The peripheral dopamine 2 receptor antagonist domperidone attenuates ethanol enhancement of dopamine levels in the nucleus accumbens.

BACKGROUND: Dopamine neuron firing in the ventral tegmental area (VTA) and dopamine release in the nucleus accumbens have been implicated in reward learning. Ethanol is known to increase both dopamine neuron firing in the VTA and dopamine levels in the nucleus accumbens. Despite this, some discrepancies exist between the dose of ethanol required to enhance firing in vivo and ex vivo. In the present study we investigated the effects of peripheral dopamine 2 subtype receptor antagonism on ethanol's effects on dopamine neurotransmission. METHODS: Plasma catecholamine levels were assessed following ethanol administration across four different doses of EtOH. Microdialysis and voltammetry were used to assess the effects of domperidone pretreatment on ethanol-mediated increases in dopamine release in the nucleus accumbens. A place conditioning paradigm was used to assess conditioned preference for ethanol and whether domperidone pretreatment altered this preference. Open-field and loss-of-righting reflex paradigms were used to assess the effects of domperidone on ethanol-induced sedation. A rotarod apparatus was used to assess the effects of domperidone on ethanol-induced motor impairment. RESULTS: Domperidone attenuated ethanol's enhancement of mesolimbic dopamine release under non-physiological conditions at intermediate (1.0 and 2.0 g/kg) doses of ethanol. Domperidone also decreased EtOH-induced sedation at 2.0 g/kg. Domperidone did not alter ethanol conditioned place preference nor did it affect ethanol-induced motor impairment. CONCLUSIONS: These results show that peripheral dopamine 2 receptors mediate some of the effects of ethanol on nonphysiological dopamine neurotransmission, although these effects are not related to the rewarding properties of ethanol.

The role of substance P in acupuncture signal transduction and effects.

BACKGROUND: Acupuncture has been used to treat a wide variety of diseases, disorders, and conditions for more than 2500 years. While the anatomical structures of acupuncture points (or acupoints) are largely unknown, our previous studies have suggested that many acupoints can be identified as cutaneous neurogenic inflammatory spots (neurogenic spots or Neuro-Sps), arising from the release of neuropeptides from activated small diameter sensory afferents at topographically distinct body surfaces due to the convergence of visceral and somatic afferents. In turn, the neuropeptides released during neurogenic inflammation may play important roles in the effects of acupuncture as well as the formation of active acupoints. Thus, the present study has focused on the role of substance P (SP) in acupuncture signal transduction and effects. METHODS: Neuro-Sps were detected by using in vivo fluorescence imaging after intravenous injection of Evans blue dye (EBD) and compared with traditional acupoints. Stimulatory effects of the Neuro-Sps were examined in a rat model of immobilization-induced hypertension (IMH). The roles of increased SP in Neuro-Sps were also investigated by using immunohistochemistry, in vivo single-fiber peripheral nerve recordings, and in vivo midbrain extracellular recordings. RESULTS: Neurogenic inflammation quickly appeared at acupoints on the wrist and was fully developed within 15 min in IMH model. The Neuro-Sps showed an increased release of SP from afferent nerve terminals. Mechanical stimulation of these Neuro-Sps increased cell excitability in the midbrain (rostral ventrolateral medulla) and alleviated the development of hypertension, which was blocked by the local injection of the SP receptor antagonist CP-99994 into Neuro-Sps prior to acupuncture and mimicked by the local injection of capsaicin. Single fiber recordings of peripheral nerves showed that increased SP into the Neuro-Sps elevated the sensitivity of A- and C-fibers in response to acupuncture stimulation. In addition, the discharge rates of spinal wide dynamic response (WDR) neurons significantly increased following SP or acupuncture treatment in Neuro-Sps in normal rats, but decreased following the injection of CP-99994 into Neuro-Sps in IMH rats. CONCLUSIONS: Our findings suggest that SP released during neurogenic inflammation enhances the responses of sensory afferents to the needling of acupoints and triggers acupuncture signaling to generate acupuncture effects.

Role of the central amygdala in acupuncture inhibition of methamphetamine-induced behaviors in rats.

