Activation of trace amine-associated receptor 1 attenuates nicotine withdrawal-related effects.

Nicotine addiction is a leading avoidable brain disorder globally. Although nicotine induces a modest reinforcing effect, which is important for the initial drug use, the transition from nicotine use to nicotine addiction involves the mechanisms responsible for the negative consequences of drug abstinence. Recent study suggested that trace amine-associated receptor 1 (TAAR1) is a promising pharmacological target for the modulation of positive reinforcing effects of nicotine. However, whether TAAR1 plays a part in the negative reinforcement of nicotine withdrawal remains to be determined. Here, using a long-access (LA) self-administration model, we investigated whether LA rats show increased nicotine intake and withdrawal symptoms in comparison with saline and ShA rats and then tested the effect of TAAR1 partial agonist RO5263397 on nicotine withdrawal effects. We found that rats from long-access group showed significant abstinence-induced anxiety-like behaviour, mechanic hypersensitivity, increased number of precipitated withdrawal signs and higher motivation for the drug, while rats from short-access did not differ from saline group. TAAR1 partial agonist RO5263397 significantly reduced the physical and motivational withdrawal effects of nicotine in LA rats, as reflected by increased time spent on the open arm in the elevated plus maze (EPM) test, normalized paw withdrawal threshold, decreased withdrawal signs and motivation to self-administer nicotine. This study indicates that activation of TAAR1 attenuates the negative-reinforcing effects of nicotine withdrawal and further suggests TAAR1 as a promising target to treat nicotine addiction.

The Effect of TCM-Induced HAMP on Key Enzymes in the Hydrolysis of AD Model Cells.

Alzheimer's disease (AD) process is characterized classically by two hallmark pathologies: ß-amyloid (Aß) plaque deposition and neurofibrillary tangles of hyperphosphorylated tau. Aß peptides play an important role in AD, but despite much effort the molecular mechanisms of how Aß contributes to AD remain unclear. The present study evaluated the effects of the active components of Epimedium, Astragalus and Radix Puerariae induced HAMP on key enzymes in the hydrolysis of APP in HT22 cells. The active components of Epimedium, Astragalus and Radix Puerariae could effectively up-regulate the expression of HAMP, alleviate the iron overload in the brain tissues of mice, significantly improve the learning and memory ability of AD, down-regulate the expression of Aß and reduce the deposition of SP in an APPswe/PS1ΔE9 transgenic mouse model of AD. HAMP and Aß25-35 induced HT22 cells are used as AD cell models in this study to investigate the effect of the compound consisting of the effective components of Epimedium, Astragalus and Pueraria on the key enzymes in the hydrolysis of APP. After the administration of traditional Chinese medicine (TCM), the expression levels of ADAM10 and ADAM17 were increased while the expression level of BACE1 decreased. This indicates that TCM can promote the expression level of ADAM10 and ADAM17, inhibit the expression level of BACE1, thus further inhibiting the production of amyloid protein and reducing the production of Aß and SP. Compared with RNAi group, the expression level of ADAM10 and ADAM17 in Aß + RNAi group was decreased while the expression level of BACE1 increased. Compared with the Aß + RNAi group the expression level of ADAM10 and ADAM17 in the Aß + RNAi + TCM group was increased while the expression level of BACE1 was decreased. The present study indicated the effects of the active components of Epimedium, Astragalus and Radix Puerariae may alleviate AD by up-regulating the expression of HAMP, thus reducing brain iron overload, promoting the expression of ADAM10 and ADAM17, inhibiting the expression of BACE1, and reducing the deposition of Aß.

Synthesis and Pharmacological Evaluation of 1-Phenyl-3-Thiophenylurea Derivatives as Cannabinoid Type-1 Receptor Allosteric Modulators.

