Adenosine reduces glutamate release in rat spinal synaptosomes

BACKGROUND: A1 adenosine receptor activation reduces hypersensitivity in animal models of chronic pain, but intrathecal adenosine does not produce analgesia to acute noxious stimuli. Here, the authors test whether increased inhibition by adenosine of glutamate release from afferents after injury accounts for this difference. METHODS: Synaptosomes were prepared from the dorsal half of the lumbar spinal cord of normal rats or those with spinal nerve ligation. Glutamate release evoked by the TRPV-1 receptor agonist, capsaicin, was measured. Adenosine with or without adenosine A1 and A2 receptor antagonists was applied to determine the efficacy and mechanism of adenosine to reduce capsaicin-evoked glutamate release. RESULTS: Capsaicin produced a concentration-dependent glutamate release similarly in normal and nerve-injured rats. Capsaicin-evoked glutamate release was inhibited by adenosine or R-PIA (R-N6-(2- phenylisopropyl)-adenosine) in a concentration-dependent manner, with a threshold of 10 nm in both normal and nerve-ligated synaptosomes. Blockade of capsaicin-evoked glutamate release by adenosine was reversed similarly in synaptosomes from normal and spinal nerve-ligated animals by an A1 adenosine receptor antagonist DPCPX (8-cyclopentyl-1,3-dipropylxanthine) but not by an A2 adenosine receptor antagonist DMPX (3'7-dimethyl-1-proparaglyxanthine). Capsaicin-evoked glutamate release, as well as its inhibition by adenosine, did not differ between synaptosomes prepared from tissue ipsilateral and contralateral to spinal nerve ligation. CONCLUSION: These observations confirm previous neurophysiologic studies that presynaptic adenosine A1 receptor activation inhibits glutamate release from primary afferents. This effect is unaltered after peripheral nerve injury and thereby is unlikely to account for the enhanced analgesic efficacy of intrathecal adenosine in this setting.     

Norepinephrine stimulates amylase release from pancreatic acini

alpha-Adrenergic blockade decreases food-stimulated amylase secretion in dogs, suggesting that physiologic sympathetic nerve discharge of norepinephrine enhances pancreatic enzyme secretion. Previous studies have not separated direct effects of adrenergic agonists on pancreatic exocrine cells from effects on blood flow. An in vitro preparation of dispersed acini from guinea pig pancreas was modified and amylase release in response to common pancreatic stimulants was measured. It was demonstrated that physiologic concentrations of norepinephrine enhance amylase release from dispersed pancreatic acini evoked by supramaximal concentrations of cholecystokinin. These observations suggest that the sympathetic nervous system plays a role in modulating pancreatic enzyme secretion independent of effects on blood flow.     

Norepinephrine and serotonin release upon impact injury to rat spinal cord.

Microdialysis sampling was used to characterize the release of norepinephrine and serotonin upon impact injury to the rat spinal cord. Increases in extracellular norepinephrine concentrations in response to injury were small and of short duration. In contrast, serotonin concentrations quickly rose 35-90 times following injury and took 30-45 min to return to control levels. Bleeding caused by injury was probably the major source of the increased serotonin levels. Our results allow a role for serotonin in secondary damage upon injury to the spinal cord but suggest that norepinephrine is not a very significant contributor to such damage.     

