大蒜素对可卡因致小鼠急性肝损伤的防治作用

目的探讨大蒜素对可卡因所致急性肝损伤的防治作用。方法采用可卡因致小鼠急性肝损伤模型,分别预防性和治疗性给予大蒜素。预防性给药时,分别给小鼠ip大蒜素7.5,15和30mg·kg-1,每天1次,共4d,d4给大蒜素30min后sc可卡因75mg·kg-1制备急性肝损伤模型;治疗性给药时,在sc可卡因75mg·kg-130min后分别一次性ip大蒜素10,20和40mg·kg-1。在给予可卡因(预防性给药)或大蒜素(治疗性给药)24h后处死小鼠,观察血清中谷丙转氨酶(GPT)、谷草转氨酶(GOP)和乳酸脱氢酶(LDH)活性,测定肝组织中还原性谷胱甘肽(GSH)、氧化性谷胱甘肽(GSSG)和丙二醛(MDA)含量,并进行组织病理学观察。结果单纯给予可卡因,血清中GPT,GOT和LDH活性升高,肝组织中GSH/GSSG比值下降,MDA含量增加,肝小叶中心出现大量变性坏死细胞。与单纯给予可卡因相比,预防性和治疗性给予大蒜素可明显降低血清中GPT,GOT和LDH活性,并使肝组织中GSH/GSSG比值升高,MDA含量下降,肝小叶中心变性坏死细胞减少,坏死区域缩小。结论大蒜素可抑制可卡因引起的急性肝损伤,对可卡因所致急性肝中毒可能具有一定的治疗作用。     

Protective efficacy of neuroactive steroids against cocaine kindled-seizures in mice

Neuroactive steroids demonstrate pharmacological actions that have relevance for a host of neurological and psychiatric disorders. They offer protection against seizures in a range of models and seem to inhibit certain stages of drug dependence in preclinical assessments. The present study was designed to evaluate two endogenous and one synthetic neuroactive steroid that positively modulate the gamma-aminobutyric acid (GABA(A)) receptor against the increase in sensitivity to the convulsant effects of cocaine engendered by repeated cocaine administration (seizure kindling). Allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one), pregnanolone (3alpha-hydroxy-5beta-pregnan-20-one) and ganaxolone (a synthetic derivative of allopregnanolone 3alpha-hydroxy-3beta-methyl-5alpha-pregnan-20-one) were tested for their ability to suppress the expression (anticonvulsant effect) and development (antiepileptogenic effect) of cocaine-kindled seizures in male, Swiss-Webster mice. Kindled seizures were induced by daily administration of 60 mg/kg cocaine for 5 days. All of these positive GABA(A) modulators suppressed the expression of kindled seizures, whereas only allopregnanolone and ganaxolone inhibited the development of kindling. Allopregnanolone and pregnanolone, but not ganaxolone, also reduced cumulative lethality associated with kindling. These findings demonstrate that some neuroactive steroids attenuate convulsant and sensitizing properties of cocaine and add to a growing literature on their potential use in the modulation of effects of drugs of abuse.     

Neuroactive steroids attenuate cocaine-induced sucrose intake in rats, but not cocaine-induced hyperactivity in mice

Rationale: Neuroactive steroids, including the potent anticonvulsants ganaxolone (3α-hydroxy-3β-methyl-5α-pregnan-20-one) and Co 2-1068 (3β-(4acetylphenyl)ethynyl-3α,21-dihydroxy-5β-20-one-21-hemisuccinate), have recently been shown to protect against cocaine-induced seizures. Objectives: The purpose of the present experiments was to determine whether ganaxolone and Co 2-1068 attenuate acute behavioral effects of cocaine unrelated to seizures. Methods: In the first experiment, the locomotor effects of Co 2-1068 (10–100 mg/ kg), pentobarbital (10–100 mg/kg) and haloperidol (0.03–0.3 mg/kg), alone or in combination with cocaine (5.6–30 mg/kg), were determined in mice. In the second experiment, the effects on sucrose intake of ganaxolone (4–16 mg/kg), Co 2-1068 (8–64 mg/kg), pentobarbital (4–32 mg/kg), and haloperidol (0.04–0.4 mg/kg), alone or in combination with cocaine (4–16 mg/kg), were determined in rats. Results: Cocaine caused a dose-related increase in locomotor activity in mice, whereas Co 2-1068, pentobarbital and haloperidol caused dose-related decreases. The dopamine antagonist haloperidol, at a dose that had no effect on activity by itself, but not Co 2-1068 or pentobarbital, attenuated the cocaine-induced increase in locomotor activity. Cocaine, ganaxolone, Co 2-1068, and haloperidol produced dose-related decreases in sucrose intake in rats; the effects of pentobarbital on sucrose intake were variable. As with locomotor effects, haloperidol attenuated the cocaine-induced decrease in sucrose intake. In addition, cocaine-induced decreases in sucrose intake were attenuated by ganaxolone and Co 2-1068. Pentobarbital had no statistically significant effect on the cocaine dose-response function. Conclusions: These results suggest that the interaction of neuroactive steroids with cocaine extends to pharmacologic actions beyond anticonvulsant efficacy, but that the blockade of behavioral effects of cocaine by neuroactive steroids does not apply to all acute behaviors. Received: 7 September 1999 / Final version: 8 November 1999     

