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1.
Abstract: Cross talk between two phospholipase C (PLC)-linked receptor signalings was investigated in SK-N-BE(2)C human neuroblastoma cells. Sequential stimulation with two agonists at 5-min intervals was performed to examine the interaction between muscarinic and bradykinin (BK) receptors. Pretreatment of cells with a maximal effective concentration (5 µ M ) of BK did not affect the subsequent carbachol (CCh)-induced [Ca2+]i rise, but CCh (1 m M ) pretreatment completely abolished the BK-induced [Ca2+]i rise without inhibition of BK-induced inositol 1,4,5-trisphosphate (IP3) generation. Thapsigargin (1 µ M ) pretreatment abolished the subsequent BK- and CCh-induced [Ca2+]i rise, though it did not affect agonist-induced IP3 generation. However, the addition of atropine at plateau phases of CCh-induced [Ca2+]i rise and IP3 production caused a rapid decline to the basal levels and then restored the [Ca2+]i rise by BK. Treatment of cells with both CCh and BK at the same time showed additive effects in IP3 production. However, the [Ca2+]i rise induced by both agonists in the presence or absence of extracellular Ca2+ was the same as the responses triggered by CCh alone. The results suggest that each receptor or receptor-linked PLC activity is not influenced by pretreatment with the other agonist but IP3-sensitive Ca2+ stores are shared by signal pathways from both receptors.  相似文献   

2.
3.
Abstract: Intrastriatal microdialysis was used to administer muscarinic drugs in freely moving rats for 40 min at a flow rate of 2 µl/min. Administration of the nonselective agonist pilocarpine at 10 m M increased striatal dopamine release and decreased extracellular GABA and glutamate overflow. Perfusion with the muscarinic M2 antagonist methoctramine at 75 µ M increased extracellular dopamine and glutamate concentrations but exerted no changes on extracellular GABA levels. Intrastriatal administration of the M1 antagonist pirenzepine at 0.05 µ M decreased extracellular dopamine overflow. Application of pirenzepine (0.05 and 5 µ M ) exerted no effects on the measured GABA or glutamate levels. There are thus important differences in applied doses of muscarinic drugs needed to obtain modulatory effects. High doses of agonists are probably needed to superimpose on the background of tonic influences of striatal acetylcholine, whereas antagonists can block the receptors in small doses. We further suggest that M1 receptors might tonically facilitate striatal dopamine release, that M2 receptors might tonically inhibit striatal glutamate efflux, and that acetylcholine does not exert tonic effects on striatal GABA release. The link with the pilocarpine animal model for temporal lobe epilepsy will be discussed.  相似文献   

4.
Abstract: The effects of benzazepine derivatives on extracellular levels of dopamine (DA) and l -3,4-dihydroxyphenylacetic acid (DOPAC) in the dorsal striatum of freely moving rats were studied using in vivo microdialysis. Direct injection of SKF-38393 (0.5 or 1.5 µg/0.5 µl), a selective D1 receptor agonist, into the striatum through a cannula secured alongside a microdialysis probe produced a rapid dose-dependent transient increase in striatal DA efflux and a more gradual reduction in efflux of DOPAC. The rapid increase in DA efflux was not affected by infusion of tetrodotoxin (TTX; 2 µ M ) or Ca2+-free Ringer's solution and occurred after either enantiomer of SKF-38393. A TTX-insensitive increase in DA level similar to that induced by SKF-38393 was also seen after other benzazepines acting as agonists (SKF-75670 and SKF-82958, each 1.5 µg in 0.5 µl) and antagonists (SCH-23390, 1.5 µg in 0.5 µl) at the D1 receptor and after (+)-amphetamine. These effects were inhibited by infusion of nomifensine (100 µ M ). It is concluded that the transient increases in striatal DA efflux seen after intrastriatal injection of SKF-38393 and other benzazepines are not mediated by presynaptic D1 receptors but by an amphetamine-like action on the dopamine transporter.  相似文献   

