Microarray analysis reveals distinctive signaling between the bed nucleus of the stria terminalis, nucleus accumbens, and dorsal striatum

The life and times of endogenous opioid peptides: Updated understanding of synthesis, spatiotemporal dynamics, and the clinical impact in alcohol use disorder

The opioid G-protein coupled receptors (GPCRs) strongly modulate many of the central nervous system structures that contribute to neurological and psychiatric disorders including pain, major depressive disorder, and substance use disorders. To better treat these and related diseases, it is essential to understand the signaling of their endogenous ligands. In this review, we focus on what is known and unknown about the regulation of the over two dozen endogenous peptides with high affinity for one or more of the opioid receptors. We briefly describe which peptides are produced, with a particular focus on the recently proposed possible synthesis pathways for the endomorphins. Next, we describe examples of endogenous opioid peptide expression organization in several neural circuits and how they appear to be released from specific neural compartments that vary across brain regions. We discuss current knowledge regarding the strength of neural activity required to drive endogenous opioid peptide release, clues about how far peptides diffuse from release sites, and their extracellular lifetime after release. Finally, as a translational example, we discuss the mechanisms of action of naltrexone (NTX), which is used clinically to treat alcohol use disorder. NTX is a synthetic morphine analog that non-specifically antagonizes the action of most endogenous opioid peptides developed in the 1960s and FDA approved in the 1980s. We review recent studies clarifying the precise endogenous activity that NTX prevents. Together, the works described here highlight the challenges and opportunities the complex opioid system presents as a therapeutic target.

Gene expression changes following chronic antipsychotic exposure in single cells from mouse striatum

Schizophrenia is an idiopathic psychiatric disorder with a high degree of polygenicity. Evidence from genetics, single-cell transcriptomics, and pharmacological studies suggest an important, but untested, overlap between genes involved in the etiology of schizophrenia and the cellular mechanisms of action of antipsychotics. To directly compare genes with antipsychotic-induced differential expression to genes involved in schizophrenia, we applied single-cell RNA-sequencing to striatal samples from male C57BL/6 J mice chronically exposed to a typical antipsychotic (haloperidol), an atypical antipsychotic (olanzapine), or placebo. We identified differentially expressed genes in three cell populations identified from the single-cell RNA-sequencing (medium spiny neurons [MSNs], microglia, and astrocytes) and applied multiple analysis pipelines to contextualize these findings, including comparison to GWAS results for schizophrenia. In MSNs in particular, differential expression analysis showed that there was a larger share of differentially expressed genes (DEGs) from mice treated with olanzapine compared with haloperidol. DEGs were enriched in loci implicated by genetic studies of schizophrenia, and we highlighted nine genes with convergent evidence. Pathway analyses of gene expression in MSNs highlighted neuron/synapse development, alternative splicing, and mitochondrial function as particularly engaged by antipsychotics. In microglia, we identified pathways involved in microglial activation and inflammation as part of the antipsychotic response. In conclusion, single-cell RNA sequencing may provide important insights into antipsychotic mechanisms of action and links to findings from psychiatric genomic studies.

Striatal topographical organization: Bridging the gap between molecules, connectivity and behavior

The striatum represents the major hub of the basal ganglia, receiving projections from the entire cerebral cortex and it is assumed to play a key role in a wide array of complex behavioral tasks. Despite being extensively investigated during the last decades, the topographical organization of the striatum is not well understood yet. Ongoing efforts in neuroscience are focused on analyzing striatal anatomy at different spatial scales, to understand how structure relates to function and how derangements of this organization are involved in various neuropsychiatric diseases. While being subdivided at the macroscale level into dorsal and ventral divisions, at a mesoscale level the striatum represents an anatomical continuum sharing the same cellular makeup. At the same time, it is now increasingly ascertained that different striatal compartments show subtle histochemical differences, and their neurons exhibit peculiar patterns of gene expression, supporting functional diversity across the whole basal ganglia circuitry. Such diversity is further supported by afferent connections which are heterogenous both anatomically, as they originate from distributed cortical areas and subcortical structures, and biochemically, as they involve a variety of neurotransmitters. Specifically, the cortico-striatal projection system is topographically organized delineating a functional organization which is maintained throughout the basal ganglia, subserving motor, cognitive and affective behavioral functions. While such functional heterogeneity has been firstly conceptualized as a tripartite organization, with sharply defined limbic, associative and sensorimotor territories within the striatum, it has been proposed that such territories are more likely to fade into one another, delineating a gradient-like organization along medio-lateral and ventro-dorsal axes. However, the molecular and cellular underpinnings of such organization are less understood, and their relations to behavior remains an open question, especially in humans. In this review we aimed at summarizing the available knowledge on striatal organization, especially focusing on how it links structure to function and its alterations in neuropsychiatric diseases. We examined studies conducted on different species, covering a wide array of different methodologies: from tract-tracing and immunohistochemistry to neuroimaging and transcriptomic experiments, aimed at bridging the gap between macroscopic and molecular levels.

