Novel benzo[b]xanthene derivatives: Bismuth(III) triflate-catalyzed one-pot synthesis,characterization, and acetylcholinesterase,glutathione S-transferase,and butyrylcholinesterase inhibitory properties

In this study, 3,4-dihydro-12-aryl-1H-benzo[b]xanthene-1,6,11-(2H,12H)trione compounds were obtained through one-pot condensation of various substituted aromatic aldehydes, 2-hydroxy-1,4-naphthoquinone, and dimedone in the presence of Bi(OTf)₃ as a green and reusable catalyst. The structural characterization of these novel substituted benzo[b]xanthenes was performed by spectroscopic methods, and their inhibitory actions against butyrylcholinesterase (BChE), acetylcholinesterase (AChE), and glutathione S-transferase (GST) were investigated. GST is an enzyme responsible for removing toxic molecules during Phase II reactions in the detoxification mechanism. The AChE and BChE enzymes, which are called cholinesterases, are among the enzymes that occur especially during dementia such as brain damage or Alzheimer's disease. Inhibition effects of the benzo[b]xanthene derivatives on AChE, BChE, and GST were found at the millimolar level. The best inhibitor for GST is compound 4a (31.18 ± 6.13 mM), for AChE, it is compound 4d (28.16 ± 3.46 mM), and for BChE, it is compound 4f (36.24 ± 3.19 mM). Compound 4a inhibited the dimerization of GST subunits, and compounds 4d and 4f directly inhibited the catalytic activity by interacting with the catalytic active site or a related site of the AChE and BChE enzymes, respectively.     

Naphthoquinones,benzoquinones, and anthraquinones: Molecular docking,ADME and inhibition studies on human serum paraoxonase-1 associated with cardiovascular diseases

Paraoxonase-1 (PON1) has essential roles such as protecting low-density lipoprotein against detoxification and oxidation of highly toxic compounds. Quinones are a class of compounds and a type of plant-derived secondary metabolites. Here, PON1 was purified using very simple methods and evaluation of the interactions between the enzyme and some quinones. It was found that these quinones displayed effective inhibitor properties for PON1 with the IC₅₀ values in the range of 3.27–82.90 μM and the K _i values in the range of 2.50 ± 0.65 to 30.90 ± 7.20 μM. These quinones displayed distinct inhibition mechanisms. It was determined that except for 5-hydroxy-2-methyl-1,4-naphthoquinone and 2-methyl-1,4-naphthoquinone all quinones exhibit competitive inhibition effects. Also, molecular docking and in silico ADME studies were performed. Usage of drugs including quinone derivatives in structure with biological activity would be hazardous in some cases.     

托莫西汀与氟西汀在大鼠体内药动学的相互作用

目的:考察托莫西汀和氟西汀在大鼠体内的药动学特性及合用时的相互作用.方法:采用柱前衍生-高效液相色谱法测定大鼠给药后不同时间的托莫西汀和氟西汀的血浆浓度.血浆浓度-时间数据用3P97程序拟合,求得药动学参数.结果:托莫西汀与氟西汀均符合二室模型特征,两药合用时,托莫西汀的t1/2、Cmax、AUC均明显增加,而氟西汀的药动学参数无统计学差异.结论:两药合用时,氟西汀会对托莫西汀的体内药代动力学产生显著影响,临床上应对托莫西汀的剂量以及给药间隔做相应的调整,必要时进行血药浓度监测.     

Synthesis,characterization, biological evaluation,and in silico studies of novel 1,3-diaryltriazene-substituted sulfathiazole derivatives

In the present study, a series of eleven novel 1,3-diaryltriazene-substituted sulfathiazole moieties ( ST1 – 11 ) was synthesized by the reaction of diazonium salt of sulfathiazole with substituted aromatic amines and their chemical structures were characterized by Fourier transform infrared, ¹H-NMR (nuclear magnetic resonance), ¹³C-NMR, and high-resolution mass spectroscopy methods. These synthesized novel derivatives were found to be effective inhibitor molecules for α-glycosidase (α-GLY), human carbonic anhydrase (hCA), and acetylcholinesterase (AChE), with K_I values in the range of 426.84 ± 58.42–708.61 ± 122.67 nM for α-GLY, 450.37 ± 50.35–1,094.34 ± 111.37 nM for hCA I, 504.37 ± 57.22–1,205.36 ± 195.47 nM for hCA II, and 68.28 ± 10.26–193.74 ± 19.75 nM for AChE. Among the synthesized novel compounds, several lead compounds were investigated against the tested metabolic enzymes. More specifically, ST11 (4-[3-(perfluorophenyl)triaz-1-en-1-yl]-N-(thiazol-2-yl)benzenesulfonamide) showed a highly efficient inhibition profile against hCA I, hCA II, and AChE, with K_I values of 450.37 ± 50.35, 504.37 ± 57.22, and 68.28 ± 10.26 nM, respectively. Due to its significant biological inhibitory potency, this derivative may be considered as an interesting lead compound against these enzymes.     

