Cell adhesion factors in the orbitofrontal cortex control cue-induced reinstatement of cocaine seeking and amygdala-dependent goal seeking.

Repeated cocaine exposure causes dendritic spine loss in the orbitofrontal cortex, which might contribute to poor orbitofrontal cortical function following drug exposure. One challenge, however, has been verifying links between neuronal structural plasticity and behavior, if any. Here we report that cocaine self-administration triggers the loss of dendritic spines on excitatory neurons in the orbitofrontal cortex of male and female mice (as has been reported in rats). To understand functional consequences, we locally ablated neuronal ß1-integrins, cell adhesion receptors that adhere cells to the extracellular matrix and thus support dendritic spine stability. Degradation of ß1-integrin tone: 1) caused dendritic spine loss; 2) exaggerated cocaine-seeking responses in a cue-induced reinstatement test; and 3) impaired the ability of mice to integrate new learning into familiar routines - a key function of the orbitofrontal cortex. Stimulating Abl-related gene (Arg) kinase, over-expressing Proline-rich tyrosine kinase (Pyk2), and inhibiting Rho-associated coiled-coil containing kinase (ROCK) corrected response strategies, uncovering a ß1-integrin-mediated signaling axis that controls orbitofrontal cortical function. Finally, use of a combinatorial gene silencing/chemogenetic strategy revealed that ß1-integrins support the ability of mice to integrate new information into established behaviors by sustaining orbitofrontal cortical connections with the basolateral amygdala.SIGNIFICANCE STATEMENTCocaine degenerates dendritic spines in the orbitofrontal cortex, a region of the brain involved in interlacing new information into established behaviors. One challenge has been verifying links between cellular structural stability and behavior, if any. In this second of two related investigations, we study integrin family receptors, which adhere cells to the extracellular matrix and thereby stabilize dendritic spines (see also DePoy et al., 2019, Journal of Neuroscience). We reveal that ß1-integrins in the orbitofrontal cortex control food- and cocaine-seeking behaviors. For instance, ß1-integrin loss amplifies cocaine-seeking behavior and impairs the ability of mice to integrate new learning into familiar routines. We identify likely intracellular signaling partners by which ß1-integrins support orbitofrontal cortical function and connectivity with the basolateral amygdala.

ß1-Integrins in the Developing Orbitofrontal Cortex Are Necessary for Expectancy Updating in Mice.

Navigating a changing environment requires associating stimuli and actions with their likely outcomes and modifying these associations when they change. These processes involve the orbitofrontal cortex (OFC). Although some molecular mediators have been identified, developmental factors are virtually unknown. We hypothesized that the cell adhesion factor ß1-integrin is essential to OFC function, anticipating developmental windows during which ß1-integrins might be more influential than others. We discovered that OFC-selective ß1-integrin silencing before adolescence, but not later, impaired the ability of mice to extinguish conditioned fear and select actions based on their likely outcomes. Early-life knock-down also reduced the densities of dendritic spines, the primary sites of excitatory plasticity in the brain, and weakened sensitivity to cortical inputs. Notwithstanding these defects in male mice, females were resilient to OFC (but not hippocampal) ß1-integrin loss. Existing literature suggests that resilience may be explained by estradiol-mediated transactivation of ß1-integrins and tropomyosin receptor kinase B (trkB). Accordingly, we discovered that a trkB agonist administered during adolescence corrected reward-related decision making in ß1-integrin-deficient males. In sum, developmental ß1-integrins are indispensable for OFC function later in life.SIGNIFICANCE STATEMENT The orbitofrontal cortex (OFC) is a subregion of the frontal cortex that allows organisms to link behaviors and stimuli with anticipated outcomes, and to make predictions about the consequences of one's behavior. Aspects of OFC development are particularly prolonged, extending well into adolescence, likely optimizing organisms' abilities to prospectively calculate the consequences of their actions and select behaviors appropriately; these decision making strategies improve as young individuals mature into adulthood. Molecular factors are not, however, well understood. Our experiments reveal that a cell adhesion protein termed "ß1-integrin" is necessary for OFC neuronal maturation and function. Importantly, ß1-integrins operate during a critical period equivalent to early adolescence in humans to optimize the ability of organisms to update expectancies later in life.

