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M A Sortino

Publications and source records attributed to M A Sortino.

At least 37 records · Page 2Linked to original sources
PubMed1996

Different responses of gonadotropin-releasing hormone (GnRH) release to glutamate receptor agonists during aging.

GnRH release from hypothalamic explants from young and aged male Wistar-Kyoto rats was evaluated following stimulation with glutamate receptor agonists. Glutamate stimulated GnRH release to a similar extent in hypothalami from young and old animals, whereas N-methyl-D-Aspartate (NMDA) and kainate appeared more efficacious in young and old rats, respectively. Old rats were unable to respond to a maximal stimulating concentration of glutamate when they had been previously exposed to a challenge with the same agent. These results demonstrate that responsiveness to glutamate receptor agonists changes during aging, suggesting the involvement of distinct glutamate receptors in the control of GnRH release during different phases of lifespan.

Age Factors↗
PubMed1996

Immortalized hypothalamic neurons express metabotropic glutamate receptors positively coupled to cyclic AMP formation.

We have characterized the expression pattern and pharmacological profile of activation of metabotropic glutamate receptors (mGluRs) in immortalized, gonadotropin releasing hormone (GnRH)-secreting GT1-7 cells, which represent a homogeneous cellular population of hypothalamic origin. These cells are known to respond to the mGluR agonist (1S,3R)-cyclopentanedicarboxylic acid (1S,3R-ACPD) with increased GnRH release. To establish which specific mGluR subtypes are expressed by GT1-7 cells, we used polyclonal antibodies raised against non-conserved regions of the carboxy-terminal domains of individual subtypes. The selectivity of these antibodies was tested in HEK 293 cells transiently transfected with each mGluR subtype. GT1-7 cells stained positively for the subtypes mGluR1a, -1b and -5 (belonging to group I mGluR2/3 (group II) and mGluR7 (group III). Agonists of group I mGluRs, including 1S,3R-ACPD, activated phosphoinositide hydrolysis in GT1-7 cells. This effect, however, was manifested only when cell density was low, and it disappeared when cells reached confluence. Stimulation of phosphoinositide hydrolysis could not therefore have been related to hormone secretion because 1S,3R-ACPD effectively released GnRH in confluent cultures. We then focused on group II and III mGluRs, which in transfected cells are negatively linked to adenylate cyclase activity. Unexpectedly, however, agonist which preferentially activate group II and III mGluRs increased both basal and forskolin-stimulated cAMP accumulation in GT1-7 cells. Stimulation of cAMP accumulation by mGluR agonists was not prevented by enzymatic depletion of endogenous adenosine, but was obliterated when cells were incubated with agonists of receptors positively coupled to adenylate cyclase, such as beta-adrenergic and prostaglandin E2 receptors. These results suggest that GT1-7 cells express a novel mGluR subtype positively coupled to adenylate cyclase, which shares the same transduction pathway of other classical receptors coupled with a Gs-type of GTP-binding protein.

Animals↗
PubMed1996

Neuroprotective effect of insulin-like growth factor I in immortalized hypothalamic cells.

The neuroprotective action of insulin-like growth factor I (IGF-I) was tested in immortalized hypothalamic GT1-7 cells exposed to reduced glutathione depleting agents, which cause oxidative stress and cell death. The extent of cell survival was assessed by either using the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide cytotoxicity assay or counting at the fluorescence microscope GT1-7 cells prelabeled with fluorescent dyes selective for viable and dead cells. Treatments with buthionine sulfoximine (500 microns), diethylmaleate (1 mM), and ethacrynic acid (200 microns) caused diffuse GT1-7 cell death (40-60%). Exposure of the same cells to IGF-I (either before or concomitant to the toxic agent, depending on the drug used) significantly prevented neuronal death. This effect was rapid, concentration-dependent, maximal at concentrations of 25-50 ng/ml, and mimicked by IGF-II, fibroblast growth factor, and the potent antioxidant idebenone. In contrast, IGF-I, as well as idebenone, were completely ineffective in antagonizing the toxic effect produced by different concentrations of menadione. In conclusion, the present data demonstrate a protective role for IGF-I against glutathione depleting agents-induced damage in GT1-7 cells suggesting an antioxidant action of this growth factor in hypothalamic neurons.

