Biomedical subjects

M Simonato

Publications and source records attributed to M Simonato.

At least 37 records · Page 2Linked to original sources

PubMed1998

Pyran derivatives. XX. 2-Aminochromone benzo-fused derivatives with antiproliferative properties.

The N-substituted 2-aminochromones 1 and their benzo-fused derivatives 2-4 described herein were mostly prepared by treating the corresponding (methylthio) derivatives 10-13 with an excess of the proper amines. Only the morpholino derivatives 3d and 4c were obtained from the reaction of the ethyl 3-morpholino-3-oxopropanoate/POCl3 reagent with 1-naphthol or 1-methyl-2-naphthol, respectively. The amino derivatives 1-4, as well as their methylthio analogues 10-13, were tested in vitro for their inhibitory activity on the infectivity of T2 bacteriophage, on the macromolecular synthesis in Ehrlich cells and on the clonal growth capacity of HeLa cells. Several of the angular or linear aminonaphthopyranones 2 and 3 or 4, respectively, and the (methylthio) derivatives 10, 11 and 13 induced a significant inhibition of DNA synthesis, but usually a clearly lower inhibition of clonal growth. Only the linear 2-amino-10-methyl-4H-naphtho[2,3-b]pyran-4-ones 4a and 4b significantly inhibited the clonal growth in HeLa cells and T2 bacteriophage infectivity, respectively.

Animals↗

PubMed1998

Synthesis and biological properties of a new series of N-pyrido substituted tetrahydrocarbazoles.

A series of methyl and ethyl quaternary pyridiniumtetrahydrocarbazoles was synthesized and studied in comparison with ellipticine, chosen as a reference. In general, their antiproliferative activity, tested in different biological substrates, appeared to be higher than that of the corresponding non-quaternarized compounds. This fact could be attributed to the introduction of a positive charge in the molecule, which can stabilize the molecular complex they form with DNA. In a prokaryotic system, the T2 bacteriophage, both quaternarized and non-quaternarized compounds inhibited its infectivity moderately, in a similar way to ellipticine. This effect seemed to be connected to a direct activity on the virions rather than on the indicator bacteria. In mammalian cells, the pyridiniumtetrahydrocarbazoles were more effective. In particular, they appeared to be very active in inhibiting DNA synthesis in Ehrlich ascites cells; some of them were as effective as ellipticine. However, pyridiniumtetrahydrocarbazoles were less active in comparison with ellipticine when their capacity for inhibiting the clonal growth in Chinese hamster ovary (CHO) cells was tested. A similar picture was obtained studying the formation of chromosome aberrations and of sister chromatid exchanges in the same cells. These different responses can be explained considering that the data on DNA synthesis reflect effects only on DNA replication within a short time, without considering any later consequences; on the contrary, in the long-term tests, other events, which lead to cell killing or genotoxicity, can take place. Pyridiniumtetrahydrocarbazoles damage DNA, inducing double-strand breaks efficiently. These observations, together with the data already obtained on unsubstituted derivatives, suggest the pyridiniumtetrahydrocarbazoles induce antiproliferative and genotoxic effects, very probably by inhibiting topoisomerase II.

Animals↗

PubMed1998

Different patterns of induction of FGF-2, FGF-1 and BDNF mRNAs during kindling epileptogenesis in the rat.

Neurotrophic factors (NTF) play important roles in the developing and in the adult brain. NTF involvement in neuronal plasticity is suggested by the modulation of NTF expression patterns in different physiological and pathological situations and by the effects they produce in the adult brain (e.g. axonal sprouting induction and neuroprotection). We used the RNAase protection assay to investigate the expression patterns of some NTFs during amygdala kindling, an animal model of epilepsy in which 'pathological' neuronal plasticity appears to occur. After a single kindling stimulation, fibroblast growth factor-2 (FGF-2) mRNA levels were increased in the hippocampus, the cortex and the hypothalamus, whereas they were not significantly altered in the thalamus and the striatum. A single stimulation did not alter fibroblast growth factor-1 (FGF-1) and brain-derived neurotrophic factor (BDNF) gene expression. Fully kindled animals, left unstimulated for a week, did not exhibit any alteration in the mRNA levels for any of the NTFs examined. However, in contrast with the effect of a single stimulation, amygdala stimulation of kindled animals (evoking a generalized tonic-clonic seizure) produced a great increase in hippocampal and cortical BDNF mRNA levels, but FGF-1 mRNA levels were not altered, and FGF-2 mRNA levels were significantly increased only in the cortex. These results suggest that different NTFs can be recruited at different stages of kindling epileptogenesis and, accordingly, may play different parts in the adaptive changes taking place in this experimental paradigm.

