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G Racagni

Publications and source records attributed to G Racagni.

At least 19 recordsLinked to original sources
PubMed1995

Aminoacid recovery via microdialysis and photoinduced focal cerebral ischemia in brain cortex of rats.

A photochemical method using the Rose Bengal dye as thrombogenic agent was employed to induce focal cerebral ischemia in frontoparietal cortex of rats. A transcerebral microdialysis probe was used to collect samples from ischemic cortical area. An increase in glutamate (6-fold) and in taurine (4-fold) within the first hour occurred. Neuropathological investigations demonstrate a reproducible damaged area surrounded by a thin peripheral area showing neuronal apoptotic phenomena. The method represents a reproducible model of focal cerebral ischemia with neuropathological aspects superimposable to those characteristic of thrombogenic stroke in man. This method could also be relevant in the study of neurotransmitters during the evolution of ischemia. Furthermore, the presence of apoptotic phenomena in the perilesional halo confirms an ischemic penumbra suggesting the significance of preclinical pharmacological trials.

Amino Acids↗
PubMed1995

Inhibition of nitric oxide synthase dramatically potentiates seizures induced by kainic acid and pilocarpine in rats.

We investigated whether the severity of convulsions evoked by kainic acid and pilocarpine is modified in nitric oxide synthase inhibitor-treated rats. We found that chronic treatment (4 days) with NW-nitro-L-arginine greatly potentiates seizures induced by both convulsants suggesting a potential role for nitric oxide in mechanisms regulating seizure induction and propagation.

Amino Acid Oxidoreductases↗
PubMed1995

Arachidonic acid inhibits a purified and reconstituted glutamate transporter directly from the water phase and not via the phospholipid membrane.

Glutamate is believed to be the major excitatory transmitter in the mammalian central nervous system. Keeping the extracellular concentration of glutamate low, the glutamate transporters are required for normal brain function. Arachidonic acid (AA) inhibits glutamate uptake in relatively intact preparations (cells, tissue slices, and synaptosomes (Rhoads, D.E., Ockner, R. K., Peterson, N. A., and Raghupathy, E. (1983) Biochemistry 22, 1965-1970 and Volterra, A., Trotti, D., Cassutti, P., Tromba, C., Salvaggio, A., Melcangi, R. C., and Racagni, G. (1992b) J. Neurochem. 59, 600-606). The present study demonstrates that the effect of AA occurs also in a reconstituted system, consisting of a purified glutamate transporter protein incorporated into artificial cell membranes (liposomes). The characteristics of the AA effect in this system and in intact cells are similar with regard to specificity, sensitivity, time course, changes in Vmax, and affinity. AA-ethyl ester is inactive, suggesting that the free carboxylic group is required for inhibitory activity. When incubated with proteoliposomes, AA (300 microM, 15 min) mostly partitions to the lipid phase (lipid/water about 95:5). However, uptake inhibition is abolished by rapid dilution (6.5-fold) of the incubation medium (water phase), a procedure that does not modify the amount of AA associated with lipids. On the contrary, inhibition remains sustained if the same dilution volume contains as little as 5 microM AA, a concentration inactive before saturation of liposome lipids with 300 microM AA. The same degree of inhibition (60%) is obtained by 5 microM AA following preincubation with the inactive AA-ethyl ester (300 microM) instead of AA. The lipids apparently inactivate AA by extracting it from the water phase. The results suggest that AA acts on the transporter from the water phase rather than via the membrane. This could be true for other proteins as well since gamma-aminobutyric acid uptake is similarly affected by AA.

ATP-Binding Cassette Transporters↗
PubMed1995

[Ca2+] modulates the ratio between cycloxygenase and lipoxygenase metabolism of arachidonic acid in homogenates of hippocampal astroglial cultures.

