Destabilization of fear memory by Rac1-driven engram-microglia communication in hippocampus.

Rac1 is a key regulator of the cytoskeleton and neuronal plasticity, and is known to play a critical role in psychological and cognitive brain disorders. To elucidate the engram specific Rac1 signaling in fear memory, a doxycycline (Dox)-dependent robust activity marking (RAM) system was used to label dorsal dentate gyrus (DG) engram cells in mice during contextual fear conditioning. Rac1 mRNA and protein levels in DG engram cells were peaked at 24 h (day 1) after fear conditioning and were more abundant in the fear engram cells than in the non-engram cells. Optogenetic activation of Rac1 in a temporal manner in DG engram cells before memory retrieval decreased the freezing level in the fear context. Optogenetic activation of Rac1 increased autophagy protein 7 (ATG7) expression in the DG engram cells and activated DG microglia. Microglia-specific transcriptomics and fluorescence in situ hybridization revealed that overexpression of ATG7 in the fear engram cells upregulated the mRNA of Toll-like receptor TLR2/4 in DG microglia. Knockdown of microglial TLR2/4 rescued fear memory destabilization induced by ATG7 overexpression or Rac1 activation in DG engram cells. These results indicate that Rac1-driven communications between engram cells and microglia contributes to contextual fear memory destabilization, and is mediated by ATG7 and TLR2/4, and suggest a novel mechanistic framework for the cytoskeletal regulator in fear memory interference.

Accumulation of NMDA receptors in accumbal neuronal ensembles mediates increased conditioned place preference for cocaine after prolonged withdrawal.

Cue-induced cocaine craving gradually intensifies following abstinence, a phenomenon known as the incubation of drug craving. Neuronal ensembles activated by initial cocaine use, are critically involved in this process. However, the mechanisms by which neuronal changes occurring in the ensembles after withdrawal contribute to incubation remain largely unknown. Here we labeled neuronal ensembles in the shell of nucleus accumbens (NAcSh) activated by cocaine conditioned place preference (CPP) training. NAcSh ensembles showed an increasing activity induced by CPP test after 21-day withdrawal. Inhibiting synaptic transmission of NAcSh ensembles suppressed the preference for cocaine paired-side after 21-day withdrawal, demonstrating a critical role of NAcSh ensembles in increased preference for cocaine. The density of dendritic spines in dopamine D1 receptor expressing ensembles was increased after 21-day withdrawal. Moreover, the expression of Grin1, a subunit of the N-methyl-D-aspartate (NMDA) receptor, specifically increased in the NAcSh ensembles after cocaine withdrawal in both CPP and self-administration (SA) mouse models. Targeted knockdown or dysfunction of Grin1 in NAcSh ensembles significantly suppressed craving for cocaine. Our results suggest that the accumulation of NMDA receptors in NAcSh ensembles mediates increased craving for cocaine after prolonged withdrawal, thereby providing potential molecular targets for treatment of drug addiction.

Transcriptomic effects of paternal cocaine-seeking on the reward circuitry of male offspring.

It has been previously established that paternal development of a strong incentive motivation for cocaine can predispose offspring to develop high cocaine-seeking behavior, as opposed to sole exposure to the drug that results in drug resistance in offspring. However, the adaptive changes of the reward circuitry have not been fully elucidated. To infer the key nuclei and possible hub genes that determine susceptibility to addiction in offspring, rats were randomly assigned to three groups, cocaine self-administration (CSA), yoked administration (Yoke), and saline self-administration (SSA), and used to generate F1. We conducted a comprehensive transcriptomic analysis of the male F1 offspring across seven relevant brain regions, both under drug-naïve conditions and after cocaine self-administration. Pairwise differentially expressed gene analysis revealed that the orbitofrontal cortex (OFC) exhibited more pronounced transcriptomic changes in response to cocaine exposure, while the dorsal hippocampus (dHip), dorsal striatum (dStr), and ventral tegmental area (VTA) exhibited changes that were more closely associated with the paternal voluntary cocaine-seeking behavior. Consistently, these nuclei showed decreased dopamine levels, elevated neuronal activation, and elevated between-nuclei correlations, indicating dopamine-centered rewiring of the midbrain circuit in the CSA offspring. To determine if possible regulatory cascades exist that drive the expression changes, we constructed co-expression networks induced by paternal drug addiction and identified three key clusters, primarily driven by transcriptional factors such as MYT1L, POU3F4, and NEUROD6, leading to changes of genes regulating axonogenesis, synapse organization, and membrane potential, respectively. Collectively, our data highlight vulnerable neurocircuitry and novel regulatory candidates with therapeutic potential for disrupting the transgenerational inheritance of vulnerability to cocaine addiction.

