Zheng-Xiong Xi, M.D., Ph.D.

@article{pmid37479780,

title = {PPARα and PPARγ are expressed in midbrain dopamine neurons and modulate dopamine- and cannabinoid-mediated behavior in mice},

author = {Briana Hempel and Madeline Crissman and Sruti Pari and Benjamin Klein and Guo-Hua Bi and Hannah Alton and Zheng-Xiong Xi},

url = {https://pubmed.ncbi.nlm.nih.gov/37479780/},

doi = {10.1038/s41380-023-02182-0},

issn = {1476-5578},

year  = {2023},

date = {2023-07-01},

urldate = {2023-07-01},

journal = {Mol Psychiatry},

abstract = {Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear receptors that regulate gene expression. Δ-tetrahydrocannabinol (Δ-THC) is a PPARγ agonist and some endocannabinoids are natural activators of PPARα and PPARγ. However, little is known regarding their cellular distributions in the brain and functional roles in cannabinoid action. Here, we first used RNAscope in situ hybridization and immunohistochemistry assays to examine the cellular distributions of PPARα and PPARγ expression in the mouse brain. We found that PPARα and PPARγ are expressed in ~70% of midbrain dopamine (DA) neurons. In the amygdala, PPARα is expressed in ~60% of glutamatergic neurons, while PPARγ is expressed in ~60%  of GABA neurons. However, no PPARα/γ signal was detected in GABA neurons in the nucleus accumbens. We then used a series of behavioral assays to determine the functional roles of PPARα/γ in the CNS effects of Δ-THC. We found that optogenetic stimulation of midbrain DA neurons was rewarding as assessed by optical intracranial self-stimulation (oICSS) in DAT-cre mice. Δ-THC and a PPARγ (but not PPARα) agonist dose-dependently inhibited oICSS. Pretreatment with PPARα or PPARγ antagonists attenuated the Δ-THC-induced reduction in oICSS and Δ-THC-induced anxiogenic effects. In addition, a PPARγ agonist increased, while PPARα or PPARγ antagonists decreased open-field locomotion. Pretreatment with PPARα or PPARγ antagonists potentiated Δ-THC-induced hypoactivity and catalepsy but failed to alter Δ-THC-induced analgesia, hypothermia and immobility. These findings provide the first anatomical and functional evidence supporting an important role of PPARα/γ in DA-dependent behavior and cannabinoid action.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{pmid36517243,

title = {Cannabinoid CB_{1} Receptors Are Expressed in a Subset of Dopamine Neurons and Underlie Cannabinoid-Induced Aversion, Hypoactivity, and Anxiolytic Effects in Mice},

author = {Xiao Han and Ying Liang and Briana Hempel and Chloe J Jordan and Hui Shen and Guo-Hua Bi and Jin Li and Zheng-Xiong Xi},

