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A Pittaluga

Publications and source records attributed to A Pittaluga.

At least 37 records · Page 2Linked to original sources
PubMed1992

N-methyl-D-aspartic acid (NMDA) and non-NMDA receptors regulating hippocampal norepinephrine release. I. Location on axon terminals and pharmacological characterization.

UNLABELLED: The effects of endogenous and exogenous agonists at excitatory amino acid receptors mediating enhancement of [3H]norepinephrine [( 3H]NE) release have been investigated using superfused rat hippocampal synaptosomes. In Mg(++)-free medium L-glutamic acid (L-Glu), L-aspartic acid (L-Asp), N-methyl-D-aspartic acid (NMDA), kainic acid, (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and quisqualic acid (QA) all increased the release of [3H]NE. L-Glu produced the largest effect. In the presence of Mg++ (1.2 mM), the effect of L-Glu decreased by about 40%; L-Asp and NMDA lost completely their activity while the effects of kainic acid, QA and AMPA did not change significantly. Similarly to NMDA, the effect of L-Asp was augmented by glycine and blocked by NMDA receptor antagonists, while it was insensitive to the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). The effect of L-Glu on [3H] NE release was partly decreased by the NMDA receptor channel blocker (+)-5-methyl-10,11-dihydro-5-H-dibenzo[a,d]cycloepten-5,10-imine (MK-801) and partly by CNQX; when present together, the two antagonists completely abolished the L-Glu effect. The QA enhancement of [3H]NE release was antagonized by CNQX but it was insensitive to other classical non-NMDA receptor antagonists. IN CONCLUSION: 1) release-enhancing NMDA and non-NMDA receptors exist on noradrenergic axon terminals of rat hippocampus; 2) L-Asp appears to be a potent selective NMDA receptor agonist while L-Glu can activate also non-NMDA receptors; 3) the NE-releasing receptor activated by QA may represent a QA/AMPA receptor subtype.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1992

N-methyl-D-aspartic acid (NMDA) and non-NMDA receptors regulating hippocampal norepinephrine release. II. Evidence for functional cooperation and for coexistence on the same axon terminal.

The possible interactions between activation of N-methyl-D-aspartic acid (NMDA) receptors and non-NMDA receptors regulating the release of [3H]norepinephrine [( 3H]NE) have been investigated in superfused synaptosomes from rat hippocampus. NMDA--at a concentration (100 microM) which, in a medium containing 1.2 mM Mg++ ions, did not evoke [3H]NE release--acquired releasing activity in the presence of equimolar concentrations of quisqualic acid (QA), (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) or kainic acid. The [3H] NE release evoked by NMDA plus QA in the presence of Mg++ ions was Ca(++)-dependent, partly tetrodotoxin-sensitive, inhibited by clonidine but insensitive to desipramine. The NMDA receptor antagonists D-2-amino-5-phosphonopentanoic acid (D-AP5) and (+)-5-methyl-10,11-dihydro-5-H-dibenzo[a,d]cycloepten-5,10-imine (MK-801) antagonized the NMDA-induced [3H]NE release in Mg(++)-free medium; the IC50 values amounted, respectively, to 81.4 microM and to 1.11 microM. When NMDA was tested in the presence of QA and Mg++ ions, the affinity of D-AP5 was enormously increased (IC50 = 40 nM; i.e., more than 6 orders of magnitude); the affinity of MK-801 was found to be augmented by 350-fold.(ABSTRACT TRUNCATED AT 250 WORDS)

2-Amino-5-phosphonovalerate↗
PubMed1991

Specific role of N-acetyl-aspartyl-glutamate in the in vivo regulation of dopamine release from dendrites and nerve terminals of nigrostriatal dopaminergic neurons in the cat.

