Interneuron FGF13 regulates seizure susceptibility via a sodium channel-independent mechanism.

Developmental and Epileptic Encephalopathies (DEEs), a class of devastating neurological disorders characterized by recurrent seizures and exacerbated by disruptions to excitatory/inhibitory balance in the brain, are commonly caused by mutations in ion channels. Disruption of, or variants in, FGF13 were implicated as causal for a set of DEEs, but the underlying mechanisms were clouded because FGF13 is expressed in both excitatory and inhibitory neurons, FGF13 undergoes extensive alternative splicing producing multiple isoforms with distinct functions, and the overall roles of FGF13 in neurons are incompletely cataloged. To overcome these challenges, we generated a set of novel cell type-specific conditional knockout mice. Interneuron-targeted deletion of Fgf13 led to perinatal mortality associated with extensive seizures and impaired the hippocampal inhibitory/excitatory balance while excitatory neuron-targeted deletion of Fgf13 caused no detectable seizures and no survival deficits. While best studied as a voltage-gated sodium channel (Nav) regulator, we observed no effect of Fgf13 ablation in interneurons on Navs but rather a marked reduction in K+ channel currents. Re-expressing different Fgf13 splice isoforms could partially rescue deficits in interneuron excitability and restore K+ channel current amplitude. These results enhance our understanding of the molecular mechanisms that drive the pathogenesis of Fgf13-related seizures and expand our understanding of FGF13 functions in different neuron subsets.

A Genetically Encoded Actuator Selectively Boosts L-type Calcium Channels in Diverse Physiological Settings.

L-type Ca 2+ channels (Ca V 1.2/1.3) convey influx of calcium ions (Ca 2+ ) that orchestrate a bevy of biological responses including muscle contraction and gene transcription. Deficits in Ca V 1 function play a vital role in cardiac and neurodevelopmental disorders. Yet conventional pharmacological approaches to upregulate Ca V 1 are limited, as excessive Ca 2+ influx leads to cytotoxicity. Here, we develop a genetically encoded enhancer of Ca V 1.2/1.3 channels (GeeC) to manipulate Ca 2+ entry in distinct physiological settings. Specifically, we functionalized a nanobody that targets the Ca V macromolecular complex by attaching a minimal effector domain from a Ca V enhancer-leucine rich repeat containing protein 10 (Lrrc10). In cardiomyocytes, GeeC evoked a 3-fold increase in L-type current amplitude. In neurons, GeeC augmented excitation-transcription (E-T) coupling. In all, GeeC represents a powerful strategy to boost Ca V 1.2/1.3 function in distinct physiological settings and, in so doing, lays the groundwork to illuminate new insights on neuronal and cardiac physiology and disease.

Repeat investigation during social preference behavior is suppressed in male mice with prefrontal cortex cacna1c (Cav1.2)-deficiency through the dysregulation of neural dynamics.

Impairments in social behavior are observed in a range of neuropsychiatric disorders and several lines of evidence have demonstrated that dysfunction of the prefrontal cortex (PFC) plays a central role in social deficits. We have previously shown that loss of neuropsychiatric risk gene Cacna1c that codes for the Cav1.2 isoform of L-type calcium channels (LTCCs) in the PFC result in impaired sociability as tested using the three-chamber social approach test. In this study we aimed to further characterize the nature of the social deficit associated with a reduction in PFC Cav1.2 channels (Cav1.2PFCKO mice) by testing male mice in a range of social and nonsocial tests while examining PFC neural activity using in vivo GCaMP6s fiber photometry. We found that during the first investigation of the social and non-social stimulus in the three-chamber test, both Cav1.2PFCKO male mice and Cav1.2PFCGFP controls spent significantly more time with the social stimulus compared to a non-social object. In contrast, during repeat investigations while Cav1.2PFCWT mice continued to spend more time with the social stimulus, Cav1.2PFCKO mice spent equal amount of time with both social and non-social stimuli. Neural activity recordings paralleled social behavior with increase in PFC population activity in Cav1.2PFCWT mice during first and repeat investigations, which was predictive of social preference behavior. In Cav1.2PFCKO mice, there was an increase in PFC activity during first social investigation but not during repeat investigations. These behavioral and neural differences were not observed during a reciprocal social interaction test nor during a forced alternation novelty test. To evaluate a potential deficit in reward-related processes, we tested mice in a three-chamber test wherein the social stimulus was replaced by food. Behavioral testing revealed that both Cav1.2PFCWT and Cav1.2PFCKO mice showed a preference for food over object with significantly greater preference during repeat investigation. Interestingly, there was no increase in PFC activity when Cav1.2PFCWT or Cav1.2PFCKO first investigated the food however activity significantly increased in Cav1.2PFCWT mice during repeat investigations of the food. This was not observed in Cav1.2PFCKO mice. In summary, a reduction in Cav1.2 channels in the PFC suppresses the development of a sustained social preference in mice that is associated with lack of PFC neuronal population activity that may be related to deficits in social reward.