Characterization of the relaxin family peptide receptor 3 system in the mouse bed nucleus of the stria terminalis

The bed nucleus of the stria terminalis (BNST) is a critical node involved in stress and reward-related behaviors. Relaxin family peptide receptor 3 (RXFP3) signaling in the BNST has been implicated in stress-induced alcohol seeking behavior. However, the neurochemical phenotype and connectivity of BNST RXFP3-expressing (RXFP3+) cells have yet to be elucidated. We interrogated the molecular signature and electrophysiological properties of BNST RXFP3+ neurons using a RXFP3-Cre reporter mouse line. BNST RXFP3+ cells are circumscribed to the dorsal BNST (dBNST) and are neurochemically heterogeneous, comprising a mix of inhibitory and excitatory neurons. Immunohistochemistry revealed that ~48% of BNST RXFP3+ neurons are GABAergic, and a quarter of these co-express the calcium-binding protein, calbindin. A subset of BNST RXFP3+ cells (~41%) co-express CaMKIIα, suggesting this subpopulation of BNST RXFP3+ neurons are excitatory. Corroborating this, RNAscope® revealed that ~35% of BNST RXFP3+ cells express vVGluT2 mRNA, indicating a subpopulation of RXFP3+ neurons are glutamatergic. RXFP3+ neurons show direct hyperpolarization to bath application of a selective RXFP3 agonist, RXFP3-A2, while around 50% of cells were depolarised by exogenous corticotrophin releasing factor. In behaviorally naive mice the majority of RXFP3+ neurons were Type II cells exhibiting I_h and T type calcium mediated currents. However, chronic swim stress caused persistent plasticity, decreasing the proportion of neurons that express these channels. These studies are the first to characterize the BNST RXFP3 system in mouse and lay the foundation for future functional studies appraising the role of the murine BNST RXFP3 system in more complex behaviors.

Neocortical Microdissection at Columnar and Laminar Resolution for Molecular Interrogation

The heterogeneous organization of the mammalian neocortex poses a challenge for elucidating the molecular mechanisms underlying its physiological processes. Although high-throughput molecular methods are increasingly deployed in neuroscience, their anatomical specificity is often lacking. In this unit, we introduce a targeted microdissection technique that enables extraction of high-quality RNA and proteins at high anatomical resolution from acutely prepared brain slices. We exemplify its utility by isolating single cortical columns and laminae from the mouse primary somatosensory (barrel) cortex. Tissues can be isolated from living slices in minutes, and the extracted RNA and protein are of sufficient quantity and quality to be used for RNA sequencing and mass spectrometry. This technique will help to increase the anatomical specificity of molecular studies of the neocortex, and the brain in general, as it is applicable to any brain structure that can be identified using optical landmarks in living slices. © 2018 by John Wiley & Sons, Inc.