Levels of N-acetyl-aspartyl-glutamate measured by high-pressure liquid chromatography were found to be very high in the cat substantia nigra, particularly in the pars compacta, while those in the caudate nucleus were much lower. In halothane-anaesthetized cats implanted with push-pull cannulae, N-acetyl-aspartyl-glutamate (10(-8) M) induced a marked and prolonged release of newly synthesized [3H]dopamine, when infused into the posterior but not into the anterior part of the caudate nucleus. In contrast, in the presence of tetrodotoxin (10(-6) M), N-acetyl-aspartyl-glutamate (10(-8) M) reduced the residual release of [3H]dopamine; this effect was also more pronounced in the posterior than in the anterior part. In the conditions used, as indicated by experiments with [3H]N-acetyl-aspartyl-glutamate no glutamate was formed from the infused N-acetyl-aspartyl-glutamate. Ibotenate (10(-5) M) induced changes in [3H]dopamine release in both the absence and presence of tetrodotoxin, which were closely similar to those observed with N-acetyl-aspartyl-glutamate. Responses induced by either N-acetyl-aspartyl-glutamate or ibotenate were not mediated by N-methyl-D-aspartate receptors since N-methyl-D-aspartate stimulated the release of [3H]dopamine only when used in a high concentration (10(-4) M) and applied in a magnesium-free superfusion medium in both the presence of glycine (10(-6) M) and strychnine (10(-6) M). In addition, the stimulatory effect of N-methyl-D-aspartate persisted in the presence of tetrodotoxin; it was of similar amplitude in both parts of the caudate nucleus and of shorter duration than that evoked by either N-acetyl-aspartyl-glutamate or ibotenate alone. N-Acetyl-aspartyl-glutamate interacted with dopaminergic neurons not only presynaptically in the caudate nucleus but also in the substantia nigra since a marked increase in [3H]dopamine release was observed both from local dendrites and from nerve terminals in the ipsilateral caudate nucleus when N-acetyl-aspartyl-glutamate (10(-7) M) was infused locally into the substantia nigra pars compacta. No effect could be seen in contralateral structures. The isomer of natural N-acetyl-aspartyl-glutamate, beta-N-acetyl-aspartyl-glutamate (10(-7) M), had no effect on [3H]dopamine release when applied similarly in the substantia nigra, thus confirming the specificity of the action of N-acetyl-aspartyl-glutamate.

Animals↗
PubMed1991

Clonidine differentially modulates the release of endogenous GABA in various rat brain areas.

The effects of clonidine on the release of endogenous gamma-aminobutyric acid (GABA) have been studied in superfused synaptosomes prepared from rat hypothalamus, nucleus tractus solitarii (NTS) and cerebellum. Clonidine enhanced in a concentration-dependent manner the basal release of GABA from hypothalamus and NTS synaptosomes. In contrast, the imidazoline did not affect the release of the amino acid from the cerebellar preparation. The alpha 2-adrenoceptor antagonist yohimbine prevented the releasing effect of clonidine, while the alpha 1-adrenoceptor antagonist prazosin was ineffective. The results show that the release of GABA from hypothalamus or NTS nerve endings can be enhanced by clonidine through the activation of adrenoceptors of the alpha 2 subtype. The GABAergic nerve terminals of cerebellum do not seem to possess presynaptic adrenoceptors by which clonidine can regulate the basal outflow of the amino acid. The results suggest that some of the clonidine effects may occur through activation of the GABA system.

Animals↗
PubMed1990

Release-enhancing glycine-dependent presynaptic NMDA receptors exist on noradrenergic terminals of hippocampus.

The release of [3H]noradrenaline ([3H]NA) in superfused rat hippocampal synaptosomes was increased concentration dependently by N-methyl-D-aspartate (NMDA). Glycine (1 microM), ineffective on its own, doubled the efficacy of NMDA with no significant change in affinity. The effects of NMDA alone and those of NMDA + glycine were antagonized by D-2-amino-5-phosphonopentanoate (D-AP5), Mg2+, (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohept-5,10-imine hydrogen maleate (MK-801) or 7-chloro-kynurenate (7-Cl-KYNA) but not by strychnine. The data provide a direct demonstration of the existence of presynaptic NMDA receptors.

Animals↗
PubMed1990

Glycine enhances [3H]noradrenaline release from slices of rat hippocampus.

The effects of glycine on the release of [3H]noradrenaline ([3H]NA) have been investigated using rat hippocampus slices previously labeled with the radioactive catecholamine. Glycine (30-1000 microM) produced a potent and concentration-dependent increase of the release of [3H]NA evoked by 12 mM KCl. The effect of 1000 microM glycine was totally antagonized by 3 microM strychnine suggesting that, in rat hippocampus, glycine may regulate the release of NA by activating a receptor of the strychnine-sensitive subtype.

Animals↗
PubMed1990

Respective contributions of neuronal activity and presynaptic mechanisms in the control of the in vivo release of dopamine.

