hybridization histochemistry to examine the time course of expression of mRNAs of the immediate early genes (IEGs) c-fos, c-jun, NGFI-A, and c-myc within the dorsal hippocampus of rats following a kindling AD. Three principal findings resulted from this study. First, the expression of all mRNAs except c-myc was significantly increased (P less than 0.05) within discrete neuronal populations. Second, the time course of expression of the IEGs differed markedly within the same neuronal population. Third, for a given IEG, the time course and anatomic pattern of expression were strikingly different among different neuronal populations of the hippocampus. The prolonged and distinctly different patterns of IEG expression suggest that target genes are differentially regulated in these neuronal populations for prolonged periods following a kindling AD.

Animals↗

PubMed1991

Alpha-2 adrenoreceptor-mediated decrease in gamma-aminobutyric acid outflow in cortical slices and synaptosomes during morphine tolerance.

Morphine tolerance has proven to be accompanied by alterations in the efficiency of many neuronal signals, as well as by an inversion of the noradrenergic signal response of cortical acetylcholine terminals and gamma-aminobutyric acid (GABA) neurons in vivo (decreased acetylcholine and increased GABA release in normal animals, vice versa in tolerant). The latter observation may be relevant in interpreting morphine withdrawal, because the noradrenergic neuron firing rate increases dramatically during its course. This study was designed as an attempt to anatomically localize the inversion of the GABA response to norepinephrine. Because this phenomenon is observed in cortical slices and synaptosomes, it can be postulated that it occurs in the neocortex at the level of the intracortical GABA nerve terminals. Pharmacological analysis demonstrates that although the stimulation observed in controls is alpha-1 adrenoreceptor-mediated, the inhibition in tolerant animals is exerted via alpha-2 adrenoreceptors. Therefore, an increase in number or an improved coupling to the transduction system of alpha-2 adrenoreceptors is hypothesized. This observation gives a clue to a molecular interpretation of the inversion of GABA response to norepinephrine in tolerant animals, which may be of heuristic value in terms of biological interpretation of morphine tolerance.

Animals↗

PubMed1989

Lack of excitatory amino acid-induced effects on calcium fluxes measured with 45Ca2+ in rat cerebral cortex synaptosomes.

Ca2+ uptake was measured in purified rat cerebral cortex synaptosomes (P3 pellets) using 45Ca2+ as a tracer. Ca2+ influx increased in time, and with an increase in external K+ concentration and temperature. The net (external K+-induced, depolarization-dependent) uptake follows a two-component course. The exponential term, due to the opening of voltage-operated calcium channels (VOC), has a rate constant which increases with an increase in the depolarization level (1.04 versus 0.54 nmol/s/mg protein for 50 mM - versus 15 mM [K+]-dependent net influx). The linear term, due to the Na+/Ca2+ exchange system, has a similar rate constant at all depolarization levels (0.16 +/- 0.05 and 0.11 +/- 0.02 nmol/s/mg protein). Excitatory amino acids (glutamate, kainate and n-methyl-d-aspartate-NMDA-) were tested on this preparation at doses ranging between 5 x 10(-5) M and 5 x 10(-3) M and at multiple incubation times, under resting conditions and under two depolarizing conditions (partial depolarization: 15 mM external K+ and maximal depolarization: 50 mM external K+). NMDA was also tested in the absence of Mg2+. No effect was detectable under any of these experimental conditions. Hypotheses to interpret these data are discussed. Further studies on other preparations are needed in order to directly investigate the presynaptic effects of excitatory amino acids.

Amino Acids↗

PubMed1989

Alpha 1-adrenoreceptor-mediated increase in acetylcholine release in brain slices during morphine tolerance.

Norepinephrine, clonidine, and phenylephrine increased the electrically evoked release of endogenous acetylcholine in cortical slices taken from morphine-tolerant guinea pigs. This effect was alpha 1-adrenoreceptor mediated and was opposite to the alpha 2-adrenoreceptor-mediated inhibition of acetylcholine release, normally elicited by norepinephrine and clonidine. In the presence of prazosin, clonidine recovered its normal inhibitory properties, suggesting that morphine tolerance induced the appearance of an alpha 1-adrenoreceptor-mediated response that overshadowed, but did not cancel, the still present alpha 2-adrenoreceptor inhibitory control. The attempt to prove the presence of alpha-adrenoreceptors on the nerve endings by testing the effect of norepinephrine in synaptosomal preparations (preloaded with [3H]choline and depolarized with KCl and veratridine) was unsuccessful. Therefore the problem of the exact location of this excitatory input remains to be solved. These results confirm previous findings reporting the increase in cortical acetylcholine release induced by the alpha-adrenoreceptor agonists in morphine-tolerant, freely moving guinea pigs and demonstrate that opiate tolerance inverts the direction of the noradrenergic modulation even in the isolated intracortical cholinergic structures.