Common Regulatory Targets of NFIA, NFIX and NFIB during Postnatal Cerebellar Development.

Transcriptional regulation plays a central role in controlling neural stem and progenitor cell proliferation and differentiation during neurogenesis. For instance, transcription factors from the nuclear factor I (NFI) family have been shown to co-ordinate neural stem and progenitor cell differentiation within multiple regions of the embryonic nervous system, including the neocortex, hippocampus, spinal cord and cerebellum. Knockout of individual Nfi genes culminates in similar phenotypes, suggestive of common target genes for these transcription factors. However, whether or not the NFI family regulates common suites of genes remains poorly defined. Here, we use granule neuron precursors (GNPs) of the postnatal murine cerebellum as a model system to analyse regulatory targets of three members of the NFI family: NFIA, NFIB and NFIX. By integrating transcriptomic profiling (RNA-seq) of Nfia- and Nfix-deficient GNPs with epigenomic profiling (ChIP-seq against NFIA, NFIB and NFIX, and DNase I hypersensitivity assays), we reveal that these transcription factors share a large set of potential transcriptional targets, suggestive of complementary roles for these NFI family members in promoting neural development.

Rho-kinase inhibition has antidepressant-like efficacy and expedites dendritic spine pruning in adolescent mice.

Adolescence represents a critical period of neurodevelopment, defined by structural and synaptic pruning within the prefrontal cortex. While characteristic of typical development, this structural instability may open a window of vulnerability to developing neuropsychiatric disorders, including depression. Thus, therapeutic interventions that support or expedite neural remodeling in adolescence may be advantageous. Here, we inhibited the neuronally-expressed cytoskeletal regulatory factor Rho-kinase (ROCK), focusing primarily on the clinically-viable ROCK inhibitor fasudil. ROCK inhibition had rapid antidepressant-like effects in adolescent mice, and its efficacy was comparable to ketamine and fluoxetine. It also modified levels of the antidepressant-related signaling factors, tropomyosin/tyrosine receptor kinase B and Akt, as well as the postsynaptic marker PSD-95, in the ventromedial prefrontal cortex (vmPFC). Meanwhile, adolescent-typical dendritic spine pruning on excitatory pyramidal neurons in the vmPFC was expedited. Further, vmPFC-specific shRNA-mediated reduction of ROCK2, the dominant ROCK isoform in the brain, had antidepressant-like consequences. We cautiously suggest that ROCK inhibitors may have therapeutic potential for adolescent-onset depression.

Kalirin-7 prevents dendritic spine dysgenesis induced by amyloid beta-derived oligomers.

Synapse degeneration and dendritic spine dysgenesis are believed to be crucial early steps in Alzheimer's disease (AD), and correlate with cognitive deficits in AD patients. Soluble amyloid beta (Aß)-derived oligomers, also termed Aß-derived diffusible ligands (ADDLs), accumulate in the brain of AD patients and play a crucial role in AD pathogenesis. ADDLs bind to mature hippocampal neurons, induce structural changes in dendritic spines and contribute to neuronal death. However, mechanisms underlying structural and toxic effects are not fully understood. Here, we report that ADDLs bind to cultured mature cortical pyramidal neurons and induce spine dysgenesis. ADDL treatment induced the rapid depletion of kalirin-7, a brain-specific guanine-nucleotide exchange factor for the small GTPase Rac1, from spines. Kalirin-7 is a key regulator of dendritic spine morphogenesis and maintenance in forebrain pyramidal neurons and here we show that overexpression of kalirin-7 prevents ADDL-induced spine degeneration. Taken together, our results suggest that kalirin-7 may play a role in the early events leading to synapse degeneration, and its pharmacological activation may prevent or delay synapse pathology in AD.