Modification of behavioral effects of drugs in mice by neuroactive steroids

Rationale: Neuroactive steroids represent a novel class of potential therapeutic agents (epilepsy, anxiety, migraine, drug dependence) thought to act through positive allosteric modulation of the GABA_A receptor. A synthetically derived neuroactive steroid, ganaxolone (3α-hydroxy-3β-methyl-5α-pregnan-20-one), is in phase-II clinical trials for epilepsy. Unlike traditional anticonvulsants such as diazepam and phenobarbital, ganaxolone shows equipotent suppression of both the seizure activity and the behavioral effects of pentylenetetrazol (PTZ) administration. Objectives: The present study explored possible reversal by ganaxolone and related neuroactive steroids of some behavioral effects of additional pharmacological challenges. Methods: Direct behavioral observation and photocell-counted locomotor activity of male, Swiss-Webster mice were made with various compounds alone and in conjunction with ganaxolone. Results: Ganaxolone both prevented and reversed PTZ-induced locomotor depression in mice. Further, ganaxolone reversed the locomotor depression induced by other convulsant/anxiogenic stimuli: bicuculline, picrotoxin and, to a lesser extent, yohimbine. Ganaxolone failed to reverse the locomotor stimulation induced by cocaine, methamphetamine, dizocilpine, and phencyclidine. In addition to ganaxolone, the endogenous neuroactive steroids allopregnanolone and pregnanolone and the synthetic neuroactive steroid Co 2-1068 also reversed observed behaviors and locomotor depression induced by PTZ. Conclusions: The present findings support the unique pharmacological effects of neuroactive steroids as a novel class of positive allosteric modulators of GABA. Received: 19 December 1998 / Final version: 22 September 1999     

Sigma1 receptor ligands and related neuroactive steroids interfere with the cocaine-induced state of memory.

The present series of experiments examined the involvement of the sigma(1) receptor and related neuroactive steroids in the memory state induced by a very low dose of cocaine. Using a modified passive avoidance procedure in mice, we examined whether cocaine induces state-dependent (StD) learning. Animals trained and tested with saline or the same dose of cocaine (0.1 or 0.3 mg/kg) showed correct retention, measured using two independent parameters: the retention latency and a ratio between the retention latency and the last training latency. Animals trained with cocaine (0.1 mg/kg) and tested with saline or cocaine (0.03, 0.3 mg/kg), or trained with saline and tested with cocaine, showed altered retention parameters, demonstrating that StD occurred. Therefore, cocaine administered before training produced a chemical state used as an endogenous cue to insure optimal retention. Since sigma(1) receptor activation is an important event during the acquisition of cocaine reward, we tested several sigma(1) ligands and related neurosteroids. The sigma(1) agonist igmesine or antagonist BD1047 failed to produce StD, but modified the cocaine state. Among neuroactive steroids, pregnanolone and allopregnanolone, positive modulators of the gamma-aminobutyric acid type A (GABA(A)) receptor, produced StD. However, steroids also acting as sigma(1) agonists, dehydroepiandrosterone (3beta-hydroxy-5alpha-androsten-17-one (DHEA)), pregnenolone, or antagonist, progesterone, failed to induce StD but modified the cocaine state. Furthermore, optimal retention was observed with mice trained with (igmesine or DHEA)+cocaine and tested with a higher dose of cocaine, or with mice trained with (BD1047 or progesterone)+cocaine and tested with vehicle. This study demonstrated that: (i) low doses of cocaine induce a chemical state/memory trace sustaining StD; (ii) modulation of the sigma(1) receptor activation, although insufficient to provoke StD, modulates the cocaine state; (iii) neuroactive steroids exert a unique role in state-dependent vs state-independent learning, via GABA(A) or sigma(1) receptor modulation, and are able to affect the cocaine-induced mnesic trace at low brain concentrations.     