url = {https://pubmed.ncbi.nlm.nih.gov/36517243/},

doi = {10.1523/JNEUROSCI.1493-22.2022},

issn = {1529-2401},

year  = {2023},

date = {2023-01-01},

urldate = {2023-01-01},

journal = {J Neurosci},

volume = {43},

number = {3},

pages = {373--385},

abstract = {Cannabinoids modulate dopamine (DA) transmission and DA-related behavior, which has been thought to be mediated initially by activation of cannabinoid CB1 receptors (CB1Rs) on GABA neurons. However, there is no behavioral evidence supporting it. In contrast, here we report that CB1Rs are also expressed in a subset of DA neurons and functionally underlie cannabinoid action in male and female mice. RNAscope in situ hybridization (ISH) assays demonstrated CB1 mRNA in tyrosine hydroxylase (TH)-positive DA neurons in the ventral tegmental area (VTA) and glutamate decarboxylase 1 (GAD1)-positive GABA neurons. The CB1R-expressing DA neurons were located mainly in the middle portion of the VTA with the number of CB1-TH colocalization progressively decreasing from the medial to the lateral VTA. Triple-staining assays indicated CB1R mRNA colocalization with both TH and vesicular glutamate transporter 2 (VgluT2, a glutamate neuronal marker) in the medial VTA close to the midline of the brain. Optogenetic activation of this population of DA neurons was rewarding as assessed by optical intracranial self-stimulation. Δ-tetrahydrocannabinol (Δ-THC) or ACEA (a selective CB1R agonist) dose-dependently inhibited optical intracranial self-stimulation in DAT-Cre control mice, but not in conditional knockout mice with the CB1R gene absent in DA neurons. In addition, deletion of CB1Rs from DA neurons attenuated Δ-THC-induced reduction in DA release in the NAc, locomotion, and anxiety. Together, these findings indicate that CB1Rs are expressed in a subset of DA neurons that corelease DA and glutamate, and functionally underlie cannabinoid modulation of DA release and DA-related behavior. Cannabinoids produce a series of psychoactive effects, such as aversion, anxiety, and locomotor inhibition in rodents. However, the cellular and receptor mechanisms underlying these actions are not fully understood. Here we report that CB1 receptors are expressed not only in GABA neurons but also in a subset of dopamine neurons, which are located mainly in the medial VTA close to the midline of the midbrain and corelease dopamine and glutamate. Optogenetic activation of these dopamine neurons is rewarding, which is dose-dependently inhibited by cannabinoids. Selective deletion of CB1 receptor from dopamine neurons blocked cannabinoid-induced aversion, hypoactivity, and anxiolytic effects. These findings demonstrate that dopaminergic CB1 receptors play an important role in mediating cannabinoid action.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{pmid36054363,

title = {A red nucleus-VTA glutamate pathway underlies exercise reward and the therapeutic effect of exercise on cocaine use},

author = {Yi He and Graziella Madeo and Ying Liang and Cindy Zhang and Briana Hempel and Xiaojie Liu and Lianwei Mu and Shui Liu and Guo-Hua Bi and Ewa Galaj and Hai-Ying Zhang and Hui Shen and Ross A McDevitt and Eliot L Gardner and Qing-Song Liu and Zheng-Xiong Xi},

url = {https://pubmed.ncbi.nlm.nih.gov/36054363/},

doi = {10.1126/sciadv.abo1440},

issn = {2375-2548},

year  = {2022},

date = {2022-09-01},

urldate = {2022-09-01},

journal = {Sci Adv},

volume = {8},

number = {35},

pages = {eabo1440},

abstract = {Physical exercise is rewarding and protective against drug abuse and addiction. However, the neural mechanisms underlying these actions remain unclear. Here, we report that long-term wheel-running produced a more robust increase in c-fos expression in the red nucleus (RN) than in other brain regions. Anatomic and functional assays demonstrated that most RN magnocellular portion (RNm) neurons are glutamatergic. Wheel-running activates a subset of RNm glutamate neurons that project to ventral tegmental area (VTA) dopamine neurons. Optogenetic stimulation of this pathway was rewarding, as assessed by intracranial self-stimulation and conditioned place preference, whereas optical inhibition blocked wheel-running behavior. Running wheel access decreased cocaine self-administration and cocaine seeking during extinction. Last, optogenetic stimulation of the RNm-to-VTA glutamate pathway inhibited responding to cocaine. Together, these findings indicate that physical exercise activates a specific RNm-to-VTA glutamatergic pathway, producing exercise reward and reducing cocaine intake.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{pmid35851573,

title = {Therapeutic potential of PIMSR, a novel CB1 receptor neutral antagonist, for cocaine use disorder: evidence from preclinical research},

author = {Ewa Galaj and Briana Hempel and Allamar Moore and Benjamin Klein and Guo-Hua Bi and Eliot L Gardner and Herbert H Seltzman and Zheng-Xiong Xi},