Amygdala↗

PubMed1998

Time- and region-specific variations in somatostatin release following amygdala kindling in the rat.

Somatostatin biosynthesis is activated during and following kindling epileptogenesis. The aim of this study was to investigate whether this phenomenon translates into enhanced release of the peptide and whether it is involved in kindling maintenance. A marked increase in somatostatin-like immunoreactivity (somatostatin-LI) was observed in hilar interneurons of the hippocampus and in their presumed projections to the outer molecular layer 1 week, but not 1 month, after the last kindled seizure. No overt changes were observed in the striatum or in the cortex. Compared with sham-stimulated controls, (a) in the hippocampus, high-K+-evoked somatostatin-LI release was unchanged in synaptosomes taken from rats killed 7 days after the last kindled seizure but was bilaterally reduced after 30 days; (b) in the striatum, it was increased (mainly ipsilaterally to stimulation) 7, but not 30, days after the last seizure; and (c) in the cortex, somatostatin-LI release was bilaterally increased in synaptosomes taken from kindled rats 30, but not 7, days after the last seizure. This study shows that distinct changes occur in synaptosomal somatostatin-LI release after kindling acquisition, depending on the brain area analyzed and on the time elapsed from the last generalized seizure.

Amygdala↗

PubMed1997

Prostaglandin F2alpha is required for NMDA receptor-mediated induction of c-fos mRNA in dentate gyrus neurons.

Activation of NMDA receptors has been linked to a diversity of lasting physiological and pathological changes in the mammalian nervous system. The cellular and molecular mechanisms underlying permanent modifications of nervous system structure and function after brief episodes of neuronal activity are unknown. Immediate-early genes (IEGs) have been implicated in the conversion of short-term stimuli to long-term changes in cellular phenotype by regulation of gene expression. The intracellular signaling pathways coupling activation of receptors at the cell surface with induction of IEGs in the nucleus are incompletely understood. NMDA produces a striking increase in the IEG c-fos in dentate gyrus (DG) neurons in vitro; this induction is dependent, in part, on the arachidonic acid cascade. Here we show that NMDA receptor activation triggers the synthesis of the prostaglandins PGF2alpha and PGE2, but not PGD2, in rat cerebral cortical neurons in vitro. We further demonstrate that PGF2alpha, but not PGE2 or PGD2, is necessary but not sufficient for NMDA induction of c-fos mRNA in DG neurons. These findings provide insight into the molecular events coupling activation of the NMDA receptor with regulation of the IEG c-fos and identify the diffusable messenger PGF2alpha as obligatory for NMDA receptor-mediated transcription of a nuclear IEG.

Animals↗

PubMed1997

Characterization of glutamate and [3H]D-aspartate outflow from various in vitro preparations of the rat hippocampus.