Adenylyl Cyclase 1 Is Required for Ethanol-Induced Locomotor Sensitization and Associated Increases in NMDA Receptor Phosphorylation and Function in the Dorsal Medial Striatum

Neuroadaptive responses to chronic ethanol, such as behavioral sensitization, are associated with N-methyl-D-aspartate receptor (NMDAR) recruitment. Ethanol enhances GluN2B-containing NMDAR function and phosphorylation (Tyr-1472) of the GluN2B-NMDAR subunit in the dorsal medial striatum (DMS) through a protein kinase A (PKA)-dependent pathway. Ethanol-induced phosphorylation of PKA substrates is partially mediated by calcium-stimulated adenylyl cyclase 1 (AC1), which is enriched in the dorsal striatum. As such, AC1 is poised as an upstream modulator of ethanol-induced DMS neuroadaptations that promote drug responding, and thus represents a therapeutic target. Our hypothesis is that loss of AC1 activity will prevent ethanol-induced locomotor sensitization and associated DMS GluN2B-NMDAR adaptations. We evaluated AC1's contribution to ethanol-evoked locomotor responses and DMS GluN2B-NMDAR phosphorylation and function using AC1 knockout (AC1KO) mice. Results were mechanistically validated with the AC1 inhibitor, NB001. Acute ethanol (2.0 g/kg) locomotor responses in AC1KO and wild-type (WT) mice pretreated with NB001 (10 mg/kg) were comparable to WT ethanol controls. However, repeated ethanol treatment (10 days, 2.5 g/kg) failed to produce sensitization in AC1KO or NB001 pretreated mice, as observed in WT ethanol controls, following challenge exposure (2.0 g/kg). Repeated exposure to ethanol in the sensitization procedure significantly increased pTyr-1472 GluN2B levels and GluN2B-containing NMDAR transmission in the DMS of WT mice. Loss of AC1 signaling impaired ethanol-induced increases in DMS pGluN2B levels and NMDAR-mediated transmission. Together, these data support a critical and specific role for AC1 in striatal signaling that mediates ethanol-induced behavioral sensitization, and identify GluN2B-containing NMDARs as an important AC1 target.

Deficits in behavioral sensitization and dopaminergic responses to methamphetamine in adenylyl cyclase 1/8-deficient mice

The cAMP/protein kinase A pathway regulates methamphetamine (METH)-induced neuroplasticity underlying behavioral sensitization. We hypothesize that adenylyl cyclases (AC) 1/8 mediate these neuroplastic events and associated striatal dopamine regulation. Locomotor responses to METH (1 and 5 mg/kg) and striatal dopamine function were evaluated in mice lacking AC 1/8 (DKO) and wild-type (WT) mice. Only 5 mg/kg METH induced an acute locomotor response in DKO mice, which was significantly attenuated versus WT controls. DKO mice showed a marked attenuation in the development and expression of METH-induced behavioral sensitization across doses relative to WT controls. While basal and acute METH (5 mg/kg)-evoked accumbal dialysate dopamine levels were similar between genotypes, saline-treated DKO mice showed elevated tissue content of dopamine and homovanillic acid in the dorsal striatum (DS), reflecting dysregulated dopamine homeostasis and/or metabolism. Significant reductions in DS dopamine levels were observed in METH-sensitized DKO mice compared to saline-treated controls, an effect not observed in WT mice. Notably, saline-treated DKO mice had significantly increased phosphorylated Dopamine- and cAMP-regulated phosphoprotein levels, which were not further augmented following METH sensitization, as observed in WT mice. These data indicate that AC 1/8 are critical to mechanisms subserving drug-induced behavioral sensitization and mediate nigrostriatal pathway METH sensitivity. Calcium/calmodulin-stimulated adenylyl cyclase (AC) isoforms 1 and 8 were studied for their involvement in the adaptive neurobehavioral responses to methamphetamine. AC 1/8 double knockout (DKO) mice showed heightened basal locomotor activity and dorsal striatal dopamine responsivity. Conversely, methamphetamine-induced locomotor activity was attenuated in DKO mice, accompanied by reductions in dopamine and HVA content and impaired DARPP-32 activation. These findings indicate AC 1/8 signaling regulates the sensitivity of the nigrostriatal pathway subserving stimulant and neuroadaptive sensitizing effects of methamphetamine. 3-MT, 3-methoxytyramine; Ca(2+), calcium; CaM, calmodulin; cdk5; cyclin-dependent kinase 5; DA, dopamine; DARPP-32, dopamine- and cAMP-regulated phosphoprotein; D1R, dopamine D1 receptor; HVA, homovanillic acid; PKA, protein kinase A.

