Radioautographic study of uptake and storage of indoleamines in the rabbit enterochromaffin cells

After in vitro intra-arterial injection of tritium-labeled 5-hydroxytryptamine or -hydroxytrytophan ([³H]5-HT or [³H]5-HTP) (5·10^?7 M) in the presence of cold noradrenaline (5·10^?6 m) into rabbit colon, a clear-cut labelling pattern was observed by radioautography. Labelled cells were observed within the mucosa. The labeling was less important after [³H]5-HTP than after [³H]5-HT injection. Ultrastructural study indicates that labeling is confined to the cytoplasm and coincides with polymorphic secretory granules.Hence these labeled cells display not only APUD cells characteristics but also true neuronal properties.     

Inhibition by acetylcholine of the stimulation-evoked release of [3H]acetylcholine from the guinea-pig myenteric plexus

The longitudinal muscle-myenteric plexus preparation of the guinea-pig ileum was incubated with [³H]choline and then superfused with Tyrode's solution. Exposure to [³H]choline resulted in the formation of [³H]acetylcholine which was released upon electrical field stimulation. The effects of exogenous acetylcholine, physostigmine and scopolamine on the stimulation-evoked release of [³H]acetylcholine were studied.In the absence of a cholinesterase inhibitor exogenous acetylcholine (10^?5 M) only slightly inhibited (by 26%) the evoked release of [³H]acetylcholine. If the cholinesterase activity of the preparation was reduced by about 50% in the presence of 10^?7M physostigmine, exogenous acetylcholine caused a concentration-dependent depression of the release evoked at 1 Hz. At a concentration of 10^?5 M acetylcholine the release was reduced by 76%. Scopolamine (10^?9 M) shifted the concentration-response curve for the inhibitory action of acetylcholine in a parallel manner to the right. From the dose ratio a pA₂ value of 9.8 for scopolamine against the release-inhibitory effect of acetylcholine was calculated. Physostigmine also inhibited the stimulation-evoked release of [³H]acetylcholine in a concentration-dependent manner, the maximal effect measured being an 85% reduction by 10^?5 M physostigmine. In the absence of a cholinesterase inhibitor scopolamine enhanced the evoked release of [³H]acetylcholine. The facilitatory effect was more marked at a stimulation frequency of 3 Hz (2-fold increase) than at 1 Hz (1.4-fold increase).It is concluded that extracellular acetylcholine decreases the stimulation-evoked release of neuronal acetylcholine. This inhibition is specifically mediated by a stimulation of presynaptic muscarinic receptors. The increase by scopolamine of the evoked release of [³H]acetylcholine suggests that previously liberated acetylcholine may trigger the negative feedback mechanism of acetylcholine release even if the cholinesterase activity is not inhibited, and that the presynaptic muscarinic receptors of the myenteric plexus have a physiological role in regulating the release of acetylcholine.     

Attenuation of induced-anxiety in rats by chlordiazepoxide: Role of raphe dorsalis benzodiazepine binding sites and serotoninergic neurons

In chronically implanted awake rats, microinjections of chlordiazepoxide (5 × 10^?7M) into the dorsal raphésignificantly attenuated the inhibition of lever-pressing for food elicited by a signal of punishment. This effect is abolished by prior application of 5,7-dihydroxytryptamine into the dorsal raphé(3 weeks after the infusion of the neurotoxin, dorsal raphétryptophan hydroxylase activity was reduced to 25% of control values). Furthermore, the disinhibitory effect of intra raphéchlordiazepoxide can be mimicked or potentiated by intra raphédorsalis application of serotonin (10^?7 or 10^?8 M, respectively). Further evidence for a crucial interaction between benzodiazepines and serotoninergic processes are provided by in vitro experiments showing that chlordiazepoxide or diazepam (10^?5 M) are able to facilitate the K⁺ -evoked [³H]serotonin release from rat midbrain slices. Finally, a high density of [³H]flunitrazepam binding sites was found in the dorsal (and the median) raphénucleus, the Kd and B_max values being not altered by prior infusion of 5,7-dihydroxytryptamine.These in vitro data suggest possible means by which intra raphé(and perhaps peripherally administered) benzodiazepines may affect the activity of serotoninergic neurons and thereby produce their effects on experimental anxiety.     