We previously reported diarylurea derivatives as cannabinoid type-1 receptor (CB1) allosteric modulators, which were effective in attenuating cocaine-seeking behavior. Herein, we extended the structure-activity relationships of PSNCBAM-1 (2) at the central phenyl ring directly connected to the urea moiety. Replacement with a thiophene ring led to 11 with improved or comparable potencies in calcium mobilization, [35S]GTPγS binding, and cAMP assays, whereas substitution with nonaromatic rings led to significant attenuation of the modulatory activity. These compounds had no inverse agonism in [35S]GTPγS binding, a characteristic that is often thought to contribute to adverse psychiatric effects. While 11 had good metabolic stability in rat liver microsomes, it showed modest solubility and blood-brain barrier permeability. Compound 11 showed an insignificant attenuation of cocaine seeking behavior in rats, most likely due to its limited CNS penetration, suggesting that pharmacokinetics and distribution play a role in translating the in vitro efficacy to in vivo behavior.

Effects of imidazoline I2 receptor agonists on reserpine-induced hyperalgesia and depressive-like behavior in rats.

Pharmacotherapies for fibromyalgia treatment are lacking. This study examined the antinociceptive and antidepressant-like effects of imidazoline I2 receptor (I2R) agonists in a reserpine-induced model of fibromyalgia in rats. Rats were treated for 3 days with vehicle or reserpine. The von Frey filament test was used to assess the antinociceptive effects of I2 receptor agonists, and the forced swim test was used to assess the antidepressant-like effects of these drugs. 2-BFI (3.2-10 mg/kg, intraperitoneally), phenyzoline (17.8-56 mg/kg, intraperitoneally), and CR4056 (3.2-10 mg/kg, intraperitoneally) all dose-dependently produced significant antinociceptive effects, which were attenuated by the I2R antagonist idazoxan. Only CR4056 significantly reduced the immobility time in the forced swim test in both vehicle-treated and reserpine-treated rats. These data suggest that I2R agonists may be useful to treat fibromyalgia-related pain and comorbid depression.

Hippocampal Salt-Inducible Kinase 2 Plays a Role in Depression via the CREB-Regulated Transcription Coactivator 1-cAMP Response Element Binding-Brain-Derived Neurotrophic Factor Pathway.

BACKGROUND: Developing novel pharmacological targets beyond monoaminergic systems is now a popular strategy for finding new ways to treat depression. Salt-inducible kinase (SIK) is a kinase that regulates the nuclear translocation of cyclic adenosine monophosphate response element binding protein (CREB)-regulated transcription coactivator (CRTC) by phosphorylation. Here, we hypothesize that dysfunction of the central SIK-CRTC system may contribute to the pathogenesis of depression. METHODS: Chronic social defeat stress (CSDS) and chronic unpredictable mild stress (CUMS) models of depression, various behavioral tests, viral-mediated gene transfer, Western blotting, coimmunoprecipitation, quantitative real-time reverse transcription polymerase chain reaction, and immunohistochemistry were used in this study (for in vivo studies, n = 10; for in vitro studies, n = 5). RESULTS: Both CSDS and CUMS markedly increased the expression of hippocampal SIK2, which reduced CRTC1 nuclear translocation and binding of CRTC1 and CREB in the hippocampus. Genetic overexpression of hippocampal SIK2 in naïve mice simulated chronic stress, inducing depressive-like behaviors in the forced swim test, tail suspension test, sucrose preference test, and social interaction test, as well as decreasing the brain-derived neurotrophic factor signaling cascade and neurogenesis in the hippocampus. In contrast, genetic knockdown and knockout of hippocampal SIK2 protected against CSDS and CUMS, exerting significant antidepressant-like effects that were mediated via the downstream CRTC1-CREB-brain-derived neurotrophic factor pathway. Moreover, fluoxetine, venlafaxine, and mirtazapine all significantly restored the effects of CSDS and CUMS on the hippocampal SIK2-CRTC1 pathway, which was necessary for their antidepressant actions. CONCLUSIONS: The hippocampal SIK2-CRTC1 pathway is involved in the pathogenesis of depression, and hippocampal SIK2 could be a novel target for the development of antidepressants.

Role of trace amine-associated receptor 1 in nicotine's behavioral and neurochemical effects.