url = {https://pubmed.ncbi.nlm.nih.gov/35851573/},

doi = {10.1038/s41398-022-02059-w},

issn = {2158-3188},

year  = {2022},

date = {2022-07-01},

urldate = {2022-07-01},

journal = {Transl Psychiatry},

volume = {12},

number = {1},

pages = {286},

abstract = {Cannabinoid CB1 receptors (CB1Rs) have been major targets in medication development for the treatment of substance use disorders. However, clinical trials with rimonabant, a CB1R antagonist/inverse agonist, failed due to severe side effects. Here, we evaluated the therapeutic potential of PIMSR, a neutral CB1R antagonist lacking an inverse agonist profile, against cocaine's behavioral effects in experimental animals. We found that systemic administration of PIMSR dose-dependently inhibited cocaine self-administration under fixed-ratio (FR5), but not FR1, reinforcement, shifted the cocaine self-administration dose-response curve downward, decreased incentive motivation to seek cocaine under progressive-ratio reinforcement, and reduced cue-induced reinstatement of cocaine seeking. PIMSR also inhibited oral sucrose self-administration. Importantly, PIMSR alone is neither rewarding nor aversive as assessed by place conditioning. We then used intracranial self-stimulation (ICSS) to explore the possible involvement of the mesolimbic dopamine system in PIMSR's action. We found that PIMSR dose-dependently attenuated cocaine-enhanced ICSS maintained by electrical stimulation of the medial forebrain bundle in rats. PIMSR itself failed to alter electrical ICSS, but dose-dependently inhibited ICSS maintained by optical stimulation of midbrain dopamine neurons in transgenic DAT-Cre mice, suggesting the involvement of dopamine-dependent mechanisms. Lastly, we examined the CB1R mechanisms underlying PIMSR's action. We found that PIMSR pretreatment attenuated Δ-tetrahydrocannabinol (Δ-THC)- or ACEA (a selective CB1R agonist)-induced reduction in optical ICSS. Together, our findings suggest that the neutral CB1R antagonist PIMSR deserves further research as a promising pharmacotherapeutic for cocaine use disorder.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{pmid35091501,

title = {Elevation of Extracellular Glutamate by Blockade of Astrocyte Glutamate Transporters Inhibits Cocaine Reinforcement in Rats via a NMDA-GluN2B Receptor Mechanism},

author = {Hong-Ju Yang and Briana J Hempel and Guo-Hua Bi and Yi He and Hai-Ying Zhang and Eliot L Gardner and Zheng-Xiong Xi},