Regulation of social interaction in mice by a frontostriatal circuit modulated by established hierarchical relationships.

Social hierarchies exert a powerful influence on behavior, but the neurobiological mechanisms that detect and regulate hierarchical interactions are not well understood, especially at the level of neural circuits. Here, we use fiber photometry and chemogenetic tools to record and manipulate the activity of nucleus accumbens-projecting cells in the ventromedial prefrontal cortex (vmPFC-NAcSh) during tube test social competitions. We show that vmPFC-NAcSh projections signal learned hierarchical relationships, and are selectively recruited by subordinate mice when they initiate effortful social dominance behavior during encounters with a dominant competitor from an established hierarchy. After repeated bouts of social defeat stress, this circuit is preferentially activated during social interactions initiated by stress resilient individuals, and plays a necessary role in supporting social approach behavior in subordinated mice. These results define a necessary role for vmPFC-NAcSh cells in the adaptive regulation of social interaction behavior based on prior hierarchical interactions.

L-type calcium channels and neuropsychiatric diseases: Insights into genetic risk variant-associated genomic regulation and impact on brain development.

Recent human genetic studies have linked a variety of genetic variants in the CACNA1C and CACNA1D genes to neuropsychiatric and neurodevelopmental disorders. This is not surprising given the work from multiple laboratories using cell and animal models that have established that Cav1.2 and Cav1.3 L-type calcium channels (LTCCs), encoded by CACNA1C and CACNA1D, respectively, play a key role in various neuronal processes that are essential for normal brain development, connectivity, and experience-dependent plasticity. Of the multiple genetic aberrations reported, genome-wide association studies (GWASs) have identified multiple single nucleotide polymorphisms (SNPs) in CACNA1C and CACNA1D that are present within introns, in accordance with the growing body of literature establishing that large numbers of SNPs associated with complex diseases, including neuropsychiatric disorders, are present within non-coding regions. How these intronic SNPs affect gene expression has remained a question. Here, we review recent studies that are beginning to shed light on how neuropsychiatric-linked non-coding genetic variants can impact gene expression via regulation at the genomic and chromatin levels. We additionally review recent studies that are uncovering how altered calcium signaling through LTCCs impact some of the neuronal developmental processes, such as neurogenesis, neuron migration, and neuron differentiation. Together, the described changes in genomic regulation and disruptions in neurodevelopment provide possible mechanisms by which genetic variants of LTCC genes contribute to neuropsychiatric and neurodevelopmental disorders.

Cav1.3 L-type Ca2+ channel-activated CaMKII/ERK2 pathway in the ventral tegmental area is required for cocaine conditioned place preference.

