Eun Young Jang

Isoliquiritigenin suppresses cocaine-induced extracellular dopamine release in rat brain through GABAB receptor

Glycyrrhizae radix (licorice) comprises a variety of flavonoids as major constituents including isoliquiritigenin, liquiritin, liquiritigenin, and glycyrrihizin. It has shown various biological activities such as anti-inflammatory, anti-carcinogenic and antihistamic. As very little is known in regard to drug addiction, we carried out a study on the effect of G. radix and its active component, isoliquiritigenin, on acute cocaine-induced extracellular dopamine release in moving rats. Male Sprague-Dawley rats were orally administered with methanolic extracts of G. radix or isoliquiritigenin 1 h prior to an injection of cocaine (20 mg/kg, intraperitoneal (i.p.)). Extracellular dopamine was measured by in vivo microdialysis. Extract of G. radix and isoliquiritigenin inhibited cocaine-induced extracellular dopamine level in the nucleus accumbens by dose-dependent manner. Inhibition of dopamine release by isoliquiritigenin resulted in attenuation of the expression of c-Fos, an immediately early gene induced by cocaine. Effect of isoliquiritigenin was completely prevented by a GABA(B) receptor antagonist. Thus, these results showed that G. radix and isoliquiritigenin inhibit cocaine-induced dopamine release by modulating GABA(B) receptor, suggesting that isoliquiritigenin might be effective in blocking the reinforcing effects of cocaine.

Involvement of reactive oxygen species in cocaine-taking behaviors in rats

Reactive oxygen species (ROS) have been implicated in the development of behavioral sensitization following repeated cocaine exposure. We hypothesized that increased ROS following cocaine exposure would act as signaling molecules in the mesolimbic dopamine (DA) system, which might play an important role in mediating the reinforcing effects of cocaine. The aim of this study was to evaluate cocaine enhancement of brain metabolic activity and the effects of ROS scavengers on cocaine self‐administration behavior, cocaine‐induced ROS production in the nucleus accumbens (NAc) and cocaine enhancement of DA release in the NAc. Metabolic neural activity monitored by temperature and oxidative stress were increased in NAc following cocaine exposure. Systemic administration of the ROS scavenger N‐tert‐butyl‐α‐phenylnitrone (PBN) or 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPOL), either pre‐ or post‐treatment, significantly decreased cocaine self‐administration without affecting food intake. Infusion of TEMPOL into the NAc inhibited cocaine self‐administration. Increased oxidative stress was found mainly on neurons, but not astrocytes, microglia or oligodendrocytes, in NAc of rats self‐administering cocaine. TEMPOL significantly attenuated cocaine‐induced enhancement of DA release in the NAc, compared to saline controls. TEMPOL had no effect on the enhancement of DA release produced by the DA transporter inhibitor GBR12909. Taken together, these findings suggest that enhancement of ROS production in NAc neurons contributes to the reinforcing effect of cocaine.

Effect of acupuncture on naloxone-precipitated withdrawal syndrome in morphine-experienced rats: The mediation of GABA receptors

Repeated morphine administration increases extracellular dopamine levels in the nucleus accumbens, which results in behavioral sensitization that can be suppressed by acupuncture at Shenmen (HT7) points. The present study was conducted to investigate the effects of acupuncture at HT7 on morphine withdrawal syndrome as well as to explore the role of GABA receptors in mediating the effects of HT7 acupuncture. We induced morphine withdrawal by injecting naloxone to rats that self-administer morphine and evaluated the effects of acupuncture and/or GABA receptor antagonists on their withdrawal symptoms. Acupuncture at HT7, but not at the control point LI5, significantly decreased symptoms of morphine withdrawal. HT7 inhibition of the withdrawal syndrome was blocked by pretreatment with either the GABA(A) receptor antagonist bicuculline or the GABA(B) antagonist SCH 50911. These findings suggest that the effects of acupuncture on suppression of morphine withdrawal syndrome are mediated, at least in part, through GABA receptors.

Acupuncture at SI5 attenuates morphine seeking behavior after extinction.