Paternal cocaine-seeking motivation defines offspring's vulnerability to addiction by down-regulating GABAergic GABRG3 in the ventral tegmental area.

Epidemiological investigations indicate that parental drug abuse experiences significantly influenced the addiction vulnerability of offspring. Studies using animal models have shown that paternal cocaine use and highly motivated drug-seeking behavior are important determinants of offspring addiction susceptibility. However, the key molecules contributing to offspring addiction susceptibility are currently unclear. The motivation for cocaine-seeking behavior in offspring of male rats was compared between those whose fathers self-administered cocaine (SA) and those who were yoked with them and received non-contingent cocaine administrations (Yoke). We found that paternal experience with cocaine-seeking behavior, but not direct cocaine exposure, could lead to increased lever-pressing behavior in male F1 offspring. This effect was observed without significant changes to the dose-response relationship. The transcriptomes of ventral tegmental area (VTA) in offspring were analyzed under both naive state and after self-administration training. Specific transcriptomic changes in response to paternal cocaine-seeking experiences were found, which mainly affected biological processes such as synaptic connections and receptor signaling pathways. Through joint analysis of these candidate genes and parental drug-seeking motivation scores, we found that gamma-aminobutyric acid receptor subunit gamma-3 (Gabrg3) was in the hub position of the drug-seeking motivation-related module network and highly correlated with parental drug-seeking motivation scores. The downregulation of Gabrg3 expression, caused by paternal motivational cocaine-seeking, mainly occurred in GABAergic neurons in the VTA. Furthermore, down-regulating GABAergic Gabrg3 in VTA resulted in an increase in cocaine-seeking behavior in the Yoke F1 group. This down-regulation also reduced transcriptome differences between the Yoke and SA groups, affecting processes related to synaptic formation and neurotransmitter transmission. Taken together, we propose that paternal cocaine-seeking behavior, rather than direct drug exposure, significantly influences offspring addiction susceptibility through the downregulation of Gabrg3 in GABAergic neurons of the VTA, highlighting the importance of understanding specific molecular pathways in the intergenerational inheritance of addiction vulnerability.

O-GlcNAcylation mediates H2O2-induced apoptosis through regulation of STAT3 and FOXO1.

The O-linked-ß-N-acetylglucosamine (O-GlcNAc) glycosylation (O-GlcNAcylation) is a critical post-translational modification that couples the external stimuli to intracellular signal transduction networks. However, the critical protein targets of O-GlcNAcylation in oxidative stress-induced apoptosis remain to be elucidated. Here, we show that treatment with H2O2 inhibited O-GlcNAcylation, impaired cell viability, increased the cleaved caspase 3 and accelerated apoptosis of neuroblastoma N2a cells. The O-GlcNAc transferase (OGT) inhibitor OSMI-1 or the O-GlcNAcase (OGA) inhibitor Thiamet-G enhanced or inhibited H2O2-induced apoptosis, respectively. The total and phosphorylated protein levels, as well as the promoter activities of signal transducer and activator of transcription factor 3 (STAT3) and Forkhead box protein O 1 (FOXO1) were suppressed by OSMI-1. In contrast, overexpressing OGT or treating with Thiamet-G increased the total protein levels of STAT3 and FOXO1. Overexpression of STAT3 or FOXO1 abolished OSMI-1-induced apoptosis. Whereas the anti-apoptotic effect of OGT and Thiamet-G in H2O2-treated cells was abolished by either downregulating the expression or activity of endogenous STAT3 or FOXO1. These results suggest that STAT3 or FOXO1 are the potential targets of O-GlcNAcylation involved in the H2O2-induced apoptosis of N2a cells.

