Jian-Feng Liu

Basolateral Amygdala Cdk5 Activity Mediates Consolidation and Reconsolidation of Memories for Cocaine Cues

Cocaine use and relapse involves learned associations between cocaine-associated environmental contexts and discrete stimuli and cocaine effects. Initially, these contextual and discrete cues undergo memory consolidation after being paired with cocaine exposure. During abstinence, cocaine cue memories can undergo memory reconsolidation after cue exposure without the drug. We used a conditioned place preference (CPP) procedure in rats to study the role of neuronal protein kinase cyclin-dependent kinase 5 (Cdk5) in consolidation and reconsolidation of cocaine cue memories. We found that the expression of cocaine CPP in drug-free tests 1 d after CPP training (four pairings of 10 mg/kg cocaine with one context and four pairings of saline with a different context) increased Cdk5 activity, and levels of the Cdk5 activator p35 in basolateral but not central amygdala. We also found that basolateral (but not central) amygdala injections of the Cdk5 inhibitor β-butyrolactone (100 ng/side) immediately (but not 6 h) after cocaine–context pairings during training prevented subsequent cocaine CPP expression. After training, acute basolateral (but not central) amygdala β-butyrolactone injections immediately before testing prevented the expression of cocaine CPP; this effect was also observed on a second test performed 1 d later, suggesting an effect on reconsolidation of cocaine cue memories. In support, basolateral β-butyrolactone injections, given immediately (but not 6 h) after a single exposure to the cocaine-paired context, prevented cocaine CPP expression 1 and 14 d after the injections. Results indicate that basolateral amygdala Cdk5 activity is critical for consolidation and reconsolidation of the memories of cocaine-associated environmental cues.

Depletion of Perineuronal Nets in the Amygdala to Enhance the Erasure of Drug Memories

Extinction therapy has been suggested to suppress the conditioned motivational effect of drug cues to prevent relapse. However, extinction forms a new inhibiting memory rather than erasing the original memory trace and drug memories invariably return. Perineuronal nets (PNNs) are a specialized extracellular matrix around interneurons in the brain that have been suggested to be a permissive factor that allows synaptic plasticity in the adolescent brain. The degradation of PNNs caused by chondroitinase ABC (ChABC) may generate induced juvenile-like plasticity (iPlasticity) and promote experience-dependent plasticity in the adult brain. In the present study, we investigated the effect of removing PNNs in the amygdala of rat on the extinction of drug memories. We found that extinction combined with intra-amygdala injections of ChABC (0.01 U/side) prevented the subsequent priming-induced reinstatement of morphine-induced and cocaine-induced, but not food -induced, conditioned place preference (CPP). Intra-amygdala injections of ChABC alone had no effect on the retention, retrieval, or relearning of morphine-induced CPP and storage of acquired food-induced CPP. Moreover, we found that the procedure facilitated the extinction of heroin- and cocaine-seeking behavior and prevented the spontaneous recovery and drug-induced reinstatement of heroin- and cocaine-seeking behavior. We also found that the effect of PNNs degradation combined with extinction may be mediated by the potentiation of several plasticity-related proteins in the amygdala. Altogether, our findings demonstrate that a combination of extinction training with PNNs degradation in the amygdala erases drug memories and suggest that ChABC may be an attractive candidate for the prevention of relapse.

Predictable chronic mild stress in adolescence increases resilience in adulthood.

