Extinction of Contextual Cocaine Memories Requires Cav1.2 within D1R-Expressing Cells and Recruits Hippocampal Cav1.2-Dependent Signaling Mechanisms.

Exposure to cocaine-associated contextual cues contributes significantly to relapse. Extinction of these contextual associations, which involves a new form of learning, reduces cocaine-seeking behavior; however, the molecular mechanisms underlying this process remain largely unknown. We report that extinction, but not acquisition, of cocaine conditioned place preference (CPP) in male mice increased Cav1.2 L-type Ca2+ channel mRNA and protein in postsynaptic density (PSD) fractions of the hippocampus, a brain region involved in drug-context associations. Moreover, viral-mediated deletion of Cav1.2 in the dorsal hippocampus attenuated extinction of cocaine CPP. Molecular studies examining downstream Cav1.2 targets revealed that extinction recruited calcium/calmodulin (Ca2+/CaMK)-dependent protein kinase II (CaMKII) to the hippocampal PSD. This occurred in parallel with an increase in phosphorylation of the AMPA GluA1 receptor subunit at serine 831 (S831), a CaMKII site, along with an increase in total PSD GluA1. The necessity of S831 GluA1 was further demonstrated by the lack of extinction in S831A GluA1 phosphomutant mice. Of note hippocampal GluA1 levels remained unaltered at the PSD, but were reduced near the PSD and at perisynaptic sites of dendritic spines in extinction-resistant S831A mutant mice. Finally, conditional knock-out of Cav1.2 in dopamine D1 receptor (D1R)-expressing cells resulted in attenuation of cocaine CPP extinction and lack of extinction-dependent changes in hippocampal PSD CaMKII expression and S831 GluA1 phosphorylation. In summary, we demonstrate an essential role for the hippocampal Cav1.2/CaMKII/S831 GluA1 pathway in cocaine CPP extinction, with data supporting contribution of hippocampal D1R-expressing cells in this process. These findings demonstrate a novel role for Cav1.2 channels in extinction of contextual cocaine-associated memories.SIGNIFICANCE STATEMENT Continued drug-seeking behavior, a defining characteristic of cocaine addiction, can be precipitated by contextual cues, yet the molecular mechanisms required for extinction of these context-specific memories remain poorly understood. Here, we have uncovered a novel and selective role of the Cav1.2 L-type Ca2+ channel and its downstream signaling pathway in the hippocampus that mediate extinction of cocaine conditioned place preference (CPP). We additionally provide evidence that supports a role of Cav1.2 within dopamine D1 receptor-expressing cells of the hippocampus for extinction of cocaine CPP. Therefore, these findings reveal a previously unknown role of Cav1.2 channels within the hippocampus and in D1 receptor-expressing cells in extinction of cocaine-associated memories, providing a framework for further exploration of mechanisms underlying extinction of cocaine-seeking behavior.

Mutations in FLVCR1 cause posterior column ataxia and retinitis pigmentosa.

The study of inherited retinal diseases has advanced our knowledge of the cellular and molecular mechanisms involved in sensory neural signaling. Dysfunction of two specific sensory modalities, vision and proprioception, characterizes the phenotype of the rare, autosomal-recessive disorder posterior column ataxia and retinitis pigmentosa (PCARP). Using targeted DNA capture and high-throughput sequencing, we analyzed the entire 4.2 Mb candidate sequence on chromosome 1q32 to find the gene mutated in PCARP in a single family. Employing comprehensive bioinformatic analysis and filtering, we identified a single-nucleotide coding variant in the feline leukemia virus subgroup C cellular receptor 1 (FLVCR1), a gene encoding a heme-transporter protein. Sanger sequencing confirmed the FLVCR1 mutation in this family and identified different homozygous missense mutations located within the protein's transmembrane channel segment in two other unrelated families with PCARP. To determine whether the selective pathologic features of PCARP correlated with FLVCR1 expression, we examined wild-type mouse Flvcr1 mRNA levels in the posterior column of the spinal cord and the retina via quantitative real-time reverse-transcriptase PCR. The Flvcr1 mRNA levels were most abundant in the retina, followed by the posterior column of the spinal cord and other brain regions. These results suggest that aberrant FLVCR1 causes a selective degeneration of a subpopulation of neurons in the retina and the posterior columns of the spinal cord via dysregulation of heme or iron homeostasis. This finding broadens the molecular basis of sensory neural signaling to include common mechanisms that involve proprioception and vision.

Stress differentially alters mu opioid receptor density and trafficking in parvalbumin-containing interneurons in the female and male rat hippocampus.

Stress differentially affects hippocampal-dependent learning relevant to addiction and morphology in male and female rats. Mu opioid receptors (MORs), which are located in parvalbumin (PARV)-containing GABAergic interneurons and are trafficked in response to changes in the hormonal environment, play a critical role in promoting principal cell excitability and long-term potentiation. Here, we compared the effects of acute and chronic immobilization stress (AIS and CIS) on MOR trafficking in PARV-containing neurons in the hilus of the dentate gyrus in female and male rats using dual label immunoelectron microscopy. Following AIS, the density of MOR silver-intensified gold particles (SIGs) in the cytoplasm of PARV-labeled dendrites was significantly reduced in females (estrus stage). Conversely, AIS significantly increased the proportion of cytoplasmic MOR SIGs in PARV-labeled dendrites in male rats. CIS significantly reduced the number of PARV-labeled neurons in the dentate hilus of males but not females. However, MOR/PARV-labeled dendrites and terminals were significantly smaller in CIS females, but not males, compared with controls. Following CIS, the density of cytoplasmic MOR SIGs increased in PARV-labeled dendrites and terminals in females. Moreover, the proportion of near-plasmalemmal MOR SIGs relative to total decreased in large PARV-labeled dendrites in females. After CIS, no changes in the density or trafficking of MOR SIGs were seen in PARV-labeled dendrites or terminals in males. These data show that AIS and CIS differentially affect available MOR pools in PARV-containing interneurons in female and male rats. Furthermore, they suggest that CIS could affect principal cell excitability in a manner that maintains learning processes in females but not males.