Acetylcholine↗

PubMed1989

Changes in cortical acetylcholine and gamma-aminobutyric acid outflow during morphine withdrawal involve alpha-1 and alpha-2 receptors.

Naloxone (0.3-9 mumol kg-1), electrical stimulation of locus ceruleus or clonidine at low doses (7.5-112 nmol kg-1) increased the release of acetylcholine from the exposed parietal cortex of freely moving, morphine-tolerant guinea pigs. This increase was not additive and was prevented by prazosin (35.8 nmol kg-1), suggesting the involvement of alpha-1 receptors. At high doses (374 nmol kg-1 or more) clonidine inhibited acetylcholine release through alpha-2 receptors, as it did in naive animals at 7.5 nmol kg-1. Clonidine (374 nmol kg-1) and prazosin (35.8 nmol kg-1) reduced the objective signs of naloxone-precipitated withdrawal. Electrical stimulation of the locus ceruleus or naloxone treatment reduced the release of gamma-aminobutyric acid (GABA) from the exposed parietal cortex of morphine-tolerant guinea pigs. This reduction was not additive and was prevented by idazoxan (84 nmol kg-1), suggesting the involvement of alpha-2 receptors. Clonidine (7.5 nmol kg-1), too, reduced the release of GABA in morphine-tolerant animals. However, when tested jointly with naloxone, clonidine (7.5-112 nmol kg-1) induced alpha-1-mediated facilitation of GABA release (like that elicited in naive animals at 112-374 nmol kg-1) leaving the signs of withdrawal unchanged. This points to the stimulation of alpha-1 receptors highly responsive to this agonist (but not to locus ceruleus stimulation) during naloxone-precipitated withdrawal. In conclusion, chronic morphine treatment modifies the alpha-1- and alpha-2-mediated control of GABA and acetylcholine neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1988

Dose- and time-dependent hippocampal cholinergic lesions induced by ethylcholine mustard aziridinium ion: effects of nerve growth factor, GM1 ganglioside, and vitamin E.

Ethylcholine mustard aziridinium ion (ECMA) was infused intracerebroventricularly (icv) to rats followed by measurement of two markers of presynaptic cholinergic neurons, choline acetyltransferase (ChAT) activity and high affinity choline transport (HAChT), in the hippocampus and cortex. Bilateral icv administration of 1, 2, or 3 nmol of ECMA per side produced dose-dependent reductions in each marker in the hippocampus, but not in the cortex, one week after treatment. Reductions of 52% and 46% for ChAT activity and HAChT, respectively, were produced in the hippocampus by 3 nmol ECMA. Measurement of these two markers at different times after icv infusion of 2 nmol ECMA/ventricle revealed that the activity of ChAT was reduced to a greater extent than was HAChT in the hippocampus 1 day and 1, 2, 4, and 6 weeks after treatment. The maximal reductions of ChAT activity and HAChT (61% and 53%, respectively) were reached between 1 and 2 weeks after ECMA administration. There was no evidence of regeneration of either marker at 4 or 6 weeks posttreatment. HAChT and ChAT activity in the cortex were not altered at any of the posttreatment times examined. ECMA-induced deficits in hippocampal ChAT activity and HAChT were not counteracted by the following treatments: (i) daily administration of GM1 ganglioside (10 mg/kg, intraperitoneally (ip)) from the day prior to infusion of ECMA until 2 weeks later; (ii) daily administration of GM1 ganglioside between 2 and 6 weeks after infusion of ECMA; and (iii) icv administration of nerve growth factor (NGF) twice per week for 2 weeks after ECMA treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Inversion of the alpha-2 and alpha-1 noradrenergic control of the cortical release of acetylcholine and gamma-aminobutyric acid in morphine-tolerant guinea pigs.

In normal guinea pigs the adrenergic agonists clonidine and norepinephrine are known to inhibit directly the cortical outflow of acetylcholine (ACh) through alpha-2 receptors and to increase the cortical outflow of gamma-aminobutyric acid (GABA) through alpha-1 receptors. GABA, in turn, contributes to inhibit ACh through GABAA receptors. This scheme is changed drastically by morphine tolerance. In morphine-tolerant guinea pigs, clonidine at 7.5, 18.7 and 112 nmol/kg i.p. stimulates the cortical release of ACh through alpha-1 receptors. This effect is prevented by prazosin, 35.8 nmol/kg i.p. Clonidine reduces ACh release at high doses only (374 and 1122 nmol/kg i.p.). Furthermore, electrical stimulation of locus ceruleus also gives rise to a prazosin-sensitive increase in ACh release. In addition, locus ceruleus stimulation often causes behavioral activation rather than sedation. In morphine-tolerant guinea pigs, clonidine at 7.5 and 18.7 nmol/kg i.p. reduces GABA efflux through alpha-2 receptors, as the drug effect is prevented by idazoxan, 84 nmol/kg i.p. Clonidine increases GABA efflux at high doses only (112 and 374 nmol/kg i.p.). Locus ceruleus stimulation also gives rise to an idazoxan-sensitive reduction in GABA outflow. This new condition, evident after 7 days of morphine treatment, can be defined as inversion of the physiological norepinephrine control over ACh and GABA outflow and can represent a major part of the neurochemical derangement associated with opioid tolerance.