Methamphetamine (METH) enhances dopamine (DA) transmission in the mesolimbic system implicated in its reinforcing effects. Our previous studies have shown that acupuncture attenuates drug-seeking behaviors by modulating GABAergic transmission in the ventral tegmental area and DA release in the nucleus accumbens (NAc) of the striatum. The effects of acupuncture on METH-induced behaviors and its mediation by neural pathways remain a relatively understudied area of research. The central amygdala (CeA) plays a critical role in physiological and behavioral responses to somatosensory and drug stimuli and has been implicated in negative reinforcement. Thus, we evaluated the role of the CeA in acupuncture effects on locomotor activity, positive affective states, and DA release in the NAc following acute administration of METH. Acupuncture at acupoint HT7 reduced locomotor activity, 50-kHz ultrasonic vocalizations (USVs), and NAc DA release following systemic injection of METH, which was prevented by electrolytic lesions or optogenetic inhibition of the CeA. Acupuncture alone excited CeA neurons and reversed the suppression of CeA neurons induced by METH. These results suggest that acupuncture can relieve psychomotor responses and positive affective states following METH by inhibiting NAc DA release and this effect is mediated by activation of CeA neurons.

Acupuncture reduces cocaine psychomotor responses by activating the rostromedial tegmental nucleus.

The rostromedial tegmental nucleus (RMTg), a GABAergic afferent to midbrain dopamine (DA) neurons, has emerged as an integral player in both rewarding and nociceptive responses. While previous studies have demonstrated that acupuncture modulates DA transmission in the mesolimbic reward system originating in the ventral tegmental area (VTA) and projecting to the nucleus accumbens (NAc) and can reduce drug self-administration, the central links between peripheral acupuncture signals and brain reward systems are not well-characterized. Thus, we hypothesised that acupuncture would elicit inhibitory signals from RMTg neurons to brain reward systems. Acupuncture reduced acute cocaine-induced locomotor activity and DA release in a point-specific manner, which was blocked by optogenetic silencing or chemical lesion of the RMTg. The acupuncture effect was mimicked by chemical activation of the RMTg. Acupuncture activated RMTg GABA neurons. In addition, the inhibitory effects of acupuncture on acute cocaine-induced locomotor activity were prevented by electrolytic lesions of the lateral habenula (LHb) or fasciculus retroflexus (FR), areas known to project to the RMTg. These findings suggest that acupuncture recruits the RMTg to reduce the psychomotor responses enhanced by acute cocaine.

Acupuncture Modulates Intracranial Self-Stimulation of the Medial Forebrain Bundle in Rats.

Acupuncture affects the central nervous system via the regulation of neurotransmitter transmission. We previously showed that Shemen (HT7) acupoint stimulation decreased cocaine-induced dopamine release in the nucleus accumbens. Here, we used the intracranial self-stimulation (ICSS) paradigm to evaluate whether HT stimulation regulates the brain reward function of rats. We found that HT stimulation triggered a rightward shift of the frequency-rate curve and elevated the ICSS thresholds. However, HT7 stimulation did not affect the threshold-lowering effects produced by cocaine. These results indicate that HT7 points only effectively regulates the ICSS thresholds of the medial forebrain bundle in drug-naïve rats.

Acupuncture inhibition of methamphetamine-induced behaviors, dopamine release and hyperthermia in the nucleus accumbens: mediation of group II mGluR.

Methamphetamine (METH) increases metabolic neuronal activity in the mesolimbic dopamine (DA) system and mediates the reinforcing effect. To explore the underlying mechanism of acupuncture intervention in reducing METH-induced behaviors, we investigated the effect of acupuncture on locomotor activity, ultrasonic vocalizations, extracellular DA release in the nucleus accumbens (NAcs) using fast-scan cyclic voltammetry and alterations of brain temperature (an indicator of local brain metabolic activity) produced by METH administration. When acupuncture was applied to HT7, but not TE4, both locomotor activity and 50-kHz ultrasonic vocalizations were suppressed in METH-treated rats. Acupuncture at HT7 attenuated the enhancement of electrically stimulated DA release in the NAc of METH-treated rats. Systemic injection of METH produced a sustained increase in NAc temperature, which was reversed by the DA D1 receptor antagonist SCH 23390 or acupuncture at HT7. Acupuncture inhibition of METH-induced NAc temperature was prevented by pre-treatment with a group II metabotropic glutamate receptors (mGluR2/3) antagonist EGLU into the NAc or mimicked by injection of an mGluR2/3 agonist DCG-IV into the NAc. These results suggest that acupuncture reduces extracellular DA release and metabolic neuronal activity in the NAc through activation of mGluR2/3 and suppresses METH-induced affective states and locomotor behavior.