Animals↗
PubMed1995

The inhibition of peroxide formation as a possible substrate for the neuroprotective action of dihydroergocryptine.

Dihydroergocryptine is an ergot alkaloid endowed with pharmacological actions mainly related to its dopaminomimetic activity. Free radical formation and subsequent lipid peroxidation had been postulated to participate broadly to the pathogenesis of tissue injury, including the brain injury induced by hypoxia, ischemia or trauma, as well as in the physiopathology of chronic neurodegenerative diseases, such as Parkinson's disease. Here we report that dihydroergocryptine protects cultured rat cerebellar granule cells against age-dependent and glutamate-induced neurotoxicity. Dihydroergocryptine antagonizes in fact both the neuronal death produced by acute exposure to a toxic glutamate concentration as well as the normal age-dependent degeneration in culture, presumably by exerting a scavenger action. This effect does not seem mediated entirely by interactions with the dopamine D2 receptors. The neuroprotective action of dihydroergocryptine suggests a potential usefulness in halting the acute and chronic neurodegenerative diseases related to excitotoxic damage and free radical formation, including Parkinson's disease.

Animals↗
PubMed1994

Protective action of idebenone against excitotoxic degeneration in cultured cortical neurons.

The novel free radical scavenger and electron-trapping agent, idebenone, protects cultured cortical neurons against necrotic degeneration induced by either a brief exposure to N-methyl-D-aspartate (NMDA) or a prolonged exposure to kainate. As opposed to the NMDA receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]- cyclohepten-5,10-imine hydrogen maleate (MK801), idebenone rescued cortical neurons even when applied 30 min after the NMDA pulse, suggesting that the drug interferes with the chain of toxic reactions triggered by an excessive stimulation of excitatory amino acid receptors.

Animals↗
PubMed1994

Chronic L-alpha-glyceryl-phosphoryl-choline increases inositol phosphate formation in brain slices and neuronal cultures.

Repeated, but not single injections of L-alpha-glyceryl-phosphorylcholine (alpha GPC) significantly increased basal [3H]inositol monophosphate (InsP) formation in hippocampal, cortical, and striatal slices of male rats. The effect was dose-dependent and was accompanied by an increased incorporation of [3H]inositol into the phospholipid fraction. Incubation of brain slices with different neurotransmitter antagonists, such as atropine, prazosin, or L-2-amino-4-phosphonobutanoate (L-AP4) did not modify the increase in [3H]InsP formation produced by alpha GPC, suggesting that the effect is not mediated by an increased availability of a specific neurotransmitter. Similar results were obtained in cerebellar and cortico-striatal neurones in primary culture exposed to daily addition of alpha GPC since the second day of maturation in vitro. We suggest that alpha GPC treatment may result in an increased rate of phospholipid synthesis, including the phosphoinositides available for signal transduction at central nervous system level.

Animals↗
PubMed1994

Involvement of nitric oxide in the regulation of gonadotropin-releasing hormone release from the GT1-1 neuronal cell line.