url = {https://pubmed.ncbi.nlm.nih.gov/35091501/},

doi = {10.1523/JNEUROSCI.1432-21.2022},

issn = {1529-2401},

year  = {2022},

date = {2022-01-01},

urldate = {2022-01-01},

journal = {J Neurosci},

volume = {42},

number = {11},

pages = {2327--2343},

abstract = {It is well established that glutamate plays an important role in drug-induced and cue-induced reinstatement of drug seeking. However, the role of glutamate in drug reward is unclear. In this study, we systemically evaluated the effects of multiple glutamate transporter (GLT) inhibitors on extracellular glutamate and dopamine (DA) in the nucleus accumbens (NAc), intravenous cocaine self-administration, intracranial brain-stimulation reward (BSR), and reinstatement of cocaine seeking in male and female rats. Among the five GLT inhibitors we tested, TFB-TBOA was the most potent. Microinjections of TFB-TBOA into the NAc, but not the ventral tegmental area (VTA), or dorsal striatum (DS), dose-dependently inhibited cocaine self-administration under fixed-ratio and progressive-ratio (PR) reinforcement schedules, shifted the cocaine dose-response curve downward, and inhibited intracranial BSR. Selective downregulation of astrocytic GLT-1 expression in the NAc by GLT-1 antisense oligonucleotides also inhibited cocaine self-administration. The reduction in cocaine self-administration following TFB-TBOA administration was NMDA GluN2B receptor dependent, and rats self-administering cocaine showed upregulation of GluN2B expression in NAc DA- and cAMP-regulated phosphoprotein 32 (DARPP-32)-positive medium-spiny neurons (MSNs). In contrast, TFB-TBOA, when locally administered into the NAc, VTA, or ventral pallidum (VP), dose-dependently reinstated cocaine-seeking behavior. Intra-NAc TFB-TBOA-evoked drug-seeking was long-lasting and NMDA/AMPA receptor dependent. These findings, for the first time, indicate that glutamate in the NAc negatively regulates cocaine's rewarding effects, while an excess of glutamate in multiple brain regions can trigger reinstatement of drug-seeking behavior. It is well known that glutamate plays an important role in relapse to drug seeking. However, the role of glutamate in drug reward is less clear. Here, we report that TFB-TBOA, a highly potent glutamate transporter (GLT) inhibitor, dose-dependently elevates extracellular glutamate and inhibits cocaine self-administration and brain-stimulation reward (BSR), when administered locally into the nucleus accumbens (NAc), but not other brain regions. Mechanistic assays indicate that cocaine self-administration upregulates NMDA-GluN2B receptor subtype expression in striatal dopaminoceptive neurons and activation of GluN2B by TFB-TBOA-enhanced glutamate inhibits cocaine self-administration. TFB-TBOA also reinstates cocaine-seeking behavior when administered into the NAc, ventral tegmental area (VTA), and ventral pallidum (VP). These findings demonstrate that glutamate differentially regulates cocaine reward versus relapse, reducing cocaine reward, while potentiating relapse to cocaine seeking.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{pmid33789118,

title = {Cannabinoid CB_{2} receptors are expressed in glutamate neurons in the red nucleus and functionally modulate motor behavior in mice},

author = {Hai-Ying Zhang and Hui Shen and Ming Gao and Zegang Ma and Briana J Hempel and Guo-Hua Bi and Eliot L Gardner and Jie Wu and Zheng-Xiong Xi},

url = {https://pubmed.ncbi.nlm.nih.gov/33789118/},

doi = {10.1016/j.neuropharm.2021.108538},

issn = {1873-7064},

year  = {2021},

date = {2021-05-01},

urldate = {2021-05-01},

journal = {Neuropharmacology},

volume = {189},

pages = {108538},

abstract = {Cannabinoids produce a number of central nervous system effects via the CB receptor (CBR), including analgesia, antianxiety, anti-reward, hypoactivity and attenuation of opioid-induced respiratory depression. However, the cellular distributions of the CBRs in the brain remain unclear. We have reported that CBRs are expressed in midbrain dopamine (DA) neurons and functionally regulate DA-mediated behavior(s). Unexpectedly, high densities of CB-like signaling were also found in a neighboring motor structure - the red nucleus (RN) of the midbrain. In the present study, we systematically explored CBR expression and function in the RN. Immunohistochemistry and in situ hybridization assays showed high densities of CBR-immunostaining and mRNA signal in RN magnocellular glutamate neurons in wildtype and CB-knockout, but not CB-knockout, mice. Ex vivo electrophysiological recordings in midbrain slices demonstrated that CBR activation by JWH133 dose-dependently inhibited firing rates of RN magnocellular neurons in wildtype, but not CB-knockout, mice, while having no effect on RN GABA neurons in transgenic GAD67-GFP reporter mice, suggesting CB-mediated effects on glutamatergic neurons. In addition, microinjection of JWH133 into the RN produced robust ipsilateral rotations in wildtype, but not CB-knockout mice, which was blocked by pretreatment with either a CB or DA D1 or D2 receptor antagonist, suggesting a DA-dependent effect. Finally, fluorescent tract tracing revealed glutamatergic projections from the RN to multiple brain areas including the ventral tegmental area, thalamus, and cerebellum. These findings suggest that CBRs in RN glutamate neurons functionally modulate motor activity, and therefore, constitute a new target in cannabis-based medication development for motor disorders.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Galaj:2021aa,