5.
Abstract: Recent in vivo microdialysis studies have demonstrated the presence of extracellular levels of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] that can be increased in a concentration-dependent manner by muscarinic receptor activation. The aim of the present study was to determine whether extracellular levels of Ins(1,4,5)P3 could be measured in vitro. Despite rapid increases in internal Ins(1,4,5)P3 levels after stimulation with 1 m M carbachol, there was no change in external levels in both rat brain cortical slices and human neuroblastoma SH-SY5Y cells. Suprafusion of myo -[3H]inositol-prelabelled hippocampal slices with 1 m M carbachol caused an increase in 3H-inositol phosphates over basal levels in the perfusate after 10 min, reaching a peak (223 ± 56% of basal) 20 min after suprafusion with carbachol was started. This response to carbachol was potentiated in the presence of 30 m M K+. Analysis of the individual 3H-inositol phosphates in the perfusate revealed that levels of [3H]inositol monophosphate, [3H]inositol bisphosphate, [3H]inositol trisphosphate, and [3H]inositol tetrakisphosphate were all significantly increased. A similar increase in extracellular 3H-inositol phosphates was demonstrated in SH-SY5Y cells incubated with 1 m M carbachol for 30 min. This response was again enhanced by 30 m M K+, although the intracellular response was not potentiated. Possible roles for extracellular inositol phosphates are discussed.  相似文献   

6.
Abstract: This study was aimed at identifying the neuronal pathways that mediate the eating-induced increase in the release of dopamine in the nucleus accumbens of the rat brain. For that purpose, a microdialysis probe was implanted in the ventral tegmental area and a second probe was placed in the ipsilateral nucleus accumbens. Receptor-specific compounds acting on GABAA (40 µ M muscimol; 50 µ M bicuculline), GABAB (50 µ M baclofen), acetylcholine (50 µ M carbachol), NMDA [30 µ M (±)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP)], and non-NMDA [300 µ M 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX)] receptors were infused into the ventral tegmental area by retrograde dialysis, whereas extracellular dopamine was recorded in the ipsilateral nucleus accumbens. Intrategmental infusion of muscimol or baclofen decreased extracellular dopamine in the ipsilateral nucleus accumbens; CPP and CNQX were without effect, and bicuculline and carbachol increased dopamine release. During infusion of the various compounds, food-deprived rats were allowed to eat for 10 min. The infusions of muscimol, bicuculline, baclofen, carbachol, and CNQX did not prevent the eating-induced increase in extracellular dopamine in the nucleus accumbens. However, during intrategmental infusion of CPP, the eating-induced increase in extracellular dopamine in the nucleus accumbens was suppressed. These results indicate that a glutamatergic projection to the ventral tegmental area mediates, via an NMDA receptor, the eating-induced increase in dopamine release from mesolimbic dopamine neurons.  相似文献   

7.
Abstract: Serotonin (5-HT) applied at 1, 3, and 10 µ M into the striatum of halothane-anesthetized rats by in vivo microdialysis enhanced dopamine (DA) outflow up to 173, 283, and 584% of baseline values, respectively. The 5-HT effect was partially reduced by 1 or 10 µ M GR 125,487, a 5-HT4 antagonist, and by 100 µ M DAU 6285, a 5-HT3/4 antagonist, whereas the 5-HT1/2/6 antagonist methiothepin (50 µ M ) was ineffective. In the presence of tetrodotoxin the effect of 1 µ M 5-HT was not affected by 5-HT4 antagonists. In addition, tetrodotoxin abolished the increase in DA release induced by the 5-HT4 agonist ( S )-zacopride (100 µ M ). In striatal synaptosomes, 1 and 10 µ M 5-HT increased the outflow of newly synthesized [3H]DA up to 163 and 635% of control values, respectively. The 5-HT4 agonists BIMU 8 and ( S )-zacopride (1 and 10 µ M ) failed to modify [3H]DA outflow, whereas 5-methoxytryptamine (5-MeOT) at 10 µ M increased it (62%). In prelabeled [3H]DA synaptosomes, 1 µ M 5-HT, but not ( S )-zacopride (1 and 10 µ M ), increased [3H]DA outflow. DAU 6285 (10 µ M ) failed to modify the enhancement of newly synthesized [3H]DA outflow induced by 5-MeOT or 5-HT (1 µ M ), whereas the effect of 5-HT was reduced to the same extent by the DA reuptake inhibitor nomifensine (1 µ M ) alone or in the presence of DAU 6285. These results show that striatal 5-HT4 receptors are involved in the 5-HT-induced enhancement of striatal DA release in vivo and that they are not located on striatal DA terminals.  相似文献   