Aaptamine – a dual acetyl – and butyrylcholinesterase inhibitor as potential anti-Alzheimer’s disease agent

ContextAlzheimer’s disease (AD) is a neurodegenerative disorder that affects millions of people worldwide. Acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) are promising therapeutic targets for AD.ObjectiveTo evaluate the inhibitory effects of aaptamine on two cholinesterases and investigate the in vivo therapeutic effect on AD in a zebrafish model.Materials and methodsAaptamine was isolated from the sponge Aaptos suberitoides Brøndsted (Suberitidae). Enzyme inhibition, kinetic analysis, surface plasmon resonance (SPR) and molecular docking assays were used to determine its inhibitory effect on AChE and BuChE in vitro. Zebrafish were divided into six groups: control, model, 8 μM donepezil, 5 , 10  and 20 μM aaptamine. After three days of drug treatment, the behaviour assay was performed.ResultsThe IC₅₀ values of aaptamine towards AChE and BuChE were 16.0 and 4.6 μM. And aaptamine directly inhibited the two cholinesterases in the mixed inhibition type, with K_i values of 6.96 ± 0.04 and 6.35 ± 0.02 μM, with K_d values of 87.6 and 10.7 μM. Besides, aaptamine interacts with the crucial anionic sites of AChE and BuChE. In vivo studies indicated that the dyskinesia recovery rates of 5 , 10  and 20 μM aaptamine group were 34.8, 58.8 and 60.0%, respectively, and that of donepezil was 63.7%.Discussion and conclusionsAaptamine showed great potential to exert its anti-AD effects by directly inhibiting the activities of AChE and BuChE. Therefore, this study identified a novel medicinal application of aaptamine and provided a new structural scaffold for the development of anti-AD drugs.     

Molecular interactions of 4-acetoxy-plakinamine B with peripheral anionic and other catalytic subsites of the aromatic gorge of acetylcholinesterase: Computational and structural insights

Abstract

Context: A steroidal alkaloid, 4-acetoxy-plakinamine B (4APB), is a recently discovered marine natural product with inhibitory effect against acetylcholinesterase (AChE), but its mechanism of interaction with the enzyme remains to be elucidated.

Objective: The main objective was to study molecular binding mode of the compound, its interactions with catalytic subsites and molecular mechanism behind its significant inhibitory effect.

Materials and methods: All possible interactions of ligands in the binding sites were analyzed using FRED 2.1 and the OMEGA pre-generated multi-conformer library.

Results: Dipole–dipole interactions were observed between the secondary amino group of 4APB and Ser200 at a distance of 3.91?Å and also with Gly117 and Gly118. A further dipole–dipole interaction was between Arg289 and the heterocyclic nitrogen. Hydrogen bonding interactions were observed between Tyr130 and secondary amino and C-4 acetyl groups as well as between heterocyclic nitrogen and Phe288 at a distance of 3.04?Å. Hydrophobic interactions were evident between rings C/D of 4APB and with Phe288, Phe330 and Phe331. The computational studies revealed 4APB’s critical molecular interaction with amino acids of peripheral active (PAS) and anionic (AS) subsites.

Discussion: Our data provided molecular evidence for the mixed competitive inhibitory effect of 4APB. For lead optimization, structural insights revealed the N-methyl group of 4APB could be replaced by NH₂ moiety to generate a more favorable hydrogen bonding with Glu199. A polar group insertion such as NH₂ or OH at certain sites of the 4APB skeleton is also recommended.

Conclusion: These computational insights explained the mixed-competitive enzyme kinetic behavior of 4APB. This study outlines a strategy for designing novel derivatives of 4APB with potentially better AChE inhibitory activities through interaction at the PAS and AS sites.     