GABAA受体介导硫喷妥钠对大鼠前额皮层突触体谷氨酸释放的抑制作用

目的观察硫喷妥钠对大鼠前额皮层突触体谷氨酸释放的影响以及γ-氨基丁酸受体(GABAA)在其中的作用.方法 SD大鼠断头取脑,分离前额皮层,加入到冰冷蔗糖溶液中进行匀浆,在0℃～4℃下以1 000 g离心5 min,取上清液再以12 000 g离心20 min,所得沉淀为粗突触体,用人工脑脊液孵育.分为5组对照组(C组)、硫喷妥钠10 μmol/L组(THS10组)、硫喷妥钠30 μmol/L组(THS30组)、硫喷妥钠100 μmol/L组(THS100组)、硫喷妥钠300 μmol/L组(THS300组),每组含8份突触体.向各组人工脑脊液中分别加入10～300 μmol/L不同浓度的硫喷妥钠(C组中不加入),于37℃水浴中自发释放或应用30 mmol/L KCl诱发释放谷氨酸,应用高效液相色谱法测定反应液中谷氨酸含量,于水浴前向人工脑脊液中加入0.1 mmol/L的荷包牡丹碱,观察其对硫喷妥钠影响谷氨酸释放的作用.结果硫喷妥钠30、100、300 μmol/L可明显抑制谷氨酸的自发释放(P＜0.01)及KCl诱发的谷氨酸释放(P均＜0.01),THS10、THS30、THS100三组之间差异有显著性(P＜0.01),但THS100与THS300两组之间差异无显著性(P＞0.05).0.1 mmol/L荷包牡丹碱本身对突触体自发释放和KCl诱发释放谷氨酸无明显影响,但硫喷妥钠各浓度组中加入荷包牡丹碱后,谷氨酸释放水平与C组比较差异无显著性(P＞0.05).结论硫喷妥钠可浓度依赖性地抑制大鼠前额皮层突触体自发释放及高浓度KCl诱发释放谷氨酸,这种效应是由GABAA受体介导的.     

Nicotinic acetylcholine receptor regulation of spinal norepinephrine release

BACKGROUND: Neuronal nicotinic acetylcholine receptor (nAChR) agonists produce antinociception in animals. nAChRs exist almost exclusively on presynaptic terminals in the central nervous system and stimulate neurotransmitter release. This study tested whether nAChR agonists stimulate spinal release of the neurotransmitter norepinephrine either by direct actions on noradrenergic terminals or indirectly by stimulating release of other neurotransmitters to induce norepinephrine release. METHODS: Adult male rats were anesthetized and microdialysis probes inserted in the L2-L4 dermatomes of the spinal cord. Probes were perfused with artificial cerebrospinal fluid containing nicotine, the specific alpha(4)beta(2*) nAChR agonist metanicotine, or nicotine plus nAChR antagonists and norepinephrine measured in the microdialysates. The effects of specific glutamate receptor antagonists and nitric oxide synthase inhibitors were also examined. To determine direct effects on noradrenergic terminals, synaptosomes were prepared from spinal cord and incubated with nAChR agonists and antagonists. RESULTS: Both nicotine and metanicotine induced norepinephrine release in spinal microdialsyates, an effect reduced by nicotinic antagonists but not glutamate antagonists or nitric oxide synthase inhibitors. Both of the nicotinic agonists stimulated norepinephrine release in synaptosomes, and the effect of metanicotine was blocked at lower concentrations of alpha(4)beta(2*)- than alpha(7*)-preferring nAChR antagonists. CONCLUSION: These results suggest that one mechanism by which nAChR agonists act for analgesia is to stimulate spinal norepinephrine release. They do so by actions on alpha(4)beta(2*) nAChRs, and perhaps other subtypes, most likely located on noradrenergic terminals, rather than by indirectly stimulating norepinephrine release through glutamate release or nitric oxide synthesis.     

Beta-adrenergic stimulation modulation of heart rate via synchronization of ryanodine receptor Ca2+ release

A robust "fight or flight response", largely mediated via acute beta-adrenergic receptor (beta-AR) stimulation to the heart to increase its beating rate and contractile performance, is an essential component of the vertebrate survival instinct. While it has long been recognized that activation of beta-AR increases the spontaneous beating rate of sinoatrial nodal cells (SANC), specific links between stimulation of beta-ARs and the resultant increase in firing rate have not been evaluated. Our recent studies employed imaging of subcellular Ca2+ release coupled with recording of membrane potential or current in single, isolated cardiac SANC, to seek novel links between beta-AR stimulation and ryanodine receptor Ca2+ release and heart rate. An overview of these recent results, which provides novel insights into mechanisms of cardiac reserve that underlie the "fight or flight instinct, is presented here.     