8.
Abstract: Acetylcholine plays an important role in cortical arousal. Adenosine is released during increased metabolism and has been suggested to be a sleep-promoting factor. To understand the interaction of acetylcholine and adenosine in regulating cortical excitability, we examined the effect of carbachol on NMDA-evoked adenosine release and identified the muscarinic receptor subtype that mediated this effect in adult rat cortical slices in vitro. Carbachol (to 300 µ M ) alone did not affect the basal release of adenosine. However, carbachol (100 µ M ) induced a 253% increase in NMDA (20 µ M )-evoked adenosine release in the presence of Mg2+. In the absence of Mg2+, carbachol's potentiating effect was less (60% increase). The nonselective muscarinic antagonist atropine (1.5 µ M ) blocked the facilitatory effect of carbachol on NMDA-evoked adenosine release, and this was mimicked by the M3-selective antagonist 4-diphenylacetoxy- N -methylpiperidine (1 µ M ). Neither an M1-selective dose of pirenzepine (50 n M ) nor the M2-selective antagonist methoctramine (1 µ M ) affected carbachol's action on NMDA-evoked adenosine release. Carbachol had no effect on adenosine release evoked by α-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA). These results suggest that acetylcholine does not affect basal adenosine release but enhances NMDA receptor-mediated evoked adenosine release by acting at M3 receptors in the cortex. This interaction may have a role in regulating cortical neuronal excitability on a long-term basis.  相似文献   

9.
Abstract: The regulation of striatal cholinergic function by tachykinins was examined in urethane-anesthetized rats by using microdialysis. Substance P (0.01–1 µ M ), [Sar9,Met(O2)11]substance P (1–10 µ M ), septide (0.1–3 µ M ), neurokinin (NK) A (0.1–10 µ M ), and senktide (0.1–10 µ M ) produced concentration-dependent increases in striatal acetylcholine (ACh) release. Septide was the most potent agonist for inducing release of ACh, whereas the stimulating effect of senktide was less pronounced and more progressive in onset. The response to septide was prevented by intraperitoneal administration of the nonpeptide NK1 antagonist SR 140333 (1–3 mg/kg) but not by the nonpeptide NK2 receptor antagonist SR 48968, indicating that the effect was mediated specifically by NK1 receptors. ACh release caused by NKA was reduced by SR 48968 (1–3 mg/kg) and slightly affected by SR 140333, indicating a principal role for NK2 receptors in the peptide response. The similar efficacy of SR 140333 and SR 48968 in blocking substance P-induced ACh release suggested that the effect of this peptide involves the stimulation of both NK1 and NK2 receptors. Finally, our results indicate that the increase in striatal ACh release induced by the D1 agonist (+)-SKF-38393 (3 µ M ) may be mediated indirectly through local release of NKA or substance P acting at NK2 receptors.  相似文献   