Characterization of the bed nucleus of the stria terminalis in the forebrain of anuran amphibians

Major common features have been reported for the organization of the basal telencephalon in amniotes, and most characteristics were thought to be acquired in the transition from anamniotes to amniotes. However, gene expression, neurochemical, and hodological data obtained for the basal ganglia and septal and amygdaloid complexes in amphibians (anamniotic tetrapods) have strengthened the idea of a conserved organization in tetrapods. A poorly characterized region in the forebrain of amniotes has been the bed nucleus of the stria terminalis (BST), but numerous recent investigations have characterized it as a member of the extended amygdala. Our study analyzes the main features of the BST in anuran amphibians to establish putative homologies with amniotes. Gene expression patterns during development identified the anuran BST as a subpallial, nonstriatal territory. The BST shows Nkx2.1 and Lhx7 expression and contains an Islet1-positive cell subpopulation derived from the lateral ganglionic eminence. Immunohistochemistry for diverse peptides and neurotransmitters revealed that the distinct chemoarchitecture of the BST is strongly conserved among tetrapods. In vitro tracing techniques with dextran amines revealed important connections between the BST and the central and medial amygdala, septal territories, medial pallium, preoptic area, lateral hypothalamus, thalamus, and prethalamus. The BST receives dopaminergic projections from the ventral tegmental area and is connected with the laterodorsal tegmental nucleus and the rostral raphe in the brainstem. All these data suggest that the anuran BST shares many features with its counterpart in amniotes and belongs to a basal continuum, likely controlling similar reflexes, reponses, and behaviors in tetrapods.

Chronic exposure to low levels of inorganic arsenic causes alterations in locomotor activity and in the expression of dopaminergic and antioxidant systems in the albino rat

Several studies have associated chronic arsenicism with decreases in IQ and sensory and motor alterations in humans. Likewise, studies of rodents exposed to inorganic arsenic ((i)As) have found changes in locomotor activity, brain neurochemistry, behavioral tasks, oxidative stress, and in sensory and motor nerves. In the current study, male Sprague-Dawley rats were exposed to environmentally relevant doses of (i)As (0.05, 0.5 mg (i)As/L) and to a high dose (50 mg (i)As/L) in drinking water for one year. Hypoactivity and increases in the striatal dopamine content were found in the group treated with 50 mg (i)As/L. Exposure to 0.5 and 50 mg (i)As/L increased the total brain content of As. Furthermore, (i)As exposure produced a dose-dependent up-regulation of mRNA for Mn-SOD and Trx-1 and a down-regulation of DAR-D₂ mRNA levels in the nucleus accumbens. DAR-D₁ and Nrf2 mRNA expression were down-regulated in nucleus accumbens in the group exposed to 50 mg (i)As/L. Trx-1 mRNA levels were up-regulated in the cortex in an (i)As dose-dependent manner, while DAR-D₁ mRNA expression was increased in striatum in the 0.5 mg (i)As/L group. These results show that chronic exposure to low levels of arsenic causes subtle but region-specific changes in the nervous system, especially in antioxidant systems and dopaminergic elements. These changes became behaviorally evident only in the group exposed to 50 mg (i)As/L.

The small-conductance calcium-activated potassium channel is a key modulator of firing and long-term depression in the dorsal striatum

The striatum is considered to be critical for the control of goal-directed action, with the lateral dorsal striatum (latDS) being implicated in modulation of habits and the nucleus accumbens thought to represent a limbic-motor interface. Although medium spiny neurons from different striatal subregions exhibit many similar properties, differential firing and synaptic plasticity could contribute to the varied behavioral roles across subregions. Here, we examined the contribution of small-conductance calcium-activated potassium channels (SKs) to action potential generation and synaptic plasticity in adult rat latDS and nucleus accumbens shell (NAS) projection neurons in vitro. The SK-selective antagonist apamin exerted a prominent effect on latDS firing, significantly decreasing the interspike interval. Furthermore, prolonged latDS depolarization increased the interspike interval and reduced firing, and this enhancement was reversed by apamin. In contrast, NAS neurons exhibited greater basal firing rates and less regulation of firing by SK inhibition and prolonged depolarization. LatDS neurons also had greater SK currents than NAS neurons under voltage-clamp. Importantly, SK inhibition with apamin facilitated long-term depression (LTD) induction in the latDS but not the NAS, without alterations in glutamate release. In addition, SK activation in the latDS prevented LTD induction. Greater SK function in the latDS than in the NAS was not secondary to differences in sodium or inwardly rectifying potassium channel function, and apamin enhancement of firing did not reflect indirect action through cholinergic interneurons. Thus, these data demonstrate that SKs are potent modulators of action potential generation and LTD in the dorsal striatum, and could represent a fundamental cellular mechanism through which habits are regulated.