The effect of amygdala kindling on spontaneous and cocaine-induced motor activity and lidocaine seizures

Interactions of amygdala kindling and drug effects were explored in two experiments. Pretreatment with cocaine (40 mg/kg, IP) for 10 days did not significantly affect the rate of amygdala kindling compared to saline or non-kindled controls. In contrast, daily amygdala kindling with 200 A for 0.5 s for 20 days substantially altered subsequent behavioral responses in a long-lasting fashion. Animals showed decreased spontaneous vertical rearing activity, as well as decreased cocaine-induced vertical activity. In contrast, they were more reactive to the direct dopamine receptor agonist apomorphine. Eighteen days following completion of amygdala kindling, kindled animals were more sensitive to lidocaine-induced convulsions; 88% of kindled animals, but only 24% of the implanted sham-stimulated controls, had seizures. These data suggest that amygdala kindling may produce longlasting changes in selected spontaneous and drug-induced behaviors, as well as convulsive thresholds. Possible physiological and neurological changes underlying this altered responsivity are discussed.     

Lack of effect of sildenafil on cocaine-induced convulsions in mice

The convulsant action of cocaine and the proconvulsant effects of sildenafil, a drug which is widely used in the treatment of erectile dysfunction, have been documented both in humans and mice. Since it was reported that sildenafil alone, and in conjunction with cocaine, is used recreationally, the present study was performed to examine the influence of sildenafil on cocaine-induced seizures in mice. We showed that administration of sildenafil (5–20 mg/kg, ip) did not affect latency to clonic seizures induced by ip administration of cocaine at a dose of 85 mg/kg, nor did it influence seizure incidence and mortality. We conclude that sildenafil does not significantly increase the risk of seizures when co-administered with cocaine.     

The effects of nandrolone decanoate on cocaine-induced kindling in male rats

Use and abuse of various controlled substances in recent years has reached alarming levels. Among these are cocaine and anabolic steroids. The two contrasting types of drug have common sites of action within the limbic system of the central nervous system. The ability of cocaine to provoke seizures is well documented, and sex hormones also have been shown to alter seizure types and characteristics. This project studied the consequences of co-administration of cocaine and a representative anabolic-androgenic steroid, nandrolone decanoate. Specifically, the effects of nandrolone on cocaine-induced kindling of seizures were examined. Nandrolone was shown to increase seizure rate when given in high (20mg twice weekly) intermittent doses. No statistically significant differences were observed with low (2mg) daily doses of nandrolone. The results support the hypothesis that an androgen may interact so as to modify the pattern of cocaine-related kindling. However, the potential of either pharmacodynamic and/or pharmacokinetic mechanism(s) for this interaction exists, and the nature of these interactions remains to be fully elucidated.     

Auto-modulation of neuroactive steroids on GABA A receptors: a novel pharmacological effect

GABA(A) receptor function is modulated by various important drugs including neuroactive steroids that act on allosteric modulatory sites and can directly activate GABA(A) receptor channels at high concentrations. We used whole cell patch-clamp recordings and rapid applications of the neuroactive steroid alphaxalone to investigate repetitive steroid effects. Alphaxalone potentiation of submaximal GABA-evoked currents was enhanced significantly by repetitive coapplications at all investigated recombinant isoforms (alpha1beta3delta, alpha1beta3gamma2L, alpha6beta3delta, alpha6beta3gamma2L) and at GABA(A) receptors of differentiated human NT2 neurons. A similar increase of current amplitudes was induced by repetitive applications of a high steroid concentration without GABA. We refer to these reversible effects as auto-modulation because repeated interactions of steroids enhanced their own pharmacological impact at the receptor sites in a time and concentration dependent manner without affecting GABA controls. Pronounced auto-modulatory actions were also measured using the neurosteroid 5alpha-THDOC in contrast to indiplon, THIP, and pentobarbital indicating a steroid specificity. Protein kinase A inhibition significantly reduced alphaxalone auto-modulation at alpha1beta3gamma2L, alpha6beta3gamma2L, and alpha6beta3delta subtypes while it enhanced potentiation at alpha1beta3delta isoforms suggesting a crucial influence of receptor subunit composition and phosphorylation for steroid actions. Especially at extrasynaptic GABA(A) receptor sites containing the delta subunit steroid auto-modulation may have a critical role in enhancing potentiation of GABA-induced currents.     

