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ANESTHETIC PHARMACOLOGY

Modulation of Gamma-Aminobutyric Acid_A Receptor Function by Thiopental in the Rat Spinal Dorsal Horn Neurons

Chuan-Xiu Yang, MS^*, Han Xu, PhD^*, Ke-Qing Zhou^*, Meng-Ya Wang, PhD, and Tian-Le Xu, PhD, MD^*

*School of Life Sciences, University of Science and Technology of China, Hefei; Institute of Neuroscience and Key Laboratory of Neurobiology, Chinese Academy of Sciences, Shanghai; and Laboratory of Cell Electrophysiology, Wannan Medical College, Wuhu, China

Address correspondence and reprint requests to Tian-Le Xu, PhD, MD, Institute of Neuroscience and Key Laboratory of Neurobiology, Chinese Academy of Sciences, 320 Yue-Yang Rd., Shanghai 200031, China. Address e-mail to tlxu{at}ion.ac.cn.

	Abstract

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To assess the actions of thiopental at the spinal dorsal horn level, we examined the effects of thiopental using the whole cell patch-clamp technique on mechanically dissociated rat spinal dorsal horn neurons. Thiopental, at large concentrations, elicited a current (I_Thio) through activation of chloride conductance, and its threshold concentration was approximately 50 µM. I_Thio was sensitive to bicuculline, a -aminobutyric acid (GABA)_A receptor antagonist, but not to strychnine, a glycine receptor antagonist. At a clinically relevant concentration (30 µM), thiopental markedly enhanced the peak amplitude of a subsaturating GABA-induced current (I_GABA) but not that of a saturating GABA-induced cur-rent. Furthermore, thiopental prolonged the time constants of both desensitization and deactivation of I_GABA. At a large concentration (300 µM), it inhibited the peak amplitude of I_GABA, which may be the result of open-channel blockade. In addition, at 30 µM, thiopental increased the duration and decreased the frequency of GABAergic miniature inhibitory postsynaptic currents. These results indicate that thiopental enhances GABAergic inhibitory transmission and suggest that GABA_A receptors in the spinal cord are a potential target through which thiopental causes immobility and depresses the response to noxious stimuli.

	Introduction

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General anesthetics, with a diverse range of chemical structures, have been used for more than 150 years in clinical practice, but it is only recently that progress has been made in our understanding of how they exert their effects. In the early 1990s, pioneering studies by Rampil (1) and Antognini (2) clearly showed that, within the central nervous system, the spinal cord and brain have different minimum alveolar anesthetic concentrations for volatile anesthetics. Because the -aminobutyric acid (GABA)_Areceptor is one of most important targets for general anesthetics, this discrepancy may reflect differences in GABA_A receptor subunit composition between spinal cord and brain. Additional evidence has arisen suggesting that the spinal cord plays an important role in two anesthetic end-points: analgesia and immobility after a noxious stimulus (3). A better understanding of the nature of the difference between the response of the spinal cord and brain to anesthetics may eventually lead to the development of drugs better able to target the spinal cord in favor of higher brain regions. Such drugs should have greater antinociceptive and less sedating effects and be ideal for use in painful outpatient procedures.

Because of its rapid onset of action and its rapid redistribution, thiopental (Thio) has been one of the most widely used IV general anesthetics since it was first introduced into clinical practice. Surprisingly, there have been very few in vitro studies on the mechanism of anesthetic action of this barbiturate. Barbiturates, like many other general anesthetics, exert their sedative and anesthetic effects primarily by enhancing the response to GABA of GABA_A receptors (4). Cordato et al. (5) reported that Thio stereoselectively enhanced GABA-activated Cl^– currents at GABA_A receptors expressed in Xenopus oocytes. In cultured hippocampal neurons, Thio was reported to potentiate GABAergic inhibitory synaptic transmission (6). However, direct evidence demonstrating Thio modulation of native GABA_A receptors is lacking. We believe that the inhibitory effects of Thio on the noxious stimuli-induced response in spinal dorsal horn are mediated by direct enhancement of the GABA_A receptor. Therefore, in the present study, we examined the effects of Thio on GABA_A receptors and GABAergic miniature inhibitory postsynaptic currents (mIPSCs) in acutely dissociated rat spinal dorsal horn neurons. The relevant free aqueous concentrations of Thio for a variety of anesthetic end-points have been measured (7). At a free aqueous concentration of approximately 25 µM of Thio (corresponding to a total plasma concentration of 40 µg/mL), rats (7) failed to respond to a noxious stimulus (tail clamp). We used 30 µM as the clinical relevant concentration of Thio in the present study.