Targeting mitochondrial dynamics of morphine-responsive dopaminergic neurons ameliorates opiate withdrawal.

Converging studies demonstrate the dysfunction of the dopaminergic neurons following chronic opioid administration. However, the therapeutic strategies targeting opioid-responsive dopaminergic ensembles that contribute to the development of opioid withdrawal remain to be elucidated. Here, we used the neuronal activity-dependent Tet-Off system to label dopaminergic ensembles in response to initial morphine exposure (Mor-Ens) in the ventral tegmental area (VTA). Fiber optic photometry recording and transcriptome analysis revealed downregulated spontaneous activity and dysregulated mitochondrial respiratory, ultrastructure, and oxidoreductase signal pathways after chronic morphine administration in these dopaminergic ensembles. Mitochondrial fragmentation and the decreased mitochondrial fusion gene mitofusin 1 (Mfn1) were found in these ensembles after prolonged opioid withdrawal. Restoration of Mfn1 in the dopaminergic Mor-Ens attenuated excessive oxidative stress and the development of opioid withdrawal. Administration of Mdivi-1, a mitochondrial fission inhibitor, ameliorated the mitochondrial fragmentation and maladaptation of the neuronal plasticity in these Mor-Ens, accompanied by attenuated development of opioid withdrawal after chronic morphine administration, without affecting the analgesic effect of morphine. These findings highlighted the plastic architecture of mitochondria as a potential therapeutic target for opioid analgesic-induced substance use disorders.

Morphine- and foot shock-responsive neuronal ensembles in the VTA possess different connectivity and biased GPCR signaling pathway.

Background: Neurons in the ventral tegmental area (VTA) are sensitive to stress and their maladaptation have been implicated in the psychiatric disorders such as anxiety and addiction, etc. The cellular properties of the VTA neurons in response to different stressors related to different emotional processing remain to be investigated. Methods: By combining immediate early gene (IEG)-dependent labeling, rabies virus tracing, ensemble-specific transcriptomic analysis and fiber photometry recording in the VTA of male mice, the spatial distribution, brain-wide connectivity and cellular signaling pathways in the VTA neuronal ensembles in response to morphine (Mor-Ens) or foot shock (Shock-Ens) stimuli were investigated. Results: Optogenetic activation of the Mor-Ens drove approach behavior, whereas chemogenetic activation of the Shock-Ens increased the anxiety level in mice. Mor-Ens were clustered and enriched in the ventral VTA, contained a higher proportion of dopaminergic neurons, received more inputs from the dorsal medial striatum and the medial hypothalamic zone, and exhibited greater axonal arborization in the zona incerta and ventral pallidum. Whereas Shock-Ens were more dispersed, contained a higher proportion of GABAergic neurons, and received more inputs from the ventral pallidum and the lateral hypothalamic area. The downstream targets of the G protein and ß-arrestin pathways, PLCß3 and phosphorylated AKT1Thr308, were relatively enriched in the Mor-Ens and Shock-Ens, respectively. Cariprazine, the G-protein-biased agonist for the dopamine D2 receptor, increased the response of Mor-Ens to sucrose water and decreased the anxiety-like behavior during morphine withdrawal, whereas the ß-arrestin-biased agonist UNC9994 decreased the response of Shock-Ens to tail suspension. Conclusions: Taken together, these findings reveal the heterogeneous connectivity and signaling pathways of the VTA neurons in response to morphine and foot shock, providing new insights for development of specific interventions for psychiatric disorders caused by various stressors associated with different VTA neuronal functions.

Cellular and molecular basis of drug addiction: The role of neuronal ensembles in addiction.