10.
Abstract: Acetylcholine and other muscarinic agonists stimulate the proliferation of rat cortical astrocytes and 132 1N1 human astrocytoma cells by activating muscarinic m3 cholinergic receptors. Ethanol was a potent inhibitor of carbachol-stimulated proliferation, measured by [3H]thymidine incorporation, with an IC50 of 10 m M . On the other hand, basal and serum-stimulated proliferation of astrocytes and astrocytoma cells was inhibited by ethanol with lower potency (IC50 = 200–250 m M ). Concentration-response experiments with carbachol, in the presence of 10 m M ethanol, suggested that inhibition of proliferation by the alcohol was of the noncompetitive type. Experiments with acetaldehyde and with the alcohol dehydrogenase inhibitor 4-methylpyrazole suggested that the inhibitory effect of alcohol was due to ethanol itself and not to its metabolite acetaldehyde. Proliferation of astrocytoma cells induced by carbachol and the inhibitory effects of ethanol were also confirmed by flow cytometry using the 5-bromodeoxyuridine-Hoechst 33258 method. Ethanol (10 m M ) had no effect on proliferation induced by 50 µg/ml insulin and 100 ng/ml platelet-derived growth factor BB; on the other hand, the mitogenic effect of 1 m M histamine, 100 U/ml interleukin-1, and 100 ng/ml 12- O -tetradecanoylphorbol 13-acetate were inhibited by ∼50%. These results indicate that proliferation of glial cells induced by muscarinic agonists is especially sensitive to the inhibitory effect of ethanol. This action of ethanol may be relevant to its developmental neurotoxicity, particularly microencephaly, which is one of the common features of the fetal alcohol syndrome.  相似文献   

11.
Abstract: In cultured bovine adrenal medullary cells, stimulation of nicotinic receptors by carbachol evoked the Ca2+-dependent exocytotic cosecretion of proadrenomedullin N-terminal 20 peptide (PAMP) (EC50 = 50.1 µ M ) and catecholamines (EC50 = 63.0 µ M ), with the molar ratio of PAMP/catecholamines secreted being equal to the ratio in the cells. Addition of PAMP[1–20]NH2 inhibited carbachol-induced 22Na+ influx via nicotinic receptors (IC50 = 2.5 µ M ) in a noncompetitive manner and thereby reduced carbachol-induced 45Ca2+ influx via voltage-dependent Ca2+ channels (IC50 = 1.0 µ M ) and catecholamine secretion (IC50 = 1.6 µ M ). It did not alter high K+-induced 45Ca2+ influx via voltage-dependent Ca2+ channels or veratridine-induced 22Na+ influx via voltage-dependent Na+ channels. PAMP seems to be a novel antinicotinic peptide cosecreted with catecholamines by a Ca2+-dependent exocytosis in response to nicotinic receptor stimulation.  相似文献   

12.
Abstract: The effect of (±)-8-hydroxy-2-(di- n -propylamino)tetralin (8-OH-DPAT), a selective serotonin 5-HT1A agonist, on levels of extracellular norepinephrine (NE), dopamine (DA), and 5-HT (measured simultaneously) was investigated by microdialysis in the ventral tegmental area (VTA) of freely moving rats, and their behavioral activity was monitored. At 50 µg/kg s.c., 8-OH-DPAT reduced 5-HT levels but enhanced NE and DA levels in VTA dialysate. These effects were not altered by pretreatment with systemic idazoxan (5 mg/kg i.p.), a selective α2 antagonist, or local sulpiride (10 µ M ), a selective D2/D3 antagonist. At 500 µg/kg s.c., 8-OH-DPAT further enhanced or more persistently reduced dialysate NE or 5-HT content but had little effect on dialysate DA content. Its DA level-increasing effect could be seen dramatically with local infusion of cocaine (30 µ M ) and, to a lesser extent, sulpiride (10 µ M ). Depletion of endogenous 5-HT with p -chlorophenylalanine attenuated both the 5-HT level-reducing and DA level-enhancing effects of 8-OH-DPAT without affecting its maximal NE effect and the locomotor-stimulatory effect. Partial depletion of endogenous NE with N -(2-chloroethyl)- N -ethyl-2-bromobenzylamine failed to change the monoamine response but diminished the locomotion induced by 8-OH-DPAT. These results suggested that (a) the low dose of 8-OH-DPAT may act at presynaptic 5-HT1A receptors to modulate 5-HT and DA release, while acting at postsynaptic 5-HT1A receptors to modulate NE release; (b) the high dose of 8-OH-DPAT may activate D2 receptors to offset its DA level-increasing effect; and (c) the locomotor-stimulatory effect of 8-OH-DPAT might be mediated primarily by postsynaptic 5-HT1A receptors and the NE system.  相似文献   