title = {Beta-caryophyllene inhibits cocaine addiction-related behavior by activation of PPARαand PPARγ: repurposing a FDA-approved food additive for cocaine use disorder},

author = {Ewa Galaj and Guo-Hua Bi and Allamar Moore and Kai Chen and Yi He and Eliot Gardner and Zheng-Xiong Xi},

url = {https://pubmed.ncbi.nlm.nih.gov/33069159/},

doi = {10.1038/s41386-020-00885-4},

isbn = {1740-634X},

year  = {2021},

date = {2021-01-01},

journal = {Neuropsychopharmacology},

volume = {46},

number = {4},

pages = {860--870},

abstract = {Cocaine abuse continues to be a serious health problem worldwide. Despite intense research, there is still no FDA-approved medication to treat cocaine use disorder (CUD). In this report, we explored the potential utility of beta-caryophyllene (BCP), an FDA-approved food additive for the treatment of CUD. We found that BCP, when administered intraperitoneally or intragastrically, dose-dependently attenuated cocaine self-administration, cocaine-conditioned place preference, and cocaine-primed reinstatement of drug seeking in rats. In contrast, BCP failed to alter food self-administration or cocaine-induced hyperactivity. It also failed to maintain self-administration in a drug substitution test, suggesting that BCP has no abuse potential. BCP was previously reported to be a selective CB2 receptor agonist. Unexpectedly, pharmacological blockade or genetic deletion of CB1, CB2, or GPR55 receptors in gene-knockout mice failed to alter BCP's action against cocaine self-administration, suggesting the involvement of non-CB1, non-CB2, and non-GPR55 receptor mechanisms. Furthermore, pharmacological blockade of μopioid receptor or Toll-like receptors complex failed to alter, while blockade of peroxisome proliferator-activated receptors (PPARα, PPARγ) reversed BCP-induced reduction in cocaine self-administration, suggesting the involvement of PPARαand PPARγin BCP's action. Finally, we used electrical and optogenetic intracranial self-stimulation (eICSS, oICSS) paradigms to study the underlying neural substrate mechanisms. We found that BCP is more effective in attenuation of cocaine-enhanced oICSS than eICSS, the former driven by optical activation of midbrain dopamine neurons in DAT-cre mice. These findings indicate that BCP may be useful for the treatment of CUD, likely by stimulation of PPARαand PPARγin the mesolimbic system.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{pmid34566647,

title = {β-caryophyllene, an FDA-Approved Food Additive, Inhibits Methamphetamine-Taking and Methamphetamine-Seeking Behaviors Possibly  CB2 and Non-CB2 Receptor Mechanisms},

author = {Xiang-Hu He and Ewa Galaj and Guo-Hua Bi and Yi He and Briana Hempel and Yan-Lin Wang and Eliot L Gardner and Zheng-Xiong Xi},

