Probes for INS

Background A salient effect of addictive drugs is to hijack the dopamine reward system, an evolutionarily conserved driver of goal-directed behavior and learning. Reduced dopamine type-II receptor (D2R) availability in the striatum is an important pathophysiological mechanism for addiction that is both consequential and causal for other molecular, cellular, and neuronal network differences etiologic for this disorder. Here, we sought to identify gene expression changes attributable to innate low expression of the Drd2 gene in the striatum and specific to striatal indirect medium spiny neurons (iMSNs). Methods Cre-conditional, Translating Ribosome Affinity Purification (TRAP) was used to purify and analyze the translatome (ribosome-bound mRNA) of iMSNs from mice with low/heterozygous or wild-type Drd2 expression in iMSNs. Complementary electrophysiological recordings and gene expression analysis of postmortem brain tissue from human cocaine users were performed. Results Innate low expression of Drd2 in iMSNs led to differential expression of genes involved in GABA and cAMP signaling, neural growth, lipid metabolism, neural excitability, and inflammation. Creb1 was identified as a likely upstream regulator, among others. In human brain, expression of FXYD2, a modulatory subunit of the Na/K pump, was negatively correlated with DRD2 mRNA expression. In iMSN-TRAP-Drd2HET mice, increased Cartpt and reduced S100a10 (p11) expression recapitulated previous observations in cocaine paradigms. Electrophysiology experiments supported a higher GABA tone in iMSN-Drd2HET mice. Conclusion This study provides strong molecular evidence that in addiction inhibition by the indirect pathway is constitutively enhanced through neural growth and increased GABA signaling.

Background Over the course of chronic drug use, brain transcriptional neuroadaptation are thought to contribute to a change in drug use behavior over time. The function of the transcription factor CREB within the nucleus accumbens (NAc) has been well documented in opposing the rewarding properties of many classes of drugs, yet the gene targets through which CREB causally manifests these lasting neuroadaptations remain unknown. Here, we identify zinc finger protein 189 (Zfp189) as a CREB target gene that is transcriptionally responsive to acute and chronic cocaine use within mouse NAc. Methods To query the role of the CREB-Zfp189 interaction in cocaine use, we virally delivered modified CRISPR/dCas9 constructs, capable of selectively localizing CREB to the Zfp189 gene promoter in the NAc of mice. Results We observe that CREB binding to the Zfp189 promoter increases Zfp189 expression and diminishes the reinforcing responses to cocaine. We show further that NAc Zfp189 expression is increased within D1 medium spiny neurons (MSNs) in response to acute cocaine, but increased in both D1 and D2 MSNs in response to chronic cocaine. CREB-mediated induction of Zfp189 potentiates electrophysiological activity of D1 and D2 MSNs - recapitulating the known effect of CREB on these neurons. Lastly, targeting CREB to the Zfp189 promoter within NAc Drd2-expressing neurons, but not Drd1-expressing neurons, was sufficient to diminish cocaine-conditioned behaviors. Conclusions Together, these findings point to the CREB-Zfp189 interaction within NAc Drd2+ neurons as a molecular signature of chronic cocaine use that is causal in counteracting the reinforcing effects of cocaine.

Background The formation and retrieval of fear memories depends on orchestrated synaptic activity of neuronal ensembles within the hippocampus and it is becoming increasingly evident that astrocytes residing in the environment of these synapses play a central role in shaping cellular memory representations. Astrocyte distal processes, known as leaflets, fine-tune synaptic activity by clearing neurotransmitters and limiting glutamate diffusion. However, how astroglial synaptic coverage contributes to mnemonic processing of fearful experiences remains largely unknown. Methods We used electron microscopy to observe changes in astroglial coverage of hippocampal synapses during consolidation of fear memory in mice. To manipulate astroglial synaptic coverage, we depleted Ezrin, an integral leaflet-structural protein, from hippocampal astrocytes using CRISRP/Cas9 gene editing. Next, a combination of FRET analysis, genetically encoded glutamate sensors and whole-cell patch-clamp recordings was used to determine whether the proximity of astrocyte leaflets to the synapse is critical for synaptic integrity and function. Results We found that consolidation of a recent fear memory is accompanied by a transient retraction of astrocyte leaflets from hippocampal synapses and increased activation of NMDA-receptors. Accordingly, astrocyte-specific depletion of Ezrin resulted in shorter astrocyte leaflets and reduced astrocyte contact with the synaptic cleft, which consequently boosted extrasynaptic glutamate diffusion and NMDA-receptor activation. Importantly, after fear conditioning, these cellular phenotypes translated to increased retrieval-evoked activation of CA1 pyramidal neurons and enhanced fear memory expression. Conclusion Together, our data show that withdrawal of astrocyte leaflets from the synaptic cleft is an experience-induced temporally-regulated process that gates the strength of fear memories.