Corticosteroid-induced dendrite loss and behavioral deficiencies can be blocked by activation of Abl2/Arg kinase.

Stressor exposure induces neuronal remodeling in specific brain regions. Given the persistence of stress-related illnesses, key next steps in determining the contributions of neural structure to mental health are to identify cell types that fail to recover from stressor exposure and to identify "trigger points" and molecular underpinnings of stress-related neural degeneration. We evaluated dendrite arbor structure on hippocampal CA1 pyramidal neurons before, during, and following prolonged exposure to one key mediator of the stress response - corticosterone (cortisol in humans). Basal dendrite arbors progressively simplified during a 3-week exposure period, and failed to recover when corticosterone was withdrawn. Corticosterone exposure decreased levels of the dendrite stabilization factor Abl2/Arg nonreceptor tyrosine kinase and phosphorylation of its substrates p190RhoGAP and cortactin within 11days, suggesting that disruption of Arg-mediated signaling may trigger dendrite arbor atrophy and, potentially, behavioral abnormalities resulting from corticosterone exposure. To test this, we administered the novel, bioactive Arg kinase activator, 5-(1,3-diaryl-1H-pyrazol-4-yl)hydantoin, 5-[3-(4-fluorophenyl)-1-phenyl-1H-pyrazol-4-yl]-2,4-imidazolidinedione (DPH), in conjunction with corticosterone. We found that repeated treatment corrected CA1 arbor structure, otherwise simplified by corticosterone. DPH also corrected corticosterone-induced errors in a hippocampal-dependent reversal learning task and anhedonic-like behavior. Thus, pharmacological compounds that target cytoskeletal regulators, rather than classical neurotransmitter systems, may interfere with stress-associated cognitive decline and mental health concerns.

Differential expression of cytoskeletal regulatory factors in the adolescent prefrontal cortex: Implications for cortical development.

The prevalence of depression, anxiety, schizophrenia, and drug and alcohol use disorders peaks during adolescence. Further, up to 50% of "adult" mental health disorders emerge in adolescence. During adolescence, the prefrontal cortex (PFC) undergoes dramatic structural reorganization, in which dendritic spines and synapses are refined, pruned, and stabilized. Understanding the molecular mechanisms that underlie these processes should help to identify factors that influence the development of psychiatric illness. Here we briefly discuss the anatomical connections of the medial and orbital prefrontal cortex (mPFC and OFC, respectively). We then present original findings suggesting that dendritic spines on deep-layer excitatory neurons in the mouse mPFC and OFC prune at different adolescent ages, with later pruning in the OFC. In parallel, we used Western blotting to define levels of several cytoskeletal regulatory proteins during early, mid-, and late adolescence, focusing on tropomyosin-related kinase receptor B (TrkB) and ß1-integrin-containing receptors and select signaling partners. We identified regional differences in the levels of several proteins in early and midadolescence that then converged in early adulthood. We also observed age-related differences in TrkB levels, both full-length and truncated isoforms, Rho-kinase 2, and synaptophysin in both PFC subregions. Finally, we identified changes in protein levels in the dorsal and ventral hippocampus that were distinct from those in the PFC. We conclude with a general review of the manner in which TrkB- and ß1-integrin-mediated signaling influences neuronal structure in the postnatal brain. Elucidating the role of cytoskeletal regulatory factors throughout adolescence may identify critical mechanisms of PFC development. © 2016 Wiley Periodicals, Inc.

Adolescent-onset GABAA α1 silencing regulates reward-related decision making.