Studies performed in several in vivo and in vitro conditions have demonstrated that the release of dopamine from nerve terminals of the nigrostriatal dopaminergic neurons depends not only on the activity of dopaminergic cells but also on presynaptic regulations by heterologous fibers. The presynaptic facilitation of dopamine release by the cortico-striatal glutamatergic neurons has been particularly investigated. A quisqualate/kainate receptor subtype is involved in the direct (tetrodotoxine-resistant) presynaptic regulation of dopamine release by glutamate. The respective roles of presynaptic events and nerve activity in the control of dopaminergic transmission are discussed.

Animals↗
PubMed1990

Competitive inhibition of N-acetylated-alpha-linked acidic dipeptidase activity by N-acetyl-L-aspartyl-beta-linked L-glutamate.

The endogenous neuropeptide N-acetyl-L-aspartyl-L-glutamate (NAAG) fulfills several criteria required to be accepted as a neurotransmitter. NAAG inactivation may proceed through enzymatic hydrolysis into N-acetyl-L-aspartate and glutamate by an N-acetylated-alpha-linked acidic dipeptidase (NAALADase). Therefore, some properties of NAALADase activity were investigated using crude membranes from the rat forebrain. Kinetic parameters of the hydrolysis of [Glu-3H]NAAG were determined first (Km = 0.40 +/- 0.05 microM; Vmax = 155 +/- 20 pmol/min/mg of protein). The enzymatic activity, i.e., NAALADase, was inhibited noncompetitively by the glutamatergic agonist quisqualate (Ki = 1.9 +/- 0.3 microM), and competitively by N-acetyl-L-aspartyl-beta-linked L-glutamate (beta-NAAG; Ki = 0.70 +/- 0.05 microM). To determine whether glutamate-containing dipeptides, such as NAAG, beta-NAAG, N-acetyl-L-aspartyl-D-glutamate, L-aspartyl-L-glutamate, L-alanyl-L-glutamate, L-glutamyl-L-glutamate, and L-glutamyl-gamma-linked L-glutamate, were substrates of NAALADase, rat brain membranes were immobilized on a C-8 column. Thus, endogenous trapped glutamate was washed away and formation of unlabelled glutamate could be estimated using an o-phthaldialdehyde/reverse-phase HPLC detection procedure. beta-NAAG was shown to be a nonhydrolyzable competitive inhibitor of NAALADase. L-Aspartyl-L-glutamate was hydrolyzed faster than NAAG, suggesting that the acetylated moiety is not essential for NAALADase specificity. Rat brain membranes also contained nonspecific peptidase activities (insensitive to both quisqualate and beta-NAAG), which, in the case of L-alanyl-L-glutamate, for instance, accounted for all observed hydrolysis.

Animals↗
PubMed1990

Muscarinic receptors mediating inhibition of gamma-aminobutyric acid release in rat corpus striatum and their pharmacological characterization.

The effects of acetylcholine (ACh) and of cholinergic agonists on the release of tritiated gamma-aminobutyric acid ([3H]GABA) were studied in superfused synaptosomes prepared from rat corpus striatum and prelabeled with the radioactive amino acid. ACh, oxotremorine or (-)-nicotine, all tested at 100 microM had no effect on the spontaneous outflow of [3H]GABA. The depolarization-evoked overflow obtained by exposing the synaptosomes to 9 mM KCl was decreased in a concentration-dependent manner by ACh, oxotremorine, oxotremorine-M or carbachol. The maximal inhibition caused by ACh was 50%. The EC50 (agonist concentration causing half-maximal effect) amounted to 1 microM. Oxotremorine and oxotremorine-M were almost equipotent to ACh, whereas the concentration-response curve of carbachol was slightly (although not significantly) shifted to the right with respect to that of ACh. (-)-Nicotine (100 microM) did not affect the K(+)-evoked [3H]GABA overflow. ACh also inhibited the K(+)-evoked release of endogenous GABA. The inhibitory effect of 10 microM ACh on the release of [3H]GABA evoked by 9 mM KCl was insensitive to the nicotinic antagonist mecamylamine (10 microM) but it was potently blocked by the muscarinic antagonist atropine (IC50 = 5 nM) and weakly antagonized by pirenzepine, dicyclomine and AF-DX 116. The pharmacological profile of this receptor was very similar to that of the muscarinic autoreceptors regulating [3H]ACh release. The extent of [3H]GABA release inhibition caused by ACh did not differ between dorsal and ventral striatum. The inhibitory effect of ACh was much less pronounced in hippocampus and cortex than in the striatum.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1989

Activation of the bilateral corticostriatal glutamatergic projection by infusion of GABA into thalamic motor nuclei in the cat: an in vivo release study.

