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.

A homozygous nonsense mutation in the cereblon (CRBN) gene results in autosomal recessive, nonsyndromic intellectual disability that is devoid of other phenotypic features, suggesting a critical role of CRBN in mediating learning and memory. In this study, we demonstrate that adult male Crbn knock-out (CrbnKO) mice exhibit deficits in hippocampal-dependent learning and memory tasks that are recapitulated by focal knock-out of Crbn in the adult dorsal hippocampus, with no changes in social or repetitive behavior. Cellular studies identify deficits in long-term potentiation at Schaffer collateral CA1 synapses. We further show that Crbn is robustly expressed in the mouse hippocampus and CrbnKO mice exhibit hyperphosphorylated levels of AMPKα (Thr172). Examination of processes downstream of AMP-activated protein kinase (AMPK) finds that CrbnKO mice have a selective impairment in mediators of the mTORC1 translation initiation pathway in parallel with lower protein levels of postsynaptic density glutamatergic proteins and higher levels of excitatory presynaptic markers in the hippocampus with no change in markers of the unfolded protein response or autophagy pathways. Acute pharmacological inhibition of AMPK activity in adult CrbnKO mice rescues learning and memory deficits and normalizes hippocampal mTORC1 activity and postsynaptic glutamatergic proteins without altering excitatory presynaptic markers. Thus, this study identifies that loss of Crbn results in learning, memory, and synaptic defects as a consequence of exaggerated AMPK activity, inhibition of mTORC1 signaling, and decreased glutamatergic synaptic proteins. Thus, CrbnKO mice serve as an ideal model of intellectual disability to further explore molecular mechanisms of learning and memory.SIGNIFICANCE STATEMENT Intellectual disability (ID) is one of the most common neurodevelopmental disorders. The cereblon (CRBN) gene has been linked to autosomal recessive, nonsyndromic ID, characterized by an intelligence quotient between 50 and 70 but devoid of other phenotypic features, making cereblon an ideal protein for the study of the fundamental aspects of learning and memory. Here, using the cereblon knock-out mouse model, we show that cereblon deficiency disrupts learning, memory, and synaptic function via AMP-activated protein kinase hyperactivity, downregulation of mTORC1, and dysregulation of excitatory synapses, with no changes in social or repetitive behaviors, consistent with findings in the human population. This establishes the cereblon knock-out mouse as a model of pure ID without the confounding behavioral phenotypes associated with other current models of ID.

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.

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.

Genetic variations in CACNA1C, which encodes the Cav1.2 subunit of L-type calcium channels (LTCCs), are associated with multiple forms of neuropsychiatric disease that manifest high anxiety in patients. In parallel, mice harboring forebrain-specific conditional knockout of cacna1c (forebrain-Cav1.2 cKO) display unusually high anxiety-like behavior. LTCCs in general, including the Cav1.3 subunit, have been shown to mediate differentiation of neural precursor cells (NPCs). However, it has not previously been determined whether Cav1.2 affects postnatal hippocampal neurogenesis in vivo. Here, we show that forebrain-Cav1.2 cKO mice exhibit enhanced cell death of young hippocampal neurons, with no change in NPC proliferation, hippocampal size, dentate gyrus thickness, or corticosterone levels compared with wild-type littermates. These mice also exhibit deficits in brain levels of brain-derived neurotrophic factor (BDNF), and Cre recombinase-mediated knockdown of adult hippocampal Cav1.2 recapitulates the deficit in young hippocampal neurons survival. Treatment of forebrain-Cav1.2 cKO mice with the neuroprotective agent P7C3-A20 restored the net magnitude of postnatal hippocampal neurogenesis to wild-type levels without ameliorating their deficit in BDNF expression. The role of Cav1.2 in young hippocampal neurons survival may provide new approaches for understanding and treating neuropsychiatric disease associated with aberrations in CACNA1C. Visual Abstract.

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.

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.

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'.

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.

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.

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.