The GABAA receptor mediates fast, inhibitory signaling, and cortical expression of the α1 subunit increases during postnatal development. Certain pathological stimuli such as stressors or prenatal cocaine exposure can interfere with this process, but causal relationships between GABAA α1 deficiency and complex behavioral outcomes remain unconfirmed. We chronically reduced GABAA α1 expression selectively in the medial prefrontal cortex (prelimbic subregion) of mice using viral-mediated gene silencing of Gabra1. Adolescent-onset Gabra1 knockdown delayed the acquisition of a cocaine-reinforced instrumental response but spared cocaine seeking in extinction and in a cue-induced reinstatement procedure. To determine whether response acquisition deficits could be associated with impairments in action-outcome associative learning and memory, we next assessed behavioral sensitivity to instrumental contingency degradation. In this case, the predictive relationship between familiar actions and their outcomes is violated. Adolescent-onset knockdown, although not adult-onset knockdown, delayed the expression of goal-directed response strategies in this task, resulting instead in inflexible habit-like modes of response. Thus, the maturation of medial prefrontal cortex GABAA α1 systems during adolescence appears necessary for goal-directed reward-related decision making in adulthood. These findings are discussed in the light of evidence that prolonged Gabra1 deficiency may impair synaptic plasticity.

A molecularly defined orbitofrontal cortical neuron population controls compulsive-like behavior, but not inflexible choice or habit.

Habits are familiar behaviors triggered by cues, not outcome predictability, and are insensitive to changes in the environment. They are adaptive under many circumstances but can be considered antecedent to compulsions and intrusive thoughts that drive persistent, potentially maladaptive behavior. Whether compulsive-like and habit-like behaviors share neural substrates is still being determined. Here, we investigated mice bred to display inflexible reward-seeking behaviors that are insensitive to action consequences. We found that these mice demonstrate habitual response biases and compulsive-like grooming behavior that was reversible by fluoxetine and ketamine. They also suffer dendritic spine attrition on excitatory neurons in the orbitofrontal cortex (OFC). Nevertheless, synaptic melanocortin 4 receptor (MC4R), a factor implicated in compulsive behavior, is preserved, leading to the hypothesis that Mc4r+ OFC neurons may drive aberrant behaviors. Repeated chemogenetic stimulation of Mc4r+ OFC neurons triggered compulsive and not inflexible or habitual response biases in otherwise typical mice. Thus, Mc4r+ neurons within the OFC appear to drive compulsive-like behavior that is dissociable from habitual behavior. Understanding which neuron populations trigger distinct behaviors may advance efforts to mitigate harmful compulsions.

The roles of phospholipase C activation and alternative ADAR1 and ADAR2 pre-mRNA splicing in modulating serotonin 2C-receptor editing in vivo.

The serotonin 2C receptor (5-HT2CR), a Gq-protein-coupled neurotransmitter receptor, exists in multiple isoforms that result from RNA editing of five exonic adenosines that are converted to inosines. In the adult brain, editing of 5-HT2C pre-mRNA exhibits remarkable plasticity in response to environmental and neurochemical stimuli. Here, we investigated two potential mechanisms underlying these plastic changes in adult 5-HT2CR editing phenotypes in vivo: activation of phospholipase C (PLC) and alternative splicing of pre-mRNA encoding the editing enzymes ADAR1 and ADAR2. Studies on two inbred strains of mice (C57Bl/6 and Balb/c) revealed that sustained stimulation of PLC--a downstream effector of activated G alpha q protein--increased editing of forebrain neocortical 5-HT2C pre-mRNA at two sites known to be targeted by ADAR2. Moreover, changes in relative expression of the alternatively spliced "a" and "b" mRNA isoforms of ADAR1 and ADAR2 also correlate with changes in 5-HT2CR editing. The site-specific changes in 5-HT2CR editing detected in mice with different "a" over "b" ADAR mRNA isoform ratios only partially overlap with those evoked by sustained PLC activation and are best explained by the increased editing efficiency of ADAR1. Thus, activation of PLC and alternative splicing of ADAR pre-mRNA have both overlapping and specific roles in modulating 5-HT2CR editing phenotypes.