Moxonidine, a selective imidazoline-alpha2 -adrenergic receptor agonist, produces spinal synergistic antihyperalgesia with morphine in nerve-injured mice

BACKGROUND: Moxonidine, a novel imidazoline-alpha2-adrenergic receptor-selective analgesic, was recently identified as antinociceptive but has yet to be evaluated in neuropathic pain models. alpha2-adrenergic receptor-selective analgesics, and high-efficacy opioids, effectively inhibit neuropathic pain behaviors in rodents. In contrast, morphine potency and efficacy decreases in states of neuropathic pain, both in rodents and in humans, but may be restored or enhanced by coadministration of morphine with alpha2-adrenergic receptor-selective analgesics. The current experiments extend the evaluation of opioid-coadjuvant interactions in neuropathic subjects by testing the respective antihyperalgesic interactions of moxonidine and clonidine with morphine in a test of mechanical hyperalgesia. METHODS: Nerve-injured mice (Chung model) were spinally administered moxonidine, clonidine, morphine, and the combinations moxonidine-morphine and clonidine-morphine. Hyperalgesia was detected by von Frey monofilament stimulation (3.3 mN) to the hind paws (plantar surface). The ED50 values were calculated and the interactions tested by isobolographic analysis. RESULTS: In nerve-injured mice, moxonidine, clonidine, and morphine all dose-dependently inhibited mechanical hyperalgesia. Furthermore, the combinations of moxonidine-morphine and clonidine-morphine resulted in substantial leftward shifts in the dose-response curves compared with those of each agonist administered separately. The calculated ED50 values of the dose-response curves of these combinations were significantly lower than their corresponding theoretical additive ED50 values. These results confirmed that both interactions were synergistic. CONCLUSIONS: Moxonidine and clonidine both synergize with morphine to inhibit paw withdrawal from nociceptive mechanical stimuli in nerve-injured mice.     

高位脊髓损伤大鼠外周a1-肾上腺素受体敏感性的变化

目的 评价高位脊髓损伤大鼠外周a1-肾上腺素受体敏感性的变化。方法 健康雄性Wistar大鼠30只，随机分为脊髓损伤组（L组，n=24）和对照组（C组，n=6）。L组大鼠采用改良Aliens打击法建立脊髓胸。节段损伤动物模型，术后3周随机分为4个亚组（n=6），分别静脉注射苯福林1btg,／kg（P1亚组）、2μg,／kg（P2亚组）、3μg/kg（P3亚组）和4μg,／kg（P4亚组），C组亦分次分别静脉注射苯福林1、2．3和4μg／kg，观察注药前、后大鼠心率、收缩压及舒张压的变化。结果 与C组比较，L组大鼠给药前体重减轻、心率减慢，收缩压和舒张压降低。与基础值比较，C组和L组给药后心率减慢，收缩压和舒张压升高。与C组比较，L组给药后心率、收缩压、舒张压变化率增高（P〈0．05或0．01）。结论 高位脊髓损伤后，大鼠外周a1-肾上腺素受体敏感性增强。     

高位脊髓损伤大鼠外周α1-肾上腺素受体敏感性的变化

目的评价高位脊髓损伤大鼠外周α1-肾上腺素受体敏感性的变化.方法健康雄性Wistar大鼠30只,随机分为脊髓损伤组(L组,n=24)和对照组(C组,n=6).L组大鼠采用改良Allens打击法建立脊髓胸4节段损伤动物模型,术后3周随机分为4个亚组(n=6),分别静脉注射苯福林1μg/kg(P1亚组)、2μg/kg(P2亚组)、3μg/kg(P3亚组)和4μg/kg(P4亚组),C组亦分次分别静脉注射苯福林1、2、3和4μg/kg,观察注药前、后大鼠心率、收缩压及舒张压的变化.结果与C组比较,L组大鼠给药前体重减轻、心率减慢,收缩压和舒张压降低.与基础值比较,C组和L组给药后心率减慢,收缩压和舒张压升高.与C组比较,L组给药后心率、收缩压、舒张压变化率增高(P＜0.05或0.01).结论高位脊髓损伤后,大鼠外周α1-肾上腺素受体敏感性增强.     

黑皮质素4型受体在大鼠脊髓星形胶质细胞释放兴奋性氨基酸中的作用

目的 探讨黑皮质素4型受体(MC4R)在大鼠脊髓星形胶质细胞释放兴奋性氨基酸中的作用.方法 原代培养大鼠脊髓星形胶质细胞,随机分为3组,每组6孔:正常白对照组(C组)、T组和TH组.C组未作任何处理,T组加入终浓度为10μg/L的TNF-α;TH组同时加入终浓度为10μg/L的TNF-α和终浓度为1 μmol/L的MC4R特异性阻断剂HS014.各组孵育3 h后采用高效液相-串联四级杆质谱法检测上清液谷氨酸(Glu)和天门冬氨酸(Asp)的浓度.结果 与C组比较,T组Glu和Asp浓度升高(P＜0.01),TH组Glu和Asp浓度差异无统计学意义(P＞0.05);与T组比较,TH组Glu和Asp浓度降低(P＜0.01).结论 MC4R介导了大鼠脊髓星形胶质细胞释放兴奋性氨基酸的作用.     