In vivo evidence for acetylcholine control of serotonin release in the cat caudate nucleus: influence of halothane anaesthesia

Using a push-pull cannula technique and an isotopic method for the estimation of [3H]serotonin continuously synthesized from [3H]tryptophan, the effects of acetylcholine were investigated on the in vivo release of [3H]serotonin in the cat basal ganglia and the dorsal raphe nucleus. The unilateral striatal application of acetylcholine (5 x 10(-5) M) reduced local release of [3H]serotonin. This effect was mimicked by nicotine (5 x 10(-5) M) and prevented by mecamylamine (10(-6) M. Oxotremorine (5 x 10(-5) M) had no effect on the local release of [3H]serotonin. All these treatments failed to modify [3H]serotonin release in the ipsilateral substantia nigra or in the dorsal raphe nucleus. The superfusion of serotonergic nerve terminals of the caudate nucleus with tetrodotoxin prevented the inhibitory acetylcholine-induced effect on serotonin release. Furthermore, bicuculline (5 x 10(-5) M) in the caudate nucleus blocked the effect of nicotine, while gamma-aminobutyric acid (10(-5) M) induced a decrease in local release of [3H]serotonin. These data strongly suggest that the inhibitory control exerted by acetylcholine on serotonergic transmission could involve gamma-aminobutyric acid interneurons. Acetylcholine-induced changes in [3H]serotonin release were only observed in non-anaesthetized "encéphale isolé" cats and not in halothane-anaesthetized animals. The possibility that such a regulation could be presynaptic (direct or through other neurotransmitters) or related to a change in the activity of the serotonergic raphe-striatal neuronal system is discussed.     

Involvement of the thalamus in the reciprocal regulation of the two nigrostriatal dopaminergic pathways

The effects of various sagittal sections on the asymmetric changes in [³H]dopamine release from nerve terminals and dendrites of the two nigrostriatal dopaminergic pathways induced by the application of α-methylparatyrosine ord-amphetamine in the left substantia nigra were examined in halothane-anaesthetized cats implanted with push-pull cannulae in both caudate nuclei and both substantiae nigrae. [³H]tyrosine was continuously delivered to each push-pull cannula and [³H]dopamine was estimated in serial fractions of superfusates. In cats without a lesion, α-methylparatyrosine (10^?4M) reduced the release of [³H]dopamine in the left substantia nigra and induced an opposite effect in the left caudate nucleus. In contrast, [³H]dopamine release was enhanced in the right substantia nigra and reduced in the right caudate nucleus. Opposite asymmetric responses were observed in the four structures during application ofd-amphetamine (10^?6M) into the left substantia nigra. The sagittal section of the mesencephalic decussations was without effect on the changes in [³H]dopamine release induced either by α-methylparatyrosine ord-amphetamine. The section of the corpus callosum and of the commissura anterior potentiated, whereas the section of the thalamic massa intermedia prevented thed-amphetamine-induced reduction of [³H]dopamine release in the left caudate nucleus. This could indicate that neuronal circuits under the control of contralateral structures may contribute to the regulation of the activity of ipsilateral dopaminergic neurons. Only the section of the thalamic massa intermedia prevented the contralateral responses evoked by the unilateral nigral application of α-methylparatyrosine ord-amphetamine.These results suggest that nigrothalamic neurons and thalamic nuclei are involved in the reciprocal regulation of both nigrostriatal dopaminergic pathways.     

The effect of some putative neurotransmitters on the release of 5-hydroxytryptamine and gamma-aminobutyric acid from slices of the rat midbrain raphe area.