Cell adhesion presence during adolescence controls the architecture of projection-defined prefrontal cortical neurons and reward-related action strategies later in life.

Adolescent brain development is characterized by neuronal remodeling in the prefrontal cortex; relationships with behavior are largely undefined. Integrins are cell adhesion factors that link the extracellular matrix with intracellular actin cytoskeleton. We find that ß1-integrin presence in the prelimbic prefrontal cortex (PL) during adolescence, but not adulthood, is necessary for mice to select actions based on reward likelihood and value. As such, adult mice that lacked ß1-integrin during adolescence failed to modify response strategies when rewards lost value or failed to be delivered. This pattern suggests that ß1-integrin-mediated neuronal development is necessary for PL function in adulthood. We next visualized adolescent PL neurons, including those receiving input from the basolateral amygdala (BLA) - thought to signal salience - and projecting to the dorsomedial striatum (DMS) - the striatal output by which the PL controls goal-seeking behavior. Firstly, we found that these projection-defined neurons had a distinct morphology relative to general layer V PL neurons. Secondly, ß1-integrin loss triggered the overexpression of stubby-type dendritic spines at the expense of mature spines, including on projection-defined neurons. This phenotype was not observed when ß1-integrins were silenced before or after adolescence. Altogether, our experiments localize ß1-integrin-mediated cell adhesion within a developing di-synaptic circuit coordinating adaptive action.

Inter-individual variability amplified through breeding reveals control of reward-related action strategies by Melanocortin-4 Receptor in the dorsomedial striatum.

In day-to-day life, we often must choose between pursuing familiar behaviors or adjusting behaviors when new strategies might be more fruitful. The dorsomedial striatum (DMS) is indispensable for arbitrating between old and new action strategies. To uncover molecular mechanisms, we trained mice to generate nose poke responses for food, then uncoupled the predictive relationship between one action and its outcome. We then bred the mice that failed to rapidly modify responding. This breeding created offspring with the same tendencies, failing to inhibit behaviors that were not reinforced. These mice had less post-synaptic density protein 95 in the DMS. Also, densities of the melanocortin-4 receptor (MC4R), a high-affinity receptor for α-melanocyte-stimulating hormone, predicted individuals' response strategies. Specifically, high MC4R levels were associated with poor response inhibition. We next found that reducing Mc4r in the DMS in otherwise typical mice expedited response inhibition, allowing mice to modify behavior when rewards were unavailable or lost value. This process required inputs from the orbitofrontal cortex, a brain region canonically associated with response strategy switching. Thus, MC4R in the DMS appears to propel reward-seeking behavior, even when it is not fruitful, while moderating MC4R presence increases the capacity of mice to inhibit such behaviors.

KALRN: A central regulator of synaptic function and synaptopathies.

The synaptic regulator, kalirin, plays a key role in synaptic plasticity and formation of dendritic arbors and spines. Dysregulation of the KALRN gene has been linked to various neurological disorders, including autism spectrum disorder, Alzheimer's disease, schizophrenia, addiction and intellectual disabilities. Both genetic and molecular studies highlight the importance of normal KALRN expression for healthy neurodevelopment and function. This review aims to give an in-depth analysis of the structure and molecular mechanisms of kalirin function, particularly within the brain. These data are correlated to genetic evidence of patient mutations within KALRN and animal models of Kalrn that together give insight into the manner in which this gene may be involved in neurodevelopment and the etiology of disease. The emerging links to human disease from post-mortem, genome wide association (GWAS) and exome sequencing studies are examined to highlight the disease relevance of kalirin, particularly in neurodevelopmental diseases. Finally, we will discuss efforts to pharmacologically regulate kalirin protein activity and the implications of such endeavors for the treatment of human disease. As multiple disease states arise from deregulated synapse formation and altered KALRN expression and function, therapeutics may be developed to provide control over KALRN activity and thus synapse dysregulation. As such, a detailed understanding of how kalirin regulates neuronal development, and the manner in which kalirin dysfunction promotes neurological disease, may support KALRN as a valuable therapeutic avenue for future pharmacological intervention.