Parvalbumin-expressing, fast spiking interneurons have high-energy demands, which make them particularly susceptible to energy impairment. Recent evidence suggests a link between mitochondrial dysfunction in fast spiking cortical interneurons and neuropsychiatric disorders. However, the effect of mitochondrial dysfunction restricted to parvalbumin interneurons has not been directly addressed in vivo. To investigate the consequences of mitochondrial dysfunction in parvalbumin interneurons in vivo, we generated conditional knockout mice with a progressive decline in oxidative phosphorylation by deleting cox10 gene selectively in parvalbumin neurons (PV-Cox10 CKO). Cox10 ablation results in defective assembly of cytochrome oxidase, the terminal enzyme of the electron transfer chain, and leads to mitochondrial bioenergetic dysfunction. PV-Cox10 CKO mice showed a progressive loss of cytochrome oxidase in cortical parvalbumin interneurons. Cytochrome oxidase protein levels were significantly reduced starting at postnatal day 60, and this was not associated with a change in parvalbumin interneuron density. Analyses of intrinsic electrophysiological properties in layer 5 primary somatosensory cortex revealed that parvalbumin interneurons could not sustain their typical high frequency firing, and their overall excitability was enhanced. An increase in both excitatory and inhibitory input onto parvalbumin interneurons was observed in PV-Cox10 CKO mice, resulting in a disinhibited network with an imbalance of excitation/inhibition. Investigation of network oscillations in PV-Cox10 CKO mice, using local field potential recordings in anesthetized mice, revealed significantly increased gamma and theta frequency oscillation power in both medial prefrontal cortex and hippocampus. PV-Cox10 CKO mice did not exhibit muscle strength or gross motor activity deficits in the time frame of the experiments, but displayed impaired sensory gating and sociability. Taken together, these data reveal that mitochondrial dysfunction in parvalbumin interneurons can alter their intrinsic physiology and network connectivity, resulting in behavioral alterations similar to those observed in neuropsychiatric disorders, such as schizophrenia and autism.

Gastrointestinal symptoms are a common feature in children with autism, drawing attention to a potential association with celiac disease or gluten sensitivity. However, studies to date regarding the immune response to gluten in autism and its association with celiac disease have been inconsistent. The aim of this study was to assess immune reactivity to gluten in pediatric patients diagnosed with autism according to strict criteria and to evaluate the potential link between autism and celiac disease.

Rett syndrome (RTT), a leading cause of intellectual disability in girls, is predominantly caused by mutations in the X-linked gene MECP2. Disruption of Mecp2 in mice recapitulates major features of RTT, including neurobehavioral abnormalities, which can be reversed by re-expression of normal Mecp2. Thus, there is reason to believe that RTT could be amenable to therapeutic intervention throughout the lifespan of patients after the onset of symptoms. A common feature underlying neuropsychiatric disorders, including RTT, is altered synaptic function in the brain. Here, we show that Mecp2tm1.1Jae/y mice display lower presynaptic function as assessed by paired pulse ratio, as well as decreased long term potentiation (LTP) at hippocampal Schaffer-collateral-CA1 synapses. Treatment of Mecp2tm1.1Jae/y mice with D-cycloserine (DCS), an FDA-approved analog of the amino acid D-alanine with antibiotic and glycinergic activity, corrected the presynaptic but not LTP deficit without affecting deficient hippocampal BDNF levels. DCS treatment did, however, partially restore lower BDNF levels in the brain stem and striatum. Thus, treatment with DCS may mitigate the severity of some of the neurobehavioral symptoms experienced by patients with Rett syndrome.