13.
Abstract: The human neuroblastoma cell line SK-N-BE expresses δ-opioid receptors negatively coupled to adenylyl cyclase. Prolonged treatment (2 h) of the cells with 100 n M etorphine leads to an almost complete desensitization (8.2 ± 5.9 vs. 45.8 ± 8.7% for the control). Other receptors negatively coupled to adenylyl cyclase, namely, D2-dopaminergic, α2-adrenergic, and m2/m4-muscarinic, were identified by screening of these cells, and it was shown that prolonged treatment (2 h) with 1 µ M 2-bromo-α-ergocryptine or 1 µ M arterenol resulted in a marked desensitization of D2-dopaminergic and α2-adrenergic receptors, respectively. Cross-desensitization experiments revealed that pretreatment with etorphine desensitized with the same efficiency the δ-opioid receptor and the D2-dopaminergic receptor, and pretreatment with 2-bromo-α-ergocryptine also desensitized both receptors. In contrast, pretreatment with etorphine desensitized only partly the α2-adrenergic receptor response, whereas pretreatment with 1 µ M arterenol partly desensitized the δ-opioid receptor response. It is concluded that the δ-opioid receptor-mediated inhibitory response of adenylyl cyclase undergoes heterologous desensitization, and it is suggested that δ-opioid and D2-dopaminergic receptors are coupled to adenylyl cyclase via a Gi2 protein, whereas α2-adrenergic receptor could be coupled to the enzyme via two G proteins, Gi2 and another member of the Gi/Go family.  相似文献   

14.
Abstract: We investigated the modulation of (±)-α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-induced increases in intracellular free Ca2+ ([Ca2+]i) and intracellular free Mg2+ ([Mg2+]i) by cyclothiazide and GYKI 52466 using microspectrofluorimetry in single cultured rat brain neurons. AMPA-induced changes in [Ca2+]i were increased by 0.3–100 µ M cyclothiazide, with an EC50 value of 2.40 µ M and a maximum potentiation of 428% of control values. [Ca2+]i responses to glutamate in the presence of N -methyl- d -aspartate (NMDA) receptor antagonists were also potentiated by 10 µ M cyclothiazide. The response to NMDA was not affected, demonstrating specificity of cyclothiazide for non-NMDA receptors. Almost all neurons responded with an increase in [Ca2+]i to both kainate and AMPA in the absence of extracellular Na+, and these Na+-free responses were also potentiated by cyclothiazide. GYKI 52466 inhibited responses to AMPA with an IC50 value of 12.0 µ M . Ten micromolar cyclothiazide significantly decreased the potency of GYKI 52466. However, the magnitude of this decrease in potency was not consistent with a competitive interaction between the two ligands. Cyclothiazide also potentiated AMPA- and glutamate-induced increases in [Mg2+]i. These results are consistent with the ability of cyclothiazide to decrease desensitization of non-NMDA glutamate receptors and may provide the basis for the increase in non-NMDA receptor-mediated excitotoxicity produced by cyclothiazide.  相似文献   