Addiction has been conceptualized as a disease of learning and memory. Learned associations between environmental cues and unconditioned rewards induced by drug administration, which play a critical role in addiction, have been shown to be encoded in sparsely distributed populations of neurons called neuronal ensembles. This review aims to highlight how synaptic remodeling and alterations in signaling pathways that occur specifically in neuronal ensembles contribute to the pathogenesis of addiction. Furthermore, a causal link between transcriptional and epigenetic modifications in neuronal ensembles and the development of the addictive state is proposed. Translational studies of molecular and cellular changes in neuronal ensembles that contribute to drug-seeking behavior, will allow the identification of molecular and circuit targets and interventions for substance use disorders.

Enhanced heroin analgesic effect in male offspring of sires who self-administered heroin.

Introduction: A growing body of evidence suggests that parental substance abuse, even prior to conception, may induce phenotypic changes in offspring. Parental opioid exposure has been shown to affect developmental processes, induce memory deficits, and lead to psycho-emotional disorders in offspring. However, how parental, especially paternal, chronic drug exposure affects offspring remains unexplored. Methods: Adult male rats were subjected to 31 days of heroin self-administration followed by mating with naïve females. Litter size and body weight of F1 offspring were recorded. Object-based attention tests, cocaine self-administration tests, and hot plate tests were used to test for potential effects of chronic paternal heroin seeking on cognition, reward, or analgesic sensitivity in the offspring. Results: Body weight and litter size of the heroin F1 generation were not altered compared to the saline F1 generation. Furthermore, paternal chronic heroin self-administration experience had no significant effect on object-based attention tests or cocaine self-administration behavior in either sex. However, in the hot plate test, although no difference in basal latency was found between the two groups in either sex, a significant increase in the analgesic effect of heroin was observed in the male heroin F1 generation. Conclusions: Taken together, these data provide evidence that paternal chronic heroin self-administration experience could sex-dimorphically increase the analgesic effect of heroin in male offspring, but had no significant effect on response to cocaine reinforcement or attentional behavior.

Persistent increase of accumbens cocaine ensemble excitability induced by IRK downregulation after withdrawal mediates the incubation of cocaine craving.

The incubation phenomenon, cue-induced drug craving progressively increasing over prolonged withdrawal, accounts for persistent relapse, leading to a dilemma in the treatment of cocaine addiction. The role of neuronal ensembles activated by initial cocaine experience in the incubation phenomenon was unclear. In this study, with cocaine self-administration (SA) models, we found that neuronal ensembles in the nucleus accumbens shell (NAcSh) showed increasing activation induced by cue-induced drug-seeking after 30-day withdrawal. Inhibition or activation of NAcSh cocaine-ensembles suppressed or promoted craving for cocaine, demonstrating a critical role of NAcSh cocaine-ensembles in incubation for cocaine craving. NAcSh cocaine-ensembles showed a specific increase of membrane excitability and a decrease of inward rectifying channels Kir2.1 currents after 30-day withdrawal. Overexpression of Kir2.1 in NAcSh cocaine-ensembles restored neuronal membrane excitability and suppressed cue-induced drug-seeking after 30-day withdrawal. Expression of dominant-negative Kir2.1 in NAcSh cocaine-ensembles enhanced neuronal membrane excitability and accelerated incubation of cocaine craving. Our results provide a cellular mechanism that the downregulation of Kir2.1 functions in NAcSh cocaine-ensembles induced by prolonged withdrawal mediates the enhancement of ensemble membrane excitability, leading to incubation of cocaine craving.

A distinct D1-MSN subpopulation down-regulates dopamine to promote negative emotional state.