	Methods

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The care and use of animals used for these experiments followed the guidelines and protocols approved by the Care and Use of Animals Committee of University of Science and Technology of China. Wistar rats (age, 2 wk) were anesthetized with urethane (1 g/kg ip). The dorsal horn neurons with intact presynaptic terminals attached were mechanically dissociated, as previously described (8). In brief, rats were killed by decapitation, a segment of lumbosacral (L4-S2) spinal cord was dissected out, and transverse slices (400 µm) of spinal cord were sectioned using a vibrotome tissue slicer (VT1000S; Leica Instruments Ltd, Wetzlar, Germany). After incubation at room temperature (22°C–25°C) for 50 min in incubation solution aerated with 95% O₂ + 5% CO₂, the slices were transferred into standard external solution. A vibration-isolation system (9) was then used to mechanically dissociate the dorsal horn neurons. A fire-polished glass pipette mounted on a vibrator touched lightly and vibrated horizontally, at approximately 5–10 Hz, the surface of the slice under the control of a pulse generator. The vibration-dissociation lasted approximately 3 min, and then the slices were removed from the dish. Neurons were attached to the bottom of the culture dish and were ready for electrophysiological experiments within 20 min. Consistent with our previous reports (8), the acutely isolated neurons were medium-sized (10–15 µm in diameter), with oval or triangular soma and 1 to 3 apical stem dendrites. These neurons, which were dissociated without using enzymes, retained some of their original morphological features, including the proximal dendritic processes. At a holding potential (V_H) of –50 mV, application of GABA to these dissociated dorsal horn neurons evoked an inward Cl^– current (I_GABA) with 50% effective concentration (EC₅₀) value of 10 µM (10).

Whole cell patch-clamp recordings under voltage-clamp mode were made at room temperature (22°C–25°C) using an Axopatch 200B patch-clamp amplifier (Axon Instruments, Foster City, CA), which was connected to a Pentium III computer equipped with a Digidata 1320A analog-to-digital converter and pClamp7.0 software (Axon Instruments) for data acquisition and analysis. In most experiments, approximately 80% series resistance compensation was applied. Unless otherwise noted, the membrane potential was held at –50 mV.

All drugs used were purchased from Sigma (St. Louis, MO) except Thio, which was obtained from Shanghai New Asiatic Pharmaceutical CO, Ltd. The recording solutions were as described (8). Drugs were first dissolved in ion-free water and then diluted to the final concentrations in the standard external solution just before use. The pH value of Thio solution was adjusted to 7.4 with 2 M of HCl, where appropriate. Drugs were applied using a rapid application technique termed the ‘Y-tube‘ method throughout the experiments (8). This system allows a complete exchange of external solution surrounding a neuron within 20 ms.

The Mini Analysis Program (version 6.0, Synaptosoft Inc., Decatur, GA) was used to analyze mIPSCs. The Kolmogorov-Smirnov test was used to assess differences in mean values of mIPSCs under different conditions. Decay kinetics were measured as the time for the mIPSCs to decay to 37% of its peak amplitude. Current deactivation and desensitization were fitted by exponential functions (Clampfit 8.1; Axon Instruments). During the fitting process, the goodness of fit was evaluated by the ² value. The current desensitization was fitted beginning shortly after the peak of response and deactivation trace began from the peak of the tail current when the tail current appeared; otherwise, the fit began from the removal of drug(s). Origin (MicroCal Inc, Northampton, MA) and Excel (Microsoft, Seattle, WA) were used for data display and analysis. Statistical comparisons were performed using Student’s t-test for comparisons between two groups and analysis of variance for comparisons involving three or more groups. P < 0.05 was considered statistically significant. n represents the number of neurons studied. All data are expressed as the mean ± sem.