Potential clinical uses of neuroactive steroids

Neuroactive steroids rapidly modulate gamma-aminobutyric acid (GABA) and glutamate receptors. GABA-enhancing steroids have potential clinical utility as anesthetics, hypnotics, anticonvulsants and anxiolytics. Furthermore, GABAergic neurosteroids may participate in regulating mood and the effects of alcohol on the nervous system, suggesting a potential role in major psychiatric disorders. Neuroactive steroids that alter the function of glutamate receptors could be useful for treating neurodegenerative disorders, and as cognitive enhancers. Recent progress in developing water-soluble steroids and steroids with enhanced oral efficacy foster optimism that certain neuroactive steroids will be developed for clinical use.     

Potential clinical uses of neuroactive steroids

Neuroactive steroids rapidly modulate gamma-aminobutyric acid (GABA) and glutamate receptors. GABA-enhancing steroids have potential clinical utility as anesthetics, hypnotics, anticonvulsants and anxiolytics. Furthermore, GABAergic neurosteroids may participate in regulating mood and the effects of alcohol on the nervous system, suggesting a potential role in major psychiatric disorders. Neuroactive steroids that alter the function of glutamate receptors could be useful for treating neurodegenerative disorders, and as cognitive enhancers. Recent progress in developing water-soluble steroids and steroids with enhanced oral efficacy foster optimism that certain neuroactive steroids will be developed for clinical use.     

草乌甲素对Balb/c小鼠的部分免疫功能的抑制作用

目的:研究草乌甲素对Balb/c小鼠部分免疫功能的影响。方法:Balb/c小鼠随机分为空白对照组、草乌甲素3个剂量(0.08、0.16、0.32 mg·kg~(-1),肌注7d)组、氢化可的松组(阳性对照药,10mg·kg~(-1))。小鼠d7处死,检测药物对小鼠胸腺指数、脾脏指数的影响;测定小鼠T、B淋巴细胞转化功能;酶联免疫法(ELISA)测定小鼠血清总IgG水平;中性红比色法测定小鼠腹腔巨噬细胞吞噬功能;硝酸还原酶法测定巨噬细胞培养上清一氧化氮(NO)水平。结果:草乌甲素0.32 mg·kg~(-1)能抑制致裂原刺激T、B淋巴细胞增殖(P<0.01),降低腹腔巨噬细胞培养上清中NO水平(P<0.05)。草乌甲素(0.16、0.32 mg·kg~(-1))降低小鼠的胸腺指数,降低小鼠血清中总IgG水平(P<0.05,P<0.01),草乌甲素还能抑制腹腔巨噬细胞吞噬功能(P<0.05,P<0.01)。结论:草乌甲素对Balb/c小鼠的免疫功能有一定的抑制作用。     

Influence of sleep deprivation on neuroactive steroids in major depression.

There is evidence from preclinical and clinical studies that concentrations of neuroactive steroids are altered in depression and normalize after antidepressant pharmacotherapy. However, no data are available concerning the impact of sleep deprivation on the concentrations of neuroactive steroids. A total of 29 drug-free patients (12 men, 17 women) suffering from major depression according to DSM-IV criteria were treated with partial sleep deprivation (PSD). Response to PSD was defined as a reduction of at least 30% according to the six-item version of the Hamilton depression scale (6-HAMD). Plasma samples were taken the day before and after PSD (days 0 and 1) and after one night of recovery sleep (day 2) at 8:00 am. The samples were quantified for neuroactive steroids by means of a highly sensitive and specific combined gas chromatography/mass spectrometry analysis. There was no influence of PSD on the concentrations of neuroactive steroids either in PSD responders (n=20) or in nonresponders (n=9). However, nonresponders showed significantly higher concentrations of 3alpha,5alpha-tetrahydroprogesterone (3alpha,5alpha-THP), 3alpha,5beta-tetrahydroprogesterone (3alpha,5beta-THP), and dehydroepiandrosterone (DHEA) before or after PSD compared to responders. In contrast to antidepressant drugs, which correct the dysequilibrium of neuroactive steroids in major depression within several weeks, PSD does not affect the concentrations of neuroactive steroids either in responders or in nonresponders.     