While studying the enzymatic processing of arachidonic acid (AA) to eicosanoids in homogenates of hippocampal astrocytes, we observed that all the HPLC peaks corresponding to AA metabolites displayed significantly different levels depending on the presence or not of free Ca2+ in the incubation medium. A specific pattern was noticed, i.e. lipoxygenase (LOX) derivatives, in particular 12-hydroxyeicosatetraenoic acid (12-HETE), showed higher levels in medium containing 1 mM Ca2+, while cycloxygenase (COX) products including prostaglandins (PG) F2 alpha, E2 and D2 and 12-hydroxyhepatadecatrienoic acid (12-HHT), were higher in Ca(2+)-free medium. COX metabolism exceeded LOX metabolism by threefold in Ca(2+)-free medium, while it was only 60% of it in 1 mM Ca2+. The total amount of AA processed under the two conditions was identical. These data suggest that free [Ca2+] influences the pattern of AA metabolites formed in hippocampal astrocytes, with possible important implications in view of the distinct roles played by COX and LOX eicosanoids in synaptic transmission and neurotoxicity in this area.

Animals↗
PubMed1995

Opposite regulation of basic fibroblast growth factor and nerve growth factor gene expression in rat cortical astrocytes following dexamethasone treatment.

Growth factors are peptides that exert different activities in the CNS, supporting the survival of different cell populations and playing an important role in the maintenance of cell homeostasis. Much evidence has suggested that these molecules can protect neurons from degeneration induced by mechanical injury or excitotoxic stimuli. Different factors can contribute to the regulation of neurotrophic factor expression in the brain. Such mechanisms may therefore be important in the manipulation of the levels of these peptides in specific brain areas as a therapeutic intervention in acute and chronic neurodegenerative diseases. We have used a primary culture of rat cortical astrocytes to investigate the regulation of basic fibroblast growth factor (bFGF) gene expression in comparison with other neurotrophic molecules. Our results indicate that the glucocorticoid analogue dexamethasone markedly elevates bFGF mRNA levels but reduces the expression of nerve growth factor. The induction of bFGF was transient, as it peaked after 6 h and returned to basal levels within 24 h and was not blocked by coincubation of cycloheximide, thus indicating that it did not require de novo protein synthesis. This effect was also observed in vivo, as systemic injection of dexamethasone (1 or 10 mg/kg) produced a significant increase in the amount of bFGF mRNA in cerebral cortex and hippocampus. The effect we describe can contribute to the regulation of bFGF expression in the brain and may be important in relation to the protective effect exerted by this growth factor in different models of neuronal injury.

Aldosterone↗
PubMed1995

Abnormalities of cAMP-dependent endogenous phosphorylation in platelets from patients with bipolar disorder.

OBJECTIVE: The aim of the study was to assess cAMP-dependent endogenous phosphorylation in platelets from euthymic bipolar patients. METHOD: Platelets from 10 drug-free euthymic patients with bipolar disorder were compared with those from 10 age- and sex-matched healthy subjects. Basal and cAMP-stimulated protein phosphorylation was examined in each group. RESULTS: Endogenous phosphorylation in both the healthy volunteers and the bipolar patients was significantly stimulated by cAMP; the major polypeptides had apparent molecular weights of 38 and 22 kDa. The cAMP-stimulated 32P incorporation differed between the bipolar patients and the comparison subjects only in the 22-kDa band. CONCLUSIONS: These data suggest a possible role of cAMP-dependent protein phosphorylation in the pathophysiology of bipolar disorder.

Adult↗
PubMed1995

Presynaptic Ca2+/calmodulin-dependent protein kinase II: autophosphorylation and activity increase in the hippocampus after long-term blockade of serotonin reuptake.