Localization and function of the cannabinoid CB1 receptor in the anterolateral bed nucleus of the stria terminalis

BACKGROUND

The bed nucleus of the stria terminalis (BNST) is involved in behaviors related to natural reward, drug addiction and stress. In spite of the emerging role of the endogenous cannabinoid (eCB) system in these behaviors, little is known about the anatomy and function of this system in the anterolateral BNST (alBNST). The aim of this study was to provide a detailed morphological characterization of the localization of the cannabinoid 1 (CB1) receptor a necessary step toward a better understanding of the physiological roles of the eCB system in this region of the brain.

METHODOLOGY/PRINCIPAL FINDINGS

We have combined anatomical approaches at the confocal and electron microscopy level to ex-vivo electrophysiological techniques. Here, we report that CB1 is localized on presynaptic membranes of about 55% of immunopositive synaptic terminals for the vesicular glutamate transporter 1 (vGluT1), which contain abundant spherical, clear synaptic vesicles and make asymmetrical synapses with alBNST neurons. About 64% of vGluT1 immunonegative synaptic terminals show CB1 immunolabeling. Furthermore, 30% and 35% of presynaptic boutons localize CB1 in alBNST of conditional mutant mice lacking CB1 mainly from GABAergic neurons (GABA-CB1-KO mice) and mainly from cortical glutamatergic neurons (Glu-CB1-KO mice), respectively. Extracellular field recordings and whole cell patch clamp in the alBNST rat brain slice preparation revealed that activation of CB1 strongly inhibits excitatory and inhibitory synaptic transmission.

CONCLUSIONS/SIGNIFICANCE

This study supports the anterolateral BNST as a potential neuronal substrate of the effects of cannabinoids on stress-related behaviors.

A role for calmodulin-stimulated adenylyl cyclases in cocaine sensitization

Cocaine sensitization is produced by repeated exposure to the drug and is thought to reflect neuroadaptations that contribute to addiction. Here, we identify the Ca(2+)/calmodulin-stimulated adenylyl cyclases, type 1 (AC1) and type 8 (AC8), as novel regulators of this behavioral plasticity. We show that, whereas AC1 and AC8 single knock-out mice (AC1(-/-) and AC8(-/-)) exhibit Ca(2+)-stimulated adenylyl cyclase activity in striatal membrane fractions, AC1/8 double-knock-out (DKO) mice do not. Furthermore, DKO mice are acutely supersensitive to low doses of cocaine and fail to display locomotor sensitization after chronic cocaine treatment. Because of the known role for the extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase signaling pathway in cocaine-induced behavioral plasticity and its coupling to calcium-stimulated cAMP signaling in the hippocampus, we measured phosphorylated ERK (pERK) levels in the striatum. Under basal conditions, pERK is upregulated in choline acetyltransferase-positive interneurons in DKO mice relative to wild-type (WT) controls. After acute cocaine treatment, pERK signaling is significantly suppressed in medium spiny neurons (MSNs) of DKO mice relative to WT mice. In addition to the lack of striatal ERK activation by acute cocaine, signaling machinery downstream of ERK is uncoupled in DKO mice. We demonstrate that AC1 and AC8 are necessary for the phosphorylation of mitogen and stress-activated kinase-1 (pMSK1) at Ser376 and Thr581 and cAMP response element-binding protein (pCREB) at Ser133 after acute cocaine treatment. Our results demonstrate that the Ca(2+)-stimulated adenylyl cyclases regulate long-lasting cocaine-induced behavioral plasticity via activation of the ERK/MSK1/CREB signaling pathway in striatonigral MSNs.