The effect of various putative transmitters has been studied on the efflux of [³H]5-hydroxytryptamine and [³H]γ-aminobutyric acid from small superfused slices of the midbrain raphe area of the rat. The slices apparently contained functionally intact terminals for these transmitters since a depolarizing stimulus (50 mM KCl) stimulated the rate of efflux of [³H]5-hydroxytryptamine and [³H]γ-aminobutyric acid in a calcium-dependent fashion. Furthermore, slices accumulated radioactivity with apparent high affinity mechanisms. γ-Aminobutyric acid (50 and 100 μ m) and substance P (100 and 500μ m) stimulated the efflux of [³H]5-hydroxytryptamine. The effect of γ-aminobutyrate was blocked by picrotoxin (50 μ m) but not by strychnine (1 μ m). Other inhibitory amino acids (β-alanine, taurine and glycine) were without effect on the release of [³H]5-hydroxytryptamine. l-Noradrenaline (0.2–1 mM) stimulated the efflux of [³H]γ-aminobutyric acid but not that of [3H]5-hydroxytryptamine. Phentolamine (10μ m) but not (±)-propranolol (10 μ m) abolished the effect of 1 mM noradrenaline. Neither dopamine nor 5-hydroxytryptamine influenced the efflux of [3H]γ-aminobutyric acid.It is possible that interactions in the midbrain raphe area proposed from other studies can be mediated through presynaptic influences on transmitter release.     

Effects of nigral application of muscimol on release of [3H]γ-aminobutyrate and on multi-unit activity in various cat thalamic nuclei

The release of [³H]γ-aminobutyrate (GABA) neosynthesized from [³H]glutamine was estimated in one substantia nigra and in the ipsilateral thalamus of halothane-anesthetized cats by perfusing a [³H]glutamine-enriched physiological medium through a push-pull cannula implanted in the two structures under investigation. After two hours of superfusion, muscimol (10^?6 M) was delivered through the nigral push-pull cannula for 50–60 min and local- and distal-evoked changes of [³H]GABA release were analyzed. In some experiments, changes of global neuronal activity induced by muscimol application were recorded in different thalamic nuclei, using a bipolar electrode. In a few of the above experiments, biochemical and electrophysiological determinations were simultaneously performed in the substantia nigra and the thalamus. The nigral application of muscimol (10^?6 M) induced locally an activation of the substantia nigra reticulata cells, as well as an increase in release of [³H]GABA.Distally, in the thalamus, two types of biochemical and electrophysiological responses were observed according to the localization of the tip of the push-pull cannula or the electrode. (1) An increased release of [³H]GABA and a depression of the global multi-unit cellular activity were obtained in the ventralis medialis-ventralis lateralis, the centralis lateralis and the paracentralis nuclei. These effects could reflect an activation of the GABAergic nigrothalamic neurons projecting to these different thalamic nuclei. (2) In contrast, in the medialis dorsalis paralamellar zone adjacent to the intralaminar nuclei of the thalamus, a decrease of [³H]GABA release and an activation of the multi-unit activity were obtained. These latter results may suggest either a polysynaptic response or the non-GABAergic nature of the nigrothalamic neurons afferent to the medialis dorsalis paralamellar zone.     

A comparison of the effects of acute and one year's continuous neuroleptic treatment on the release of [3H]glutamate and [3H]acetylcholine from rat striatal slices

The effect of neuroleptic drugs administered acutely or continuously for 1 year on the release of [³H]glutamate and [³H]acetylcholine from striatal slices in vitro has been compared.Acute in vivo administration of haloperidol, trifluoperazine and clozapine increased the potassium-evoked release of [³H]acetylcholine from striatal slices in a dose-dependent fashion, whereas sulpiride was without effect. None of the neuroleptics given acutely had any effect on the potassium-evoked striatal release of [³H]glutamate.Potassium-evoked striatal release of [³H]acetylcholine in animals receiving 1 year's continuous administration of haloperidol, trifluoperazine or sulpiride was no different from that in age-matched control animals, but was less than controls in animals receiving clozapine for 1 year. All drugs caused a decrease in potassium-evoked striatal [³H]glutamate release following drug administration for 1 year compared to age-matched controls.The reversal of the acute action of neuroleptic drugs on striatal [³H]acetylcholine and [³H]glutamate release is consistent with a functional increase in striatal dopamine transmission following long-term neuroleptic treatment.     