It is known that long-term treatment with antidepressants induces an enhancement of neurotransmission in the pathway projecting from raphe nuclei to the hippocampus. In the case of selective serotonin (5-HT) reuptake inhibitors, this enhancement is due to a desensitization of presynaptic 5-HT autoreceptors and a concomitant increase in 5-HT release in terminal areas. To investigate whether this effect is accompanied by adaptive changes in the molecular machinery regulating transmitter release at serotonergic terminals, autophosphorylation and activity of Ca2+/calmodulin-dependent protein kinase II were measured in subsynaptosomal fractions from hippocampus and total cortex. Long-term treatment with two selective serotonin reuptake inhibitors (paroxetine and fluvoxamine) and with a nonselective reuptake inhibitor (venlafaxine) induces a large increase of kinase autophosphorylation in synaptic vesicles and synaptic cytosol in the hippocampus but not in synaptosomal membranes. No significant change was detected in total cortex. The change is not reproduced by the direct addition of the drugs to the phosphorylation system and is not elicited by acute treatment of the animals. The increase in autophosphorylation is not accounted for by neosynthesis or translocation of the kinase to synaptic terminals. The change is restricted to the kinase located inside the terminals and is not detected in synaptosomal membranes, containing predominantly postsynaptic kinase, suggesting that only presynaptic kinase is affected. In the same fractions, the kinase activity is increased. These results are in agreement with reports suggesting a presynaptic effect for the SSRIs and disclose a new putative site of action for psychotropic drugs.

Amino Acid Sequence↗
PubMed1995

Metabotropic glutamate receptors negatively coupled to adenylate cyclase inhibit N-methyl-D-aspartate receptor activity and prevent neurotoxicity in mesencephalic neurons in vitro.

The functional effects of G protein-linked glutamate receptor activation have been studied in mouse mesencephalic neurons in vitro. We have been able to identify two receptor classes, one linked to phosphoinositide hydrolysis and another that inhibits adenylate cyclase. The agonist (1S,3R)-aminocyclopentane-1,3-dicarboxylate (ACPD) affected the two responses with similar potency (EC50 = 2 and 7 microM, respectively). In contrast, (2S,3S,4S)-alpha-(carboxycyclopropyl)glycine selectively decreased adenylate cyclase activity (EC50 = 150 nM), without interfering with the phosphoinositide pathway. Activation of ion channel-linked glutamate receptors in mesencephalic neurons leads to cGMP formation. In this study, we demonstrate that cell pretreatment with ACPD or (2S,3S,4S)-alpha-(carboxycyclopropyl)glycine prevented, in a dose-dependent fashion, N-methyl-D-aspartate (NMDA)-induced cGMP formation but not the kainate-stimulated response. The pharmacological profile suggests that receptors that are negatively coupled to adenylate cyclase are responsible for this effect. Coexposure of neurons to ACPD and Ba2+, a K+ channel blocker, counteracted the ACPD-induced blockade of NMDA receptors, suggesting that activation of K+ conductances could be involved in the post-transduction events triggered by metabotropic receptors in the mesencephalon. Neuronal treatment with NMDA for 10 min caused a reduction in mitochondrial activity. Direct inhibition of nitric oxide synthase with the inhibitor NG-nitro-L-arginine or removal of extracellular nitric oxide with reduced hemoglobin did not prevent this metabolic impairment, thus excluding a role for nitric oxide in this test for excitotoxicity. On the contrary, the mitochondrial function was maintained when neurons exposed to NMDA were preincubated with metabotropic receptor agonists. To summarize, our results suggest that metabotropic receptors that are negatively coupled to adenylate cyclase exert modulatory control specifically on NMDA receptor activity. This event could also contribute to the reduction of neurotoxic effects due to NMDA receptor hyperactivity.

Adenylyl Cyclase Inhibitors↗
PubMed1994

Hippocampal hypoglycaemia-activated K+ channels: single-channel analysis of glucose and voltage dependence.

The effect of glucose on kinetics and the voltage-dependent characteristics of glucose-sensitive channels in hippocampal neurons were examined with the cell-attached mode of the patch-clamp technique. Recordings of a 100-pS K+ channel in the presence or absence of glucose demonstrate that the increase in channel open state probability (Po) induced by glucose deprivation (40- to 400-times the control in high-glucose medium) was largely due to a decrease in the global amount of time spent by the channel in a long-lived closed state. The Po value of the same 100-pS channel was also found to increase (by approx. 80-times) following a depolarization of 40 mV from rest, the main factor responsible for this being a dramatic shortening of the long closed-times on depolarization. Another glucose-sensitive channel of smaller conductance (approx. 10 pS) showed a similar dependence of Po on glucose, but different dependence on voltage, with long openings at the same hyperpolarized potentials where the 100-pS channel was almost always closed. Our results indicate that the action of glucose on the kinetics of hippocampal channels closely resembles that of ATP-sensitive channels in pancreatic beta-cells. Furthermore, they indicate that the two types of glucose-sensitive channels found in hippocampal neurons, differing not only in their single-channel conductance but also in the dependence on voltage, could play different roles in the responses of these cells to modified energetic supply.