琥珀酸对大鼠化学性点燃和杏仁核电刺激性点燃的抑制作用

目的:研究琥珀酸对大鼠戊四哇化学性点燃(kindling)发作及杏仁核电刺激点燃发作的影响及作用机制.方法:建立大鼠戊四唑化学性点燃模型和杏仁核电刺激点燃癫痫模型,测定琥珀酸对点燃发作的脑电活动及行为变化指标的影响.测定琥珀酸对GABA_A受体拮抗剂印防己毒素诱发小鼠惊厥的影响.结果:琥珀酸(100-400 mg/kg,iP)对两种点燃模型有显著抑制作用,降低发作强度和全身性发作百分率(P<0.05,P<0.01),可升高杏仁核电刺激点燃大鼠的局灶性后放电阈值(P<0.05,P<0.01),以上反应呈剂量效应关系。琥珀酸可延长印防己毒素诱发小鼠惊厥的潜伏期(P<0.05,P<0.01).结论:琥珀酸对大鼠戊四唑化学性点燃和脑杏仁核电刺激点燃发作有抑制作用,其机制可能与增强GABA_A受体功能有关.     

Inhibitory effect of GABAergic drugs in cocaine-induced genital reflexes in paradoxical sleep-deprived male rats

The aim of this study was to seek whether GABAergic drugs were involved in the action of cocaine on spontaneous genital reflexes (penile erection-PE, and ejaculation-EJ) of paradoxical sleep-deprived (PSD) male rats. After a 4-day period of PSD, each group was administered with GABAergic drugs 1 h prior to cocaine and placed in observation cages. The administration of gamma-aminobutyric acid (GABA)-A agonist (muscimol, 2 and 3 mg/kg sc) reduced the number of animals displaying PE, whereas all doses tested of muscimol and bicuculline significantly reduced the frequency of PE. Pretreatment with the lower doses of GABA-B antagonist, phaclofen (1 and 2 mg/kg sc), also significantly reduced the percentage of rats showing PE; however, after the higher dose injection, the proportion of animals with PE was similar to those seen after vehicle pretreatment. Both GABA-B agonist and antagonist significantly reduced the PE frequency for all doses used compared with the vehicle group. There were no significant differences between control and GABA-A drugs in EJ behavior, whereas phaclofen 2 mg/kg pretreatment increased the ejaculatory latency. These data show that GABAergic compounds inhibited PE in male PSD rats suggesting that this inhibition points to a differential role of GABA receptor subtypes.     

Quantification of ten neuroactive steroids in plasma in Withdrawal Seizure-Prone and -Resistant mice during chronic ethanol withdrawal

Rationale

The rapid membrane actions of neuroactive steroids, particularly via an enhancement of γ-aminobutyric acid_A receptors (GABA_ARs), participate in the regulation of central nervous system excitability. Prior evidence suggests an inverse relationship between endogenous GABAergic neuroactive steroid levels and behavioral changes in excitability during ethanol withdrawal.

Objectives

Previously, we found that ethanol withdrawal significantly decreased plasma allopregnanolone (ALLO) levels, a potent GABAergic neuroactive steroid, and decreased GABA_AR sensitivity to ALLO in Withdrawal Seizure-Prone (WSP) but not in Withdrawal Seizure-Resistant (WSR) mice. However, the effect of ethanol withdrawal on levels of other endogenous GABA_AR-active steroids is not known.

Methods

After validation of a gas chromatography-mass spectrometry method for the simultaneous quantification of ten neuroactive steroids, we analyzed plasma from control male WSP-1 and WSR-1 mice and during ethanol withdrawal.

Results

We quantified levels of nine neuroactive steroids in WSP-1 and WSR-1 plasma; levels of pregnanolone were not detectable. Basal levels of five neuroactive steroids were higher in WSR-1 versus WSP-1 mice. Ethanol withdrawal significantly suppressed five neuroactive steroids in WSP-1 and WSR-1 mice, including ALLO.

Conclusions

Due to lower basal levels of some GABA_AR-active steroids in WSP-1 mice, a withdrawal-induced decrease in WSP-1 mice may have a greater physiological consequence than a similar decrease in WSR-1 mice. Because WSP-1 mice also exhibit a reduction in GABA_AR sensitivity to neuroactive steroids during withdrawal, it is possible that the combined decrease in neuroactive steroids and GABA_AR sensitivity during ethanol withdrawal in WSP-1 mice represents a neurochemical substrate for severe ethanol withdrawal.     