Nicotine addiction and abuse remains a global health issue. To date, the fundamental neurobiological mechanism of nicotine addiction remains incompletely understood. Trace amine-associated receptor 1 (TAAR1) is thought to directly modulate dopaminergic system and are thought to be a neural substrate underlying addictive-like behaviors. We aimed to investigate the role of TAAR1 in nicotine addictive-like behaviors. TAAR1 expression after nicotine treatment was evaluated by western blotting. c-Fos immunofluorescence and in vivo fast-scan cyclic voltammetry were used to examine the activation of brain regions and dopamine release, respectively. We then thoroughly and systematically examined the role of TAAR1 in mediating nicotine-induced sensitization, nicotine discrimination, nicotine self-administration, nicotine demand curve, and the reinstatement of nicotine-seeking. Local pharmacological manipulation was conducted to determine the role of TAAR1 in the nucleus accumbens (NAcs) in the reinstatement of nicotine-seeking. We found that the expression of TAAR1 protein was selectively downregulated in the NAc, with no change in either dorsal striatum or prefrontal cortex. TAAR1 activation was sufficient to block nicotine-induced c-Fos expression in the NAc, while also reducing nicotine-induced dopamine release in the NAc. Systemic administration of TAAR1 agonists attenuated the expression and development of nicotine-induced sensitization, nicotine self-administration, the reinstatement of nicotine-seeking, and increased the elasticity of nicotine demand curve, while intra-NAc infusions of a TAAR1 agonist was sufficient to attenuate nicotine reinstatement. Moreover, TAAR1-knockout rats showed augmented cue-induced and drug-induced reinstatement of nicotine-seeking. These results indicated that modulation of TAAR1 activity regulates nicotine addictive-like behaviors and TAAR1 represents a novel target towards the treatment of nicotine addiction.

Ventral tegmental area D2 receptor knockdown enhances choice impulsivity in a delay-discounting task in rats.

Impulsivity associated with abnormal dopamine (DA) function has been observed in several disorders, including addiction. Choice impulsivity is the preference for small, immediate rewards over larger rewards after a delay, caused by excessive discounting of future rewards. Addicts have abnormally high discount rates and prefer the smaller rewards sooner. While impulsivity has been inversely correlated with DA D2 receptor (D2R) availability in the midbrain and striatum, it is difficult to mechanistically link the two, due to the diverse neuroanatomical localization of D2Rs, which are found throughout the brain, in many types of neurons and neuronal subcompartments. To determine if ventral tegmental area (VTA) D2R hypofunction is linked to impulsivity, we knocked down D2 receptors from the VTA, using an adeno-associated viral (AAV) vector that delivers short hairpin RNAs (shRNA) targeted against the D2R. The D2R knockdown is restricted to neurons whose cell bodies reside in the VTA, leaving postsynaptic D2Rs intact in the striatum, prefrontal cortex, and other mesocorticolimbic structures. Rats were trained in a delay-discounting task to assess impulsive choice until a stable discounting curve was obtained, and then received bilateral VTA infusions of the D2R shRNA or a scrambled control virus. Over the next six weeks, the discounting curve of the VTA D2R knockdown rats shifted to the left, indicating a preference for the smaller, immediate reward, whereas the curve for control rats remained stable and unchanged. Together these results demonstrate that a decrease in VTA D2Rs enhances choice impulsivity.

A review on the pharmacological effects of vitexin and isovitexin.

Vitexin and isovitexin are active components of many traditional Chinese medicines, and were found in various medicinal plants. Vitexin (apigenin-8-C-glucoside) has recently received increased attention due to its wide range of pharmacological effects, including but not limited to anti-oxidant, anti-cancer, anti-inflammatory, anti-hyperalgesic, and neuroprotective effects. Isovitexin (apigenin-6-C-glucoside), an isomer of vitexin, generally purified together with vitexin, also exhibits diverse biological activities. Latest research has suggested that vitexin and isovitexin could be potential substitute medicines for diversity diseases, and may be adjuvants for stubborn diseases or health products. This review summarized recent findings on various pharmacological activities and associative signalling pathways of vitexin and isovitexin to provide a reference for future research and clinical applications.