15.
Abstract: The ability of receptors coupled to phosphoinositide turnover to evoke accumulation of inositol 1,4,5-trisphosphate (InsP3) over extended incubation periods, and consequently to affect the level of InsP3 receptor expression, was studied in cultured cerebellar granule cells. The cholinergic agonist carbachol (CCh; 1 m M ) evoked a biphasic accumulation of InsP3, a rapid three- to fourfold peak increase over control levels at ∼10 s, decreasing within 1 min to a long-lasting plateau elevation. Using an antibody against the type I InsP3 receptor, it was demonstrated that >50% down-regulation of type I InsP3 receptor expression in cerebellar granule cells occurred within 1 h of incubation with 1 m M CCh. Over 24 h, 1 m M CCh caused an ∼85% decrease in type I InsP3 receptor levels, and significant decreases in immunoreactivity were evident at much lower concentrations of CCh. Direct assessment of total InsP3 receptor expression using a radioligand binding method also detected down-regulation, but to an apparently lesser extent. 1-Aminocyclopentane-1 S ,3 R -dicarboxylic acid (200 µ M ), an agonist of metabotropic glutamate receptors, evoked a marked decrease in type I InsP3 receptors after 24 h of incubation. These findings demonstrate that a functional consequence of maintained InsP3 production in cerebellar granule cells is the down-regulation of InsP3 receptor expression and that this down-regulation may be a common mechanism of action of phosphoinositide-linked receptors during prolonged stimulation.  相似文献   

16.
Abstract: It is generally believed that the neuronal form of nitric oxide synthase (nNOS) is constitutively expressed and that regulation of this enzyme's activity is mediated solely by changes in cytosolic calcium concentration. Serendipitously, however, we observed that pretreatment of Chinese hamster ovary (CHO) cells, which coexpress muscarinic M1 receptors and nNOS, with 3.3 µ M or 1 m M carbachol (CCh) for 48 h resulted in marked enhancement of maximal muscarinic receptor-stimulated nNOS activity as determined by l -[3H]citrulline and cyclic [3H]GMP production. This was accompanied by a decrease in the potency of CCh. Muscarinic receptor density was reduced in the agonist-pretreated cells, as determined by specific [ N-methyl -3H]scopolamine methyl chloride binding, whereas competition binding studies revealed no changes in agonist affinity. Both receptor-stimulated inositol phosphate formation and elevation of intracellular calcium concentrations were found to be desensitized in agonist-pretreated cells in a manner dependent on CCh pretreatment concentration. It is interesting that ionomycin-stimulated nNOS activity was greater in CCh-pretreated cells. Also, western analysis revealed increased nNOS immunoreactivity in pretreated cells. A similar increase in nNOS immunoreactivity following agonist treatment was demonstrated in N1E-115 neuroblastoma cells, which endogenously express nNOS and muscarinic M1 receptors. Thus, the enhancement of maximal receptor-stimulated nNOS activity following agonist pretreatment can be attributed to up-regulation of nNOS. It is interesting that this augmentation of the response takes place in spite of receptor down-regulation and desensitization of multiple steps involved in nNOS activation.  相似文献   

17.
Abstract: Using microdialysis in the hippocampus of anaesthetised rats, the concentration of extracellular adenosine was estimated to be 0.8 µ M . Kainic acid (0.1–25 m M ) in the perfusate evoked a concentration-dependent release of adenosine with an EC50 of 940 µ M . Two 5-min pulses of 1 m M kainic acid in the perfusate increased the dialysate levels with an S2/S1 ratio of 0.52 ± 0.03. Kainate-evoked release of adenosine was reduced significantly by 10 µ M tetrodotoxin and by a κ-receptor agonist, U50,488H (100 µ M ). The S2/S1 ratio was reduced by 4.5 µ M 6-cyano-7-nitroquinoxaline-2,3-dione, a non-NMDA receptor antagonist, but not by the NMDA receptor blockers (+)-MK-801 (dizocilpine; 100 µ M ) or (±)-2-amino-5-phosphonopentanoic acid (1 m M ), indicating a non-NMDA receptor-mediated process. The S2/S1 ratio was also reduced significantly by 10 m M ascorbic acid, 10 m M glutathione (a scavenger of hydroperoxides), and 1 m M oxypurinol (a xanthine oxidase inhibitor), indicating the possible involvement of free radicals. Neither the adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dimethylxanthine (100 µ M ) nor the A1 adenosine receptor agonist R (−)- N 6-(2-phenylisopropyl)adenosine (100 µ M ) affected release. Adenosine release evoked by kainic acid is therefore mediated by activation of non-NMDA receptors and may involve the propagation of action potentials and the production of free radicals.  相似文献   