	Results

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Whole cell patch-clamp recordings were performed randomly from the acutely isolated neurons. At a V_H of –50 mV, the application of Thio 50 µM evoked an inward current (Fig. 1Aa). In the following experiments, the interval of Thio applications was more than 200 s, at which the Thio-induced current (I_Thio) had completely recovered from desensitization. Thio dissolved in ion-free water (100 mM) was strongly alkaline (pH >10). At a pH value of 7.4, Thio precipitated from standard external solution at concentrations larger than 300 µM. For this reason, Thio concentrations larger than 300 µM were not used in our experiments. The concentration-response curve over the range of 50–300 µM reaches a maximum at 200 µM (Fig. 1Ba). Washout of Thio at large concentrations (>100 µM) induced a transient tail (rebound) current in some neurons (Fig. 1Aa). I_Thio showed little desensitization, even at large concentrations.

View larger version (22K): [in this window] [in a new window]   Figure 1. Thiopental (Thio)-induced inward currents (IThio) in spinal dorsal horn neurons and effects of bicuculline (Bic) and strychnine (Str) on IThio. (Aa) Representative current traces from the same neuron, induced by various concentrations of Thio at a holding potential of –50mV. The bars above each indicate the drug application periods. (Ab) Representative current traces induced by Thio obtained in the absence or presence of Bic or Str. Bic was effective in antagonizing IThio (200 µM), but Str had no significant effect on IThio. (Ba) Concentration-response curve for IThio. IThio was normalized to the peak current amplitude induced by 100 µM of Thio (*). Data were expressed as mean ± sem (n = 9). (Bb) The amplitude of IThio in the presence of Bic or Str was normalized to control values. Bic at 30 µM and 300 µM inhibited the IThio to 11.1% ± 1.0% and 11.2% ± 1.2%, respectively. Each column represents mean ± sem (n = 5 or 6). Compared with control IThio, **P < 0.01 and ***P < 0.001.

The pharmacological properties of I_Thio were studied using specific antagonists of GABA_A and glycine receptors, i.e., bicuculline (Bic) and strychnine (Str), respectively. I_Thio induced by 200 µM of Thio was reversibly inhibited to 11.1% ± 1.0% by 30 µM of Bic but was unaffected by 1 µM of Str (Fig. 1Ab and Fig. 1Bb). However, Bic did not block I_Thio completely, even at a concentration of 300 µM (Fig. 1B). Compared with 30 µM of Bic, 300 µM of Bic did not further reduce the amplitude of I_Thio. Application of Thio increased baseline noise (Fig. 1, Aa and Ba), suggesting that Thio also changed the membrane conductance. Therefore, the ionic basis of I_Thio was examined by the double-ramp voltage-clamp technique (Fig. 2A). A pair of voltage ramps ranging from + 80 to –80 mV were applied, and the voltage-gated Na⁺, Ca²⁺, and K⁺ channels were blocked by adding 0.3 µM of tetrodotoxin and 0.1 mM of NiCl₂ to the external solution and using Cs⁺-containing internal solution, respectively. Under these conditions, the intersection of the current-voltage curve directly revealed the reversal potential of I_Thio. The reversal potential measured for I_Thio (E_Thio) was 3.9 ± 3.9 mV (n = 5) (Fig. 2B), which was close to the Cl^– equilibrium potential (E_Cl) of -2.5 mV calculated using the Nernst equation based on the extra- and intracellular Cl^– concentrations, but far from the equilibrium potential of the other principal ions, such as Na⁺ (+ 40.5 mV), K⁺ (- 80.1 mV) etc. These data indicate that I_Thio was primarily due to the influx of Cl^– resulting from the activation of GABA_A receptors.

View larger version (13K): [in this window] [in a new window]   Figure 2. Current-voltage (I-V) relationship of thiopental (Thio)-induced inward currents (IThio). (A) A representative current trace obtained from the double-ramp voltage command. The experimental protocol is shown above the current trace. A pair of voltage ramps ranging from –80 mV to +80 mV was applied. The trace obtained from the first ramp measured background or leakage currents. (B) I-V curve for IThio. ECl represents the theoretical Cl– equilibrium potential. Application of Thio was also accompanied by increased baseline noise.

Figure 3 shows the effect of Thio at a clinically relevant concentration (30 µM) on I_GABA induced by its EC₅₀ (10 µM). The peak amplitude of I _GABA was markedly enhanced. The enhancement of I_GABA by Thio was dependent on the GABA concentration. At 10 µM GABA, the enhancement was 3.61- ± 0.34-fold, whereas at a saturating concentration (1 mM), little effect was observed (Fig. 3B). In addition, Thio changed the kinetic properties of I_GABA. In the presence of 30 µM of Thio, the time constants of I_GABA desensitization (the progressive closing of ligand-gated channels despite the continued presence of the ligand) and deactivation (the closing of ligand-gated channels after the removal of the ligand) were both prolonged (Fig. 3C).

