General anesthetics do not affect release of the neuropeptide cholecystokinin from isolated rat cortical nerve terminals

BACKGROUND: General anesthetics inhibit evoked release of classic neurotransmitters. However, their actions on neuropeptide release in the central nervous system have not been well characterized. METHODS: The effects of representative intravenous and volatile anesthetics were studied on the release of sulfated cholecystokinin 8 (CCK8s), a representative excitatory neuropeptide, from isolated rat cerebrocortical nerve terminals (synaptosomes). Basal, elevated KCl depolarization-evoked and veratridine-evoked release of CCK8s from synaptosomes purified from rat cerebral cortex was evaluated at 35 degrees C in the absence or presence of extracellular Ca2+. CCK8s released into the incubation medium was determined by enzyme-linked immunoassay after filtration. RESULTS: Elevation of extracellular KCl concentration (to 15-30 mM) or veratridine (10-20 microm) stimulated Ca2+ -dependent CCK8s release. Basal, elevated KCl- or veratridine-evoked CCK8s release was not affected significantly by propofol (12.5-50 microm), pentobarbital (50 and 100 microm), thiopental (20 microm), etomidate (20 microm), ketamine (20 microm), isoflurane (0.6-0.8 mM), or halothane (0.6-0.8 mMm). CONCLUSIONS: Clinically relevant concentrations of several classes of general anesthetics did not affect basal, KCl-evoked, or veratridine-evoked CCK8s release from isolated rat cortical nerve terminals. This is in contrast to the demonstrable effects of certain general anesthetics on the release of amino acid and catecholamine transmitters. These transmitter-specific presynaptic effects of general anesthetics suggest that anesthetic-sensitive presynaptic targets are not common to all transmitter classes.     

Different effects of volatile anesthetics and polyhalogenated alkanes on depolarization-evoked glutamate release in rat cortical brain slices.

Anesthetics cause a reduction in excitatory neurotransmission that may be important in the mechanisms of in vivo anesthetic action. Because glutamate is the major excitatory neurotransmitter in mammalian brain, evaluation of anesthetic effects on induced glutamate release is relevant for studying this potential mechanism of anesthetic action. In the present study, we compared the effects of anesthetics and nonanesthetics (halogenated alkanes that disobey the Meyer-Overton hypothesis) on depolarization-evoked glutamate release. Glutamate released from rat cortical brain slices after chemically induced depolarization (50 mM KCl) was measured continuously using an enzymatic fluorescence assay. The effects of the volatile anesthetics isoflurane and enflurane were compared with the effects of the transitional compound 1,1,2-trichlorotrifluoroethane, the nonanesthetic compound 1,2-dichlorohexafluorocyclobutane, and other polyhalogenated alkanes. Tested concentrations included effective anesthetic concentrations for the anesthetics and transitional compounds, and concentrations predicted to be anesthetic based on lipid solubility for the nonanesthetics. Isoflurane dose-dependently reduced depolarization-evoked glutamate release in cortical brain slices. Isoflurane and enflurane at concentrations equivalent to 1 minimum alveolar anesthetic concentration (MAC) reduced the KCl-evoked release to 20% and 17% of control, respectively. The transitional compound 1,1,2-trichlorotrifluoroethane at 210 microM (approximately 1.2 MAC) reduced glutamate release to 47%, and the nonanesthetic 1,2-dichlorohexafluorocyclobutane increased glutamate release at 70 microM (approximately 3 MAC). These findings support the hypothesis that the modulation of excitatory neurotransmission might be responsible, in part, for in vivo anesthetic action. IMPLICATIONS: The volatile anesthetics isoflurane and enflurane reduce depolarization-evoked glutamate release in rat brain slices. The transitional compound 1,1,2-trichlorotrifluoroethane reduces glutamate release to a much lesser extent, and the nonanesthetic 1,2-dichlorohexafluorocyclobutane does not reduce glutamate release. These findings support the hypothesis that the modulation of excitatory neurotransmission might be responsible, in part, for in vivo anesthetic action.     