ebTrack: an environmental bioinformatics system built upon ArrayTrack

ebTrack is being developed as an integrated bioinformatics system for environmental research and analysis by addressing the issues of integration, curation, management, first level analysis and interpretation of environmental and toxicological data from diverse sources. It is based on enhancements to the US FDA developed ArrayTrack™ system through additional analysis modules for gene expression data as well as through incorporation and linkages to modules for analysis of proteomic and metabonomic datasets that include tandem mass spectra. ebTrack uses a client-server architecture with the free and open source PostgreSQL as its database engine, and java tools for user interface, analysis, visualization, and web-based deployment. Several predictive tools that are critical for environmental health research are currently supported in ebTrack, including Significance Analysis of Microarray (SAM). Furthermore, new tools are under continuous integration, and interfaces to environmental health risk analysis tools are being developed in order to make ebTrack widely usable. These health risk analysis tools include the Modeling ENvironment for TOtal Risk studies (MENTOR) for source-to-dose exposure modeling and the DOse Response Information ANalysis system (DORIAN) for health outcome modeling. The design of ebTrack is presented in detail and steps involved in its application are summarized through an illustrative application.

Transcriptome analysis identifies genes with enriched expression in the mouse central extended amygdala

The central extended amygdala (EAc) is an ensemble of highly interconnected limbic structures of the anterior brain, and forms a cellular continuum including the bed nucleus of the stria terminalis (BNST), the central nucleus of the amygdala (CeA) and the nucleus accumbens shell (AcbSh). This neural network is a key site for interactions between brain reward and stress systems, and has been implicated in several aspects of drug abuse. In order to increase our understanding of EAc function at the molecular level, we undertook a genome-wide screen (Affymetrix) to identify genes whose expression is enriched in the mouse EAc. We focused on the less-well known BNST-CeA areas of the EAc, and identified 121 genes that exhibit more than twofold higher expression level in the EAc compared with whole brain. Among these, 43 genes have never been described to be expressed in the EAc. We mapped these genes throughout the brain, using non-radioactive in situ hybridization, and identified eight genes with a unique and distinct rostro-caudal expression pattern along AcbSh, BNST and CeA. Q-PCR analysis performed in brain and peripheral organ tissues indicated that, with the exception of one (Spata13), all these genes are predominantly expressed in brain. These genes encode signaling proteins (Adora2, GPR88, Arpp21 and Rem2), a transcription factor (Limh6) or proteins of unknown function (Rik130, Spata13 and Wfs1). The identification of genes with enriched expression expands our knowledge of EAc at a molecular level, and provides useful information to toward genetic manipulations within the EAc.

Chronic ethanol exposure leads to divergent control of dopaminergic synapses in distinct target regions

Neuroadaptations following chronic exposure to alcohol are hypothesized to play important roles in alcohol-induced alterations in behavior, in particular increased alcohol drinking and anxiety-like behavior. Dopaminergic signaling plays a key role in reward-related behavior, with evidence suggesting it undergoes modification following exposure to drugs of abuse. A large literature indicates an involvement of dopaminergic signaling in response to alcohol. Using a chronic inhalation model of ethanol exposure in mice, we have begun to investigate the effects of alcohol intake on dopaminergic signaling by examining protein levels of tyrosine hydroxylase and the dopamine transporter, as well as monoamine metabolites in three different target fields of three different dopaminergic nuclei. We have focused on the dorsal lateral bed nucleus of the stria terminalis because of the reported involvement of dorsal lateral bed nucleus of the stria terminalis dopamine in ethanol intake, and the nucleus accumbens and dorsal striatum because of their dense dopaminergic innervation. After either a chronic intermittent exposure or continuous exposure regimen, mice were killed, and tissue punches collected from the dorsal lateral bed nucleus of the stria terminalis, nucleus accumbens, and striatum for Western analysis. Strikingly, we found divergent regulation of tyrosine hydroxylase and dopamine transporter protein levels across these three regions that was dependent upon the means of exposure. These data thus suggest that distinct populations of catecholamine neurons may be differentially regulated by ethanol, and that ethanol and withdrawal interact to produce differential adaptations in these systems.