Hormonal regulation of beta2-adrenergic receptor level in prostate cancer

BACKGROUND: Androgen deprivation is the only effective systemic therapy available for patients with prostatic carcinoma, but is associated with a gradual transition to a hormone-refractory prostate cancer (HRCAP) in which ligand-independent activation of the androgen receptor has been implicated. The beta(2)-adrenergic receptor (beta(2)-AR) is a well-known activator of the androgen receptor. METHODS: Prostatic cell lines were analyzed using cDNA micro-array, real time RT-PCR, radioligand binding assay, cAMP measurements, transfection and thymidine incorporation assay. Clinical specimens were studied by immunohistochemistry and Affymetrix microarrays. RESULTS: Here, we show that beta(2)-AR was transiently down-regulated both at mRNA- and protein levels when hormone-sensitive prostate cancer cells, LNCaP, were cultured in steroid stripped medium (charcoal-stripped fetal calf serum) or when the cells were treated with the anti-androgen, bicalutamide (Casodex). The number of beta-adrenergic receptors was modestly up-regulated in androgen independent cell lines (LNCaP-C4, LNCaP-C4-2 and DU145) compared to LNCaP. Triiodothyronine (T3) increased the level of beta(2)-AR and the effect of T3 was inhibited by bicalutamide. Immunohistochemical staining of human prostate specimens showed high expression of beta(2)-AR in glandular, epithelial cells and increased expression in malignant cells compared to benign hyperplasia and normal tissue. Interestingly, beta(2)-AR mRNA was strongly down-regulated by androgen ablation therapy of prostate cancer patients. CONCLUSION: The level of beta(2)-AR was increased by T3 in prostatic adenocarcinoma cells and reduced in prostate cancer patients who had received androgen ablation therapy for 3 months.     

Alpha 2-adrenergic receptor levels in obstructive and spastic Raynaud's syndrome

The present study examines the hypothesis that alterations in the activity of alpha 2-adrenergic receptors (A2R) may underlie the clinical vasospasm seen in patients with Raynaud's syndrome. Platelets were isolated from 13 normal subjects, from 50 patients with vasospastic Raynaud's syndrome, and from 20 patients with obstructive Raynaud's syndrome and A2R levels measured. Binding capacity as determined in femtomoles per milligram of protein (fmol/mg of protein) and affinity were measured by Scatchard plot analysis. In a separate experiment normal human platelets were incubated with either buffer, normal serum, or serum from patients with spastic Raynaud's syndrome and A2R levels were measured. A2R levels in normal subjects averaged 112 +/- 18 fmol/mg; in the patients with spastic Raynaud's syndrome, 191 +/- 14 fmol/mg, p less than 0.01; and in the patients with obstructive Raynaud's syndrome, 164 +/- 31 fmol/mg, p greater than 0.05 (ns). Of the patients with spastic Raynaud's syndrome, 26% had values that were less than the mean value of the normal subjects (69 +/- 7 fmol/mg, p less than 0.05). The A2R levels decreased after incubation with serum from patients who had spastic Raynaud's syndrome by 17.4 +/- 3.1 fmol/mg (p less than 0.05). These results indicate that most patients with vasospastic Raynaud's syndrome have increased platelet A2R levels, which may constitute a primary pathophysiologic abnormality underlying this condition. The presence of subnormal A2R levels in a portion of the patients and the finding of a decrease in measurable A2R levels after incubation in serum from patients with spastic Raynaud's syndrome suggests the possibility of receptor modulation as a mechanism for increased cellular receptor synthesis.     