Cacna1c in the Prefrontal Cortex Regulates Depression-Related Behaviors via REDD1.

The CACNA1C gene that encodes the L-type Ca2+ channel (LTCC) Cav1.2 subunit has emerged as a candidate risk gene for multiple neuropsychiatric disorders including bipolar disorder, major depressive disorder, and schizophrenia, all marked with depression-related symptoms. Although cacna1c heterozygous (HET) mice have been previously reported to exhibit an antidepressant-like phenotype, the molecular and circuit-level dysfunction remains unknown. Here we report that viral vector-mediated deletion of cacna1c in the adult prefrontal cortex (PFC) of mice recapitulates the antidepressant-like effect observed in cacna1c HET mice using the sucrose preference test (SPT), forced swim test (FST), and tail suspension test (TST). Molecular studies identified lower levels of REDD1, a protein previously linked to depression, in the PFC of HET mice, and viral-mediated REDD1 overexpression in the PFC of these HET mice reversed the antidepressant-like effect in SPT and TST. Examination of downstream REDD1 targets found lower levels of active/phosphorylated Akt (S473) with no change in mTORC1 phosphorylation. Examination of the transcription factor FoxO3a, previously linked to depression-related behavior and shown to be regulated in other systems by Akt, revealed higher nuclear levels in the PFC of cacna1c HET mice that was further increased following REDD1-mediated reversal of the antidepressant-like phenotype. Collectively, these findings suggest that REDD1 in cacna1c HET mice may influence depression-related behavior via regulation of the FoxO3a pathway. Cacna1c HET mice thus serve as a useful mouse model to further study cacna1c-associated molecular signaling and depression-related behaviors relevant to human CACNA1C genetic variants.

Sensory-Derived Glutamate Regulates Presynaptic Inhibitory Terminals in Mouse Spinal Cord.

Circuit function in the CNS relies on the balanced interplay of excitatory and inhibitory synaptic signaling. How neuronal activity influences synaptic differentiation to maintain such balance remains unclear. In the mouse spinal cord, a population of GABAergic interneurons, GABApre, forms synapses with the terminals of proprioceptive sensory neurons and controls information transfer at sensory-motor connections through presynaptic inhibition. We show that reducing sensory glutamate release results in decreased expression of GABA-synthesizing enzymes GAD65 and GAD67 in GABApre terminals and decreased presynaptic inhibition. Glutamate directs GAD67 expression via the metabotropic glutamate receptor mGluR1ß on GABApre terminals and regulates GAD65 expression via autocrine influence on sensory terminal BDNF. We demonstrate that dual retrograde signals from sensory terminals operate hierarchically to direct the molecular differentiation of GABApre terminals and the efficacy of presynaptic inhibition. These retrograde signals comprise a feedback mechanism by which excitatory sensory activity drives GABAergic inhibition to maintain circuit homeostasis.

The kappa-opioid receptor antagonist, nor-binaltorphimine (nor-BNI), decreases morphine withdrawal and the consequent conditioned place aversion in rats.

Much data suggest that the binding of dynorphin-like peptides to kappa-opioid receptors (KORs) during the administration of and withdrawal from a variety of addictive drugs is aversive and serves to limit the reinforcing properties of those drugs and to enhance tolerance, withdrawal, and the probability of stress-induced relapse. In this study, we examined the role of KORs in mediating opioid withdrawal and its aversive consequences in rats. We found that selective blockade of KORs by i.p. administration of 20mg/kg nor-binaltorphimine (nor-BNI) 5h prior to naltrexone-precipitated withdrawal in morphine-dependent rats decreased feces excreted during a 30-min withdrawal session. More critically, this injection of nor-BNI decreased the subsequent conditioned place aversion (CPA) for the withdrawal chamber 2 days later. The subsequent finding that administration of nor-BNI 2h following withdrawal did not affect the CPA 2 days later suggested that nor-BNI reduced the CPA in the prior experiment because it reduced the aversive effects of withdrawal, not because it reduced the aversive/anxiogenic effects of the withdrawal chamber at the time of CPA testing. These data indicate that the binding of dynorphin-like peptides to KORs during opioid withdrawal serves to enhance withdrawal and its aversive consequences and suggest that selective KOR antagonists may be useful in reducing these aversive effects and consequent relapse.

Stereotaxic microinjection of viral vectors expressing Cre recombinase to study the role of target genes in cocaine conditioned place preference.

Microinjecting recombinant adenoassociated viral (rAAV) vectors expressing Cre recombinase into distinct mouse brain regions to selectively knockout genes of interest allows for enhanced temporally- and regionally-specific control of gene deletion, compared to existing methods. While conditional deletion can also be achieved by mating mice that express Cre recombinase under the control of specific gene promoters with mice carrying a floxed gene, stereotaxic microinjection allows for targeting of discrete brain areas at experimenter-determined time points of interest. In the context of cocaine conditioned place preference, and other cocaine behavioral paradigms such as self-administration or psychomotor sensitization that can involve withdrawal, extinction and/or reinstatement phases, this technique is particularly useful in exploring the unique contribution of target genes to these distinct phases of behavioral models of cocaine-induced plasticity. Specifically, this technique allows for selective ablation of target genes during discrete phases of a behavior to test their contribution to the behavior across time. Ultimately, this understanding allows for more targeted therapeutics that are best able to address the most potent risk factors that present themselves during each phase of addictive behavior.