Noradrenergic consolidation of social recognition memory is mediated by ß-arrestin-biased signaling in the mouse prefrontal cortex.

Social recognition memory (SRM) is critical for maintaining social relationships and increasing the survival rate. The medial prefrontal cortex (mPFC) is an important brain area associated with SRM storage. Norepinephrine (NE) release regulates mPFC neuronal intrinsic excitability and excitatory synaptic transmission, however, the roles of NE signaling in the circuitry of the locus coeruleus (LC) pathway to the mPFC during SRM storage are unknown. Here we found that LC-mPFC NE projections bidirectionally regulated SRM consolidation. Propranolol infusion and ß-adrenergic receptors (ß-ARs) or ß-arrestin2 knockout in the mPFC disrupted SRM consolidation. When carvedilol, a ß-blocker that can mildly activate ß-arrestin-biased signaling, was injected, the mice showed no significant suppression of SRM consolidation. The impaired SRM consolidation caused by ß1-AR or ß-arrestin2 knockout in the mPFC was not rescued by activating LC-mPFC NE projections; however, the impaired SRM by inhibition of LC-mPFC NE projections or ß1-AR knockout in the mPFC was restored by activating the ß-arrestin signaling pathway in the mPFC. Furthermore, the activation of ß-arrestin signaling improved SRM consolidation in aged mice. Our study suggests that LC-mPFC NE projections regulate SRM consolidation through ß-arrestin-biased ß-AR signaling.

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.

[ß-arrestin2 recruitment by ß-adrenergic receptor agonists and antagonists].

A large number of ß-adrenergic receptor (ß-AR) agonists and antagonists are widely used in the treatment of cardiovascular diseases and other diseases. Nonetheless, it remains unclear whether these commonly used ß-AR drugs can activate downstream ß- arrestin-biased signaling pathways. The objective of this study was to investigate ß-arrestin2 recruitment effects of ß-AR agonists and antagonists that were commonly used in clinical practice. We used TANGO (transcriptional activation following arrestin translocation) assay to detect the ß-arrestin2 recruitment by ß-AR ligands in HEK293 cell line (HTLA cells) stably transfected with tetracycline transactivator protein (tTA) dependent luciferase reporter and ß-arrestin2-TEV fusion gene. Upon activation of ß-AR by a ß-AR ligand, ß-arrestin2 was recruited to the C terminus of the receptor, followed by cleavage of the G protein-coupled receptors (GPCRs) fusion protein at the TEV protease-cleavage site. The cleavage resulted in the release of tTA, which, after being transported to the nucleus, activated transcription of the luciferase reporter gene. The results showed that ß-AR non-selective agonists epinephrine, noradrenaline and isoprenaline all promoted ß-arrestin2 recruitment at ß1-AR and ß2-AR. ß1-AR selective agonists dobutamine and denopamine both promoted ß-arrestin2 recruitment at ß1-AR. ß2-AR selective agonists procaterol and salbutamol promoted ß-arrestin2 recruitment at ß2-AR. ß-AR non-selective antagonists alprenolol and pindolol promoted ß-arrestin2 recruitment at ß1-AR. ß1-AR selective antagonists celiprolol and bevantolol showed ß-arrestin2 recruitment at ß1-AR. ß2-AR selective antagonists butoxamine showed ß-arrestin2 recruitment at ß1-AR. These results provide some clues for the potential action of ß-AR drugs, and lay a foundation for the screening of ß-arrestin-biased ß-AR ligands.

The Projection From Ventral CA1, Not Prefrontal Cortex, to Nucleus Accumbens Core Mediates Recent Memory Retrieval of Cocaine-Conditioned Place Preference.

Drug-paired cues inducing memory retrieval by expressing drug-seeking behaviors present a major challenge to drug abstinence. How neural circuits coordinate for drug memory retrieval remains unclear. Here, we report that exposure of the training chamber where cocaine-conditioned place preference (CPP) was performed increased neuronal activity in the core of nucleus accumbens (AcbC), ventral CA1 (vCA1), and medial prefrontal cortex (mPFC), as shown by elevated pERK and c-Fos levels. Chemogenetic inhibition of neuronal activity in the vCA1 and AcbC, but not mPFC, reduced the time spent in the cocaine-paired compartment, suggesting that the vCA1 and AcbC are required for the retrieval of cocaine-CPP memory and are key nodes recruited for cocaine memory storage. Furthermore, chemogenetic inhibition of the AcbC-projecting vCA1 neurons, but not the AcbC-projecting mPFC neurons, decreased the expression of cocaine-CPP. Optogenetic inhibition of the vCA1-AcbC projection, but not the mPFC-AcbC projection, also reduced the preference for the cocaine-paired compartment. Taken together, the cue-induced natural recall of cocaine memory depends on vCA1-AcbC circuits. The connectivity from the vCA1 to the AcbC may store the information of the cue-cocaine reward association critically required for memory retrieval. These data thus provide insights into the neural circuit basis of retrieval of drug-related memory.

ß-Arrestin-biased ß-adrenergic signaling promotes extinction learning of cocaine reward memory.

Extinction learning of cocaine-associated contextual cues can help prevent cocaine addicts from relapsing. Pharmacological manipulation of ß-adrenergic receptor (ß-AR) during extinction learning is being developed as a potential strategy to treat drug addiction. We demonstrated that the extinction learning of cocaine-associated memory was mediated by ß-arrestin2-biased but not heterotrimeric guanine nucleotide-binding protein (G protein)-dependent ß-adrenergic signaling. We found that administration of the nonbiased ß-AR antagonist propranolol, but not the G protein-biased ß-AR antagonist carvedilol, blocked extinction learning of cocaine-conditioned place preference and the associated ERK activation in the infralimbic prefrontal cortex. Overexpression of ß-arrestin2 in the infralimbic prefrontal cortex promoted extinction learning, which was blocked by propranolol. Knockout of ß-arrestin2 in the infralimbic prefrontal cortex, specifically in excitatory neurons, impaired extinction learning of cocaine-conditioned place preference, which was not rescued by carvedilol. ß-Arrestin2 signaling in infralimbic excitatory neurons was also required for the extinction learning in the cocaine self-administration model. Our results suggest that ß-arrestin-biased ß-adrenergic signaling in the infralimbic prefrontal cortex regulates extinction learning of cocaine-associated memories and could be therapeutically targeted to treat addiction.

Fear Conditioning Downregulates Rac1 Activity in the Basolateral Amygdala Astrocytes to Facilitate the Formation of Fear Memory.

Astrocytes are well known to scale synaptic structural and functional plasticity, while the role in learning and memory, such as conditioned fear memory, is poorly elucidated. Here, using pharmacological approach, we find that fluorocitrate (FC) significantly inhibits the acquisition of fear memory, suggesting that astrocyte activity is required for fear memory formation. We further demonstrate that fear conditioning downregulates astrocytic Rac1 activity in basolateral amygdala (BLA) in mice and promotes astrocyte structural plasticity. Ablation of astrocytic Rac1 in BLA promotes fear memory acquisition, while overexpression or constitutive activation of astrocytic Rac1 attenuates fear memory acquisition. Furthermore, temporal activation of Rac1 by photoactivatable Rac1 (Rac1-PA) induces structural alterations in astrocytes and in vivo activation of Rac1 in BLA astrocytes during fear conditioning attenuates the formation of fear memory. Taken together, our study demonstrates that fear conditioning-induced suppression of BLA astrocytic Rac1 activity, associated with astrocyte structural plasticity, is required for the formation of conditioned fear memory.