BRG1 in the Nucleus Accumbens Regulates Cocaine-Seeking Behavior.

BACKGROUND: Drug addiction is defined as a chronic disease characterized by compulsive drug seeking and episodes of relapse despite prolonged periods of drug abstinence. Neurobiological adaptations, including transcriptional and epigenetic alterations in the nucleus accumbens, are thought to contribute to this life-long disease state. We previously demonstrated that the transcription factor SMAD3 is increased after 7 days of withdrawal from cocaine self-administration. However, it is still unknown which additional factors participate in the process of chromatin remodeling and facilitate the binding of SMAD3 to promoter regions of target genes. Here, we examined the possible interaction of BRG1-also known as SMARCA4, an adenosine triphosphatase-containing chromatin remodeler-and SMAD3 in response to cocaine exposure. METHODS: The expression of BRG1, as well as its binding to SMAD3 and target gene promoter regions, was evaluated in the nucleus accumbens and dorsal striatum of rats using western blotting, co-immunoprecipitation, and chromatin immunoprecipitation following abstinence from cocaine self-administration. Rats were assessed for cocaine-seeking behaviors after either intra-accumbal injections of the BRG1 inhibitor PFI3 or viral-mediated overexpression of BRG1. RESULTS: After withdrawal from cocaine self-administration, BRG1 expression and complex formation with SMAD3 are increased in the nucleus accumbens, resulting in increased binding of BRG1 to the promoter regions of Ctnnb1, Mef2d, and Dbn1. Intra-accumbal infusion of PFI3 attenuated, whereas viral overexpression of Brg1 enhanced, cocaine-reinstatement behavior. CONCLUSIONS: BRG1 is a key mediator of the SMAD3-dependent regulation of cellular and behavioral plasticity that mediates cocaine seeking after a period of withdrawal.

Antinociceptive effects of sinomenine in a rat model of postoperative pain.

BACKGROUND AND PURPOSE: This study examined the antinociceptive effects of sinomenine in a rat model of postoperative pain. EXPERIMENTAL APPROACH: Male and female rats were subjected to a surgical incision in the right hind paw, and the von Frey filament test was used to measure mechanical hypersensitivity after drug or vehicle treatment (p.o. or i.p.). Rats were treated daily with sinomenine before or after the surgery and the AUCs of the antinociceptive effects measured during a 4 h period were calculated to determine the ED50 values of sinomenine. The anti-hyperalgesic effects of different doses of a combination of sinomenine and acetaminophen (paracetamol) were assessed in another group of rats. Dose combinations were determined by using a fixed ratio dose-addition analysis method. KEY RESULTS: Sinomenine (5-80 mg·kg(-1) ) produced dose-dependent antinociceptive effects in rats that had been subjected to surgery and this effect lasted for 4 h. The potency of sinomenine, given i.p. or p.o., did not differ between male and female rats. However, sinomenine was fourfold more potent when given i.p. than p.o. The GABAA receptor antagonist bicuculline blocked the antinociceptive effects of sinomenine. The antinociceptive effect of a daily treatment with sinomenine remained stable throughout the course of postoperative pain. Pretreatment with sinomenine did not alter the mechanical hypersensitivity post-surgery. The combination of sinomenine with acetaminophen produced an infra-additive interaction. CONCLUSIONS AND IMPLICATIONS: Sinomenine demonstrated significant antinociceptive activity against postoperative pain and may be a useful novel pharmacotherapy for the management of postoperative pain.

Antinociceptive effects of vitexin in a mouse model of postoperative pain.