Specific inhibitory effect of amyloid-β on presynaptic muscarinic receptor subtypes modulating neurotransmitter release in the rat nucleus accumbens

In this study we investigate on the effect of amyloid-beta1-40 (Aβ1-40) on the oxotremorine (OXO)-induced release of [³H] dopamine (DA), [³H]GABA and [³H]acetylcholine (ACh) from synaptosomes in the rat nucleus accumbens (NAc). OXO in presence of himbacine (HIMBA) was able to increase the basal release of [³H]GABA. The OXO-elicited [³H]GABA overflow was significantly antagonized by atropine (A; 94%), by the M3 antagonists DAU5884 (96%) and 4-DAMP (70%), and by Aβ1-40 (65%). Exposure of NAc synaptosomes to OXO produced a dose-dependent increase of [³H]DA overflow which was antagonized by A, partially inhibited by Aβ1-40 (100 nM) but unaffected by DAU5884 and 4-DAMP. The K⁺-evoked [³H]ACh overflow was inhibited by OXO. This effect was counteracted by the M2 antagonist AFDX-116 but not by the selective M4 antagonist mamba toxin 3 (MT3). The K⁺-evoked [³H]GABA overflow was also inhibited by OXO but conversely, this effect was counteracted by MT3 and not by AFDX-116. Aβ1-40 (100 nM) did not modify the inhibitory effect of OXO both on the K⁺-evoked [³H]ACh and [³H]GABA overflow. The results show that in the rat NAc, Aβ1-40 selectively inhibits the function of the muscarinic subtypes which stimulate neurotransmitter release and not those which modulate negatively the stimulated release.     

In vivo presynaptic control of dopamine release in the cat caudate nucleus--II. Facilitatory or inhibitory influence of L-glutamate

The local effects of various concentrations of L-glutamate (from 10(-8) M up to 10(-3) M) on the release of [3H]dopamine synthesized continuously from [3H]tyrosine were examined in the caudate nucleus of halothane-anaesthetized cats implanted with push-pull cannulae. When used at a concentration of 10(-8) M or 10(-7) M, L-glutamate stimulated the release of [3H]dopamine from nerve terminals of the nigrostriatal dopamine neurons. This effect was still observed in the presence of tetrodotoxin (5 X 10(-7) M) but it was antagonized by 2-amino 6-trifluoromethoxy benzothiazole (PK 26124) (10(-5) M), an antagonist dopamine nerve terminals. While no significant change in the release of [3H]dopamine was observed with 10(-6) M L-glutamate, higher concentrations (from 10(-5) M to 10(-3) M) of the amino acid produced a long-lasting reduction in the [3H]transmitter release. This latter effect was also antagonized by PK 26124 (10(-5) M) but, unlike that observed with 10(-8) M L-glutamate, it did not persist in the presence of tetrodotoxin (5 X 10(-7) M). On the contrary, a marked stimulation of the release of [3H]dopamine was seen in the presence of this neurotoxin. The reduction in the release of [3H]dopamine produced by 10(-4) M L-glutamate was also antagonized by bicuculline (10(-5) M) and moreover a marked stimulation of [3H]dopamine release took place in the presence of this gamma-aminobutyric acid (GABA) antagonist. Therefore, high concentrations of L-glutamate exerted an inhibitory presynaptic control on [3H]dopamine release which seemed to be indirect and mediated partly by GABAergic neurons. Since a sustained reduction in the spontaneous release of [3H]dopamine was seen in the presence of PK 26124, the corticostriatal glutamatergic neurons appeared to exert a tonic facilitatory presynaptic influence on dopamine release. This effect was important since it represented 40% of the tetrodotoxin-sensitive release of the [3H]transmitter. The direct (stimulatory) and indirect (inhibitory) presynaptic controls on dopamine release mediated by corticostriatal glutamatergic fibres are discussed in light of previous findings and of the anatomical organization of the caudate nucleus.     

Chronic uridine treatment reduces the level of [3H]spiperone-labelled dopamine receptors and enhances their turnover rate in striatum of young rats: relationship to dopamine-dependent behaviours

The effect was studied of chronic uridine treatment on the recovery of striatal D-2 dopamine (DA) receptors after their irreversible blockade by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) in young (40 days old) and adult (14 months old) male rats using [³H]spiperone as radioligand. Chronic uridine treatment (15 mg kg^-1 day^-1, i.p., 14 days) causes a reduction of [³H]spiperone binding sites in striatum of young rats. This treatment also produces an increase in the rate of recovery of striatal [³H]spiperone-labelled DA receptors in young, but not in adult rats. Catalepsy and exploratory locomotor activity, two behaviours associated with blockade versus activation of DA receptors, were evaluated in the same rats. The behavioural recovery from the EEDC^induced syndrome is more rapid in the young rats treated with uridine than in the saline-treated group. The behavioural recovery in old rats was not affected by chronic uridine treatment. Thus, in young rats the pyrimidine nucleoside uridine may modulate the steady state and the turnover rate of striatal D-2 DA receptors.     