Methanol extract of semen Ziziphi Spinosae attenuates ethanol withdrawal anxiety by improving neuropeptide signaling in the central amygdala.

BACKGROUND: Ethanol withdrawal (EtOHW) anxiety is a crucial risk factor for alcoholic relapse. The neuropeptide nociceptin/orphanin FQ (N/OFQ) acts upon its receptor (NOP) to antagonize corticotropin-releasing factor (CRF) and elicit anxiolytic actions. Semen Ziziphi Spinosae (SZS), a prototypical hypnotic-sedative herb in Oriental medicine, exhibits anxiolytic effects during nicotine withdrawal by improving amygdaloid CRF/CRF1 receptor (CRFR1) signaling. Therefore, we evaluated the effects of SZS on EtOHW anxiety and the involvement of amygdaloid CRF/CRFR1 and N/OFQ/NOP pathways. METHODS: Male Sprague Dawley rats received intraperitoneal injections of 2 g/kg EtOH (20% v/v) once daily for 28 d followed by a 3-d withdrawal. During EtOHW, the rats were given once-daily intragastric treatments of a methanol extract of SZS (MESZS, 60 or 180 mg/kg/d). Anxiety-like behaviors were measured with the open field (OF) and elevated plus maze (EPM) tests, and plasma corticosterone (CORT) levels were examined by an enzyme-linked immunosorbent assay. mRNA and protein expression levels of the neuropeptides and their receptors were determined by quantitative polymerase chain reaction and Western blot assays. RESULTS: MESZS increased the distance traveled in the center zone of the OF and dose-dependently elongated the duration of staying in the center zone in EtOHW rats. MESZS increased both the number of entries into and the time spent in the open arms of the EPM by EtOHW rats. And, MESZS inhibited the over secretion of plasma CORT during EtOHW. EtOHW enhanced CRF and CRFR1 gene and protein expression in the central nucleus of the amygdala (CeA), which were inhibited by 180 mg/kg/d MESZS. EtOHW increased amygdaloid NOP mRNA and protein expression but spared N/OFQ mRNA expression, and 180 mg/kg/d MESZS further promoted these increases. Additionally, a post-MESZS intra-CeA infusion of either CRF or the selective NOP antagonist UFP-101 abolished the expected anxiolytic effect of 180 mg/kg/d MESZS. CONCLUSIONS: These results suggest that MESZS ameliorates EtOHW anxiety by improving both CRF/CRFR1 and N/OFQ/NOP transmissions in the CeA.

DRG2 Deficient Mice Exhibit Impaired Motor Behaviors with Reduced Striatal Dopamine Release.

Developmentally regulated GTP-binding protein 2 (DRG2) was first identified in the central nervous system of mice. However, the physiological function of DRG2 in the brain remains largely unknown. Here, we demonstrated that knocking out DRG2 impairs the function of dopamine neurons in mice. DRG2 was strongly expressed in the neurons of the dopaminergic system such as those in the striatum (Str), ventral tegmental area (VTA), and substantia nigra (SN), and on neuronal cell bodies in high-density regions such as the hippocampus (HIP), cerebellum, and cerebral cortex in the mouse brain. DRG2 knockout (KO) mice displayed defects in motor function in motor coordination and rotarod tests and increased anxiety. However, unexpectedly, DRG2 depletion did not affect the dopamine (DA) neuron population in the SN, Str, or VTA region or dopamine synthesis in the Str region. We further demonstrated that dopamine release was significantly diminished in the Str region of DRG2 KO mice and that treatment of DRG2 KO mice with l-3,4-dihydroxyphenylalanine (L-DOPA), a dopamine precursor, rescued the behavioral motor deficiency in DRG2 KO mice as observed with the rotarod test. This is the first report to identify DRG2 as a key regulator of dopamine release from dopamine neurons in the mouse brain.