Acetylcholine↗

PubMed1987

Acetylcholine content in rat brain is elevated by status epilepticus induced by lithium and pilocarpine.

The effects of status epilepticus on the concentration, synthesis, release, and subcellular localization of acetylcholine, the concentration of choline, and the activity of acetylcholinesterase in rat brain regions were studied. Generalized convulsive status epilepticus was induced by the administration of pilocarpine to lithium-treated rats. The concentration of acetylcholine in the cortex, hippocampus, and striatum decreased prior to the onset of spike activity or status epilepticus. Once status epilepticus began, the concentration of acetylcholine increased over time in the cortex and hippocampus, reaching peak levels that were 461% and 304% of control levels, respectively, after 2 h of seizures. Such high in vivo levels of acetylcholine had not been reported previously following any treatment. During status epilepticus, the concentration of acetylcholine in the striatum returned to control levels after the initial depression, but did not accumulate to high levels as it did in the other two regions. The in vivo cortical efflux of acetylcholine was also increased during the seizures. Choline levels were increased by status epilepticus in all three brain regions. Inhibition of seizures by pretreatment with atropine blocked the increases of acetylcholine and choline. Synaptosomes prepared from the cortex and from the hippocampus of rats with status epilepticus had elevated concentrations of acetylcholine: in the hippocampus the acetylcholine was principally in the cytoplasmic fraction, whereas in the cortex the acetylcholine was elevated in both the cytoplasmic and the vesicular fractions. The extra acetylcholine was in a releasable compartment, since increased K+ in the media or ouabain increased the release of acetylcholine from cortical slices to a greater extent in tissue from seized rats than from controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1986

Cortical acetylcholine release is increased and gamma-aminobutyric acid outflow is reduced during morphine withdrawal.

The effects of naloxone on acetylcholine (ACh) and gamma-aminobutyric acid (GABA) outflow from the cerebral cortex of freely moving, morphine-dependent guinea-pigs was studied. The cortical efflux of ACh in chronically-treated guinea-pigs was about half of that of normal animals. GABA efflux was unaffected. During opioid withdrawal precipitated by naloxone (0.1-10 mg kg-1, i.p.) the guinea-pigs showed jumping, hyperactivity and wet dog shakes, the intensity of which was directly related to the dose of naloxone. The withdrawal syndrome was accompanied by a dose-dependent increase in ACh release and reduction in GABA outflow; ACh release was increased by naloxone at doses lower (0.1-3 mg kg-1) than those acting on GABA efflux (1-10 mg kg-1). Atropine (10 mg kg-1) and diazepam (5 mg kg-1) did not prevent GABA and ACh changes.

Acetylcholine↗

PubMedDate not supplied

Region-specific changes in prodynorphin mRNA and ir-dynorphin A levels after kindled seizures.

The opioid peptide dynorphin is thought to be implicated in specific types of seizures. In particular, complex partial seizures have been shown to cause release of dynorphin, activation of prodynorphin gene expression, and new peptide synthesis in the hippocampus. In this study, the kinetics of the seizure-induced changes in prodynorphin mRNA and ir-dynorphin A levels in the hippocampus have been compared with those induced in the temporal and frontal cortex, i.e., in other regions involved in the pathophysiology of complex partial seizures. Experiments have been run using kindling, one of the most valuable models of partial epilepsy. In the hippocampus (1) prodynorphin mRNA levels transiently increase (threefold) 1 h after kindled seizures, and return to baseline by 2 h, and (2) dynorphin A levels are slightly decreased at 1 h, but increase (twofold) at 2 h and return to baseline by 6 h. In the temporal and in the frontal cortex, a late (beginning at 2 h) and prolonged (up to 24 h) decrease in both prodynorphin mRNA and ir-dynorphin A levels have been observed. These data suggest that differential changes in dynorphin metabolism occur in different brain areas after seizures. The mechanisms and functional implications of this observation remain to be investigated.

Animals↗