18.
Abstract: The cholinergic agonist carbachol, epinephrine, and the opiate morphine all inhibit prostaglandin E1 (PGE1)-stimulated adenylate cyclase in homogenates from the neuroblastoma-glioma hybrid NG108-15. Pretreatment of the hybrid with 100 μ M carbachol resulted in the rapid loss (desensitization) of the carbachol inhibition of adenylate cyclase (tM1/2< 3 min). The desensitization of the carbachol inhibition was blocked by 0.1 μ M atropine. Pretreatment with carbachol (1–24 h) did not significantly affect the inhibition of adenylate cyclase by either epinephrine or morphine, nor did it alter the PGE1-stimulated activity, that is, no supersensitization was observed. Cholate extracts of the particulate fraction from either carbachol-desensitized or of control NGlOS-15 were able to reconstitute adenylate cyclase activities of the coupling proteins (G/F)-deficient cyclymphoma cell membranes with equal efficacy. These results suggested that the coupling proteins of the adenylate cyclase were not altered by the carbachol pretreatment and that desensitization occurs at the receptor or at a receptor-associated level. However, the possibility remained that specific domains of the G/F, which interact only with muscarinic receptors, were altered.  相似文献   

19.
Abstract: Mild depolarisation (20 m M KCI) synergistically enhances the ability of a muscarinic agonist to activate phosphoinositide turnover and to elevate inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] in cerebellar granule cells in primary culture. The effects of lithium on this intense stimulation of phosphoinositide turnover was studied. Lithium causes depletion of cytoplasmic inositol and phosphoinositides, which results in the inhibition of phosphoinositide turnover within 15 min and the return of Ins(1,4,5)P3 to basal levels at this time. This inhibition could not be reversed by culturing and preincubating cerebellar granule cells in concentrations of inositol similar to those detected in the CSF. Inositol concentrations substantially in excess of those in the CSF not only reversed the effects of lithium on stimulated Ins(1,4,5)P3 levels, but significantly enhanced this level in comparison with stimulation in the absence of lithium. sn -1,2-Diacylglycerol elevation during stimulated phosphoinositide turnover was also disrupted by lithium, but in contrast to Ins(1,4,5)3, the presence of lithium resulted in a transient enhancement of the elevation evoked by carbachol plus mild KCI depolarisation, which was reversed by 500 µ M inositol, but not by 200 µ M inositol. The implications of these phenomena in relation to the mechanism of action of lithium in the treatment of manic depression are discussed.  相似文献   

20.
Abstract: Different neurotransmitter receptor agonists [carbachol, serotonin, noradrenaline, histamine, endothelin-1, and trans -(1 S ,3 R )-aminocyclopentyl-1,3-dicarboxylic acid ( trans -ACPD)], known as stimuli of phospholipase C in brain tissue, were tested for phospholipase D stimulation in [32P]Pi-prelabeled rat brain cortical and hippocampal slices. The accumulation of [32P]phosphatidylethanol was measured as an index of phospholipase D-catalyzed transphosphatidylation in the presence of ethanol. Among the six neurotransmitter receptor agonists tested, only noradrenaline, histamine, endothelin-1, and trans -ACPD stimulated phospholipase D in hippocampus and cortex, an effect that was strictly dependent of the presence of millimolar extracellular calcium concentrations. The effect of histamine (EC50 18 µ M ) was inhibited by the H1 receptor antagonist mepyramine with a K i constant of 0.7 n M and was resistant to H2 and H3 receptor antagonists (ranitidine and tioperamide, respectively). Endothelin-1-stimulated phospholipase D (EC50 44 n M ) was not blocked by BQ-123, a specific antagonist of the ETA receptor. Endothelin-3 and the specific ETB receptor agonist safarotoxin 6c were also able to stimulate phospholipase D with efficacies similar to that of endothelin-1, and EC50 values of 16 and 3 n M , respectively. These results show that histamine and endothelin-1 stimulate phospholipase D in rat brain through H1 and ETB receptors, respectively.  相似文献   

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