Elementary reactions in the cationic polymerization of oxepane. Comparison with the polymerization of tetrahydromfuran

In the polymerization of oxepane (OXP), initiated with derivatives of trifluoromethanesulfonic acid, covalent and ionic active centers were simultaneously observed by ¹H and ¹⁹F NMR spectroscopy. A higher proportion of secondary oxonium ions (these species detected by ¹⁹F NMR were independently observed by proton trapping with R₃P in the ³¹P NMR spectrum). The proportion of ionic species decreases with monomer conversion, indicating a substantial contribution of bimolecular ionization of the monomer. The effective molarity in oxepane polymerization [OXP]_eff ? 1 mol ·I^-1 was found to be lower by a factor of 10² than [THF]_eff in the polymerization of THF. The rate constant of the covalent propagation in the polymerization of OXP is similar to that measured for THF, however, due to the reduced reactivity of the oxepanium cation, the relative reactivity of the covalent active centers becomes higher than that of the ions. Thus, for OXP, in CH₃NO₂ at 25°C, K_pc = 3 · 10^?4 mol^?1 · 1 · s^?1, k_pi = 2 · 10^?4 mol^?1 · 1 · s^?1 whereas for THF k_pc = 5 · 10^?4 mol^?1 · 1 · s^?1 and k_pi = 2 · 10^?2 mol^?1 · 1 · s^?1 under similar conditions. The rates of ionization and temporary termination, measured by the “temperature jump” technique, allow to determine the contributions of inter-and intramolecular ionizations. These rates becomes equal at [OXP] = 1 mol · 1^-1 (= [OXP]_eff).     

In vivo presynaptic control of dopamine release in the cat caudate nucleus--III. Further evidence for the implication of corticostriatal glutamatergic neurons

In confirmation of previous results, experiments in halothane-anaesthetized cats implanted with push-pull cannulae showed that the unilateral application of GABA (10(-5) M for 30 min) into the left thalamic motor nuclei (either ventralis medialis, or ventralis lateralis) markedly stimulated the release of [3H]dopamine continuously synthesized from [3H]tyrosine in both caudate nuclei and in the contralateral substantia nigra. Three types of experiments confirmed that the changes in [3H]dopamine release evoked in both caudate nuclei resulted from a presynaptic facilitation mediated by the bilateral corticostriatal glutamatergic projection: The constant delivery of 2-amino 6-trifluoromethoxy benzothiazole (PK 26124) (10(-5) M) to the left caudate nucleus prevented the increased release of [3H]DA evoked by application of gamma-aminobutyric acid (GABA) (10(-5)M) into ventralis medialis-ventralis lateralis while an enhanced release of [3H]dopamine still occurred in the contralateral caudate nucleus. Since PK 26124 is an antagonist of glutamatergic transmission, the presynaptic facilitation may involve glutamatergic neurons. Single unit recordings of dopamine cells in the contralateral substantia nigra indicated that the increased release of [3H]dopamine from dendrites evoked by the application of GABA (10(-5)M) into ventralis medialis-ventralis lateralis was associated with a reduction in the firing rate of dopamine cells. Thus, the enhanced release of [3H]dopamine in the contralateral caudate nucleus may involve a presynaptic facilitatory process. Finally, the unilateral lesion of the sensory motor cortex made prior to the superfusion of caudate nucleus with [3H]tyrosine prevented the responses evoked in the two caudate nuclei by the application of GABA (10(-4) M) into ventralis medialis-ventralis lateralis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Participation of both 'enkephalinase' and aminopeptidase activities in the metabolism of endogenous enkephalins