Acupuncture reduces relapse to cocaine-seeking behavior via activation of GABA neurons in the ventral tegmental area.

There is growing public interest in alternative approaches to addiction treatment and scientific interest in elucidating the neurobiological underpinnings of acupuncture. Our previous studies showed that acupuncture at a specific Shenmen (HT7) points reduced dopamine (DA) release in the nucleus accumbens (NAc) induced by drugs of abuse. The present study was carried out to evaluate the effects of HT7 acupuncture on γ-aminobutyric acid (GABA) neuronal activity in the ventral tegmental area (VTA) and the reinstatement of cocaine-seeking behavior. Using microdialysis and in vivo single-unit electrophysiology, we evaluated the effects of HT7 acupuncture on VTA GABA and NAc DA release and VTA GABA neuronal activity in rats. Using a within-session reinstatement paradigm in rats self-administering cocaine, we evaluated the effects of HT7 stimulation on cocaine-primed reinstatement. Acupuncture at HT7 significantly reduced cocaine suppression of GABA release and GABA neuron firing rates in the VTA. HT7 acupuncture attenuated cocaine-primed reinstatement, which was blocked by VTA infusions of the selective GABAB receptor antagonist 2-hydroxysaclofen. HT7 stimulation significantly decreased acute cocaine-induced DA release in the NAc, which was also blocked by 2-hydroxysaclofen. HT7 acupuncture also attenuated cocaine-induced sensitization of extracellular DA levels in the NAc. Moreover, HT7 acupuncture reduced both locomotor activity and neuronal activation in the NAc induced by acute cocaine in a needle-penetration depth-dependent fashion. These results suggest that acupuncture may suppress cocaine-induced DA release in the NAc and cocaine-seeking behavior through activation of VTA GABA neurons. Acupuncture may be an effective therapy to reduce cocaine relapse by enhancing GABAergic inhibition in the VTA.

Altered Acoustic Startle Reflex, Prepulse Inhibition, and Peripheral Brain-Derived Neurotrophic Factor in Morphine Self-Administered Rats.

Background: Previous studies suggested that opiate withdrawal may increase anxiety and disrupt brain-derived neurotrophic factor function, but the effects of i.v. morphine self-administration on these measures remain unclear. Methods: Adult male Sprague-Dawley rats were implanted with a catheter in the jugular vein. After 1 week of recovery, the animals were allowed to self-administer either i.v. morphine (0.5 mg/kg per infusion, 4 h/d) or saline in the operant conditioning chambers. The acoustic startle reflex and prepulse inhibition were measured at a baseline and on self-administration days 1, 3, 5, and 7 (1- and 3-hour withdrawal). Blood samples were collected on self-administration days 3, 5, and 7 from separate cohorts of animals, and the levels of brain-derived neurotrophic factor and corticosterone were assayed using the enzyme-linked immunosorbent assay method. Results: Compared with the saline group, the morphine self-administration group showed hyper-locomotor activity and reduced defecation during the self-administration. The morphine self-administration increased acoustic startle reflex at 1-hour but not 3-hour withdrawal from morphine and disrupted prepulse inhibition at 3-hour but not 1-hour withdrawal. The blood brain-derived neurotrophic factor levels were decreased in the morphine self-administration group at self-administration days 3 and 5, while the corticosterone levels remained unchanged throughout the study. Conclusions: The current findings suggest that spontaneous withdrawal from i.v. morphine self-administration may have transient effects on acoustic startle, sensorimotor gating, and peripheral brain-derived neurotrophic factor levels, and these changes may contribute to the adverse effects of opiate withdrawal.

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.

Effect of acupuncture on Lipopolysaccharide-induced anxiety-like behavioral changes: involvement of serotonin system in dorsal Raphe nucleus.