We have previously demonstrated that pharmacological blockade of ventral tegmental area (VTA) Cav1.3 L-type calcium channels (LTCCs) using Cav1.2 dihydropyridine insensitive (Cav1.2DHP-/-) mutant mice attenuates cocaine conditioned place preference (CPP). However, the molecular mechanisms by which Cav1.3 channels mediate the effects of cocaine in the VTA remain largely unknown. In this study using Cav1.2DHP-/- male mice, we find that cocaine place preference increases CaM kinase IIα, ERK2, and CREB phosphorylation in the VTA, proteins strongly linked to cocaine behaviors. To further explore the causal role of these intracellular signaling proteins in cocaine preference, the CaM kinase II inhibitor, KN93 was directly injected into the VTA of male mice before each cocaine conditioning session. We found that KN93 attenuates conditioned preference for cocaine compared to vehicle treated mice and decreased VTA ERK2 and CREB phosphorylation. Additionally, blockade of the ERK pathway with the MEK inhibitor, U0126 or knockdown of ERK2 using siRNA, attenuated cocaine preference and VTA CREB phosphorylation but not CaMKIIα phosphorylation, suggesting that ERK is activated downstream of CaMKIIα. Examination of postsynaptic density (PSD) GluA1 subunit of AMPA receptors in the nucleus accumbens (NAc) that we have previously shown to be upregulated following long withdrawal periods, was blunted by KN93, U0126 and ERK2 siRNA when examined 30 days following cocaine CPP. Taken together, these findings demonstrate that Cav1.3 channels in the VTA are required for cocaine reward behavior and activation of the CaMKIIα/ERK/CREB signaling pathway in the VTA is necessary for long-lasting changes in the NAc. This article is part of the Special Issue on 'L-type calcium channel mechanisms in neuropsychiatric disorders'.

Sex differences in the medial prefrontal cortical glutamate system.

BACKGROUND: Dysregulation in the prefrontal cortex underlies a variety of psychiatric illnesses, including substance use disorder, depression, and anxiety. Despite the established sex differences in prevalence and presentation of these illnesses, the neural mechanisms driving these differences are largely unexplored. Here, we investigate potential sex differences in glutamatergic transmission within the medial prefrontal cortex (mPFC). The goal of these experiments was to determine if there are baseline sex differences in transmission within this region that may underlie sex differences in diseases that involve dysregulation in the prefrontal cortex. METHODS: Adult male and female C57Bl/6J mice were used for all experiments. Mice were killed and bilateral tissue samples were taken from the medial prefrontal cortex for western blotting. Both synaptosomal and total GluA1 and GluA2 levels were measured. In a second set of experiments, mice were killed and ex vivo slice electrophysiology was performed on prepared tissue from the medial prefrontal cortex. Spontaneous excitatory postsynaptic currents and rectification indices were measured. RESULTS: Females exhibit higher levels of synaptosomal GluA1 and GluA2 in the mPFC compared to males. Despite similar trends, no statistically significant differences are seen in total levels of GluA1 and GluA2. Females also exhibit both a higher amplitude and higher frequency of spontaneous excitatory postsynaptic currents and greater inward rectification in the mPFC compared to males. CONCLUSIONS: Overall, we conclude that there are sex differences in glutamatergic transmission in the mPFC. Our data suggest that females have higher levels of glutamatergic transmission in this region. This provides evidence that the development of sex-specific pharmacotherapies for various psychiatric diseases is important to create more effective treatments.

Scn2a severe hypomorphic mutation decreases excitatory synaptic input and causes autism-associated behaviors.

SCN2A, encoding the neuronal voltage-gated Na+ channel NaV1.2, is one of the most commonly affected loci linked to autism spectrum disorders (ASDs). Most ASD-associated mutations in SCN2A are loss-of-function mutations, but studies examining how such mutations affect neuronal function and whether Scn2a mutant mice display ASD endophenotypes have been inconsistent. We generated a protein truncation variant Scn2a mouse model (Scn2aΔ1898/+) by CRISPR that eliminates the NaV1.2 channel's distal intracellular C-terminal domain, and we analyzed the molecular and cellular consequences of this variant in a heterologous expression system, in neuronal culture, in brain slices, and in vivo. We also analyzed multiple behaviors in WT and Scn2aΔ1898/+ mice and correlated behaviors with clinical data obtained in human subjects with SCN2A variants. Expression of the NaV1.2 mutant in a heterologous expression system revealed decreased NaV1.2 channel function, and cultured pyramidal neurons isolated from Scn2aΔ1898/+ forebrain showed correspondingly reduced voltage-gated Na+ channel currents without compensation from other CNS voltage-gated Na+ channels. Na+ currents in inhibitory neurons were unaffected. Consistent with loss of voltage-gated Na+ channel currents, Scn2aΔ1898/+ pyramidal neurons displayed reduced excitability in forebrain neuronal culture and reduced excitatory synaptic input onto the pyramidal neurons in brain slices. Scn2aΔ1898/+ mice displayed several behavioral abnormalities, including abnormal social interactions that reflect behavior observed in humans with ASD and with harboring loss-of-function SCN2A variants. This model and its cellular electrophysiological characterizations provide a framework for tracing how a SCN2A loss-of-function variant leads to cellular defects that result in ASD-associated behaviors.