Effect of isoflurane on release and uptake of gamma-aminobutyric acid from rat cortical synaptosomes

We have studied the effect of isoflurane on potassium-evoked release and high-affinity uptake of gamma-aminobutyric acid (GABA) in rat cortical synaptosomes. Isoflurane 1.5% and 3% increased calcium- dependent release by 38% and 36% of control values, respectively (P < 0.05). Calcium-independent release was reduced correspondingly by 24% and 26% (P < 0.05). High-affinity uptake of GABA was not affected by isoflurane. The findings of increased synaptic GABA release combined with unaltered uptake suggest that isoflurane increases GABA in the synaptic cleft and thus may enhance inhibition.      

神经痛大鼠脊髓胶质细胞源性神经营养因子参与多巴胺D2受体激动剂对痛觉过敏的调制作用

目的 研究鞘内注射多巴胺D2受体激动剂喹吡罗对坐骨神经慢性压迫损伤大鼠脊髓水平胶质细胞源性神经营养因子表达的影响,探讨其介导抗伤害作用的可能机制. 方法 实验1：采用完全随机分组方法将30只成年雄性SD大鼠制作坐骨神经慢性压迫损伤（chronic constriction injury of sciatic nerve,CCI）模型分为5组（每组6只）：CCI＋生理盐水（NS组）、CCI＋喹吡罗0.1 μg（Q0.1组）、CCI＋喹吡罗1μg（Q1组）、CCI＋喹吡罗5 μg（Q5组）、CCI＋喹吡罗10 μg（Q10组）,分别在建模后第7天鞘内注射0.1、1、5、10 μg喹吡罗,NS组单次鞘内注射生理盐水10μl.于给药前及给药后0.5、1、2、4、8、16h测定大鼠术侧后足机械缩足反射阈值（paw withdrawal mechanical threshold,PWMT）和热缩足反射潜伏期（paw withdrawal thermal latency,PWTL）.实验2：将54只成年雄性SD大鼠制作CCI模型,并采用完全随机分组方法分为3组（Q5组、Q10组、NS组,每组18只）：Q5组、Q10组分别在建模后第7天鞘内注射5、10μg喹吡罗后0.5、1、2、4、8、16h处死取材,NS组单次鞘内注射生理盐水10μl;另取6只正常大鼠作为模型对照组（M组）,另取6只正常大鼠作为对照组（C组）.采用免疫印迹法测定脊髓背角胶质细胞源性神经营养因子（glial cell line-derived neurotrophic fact,GDNF）蛋白表达的变化. 结果 实验1：与NS组比较,Q0.1组注药后各时间点PWMT和PWTL差异无统计学意义（P＞0.05）,Q1组注药后2 h PWMT[（4.3±1.5）g]及PWTL[（13.2±1.6）s],Q5组注药后1,2、4 h PWMT[（4.7±1.6）、（5.3±1.6）、（4.7±2.1）g]和PWTL[（14.0±1.7）、（15.2±1.5）、（13.4±1.6）s],Q10组注药后1、2、4 h PWMT[（6.0±1.3）、（7.3±1.0）、（5.3±2.1）g]和PWTL [（15.3±1.8）、（17.5±1.2）、（14.9±1.7）s]明显升高（P＜0.05）.实验2：与C组比较,M组GDNF表达（0.95±0.09）明显升高（P＜0.05）.与M组和NS组比较,GDNF的表达Q     

Enflurane-induced release of an excitatory amino acid, glutamate, from mouse brain synaptosomes.

To clarify the mechanisms of enflurane-induced convulsions, we examined the effects of enflurane, halothane, and diethyl ether on the release of an excitatory neurotransmitter, glutamate, from isolated pinched-off nerve terminals (synaptosomes) of the mouse cerebral cortex. At concentrations corresponding to those used clinically (0.75 and 1.25 mM), enflurane released more glutamate than did halothane. Diethyl ether (10 and 58 mM) had no effect on glutamate release. Enflurane (0.75-15 mM) increased glutamate and aspartate release in a dose-dependent manner but had little effect on the release of the inhibitory neurotransmitters glycine and gamma-aminobutyric acid or on the release of glutamine. A glutamate uptake inhibitor, kainic acid (1 mM), did not affect enflurane-induced glutamate release. Replacement of the medium's Ca2+ by Co2+, or exposure to cold (about 2 degrees C), suppressed the enflurane-induced glutamate release. Depolarization caused by 40 mM K+ increased the basal level of glutamate released, and enflurane-induced glutamate release was lower after depolarization. Enflurane had no effect in synaptosomes prepared from the cerebellum, diencephalon and pons, or medulla oblongata. Thus, enflurane increased Ca(2+)- and temperature-dependent glutamate release, especially from synaptosomes of the cerebral cortex. These data provide a pathophysiologic explanation for enflurane-induced convulsions.     