Stress in adolescence has been widely demonstrated to have a lasting impact in humans and animal models. Developmental risk and protective factors play an important role in the responses to stress in adulthood. Mild-to-moderate stress in adolescence may resist the negative impacts of adverse events in adulthood. However, little research on resilience has been conducted. In this study, we used a predictable chronic mild stress (PCMS) procedure (5 min of daily restraint stress for 28 days) in adolescent rats (postnatal days (PNDs) 28–55) to test the resilience effect of PCMS on depressive-like behavior in the sucrose preference test and forced swim test and anxiety-like behavior in the novelty-suppressed feeding test and elevated plus maze in adulthood. We also investigated the role of mammalian target of rapamycin (mTOR) signaling in the brain during the PCMS procedure in adolescence. Moreover, we investigated the effect of PCMS in adolescence on subsequent responses to chronic unpredictable stress (CUS; PNDs 63–83) in adulthood. The results demonstrated that PCMS during adolescence produced antidepressant- and anxiolytic-like effects and increased mTOR signaling activity in the prefrontal cortex in early adulthood. Either systemic administration or intra-PFC infusion of the mTOR inhibitor rapamycin completely blocked the behavioral effects produced by PCMS in adolescence. PCMS during adolescence resisted depressive- and anxiety-like behavior caused by CUS in adulthood. These findings indicate that PCMS in adolescence can contribute to resilience against depression and anxiety caused by stress in adulthood.

PKMζ maintains drug reward and aversion memory in the basolateral amygdala and extinction memory in the infralimbic cortex.

The intense associative memories that develop between drug-paired contextual cues and rewarding stimuli or the drug withdrawal-associated aversive feeling have been suggested to contribute to the high rate of relapse. Various studies have elucidated the mechanisms underlying the formation and expression of drug-related cue memories, but how this mechanism is maintained is unknown. Protein kinase M ζ (PKMζ) was recently shown to be necessary and sufficient for long-term potentiation maintenance and memory storage. In the present study, we used conditioned place preference (CPP) and aversion (CPA) to examine whether PKMζ maintains both morphine-associated reward memory and morphine withdrawal-associated aversive memory in the basolateral amygdala (BLA). We also investigate the role of PKMζ in the infralimbic cortex in the extinction memory of morphine reward-related cues and morphine withdrawal-related aversive cues. We found that intra-BLA but not central nucleus of the amygdala injection of the selective PKMζ inhibitor ZIP 1 day after CPP and CPA training impaired the expression of CPP and CPA 1 day later, and the effect of ZIP on memory lasted at least 2 weeks. Inhibiting PKMζ activity in the infralimbic cortex, but not prelimbic cortex, disrupted the expression of the extinction memory of CPP and CPA. These results indicate that PKMζ in the BLA is required for the maintenance of associative morphine reward memory and morphine withdrawal-associated aversion memory, and PKMζ in the infralimbic cortex is required for the maintenance of extinction memory of morphine reward-related cues and morphine withdrawal-related aversive cues.

PI3K/Akt Signaling Pathway in the Basolateral Amygdala Mediates the Rapid Antidepressant-like Effects of Trefoil Factor 3

Depression is one of the most common and debilitating psychiatric illnesses around the world, but the current antidepressants used to treat depression have many limitations. Progressively more studies have shown that neuropeptide systems are potential novel therapeutic targets for depression. However, whether the neuropeptide trefoil factor 3 (TFF3) participates in the development of depression has not been examined. In the current experiments, we assessed the antidepressant effects of TFF3 using the forced swim test (FST), tail suspension test (TST), and chronic mild stress (CMS) paradigm. Furthermore, we determined the mechanism that underlies the antidepressant-like effects of TFF3 in the rat FST. TFF3 dose-dependently reduced immobility time in both FST and TST. CMS elevated plasma TFF3 and decreased basolateral amygdala (BLA) TFF3 levels in rats, and acute TFF3 (0.1 mg/kg, i.p.) treatment reversed the depressive-like behaviors induced by CMS. Furthermore, TFF3 (0.1 mg/kg, i.p.) significantly increased Fos expression in the BLA, medial prefrontal cortex, and hypothalamus in rats subjected to the FST. Intra-BLA infusions of TFF3 (1 ng/side) exerted rapid antidepressant-like effects in the rat FST. Additionally, acute systemic TFF3 administration increased the level of phosphorylated-Akt (p-Akt) in the BLA. Finally, intra-BLA infusions of LY294002 (5 mM/side), a specific phosphatidylinositol 3-kinase (PI3K) inhibitor, significantly blocked the antidepressant-like effect of TFF3. Our results demonstrated that TFF3 exerts antidepressant-like effects that might be mediated by the PI3K/Akt signaling pathway in the BLA. These findings suggest a novel neuropeptide system target in the development of new antidepressants.