Synthesis,characterization, biological evaluation,and molecular docking studies of some piperonyl-based 4-thiazolidinone derivatives

Heterocyclic compounds are of particular importance among pharmacologically active compounds. In this study, some piperonyl-based 4-thiazolidinone derivatives ( 2a–i ) were synthesized and characterized by spectroscopic assays. All molecules were tested as enzyme inhibitory factors. These compounds were effective inhibitors of the enzymes acetylcholinesterase (AChE), α-glycosidase (α-Gly), and the human carbonic anhydrase I and II isoforms (hCA I and II), with K_i values in the range of 8.90–66.51 nM for α-Gly, 94.8–289.5 nM for hCA I, 106.3–304.6 nM for hCA II, and 0.55–2.36 nM for AChE. The synthesized molecules were also studied theoretically. Molecular docking calculations were performed to investigate the interaction between the target protein and molecules. CA inhibitor compounds have been clinically used for almost 60 years as antiglaucoma and diuretic drugs. The inhibition of the AChE enzyme results in the blockage of ACh hydrolysis. On the contrary, the design of inhibitor compounds or/and modulators for AChE is of major interest as it is one of the most popular tools to prevent Alzheimer's disease.     

Estimation of the upper limit of human butyrylcholinesterase dose required for protection against organophosphates toxicity: a mathematically based toxicokinetic model.

Human butyrylcholinesterase (HuBChE) is a drug candidate for protection against organophosphates (OP) intoxication. A mathematically based model was validated and employed to better understand the role of the endogenous HuBChE in detoxification of OPs and to estimate the dose of exogenous HuBChE required for enhancing protection of humans from lethal exposure to OPs. The model addresses the relationship between the HuBChE dose needed to maintain a certain residual activity of human acetylcholinesterase (HuAChE) and the following parameters: (1) level and duration of exposure, (2) bimolecular rate constants of inhibition of HuAChE (kA) and HuBChE (kB) by OPs, and (3) time elapsed from enzyme load. The equation derived for the calculation of HuBChE dose requires the knowledge of kA/kB in human blood and the rate constant of HuBChE elimination. Predictions of HuBChE doses were validated by in vitro experiments and data of published human studies. These predictions highlight two parameters that are likely to decrease the calculated dose: (1) the rapid consumption of the less toxic isomers of OPs in human plasma, and (2) the volume of distribution of HuBChE that appears significantly greater than the volume of plasma. The first part of the analysis of the proposed model was focused on acute bolus exposures and suggests that upper limit doses of 134, 115, and 249 mg/70 kg are sufficient to protect RBC AChE above 30% of baseline activity following a challenge with 1 LD(50) VX, soman, and sarin, respectively. The principles of the validated model should be applicable for advanced predictions of HuBChE dose for protection against continuous exposures to OPs.     

光谱法结合分子对接的甲苯磺丁脲与乳清蛋白的相互作用研究

目的 在生理条件下使用紫外光谱法、荧光光谱法以及分子对接研究甲苯磺丁脲与乳清蛋白的相互作用。方法 实验选取激发波长280 nm,测定不同温度下甲苯磺丁脲与乳清蛋白的荧光猝灭光谱;通过相关参数（结合常数、结合位点数等）的计算以及热力学参数判断猝灭机制、甲苯磺丁脲与乳清蛋白的相互作用特点以及乳清蛋白构象的变化,并通过分子对接方法探究药物与乳清蛋白之间可能存在的作用形式。结果 甲苯磺丁脲可使乳清蛋白内源荧光发生作用机制为复合式静态猝灭的猝灭;以氢键、范德华力为主要作用力类型;甲苯磺丁脲与乳清蛋白结合过程中存在非辐射能量转移,促使乳清蛋白的荧光猝灭;药物与蛋白的结合对乳清蛋白的构象无明显影响;分子对接结果表明：甲苯磺丁脲分别与Glu113残基形成1个氢键,与Asp116残基形成2个氢键以及与Glu121残基形成2个氢键。结论 甲苯磺丁脲与乳清蛋白可以发生相互作用,因此建议甲苯磺丁脲不要和牛奶同服。     