Animals↗
PubMed1994

Regulation of NMDA receptor subunit mRNA expression in the rat brain during postnatal development.

Different NMDA receptor subunits have been recently cloned. The present paper describes the developmental profile of expression of the NR-1 subunit and three NR-2 subunits (A, B, C) in the rat central nervous system. A sensitive RNase protection assay was employed to determine simultaneously the mRNA levels of these receptor subunits. We found low levels of NR-1 mRNA (comprising all different splicing isoforms) in newborn rats with a progressive increase of its expression in the following 2-3 weeks. NR-2 subunits can be regarded as 'modulatory' since their expression can produce differences in the properties of NMDA receptors. More than one NR-2 subunits can be expressed in the same brain region. NR-2A and NR-2C are concomitantly expressed in the cerebellum and during development their mRNAs increase with a similar profile from low levels in P-8 rats to maximal expression in P-21 animals. NR-2A and NR-2B are concomitantly expressed in several brain regions with a different ontogenetic profile. In the hippocampus NR-2B mRNA increases rapidly during the first week of life as compared to the NR-2A subunits which at this time is expressed to low levels indicating that NR-2B will probably be dominant in determining the NMDA properties during the first period of life. Our data can provide a molecular correlate with properties of NMDA receptors such as voltage dependent Mg2+ block and deactivation kinetics which undergo significant changes during development and have been shown to depend upon the NR-2 subunit co-expressed with the common NR-1 subunit in various brain regions.

Animals↗
PubMed1994

Short- and long-term induction of basic fibroblast growth factor gene expression in rat central nervous system following kainate injection.

Both RNase protection assay and in situ hybridization were used to investigate the effect of intraperitoneal injection of kainate on the messenger RNA levels for basic fibroblast growth factor in the rat central nervous system. Limbic motor seizures were produced by kainate injection and this event was followed by a significant elevation of basic fibroblast growth factor gene expression in rat hippocampus and striatum 6 h after the convulsant injection. The increase in hippocampus was maximal at 24 h and it was delayed with respect to nerve growth factor induction, which peaked 3 h after kainate injection. Animals that suffered prolonged seizure activity also showed a significant elevation of basic fibroblast growth factor gene expression four and 14 days after kainate, when no changes in nerve growth factor gene expression were observed. We show that, within the hippocampus, the increase of basic fibroblast growth factor messenger RNA was localized in dentate gyrus and the CA1 layer 6 and 24 h after kainate injection. Long-term effects on its gene expression were measurable only in the CA1 hippocampal subfield, where major cell damage and astrocytosis have been reported to occur following kainate-induced seizure activity [Ben-Ari Y. et al. (1981) Neuroscience 7, 1361-1391; Lothman E. W. and Collins R. C. (1981) Brain Res. 218, 299-318; Schwob J. E. et al. (1980) Neuroscience 5, 991-1014]. Indeed, the animals which displayed elevated messenger RNA levels for basic fibroblast growth factor four and 14 days after kainate injection showed a marked induction of messenger RNA expression for the astroglial marker glial fibrillary acidic protein. These results indicate that the glutamate analogue kainate produces short- and long-term increases of basic fibroblast growth factor messenger RNA expression with a specific anatomical pattern. Therefore, the gene expression for this neurotrophic factor is probably regulated by neuronal activity at early points in time, whereas the induction observed at later time points is related to adaptive mechanisms taking place following kainate-induced neuronal degeneration.

Animals↗
PubMed1994

Glutamate uptake inhibition by oxygen free radicals in rat cortical astrocytes.