An Unconditioned Stimulus Retrieval Extinction Procedure to Prevent the Return of Fear Memory

BACKGROUND Conditioned fear memories can be updated by extinction during reconsolidation, and this effect is specific to the reactivated conditioned stimulus (CS). However, a traumatic event can be associated with several cues, and each cue can potentially trigger recollection of the event. We introduced a technique to target all diverse cues associated with an aversive event that causes fear. METHODS In human experiments, 161 subjects underwent modified fear conditioning, in which they were exposed to an unconditioned stimulus (US) or unreinforced CS to reactivate the memory and then underwent extinction, spontaneous recovery, and reinstatement. In animal experiments, 343 rats underwent contextual fear conditioning under a similar protocol as that used in the human experiments. We also explored the molecular alterations after US reactivation in rats. RESULTS Presentation of a lower intensity US before extinction disrupted the associations between the different CS and reactivated US in both humans and rats. This effect persisted for at least 6 months in humans and was selective to the reactivated US. This procedure was also effective for remote memories in both humans and rats. Compared with the CS, the US induced stronger endocytosis of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid glutamate receptors 1 and 2 and stronger activation of protein kinase A, p70S6 kinase, and cyclic adenosine monophosphate response element binding protein in the dorsal hippocampus in rats. CONCLUSIONS These findings demonstrate that a modified US retrieval extinction strategy may have a potential impact on therapeutic approaches to prevent the return of fear.

A novel UCS memory retrieval-extinction procedure to inhibit relapse to drug seeking.

We recently reported that a conditioned stimulus (CS) memory retrieval-extinction procedure decreases reinstatement of cocaine and heroin seeking in rats and heroin craving in humans. Here we show that non-contingent cocaine or methylphenidate injections (UCS retrieval) 1 h before the extinction sessions decreases cocaine-priming-induced reinstatement, spontaneous recovery, and renewal of cocaine seeking in rats. Unlike the CS-based memory retrieval-extinction procedure, the UCS memory retrieval manipulation decreases renewal and reinstatement of cocaine seeking in the presence of cocaine cues that were not present during extinction training and also decreases cocaine seeking when the procedure commences after 28 days of abstinence. The inhibitory effect of the UCS retrieval manipulation on cocaine-priming-induced reinstatement is mediated by regulation of AMPA-receptor endocytosis in the basolateral amygdala. The UCS memory retrieval-extinction procedure has superior relapse prevention characteristics than the CS memory retrieval-extinction procedure and could be a promising method for decreasing relapse in human addicts.

Glycine site N-methyl-d-aspartate receptor antagonist 7-CTKA produces rapid antidepressant-like effects in male rats

BACKGROUND Glutamate N-methyl-D-aspartate (NMDA) receptor antagonists exert fast-acting antidepressant effects, providing a promising way to develop a new classification of antidepressant that targets the glutamatergic system. In the present study, we examined the potential antidepressant action of 7-chlorokynurenic acid (7-CTKA), a glycine recognition site NMDA receptor antagonist, in a series of behavioural models of depression and determined the molecular mechanisms that underlie the behavioural actions of 7-CTKA. METHODS We administered the forced swim test, novelty-suppressed feeding test, learned helplessness paradigm and chronic mild stress (CMS) paradigm in male rats to evaluate the possible rapid antidepressant-like actions of 7-CTKA. In addition, we assessed phospho-glycogen synthase kinase-3β (p-GSK3β) level, mammalian target of rapamycin (mTOR) function, and postsynaptic protein expression in the medial prefrontal cortex (mPFC) and hippocampus. RESULTS Acute 7-CTKA administration produced rapid antidepressant-like actions in several behavioural tests. It increased p-GSK3β, enhanced mTOR function and increased postsynaptic protein levels in the mPFC. Activation of GSK3β by LY294002 completely blocked the antidepressant-like effects of 7-CTKA. Moreover, 7-CTKA did not produce rewarding properties or abuse potential. LIMITATIONS It is possible that 7-CTKA modulates glutamatergic transmission, thereby causing enduring alterations of GSK3β and mTOR signalling, although we did not provide direct evidence to support this possibility. Thus, the therapeutic involvement of synaptic adaptions engaged by 7-CTKA requires further study. CONCLUSION Our findings demonstrate that acute 7-CTKA administration produced rapid antidepressant-like effects, indicating that the behavioural response to 7-CTKA is mediated by GSK3β and mTOR signalling function in the mPFC.