Dopamine (DA) level in the nucleus accumbens (NAc) is critical for reward and aversion encoding. DA released from the ventral mesencephalon (VM) DAergic neurons increases the excitability of VM-projecting D1-dopamine receptor-expressing medium spiny neurons (D1-MSNs) in the NAc to enhance DA release and augment rewards. However, how such a DA positive feedback loop is regulated to maintain DA homeostasis and reward-aversion balance remains elusive. Here we report that the ventral pallidum (VP) projection of NAc D1-MSNs (D1NAc-VP) is inhibited by rewarding stimuli and activated by aversive stimuli. In contrast to the VM projection of D1-MSN (D1NAc-VM), activation of D1NAc-VP projection induces aversion, but not reward. D1NAc-VP MSNs are distinct from the D1NAc-VM MSNs, which exhibit conventional functions of D1-MSNs. Activation of D1NAc-VP projection stimulates VM GABAergic transmission, inhibits VM DAergic neurons, and reduces DA release into the NAc. Thus, D1NAc-VP and D1NAc-VM MSNs cooperatively control NAc dopamine balance and reward-aversion states.

Morphine coordinates SST and PV interneurons in the prelimbic cortex to disinhibit pyramidal neurons and enhance reward.

Opioids, such as morphine, are clinic analgesics which induce euphoria. Morphine exposure modifies the excitability and functional interactions between neurons, while the underlying cellular and molecular mechanisms, especially how morphine assembles heterogeneous interneurons (INs) in prelimbic cortex (PrL) to mediate disinhibition and reward, are not clear. Using approaches of optogenetics, electrophysiology, and cell type-specific RNA-seq, we show that morphine attenuates the inhibitory synaptic transmission from parvalbumin+ (PV)-INs onto pyramidal neurons in PrL via µ-opioid receptor (MOR) in PV-INs. Meanwhile, morphine enhances the inhibitory inputs from somatostatin+ (SST)-INs onto PV-INs, and thus disinhibits pyramidal neurons via δ-opioid receptor (DOR)-dependent Rac1 upregulation in SST-INs. We show that MOR in PV-INs is required for morphine-induced behavioral sensitization, while DOR as well as Rac1 activity in SST-INs is required for morphine-induced conditioned place preference and hyper-locomotion. These results reveal that SST- and PV-INs, functioning in PrL as a disinhibitory architecture, are coordinated by morphine via different opioid receptors to disinhibit pyramidal neurons and enhance reward.

Retrieval-Driven Hippocampal NPTX2 Plasticity Facilitates the Extinction of Cocaine-Associated Context Memory.

BACKGROUND: Postretrieval extinction attenuates the pathological memory associated with psychiatric states such as drug addiction in both humans and rodents. The extinction of a learned response requires gene transcription and protein synthesis after memory retrieval in a time-dependent manner, yet the precise physiological basis after retrieval to allow extinction to neutralize a learned behavior is not fully understood. METHODS: In a cocaine conditioned place preference paradigm, we used a ribosomal tagging strategy to measure the translational state of hippocampal pyramidal neurons after the retrieval of cocaine-associated context memory. Using approaches of electrophysiology, neuronal tracing, and a doxycycline-dependent robust activity marking system, we investigated the cellular and molecular basis of retrieval-induced plasticity that facilitated the extinction. RESULTS: Bioinformatics analysis discovered the specific translational regulation of signaling pathways by retrieval and revealed Nptx2 as the hub gene. Manipulating Nptx2 in dorsal hippocampus bidirectionally regulated the extinction of cocaine-associated context memory as well as the retrieval-driven synaptic remodeling. The pentraxin (PTX) domain of NPTX2 recruited GluA1-AMPA receptors and enhanced the extinction and excitatory synaptic transmission that was prevented by overexpressing carboxyl cytoplasmic tail of GluA1. Furthermore, Nptx2 in retrieval-activated neurons was required for the extinction. CONCLUSIONS: The retrieval-driven upregulation of Nptx2 contributes to the synaptic remodeling in dorsal hippocampus and facilitates the extinction of cocaine-associated context memory, indicating a potential target for the treatment of cue-induced cocaine seeking.

Retrieval-Induced Upregulation of Tet3 in Pyramidal Neurons of the Dorsal Hippocampus Mediates Cocaine-Associated Memory Reconsolidation.