Chronic stress is known to precipitate and exacerbate neuropsychiatric symptoms, and exposure to stress is particularly pathological in individuals with certain genetic predispositions. Recent genome wide association studies have identified single nucleotide polymorphisms (SNPs) in the gene CACNA1C, which codes for the Cav1.2 subunit of the L-type calcium channel (LTCC), as a common risk variant for multiple neuropsychiatric conditions. Cav1.2 channels mediate experience-dependent changes in gene expression and long-term synaptic plasticity through activation of downstream calcium signaling pathways. Previous studies have found an association between stress and altered Cav1.2 expression in the brain, however the contribution of Cav1.2 channels to chronic stress-induced behaviors, and the precise Cav1.2 signaling mechanisms activated are currently unknown. Here we report that chronic stress leads to a delayed increase in Cav1.2 expression selectively within the prefrontal cortex (PFC), but not in other stress-sensitive brain regions such as the hippocampus or amygdala. Further, we demonstrate that while Cav1.2 heterozygous (Cav1.2+/-) mice show chronic stress-induced depressive-like behavior, anxiety-like behavior, and deficits in working memory 1-2 days following stress, they are resilient to the effects of chronic stress when tested 5-7 days later. Lastly, molecular studies find a delayed upregulation of the p25/Cdk5-glucocorticoid receptor (GR) pathway in the PFC when examined 8 days post-stress that is absent in Cav1.2+/- mice. Our findings reveal a novel Cav1.2-mediated molecular mechanism associated with the persistent behavioral effects of chronic stress and provide new insight into potential Cav1.2 channel mechanisms that may contribute to CACNA1C-linked neuropsychiatric phenotypes.

Environment-induced relapse is a major concern in drug addiction because of the strong associations formed between drug reward and environment. Cocaine-conditioned place preference is an ideal experimental tool to examine adaptations in the molecular pathways that are activated upon re-exposure to an environment previously paired with drug reward. To better understand the mechanism of cocaine-conditioned place preference we have used western blot analysis to examine changes in phosphorylation of cAMP-response element binding protein (CREB), dopamine- and cyclic AMP-regulated phosphoprotein 32 (DARPP-32), extracellular signal-regulated kinase (ERK) and GluR1, key molecular substrates altered by cocaine, in the nucleus accumbens (NAc) and dorsal hippocampus (DHC) of C57BL/6 mice. Our studies revealed that re-exposing mice to an environment in which they were previously given cocaine resulted in increased levels of Ser133 phospho-CREB and Thr34 phospho-DARPP-32 with a corresponding decrease in Thr75 phospho-DARPP-32 in the NAc. In DHC there were increased levels of phospho-CREB, Thr183/Tyr185 phospho-ERK, and Ser845 phospho-GluR1. These data suggest that the formation of contextual drug reward associations involves recruitment of the DHC-NAc circuit with activation of the DARPP-32/CREB pathway in the NAc and the ERK/CREB pathway in the DHC.

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.

AMPA receptor (AMPAR) plasticity at glutamatergic synapses in the mesoaccumbal dopaminergic pathway has been implicated in persistent cocaine-induced behavioral responses; however, the precise mechanism underlying these changes remains unknown. Utilizing cocaine psychomotor sensitization, we have examined phosphorylation of GluA1 at key residues serine 845 (S845) and S831, as well as GluA1 cell surface levels in the nucleus accumbens (NAc) of cocaine-preexposed mice and the role of brain-specific Ca(v)1.2 and Ca(v)1.3 L-type Ca²⁺ channels (LTCCs), therein. We found higher basal levels of S845 phospho-GluA1 (P-GluA1) and cell surface GluA1 in the NAc following protracted withdrawal from cocaine exposure, changes that occur independently of LTCCs. In contrast, we found that a cocaine challenge that elicits expression of the cocaine-sensitized response increases S831 P-GluA1 that further increases surface GluA1 beyond the higher basal levels. Intra-NAc pharmacological manipulations indicate that the Ca(v)1.2-activated CaM kinase II (CaMKII) mediates cocaine-induced increase in S831 P-GluA1 and that both Ca(v)1.2-activated CaMKII and extracellular signal-regulated kinase 2 (ERK2) mediate the increase in GluA1 cell surface levels specific to the sensitized response. Experiments using adenoassociated viral vectors expressing Ca(v)1.3 and ERK2 siRNA further indicate that recruitment of the Ca(v)1.2 pathway in the NAc is dependent on ventral tegmental area Ca(v)1.3 LTCCs and ERK2. Together, these results identify candidate pathways that mediate cocaine-induced AMPAR plasticity in the NAc and provide a mechanism linking LTCCs and GluA1 plasticity to cocaine-induced persistent behavioral changes.

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 mGluR1β 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.

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.