米氮平和氟西汀治疗抑郁症的对照研究

目的比较研究米氮平和氟西汀治疗抑郁症的疗效和不良反应。方法将70例符合CCMD-3诊断标准的抑郁症患者随机分组,分别给予米氮平和氟西汀单药治疗,疗程共8周,采用汉密尔顿抑郁量表（HAMD）进行疗效评定,以不良反应症状量表（TESS）评定药物不良反应。结果 8周末米氮平组缓解率64.5%、有效率93.5%,显效率77.5%,氟西汀组缓解率39.4%、有效率91.0%,显效率72.8%。米氮平组缓解率高于氟西汀组,差异有显著性（P〈0.05）,而两组疗效无显著性差异（P〉0.05）,但米氮平对焦虑/躯体化症状起效快,需要合并服用苯二氮艹卓类药物的例数更少。两药不良反应少,TESS评分总体相当,米氮平更多引起嗜睡、头晕,氟西汀组的烦躁、恶心发生率稍高于米氮平。结论米氮平和氟西汀对抑郁症疗效相当,不良反应轻、安全性高,米氮平起效快、有更高的缓解率。     

Pharmacophore-based virtual screening and density functional theory approach to identifying novel butyrylcholinesterase inhibitors

Aim:

To identify the critical chemical features, with reliable geometric constraints, that contributes to the inhibition of butyrylcholinesterase (BChE) function.

Methods:

Ligand-based pharmacophore modeling was used to identify the critical chemical features of BChE inhibitors. The generated pharmacophore model was validated using various techniques, such as Fischer''s randomization method, test set, and decoy set. The best pharmacophore model was used as a query in virtual screening to identify novel scaffolds that inhibit BChE. Compounds selected by the best hypothesis in the virtual screening were tested for drug-like properties, and molecular docking study was applied to determine the optimal orientation of the hit compounds in the BChE active site. To find the reactivity of the hit compounds, frontier orbital analysis was carried out using density functional theory.

Results:

Based on its correlation coefficient (0.96), root mean square (RMS) deviation (1.01), and total cost (105.72), the quantitative hypothesis Hypo1 consisting of 2 HBA, 1 Hy-Ali, and 1 Hy-Ar was selected as the best hypothesis. Thus, Hypo1 was used as a 3D query in virtual screening of the Maybridge and Chembridge databases. The hit compounds were filtered using ADMET, Lipinski''s Rule of Five, and molecular docking to reduce the number of false positive results. Finally, 33 compounds were selected based on their critical interactions with the significant amino acids in BChE''s active site. To confirm the inhibitors'' potencies, the orbital energies, such as HOMO and LUMO, of the hit compounds and 7 training set compounds were calculated. Among the 33 hit compounds, 10 compounds with the highest HOMO values were selected, and this set was further culled to 5 compounds based on their energy gaps important for stability and energy transfer. From the overall results, 5 hit compounds were confirmed to be potential BChE inhibitors that satisfied all the pharmacophoric features in Hypo1.

Conclusion:

This study pinpoints important chemical features with geometric constraints that contribute to the inhibition of BChE activity. Five compounds are selected as the best hit BchE-inhibitory compounds.     

Synthesis,molecular modeling studies,ADME prediction of arachidonic acid carbamate derivatives,and evaluation of their acetylcholinesterase activity

In this work, a series of novel anandamide units containing carbamate were designed and synthesized. All the derivatives were evaluated in vitro for their inhibitory potential against the electric eel acetylcholinesterase enzyme (AChE) and showed reversible inhibitions. The compounds 7a , 7d , 7e , and 7f are mixed inhibitors of AChE, while the compounds 7b , 7c , and 7g are uncompetitive (K_i in the range 0.93–8.86 μM). The kinetic studies revealed that compounds 7b , 7c , 7f , and 7g inhibit considerably AChE activity. Molecular docking analyses were made to evaluate the binding type and interactions of the synthesized compounds to the ligand-binding site of hAChE. It was observed that the docking results were in parallel with the in vitro results. The adsorption, distribution, metabolism, and excretion properties were computed for the compounds, and were found within the acceptable range. This study suggests the compounds 7b , 7c , 7f , and 7g identified as novel reversible AChE inhibitors may be useful lead compounds for the treatment of Alzheimer's disease.     