Background: Memory retrieval refers to reexposure to information previously encoded and stored in the brain. Following retrieval, a once-consolidated memory destabilizes and undergoes reconsolidation, during which gene expression changes to restabilize memory. Investigating epigenetic regulation during reconsolidation could provide insights into normal memory formation and pathological memory associated with psychiatric disorders. Methods: We used cocaine-induced conditioned place preference to assess the cocaine-associated memory of mice and used chemogenetic methods to manipulate the activity of the pyramidal neurons in the dorsal hippocampus. We isolated the ribosome-associated transcripts from the excitatory neurons in the dorsal hippocampus by RiboTag purification to identify the potential epigenetic regulators, and we specifically knocked down gene expression in pyramidal neurons with a Cre-dependent lentivirus. Results: Chemogenetically silencing the activity of the pyramidal neurons in the dorsal hippocampus immediately after memory retrieval markedly impaired memory reconsolidation, and the ribosome-associated mRNA level of the ten-eleven translocation (Tet) family methylcytosine dioxygenase Tet3, but not Tet1 or Tet2, was dramatically upregulated 10 minutes after memory retrieval. The protein level of Tet3 in the dorsal hippocampus but not in the anterior cingulate cortex was dramatically increased 1 hour after memory retrieval. Specifically, knockdown of Tet3 in pyramidal neurons in the dorsal hippocampus decreased the activation of pyramidal neurons and impaired the reconsolidation of cocaine-associated memory. Conclusions: Our findings highlight the new function of the DNA demethylation regulator Tet3 in pyramidal neurons of the dorsal hippocampus in regulating the reconsolidation of cocaine-associated memory.

Binge-Like Sucrose Self-Administration Experience Inhibits Cocaine and Sucrose Seeking Behavior in Offspring.

Recent studies show that emotional and environmental stimuli promote epigenetic inheritance and influence behavioral development in the subsequent generations. Caloric mal- and under-nutrition has been shown to cause metabolic disturbances in the subsequent generation, but the incentive properties of paternal binge-like eating in offspring is still unknown. Here we show that paternal sucrose self-administration experience could induce inter-generational decrease in both sucrose and cocaine-seeking behavior, and sucrose responding in F1 rats, but not F2, correlated with the performance of F0 rats in sucrose self-administration. Higher anxiety level and decreased cocaine sensitivity were observed in Sucrose F1 compared with Control F1, possibly contributing to the desensitization phenotype in cocaine and sucrose self-administration. Our study revealed that paternal binge-like sucrose consumption causes decrease in reward seeking and induces anxiety-like behavior in the F1 offspring.

Drug-seeking motivation level in male rats determines offspring susceptibility or resistance to cocaine-seeking behaviour.

Liability to develop drug addiction is heritable, but the precise contribution of non-Mendelian factors is not well understood. Here we separate male rats into addiction-like and non-addiction-like groups, based on their incentive motivation to seek cocaine. We find that the high incentive responding of the F0 generation could be transmitted to F1 and F2 generations. Moreover, the inheritance of high incentive response to cocaine is contingent on high motivation, as it is elicited by voluntary cocaine administration, but not high intake of cocaine itself. We also find DNA methylation differences between sperm of addiction-like and non-addiction-like groups that were maintained from F0 to F1, providing an epigenetic link to transcriptomic changes of addiction-related signalling pathways in the nucleus accumbens of offspring. Our data suggest that highly motivated drug seeking experience may increase vulnerability and/or reduce resistance to drug addiction in descendants.

MiR-218 targets MeCP2 and inhibits heroin seeking behavior.