Dual-process brain mitochondria isolation preserves function and clarifies protein composition.

The brain requires continuously high energy production to maintain ion gradients and normal function. Mitochondria critically undergird brain energetics, and mitochondrial abnormalities feature prominently in neuropsychiatric disease. However, many unique aspects of brain mitochondria composition and function are poorly understood. Developing improved neuroprotective therapeutics thus requires more comprehensively understanding brain mitochondria, including accurately delineating protein composition and channel-transporter functional networks. However, obtaining pure mitochondria from the brain is especially challenging due to its distinctive lipid and cell structure properties. As a result, conflicting reports on protein localization to brain mitochondria abound. Here we illustrate this problem with the neuropsychiatric disease-associated L-type calcium channel Cav1.2α1 subunit previously observed in crude mitochondria. We applied a dual-process approach to obtain functionally intact versus compositionally pure brain mitochondria. One branch utilizes discontinuous density gradient centrifugation to isolate semipure mitochondria suitable for functional assays but unsuitable for protein localization because of endoplasmic reticulum (ER) contamination. The other branch utilizes self-forming density gradient ultracentrifugation to remove ER and yield ultrapure mitochondria that are suitable for investigating protein localization but functionally compromised. Through this process, we evaluated brain mitochondria protein content and observed the absence of Cav1.2α1 and other previously reported mitochondrial proteins, including the NMDA receptor, ryanodine receptor 1, monocarboxylate transporter 1, excitatory amino acid transporter 1, and glyceraldehyde 3-phosphate dehydrogenase. Conversely, we confirmed mitochondrial localization of several plasma membrane proteins previously reported to also localize to mitochondria. We expect this dual-process isolation procedure will enhance understanding of brain mitochondria in both health and disease.

Dopamine D1R-neuron cacna1c deficiency: a new model of extinction therapy-resistant post-traumatic stress.

Post-traumatic stress disorder (PTSD) is characterized by persistent fear memory of remote traumatic events, mental re-experiencing of the trauma, long-term cognitive deficits, and PTSD-associated hippocampal dysfunction. Extinction-based therapeutic approaches acutely reduce fear. However, many patients eventually relapse to the original conditioned fear response. Thus, understanding the underlying molecular mechanisms of this condition is critical to developing new treatments for patients. Mutations in the neuropsychiatric risk gene CACNA1C, which encodes the Cav1.2 isoform of the L-type calcium channel, have been implicated in both PTSD and highly comorbid neuropsychiatric conditions, such as anxiety and depression. Here, we report that male mice with global heterozygous loss of cacna1c exhibit exacerbated contextual fear that persists at remote time points (up to 180 days after shock), despite successful acute extinction training, reminiscent of PTSD patients. Because dopamine has been implicated in contextual fear memory, and Cav1.2 is a downstream target of dopamine D1-receptor (D1R) signaling, we next generated mice with specific deletion of cacna1c from D1R-expressing neurons (D1-cacna1cKO mice). Notably, D1-cacna1cKO mice also show the same exaggerated remote contextual fear, as well as persistently elevated anxiety-like behavior and impaired spatial memory at remote time points, reminiscent of chronic anxiety in treatment-resistant PTSD. We also show that D1-cacna1cKO mice exhibit elevated death of young hippocampal neurons, and that treatment with the neuroprotective agent P7C3-A20 eradicates persistent remote fear. Augmenting survival of young hippocampal neurons may thus provide an effective therapeutic approach for promoting durable remission of PTSD, particularly in patients with CACNA1C mutations or other genetic aberrations that impair calcium signaling or disrupt the survival of young hippocampal neurons.