Clinical and experimental studies on fluoxetine: effects on serotonin uptake

A decreased rate of uptake of serotonin (5HT) into platelets is recognized as a possible marker of the depressed state, being normalized only by effective antidepressant treatment. Fluoxetine is a novel antidepressant, with 5HT uptake inhibitory properties. In this study, treatment of depressed patients with fluoxetine for up to 6 months did not normalize the decreased platelet 5HT uptake rates associated with depression, although the patients showed a clinical recovery. The olfactory bulbectomized (OB) rat shows a characteristic hyperactivity in a stressful environment, which can be reversed only by chronic treatment with most antidepressants. OB rats have been found to exhibit a decreased rate of platelet 5HT uptake, similar to depressed patients, which is normalized by chronic antidepressant treatment. However, 3 weeks treatment with fluoxetine failed to reverse the hyperactivity of the OB rat and the decreased rates of uptake of 5HT. We also examined the rate of uptake of serotonin into the synaptosomes of the OB rats, in order to elucidate whether platelet 5HT uptake reflected central activity. Chronic fluoxetine treatment failed to normalize high affinity synaptosomal 5HT uptake in the OB rat. Fluoxetine, therefore, unlike most other antidepressants, does not normalize the decreased rates of platelet 5HT uptake in depressed patients on clinical recovery. OB rats also showed a deficit in their platelet and synaptosomal 5HT uptake rates, following 3 weeks treatment with fluoxetine.     

Isolation,characterization, and in silico,in vitro and in vivo antiulcer studies of isoimperatorin crystallized from Ostericum koreanum

Context: Ostericum koreanum (Maxim.) Kitagawa (Apiaceae) roots are traditionally used as an analgesic and antiulcer agent. However, the antiulcer potential of isoimperatorin isolated from O. koreanum has not yet been explored.

Aim: To evaluate the antiulcer activity of isoimperatorin isolated from the roots of O. koreanum.

Materials and methods: Isoimperatorin was isolated as cubic crystals by repeated column chromatography of the ethyl acetate fraction and structure was verified with ¹H NMR, ¹³C NMR and high-resolution mass spectrometry (HRMS-FAB). The crystals obtained were analyzed with the single crystal X-ray method. The MTT assay was used to determine its cytotoxicity against chondrocytes at different concentrations (0.0–737.74?μM, 24?h). The in vivo antiulcer activity of isoimperatorin (40?mg/kg) was determined against ethanol-, indomethacin- and pyloric ligation-induced ulcers in Sprague-Dawley rats. Furthermore, the effect of isoimperatorin (0.0–737.74?μM, 24?h) on the expression of type II collagen in chondrocytes was determined using western blot method. The in vitro urease inhibitory activity of isoimperatorin (0–80?μM) and molecular docking was also performed against urease.

Results and discussion: Isoimperatorin demonstrated significant inhibitory activity (IC₅₀ 36.43?μM) against urease as compared to the standard drug thiourea (IC₅₀ 33.57?μM) without cytotoxic effects. It provided 70.9%, 67.65% and 54.25% protection in ulcer models induced by ethanol, indomethacin and pyloric ligation, respectively. Isoimperatorin showed the highest expression level of type II collagen at 368.87?μM. The docking results confirmed strong binding affinity with the target protein.

Conclusion: Isoimperatorin may be used to develop antiulcer drugs with decreased side effects.     

DNA sequence of butyrylcholinesterase from the rat: expression of the protein and characterization of the properties of rat butyrylcholinesterase

The rat is the model animal for toxicity studies. Butyrylcholinesterase (BChE), being sensitive to inhibition by some organophosphorus and carbamate pesticides, is a biomarker of toxic exposure. The goal of this work was to characterize the purified rat BChE enzyme. The cDNA sequence showed eight amino acid differences between the active site gorge of rat and human BChE, six clustered around the acyl binding pocket and two below the active site serine. A prominent difference in rat was the substitution of arginine for leucine at position 286 in the acyl pocket. Wild-type rat BChE, the mutant R286L, wild-type human BChE, and the mutant L286R were expressed in CHO cells and purified. Arg286 was found responsible for the resistance of rat BChE to inhibition by Triton X-100. Replacement of Arg286 with leucine caused the affinity for Triton X-100 to increase 20-fold, making it as sensitive as human BChE to inhibition by Triton X-100. Wild-type rat BChE had an 8- to 9-fold higher K(m) for the positively charged substrates butyrylthiocholine, acetylthiocholine, propionylthiocholine, benzoylcholine, and cocaine compared with wild-type human BChE. Wild-type rat BChE catalyzed turnover 2- to 7-fold more rapidly than human BChE, showing the highest turnover with propionylthiocholine (201,000 min(-1)). Human BChE does not reactivate spontaneously after inhibition by echothiophate, but rat BChE reactivates with a half-life of 4.3hr. Human serum contains 5mg/L of BChE and 0.01mg/L of AChE. Male rat serum contains 0.2mg/L of BChE and approximately 0.2mg/L of AChE.     