eIF2α Dephosphorylation in Basolateral Amygdala Mediates Reconsolidation of Drug Memory

Maladaptive memories elicited by exposure to environmental stimuli associated with drugs of abuse are often responsible for relapse among addicts. Interference with the reconsolidation of drug memory can inhibit drug seeking. Previous studies have indicated that the dephosphorylation of the eukaryotic initiation factor 2 α-subunit (eIF2α) plays an important role in synaptic plasticity and long-term memory consolidation, but its role in the reconsolidation of drug memory remains unknown. The amygdala is required for the reconsolidation of a destabilized drug memory after retrieval of drug-paired stimuli. Here, we used conditioned place preference (CPP) and self-administration procedures to determine whether amygdala eIF2α dephosphorylation is required for the reconsolidation of morphine and cocaine memories in rats. We found that the levels of eIF2α phosphorylation (Ser51) and activating transcription factor 4 (ATF4) were decreased after reexposure to a previously morphine- or cocaine-paired context (i.e., a memory retrieval procedure) in the basolateral amygdala (BLA) but not in the central amygdala. Intra-BLA infusions of Sal003, a selective inhibitor of eIF2α dephosphorylation, immediately after memory retrieval disrupted the reconsolidation of morphine- or cocaine-induced CPP, leading to a long-lasting suppression of drug-paired stimulus-induced craving. Advanced knockdown of ATF4 expression in the BLA by lentivirus-mediated short-hairpin RNA blocked the disruption of the reconsolidation of morphine-induced CPP induced by Sal003 treatment. Furthermore, inhibition of eIF2α dephosphorylation in the BLA immediately after light/tone stimulus retrieval decreased subsequent cue-induced heroin-seeking behavior in the self-administration procedure. These results demonstrate that eIF2α dephosphorylation in the BLA mediates the memory reconsolidation of drug-paired stimuli.

Hippocampal CLOCK protein participates in the persistence of depressive-like behavior induced by chronic unpredictable stress

RationaleCircadian disturbances are strongly linked with major depression. The circadian proteins CLOCK and BMAL1 are abundantly expressed but function differently in the suprachiasmatic nucleus (SCN) and hippocampus. However, their roles in depressive-like behavior are still poorly understood.ObjectivesTo investigate the alterations of CLOCK and BMAL1 in the SCN and hippocampus in rats subjected to chronic unpredictable stress (CUS) and to explore the relationship of circadian protein and the depressive-like behavior.ResultsTogether with depressive-like behavior induced by CUS, CLOCK and BMAL1 in the SC were inhibited during the light period, and the peak expression of CLOCK in the hippocampus was shifted from the dark to light period. BMAL1 expression in the hippocampus was not significantly changed. Two weeks after the termination of CUS, abnormalities of CLOCK in the CA1 and CA3 endured, with unchanged depressive-like behavior, but the expression of CLOCK and BMAL1 in the SCN recovered to control levels. Knockdown of the Clock gene in CA1 induced depressive-like behavior in normal rats. CLOCK in the SCN and hippocampus may participate in the development of depressive-like behavior. However, CLOCK in the hippocampus but not SCN was involved in the long-lasting effects of CUS on depressive-like behavior. BMAL1 in the hippocampus appeared to be unrelated to the effects of CUS on depressive-like behavior.ConclusionCLOCK protein in the hippocampus but not SCN play an important role in the long-lasting depressive-like behavior induced by CUS. These findings suggest a novel therapeutic target in the development of new antidepressants focusing on the regulation of circadian rhythm.