The characteristics of high-K+ and electrically evoked endogenous glutamate and [3H]D-aspartate release have been studied in multiple in vitro preparations of the rat hippocampus (transverse slices, granule cells cultures, synaptosomes and mossy fibre synaptosomes) under similar experimental conditions. High external K+ concentrations evoked [3H]D-aspartate and endogenous glutamate overflow in a concentration-dependent manner in all preparations (except it was not possible to measure endogenous glutamate outflow from granule cells). This effect was tetrodotoxin-insensitive but partially calcium-dependent. In slices, field electrical stimulation evoked an overflow of endogenous glutamate, but not of [3H]D-aspartate, in a frequency-dependent manner. This effect was concentration-dependently amplified by the glutamate uptake inhibitor L-trans-pyrrolidine-2,4-dicarboxylic acid (t-PDC). The electrically evoked glutamate overflow in the presence of t-PDC was tetrodotoxin-sensitive and calcium-dependent. In primary dentate gyrus cell cultures, electrical stimulation evoked an overflow of [3H]D-aspartate in a frequency-dependent manner, while endogenous glutamate outflow was not detectable. This effect could be inhibited by tetrodotoxin and by the N-type calcium channel blocker omega-conotoxin GVIA. Finally, the effect of adenosine has been studied in order to assess the pharmacological modulability of [3H]D-aspartate and endogenous glutamate stimulation-induced overflow. Adenosine was found to inhibit 35 mM K(+)- and 20 Hz electrical stimulation-induced [3H]D-aspartate and endogenous glutamate overflow. These effects were all prevented by the A1 receptor antagonist 8-cyclopentyl-1,3-dimethylxanthine (CPT). These data are in line with the hypothesis that reuptake plays a role in regulating glutamate release, and that [3H]D-aspartate represents a valid marker of endogenous glutamate under most (but not all) experimental conditions.

Adenosine↗

PubMed1996

Biotin deficiency facilitates kindling hyperexcitability in rats.

Biotin-deficient conditions are frequently associated with epileptic disorders. Biotin deficiency may be caused by long-term treatment with anticonvulsants or excessive ingestion of avidin. Absence of biotinidase activity can also lead to biotin deficiency, and is characterized by developmental delay as well as neurological and dermatological abnormalities. Because seizures are one of the most frequent signs of the latter, biotin-deficient conditions could conceivably facilitate convulsive disorders. To test this hypothesis, we investigated the occurrence of a latent kindling hyperexcitability in biotin-deprived rats. In these animals, duration of after-discharge on the first stimulation was longer at threshold amplitude, kindling development through its early stages was accelerated and duration of the forelimb clonus of fully kindled seizures was increased. Biotin deprivation in mixed cerebellar granule cell-astrocyte cultures also produced a tetrodotoxin-sensitive delayed loss of the glutamatergic neuronal population. The data thus support a facilitatory role for biotin-deficient conditions in convulsive disorders.

Animals↗

PubMed1996

The neurochemistry of morphine addiction in the neocortex.

Different strategies have been used in an attempt to understand the neurobiology of opioid addiction. Here, Michéle Simonato initially discusses the identification of key anatomical areas involved in the phenomenon and purposes an explanation of opioid addiction based on the theory of complexity. The variable importance of direct and indirect effects in phenotypically different neuronal populations can imply differences in the adaptive changes that occur with chronic morphine exposure. Opioid addiction is therefore proposed as a complex multicellular event, where individual neurones differentially adapt both on the basis of the signals they receive and of their second messengers and genetic programmes.

Animals↗

PubMed1996

Dynorphin and epilepsy.

Studies on dynorphin involvement in epilepsy are summarised in this review. Electrophysiological, biochemical and pharmacological data support the hypothesis that dynorphin is implicated in specific types of seizures. There is clear evidence that this is true for complex partial (limbic) seizures, i.e. those characteristic of temporal lobe epilepsy, because; (1) dynorphin is highly expressed in various parts of the limbic system, and particularly in the granule cells of the hippocampus; (2) dynorphin appears to be released in the hippocampus (and in other brain areas) during complex partial seizures; (3) released dynorphin inhibits excitatory neurotransmission at multiple synapses in the hippocampus via activation of kappa opioid receptors; (4) kappa opioid receptor agonists are highly effective against limbic seizures. Data on generalised tonic-clonic seizures are less straightforward. Dynorphin release appears to occur after ECS seizures and kappa agonists exert a clear anticonvulsant effect in this model. However, more uncertain biochemical data and lack of efficacy of kappa agonists in other generalised tonic-clonic seizure models argue that the involvement of dynorphin in this seizure type may not be paramount. Finally, an involvement of dynorphin in generalised absence seizures appears unlikely on the basis of available data. This may not be surprising, given the presumed origin of absence seizures in alterations of the thalamo-cortical circuit and the low representation of dynorphin in the thalamus. In conclusion, it may be suggested that dynorphin plays a role as an endogenous anticonvulsant in complex partial seizures and in some cases of tonic-clonic seizures, but most likely not in generalised absence. This pattern of effects may coincide with the antiseizure spectrum of selective kappa agonists.