A role for nitric oxide (NO) in the regulation of hypothalamic neurohormone secretion has been suggested. The aim of the present study was to establish a direct involvement of this novel intracellular regulatory molecule in the control of GnRH release. For this purpose, the GT1-1 GnRH-secreting continuous cell line was treated with various agents that can modify the endogenous NO synthase activity or, alternatively, with substances that can liberate NO, mimicking an increased concentration of this molecule in the cell. Treatment of GT1-1 cells with increasing concentrations of L-arginine, the direct precursor of NO, produced a marked reduction of norepinephrine-stimulated GnRH release despite a lack of effect on basal secretion. Similarly, the NO donors SIN-1 and acidified NaNO2 potently reduced basal as well as KCl-stimulated GnRH secretion. Conversely, sodium nitroprusside caused a significant inhibition of KCl-stimulated, but not basal, GnRH secretion. Addition of these agents to GT1-1 cells resulted in a marked increase in intracellular cGMP accumulation. Addition of the NO synthase inhibitors N-nitro-L-arginine and N-nitro-L-arginine methyl ester stimulated basal GnRH secretion without modifying norepinephrine- or KCl-stimulated release. In addition, treatment of GT1-1 cells with both L-arginine analogs produced a significant inhibition of the basal cGMP concentration. Together, these data suggest an inhibitory role for NO in the control of GnRH secretion from GT1-1 cells.

Amino Acid Oxidoreductases↗
PubMed1993

Protection by dihydroergocryptine of glutamate-induced neurotoxicity.

Dihydroergocryptine is a hydrogenated ergot derivative with pharmacological actions mainly related to its dopaminomimetic activity. Here we report that dihydroergocryptine can protect cultured rat cerebellar granule cells against glutamate-induced neurotoxicity, assessing cell viability with the fluorescein diacetate-propidium iodide technique. Dihydroergocryptine antagonized both the neuronal death produced by acute exposure to a toxic glutamate concentration as well as the normal age-dependent degeneration in culture. The effect of dihydroergocryptine might be mediated by a scavenger action as suggested by the fact that the compound in a concentration-dependent manner reduced the formation of intracellular peroxides produced in cerebellar granule cells by exposure to 100 microM glutamate. This action is apparently not mediated entirely by interactions with the dopamine D2 receptors. The neuroprotective action suggests that dihydroergocryptine might be a potential useful drug in the therapy and/or prophylaxis of acute and chronic neurodegenerative diseases related to excitotoxic damage.

Aging↗
PubMed1993

Comparative effects of eel calcitonin, salmon calcitonin and [Asu1,7]eel calcitonin on hypophyseal and osteoblastic function.

Three different calcitonins: salmon calcitonin, eel calcitonin and the semi-synthetic analog [Asu1,7]eel calcitonin have been evaluated for their ability to affect phosphoinositide hydrolysis in primary cultures of anterior pituitary cells and in the osteoblast-like UMR-106 cells. In both cellular systems a repeated treatment with any form of calcitonin induced an inhibition of inositol phospholipid turnover. Eel calcitonin and its analog were always more potent than salmon calcitonin, but the efficacy of the three polypeptides was comparable. In cultured anterior pituitary cells, the inhibitory effect on phosphoinositide hydrolysis observed after chronic treatment with calcitonin was accompanied by a reduction of prolactin release. In contrast, a single treatment of cultured anterior pituitary cells with eel calcitonin or its analog [Asu1,7]eel calcitonin induced an increase of inositol phosphate accumulation, while salmon calcitonin was inactive. Accordingly, eel and [Asu1,7]eel calcitonin, but not salmon calcitonin, induced a slight but significant stimulation of prolactin secretion. In UMR-106 cells, the three calcitonins exhibited similar potency and efficacy in reducing parathyroid hormone-stimulated 4 beta[3H]-phorbol-12,13-dibutyrate ([3H]PdBu) binding, an indirect index of protein kinase C activation. Taken together, these results suggest that, either at the pituitary or in osteoblast-like cells, some of the effects exerted by calcitonin may be ascribed to an interference with the intracellular events initiated by modulation of phosphoinositide turnover.

Analysis of Variance↗
PubMed1992

Thyrotropin releasing hormone (TRH) and its analog, RGH-2202, accelerate maturation of cerebellar neurons in vitro.