The unilateral application of GABA (10(-5) M; 30 min) into thalamic motor nuclei of the cat increases the release of dopamine in both caudate nuclei. This effect has been suggested to be related to an activation of the bilateral corticostriatal glutamatergic projection, glutamate exerting a presynaptic facilitatory influence on dopamine release. To explore this hypothesis further, halothane-anesthetized cats implanted with push-pull cannulae were used in order to examine the effects of such a GABA application on the release of glutamate in both caudate nuclei. Aspartate, alanine, glutamine, serine and tyrosine were also measured in the superfusates. The unilateral application of GABA (10(-5) M; 30 min) into thalamic motor nuclei increased the release of glutamate bilaterally. Although less pronounced, ipsi- or bilateral increases in the efflux of alanine, glutamine and tyrosine were also observed. Contralateral changes in the efflux of glutamate, alanine and tyrosine were prevented following acute section of the corpus callosum. In addition, when applied continuously into one caudate nucleus, 2-amino-5-phosphonovaleric acid, a blocker of N-methyl-D-aspartate receptors, prevented the GABA-induced increase in alanine or tyrosine efflux but did not affect the enhanced release of glutamate. These results confirm that the unilateral application of GABA in thalamic motor nuclei activates a thalamo-cortico-striatal neuronal loop leading to the stimulation of glutamate release in both caudate nuclei. Changes in the efflux of other amino acids could be linked to increased metabolic activity of striatal target cells resulting from the increased release of glutamate and from its effect on N-methyl-D-aspartate receptors.

2-Amino-5-phosphonovalerate↗
PubMed1988

Enhancement of endogenous GABA release from rat synaptosomal preparations is mediated by alpha 2-adrenoceptors pharmacologically different from alpha 2-autoreceptors.

The effects of various adrenergic agents on the release of endogenous gamma-aminobutyric acid (GABA) and of [3H]GABA were studied in superfused synaptosomal preparations from rat hippocampus. Noradrenaline (NA) enhanced in a concentration-dependent way the release of endogenous GABA but did not affect the release of the radioactive amino acid. The effect of NA was mimicked by the alpha 2-adrenoceptor agonist, clonidine, but not by the alpha 1-agonist, phenylephrine. Accordingly, NA was antagonized by the alpha 2-adrenoceptor antagonist, yohimbine, but not by the alpha 1-antagonist, prazosin. Both (+)-mianserin and (-)-mianserin, used as alpha 2-adrenoceptor blockers, counteracted the NA-evoked release of endogenous GABA. The results suggest that GABA released from hippocampus crude synaptosomes is modulated by alpha 2-adrenoceptors pharmacologically different from the alpha 2-autoreceptors that modulate NA release and previously found to be blocked by (+)-mianserin but not by the (-) enantiomer (Raiteri et al., 1983).

Animals↗
PubMed1988

Clonidine enhances the release of endogenous gamma-aminobutyric acid through alpha-2 and alpha-1 presynaptic adrenoceptors differentially located in rat cerebral cortex subregions.

UNLABELLED: Clonidine (0.001-1 microM) increased the basal release of endogenous gamma-aminobutyric acid (GABA) in superfused synaptosomes from whole rat cerebral cortex. The effects of 0.1 to 1 microM clonidine were only in part sensitive to the alpha-2 adrenoceptor antagonist yohimbine; a complete antagonism by yohimbine could be seen only with 0.001 microM clonidine. The release of GABA induced by 0.1 to 1 microM clonidine was increasingly sensitive to the alpha-1 adrenoceptor antagonist prazosin. At all the concentrations tested clonidine was antagonized fully by a mixture yohimbine-prazosin (1 microM). The release of GABA was increased by phenylephrine in a concentration-dependent (0.01-1 microM) manner. At 1 microM phenylephrine was antagonized fully by 1 microM prazosin. When synaptosomes prepared from frontal, parietal, temporal and occipital cortex were exposed to clonidine (0.005 microM) or to phenylephrine (0.1 microM), the release of GABA was found to be region specific. Clonidine-induced GABA release could not be seen in temporal and occipital cortex but it was pronounced in parietal and frontal cortex. The effect of phenylephrine did not parallel that of clonidine: for instance, GABA release was most sensitive to phenylephrine in the occipital cortex where clonidine was ineffective. The opposite occurred in parietal cortex synaptosomes, where phenylephrine was much less effective than clonidine. IN CONCLUSION: 1) clonidine stimulates the release of GABA in rat cerebral cortex synaptosomes; 2) the effect is likely to occur by activation of alpha-1 and alpha-2 adrenoceptors possibly situated on GABAergic nerve endings; and 3) a differential distribution of alpha-1 and alpha-2 adrenoceptors regulating GABA release exists within the cortical subregions.