Our previous studies have shown that acupuncture attenuates morphine self-administration and sensitization behavior as well as withdrawal signs. The present study was designed to investigate the role of acupuncture in the reinstatement of morphine seeking. Male Sprague-Dawley rats weighing 270-300 g were subjected to intravenous catheterization after food training. The animals were trained to self-administer morphine (1.0mg/kg, 3 weeks), followed by extinction (1 week). Extinction conditions were introduced by substituting saline for morphine. The rats were then tested for reinstatement of morphine self-administration by a priming injection of morphine (0.25mg/kg). To see whether acupuncture can reduce morphine reinstatement, acupuncture was performed at SI5 or LI5 for 1 min immediately before a morphine injection. To further test the involvement of gamma aminobutyric acid (GABA) receptors in acupuncture effects, GABA receptor antagonists were injected before acupuncture. In the present results, acupuncture at SI5, but not at control acupoint LI5 attenuated the reinstatement of morphine seeking behavior, which was blocked by the GABA receptor antagonists. It suggests that acupuncture can reduce the reinstatement of morphine seeking, possibly due to the mediation of GABA receptor system.

Potential roles of GABA receptors in morphine self-administration in rats

It is well established that the reinforcing effect of drugs of abuse is linked to the mesolimbic dopamine (DA) system. Morphine produces an increase in DA release in the brain, which may provide positive reinforcement contributing to the development of motivational aspects of drug-seeking and maintenance behavior. Several studies suggest that the GABA receptor system may play a significant role in the modulating the mesolimbic DA system. The purpose of this study was to investigate potential roles for GABA agonists in morphine self-administration behavior. Male Sprague-Dawley rats were trained to self-administrated morphine (0.1 mg/kg per injection) during daily 1-h sessions under a fixed ratio 1 schedule. Rats received an intravenous injection of the selective GABA(B) antagonist SCH 50911 (2.0 mg/kg) or an intraperitoneal injection of the GABA(A) antagonist bicuculline (1.0 mg/kg), immediately followed by either an intraperitoneal injection of baclofen (1.25 or 1.8 mg/kg) or muscimol (0.5 or 1.0 mg/kg, i.p.), 30 min prior to the start of test session. Results showed that pretreatment with baclofen or muscimol reduced morphine-maintenance response in a dose-dependent fashion and that baclofen and muscimol effects were reversed by injections of SCH 50911 and bicuculline, respectively. These data suggest that activation of both GABA(A) and GABA(B) receptors may be effective in suppressing the reinforcing effects of morphine.

Proteomic and behavioral analysis of response to isoliquiritigenin in brains of acute cocaine treated rats.

Isoliquiritigenin (ISL) is a licorice flavonoid with chalcone structure and is an active component of the root of the plant genus Glycyrrhiza. In addition to anti-inflammatory and antioxidant effects, ISL was previously reported to antagonize increased striatal dopamine release. In the present study, we aimed to investigate whether ISL has an effect on hyperlocomotion in animals subjected to acute cocaine administration and whether ISL modulates acute cocaine-induced molecular changes. To achieve our goals, we analyzed behavior and differential proteomic changes between ISL and vehicle in acute cocaine treated rats. Locomoter activity was reduced in ISL treated animals compared to vehicle in acute cocaine treated rats. Two dimensional electrophoresis (2-DE) revealed that 56 proteins were differentially expressed in response to ISL. Further proteomic analyses using mass spectroscopy, and subsequent validation experiments confirmed that ISL induced changes in proteins related to metabolism, signal transduction, protein folding and transport, oxidative stress, and neural toxicity. Furthermore, cocaine-induced neuronal toxicity was attenuated by ISL treatment, suggesting a neuroprotective role of ISL.

Acute Ethanol Inhibits Dopamine Release in the Nucleus Accumbens via α6 Nicotinic Acetylcholine Receptors

Electrophysiology and microdialysis studies have provided compelling evidence that moderate to high ethanol concentrations enhance dopamine (DA) neurotransmission in the nucleus accumbens (NAc) through the mesolimbic DA system. However, with fast-scan cyclic voltammetry, short-term exposure to moderate to high doses of ethanol decreases evoked DA release at terminals in the NAc. The aim of this study was to evaluate the involvement of nicotinic acetylcholine receptors (nAChRs) in modulating the effects of ethanol on DA release in the NAc of C57BL/6 mice ex vivo and in vivo. Local stimulation evoked robust, frequency-dependent DA release in the NAc slice preparation, with maximal release at 40 Hz in the shell and 20 Hz in the core. Nicotine decreased DA release in a concentration-dependent (0.01–10 μM) manner in the shell and core, with an IC50 of 0.1 μM ex vivo and 0.5 mg/kg in vivo. Nicotine and ethanol inhibition of DA release was blocked by the α6*-nAChR antagonist α-conotoxins CtxMII and α-CtxMII [H9A; L15A] ex vivo (100 nM) in the core but not the shell. Furthermore, the nonspecific nAChR antagonist mecamylamine (2 mg/kg) blocked the effects of ethanol in the core in vivo. These findings suggest that DA release is inhibited by ethanol via nAChRs in the NAc and that DA modulation by nAChRs differs in the core versus the shell, with α6*-nAChRs affecting DA release in the core but not in the shell.