艾司西酞普兰与氟西汀治疗抑郁症对照研究

目的比较艾司西酞普兰与氟西汀治疗抑郁症的疗效和安全性。方法随机将77例符合CCMD-3抑郁发作的住院患者分为艾司西酞普兰组和氟西汀组,艾司西酞普兰组剂量10～20mg／d,氟西汀组20～40mg／d,疗程6周。疗效采取汉密尔顿抑郁量表（HAMD）和汉密尔顿焦虑量表（HAMA）评定,不良反应和安全性用TESS和实验室检查评定。结果两组总体疗效相当,艾司西酞普兰组有效率为87．2％,治愈率为48．7％,氟西汀组有效率为86．8％,治愈率4为7．4％,两组疗效比较差异无显著性。但1周末时HAMD评分及减分率两组间差异有显著性,说明艾司西酞普兰起效快;艾司西酞普兰组不良反应发生率明显少于氟西汀组,差异有统计学意义。结论艾司西酞普兰是安全、有效的抗抑郁药。     

Quinoline-based promising anticancer and antibacterial agents,and some metabolic enzyme inhibitors

A series of substituted quinolines was screened for their antiproliferative, cytotoxic, antibacterial activities, DNA/protein binding affinity, and anticholinergic properties by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell proliferation, lactate dehydrogenase cytotoxicity, and microdilution assays, the Wolfe–Shimmer equality method, the Ellman method, and the esterase assay, respectively. The results of the cytotoxic and anticancer activities of the compounds displayed that 6-bromotetrahydroquinoline ( 2 ), 6,8-dibromotetrahydroquinoline ( 3 ), 8-bromo-6-cyanoquinoline ( 10 ), 5-bromo-6,8-dimethoxyquinoline ( 12 ), the novel N-nitrated 6,8-dimethoxyquinoline ( 13 ), and 5,7-dibromo-8-hydroxyquinoline ( 17 ) showed a significant antiproliferative potency against the A549, HeLa, HT29, Hep3B, and MCF7 cancer cell lines (IC₅₀ = 2–50 μg/ml) and low cytotoxicity (∼7–35%) as the controls, 5-fluorouracil and cisplatin. The compound–DNA linkages are hyperchromic or hypochromic, causing variations in their spectra. This situation shows that they can be bound to DNA with the groove-binding mode, with K_b value in the range of 2.0 × 10³–2.2 × 10⁵ M^–1. Studies on human Gram(+) and Gram(−) pathogenic bacteria showed that the substituted quinolines exhibited selective antimicrobial activities with MIC values of 62.50–250 μg/ml. All tested quinoline derivatives were found to be effective inhibitors of acetylcholinesterase (AChE) and the human carbonic anhydrase I and II isoforms (hCA I and II), with K_i values of 46.04–956.82 nM for hCA I, 54.95–976.93 nM for hCA II, and 5.51–155.22 nM for AChE. As a result, the preliminary data showed that substituted quinolines displayed effective pharmacological features. Molecular docking studies were performed to investigate the binding modes and interaction energies for compounds 2–17 with AChE (PDB ID: 4EY6), hCA I (PDB ID: 1BMZ), and hCA II (PDB ID: 2ABE).     

Chronic coadministration of olanzapine and fluoxetine activates locus coeruleus neurons in rats: implications for bipolar disorder

Rationale The depressive phase of bipolar disorder (bipolar depression) is a difficult-to-treat form of depression. The olanzapine/fluoxetine combination (Symbyax) is the only medication approved to treat this disorder. The precise neural mechanisms responsible for its efficacy are not clearly understood. Objectives In order to further elucidate the neurobiological mechanisms responsible for the beneficial clinical effects of the olanzapine/fluoxetine combination, the current experiment was designed to investigate the effects of chronic coadministration of olanzapine and fluoxetine on electrophysiological activity in the locus coeruleus (LC). Methods Rats received olanzapine for 3 weeks via subcutaneous osmotic pumps while simultaneously receiving daily intraperitoneal injections of fluoxetine. These chronically treated rats were anesthetized, and single-unit recordings of LC neurons were made. Results Chronic administration of olanzapine alone significantly increased firing of LC neurons, while, as reported previously, chronic administration of fluoxetine alone significantly reduced firing of LC neurons. However, in the combination condition, olanzapine was able to block the fluoxetine-induced suppression of the LC, and a significant increase in LC activity was observed. Conclusions The observed increase in firing of LC neurons could lead to enhanced levels of norepinephrine release in projection areas and amelioration of the clinical symptoms of bipolar depression.