MicroRNAs (miRNAs) are a class of evolutionarily conserved, 18-25 nucleotide non-coding sequences that post-transcriptionally regulate gene expression. Recent studies implicated their roles in the regulation of neuronal functions, such as learning, cognition and memory formation. Here we report that miR-218 inhibits heroin-induced behavioral plasticity. First, network propagation-based method was used to predict candidate miRNAs that played potential key roles in regulating drug addiction-related genes. Microarray screening was also carried out to identify miRNAs responding to chronic heroin administration in the nucleus accumbens (NAc). Among the collapsed miRNAs, top-ranked miR-218 was decreased after chronic exposure to heroin. Lentiviral overexpression of miR-218 in NAc could inhibit heroin-induced reinforcement in both conditioned place preference (CPP) test and heroin self-administration experiments. Luciferase activity assay indicated that miR-218 could regulate 3' untranslated regions (3' UTR) of multiple neuroplasticity-related genes and directly target methyl CpG binding protein 2 (Mecp2). Consistently, Mecp2308/y mice exhibited reduced heroin seeking behavior in CPP test. These data reveal a functional role of miR-218 and its target, MeCP2, in the regulation of heroin-induced behavioral plasticity.

GRK6 regulates ROS response and maintains hematopoietic stem cell self-renewal.

G protein-coupled receptor kinases (GRKs) are critically involved in immune response through regulation of cytokine receptors in mature leukocytes, but their role in hematopoiesis is largely unknown. Here, we demonstrate that GRK6 knockout (GRK6-/-) mice exhibit lymphocytopenia, loss of the hematopoietic stem cell (HSC) and multiple progenitor populations. GRK6 deficiency leads to compromised lymphoid differentiation, largely owing to the impairment of HSC self-renewal. Transcriptome and proteomic analysis suggest that GRK6 is involved in reactive oxygen species signaling. GRK6 could interact with DNA-PKcs (DNA-dependent protein kinase, catalytic subunit) and regulate its phosphorylation. Moreover, reactive oxygen species scavenger α-lipoic acid administration could partially rescue the loss of HSC in GRK6-/- mice. Our work demonstrates the importance of GRK6 in regulation of HSC self-renewal and reveals its potential role in participation of stress response.

[Sucrose reward promotes rats' motivation for cocaine].

Caloric diet, such as fat and sugar intake, has rewarding effects, and has been indicated to affect the responses to addictive substances in animal experiments. However, the possible association between sucrose reward and the motivation for addictive drugs remains to be elucidated. Thus, we carried out behavioral tests after sucrose self-administration training to determine the effects of sucrose experience on rats' motivation for cocaine, locomotor sensitivity to cocaine, basal locomotor activity, anxiety level, and associative learning ability. The sucrose-experienced (sucrose) group exhibited higher lever press, cocaine infusion and break point, as well as upshift of cocaine dose-response curve in cocaine self-administration test, as compared with the control (chow) group. Additionally, despite similar locomotor activity in open field test and comparable score in cocaine-induced conditioned place preference, the sucrose group showed higher cocaine-induced locomotor sensitivity as compared with the chow group. The anxiety level and the performance in vocal-cue induced fear memory were similar between these two groups in elevated plus maze and fear conditioning tests, respectively. Taken together, our work indicates that sucrose experience promotes the rats' motivation for cocaine.

Astroglial ß-Arrestin1-mediated Nuclear Signaling Regulates the Expansion of Neural Precursor Cells in Adult Hippocampus.

Adult hippocampal neurogenesis is crucial for preserving normal brain function, but how it is regulated by niche cells is uncertain. Here we show that ß-arrestin 1 (ß-arr1) in dentate gyrus (DG) regulates neural precursor proliferation. ß-arr1 knockout (KO) mice show reduced neural precursor proliferation in subgranular zone (SGZ) which could be rescued by selective viral expression of ß-arr1 but not its nuclear-function-deficient mutants under control of hGFAP promotor in DG. Compared with wild type astrocytes, ß-arr1 KO astrocytes nurture less neurospheres, and this may be attributed to changed activity of soluble, heat-sensitive excretive factors, such as BMP2. RNA-sequencing reveals that ß-arr1 KO DG astrocytes exhibit an aberrant gene expression profile of niche factors, including elevated transcription of Bmp2. Taken together, our data suggest that ß-arr1 mediated nuclear signaling regulates the production of excretive factors derived from niche astrocytes and expansion of neural precursors in DG, thus maintaining homeostasis of adult hippocampal neurogenesis.