Formation of reactive oxygen species and disfunction of the excitatory amino acid (EAA) system are thought to be key events in the development of neuronal injury in several acute and long-term neurodegenerative diseases. Recent evidence suggests that the two phenomena may be interdependent. The present study is aimed at exploring possible molecular mechanisms underlying oxygen radical-EAA interaction. Exposure of cortical astrocytic cultures to either xanthine + xanthine oxidase (X/XO), a free radical-generating system, or hydrogen peroxide (H2O2) results in a marked decrease of high-affinity glutamate transport. Within 10 min of X/XO application, uptake falls to approximately 60% of its control value. In parallel no detectable release of lactate dehydrogenase occurs. X/XO effect is abolished in the presence of a mixture of scavenger enzymes (superoxide dismutase+catalase) or by the disulfide-reducing agents glutathione and dithiothreitol (DTT), but not by lipophilic antioxidants or ascorbate. The time course of inhibition shows an almost linear decline of glutamate transport during cell exposure to free radicals, while upon their inactivation the decline stops but established inhibition persists for at least 1 hr. In this situation, application of DTT significantly restores transport function. These data suggest that free radicals inhibit glutamate uptake primarily by long-lasting oxidation of protein sulfhydryl (SH) groups. Chemical modifiers of free SH groups, such as p-chloromercuribenzoate and N-ethylmaleimide, also induce uptake inhibition. Na+/K+ ATPase is a known target of oxygen radicals and may be involved in glutamate uptake inhibition. Indeed, ouabain, a blocker of the pump, reduces uptake in astrocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

2-Amino-5-phosphonovalerate↗
PubMed1994

Glutamate uptake is inhibited by arachidonic acid and oxygen radicals via two distinct and additive mechanisms.

Reuptake of glutamate in astrocytes, a critical mechanism involved in the maintenance of physiological excitatory amino acid neurotransmission, is inhibited by both arachidonic acid (AA) and reactive oxygen species (ROS), via incompletely defined molecular mechanisms. Because ROS are generated during AA metabolism and AA can be released as a result of ROS-mediated phospholipase A2 activation, it seems likely that their effects on uptake are mediated by a common mechanism. However, here we show that rapid (10-min) uptake inhibitions by AA or by ROS generated by the xanthine plus xanthine oxidase (XO) reaction are selectively abolished by distinct agents; bovine serum albumin (BSA) acts only on AA, whereas the scavenger enzymes superoxide dismutase (SOD) and catalase (CAT) and the disulfide-reducing agent dithiothreitol (DTT) act only on ROS. Moreover, when added together, xanthine/XO and AA decrease uptake in a fully additive manner. In particular, the effect of xanthine/XO is seen also in the presence of maximal AA inhibition. No major signs of cell damage or chemical reaction between AA and radicals accompany their cumulative effects on uptake. Finally, uptake inhibition elicited by AA and xanthine/XO together is attenuated but not blocked by either BSA, DTT, or SOD/CAT individually, whereas it is fully blocked and substantially reversed by a combination of SOD/CAT and BSA or SOD/CAT, DTT, and BSA. Together, these data indicate that AA and ROS act on glial glutamate transport via distinct noninteracting mechanisms. Therefore, they could independently and additively contribute to the impairment of reuptake function, a phenomenon observed in pathological conditions such as ischemia/reperfusion injury.

Animals↗
PubMed1993

Glutamate receptor-induced cyclic GMP formation in primary cultures of mesencephalic neurons.

The link between excitatory amino acid (EAA) receptor activation and the nitric oxide/cyclic GMP intracellular pathway was investigated in primary cultures of mouse mesencephalic neurons. L-glutamate, N-methyl-D-aspartate (NMDA), kainate (KA) and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate were able to induce cyclic GMP formation. NMDA and KA were the most effective and their action could be blocked, besides the specific antagonists 2-amino-5-phosphonopentanoate and 6-cyano-7-nitroquinoxaline-2,3-dione, by NG-nitro-L-arginine, a nitric oxide synthase inhibitor. This finding demonstrates that nitric oxide generation is necessary for EAA-induced cyclic GMP formation and provides indirect evidence for nitric oxide synthase activity in mesencephalic neurons. GMP increase induced by NMDA or KA was potentiated by carbachol or by exogenous activation of protein kinase C with phorbol esters. A clarification of the early intracellular events that follow EAA receptor activation may be important for understanding the physiological and excitotoxic events linked to these receptors in the mesencephalon.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1993

Evidence for the existence of cAMP-dependent protein kinase phosphorylation system associated with specific phosphoproteins in stable microtubules from rat cerebral cortex.