Sauchinone suppresses lipopolysaccharide-induced inflammatory responses through Akt signaling in BV2 cells.

Activated microglial cells play an important role in inflammatory responses in the central nervous system (CNS) that are involved in neurodegenerative diseases. Sauchinone has been shown to modulate the expression of inflammatory factors through nuclear factor-kappa B (NF-κB) signaling pathway. Here, we examined the effect of sauchinone on the inflammatory responses of microglia cells induced by lipopolysaccharide (LPS) and explored the mechanism underlying action of sauchinone. BV2 cells treated with LPS showed an up-regulation of nitric oxide (NO) and prostaglandin (PGE(2)) release, whereas sauchinone suppressed this up-regulation. Sauchinone inhibited both mRNA and protein expression of COX-2, iNOS, TNF-α and IL-1β. In addition, sauchinone blocked the activation of NF-κB through its inhibition of I-κB phosphorylation. Interestingly, sauchinone had no effect on the LPS-induced phosphorylation of mitogen activated protein kinases (MAP kinases; ERK1/2, p38, JNK), but it did inhibit Akt phosphorylation. These results suggest that the inhibitory effect of sauchinone on the LPS-induced production of inflammatory mediator in BV2 cells is associated with the suppression of the NF-κB and Akt signaling pathways. Therefore, sauchinone may be a useful treatment for neurodegenerative disease by inhibiting inflammatory responses in activated microglia.

The role of reactive oxygen species in methamphetamine self-administration and dopamine release in the nucleus accumbens

Methamphetamine (METH) markedly increases dopamine (DA) release in the mesolimbic DA system, which plays an important role in mediating the reinforcing effects of METH. METH‐induced DA release results in the formation of reactive oxygen species (ROS), leading to oxidative damage. We have recently reported that ROS are implicated in behavior changes and DA release in the nucleus accumbens (NAc) following cocaine administration. The aim of this study was to evaluate the involvement of ROS in METH‐induced locomotor activity, self‐administration and enhancement of DA release in the NAc. Systemic administration of a non‐specific ROS scavenger, N‐tert‐butyl‐α‐phenylnitrone (PBN; 0, 50 and 75 mg/kg, IP) or a superoxide‐selective scavenger, 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPOL; 0, 50 and 100 mg/kg, IP), attenuated METH‐induced locomotor activity without affecting generalized behavior in METH‐naïve rats. PBN and TEMPOL significantly attenuated METH self‐administration without affecting food intake. Increased oxidative stress was found in neurons, but not astrocytes, microglia or oligodendrocytes, in the NAc of METH self‐administering rats. In addition, TEMPOL significantly decreased METH enhancement of DA release in the NAc. Taken together, these results suggest that enhancement of ROS in the NAc contributes to the reinforcing effect of METH.

The tegmental-accumbal dopaminergic system mediates the anxiolytic effect of acupuncture during ethanol withdrawal.

This study investigated the involvement of the mesolimbic dopamine (DA) system in the anxiolytic effects of acupuncture during ethanol withdrawal (EW). Rats were intraperitoneally treated with 3g/kg/day of ethanol for 28 days and experienced 3 days of withdrawal. During EW, the rats were bilaterally treated with acupuncture at acupoints HT7 (Shenmen) or PC6 (Neiguan) or at a non-acupoint (tail) once daily for 1min over 3 days. High-performance liquid chromatographic (HPLC) analysis showed that EW significantly decreased both DA and 3,4-dihydroxyphenylacetic acid (DOPAC) levels in the nucleus accumbens shell (NaccSh); however, these processes were inhibited by acupuncture at HT7 but not at PC6. Real-time polymerase chain reaction and western blot assays also revealed that acupuncture at HT7 prevented the EW-induced reductions in tyrosine hydroxylase mRNA expression in the ventral tegmental area (VTA) and tyrosine hydroxylase protein expression in the NaccSh. A prior intra-NaccSh infusion of a cocktail of the selective DA1 receptor antagonist SCH23390 and the selective DA2 receptor antagonist eticlopride blocked the anxiolytic effect of acupuncture at HT7 in elevated plus maze tests. In addition, acupuncture at HT7 suppressed EW-induced increased BDNF levels in the VTA. These findings suggest that acupuncture at HT7 improves the VTA-Nacc DAergic function via inhibition of BDNF expression in the VTA, thereby exerting anxiolytic effects during EW.