BACKGROUND: Acupuncture has been used as a common therapeutic tool in many disorders including anxiety and depression. Serotonin transporter (SERT) plays an important role in the pathology of anxiety and other mood disorders. The aim of this study was to evaluate the effects of acupuncture on lipopolysaccharide (LPS)-induced anxiety-like behaviors and SERT in the dorsal raphe nuclei (DRN). METHODS: Rats were given acupuncture at ST41 (Jiexi), LI11 (Quchi) or SI3 (Houxi) acupoint in LPS-treated rats. Anxiety-like behaviors of elevated plus maze (EPM) and open field test (OFT) were measured and expressions of SERT and/or c-Fos were also examined in the DRN using immunohistochemistry. RESULTS: The results showed that 1) acupuncture at ST41 acupoint, but neither LI11 nor SI3, significantly attenuated LPS-induced anxiety-like behaviors in EPM and OFT, 2) acupuncture at ST41 decreased SERT expression increased by LPS in the DRN. CONCLUSIONS: Our results suggest that acupuncture can ameliorate anxiety-like behaviors, possibly through regulation of SERT in the DRN.

Blockade of nicotine sensitization by methanol extracts of Glycyrrhizae radix mediated via antagonism of accumbal oxidative stress.

BACKGROUND: We previously reported that a methanol extract of Glycyrrhizae radix (MEGR) blocked methamphetamine-induced locomotor sensitization and conditioned place preference in rats. In the present study, the effects of MEGR on repeated nicotine-induced locomotor sensitization and enhanced extracellular dopamine (DA) release in the nucleus accumbens (Nacc) were evaluated. METHODS: Male Sprague-Dawley rats received repeated administrations of nicotine (0.4 mg/kg, subcutaneous) or saline twice a day for 7 d and were challenged with nicotine 4 d after the last daily dosing. During the 4-d withdrawal period, the rats were treated once a day with MEGR (60 or 180 mg/kg/d). Extracellular DA levels were measured by in vivo microdialysis, the malondialdehyde levels and the activities of superoxide dismutase and catalase in the Nacc were biochemically evaluated, and the expression of antioxidant proteins was confirmed by Western blot assays. All data were assessed with analysis of variance tests followed by post-hoc comparison tests and p values <0.05 were considered statistically significant. RESULTS: The expression of repeated nicotine-induced locomotor sensitization was dose-dependently attenuated by MEGR, and 180 mg/kg/d MEGR significantly inhibited augmented accumbal DA release induced by a direct local challenge of nicotine. Moreover, 180 mg/kg/d MEGR reversed increases in malondialdehyde production, decreases in superoxide dismutase and catalase activities, and the reduced expression of nuclear factor erythroid 2-related factor 2 and heme oxygenase 1 in the nicotine-sensitized Nacc. CONCLUSIONS: These results suggest that MEGR inhibited nicotine-induced locomotion and dopaminergic sensitization via antioxidant action.

Exposure pattern influences the degree of drug-seeking behaviour after withdrawal.

OBJECTIVES: The occurrence of a relapse during abstinence is an important issue that must be addressed during treatment for drug addiction. We investigated the influence of drug exposure pattern on morphine-seeking behaviour following withdrawal. We also studied the role of the hippocampus in this process to confirm its involvement in drug relapse. METHODS: Male Sprague-Dawley rats that were trained to self-administer morphine (1.0 mg/kg) using 2, 4, 6, 8, or 10 h daily sessions underwent withdrawal in their home cages and were re-exposed to the operant chamber to evaluate morphine-seeking behaviour. During the relapse session, rats were intravenously injected with morphine (0.25 mg/kg) or saline before re-exposure to the chamber. In the second experiment, rats were administered a microinjection of saline or cobalt chloride (CoCl2, 1 mM), a synaptic blocker, into the CA1 of the hippocampus prior to the relapse test. RESULTS: In the first experiment, more morphine-seeking behaviour was observed in the 2 h group (animals trained to self-administer morphine during a 2 h daily session spread over 21 days) during the relapse session, despite all groups being exposed to similar amounts of morphine during the training period before withdrawal. In the second experiment, pretreatment with CoCl2 markedly reduced morphine-seeking behaviour in the 2 h group. CONCLUSIONS: The present findings suggest that the exposure pattern influences the degree of relapse and that control of memorisation is important for prevention of relapse.

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 the fragrance inhalation of essential oil from Asarum heterotropoides on depression-like behaviors in mice.