The effects of local anesthetics and epinephrine on rat sciatic nerve blood flow

The effects of topical application of local anesthetics on peripheral nerve blood flow (NBF) were studied in the rat sciatic nerve. Sciatic NBF was measured by laser doppler in 45 adult female Sprague-Dawley rats (90 nerves) after topical application of 25 microliter lidocaine and epinephrine, alone and in combination (lidocaine plus epinephrine), as well as bupivacaine, tetracaine, and normal saline, and studied in a randomized, blinded experimental design. NBF changes produced by lidocaine were dose-dependent. Compared with that for saline, blood flow reduction for lidocaine 0.5% was not significant, but it was significant for lidocaine 1.0% at 2-5 min and for lidocaine 2.0% at all time periods after 1 min (P less than 0.05). Maximum reduction was seen at all concentrations by 5 min after application. Average blood flow reduction at 5 min was 7% for lidocaine 0.5%, 12% for lidocaine 1.0% and 18% for lidocaine 2.0%. Epinephrine also produced dose-dependent changes in NBF. Epinephrine 2.5 micrograms/ml produced a transient 20% increase in NBF lasting 2-3 min (P less than 0.05), followed by a return to baseline. Epinephrine 5.0 micrograms/ml and epinephrine 10.0 micrograms/ml produced reductions of 20% and 35%, respectively (P less than 0.05), which lasted throughout the study. The effects of each of the three concentrations were significantly different from the others. The combination of lidocaine plus epinephrine resulted in synergistic reduction of NBF for all drug concentrations (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of isoflurane and propofol on glutamate and GABA transporters in isolated cortical nerve terminals

BACKGROUND: Depression of glutamate-mediated excitatory transmission and potentiation of gamma-aminobutyric acid (GABA)-mediated inhibitory transmission appear to be primary mechanisms by which general anesthetics produce anesthesia. Since effects on transmitter transport have been implicated in anesthetic actions, the authors examined the sensitivity of presynaptic glutamate and GABA transporters to the effects of a representative volatile (isoflurane) and a representative intravenous (propofol) anesthetic. METHODS: A dual-isotope (l-[3H]glutamate and [14C]GABA) approach allowed simultaneous comparisons of anesthetic effects on three independent assays of glutamate and GABA transporters in adult rat cerebral cortex: transmitter uptake into isolated nerve terminals (synaptosomes), transmitter binding to lysed and washed synaptosomes (synaptic membranes), and carrier-mediated release (reverse transport) of transmitter from preloaded synaptosomes using a modified superfusion system. RESULTS: Isoflurane produced small but statistically significant inhibition of l-[3H]glutamate and [14C]GABA uptake, while propofol had no effect. Inhibition of uptake by isoflurane was noncompetitive, an outcome that was mimicked by indirectly affecting transporter function through synaptosomal depolarization. Neither isoflurane nor propofol affected l-[3H]glutamate or [14C]GABA binding to synaptic membranes or Ca(2+)-independent carrier-mediated l-[3H]glutamate or [14C]GABA release (reverse transport). CONCLUSIONS: These findings suggest that isoflurane and propofol at clinical concentrations do not affect excitatory glutamatergic transmission or inhibitory GABAergic transmission directly effects on their presynaptic neuronal transporters.     

Widespread inhibition of sodium channel-dependent glutamate release from isolated nerve terminals by isoflurane and propofol.