We have studied the "trophic" action of thyrotropin releasing hormone (TRH) in cultured cerebellar granule cells, a pure and homogeneous population of glutamatergic neurons. As an index of neuronal maturation, we have measured the uptake of D-[3H]aspartate (a non-metabolizable analog of glutamate) at different days of maturation in vitro (DIV). In control cultures, D-[3H]Aspartate increased linearly during maturation reaching plateau values between 7 and 9 DIV; daily addition of TRH tartrate (TRH-t) or RGH-2202 (a TRH analog) accelerated in a concentration-dependent manner the maturation profile of D-[3H]aspartate uptake. This effect was more pronounced for RGH-2202: in cultures treated daily with RGH-2202, D-[3H]aspartate uptake was fully expressed after 3 DIV. Neither TRH-t nor RGH-2202 significantly increased D-[3H]aspartate uptake in mature cells, excluding a direct action on the glutamate transport system. Both compounds specifically potentiated the increase in [3H]inositol monophosphate formation (but not the stimulation of 45Ca2+ influx) induced by N-methyl-D-aspartate (NMDA) receptor agonists, without affecting the stimulation of inositol phospholipid hydrolysis by quisqualate or carbamylcholine. We suggest that, in cultured cerebellar granule cells, TRH and RGH-2202 enhance the trophic action of endogenous glutamate by amplifying some of the intracellular events that follow the influx of extracellular Ca2+ through NMDA-gated ion channels.

Analysis of Variance↗
PubMed1992

Ipriflavone inhibits phosphoinositide hydrolysis and Ca2+ uptake in the osteoblast-like UMR-106 cells.

The mechanism of action of ipriflavone, an isoflavone derivative, was studied in the osteoblastic-like UMR-106 cell line. Ipriflavone affected both phosphoinositide hydrolysis and 45Ca2+ uptake. A repeated treatment of UMR-106 cells (once a day, for 3 days) with ipriflavone decreased, in a concentration-dependent manner, [3H]inositol monophosphate accumulation. This effect was also achieved after single addition of high concentrations of ipriflavone or 100 nM [Asu1,7]eel-calcitonin, a semi-synthetic analog of eel calcitonin. When repeatedly added to UMR-106 cells, 17 beta-estradiol produced a marked inhibition of [3H]inositol monophosphate accumulation, an effect which appeared significant only at a concentration of 1 microM and which was accompanied by a reduced incorporation of [3H]inositol into membrane phospholipids. A repeated treatment with ipriflavone reduced 45Ca2+ uptake as well. This effect was observed also after a single addition of [Asu1,7]eel-calcitonin but not following single or repeated treatment with 17 beta-estradiol. The present data indicate the osteoblast as a direct and specific target for ipriflavone and suggest that this compound may share intracellular transducing mechanisms with other antiosteoporotic hormones such as estrogen and calcitonin.

Calcitonin↗
PubMed1992

Developmental changes in the modulation of cyclic AMP formation by the metabotropic glutamate receptor agonist 1S,3R-aminocyclopentane-1,3-dicarboxylic acid in brain slices.

Metabotropic glutamate receptors (mGluRs) have been recently described as a family of guanine nucleotide-binding regulatory protein-coupled receptors with multiple signal transduction pathways. At least one of these receptors appears to be negatively coupled to adenylyl cyclase when stably expressed in transfected cells. We have studied how activation of native mGluRs modulates cyclic AMP (cAMP) formation in brain slices prepared from rats at different ages. 1S,3R-1-Aminocyclopentane-1,3-dicarboxylic acid (1S,1R-ACPD), a selective agonist of mGluRs, slightly increased basal cAMP formation but reduced forskolin-stimulated cAMP formation in adult hippocampal slices, in agreement with previous results. The action of 1S,3R-ACPD on basal cAMP formation was not reproduced by the ionotropic receptor agonists N-methyl-D-aspartate, kainate, and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate and was antagonised by L-2-amino-3-phosphonopropionate (L-AP-3). L-AP-3, however, did not prevent but rather mimicked the inhibitory action of 1S,3R-ACPD on forskolin-stimulated cAMP formation. In hippocampal slices from 1-, 8-, or 15-day-old rats, 1S,3R-ACPD increased basal cAMP formation but failed to reduce the action of forskolin. A similar development pattern of modulation was observed in hypothalamic slices with the difference that 1S,3R-ACPD did not stimulate basal cAMP formation in the hypothalamus of adult animals. These results suggest that inhibition of forskolin-stimulated cAMP formation by 1S,3R-ACPD is mediated by a specific mGluR subtype that is preferentially expressed in the adult.