The pattern of hydrolysis of [³H]Met⁵-enkephalin by slices from rat striatum has been determined by Chromatographic isolation of [³H]peptide fragments and by assessment of the effects of various selective peptidase inhibitors. It consists in the formation of [³H]Tyr, [³H]Tyr-Gly and [³H]Tyr-Gly-Gly which represent 80%, 2% and 18%, respectively, of total³H-metabolite formation.The formation of [³H]Tyr, presumably occurring under the action of membrane-bound aminopeptidases, is reduced in the presence of either 10^?4 M puromycin or 2.10^?5 M bestatin by about 40% and 75%, respectively. Both aminopeptidase inhibitors display significantly higher potency on a crude particulate fraction from rat striatum. The formation of [³H]Tyr-Gly-Gly in the slice preparation is strongly reduced by addition of 10^?7 M thiorphan, an enkephalin dipeptidylcar?ypeptidase (‘enkephalinase’) inhibitor, but only slightly in the presence of 10^?6 M captopril, an angiotensin-converting enzyme inhibitor.When the aminopeptidase pathway is inhibited by bestatin, [³H]Tyr-Gly-Gly represents more than 60% of total hydrolysis products, suggesting that the tripeptide is partly hydrolysed after being formed under the action of ‘enkephalinase’. In the presence of both bestatin and thiorphan, the total hydrolysing activity of the slice preparation is reduced by 75% while [³H]Tyr-Gly level is slightly increased. These data indicate that the hydrolysis of exogenous Met⁵-enkephalin in the extracellular space of the slice preparation primarily involves the ‘enkephalinase’ as well as the aminopeptidase pathways.The participation of both pathways in the inactivation of endogenous Met⁵-enkephalin has also been evidenced by evaluating the recovery of the opioid peptide released by K⁺-induced depolarisation of striatal slices in the presence of bestatin and thiorphan. While the presence of either inhibitor allows a partial protection of the released peptide, their co-presence results in total recovery of the enkephalin in intact form in the medium.Finally, administration of either the aminopeptidase or the ‘enkephalinase’ inhibitor in mice results in antinociceptive effects as evaluated in the hot-plate jump test. These effects are additive and prevented by naloxone, an opiate receptor antagonist.Thus, the various experimental approaches used indicate that both (but only) the ‘enkephalinase’ and the aminopeptidase pathways play a critical role in the inactivation of endogenous enkephalins.     

Modulation of GABA release by α-amino-3-hydroxy-5-methylisoxazole-4-propionate and N-methyl-d-aspartate receptors in matrix-enriched areas of the rat striatum

Using a new in vitro superfusion device, the release of preloaded [³H]GABA was examined in microdiscs of tissues taken from sagittal slices in matrix-enriched areas of the rat striatum. Potassium (9 mM, 15 mM) stimulated the release of [³H]GABA in a concentration- and calcium-dependent manner and the veratridine (1 μM)-evoked release of [³H]GABA was completely abolished in the presence of tetrodotoxin (1 μM).The selective glutamatergic agonist α-amino-3-hydroxy-5-methylisoxazole-4-propionate (1 mM) enhanced the potassium-evoked release of [³H]GABA as well as the basal outflow of [³H]GABA. This latter effect was found to be calcium-dependent, partially diminished by tetrodotoxin (1 μM), completely blocked by 6,7-dinitro-quinoxaline-2,3-dione (0.1 mM), which is generally used as an antagonist of α-amino-3-hydroxy-5-methylisoxazole-4-propionate receptors, but not affected by ( + )-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK801, 10μM), a specific antagonist of N-methyl-d-aspartate receptors.Similarly, N-methyl-d-aspartate (1 mM) enhanced both the potassium (9mM) and the α-amino-3-hydroxy-5-methylisoxazole-4-propionate (1 mM )-evoked release of [³H]GABA but when used alone, due to the presence of magnesium in the superfusion medium, was ineffective on the basal efflux of [³H]GABA. A stimulatory effect of N-methyl-d-aspartate (1 mM) on the basal outflow of [³H]GABA was observed, however, when magnesium was omitted from the superfusion medium. The stimulatory effect of N-methyl-d-aspartate (1 mM) observed in the presence of α-amino-3-hydroxy-5-methylisoxazole-4-propionate was not potentiated by glycine (1 μM, in the presence of strychnine 1 gmM) and the N-methyl-d-aspartate-evoked response seen in the absence of magnesium was not enhanced byd-serine (1 mM). suggesting that endogenous glycine is already acting on N-methyl-d-aspartate receptors. In fact, in the absence of magnesium, 7-chloro-kynurenate (1 mM) completely abolished the stimulatory effect of N-methyl-d-aspartate on the release of [³H]GABA confirming that under our conditions, the glycine site of the N-methyl-d-aspartate receptor is saturated. N-methyl-d-aspartate-evoked responses were all blocked by MK801 (10 μM). Finally, the N-methyl-d-aspartate-evoked response seen in the absence of magnesium was markedly reduced in the presence of tetrodotoxin (1 μM). While potassium (9 mM) markedly stimulated the release of [³H]GABA from purified synaptosomes from the rat striatum, neither α-amino-3-hydroxy-5-methylisoxazole-4-propionate alone nor N-methyl-d-aspartate in the presence of α-amino-3-hydroxy-5-methylisoxazole-4-propionate or in the absence of magnesium enhanced the release of [³H]GABA. A slight but not significant stimulatory effect was observed with N-methyl-d-aspartateandd-serine using a magnesium-free superfusion medium.Altogether, these results strongly suggest that α-amino-3-hydroxy-5-methylisoxazole-4-propionate and N-methyl-d-aspartate receptors are present on dendrites and/or cell bodies of efferent GABAergic neurons but not on their nerve terminals in matrix-enriched areas of the rat striatum.     