Vitexin, a C-glycosylated flavone present in several medicinal herbs, has showed various pharmacological activities including antinociception. The present study investigated the antinociceptive effects of vitexin in a mouse model of postoperative pain. This model was prepared by making a surgical incision on the right hindpaw and von Frey filament test was used to assess mechanical hyperalgesia. Isobolographical analysis method was used to examine the interaction between vitexin and acetaminophen. A reliable mechanical hyperalgesia was observed at 2 h post-surgery and lasted for 4 days. Acute vitexin administration (3-10 mg/kg, i.p.) dose-dependently relieved this hyperalgesia, which was also observed from 1 to 3 days post-surgery during repeated daily treatment. However, repeated vitexin administration prior to surgery had no preventive value. The 10 mg/kg vitexin-induced antinociception was blocked by the opioid receptor antagonist naltrexone or the GABAA receptor antagonist bicuculline. The doses of vitexin used did not significantly suppress the locomotor activity. In addition, the combination of vitexin and acetaminophen produced an infra-additive effect in postoperative pain. Together, though vitexin-acetaminophen combination may not be useful for treating postoperative pain, vitexin exerts behaviorally-specific antinociception against postoperative pain mediated through opioid receptors and GABAA receptors, suggesting that vitexin may be useful for the control of postoperative pain.

Antinociceptive effects of curcumin in a rat model of postoperative pain.

Curcumin is a principal ingredient of traditional Chinese medicine, Curcuma Longa, which possesses a variety of pharmacological activities including pain relief. Preclinical studies have demonstrated that curcumin has antinociceptive effects for inflammatory and neuropathic pain. This study examined the effects of curcumin in a rat model of postoperative pain. A surgical incision on the right hind paw induced a sustained mechanical hyperalgesia that lasted for 5 days. Acute curcumin treatment (10-40 mg/kg, p.o) significantly and dose dependently reversed mechanical hyperalgesia. In addition, repeated curcumin treatment significantly facilitated the recovery from surgery. In contrast, repeated treatment with curcumin before surgery did not impact the postoperative pain threshold and recovery rate. All the doses of curcumin did not significantly alter the spontaneous locomotor activity. Combined, these results suggested that curcumin could alleviate postoperative pain and promote recovery from the surgery, although there was no significant preventive value. This study extends previous findings and supports the application of curcumin alone or as an adjunct therapy for the management of peri-operative pain.

Antihyperalgesic effects of imidazoline I(2) receptor ligands in rat models of inflammatory and neuropathic pain.

BACKGROUND AND PURPOSE: A new imidazoline I2 receptor ligand, CR4056, is effective for chronic inflammatory pain and diabetic neuropathy. However, it is unclear whether other I2 receptor ligands have similar effects and whether antinociceptive tolerance develops with repeated treatment. EXPERIMENTAL APPROACH: The Von Frey filament test was used to measure mechanical hyperalgesia and the plantar test to measure thermal hyperalgesia in rats injected with complete Freund's adjuvant (CFA) treatment or had undergone surgery to induce chronic constriction injury (CCI), models of inflammatory pain and peripheral neuropathic pain respectively. The effects of morphine and I2 receptor ligands, 2-BFI, BU224, tracizoline and CR4056, 3.2-32 mg·kg(-1) , i.p., on hyperalgesia or affective pain (as measured by a place escape/avoidance paradigm) were studied in separate experiments. KEY RESULTS: Morphine and the I2 receptor ligands (2-BFI, BU224 and tracizoline) all dose-dependently attenuated mechanical and thermal hyperalgesia in CFA-treated rats. The anti-hyperalgesic effects of 2-BFI in CFA-treated and CCI rats were attenuated by the I2 receptor antagonist idazoxan. The combination of 2-BFI and morphine produced additive effects against mechanical hyperalgesia in CFA-treated rats. Repeated treatment (daily for 7-9 days) with 2-BFI or CR4056 did not produce antinociceptive tolerance in CFA-treated or CCI rats. Morphine and the I2 receptor ligands (2-BFI, BU224 and CR4056) were all effective at attenuating place escape/avoidance behaviour in CFA-treated rats. CONCLUSIONS AND IMPLICATIONS: Imidazoline I2 receptor ligands have antihyperalgesic effects in rat models of inflammatory and neuropathic pain and may represent a new class of pharmacotherapeutics for the management of chronic pain.

Septal nuclei critically mediate the development of behavioral sensitization to a single morphine injection in rats.