Animals↗

PubMed1996

Kindled seizure-induced c-fos and prodynorphin mRNA expressions are unrelated in the rat brain.

Levels of mRNA for c-fos and prodynorphin were studied by in situ hybridization in adjacent coronal sections taken from kindled rats 30-60 min after the last seizure. Within this time frame, expression of both genes was induced in multiple brain areas. Anatomical colocalization of the induced gene expressions was found in the hippocampus. Induction of c-fos in the dentate gyrus was bilateral and symmetrical in a subgroup of rats, ipsilateral in another subgroup and absent in a third subgroup. However, no relative increase was observed in the ipsilateral compared with the contralateral prodynorphin expression in the dentate gyrus when c-fos expression was induced ipsilaterally only. These observations suggest that, at variance with other experimental situations, Fos is not involved in the mechanisms of kindled seizure-induced activation of prodynorphin transcription in the rat forebrain.

Animals↗

PubMed1995

Early changes in prodynorphin mRNA and ir-dynorphin A levels after kindled seizures in the rat.

Prodynorphin mRNA and immunoreactive dynorphin A (ir-dynorphin A) levels were measured in different brain areas at various time points after amygdala kindled seizures. In the hippocampus, striatum and hypothalamus, prodynorphin mRNA levels were not significantly changed in kindled rats (killed 1 week after the last stimulus-evoked seizure), but they were significantly increased 1 h after seizures. The relative increase was the highest in the hippocampus (approximately 3-fold). In the brainstem, midbrain and cerebral cortex no changes in prodynorphin mRNA were detected in kindled rats, 1 h or 1 week after a kindled seizure. ir-Dynorphin A levels were significantly reduced in the hippocampus and in the striatum of kindled rats, as well as 5 and 60 min after kindled seizures, but they were increased back to control levels after 120 min. In the hypothalamus, ir-dynorphin A levels were significantly increased 120 min after a kindled seizure. ir-Dynorphin A levels were also significantly reduced in the brainstem and in the frontal, parietal and temporal cortex 120 min, but not 5 or 60 min, after a kindled seizure. Taken together, these data support the hypothesis that the dynorphinergic system is activated after amygdala kindled seizures, with different kinetics in different brain areas.

Amygdala↗

PubMed1995

Changes in [3H]-UK 14304 binding to alpha 2-adrenoceptors in morphine-dependent guinea-pigs.

1. The aim of this study was to investigate the effect of a noradrenergic input in the cortex of morphine-dependent animals. Binding of the alpha 1-adrenoceptor ligand [3H]-prazosin did not change in cortical membranes taken from morphine-dependent as compared to control guinea-pigs. However, binding of the alpha 2-adrenoceptor ligand [3H]-UK 14304 showed decreased KD (-30%) in the absence of significant changes in Bmax, either in cortical membranes or in synaptosomes. 2. Several characteristics of this phenomenon were identified. First, it occurs in a time-dependent fashion, in that it takes 5 days of chronic morphine treatment to start developing. Second, it can be observed after acute administration of high doses of morphine (100 mg kg-1). Third, it does not require a connection with the locus coeruleus or with other subcortical structures, in that it can be reproduced in vitro in isolated cortical slices. Fourth, it requires the integrity of cortical structures, since it cannot be reproduced in vitro in cortical synaptosomes. 3. Release studies were run to attempt identification of a functional correlate of the above observations. No changes were observed in the ability of the alpha 2-adrenoceptor agonist UK 14304 to inhibit 35 mM K(+)-evoked [3H]-noradrenaline outflow from cortical synaptosomes taken from morphine-dependent as compared to control guinea-pigs. However, a large decrease in the IC50 of UK 14304 for the inhibition of 35 mM K(+)-evoked [3H]-gamma-aminobutyric acid ([3H]-GABA) outflow (41 vs. 501 nM) was observed in morphine-dependent as compared to control animals. 4. These data suggest that, in the guinea-pig, chronic morphine treatment is associated with a shift from a low to high affinity agonist state in alpha 2-adrenoceptors on cortical GABA terminals.