A Machine Learning Approach to Predicting Autism Risk Genes: Validation of Known Genes and Discovery of New Candidates.

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition with a strong genetic basis. The role of de novo mutations in ASD has been well established, but the set of genes implicated to date is still far from complete. The current study employs a machine learning-based approach to predict ASD risk genes using features from spatiotemporal gene expression patterns in human brain, gene-level constraint metrics, and other gene variation features. The genes identified through our prediction model were enriched for independent sets of ASD risk genes, and tended to be down-expressed in ASD brains, especially in frontal and parietal cortex. The highest-ranked genes not only included those with strong prior evidence for involvement in ASD (for example, NBEA, HERC1, and TCF20), but also indicated potentially novel candidates, such as, MYCBP2 and CAND1, which are involved in protein ubiquitination. We also showed that our method outperformed state-of-the-art scoring systems for ranking curated ASD candidate genes. Gene ontology enrichment analysis of our predicted risk genes revealed biological processes clearly relevant to ASD, including neuronal signaling, neurogenesis, and chromatin remodeling, but also highlighted other potential mechanisms that might underlie ASD, such as regulation of RNA alternative splicing and ubiquitination pathway related to protein degradation. Our study demonstrates that human brain spatiotemporal gene expression patterns and gene-level constraint metrics can help predict ASD risk genes. Our gene ranking system provides a useful resource for prioritizing ASD candidate genes.

Loss of Cav1.2 channels impairs hippocampal theta burst stimulation-induced long-term potentiation.

CACNA1 C, which codes for the Cav1.2 isoform of L-type Ca2+ channels (LTCCs), is a prominent risk gene in neuropsychiatric and neurodegenerative conditions. A role forLTCCs, and Cav1.2 in particular, in transcription-dependent late long-term potentiation (LTP) has long been known. Here, we report that elimination of Cav1.2 channels in glutamatergic neurons also impairs theta burst stimulation (TBS)-induced LTP in the hippocampus, known to be transcription-independent and dependent on N-methyl D-aspartate receptors (NMDARs) and local protein synthesis at synapses. Our expansion of the established role of Cav1.2channels in LTP broadens understanding of synaptic plasticity and identifies a new cellular phenotype for exploring treatment strategies for cognitive dysfunction.

Cereblon harnesses Myc-dependent bioenergetics and activity of CD8+ T lymphocytes.

Immunomodulatory drugs, such as thalidomide and related compounds, potentiate T-cell effector functions. Cereblon (CRBN), a substrate receptor of the DDB1-cullin-RING E3 ubiquitin ligase complex, is the only molecular target for this drug class, where drug-induced, ubiquitin-dependent degradation of known "neosubstrates," such as IKAROS, AIOLOS, and CK1α, accounts for their biological activity. Far less clear is whether these CRBN E3 ligase-modulating compounds disrupt the endogenous functions of CRBN. We report that CRBN functions in a feedback loop that harnesses antigen-specific CD8+ T-cell effector responses. Specifically, Crbn deficiency in murine CD8+ T cells augments their central metabolism manifested as elevated bioenergetics, with supraphysiological levels of polyamines, secondary to enhanced glucose and amino acid transport, and with increased expression of metabolic enzymes, including the polyamine biosynthetic enzyme ornithine decarboxylase. Treatment with CRBN-modulating compounds similarly augments central metabolism of human CD8+ T cells. Notably, the metabolic control of CD8+ T cells by modulating compounds or Crbn deficiency is linked to increased and sustained expression of the master metabolic regulator MYC. Finally, Crbn-deficient T cells have augmented antigen-specific cytolytic activity vs melanoma tumor cells, ex vivo and in vivo, and drive accelerated and highly aggressive graft-versus-host disease. Therefore, CRBN functions to harness the activation of CD8+ T cells, and this phenotype can be exploited by treatment with drugs.

Endocannabinoid genetic variation enhances vulnerability to THC reward in adolescent female mice.