BACKGROUND: Controversy persists concerning the mechanisms and role of general anesthetic inhibition of glutamate release from nerve endings. To determine the generality of this effect and to control for methodologic differences between previous studies, the authors analyzed the presynaptic effects of isoflurane and propofol on glutamate release from nerve terminals isolated from several species and brain regions. METHODS: Synaptosomes were prepared from rat, mouse, or guinea pig cerebral cortex and also from rat striatum and hippocampus. Release of endogenous glutamate evoked by depolarization with 20 microm veratridine (which opens voltage-dependent Na+ channels by preventing inactivation) or by 30 mm KCl (which activates voltage-gated Ca2+ channels by membrane depolarization) was monitored using an on-line enzyme-linked fluorometric assay. RESULTS: Glutamate release evoked by depolarization with increased extracellular KCl was not significantly inhibited by isoflurane up to 0.7 mM ( approximately 2 minimum alveolar concentration; drug concentration for half-maximal inhibition [IC50] > 1.5 mM) [corrected] or propofol up to 40 microm in synaptosomes prepared from rat, mouse, or guinea pig cerebral cortex, rat hippocampus, or rat striatum. Lower concentrations of isoflurane or propofol significantly inhibited veratridine-evoked glutamate release in all three species (isoflurane IC50 = 0.41-0.50 mm; propofol IC50 = 11-18 microm) and rat brain regions. Glutamate release was evoked by veratridine or increased KCl (from 5 to 35 mM) to assess the involvement of presynaptic ion channels as targets for drug actions [corrected]. CONCLUSIONS: Isoflurane and propofol inhibited Na+ channel-mediated glutamate release evoked by veratridine with greater potency than release evoked by increased KCl in synaptosomes prepared from three mammalian species and three rat brain regions. These findings are consistent with a greater sensitivity to anesthetics of presynaptic Na+ channels than of Ca2+ channels coupled to glutamate release. This widespread presynaptic action of general anesthetics is not mediated by potentiation of gamma-aminobutyric acid type A receptors, though additional mechanisms may be involved.     

四种静脉麻醉药物对大鼠皮层脑片缺氧缺糖损伤的作用

目的 探讨四种常用静脉麻醉药物对大鼠皮层脑片缺氧缺糖损伤的作用。方法 建立大鼠皮层脑片缺氧缺糖损伤模型,设立对照组、缺氧缺糖损伤组、药物加损伤组,利用2,3,5-三苯基氯化四氮唑(TTC)染色定量比色方法,评价氯胺酮、异丙酚、咪达唑仑和硫喷妥钠对脑片损伤的保护作用。结果 随着缺氧缺糖损伤时间的延长,皮层脑片TTC染色程度明显降低,TTC染色反映的组织损伤百分率与孵育上清液乳酸脱氢酶(LDN)释放比活性呈正相关(r=0.9609,P<0.01)。对于缺氧缺糖损伤所致脑片TTC染色降低,不同浓度氯胺酮均能完全抑制;与损伤组比较。大剂量硫喷妥钠和咪达唑仑(400μmol·L~(-1)和10μmol·L~(-1)A值明显升高(P<0.01或0.05);小剂量异丙酚(1μmol·L~(-1))对脑片TTC染色降低无作用,大剂量(100μmol·L~(-1))加重TTC染色降低(P<0.01)。结论 对于大鼠皮层脑片缺氧缺糖损伤,四种静脉麻醉药物作用效果各不相同:临床麻醉剂量的氯胺酮具有明显保护作用,咪达唑仑和硫喷妥钠在超过临床使用范围的大剂量时有部分保护作用;大剂量异丙酚会加重大鼠皮层脑片的缺氧缺糖损伤。     

Effect of bupivacaine and levobupivacaine on exocytotic norepinephrine release from rat atria