Cyclic AMP is a second messenger by which different extracellular signals are transduced into biological responses. Within the cell, most of the effects of cAMP are mediated through the cAMP protein kinase which appears to be localized in specific compartments of the cell near to their substrate proteins. In the present study, we have investigated the possible association of cAMP-dependent protein kinase, its substrate proteins and RII binding proteins in stable microtubules from rat cerebral cortex. The results show that in this fraction there is a cAMP binding protein of 52-54 kDa. This cAMP receptor is in the inactive holoenzyme form, since the addition of cAMP (5 microM) induces an increase in the endogenous phosphorylation of different stable microtubules polypeptides, which is completely inhibited in the presence of a specific protein kinase inhibitor (PKI 5-24 1 microM). Interestingly, overlay binding assay reveals that beside MAP2, 32P/R II is able to bind stable microtubule proteins of M(r) 150 and 75 kDa which, according to their electrophoretic mobility, can also be endogenous substrates for the enzyme. We conclude that cAMP-dependent phosphorylation system is indeed associated with stable microtubules from rat cerebral cortex.

Animals↗
PubMed1993

Heterologous sensitization of adenylate cyclase activity by serotonin in the rat cerebral cortex.

In vitro exposure of rat cerebrocortical slices to microM concentrations of serotonin (5HT) results in an increased response of adenylate cyclase to isoproterenol (ISO). No change in the affinity of the beta-adrenoceptor toward the agonist was found after 5HT exposure when measuring ISO displacement of [3H]CGP 12177 binding. A similar increase of adenylate cyclase response was also found when using VIP as a stimulatory agent. The dose-response curve of adenylate cyclase to the GTP analogue, GppNHp, was modified by 5HT, which promotes a significantly higher maximal response without altering the potency of GppNHp. Forskolin-stimulated adenylate cyclase activity was not affected by 5HT. Serotonergic 5HT2 receptors are involved in the sensitization of adenylate cyclase to GppNHp, since the selective 5HT2 antagonist ketanserin inhibits the effect of 5HT, whereas the 5HT2 agonist DOI mimics 5HT. The involvement of 5HT2 receptor-coupled activation of protein kinase C is also demonstrated: direct protein kinase C activators such as phorbol esters and s,n-dioctanoylglycerol behave in the same manner as 5HT, while the protein kinase C inhibitor CGP 41251 prevents 5HT from increasing adenylate cyclase responsiveness to GppNHp. Moreover, in vitro exposure of cortical slices to 5HT results in reduced inhibition of adenylate cyclase by somatostatin. Since no change was observed at the receptor level and in the direct stimulation of the catalytic subunit of the enzyme, we propose that 5HT might accomplish the sensitization of adenylate cyclase through protein kinase C by inactivating the inhibitory coupling protein Gi and facilitating the interaction of the exogenous GppNHp with the stimulatory coupling protein Gs.

Adenylyl Cyclase Inhibitors↗
PubMed1992

Hypoglycemia-activated K+ channels in hippocampal neurons.

Channels linking the electrical and metabolic activities of cells (KATP channels) have been described in various tissues, including some brain areas (hypothalamus, cerebral cortex and substantia nigra). Here we report the existence in hippocampal neurons of K+ permeant channels whose activity is regulated by extracellular glucose. They are open at the cell resting potential and respond to transient hypoglycemia with a reversible increase in activity. The one type so far characterized has a conductance of approximately 100 pS in isotonic K+, is inhibited by the sulphonylurea glibenclamide (1 microM), and is activated by the potassium channel opener lemakalim (0.1-1 microM). These data provide a direct demonstration of the presence, in hippocampal neurons, of glucose-sensitive channels that could belong to the KATP family.

Adenosine Triphosphate↗