Complex involvement of nitric oxide and cGMP at N-methyl- -aspartic acid receptors regulating γ-[H]aminobutyric acid release from striatal slices

Whilst the depolarization of postsynaptic N-methyl- -aspartic acid (NMDA) receptors leads to an influx of Ca²⁺ and subsequent synthesis of nitric oxide (NO), we examined roles for NO at striatal NMDA receptors regulating transmitter release. In superfused rat striatal slices, NMDA-evoked release of γ-[³H]aminobutyric acid ([³H]GABA) was investigated in the presence of nitrergic drugs. NMDA-induced release of [³H]GABA was attenuated by -2-aminophosphonopentanoate, tetrodotoxin and omission of Ca²⁺. -Arginine enhanced NMDA-evoked release of [³H]GABA, but exogenous NO donors were ineffective. Inhibitors of NO synthase (N^G-nitro- and N^G-amino- -arginine) and guanylate cyclase (LY83583) elevated release. Since NMDA-evoked release of [³H]GABA was partially tetrodotoxin-sensitive, nitrergic-linked NMDA receptors regulating the release are both pre- and extrasynaptic. Thus not only does NO arise from multiple sites, and involve NMDA receptors with their redox site insensitive to exogenous NO donors, but the NMDA receptors are under the influence of nitrergic and cGMP-linked negative feedback mechanisms.     

Polymerization of lactams, 54. Anionic polymerization of 2-pyrrolidone accelerated with CO2, part 3

Intrinsic viscosities in m-cresol and weight average molecular weights, M?_w, were measured for samples of high molecular weight poly(2-pyrrolidone) (poly ( 1 )) prepared by anionic polymerization of 2-pyrrolidone ( 1 ) accelerated with CO₂. It was proved that the earlier found relationship [η] = 4 · 10^?2 · M^0,77 (in cm³ · g^?1) holds for M?M_w up to 8 · 10⁵ g. mol^?1. The probable reason for the formation of poly ( 1 ) with an exceptionally high molecular weight is discussed.     

Substance P and neurokinin A regulate by different mechanisms dopamine release from dendrites and nerve terminals of the nigrostriatal dopaminergic neurons