BACKGROUND: The cardiotoxic mechanism of local anesthetics may include interruption of cardiac sympathetic reflexes. The authors undertook this investigation to determine if clinically relevant concentrations of bupivacaine and levobupivacaine interfere with exocytotic norepinephrine release from cardiac sympathetic nerve endings. METHODS: Rat atria were prepared for measurements of twitch contractile force and [H]-norepinephrine release. After nerve endings were loaded with [H]-norepinephrine, the tissue was electrically stimulated in 5-min episodes during 10 10-min sampling periods. After each period, a sample of bath fluid was analyzed for radioactivity and [H]-norepinephrine release was expressed as a fraction of tissue counts. Atria were exposed to buffer alone during sampling periods 1 and 2 (S1 and S2). Control atria received saline (100 microl each, n = 6 atria) in S3-S10. Experimental groups (n = 6 per group) received either bupivacaine or levobupivacaine at concentrations (in microM) of 5 (S3-S4), 10 (S5-S6), 30 (S7-S8), and 100 (S9-S10). RESULTS: Bupivacaine and levobupivacaine decreased stimulation-evoked fractional [H]-norepinephrine release with inhibitory concentration 50% values of 5.1 +/- 0.5 and 6.1 +/- 1.3 microM. The inhibitory effect of both local anesthetics (approximately 70%) approached that of tetrodotoxin. Local anesthetics abolished the twitch contractions of atria with inhibitory concentration 50% values of 12.6 +/- 5.0 microM (bupivacaine) and 15.7 +/- 3.9 microM (levobupivacaine). In separate experiments, tetrodotoxin inhibited twitch contractile force by only 30%. CONCLUSIONS: The results indicate that clinically relevant cardiotoxic concentrations of bupivacaine and levobupivacaine markedly depress cardiac sympathetic neurotransmission. A possible mechanism of local anesthetics in reducing evoked norepinephrine release from sympathetic endings is blockade of tetrodotoxin-sensitive fast sodium channels.     

The effects of ovariectomy and estrogen replacement on acetylcholine release from nerve fibres and passive stretch-induced acetylcholine release in female rat bladder

AIMS: The present study investigated the effects of ovariectomy and estrogen replacement on the release of acetylcholine (Ach) from cholinergic neurons as well as on the tetrodotoxin (TTX)-insensitive stretch-induced Ach release in isolated rat detrusor. In addition, the above effects on rat micturition characteristics were also studied. METHODS: Thirty female rats randomly received a sham operation, ovariectomy, or ovariectomy plus estrogen replacement. Using metabolic cages, micturition parameters were recorded. Then, in vitro functional experiments that included the measurements of nerve-mediated detrusor muscle contraction, Ach release from nerve fibres, and stretch-induced TTX-insensitive Ach release were performed. Ach release was measured using microdialysis and high-performance liquid chromatography. RESULTS: Ovariectomized rats showed a significant decrease in voided volume and significant increase in 24-hr frequency of voiding. Ovariectomy caused the significant increase in both TTX-insensitive basal Ach release and TTX-insensitive stretch-induced Ach release. On the other hand, ovariectomy caused a significant decrease in Ach release from nerve fibres, resulting in the decrease in the contractile responses of detrusor muscle to electrical nerve stimulation. Estrogen replacement restored these alterations induced by ovariectomy. CONCLUSIONS: Our findings showed that as a results of estrogen deficiency, Ach release from nerve fibres decreased, suggesting that this reduction of Ach released from cholinergic nerves may cause the decrease in detrusor contractility. Furthermore, this study also demonstrated that stretch-induced TTX-insensitive Ach release was increased by ovariectomy. This may be a contributing factor to the development of overactive bladder in elderly women.     

几种静脉麻醉药对大鼠心室肌细胞游离钙离子移动的影响

目的　观察临床常用静脉麻醉药咪唑安定、异丙酚和依托咪酯对心肌细胞内钙离子移动的作用 ,探讨其对心肌收缩性的影响。方法　急性分离的大鼠单个心室肌细胞 ,采用 Fluo- 3 / AM为钙荧光指示剂 ,观察临床诱导峰浓度及 5倍峰浓度时咪唑安定 ( 3μm ol· L- 1 或 15μmol· L- 1 )、异丙酚( 5 0μm ol· L- 1 或 2 5 0μmol· L- 1 )或依托咪酯 ( 3μmol· L- 1 或 15μmol· L- 1 )对高浓度 KCl或咖啡因所诱发细胞内钙离子浓度变化的影响。结果　临床诱导峰浓度异丙酚明显减弱 KCl所诱发的钙离子跨膜内流 ( P<0 .0 5 ) ,而咪唑安定和依托咪酯 ( 3 μm ol· L- 1 )有减弱钙离子跨膜内流趋势 ;而超临床浓度的咪唑安定、异丙酚和依托咪酯明显减弱 KCl所诱发钙离子跨膜内流 ( P<0 .0 5 )。上述两种浓度咪唑安定、异丙酚或依托咪酯对咖啡因所致胞浆内钙离子的增加均无明显影响 ( P>0 .0 5 )。结论　上述几种静脉麻醉药具有剂量依赖性地减少心肌细胞钙离子跨膜内流作用 ,以异丙酚影响最显著 ,咪唑安定次之 ,依托咪酯较弱 ,但对心肌细胞肌浆网功能尚无明显影响     