Adrenergic alpha-Agonists↗

PubMed1995

5-Hydroxytryptamine-mediated effects of nicotine on endogenous GABA efflux from guinea-pig cortical slices.

1. The effect of nicotine on endogenous basal GABA outflow was studied in guinea-pig cerebral cortex slices. 2. Nicotine 1.86-18.6 mumol l-1 significantly decreased the basal, tetrodotoxin-sensitive GABA efflux, whereas at higher concentrations (186-620 mumol l-1) nicotine increased it. The inhibition was prevented by mecamylamine while the facilitation was blocked by mecamylamine, (+)-tubocurarine and tetrodotoxin. 3. The effect of nicotine was due to an indirect 5-hydroxytryptaminergic action. In fact, MDL 72222 (1 mumol l-1) completely prevented the alkaloid inhibition and methysergide (1 mumol l-1) reversed the facilitation into inhibition; concomitant treatment with methysergide and MDL 72222 antagonized the effect of nicotine at 186 mumol l-1 4. Lower concentrations of 5-HT (3-10 mumol l-1) decreased, whereas higher concentrations (30-100 mumol l-1) increased, spontaneous GABA outflow. The inhibition of GABA efflux was prevented by MDL 72222 whereas the facilitation was reversed by methysergide (1 mumol l-1) into inhibition, and prevented by MDL 72222 1 mumol l-11. 5. These results suggest that, by activating nicotinic receptors present on 5-hydroxytryptaminergic terminals, nicotine releases 5-HT which, in turn, inhibits or increases the secretory activity of cortical GABA interneurones via 5-HT3 and methysergide-sensitive receptors, respectively.

Animals↗

PubMed1995

Differences in the anatomic distribution of immediate-early gene expression in amygdala and angular bundle kindling development.

Kindling is a model in which fleeting changes of neuronal activity produce a lifelong modification of neuronal structure and function in the mature nervous system. Immediate-early genes (IEGs) such as c-fos have been implicated as a causal link in the chain of molecular events coupling fleeting pathologic activity to lasting hyperexcitability. Identification of the brain structures exhibiting IEG expression during the evolution of kindling is necessary to guide investigations of the phenotypic consequences. We used in situ hybridization histochemistry to identify the structures exhibiting expression of multiple IEGs during the evolution of amygdala kindling and compared this to the pattern following angular bundle kindling. The principal findings included that: (1) generalized limbic and clonic motor (class 5) kindled seizures evoked by stimulation of one amygdala induced the expression of IEGs in a small subset of limbic structures with remarkable symmetry between the two hemispheres; (2) the anatomic extent of seizure-evoked expression of c-fos mRNA expanded progressively following focal limbic and motor (classes 0-3) seizures during the development of amygdala kindling; c-fos mRNA was detected first ipsilaterally in AM, ACO, and PC and with higher-class seizures in hippocampal formation and homologous structures contralaterally, and (3) class 5 seizures evoked by stimulation of two different sites in the limbic system (amygdala or angular bundle) induced IEG expression in distinct but partially overlapping anatomic structures. We propose that synaptic activation of glutamate receptors contributes to the expression of these diverse IEGs throughout the forebrain. The findings provide a constellation of anatomic structures in which to investigate the structural and functional consequences of IEG expression.

Amygdala↗

PubMed1995

Synthesis and photobiological properties of 3-acylangelicins, 3-alkoxycarbonylangelicins and related derivatives.