Numerous striatal neurons innervating the substantia nigra contain substance P and/or neurokinin A. In contrast to substance P or neurokinin A, little neurokinin B is found in the substantia nigra. This led us to compare the effects of nigral application of these tachykinins on the release of dopamine from dendrites and nerve terminals of nigrostriatal dopaminergic neurons. Experiments were made in halothane-anesthetized cats implanted with one push-pull cannula in the substantia nigra and another in the ipsilateral caudate nucleus [3H]Tyrosine was delivered continuously to each push-pull cannula and the release of newly synthesized [3H]dopamine measured in the superfusate. Unlike substance P or neurokinin A, neurokinin B (10(-8) M) applied for 30 min into the pars compacta of the substantia nigra was without effect on the release of [3H]dopamine from nerve terminals or dendrites. When either substance P (10(-8) M) or neurokinin A (10(-8) M) was applied into the pars compacta, the release of [3H]dopamine from nerve terminals was enhanced. While neurokinin A also stimulated the dendritic release of [3H]dopamine, this was reduced by substance P. At a lower concentration (10(-9) M), neurokinin A induced similar effects to those observed at 10(-8) M whereas substance P (10(-9) M) stimulated moderately [3H]dopamine release from nerve terminals but did not affect the dendritic release of the [3H]amine. When superfused into the pars reticulata, substance P (10(-8) M) still stimulated [3H]dopamine release from nerve terminals but not from dendrites while neurokinin A (10(-8) M) was without effect either in the caudate nucleus or the substantia nigra. Additional experiments were made to determine whether or not substance P (10(-8) M) or neurokinin A (10(-8) M) act directly on nigral dopaminergic neurons when applied into the pars compacta. The effects of substance P on [3H]dopamine release from nerve terminals and dendrites were prevented when 2-amino-6-trifluoromethoxy benzothiazole (10(-5) M), an antagonist of glutamatergic transmission, was applied continuously into the caudate nucleus. In contrast, the stimulatory effects of neurokinin A on [3H]dopamine release from nerve terminals and dendrites were insensitive to 2-amino-6-trifluoromethoxy benzothiazole (10(-5) M). These results suggest that neurokinin A, but not substance P, acts directly on dopaminergic cells. In the light of previous observations, we propose that the effects of substance P on dopaminergic transmission are mediated by a nigro-thalamo-cortico-striatal loop.(ABSTRACT TRUNCATED AT 400 WORDS)     

Complex involvement of nitric oxide and cGMP at N-methyl-d-aspartic acid receptors regulating γ-[H]aminobutyric acid release from striatal slices

Whilst the depolarization of postsynaptic N-methyl-d-aspartic acid (NMDA) receptors leads to an influx of Ca²⁺ and subsequent synthesis of nitric oxide (NO), we examined roles for NO at striatal NMDA receptors regulating transmitter release. In superfused rat striatal slices, NMDA-evoked release of γ-[³H]aminobutyric acid ([³H]GABA) was investigated in the presence of nitrergic drugs. NMDA-induced release of [³H]GABA was attenuated by d-2-aminophosphonopentanoate, tetrodotoxin and omission of Ca²⁺. l-Arginine enhanced NMDA-evoked release of [³H]GABA, but exogenous NO donors were ineffective. Inhibitors of NO synthase (N^G-nitro- and N^G-amino-l-arginine) and guanylate cyclase (LY83583) elevated release. Since NMDA-evoked release of [³H]GABA was partially tetrodotoxin-sensitive, nitrergic-linked NMDA receptors regulating the release are both pre- and extrasynaptic. Thus not only does NO arise from multiple sites, and involve NMDA receptors with their redox site insensitive to exogenous NO donors, but the NMDA receptors are under the influence of nitrergic and cGMP-linked negative feedback mechanisms.     

RNA synthesis in activated macrophages I. Poly(I) · poly(C)-induced triggering of cytolytic activity is associated with decrease in RNA synthesis

The effects of polyinosinic, polycytidylic acid [poly(I) · poly(C)] on the activation and RNA metabolism in murine peritoneal macrophages (MΦ) elicited by proteose-peptone (pMΦ) was investigated. Poly(I) · poly(C) triggered the cytolytic activity of pMΦ and augmented their glucose oxidation. In contrast, a profound depression of [³H]uridine incorporation into RNA was observed in poly(I) · poly(C)-activated pMΦ. The degree of depression of RNA labeling paralleled the dose of poly(I) · poly(C) used to activate the pMΦ and the expression of tumoricidal activity. This decrease in [³H]uridine incorporation into MΦ RNA could not be accounted for by decreased permeability of the activated MΦ to [³H]uridine, or by instability of the labeled RNA. Moreover, analysis of the specific activity of the intracellular uridine triphosphate (UTP) pool and studies on the labeling of MΦ RNA with [³²P] orthophosphate indicated that the decreased RNA labeling was not due to changes in the specific activity of UTP. We concluded that poly(I) · poly(C)-activated pMΦ exhibit a depressed rate of RNA synthesis. We suggest that the rate of RNA synthesis may be investigated as a potential new indicator for MΦ activation.