Adolescence represents a developmental period with the highest risk for initiating cannabis use. Little is known about whether genetic variation in the endocannabinoid system alters mesolimbic reward circuitry to produce vulnerability to the rewarding properties of the exogenous cannabinoid Δ9-tetrahydrocannabinol (THC). Using a genetic knock-in mouse model (FAAHC/A) that biologically recapitulates the human polymorphism associated with problematic drug use, we find that in adolescent female mice, but not male mice, this FAAH polymorphism enhances the mesolimbic dopamine circuitry projecting from the ventral tegmental area (VTA) to the nucleus accumbens (NAc) and alters cannabinoid receptor 1 (CB1R) levels at inhibitory and excitatory terminals in the VTA. These developmental changes collectively increase vulnerability of adolescent female FAAHC/A mice to THC preference that persists into adulthood. Together, these findings suggest that this endocannabinoid genetic variant is a contributing factor for increased susceptibility to cannabis dependence in adolescent females.

Contribution of D1R-expressing neurons of the dorsal dentate gyrus and Cav1.2 channels in extinction of cocaine conditioned place preference.

Cocaine-associated contextual cues can trigger relapse behavior by recruiting the hippocampus. Extinction of cocaine-associated contextual memories can reduce cocaine-seeking behavior, however the molecular mechanisms within the hippocampus that underlie contextual extinction behavior and subsequent reinstatement remain poorly understood. Here, we extend our previous findings for a role of Cav1.2 L-type Ca2+ channels in dopamine 1 receptor (D1R)-expressing cells in extinction of cocaine conditioned place preference (CPP) in adult male mice. We report that attenuated cocaine CPP extinction in mice lacking Cav1.2 channels in D1R-expressing cells (D1cre, Cav1.2fl/fl) can be rescued through chemogenetic activation of D1R-expressing cells within the dorsal dentate gyrus (dDG), but not the dorsal CA1 (dCA1). This is supported by the finding that Cav1.2 channels are required in excitatory cells of the dDG, but not in the dCA1, for cocaine CPP extinction. Examination of the role of S1928 phosphorylation of Cav1.2, a protein kinase A (PKA) site using S1928A Cav1.2 phosphomutant mice revealed no extinction deficit, likely due to homeostatic scaling up of extinction-dependent S845 GluA1 phosphorylation in the dDG. However, phosphomutant mice failed to show cocaine-primed reinstatement which can be reversed by chemogenetic manipulation of excitatory cells in the dDG during extinction training. These findings outline an essential role for the interaction between D1R, Cav1.2, and GluA1 signaling in the dDG for extinction of cocaine-associated contextual memories.

Cocaine- and stress-primed reinstatement of drug-associated memories elicit differential behavioral and frontostriatal circuit activity patterns via recruitment of L-type Ca2+ channels.

Cocaine-associated memories are critical drivers of relapse in cocaine-dependent individuals that can be evoked by exposure to cocaine or stress. Whether these environmental stimuli recruit similar molecular and circuit-level mechanisms to promote relapse remains largely unknown. Here, using cocaine- and stress-primed reinstatement of cocaine conditioned place preference to model drug-associated memories, we find that cocaine drives reinstatement by increasing the duration that mice spend in the previously cocaine-paired context whereas stress increases the number of entries into this context. Importantly, both forms of reinstatement require Cav1.2 L-type Ca2+ channels (LTCCs) in cells of the prelimbic cortex that project to the nucleus accumbens core (PrL→NAcC). Utilizing fiber photometry to measure circuit activity in vivo in conjunction with the LTCC blocker, isradipine, we find that LTCCs drive differential recruitment of the PrL→ NAcC pathway during cocaine- and stress-primed reinstatement. While cocaine selectively activates PrL→NAcC cells prior to entry into the cocaine-paired chamber, a measure that is predictive of duration in that chamber, stress increases persistent activity of this projection, which correlates with entries into the cocaine-paired chamber. Using projection-specific chemogenetic manipulations, we show that PrL→NAcC activity is required for both cocaine- and stress-primed reinstatement, and that activation of this projection in Cav1.2-deficient mice restores reinstatement. These data indicate that LTCCs are a common mediator of cocaine- and stress-primed reinstatement. However, they engage different patterns of behavior and PrL→NAcC projection activity depending on the environmental stimuli. These findings establish a framework to further study how different environmental experiences can drive relapse, and supports further exploration of isradipine, an FDA-approved LTCC blocker, as a potential therapeutic for the prevention of relapse in cocaine-dependent individuals.