View larger version (29K): [in this window] [in a new window]   Figure 3. The effect of thiopental (Thio) at a clinically relevant concentration (30 µM) on -aminobutyric acid (GABA)-induced currents (IGABA). (A) Representative current traces induced by GABA alone or both GABA and Thio. Thio was perfused 20 s before simultaneous application of various concentrations of GABA and 30 µM of Thio. (B) The amplitudes of IGABA in the presence of 30 µM of Thio were normalized to control values and plotted against the GABA concentration. The enhancement of peak amplitude of IGABA depended on the GABA concentration. Thio, at a 30-µM concentration, dramatically enhanced the response to 10 µM of GABA but had little effect on that of 1000 µM of GABA. (C) The time constants for desensitization (des) and deactivation (dea) of IGABA in the presence of 30 µM of Thio were normalized to control values and plotted against the GABA concentration. Each column represents mean ± sem (n = 7–11). Compared with control, *P < 0.05, **P < 0.01, and *** P < 0.001.

To evaluate whether the facilitation of I_GABA by Thio was dependent on Thio concentration, we further explored the effect of Thio at different concentrations on I_GABA. Figure 4 illustrates the enhancement ratio of the current amplitude evoked by 10 µM of GABA in the presence of Thio at various concentrations (I_GABA+Thio), which was calculated using the formula ratio = (I_GABA+Thio – I_Thio)/I_GABA. In these experiments, the neurons were not pretreated with Thio (Fig. 4A) because a large concentration of Thio induced an inward current by itself and possibly resulted in receptor desensitization to inhibit the subsequent I_GABA. The maximal current enhancement was observed at 50 µM of Thio, and a further increase of Thio concentration reduced the facilitation. When the concentration of Thio was increased to 300 µM, Thio inhibited the peak amplitude of I_GABA. A rebound current was always evident after washout of coapplication of 10 µM of GABA and Thio at large concentrations (100 µM and 300 µM).

View larger version (18K): [in this window] [in a new window]   Figure 4. Effects of thiopental (Thio) at various concentrations on the amplitude of the -aminobutyric acid (GABA)-induced current (IGABA). (A) Representative current traces induced by GABA alone (left), Thio alone (right), and GABA plus Thio (in between). (B) The ratio of the current amplitude evoked by 10 µM of GABA in the presence of Thio at various concentrations (IGABA+Thio), which was calculated according to the formula ratio = (IGABA+Thio – IThio)/IGABA. Each column represents mean ± sem (n = 7 or 8). Compared with control, *P < 0.05, **P < 0.01, and *** P < 0.001.

mIPSCs were recorded from dorsal horn neurons with intact presynaptic terminals attached (8) (Fig. 5A). In the presence of 0.3 µM of tetrodotoxin, 10 µM of 2-amino-5-phosphonovaleric acid, 3 µM of 6-cyano-7-nitroquinoxalone-2, 3-dione, and 0.3 µM of Str, the mIPSCs were completely blocked by Bic (l0 µM) in these neurons, indicating that the mIPSCs were GABAergic (data not shown). In the presence of 30 µM of Thio, the duration of GABAergic mIPSCs was significantly prolonged, with the decay time constant of the mIPSCs markedly increased to 187.7% ± 17.5% (P < 0.01), whereas the amplitudes of mIPSCs were not significantly affected (114.6% ± 4.3%; P > 0.05), and the frequency of the mIPSCs was dramatically reduced (57.1% ± 5.9%; P < 0.01) (Fig. 5).