Neuropsychopharmacological properties of neuroactive steroids in depression and anxiety disorders

Neuroactive steroids modulate neurotransmission through modulation of specific neurotransmitter receptors such as γ-aminobutyric acid type A (GABA_A) receptors. Preclinical studies suggested that neuroactive steroids may modulate anxiety- and depression-related behaviour and may contribute to the therapeutical effects of antidepressant drugs. Attenuations of 3α-reduced neuroactive steroids have been observed during major depression. This disequilibrium can be corrected by successful treatment with antidepressant drugs. However, non-pharmacological antidepressant treatment strategies did not affect neuroactive steroid composition independently from the clinical response. Further research is needed to clarify whether enhancement of neuroactive steroid levels might represent a new therapeutical approach in the treatment of affective disorders. Nevertheless, the first studies investigating the therapeutical effects of exogenously administered dehydroepiandosterone revealed promising results in the treatment of major depression. In addition, in various anxiety disorders alterations of neuroactive steroid levels have been observed. In panic disorder, in the absence of panic attacks, neuroactive steroid composition is opposite to that seen in depression, which may represent counter-regulatory mechanisms against the occurrence of spontaneous panic attacks. However, during experimentally induced panic attacks, there was a pronounced decline in GABAergic neuroactive steroids, which might contribute to the pathophysiology of panic attacks. In conclusion, neuroactive steroids contribute to the pathophysiology of affective disorders and the mechanisms of action of antidepressants. They are important endogenous modulators of depression and anxiety and may provide a basis for the development of novel therapeutic agents in the treatment of affective disorders.     

Pentylenetetrazol kindling in mice

Kindling with pentylenetetrazol to produce minimal and maximal convulsions was investigated in CF-1 mice. Like electrical kindling, the kindling effect was directly proportional to the dose or the intensity of the kindling stimulus. Similarly, the kindling effect was persistent, as was emphasized by the ability to kindle with an interdose interval of 3 days and by the convulsions produced by a challenge with pentylenetetrazol 30 days after withdrawal from the kindling treatment. The changes in excitability, associated with the kindling state, appeared to be relatively selective for pentylenetetrazol, because no changes in thresholds to either electroshock or administration of picrotoxin or N-methyl-DL-aspartate correlated temporally with the persistence of kindling. The influence of two anticonvulsant drugs, ethosuximide and cannabidiol, on kindling was also investigated. Both drugs blocked the development of kindling to pentylenetetrazol-induced minimal convulsions. Of these drugs, only ethosuximide raised the minimal convulsive threshold to pentylenetetrazol. Against pentylenetetrazol-induced kindling to maximal convulsions, only cannabidiol blocked kindling and only cannabidiol raised the maximal seizure threshold for pentylenetetrazol. Although the drugs modified the kindling effect, the mechanism of the interaction is not clear.     

Insight into the mechanism of action of neuroactive steroids

Rho(1) receptor-channels (rho(1)Rs) are GABA-gated chloride channels that exhibit slow kinetics, little desensitization, and inert pharmacology to most anesthetics, except for neuroactive steroids (NSs). NSs differentially modulate rho(1)Rs dependent on the steric arrangement of the hydrogen atom at the fifth carbon position. In particular, the NS allotetrahydrodeoxycorticosterone (5alpha-THDOC) potentiates, whereas 5beta-pregnane-3alpha-ol-20-one (pregnanolone) and 5beta-dihydroprogesterone (5beta-DHP) inhibit rho(1) GABA currents. Here, we used Xenopus laevis oocytes expressing rho(1)Rs as a model system to study the mechanism of NS modulation. The second transmembrane residue, Ile307, was mutated to 16 amino acids. Subsequent testing of these mutants with 5alpha- and 5beta-NSs, at equivalent GABA activity, showed the following paradigm. For 5beta-DHP, Ile307 mutation either altered the degree of inhibition or entirely reversed the direction of modulation, rendering 5beta-DHP a potentiator. Dependent on the mutation, pregnanolone remained an inhibitor, transformed into a potentiator, or converted to inhibitor and potentiator based on concentration. The extent of mode reversal for both 5beta compounds showed a correlation with the side-chain hydrophilicity of the 307 residue. In contrast, Ile307 substitutions did not alter the direction of modulation for 5alpha-THDOC but caused a significant increase in the level of potentiation. Paradoxical to their impact on the mode and/or the degree of modulation, none of the mutations altered the concentration range producing the response significantly for any of the above NSs. Moreover, preincubation of Ile307 mutants with 5alpha or 5beta alone produced an equivalent effect on the activation time course. Based on the above data, a universal model is presented wherein anesthetic compounds like NSs can potentiate or inhibit the activity of ligand-gated ion channels distinct from interaction with alternative binding sites.