Animals↗
PubMed1987

Studies on [3H]GABA and endogenous GABA release in rat cerebral cortex suggest the presence of autoreceptors of the GABAB type.

The presence of autoreceptors for gamma-aminobutyric acid (GABA) in the CNS was reinvestigated using rat cortex synaptosomes prelabeled with [3H]GABA and exposed to GABA by superfusion in the presence of a new GABA uptake inhibitor, N-(4,4-diphenyl-3-butenyl)-nipecotic acid (SK&F 89976A). This compound itself did not increase the basal or the depolarization-evoked release of [3H]GABA. GABA reduced in a concentration-dependent way the release of [3H]GABA evoked by 15 mM K+. The effect was not antagonized by bicuculline, picrotoxin or by the new GABAA antagonist SR 95531. The GABAA agonist muscimol did not affect [3H]GABA release. This was reduced by (-)baclofen (but not by the (+) isomer) and the concentration-inhibition curve of (-)baclofen was superimposable on to that of GABA. Also the K+-evoked release of endogenous GABA was stereoselectively and concentration dependently inhibited by the (-) enantiomer of baclofen. It is concluded that the release of GABA from rat cortical nerve endings may be inhibited through the activation of autoreceptors which appear to belong to the GABAB type.

Animals↗
PubMed1987

GABAergic nerve terminals in rat hippocampus possess alpha 2-adrenoceptors regulating GABA release.

Noradrenaline enhanced in a concentration-dependent way the basal release of endogenous GABA from superfused rat hippocampus synaptosomes. The alpha 2-adrenoceptor antagonist yohimbine prevented the releasing effect of noradrenaline while the alpha 1-adrenoceptor antagonist prazosin was ineffective. It is concluded that GABAergic nerve terminals in rat hippocampus possess adrenoceptors of the alpha 2-subtype whose activation causes enhancement of GABA release.

Animals↗
PubMed1987

Choline increases endogenous GABA release in rat hippocampus by a mechanism sensitive to hemicholinium-3.

The effects of choline (Ch) on the spontaneous release of endogenous gamma-aminobutyric acid (GABA) and of 3H-GABA were studied in superfused rat hippocampal synaptosomes. Choline enhanced in a concentration-dependent way the release of endogenous GABA but did not affect that of the radioactive aminoacid. The effect of Ch was not antagonized by atropine or mecamylamine; moreover, it was not mimicked by acetylcholine, oxotremorine or carbachol. The Ch-induced GABA release was counteracted by hemicholinium-3. Thus the release of endogenously synthesized GABA (but not that of the aminoacid taken up) may be regulated by Ch through a mechanism involving penetration into the releasing terminal through a Ch uptake system.

Acetylcholine↗
PubMed1987

[3]Pirenzepine binding in rat corpus striatum decreases after hemitransection of the nigro-striatal pathway.

The localization and pharmacologic characterization of muscarinic receptors possibly regulating the release of dopamine (DA) in rat corpus striatum were investigated by in vitro binding with [3H]pirenzepine ([3H]PZ) after hemitransection of the nigro-striatal pathway. DA levels in the corpus striatum ipsilateral to the lesion were substantially reduced by 66% compared with the unlesioned side after 8 days. The uptake of [3H]DA was also diminished by 63%. A significant decrease in the specific binding of [3H]PZ of 42% was seen in the corpus striatum ipsilateral to the lesion. The data indicate a loss of binding sites, whereas the lesion caused no change in the affinity constant for the muscarinic antagonist. The results support those previously obtained in studies of the muscarinic modulation of [3H]DA release from striatal synaptosomes and favor the idea that at least part of the muscarinic receptors regulating striatal DA release are localized on the nigro-striatal axon terminals and belong to the pirenzepine-sensitive subtype.

Animals↗