url = {https://pubmed.ncbi.nlm.nih.gov/34566647/},

doi = {10.3389/fphar.2021.722476},

issn = {1663-9812},

year  = {2021},

date = {2021-01-01},

urldate = {2021-01-01},

journal = {Front Pharmacol},

volume = {12},

pages = {722476},

abstract = {Recent research indicates that brain cannabinoid CB2 receptors are involved in drug reward and addiction. However, it is unclear whether β-caryophyllene (BCP), a natural product with a CB2 receptor agonist profile, has therapeutic effects on methamphetamine (METH) abuse and dependence. In this study, we used animal models of self-administration, electrical brain-stimulation reward (BSR) and  microdialysis to explore the effects of BCP on METH-taking and METH-seeking behavior. We found that systemic administration of BCP dose-dependently inhibited METH self-administration under both fixed-ratio and progressive-ratio reinforcement schedules in rats, indicating that BCP reduces METH reward, METH intake, and incentive motivation to seek and take METH. The attenuating effects of BCP were partially blocked by AM 630, a selective CB2 receptor antagonist. Genetic deletion of CB2 receptors in CB2-knockout (CB2-KO) mice also blocked low dose BCP-induced reduction in METH self-administration, suggesting possible involvement of a CB2 receptor mechanism. However, at high doses, BCP produced a reduction in METH self-administration in CB2-KO mice in a manner similar as in WT mice, suggesting that non-CB2 receptor mechanisms underlie high dose BCP-produced effects. In addition, BCP dose-dependently attenuated METH-enhanced electrical BSR and inhibited METH-primed and cue-induced reinstatement of drug-seeking in rats.  microdialysis assays indicated that BCP alone did not produce a significant reduction in extracellular dopamine (DA) in the nucleus accumbens (NAc), while BCP pretreatment significantly reduced METH-induced increases in extracellular NAc DA in a dose-dependent manner, suggesting a DA-dependent mechanism involved in BCP action. Together, the present findings suggest that BCP might be a promising therapeutic candidate for the treatment of METH use disorder.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Galaj8853,

title = {Dissecting the Role of GABA Neurons in the VTA versus SNr in Opioid Reward},

author = {Ewa Galaj and Xiao Han and Hui Shen and Chloe J Jordan and Yi He and Bree Humburg and Guo-Hua Bi and Zheng-Xiong Xi},

url = {https://pubmed.ncbi.nlm.nih.gov/33046548/},

doi = {10.1523/JNEUROSCI.0988-20.2020},

issn = {0270-6474},

year  = {2020},

date = {2020-01-01},

journal = {Journal of Neuroscience},

volume = {40},

number = {46},

pages = {8853--8869},

publisher = {Society for Neuroscience},

abstract = {Opioid reward has traditionally been thought to be mediated by GABA-induced disinhibition of dopamine (DA) neurons in the VTA. However, direct behavioral evidence supporting this hypothesis is still lacking. In this study, we found that the μ opioid receptor (MOR) gene, Oprm1, is highly expressed in GABA neurons, with ~50% of GABA neurons in the substantia nigra pars reticulata (SNr), ~30% in the VTA, and ~70% in the tail of the VTA (also called the rostromedial tegmental nucleus) in male rats. No Oprm1 mRNA was detected in midbrain DA neurons. We then found that optogenetic inhibition of VTA DA neurons reduced intravenous heroin self-administration, whereas activation of these neurons produced robust optical intracranial self-stimulation in DAT-Cre mice, supporting an important role of DA neurons in opioid reward. Unexpectedly, pharmacological blockade of MORs in the SNr was more effective than in the VTA in reducing heroin reward. Optogenetic activation of VTA GABA neurons caused place aversion and inhibited cocaine, but not heroin, self-administration, whereas optogenetic activation of SNr GABA neurons caused a robust increase in heroin self-administration with an extinction pattern, suggesting a compensatory response in drug intake due to reduced heroin reward. In addition, activation of SNr GABA neurons attenuated heroin-primed, but not cue-induced, reinstatement of drug-seeking behavior, whereas inhibition of SNr GABA neurons produced optical intracranial self-stimulation and place preference. Together, these findings suggest that MORs on GABA neurons in the SNr play more important roles in opioid reward and relapse than MORs on VTA GABA neurons.SIGNIFICANCE STATEMENT Opioid reward has long been believed to be mediated by inhibition of GABA interneurons in the VTA that subsequently leads to disinhibition of DA neurons. In this study, we found that more μ opioid receptors (MORs) are expressed in GABA neurons in the neighboring SNr than in the VTA, and that pharmacological blockade of MORs in the SNr is more effective in reducing heroin reward than blockade of MORs in the VTA. Furthermore, optogenetic activation of VTA GABA neurons inhibited cocaine, but not heroin, self-administration, whereas activation of SNr GABA neurons inhibited heroin reward and relapse. These findings suggest that opioid reward is more likely mediated by stimulation of MORs in GABA afferents from other brain regions than in VTA GABA neurons.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}