Correction: Cocaine- and stress-primed reinstatement of drug-associated memories elicit differential behavioral and frontostriatal circuit activity patterns via recruitment of L-type Ca2+ channels.

A correction to this paper has been published and can be accessed via a link at the top of the paper.

Anxiety, the chicken or the egg of addiction: targeting G9a for the treatment of comorbid anxiety and cocaine addiction.

Treating cocaine addiction is a major challenge and currently no FDA approved pharmacotherapies exist. One complicating factor is a high rate of comorbidity between cocaine and neuropsychiatric conditions such as anxiety. The relationship between anxiety symptoms and cocaine addiction is complicated; anxiety can be both a predisposing factor and a consequence of cocaine use as anxiety symptoms often emerge during drug use and withdrawal. Identifying and understanding the shared biological mechanisms that lead to comorbid anxiety and cocaine addiction, irrespective of which comes first, is critical for the identification of new treatments.

The L-type calcium channel blocker, isradipine, attenuates cue-induced cocaine-seeking by enhancing dopaminergic activity in the ventral tegmental area to nucleus accumbens pathway.

Previous preclinical and clinical investigations have focused on the L-type calcium channel (LTCC) as a potential therapeutic target for substance abuse. While some clinical studies have examined the ability of LTCC blockers to alter cocaine's subjective effects, very few LTCC studies have examined cocaine relapse. Here, we examined whether ventral tegmental area (VTA)-specific or systemic administration of the LTCC inhibitor, isradipine, altered cocaine-seeking behavior in a rat model. Male Sprague-Dawley rats first received 10 days of cocaine self-administration training (2 h sessions), where active lever depression resulted in delivery of a ∼0.5 mg/kg cocaine infusion paired with a tone + light cue. Rats then underwent 10 days of forced abstinence, without access to cocaine or cocaine cues. Rats were then returned to the opertant chamber for the cue-induced cocaine-seeking test, where active lever depression in the original training context resulted in tone + light cue presentation. We found VTA specific or systemic isradipine administration robustly attenuated cocaine-seeking, without altering cocaine-taking nor natural reward seeking. Dopamine (DA) signaling in the nucleus accumbens (NAc) core is necessary and sufficient for cue-induced drug-seeking. Surprisingly in our study, isradipine enhanced tonic and phasic DA signaling in cocaine abstinent rats, with no change in sucrose abstinent nor naïve rats. Strikingly, isradipine's behavioral effects were dependent upon NAc core DA receptor activation. Together, our findings reveal a novel mechanism by which the FDA-approved drug, isradipine, could act to decrease cocaine relapse.

Ligand-mediated protein degradation reveals functional conservation among sequence variants of the CUL4-type E3 ligase substrate receptor cereblon.

Upon binding to thalidomide and other immunomodulatory drugs, the E3 ligase substrate receptor cereblon (CRBN) promotes proteosomal destruction by engaging the DDB1-CUL4A-Roc1-RBX1 E3 ubiquitin ligase in human cells but not in mouse cells, suggesting that sequence variations in CRBN may cause its inactivation. Therapeutically, CRBN engagers have the potential for broad applications in cancer and immune therapy by specifically reducing protein expression through targeted ubiquitin-mediated degradation. To examine the effects of defined sequence changes on CRBN's activity, we performed a comprehensive study using complementary theoretical, biophysical, and biological assays aimed at understanding CRBN's nonprimate sequence variations. With a series of recombinant thalidomide-binding domain (TBD) proteins, we show that CRBN sequence variants retain their drug-binding properties to both classical immunomodulatory drugs and dBET1, a chemical compound and targeting ligand designed to degrade bromodomain-containing 4 (BRD4) via a CRBN-dependent mechanism. We further show that dBET1 stimulates CRBN's E3 ubiquitin-conjugating function and degrades BRD4 in both mouse and human cells. This insight paves the way for studies of CRBN-dependent proteasome-targeting molecules in nonprimate models and provides a new understanding of CRBN's substrate-recruiting function.