Aging↗
PubMed1992

Development profile of metabotropic glutamate receptor mRNA in rat brain.

We have studied the expression of metabotropic glutamate receptor (mGluR) mRNA by Northern blot analysis with a specific cDNA probe (the pmGR1 probe). In 1-day-old rats, the steady state levels of mRNA were higher in the hypothalamus and olfactory bulb, with intermediate levels in the cerebellum and low levels in the hippocampus and cerebral cortex. In the olfactory bulb, hypothalamus, and cerebral cortex, the expression of mGluR mRNA remained constant at 8 and 30 days of postnatal life. In contrast, in the cerebellum and hippocampus, mRNA levels increased progressively with age. There was no correlation between levels of mGluR mRNA and stimulation of polyphosphoinositide hydrolysis by 1-aminocyclopentane-1S,3R-dicarboxylic acid (trans-ACPD), which was much greater in brain slices from 8-day-old rats and was nearly absent in the adult cerebellum and olfactory bulb, where we have found the highest levels of mRNA. In addition, mGluR mRNA was detectable in cultured cerebellar granule cells but not in cultured neurons from cerebral hemispheres or in cultured astrocytes, which responded to trans-ACPD with an increased formation of [3H]inositol monophosphate. The discrepancies between levels of mGluR mRNA detected with the pmGR1 probe and trans-ACPD-stimulated polyphosphoinositide hydrolysis suggest either that different subtypes of mGluRs exist or that mRNA levels are not critical for the dynamic changes in the activity of mGluRs during development.

Aging↗
PubMed1991

'Metabotropic' glutamate receptors in rat hypothalamus: characterization and developmental profile.

Excitatory amino acids (EAAs) are known to stimulate neurohormone release through the activation of ion-channel-linked receptors (ionotropic receptors). Here we report that a receptor for EAAs linked to polyphosphoinositide hydrolysis (metabotropic receptor) is also present at the hypothalamus where its expression is developmentally regulated. Stimulation of [3H]inositolmonophosphate ([3H]InsP) formation by quisqualate (EC50 = 1.5 microM), ibotenate (EC50 = 100 microM) and trans-1-amino-1,3-cyclopentanedicarboxylic acid (t-ACPD; EC50 = 30 microM) is extremely high (up to 50-fold) in the first 10 days of postnatal life, progressively declines during maturation and is virtually absent in the adult. Stimulation of phosphoinositide hydrolysis by quisqualate, ibotenate and t-ACPD is more pronounced than that induced by classical neurotransmitters that stimulate inositol phosphate formation such as norepinephrine and carbamylcholine. Agonists of the ionotropic glutamate receptor such as kainate, NMDA and alpha-amino-3-hydroxy-5-methyl-5-isoxazolpropionate (AMPA), do not modify inositol phosphate accumulation in hypothalamic slices. The selective antagonist of quisqualate metabotropic receptor, D,L-2-amino-3-phosphonopropionate (AP3), produces a slight stimulation of phosphoinositide hydrolysis, but potently antagonizes the stimulation produced by quisqualate and t-ACPD.

Aging↗
PubMed1991

Bimodal action of [Asu1,7]eel-calcitonin on phosphoinositide hydrolysis in cultured anterior pituitary cells.