View larger version (27K): [in this window] [in a new window]   Figure 5. Effect of 30 µM of thiopental (Thio) on -aminobutyric acid (GABA)ergic mIPSCs in spinal dorsal horn neurons. (A) Recording of GABAergic miniature inhibitory postsynaptic currents (mIPSCs) before (control) and during the application of 30 µM of Thio in the presence of 0.3 µM of tetrodotoxin, 10 µM of 2-amino-5-phosphonovaleric acid, 3 µM of 6-cyano-7-nitroquinoxalone-2, 3-dione, and 0.3 µM of strychnine (Str). The duration of mIPSCs was prolonged, and the frequency was decreased. (B) Averaged trace of 430 and 171 GABAergic mIPSCs before and after application of Thio, respectively. They are superimposed for comparison. (C) Cumulative histograms of decay time and inter-event intervals of GABAergic mIPSCs in the absence or presence of 30 µM of Thio. The inset displays the frequency distribution of GABAergic mIPSCs in corresponding conditions. (D) Statistic analysis of the effects of Thio on the decay time, amplitude, and frequency of GABAergic mIPSCs. Each column represents mean ± sem (n = 5). Compared with control, **P < 0.01.

	Discussion

Top Abstract Introduction Methods Results Discussion References

 
Although neurons containing GABA_A receptors are widely distributed throughout the central nervous system, particular behavior effects are mediated by discrete targets in the brain. For example, Nelson et al. (11) reported that the sedative actions of anesthetics (propofol and barbiturates) are mediated by GABA_A receptors in the region of the hypothalamus (the tuberomammillary nucleus) that is critical for controlling sleep and awake states. In addition, the sensitivity to barbiturates in different regions is also diverse. There may be a cerebral site that is particularly sensitive to barbiturates. Antognini et al. (12) demonstrated that, compared with the spinal cord, selective administration of Thio to the cerebral circulation required twice the concentration to achieve immobility, whereas selective administration of isoflurane or halothane required more. Devor and Zalkind (13) discovered that micro-injecting minute quantities of pentobarbital focally in the brainstem mesopontine tegmentum of rats induced a transient, reversible anesthetic-like state with nonresponsiveness to noxious stimuli, flaccid atonia, and absence of the righting reflex. However, it is widely accepted that the spinal dorsal horn is an important site through which general anesthetics inhibit the response to noxious stimulation. In fact, Sudo et al. (14) showed that Thio directly depressed lumbar dorsal horn neuronal responses to noxious mechanical stimulation in goats using single-unit recording of lumbar dorsal horn neuron. Jewett et al.(15) also demonstrated that Thio depressed the nociceptive-related slow ventral root potential and enhanced the antinociceptive dorsal root potential, and those effects were antagonized by the GABA_A antagonist Bic. These data indicated that Thio might inhibit the noxious stimuli-induced response in spinal dorsal horn via GABA_A receptors. However, our study is the first work to explore the direct modulatory action of Thio on native GABA_A receptors of spinal dorsal horn neurons.

In the present study, we demonstrated that Thio directly activated GABA_A receptors (GABA mimetic effect) in a dose-dependent manner in freshly dissociated spinal dorsal horn neurons. Similar phenomena have been illustrated using propofol (16) and etomidate (17) in the same preparation. Whereas the concentration-response data seem to be sigmoidal, the maximum is probably truncated by open-channel blockage, as has been observed for other general anesthetics (16,17). Because of the limited solubility of Thio, we were unable to address this issue further. This is also supported by the observation that Thio concentrations larger than 100 µM typically show a tail current and that in the presence of 10 µM of GABA, Thio concentrations larger than 50 µM lead to decreased peak currents (Fig. 4).

Whereas 30 µM of Bic completely blocked the current induced by a saturating GABA concentration in the same preparation used here (10), it did not completely abolish I_Thio, even at a concentration of 300 µM. Str at 1 µM (25 times its half-maximal inhibitory concentration [IC₅₀] for inhibiting glycine receptors) did not inhibit I_Thio. Larger concentrations of Str were not used because of its inhibition of the GABA_A receptor (10). Whereas these results show that the bulk of I_Thio is mediated by the GABA_A receptor, the ionic mechanism underlying the residual current, in the presence of Bic, is not clear. In Xenopus oocytes without an injection of human ₁ß₂₂ messenger RNA of GABA_A receptors, Cordato et al. (5) also observed a current produced by Thio at concentrations larger than 100 µM, which was interpreted as endogenous receptor responses, including muscarinic chloride and voltage-sensitive calcium-dependent chloride currents. Direct endogenous responses have also been described in Xenopus oocytes (18). Whether the ionic mechanism of the residual current observed in dorsal horn neurons is consistent with that in Xenopus oocytes requires further studies.