BACKGROUND: Psychological stressors may cause affective disorders, such as depression and anxiety, by altering expressions of corticotropin releasing factor (CRF), serotonin (5-HT), and tyrosine hydroxylase (TH) in the brain. This study investigated the effects of essential oil from Asarum heterotropoides (EOAH) on depression-like behaviors and brain expressions of CRF, 5-HT, and TH in mice challenged with stress. METHODS: Male ICR mice received fragrance inhalation of EOAH (0.25, 0.5, 1.0, and 2.0 g) for 3 h in the special cage capped with a filter paper before start of the forced swimming test (FST) and tail suspension test (TST). The duration of immobility was measured for the determination of depression-like behavior in the FST and TST. The selective serotonin reuptake inhibitor fluoxetine as positive control was administered at a dose of 15 mg/kg (i.p.) 30 min before start of behavioral testing. Immunoreactivities of CRF, 5-HT, and TH in the brain were also measured using separate groups of mice subjected to the FST. RESULTS: EOAH at higher doses (1.0 and 2.0 g) reduced immobility time in the FST and TST. In addition, EOAH at a dose of 1.0 g significantly reduced the expected increases in the expression of CRF positive neurons in the paraventricular nucleus and the expression of TH positive neurons in the locus coeruleus, and the expected decreases of the 5-HT positive neurons in the dorsal raphe nucleus. CONCLUSION: These results provide strong evidence that EOAH effectively inhibits depression-like behavioral responses, brain CRF and TH expression increases, and brain 5-HT expression decreases in mice challenged with stress.

Effects of the Synthetic Cathinone α-Pyrrolidinobutiothiophenone (α-PBT) on Discriminative Stimulus Effects and Intracranial Self-Stimulation Thresholds in Male Rats.

Recently, the abuse of synthetic cathinones is increasing among young people. α-Pyrrolidinobutiothiophenone (α-PBT), a synthetic cathinone, is a designer drug that is freely traded online with no legal restrictions. Moreover, there is currently no scientific basis for legal regulation. Here, we examined the addictive properties of α-PBT using a drug discrimination (DD) task. We also investigated the role of α-PBT in brain stimulation reward (BSR) using an intracranial self-stimulation (ICSS) paradigm in rats. Initially, the rats were trained to discriminate between cocaine and saline. After the discrimination training criteria were met, we determined the dose-effect curves of cocaine and conducted generalization tests with α-PBT and α-pyrrolidinopentiothiophenone (α-PVT) using a cumulative dosing protocol. In a separate set of studies, we examined the dopaminergic mechanisms underlying the function of α-PBT as an interoceptive stimulus (17.8 mg/kg) by intraperitoneally injecting either the dopamine (DA) D1 antagonist SCH23390 (0.06 and 0.12 mg/kg) or the D2 antagonist eticlopride (0.05 and 0.1 mg/kg) 15 min before DD testing. Brain reward function was measured using an ICSS procedure to examine the effects of α-PBT on ICSS threshold under the frequency-rate procedure. Our results showed that α-PBT functioned as a discriminative cue similar to cocaine in rats. More importantly, SCH23390 abolished the effects of α-PBT as an interoceptive stimulus in a dose-dependent manner in rats trained to press a lever to receive cocaine. Similarly, eticlopride dose-dependently attenuated the effect of α-PBT used as a discriminative cue. Additionally, cumulative α-PBT administration dose-dependently lowered ICSS thresholds compared with those in saline-treated rats. Furthermore, α-PBT-induced potentiation of BSR was abolished by pretreatment with both SCH23390 and eticlopride. Taken together, our results suggest that α-PBT can function as a cocaine-like discriminative cue via the activation of D1 and D2 receptors. α-PBT also appears to influence BSR by reducing the brain reward threshold via changes in D1 and D2 receptors. The present study suggests that α-PBT could have addictive properties through DA D1 and D2 receptors and thus poses a threat to humans.

The psychomotor, reinforcing, and discriminative stimulus effects of synthetic cathinone mexedrone in male mice and rats.