Behavioral sensitization to a single morphine injection is a unique model to study the neuroanatomical substrates of long-lasting behavioral plasticity associated with opioid reward and abuse. Earlier observations have demonstrated that septal nuclei are critically involved in the processes of reward, learning and memory. In the present study, we investigated the effects of septal nuclei lesions on behavioral sensitization to a single morphine injection, morphine induced conditioned place preference and antinociception in rats. Behavioral sensitization was established by a single injection of 3-30 mg/kg morphine in rats. Bilateral electrical lesions of septal nuclei were carried out 7 days before morphine pretreatment. Acute morphine injection induced hyperactivity in the non-surgery control, sham surgery and septal nuclei-lesioned rats. Seven days later, the challenge injection with 3mg/kg morphine induced significant behavioral sensitization in rats with no surgery and sham surgery, but failed to induce behavioral sensitization in septal nuclei-lesioned rats. When the septal nuclei ablation was carried out after acute morphine pretreatment, the expression of behavioral sensitization was unaffected and not different among rats. In addition, septal nuclei lesions did not impact the rewarding and antinociceptive effects of 10 mg/kg morphine when the rats were tested in a conditioned place preference test and tail-flick test, respectively. Collectively, these results suggest that septal nuclei may be selectively involved in the initiation of behavioral sensitization to morphine, which is separable from the effects of morphine for exerting its rewarding and antinociceptive effects.

Interactions between morphine, scopolamine and nicotine: schedule-controlled responding in rats.

Functional interactions between drugs acting on either opioid or cholinergic systems have been demonstrated for both neurochemical and behavioral measures. This study used schedule-controlled responding and isobolographic analyses to examine interactions between the micro opioid receptor agonist morphine and the muscarinic acetylcholine receptor antagonist scopolamine as well as the nicotinic acetylcholine receptor agonist nicotine. In 8 rats responding under a fixed ratio 5 schedule of food presentation, morphine (3.2-10mg/kg), scopolamine (0.032-1.0mg/kg), and nicotine (0.1-1mg/kg) each dose-dependently decreased responding. Acute injection of scopolamine shifted the morphine dose-response curved leftward and downward and acute injection of morphine shifted the scopolamine and nicotine dose-response curves leftward and downward. The interaction between morphine and nicotine was additive; however, the interaction between morphine and scopolamine was infra-additive or supra-additive, depending on whether scopolamine or morphine was administered first. These results provide quantitative evidence regarding potentially important interactions between drugs acting on either opioid or cholinergic systems, although these interactions are modest and appear to depend on the specific conditions of drug administration.

Pharmacological properties and discriminative stimulus effects of a novel and selective 5-HT2 receptor agonist AL-38022A [(S)-2-(8,9-dihydro-7H-pyrano[2,3-g]indazol-1-yl)-1-methylethylamine].

AL-38022A is a novel synthetic serotonergic (5-HT) ligand that exhibited high affinity for each of the 5-HT2 receptor subtypes (Ki100-fold less) affinity for other 5-HT receptors. In addition, AL-38022A displayed a very low affinity for a broad array of other receptors, neurotransmitter transport sites, ion channels, and second messenger elements, making it a relatively selective agent. AL-38022A potently stimulated functional responses via native and cloned rat (EC50 range: 1.9-22.5 nM) and human (EC50 range: 0.5-2.2 nM) 5-HT2 receptor subtypes including [Ca2+]i mobilization and tissue contractions with apparently similar potencies and intrinsic activities and was a full agonist at all 5-HT2 receptor subtypes. The CNS activity of AL-38022A was assessed by evaluating its discriminative stimulus effects in both a rat and a monkey drug discrimination paradigm using DOM as the training drug. AL-38022A fully generalized to the DOM stimulus in each of these studies; in monkeys MDL 100907 antagonized both DOM and AL-38022A. The pharmacological profile of AL-38022A suggests that it could be a useful tool in defining 5-HT2 receptor signaling and receptor characterization where 5-HT may function as a neurotransmitter.