[Asu1,7]Eel-calcitonin, a semisynthetic analog of eel-calcitonin displaying high stability and full biological activity, was used to study the effect of calcitonin on phosphoinositide turnover in cultured anterior pituitary cells. Incubation of cells with [Asu1,7]eel-calcitonin produced a slight, concentration-dependent increase in [3H]inositol monophosphate accumulation, without modifying thyrotropin-releasing hormone (TRH)-stimulated phosphoinositide hydrolysis. This effect was correlated with a stimulatory action on prolactin secretion. Conversely, a long-term preincubation with [Asu1,7]eel-calcitonin reduced basal as well as TRH-induced [3H]inositol monophosphate formation. This effect was concentration-dependent, was not due to an increase of cyclic AMP intracellular levels, and was attenuated in the presence of maximally effective concentrations of TRH. Such a long incubation in the presence of [Asu1,7]eel-calcitonin resulted in a marked inhibition of prolactin secretion. The present data confirm and extend previous findings showing an interference of calcitonin with the intracellular cascade consequent to membrane phospholipase C activation and further support a role for calcitonin in the modulation of hormone secretion at the pituitary.

Animals↗
PubMed1991

Adenosine deaminase increases release of excitatory amino acids through a mechanism independent of adenosine depletion.

Addition of adenosine deaminase to cultured cerebellar neurones, led to large increases in the influx of 45Ca2+ and hydrolysis of polyphosphoinositide. These effects were inhibited or attenuated by glutamate receptor antagonists (AP5 or MK-801) and were not observed in cells stimulated by maximum concentrations of glutamate or quisqualate. Stimulation of the influx of 45Ca2+ and hydrolysis of phosphoinositide by adenosine deaminase may be secondary to an enhanced release of endogenous glutamate that in turn activates specific excitatory amino acid receptors. Accordingly, adenosine deaminase potently increased release of D-[3H]aspartate, an effect that requires the presence of extracellular Na+ and is insensitive to inhibition by MK-801. None of the effects of adenosine deaminase may be simply related to a fall in endogenous adenosine. In fact, the action of adenosine deaminase was neither reversed by agonists (L-PIA or NECA), nor mimicked by antagonists (IBMX or theophylline) of adenosine receptors. It is speculated that adenosine deaminase stimulates release of neurotransmitter through a mechanism independent of depletion of adenosine. A possible direct action of adenosine deaminase should be taken into account when the enzyme is used to unmask the effects of endogenous adenosine.

1-Methyl-3-isobutylxanthine↗
PubMed1991

Desensitization of metabotropic glutamate receptors in neuronal cultures.

Preexposure of cultured cerebellar neurons to glutamate reduced the stimulation of polyphosphoinositide (PPI) hydrolysis induced by subsequent addition of glutamate without affecting the response to the muscarinic receptor agonist carbamylcholine. Desensitization of glutamate-stimulated PPI hydrolysis developed rapidly and persisted up to 48 h after removal of glutamate from the incubation medium. Stimulation of PPI hydrolysis by quisqualate was abolished in cultures pretreated with quisqualate or glutamate, but not with N-methyl-D-aspartate (NMDA). In contrast, pretreatment with NMDA reduced the stimulation of PPI hydrolysis induced by a subsequent addition of NMDA, leaving the action of quisqualate intact. The lack of cross-desensitization between NMDA and quisqualate supports the existence of two distinct subtypes of glutamate receptors coupled to PPI hydrolysis. Desensitization induced by a 30-min (but not by a 6-h) exposure to glutamate was attenuated or prevented by putative protein kinase C inhibitors, including mono- and trisialogangliosides, sphingosine, and polymyxin B, but not by inhibitors of arachidonic acid metabolism, nor by the nonselective calpain inhibitor leupeptin, nor by the lectin concanavalin A. These results suggest that desensitization of metabotropic glutamate receptors involves, at least in its rapid component, activation of protein kinase C.

Amino Acids↗