The chronic use of the novel synthetic cathinone mexedrone, like other psychoactive drugs, can be considered addictive, with a high potential for abuse and the ability to cause psychological dependence in certain users. However, little is known about the neurobehavioral effects of mexedrone in association with its potential for abuse. We investigated the abuse potential for mexedrone abuse through multiple behavioral tests. In addition, serotonin transporter (SERT) levels were measured in the synaptosome of the dorsal striatum, and serotonin (5-HT) levels were measured in the dorsal striatum of acute mexedreone (50 mg/kg)-treated mice. To clarify the neuropharmacological mechanisms underlying the locomotor response of mexedrone, the 5-HT2A receptor antagonist M100907 (0.5 or 1.0 mg/kg) was administered prior to the acute injection of mexedrone in the locomotor activity experiment in mice. Mexedrone (10-50 mg/kg) produced a significant place preference in mice and mexedrone (0.1-0.5 mg/kg/infusion) maintained self-administration behavior in rats in a dose-dependent manner. In the drug discrimination experiment, mexedrone (5.6-32 mg/kg) was fully substituted for the discriminative stimulus effects of cocaine in rats. Mexedrone increased locomotor activity, and these effects were reversed by pretreatment with M100907. Acute mexedrone significantly increased c-Fos expression in the dorsal striatum and decreased SERT levels in the synaptosome of the dorsal striatum of mice, resulting in an elevation of 5-HT levels. Taken together, our results provide the possibility that mexedrone has abuse potential, which might be mediated, at least in part, by the activation of the serotonergic system in the dorsal striatum.

Metformin-induced TTP mediates communication between Kupffer cells and hepatocytes to alleviate hepatic steatosis by regulating lipophagy and necroptosis.

OBJECTIVE: Emerging evidence suggests that crosstalk between Kupffer cells (KCs) and hepatocytes protects against non-alcoholic fatty liver disease (NAFLD). However, the underlying mechanisms that lead to the reduction of steatosis in NAFLD remain obscure. METHODS: Ttp+/+ and Ttp-/- mice were fed with a high-fat diet. Hepatic steatosis was analyzed by Nile Red staining and measurement of inflammatory cytokines. Lipid accumulation and cell death were evaluated in co-culture systems with primary hepatocytes and KCs derived from either Ttp+/+ or Ttp-/- mice. RESULTS: Tristetraprolin (TTP), an mRNA binding protein, was essential for the protective effects of metformin in NAFLD. Metformin activated TTP via the AMPK-Sirt1 pathway in hepatocytes and KCs. TTP inhibited TNF-α production in KCs, which in turn decreased hepatocyte necroptosis. Downregulation of Rheb expression by TTP promoted hepatocyte lipophagy via mTORC1 inhibition and increased nuclear translocation of transcription factor-EB (TFEB). Consistently, TTP-deficient NAFLD mice failed to respond to metformin with respect to alleviation of hepatic steatosis, protection of hepatocyte necroptosis, or induction of lipophagy. CONCLUSIONS: TTP, which is essential for the protective effects of metformin, may represent a novel primary therapeutic target in NAFLD.

Activation of ROS-PERK-TFEB by filbertone ameliorates neurodegenerative diseases via enhancing the autophagy-lysosomal pathway.

The molecular mechanisms underlying the pathogenesis of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease (PD), and Huntington's disease remain enigmatic, resulting in an unmet need for therapeutics development. Here, we suggest that filbertone, a key flavor compound found in the fruits of hazel trees of the genus Corylus, can ameliorate PD via lowering the abundance of aggregated α-synuclein. We previously reported that inhibition of hypothalamic inflammation by filbertone is mediated by suppression of nuclear factor kappa-B. Here, we report that filbertone activates PERK through mitochondrial reactive oxygen species production, resulting in the increased nuclear translocation of transcription factor-EB in SH-SY5Y human neuroblastoma cells. TFEB activation by filbertone promotes the autophagy-lysosomal pathway, which in turn alleviates the accumulation of α-synuclein. We also demonstrate that filbertone prevented the loss of dopaminergic neurons in the substantia nigra and striatum of mice on high-fat diet. Filbertone treatment also reduced high-fat diet-induced α-synuclein accumulation through upregulation of the autophagy-lysosomal pathway. In addition, filbertone improved behavioral abnormalities (i.e., latency time to fall and decrease of running distance) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced PD murine model. In conclusion, filbertone may show promise as a potential therapeutic for neurodegenerative disease.