Substance P release from rat hypothalamus and spinal cord

A specific and sensitive radioimmunoassay for substance P has been developed to study the release of immunoreactive substance P from incubated rat hypothalamus and rat spinal cord in vitro. Release was significantly increased in the presence of two depolarizing stimuli (56 mM KCl and 75 microM veratrine) and was calcium-dependent. The released immunoreactive material diluted in parallel with synthetic substance P and showed close identity on Sephadex chromatography. A neuromodulator role for the peptide in the central nervous system is suggested.     

Antinociceptive interactions between alpha 2-adrenergic and opiate agonists at the spinal level in rodents

This study was undertaken to evaluate the antinociceptive interactions of alpha 2 adrenergic and opiate receptors at the spinal level. Morphine and clonidine were administered intrathecally (i.t.) by lumbar puncture to rats either alone or in the presence of either i.t. yohimbine, an alpha 2 antagonist, or systemic naloxone, an opioid antagonist. The effect of tolerance to systematically administered morphine on responses to i.t. morphine and clonidine was examined in mice. Antinociception was determined by observing the response to a clamp applied to the tail (Haffner test) in mice and by the tail-flick test in rats; log dose-response curves for antinociception were generated for morphine, clonidine, and each drug combination. Morphine and clonidine both produced dose-dependent antinociception when given i.t. in both species. The i.t. administration of yohimbine attenuated the antinociceptive effect of both clonidine and morphine, but naloxone attenuated only the response to morphine. Further, a sub-analgetic dose of i.t. clonidine potentiated the effect of i.t. morphine. In morphine-tolerant mice, i.t. morphine was not efficacious whereas clonidine retained full efficacy, although potency was slightly diminished. Thus, it appears that alpha 2 adrenoceptor-mediated antinociception is independent of opiate receptor mechanisms. Clinical use of intrathecal combinations of alpha 2 adrenergic and opiate receptor agonists to increase analgesia and use of intrathecal alpha 2 agonists for pain relief in patients tolerant to opiates might deserve evaluation.     

Halothane facilitates the translocation of GRK-2 and phosphorylation of ß2- adrenergic receptor in rat synaptosomes

PURPOSE: To examine the effect of halothane on beta2-adrenergic receptor phosphorylation and on G-protein coupled receptor kinase (GRK), responsible for beta2-receptor downregulation. METHODS: Rat forebrain synaptosomes were incubated for 30 min with halothane 1 or 2%. The cytosolic and membrane fractions were separated, and phosphorylation activity of recombinant beta2-adrenergic receptor was quantified autoradiographically using 32P labeled adenosine triphosphate. Phosphorylation activity of a specific GRK-2 substrate, was examined by measuring 32P binding. Subcellular localization of the enzyme was immunologically analyzed by Western blotting. RESULTS: Halothane 2% decreased the phosphorylation activity of the recombinant receptor in the cytosol fraction, regardless of 10 microM isoproterenol (ISP) (P<0.01), which activity in the membrane fraction was increased (P<0.01). Phosphorylation activity of the synthetic peptide decreased in the cytosol obtained from synaptosomes exposed to halothane 2% (P<0.05). In contrast, activity in the membrane increased by exposure to halothane 2% (P<0.01). The concentration of GRK-2 decreased in the cytosol obtained from synaptosomes exposed to halothane 1% or 2% (decreases of 8.3+/-1.2% @ 1%, and 18.0+/-2.1% @ 2%, P<0.05). In the membrane, exposure to halothane 1% or 2% increased the GRK-2 amount dose dependently (22.5+/-3.1% @ 1%, and by 45.7+/-6.1% @ 2%, P<0.01). CONCLUSION: Halothane could facilitate translocation of GRK-2 and possibly promote the downregulation of beta2-adrenergic receptors in the synaptic membrane. The anesthetic action and hemodynamic suppressive action of halothane may be related to this phenomenon.