Convenient synthesis of 3-acyl-2H-furo[2,3-h]-1-benzopyran-2-ones, esters of 2-oxo-2H-furo[2,3-h]-1-benzopyran-3-carboxylic acid and 2H-furo[2,3-h]-1-benzopyran-3-carboxamides was accomplished via aromatization of the adducts obtained by a reaction between (E)-5-dimethyl-aminomethylene-6,7-dihydrobenzofuran-4(5H)-one and the appropriate acylacetate or dialkyl malonate. These compounds are angelicin derivatives which were prepared with the aim of obtaining intrinsically monofunctional drugs for photochemotherapy, with only one photoreactive site in their molecule. The new angelicins appear to be free of the known phototoxicity of furocoumarins on the skin and at a genetic level. The 3-carboxylic esters showed significant antiproliferative activity in Ehrlich ascites cells and T2 bacteriophage; the other derivatives were only slightly effective. The features of these compounds are such that they represent a new model for non-toxic agents for photochemotherapy.

Animals↗

PubMed1994

Adenosine A1 receptors in the rat brain in the kindling model of epilepsy.

Adenosine and adenosine analogues have potent anticonvulsant effects on various seizure models, including kindling, an animal model of temporal lobe epilepsy. It is now reported that binding of a specific ligand (cyclohexyladenosine) to adenosine A1 receptors is not changed in the cerebral cortex of kindled rats. However, the affinity of cyclohexyladenosine to adenosine receptors is significantly increased in the hippocampus. In addition, cyclohexyladenosine is slightly more potent to inhibit [3H]D-aspartate outflow from hippocampal synaptosomes taken from kindled than from control rats. Taken together, these data suggest that an increased affinity of adenosine to A1 receptors may play a role in the anticonvulsant effect of adenosine A1 analogues in the kindling model.

Adenosine↗

PubMed1994

Effect of arachidonic acid on [3H]D-aspartate outflow in the rat hippocampus.

The aim of this study was to investigate the effect of arachidonic acid on [3H]d-aspartate outflow in rat hippocampus synaptosomes and slices. Arachidonic acid 1) increased basal outflow of [3H]d-aspartate in both synaptosomes and slices, and 2) increased K(+)-evoked overflow in slices but not in synaptosomes. The latter effect was dependent (at least in part) on arachidonic acid metabolism, most likely mediated by lipo-oxygenase metabolites and free radical production. It was prevented by nordihydroguairetic acid but not by indomethacin, and was significantly reduced by free radical scavengers (superoxide-dismutase and catalase). This effect was dependent upon stimulation since it could not be observed after a continuous perfusion of arachidonic acid in the absence of stimulation. Furthermore, it was long-lasting since a 30 min perfusion of arachidonic acid was sufficient to exert a significant effect on a stimulation following termination of the application.

Animals↗

PubMed1993

Noradrenergic modulation of gamma-aminobutyric acid outflow from the human cerebral cortex.

The noradrenergic modulation of endogenous gamma-aminobutyric acid (GABA) outflow from slices and synaptosomes prepared from human cerebral cortex biopsies has been studied. GABA outflow was responsive to depolarizing stimuli such as ouabain and high potassium. Basal GABA outflow in slices, but not in synaptosomes, appeared to be largely dependent upon neuronal activity, being prevented by tetrodotoxin (TTX). 10 mM K(+)-evoked outflow in synaptosomes also proved to be TTX sensitive. Norepinephrine (NE) concentration dependently increased basal GABA outflow both in slices and synaptosomes. This effect was alpha 1-adrenoreceptor-mediated because it was prevented by a selective antagonist of the alpha 1-adrenoreceptor class (prazosin) but not by the alpha 2 antagonist idazoxan. However, an alpha 2-mediated inhibitory modulation was also present in the preparations used, since (1) in slices, NE significantly inhibited GABA outflow in the presence of prazosin; (2) in synaptosomes, NE significantly inhibited 10 mM K(+)-evoked outflow in the presence of prazosin. Both of these effects were prevented by idazoxan. No beta-adrenoreceptor modulation could be demonstrated. A comparison between species was also conducted. The response to ouabain and to TTX proved similar in human, rat and guinea-pig cerebral cortex. In the most simple tissue preparation used (synaptosomes), a close similarity between the three species could be observed. In all species, NE stimulated basal GABA outflow, an effect prevented by prazosin. This suggests a predominant alpha 1-adrenoreceptor-mediated stimulatory effect. In a more complex preparation (slices), differences between species could be demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Agonists↗