The effect of Thio on the response to GABA was biphasic, i.e., enhancement at small concentrations and suppression at large concentrations. Our data indicate that Thio, similar to other general anesthetics, most probably binds to a distinct site of the GABA_A receptor and exerts positive allosteric modulation (GABA-modulatory effect) at small concentrations. Moreover, at large concentrations, Thio inhibited the peak amplitude of I_GABA, which may have been the result of open-channel blockage. As shown in Figure 1A, currents induced by 200 µM and 300 µM of Thio had obvious tail currents. Studies with other general anesthetics also support this finding (8,19).

In our experiments, inhibition of the frequency of GABAergic mIPSCs by Thio suggests that presynaptic terminals are also a potential site of action of Thio. Halothane decreases mIPSC frequency by reducing presynaptic calcium channel activity or by an interfering with the calcium-dependent proteins that mediate vesicular-membrane fusion in cultured rat cortical neurons (20). The inhibitory effect of Thio may also result from the depression of presynaptic voltage-dependent Ca²⁺ channels. It was shown that various types of voltage-dependent calcium channels were inhibited by Thio in rat hippocampal CA1 pyramidal neurons (21) and dorsal root ganglia sensory neurons (22). Another explanation for Thio inhibition of GABAergic mIPSC frequency may involve neuronal nicotinic acetylcholine receptors (nAChRs). Activation of presynaptic nAChRs in the spinal dorsal horn resulted in a large increase in the frequency of spontaneous IPSCs and mIPSCs (23). Thio is a competitive inhibitor at the human ₇ nACh receptor (24) and causes approximately 27% inhibition of ₄ß₄ nAChR response at its clinical EC₅₀ (25). Thus, alternatively, the observed decrease in the frequency of mIPSCs by Thio may be the result of inhibition of presynaptic nAChRs.

In conclusion, large concentrations of Thio may directly activate GABA_A receptors and block the channels, as well. A clinically relevant concentration of Thio enhanced I_GABA amplitude, increased the time constants of desensitization and deactivation of I_GABA, and prolonged the duration of GABAergic mIPSCs. These effects of Thio would enhance inhibitory transmission and reduce the probability of generating an action potential in postsynaptic neurons and thus result in anesthesia. These results suggest that the anesthetic action of Thio may involve direct enhancement of GABA_A receptor function in the spinal dorsal horn. However, because of the limitation of the whole cell patch-clamp technique, only the effects of Thio on ion channels and synaptic transmission were explored. Linking these effects of Thio on the ion channel with its anesthetics behavior will require further study on intact animals.

We thank Dr. J.J. Celentano for comments on the manuscript.

	Footnotes

 
Supported, in part, by the National Basic Research Program of China (No. 2006CB500803) and the National Natural Science Foundation of China (Nos. 30125015 and 30321002) to T.-L. Xu.

Accepted for publication November 15, 2005.

	References

Top Abstract Introduction Methods Results Discussion References

 