The inhibitory effects of local anesthetics on primary sensory nerve and parasympathetic nerve in rabbit eye

Primary sensory nerves transmit information to both the periphery and central nervous systems, and they mediate neurogenic inflammation by release of neurotransmitters, such as tachykinins, in the periphery. Because the effect of local anesthetics on neurogenic inflammation is a subject of controversy, we investigated the direct effect of local anesthetics on tachykininergic neurotransmission, comparing it with cholinergic neurotransmission in the rabbit iris sphincter muscle. Rabbit iris sphincter muscle is innervated by trigeminal tachykininergic and parasympathetic cholinergic nerves, and the electrical transmural stimulation produces tachykininergic and cholinergic contractions. Cocaine and lidocaine (1-300 microM) attenuated tachykininergic and cholinergic contractions induced by electrical transmural stimulation in concentration- and stimulus frequency-dependent manner. However, the sensitivity to both local anesthetics was slightly, but significantly, higher in tachykininergic than in cholinergic responses. Exogenous neurokinin A and carbachol produced contractions that were not inhibited by 100 microM of cocaine and lidocaine. These results show that local anesthetics have a direct inhibitory effect on tachykininergic neurotransmission of the trigeminal sensory nerve, and the effect on this nerve is more potent than on the parasympathetic nerve and suggests that local anesthetics may have antineurogenic inflammatory effects via the inhibitory effects on the peripheral transmission of primary sensory nerve.     

The effects of anesthetics on cortical spreading depression elicitation and c-fos expression in rats

The effects of anesthetics on the generation of cortical spreading depression (CSD) were investigated. Volatile anesthetics halothane, isoflurane, sevoflurane (0.5, 1.0, and 2.0 MAC), and the intravenous anesthetic pentobarbital were studied. Cortical spreading depression was induced by 3M-KCl applied to a surface of brain cortex for 30 minutes. Direct current (DC) potential was recorded, and the number, amplitude, and duration of CSDs were observed. With increasing concentrations of each volatile anesthetic, there was a dose-related reduction in CSD frequency but not in CSD amplitude. At 2.0 MAC of sevoflurane the suppression of CSD was less than with the other volatile anesthetics. In addition, the influence of anesthetics on expression of c-fos mRNA was investigated. Additional animals anesthetized by isoflurane or sevoflurane were studied. Five CSDs were elicited by electric stimulation (0.5 mV, 1 second) in each animal. In situ hybridization with 35S-labeled oligonucleotides was used to evaluate the level of c-fos mRNA. The expression of c-fos was observed in the hemisphere in which CSD was elicited, but there was no difference in expression of c-fos among the groups. We conclude that volatile anesthetics can induce suppression of CSD elicitation in a dose dependent manner, but that at high concentrations sevoflurane is significantly less effective than other volatile agents. Pentobarbital has the least effect on KCl-induced CSD. These data suggest that the choice of anesthetics can impact the results of studies examining membrane depolarization and the ionic changes initiated by CSD.     

全身麻醉药物对睡眠影响的研究进展

全身麻醉和睡眠状态均表现为意识的可逆性丧失,对外界刺激反应性下降,并在行为学和脑电图等方面具有一定的相似性.全身麻醉过程和睡眠状态的产生可能共享部分分子靶点和神经环路.全身麻醉药物可通过改变睡眠结构、影响昼夜节律和调控睡眠-觉醒环路等机制对睡眠产生双面性和多维度的影响.全身麻醉和睡眠机制至今尚未阐明.全文将从全...