1. Rampil IJ. Anesthetic potency is not altered after hypothermic spinal cord transection in rats. Anesthesiology 1994;80:606–10.[Web of Science][Medline]
2. Antognini JF. The relationship among brain, spinal cord and anesthetic requirements. Med Hypotheses 1997;48:83–7.[Web of Science][Medline]
3. Kendig JJ. In vitro networks: subcortical mechanisms of anaesthetic action. Br J Anaesth 2002;89:91–101.[Abstract/Free Full Text]
4. Franks NP, Lieb WR. Molecular and cellular mechanisms of general anaesthesia. Nature 1994;367:607–14.[Medline]
5. Cordato DJ, Chebib M, Mather LE, et al. Stereoselective interaction of thiopentone enantiomers with the GABA(A) receptor. Br J Pharmacol 1999;128:77–82.[Web of Science]
6. Dickinson R, de Sousa SL, Lieb WR, Franks NP. Selective synaptic actions of thiopental and its enantiomers. Anesthesiology 2002;96:884–92.[Medline]
7. Gustafsson LL, Ebling WF, Osaki E, Stanski DR. Quantitation of depth of thiopental anesthesia in the rat. Anesthesiology 1996;84:415–27.[Web of Science][Medline]
8. Lu H, Xu TL. The general anesthetic pentobarbital slows desensitization and deactivation of the glycine receptor in the rat spinal dorsal horn neurons. J Biol Chem 2002;277:41369–78.[Abstract/Free Full Text]
9. Wu LJ, Lu Y, Xu TL. A novel mechanical dissociation technique for studying acutely isolated maturing Drosophila central neurons. J Neurosci Methods 2001;108:199–206.[Web of Science][Medline]
10. Li Y, Wu LJ, Legendre P, Xu TL. Asymmetric cross-inhibition between GABAA and glycine receptors in rat spinal dorsal horn neurons. J Biol Chem 2003;278:38637–45.[Abstract/Free Full Text]
11. Nelson LE, Guo TZ, Lu J, et al. The sedative component of anesthesia is mediated by GABA(A) receptors in an endogenous sleep pathway. Nat Neurosci 2002;5:979–84.[Web of Science][Medline]
12. Antognini JF, Carstens E, Atherley R. Does the immobilizing effect of thiopental in brain exceed that of halothane? Anesthesiology 2002;96:980–6.[Web of Science][Medline]
13. Devor M, Zalkind V. Reversible analgesia, atonia, and loss of consciousness on bilateral intracerebral microinjection of pentobarbital. Pain 2001;94:101–12.[Web of Science][Medline]
14. Sudo M, Sudo S, Chen XG, et al. Thiopental directly depresses lumbar dorsal horn neuronal responses to noxious mechanical stimulation in goats. Acta Anaesthesiol Scand 2001;45:823–9.[Web of Science][Medline]
15. Jewett BA, Gibbs LM, Tarasiuk A, Kendig JJ. Propofol and barbiturate depression of spinal nociceptive neurotransmission. Anesthesiology 1992;77:1148–54.[Web of Science][Medline]
16. Dong XP, Xu TL. The actions of propofol on gamma-aminobutyric acid-A and glycine receptors in acutely dissociated spinal dorsal horn neurons of the rat. Anesth Analg 2002;95:907–14.[Abstract/Free Full Text]
17. Zhang ZX, Lu H, Dong XP, et al. Kinetics of etomidate actions on GABA(A) receptors in the rat spinal dorsal horn neurons. Brain Res 2002;953:93–100.[Web of Science][Medline]
18. Miledi R, Parker I. Chloride current induced by injection of calcium into Xenopus oocytes. J Physiol (Lond) 1984;357:173–83.[Abstract/Free Full Text]
19. Lim MS, Lindquist CE, Birnir B. Effects of pentobarbital on GABA-activated currents in acutely-isolated rat dentate gyrus granule neurons. Neurosci Lett 2003;353:139–42.[Medline]
20. Kitamura A, Marszalec W, Yeh JZ, Narahashi T. Effects of halothane and propofol on excitatory and inhibitory synaptic transmission in rat cortical neurons. J Pharmacol Exp Ther 2003;304:162–71.[Abstract/Free Full Text]
21. Zhan RZ, Fujiwara N, Yamakura T, et al. Differential inhibitory effects of thiopental, thiamylal and phenobarbital on both voltage-gated calcium channels and NMDA receptors in rat hippocampal slices. Br J Anaesth 1998;81:932–9.[Abstract/Free Full Text]
22. Todorovic SM, Lingle CJ. Pharmacological properties of T-type Ca2+ current in adult rat sensory neurons: effects of anticonvulsant and anesthetic agents. J Neurophysiol 1998;79:240–52.[Abstract/Free Full Text]
23. Takeda D, Nakatsuka T, Papke R, Gu JG. Modulation of inhibitory synaptic activity by a non-alpha4beta2, non-alpha7 subtype of nicotinic receptors in the substantia gelatinosa of adult rat spinal cord. Pain 2003;101:13–23.[Web of Science][Medline]
24. Coates KM, Mather LE, Johnson R, Flood P. Thiopental is a competitive inhibitor at the human alpha7 nicotinic acetylcholine receptor. Anesth Analg 2001;92:930–3.[Abstract/Free Full Text]
25. Flood P, Krasowski MD. Intravenous anesthetics differentially modulate ligand-gated ion channels. Anesthesiology 2000;92:1418–25.[Web of Science][Medline]

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Yang, C.-X. Articles by Xu, T.-L. Search for Related Content PubMed PubMed Citation Articles by Yang, C.-X. Articles by Xu, T.-L. Related Collections Mechanisms Pharmacology