The PI3-Kinase p110ß Isoform Controls Severity of Cocaine-Induced Sequelae and Alters the Striatal Transcriptome.

BACKGROUND: The PI3-kinase (PI3K) complex is a well-validated target for mitigating cocaine-elicited sequelae, but pan-PI3K inhibitors are not viable long-term treatment options. The PI3K complex is composed of p110 catalytic and regulatory subunits, which can be individually manipulated for therapeutic purposes. However, this possibility has largely not been explored in behavioral contexts. METHODS: Here, we inhibited PI3K p110ß in the medial prefrontal cortex (mPFC) of cocaine-exposed mice. Behavioral models for studying relapse, sensitization, and decision-making biases were paired with protein quantification, RNA sequencing, and cell type-specific chemogenetic manipulation and RNA quantification to determine whether and how inhibiting PI3K p110ß confers resilience to cocaine. RESULTS: Viral-mediated PI3K p110ß silencing reduced cue-induced reinstatement of cocaine seeking by half, blocked locomotor sensitization, and restored mPFC synaptic marker content after exposure to cocaine. Cocaine blocked the ability of mice to select actions based on their consequences, and p110ß inhibition restored this ability. Silencing dopamine D2 receptor-expressing excitatory mPFC neurons mimicked cocaine, impairing goal-seeking behavior, and again, p110ß inhibition restored goal-oriented action. We verified the presence of p110ß in mPFC neurons projecting to the dorsal striatum and orbitofrontal cortex and found that inhibiting p110ß in the mPFC altered the expression of functionally defined gene clusters within the dorsal striatum and not orbitofrontal cortex. CONCLUSIONS: Subunit-selective PI3K silencing potently mitigates drug seeking, sensitization, and decision-making biases after exposure to cocaine. We suggest that inhibiting PI3K p110ß provides neuroprotection against cocaine by triggering coordinated corticostriatal adaptations.

The CNTNAP2-CASK complex modulates GluA1 subcellular distribution in interneurons.

GABAergic interneurons are emerging as prominent substrates in the pathophysiology of multiple neurodevelopmental disorders, including autism spectrum disorders, schizophrenia, intellectual disability, and epilepsy. Interneuron excitatory activity is influenced by 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl) propanoic acid receptors (AMPARs), which in turn affects excitatory transmission in the central nervous system. Yet how dysregulation of interneuronal AMPARs distinctly contributes to the molecular underpinning of neurobiological disease is drastically underexplored. Contactin-associated protein-like 2 (CNTNAP2) is a neurexin-related adhesion molecule shown to mediate AMPAR subcellular distribution while calcium/calmodulin-dependent serine protein kinase (CASK) is a multi-functional scaffold involved with glutamate receptor trafficking. Mutations in both genes have overlapping disease associations, including autism spectrum disorders, intellectual disability, and epilepsy, thus suggesting converging perturbations of excitatory/inhibitory balance. Our lab has previously shown that CNTNAP2 stabilizes interneuron dendritic arbors through CASK and that CNTNAP2 regulates AMPAR subunit GluA1 trafficking in excitatory neurons. The interaction between these three proteins, however, has not been studied in interneurons. Using biochemical techniques, structured illumination microscopy (SIM) and shRNA technology, we first confirm that these three proteins interact in mouse brain, and then examined relationship between CNTNAP2, CASK and GluA1 in mature interneurons. Using SIM, we ascertain that a large fraction of endogenous CNTNAP2, CASK, and GluA1 molecules collectively colocalize together in a tripartite manner. Finally, individual knockdown of either CNTNAP2 or CASK similarly alter GluA1 levels and localization. These findings offer insight to molecular mechanisms underlying GluA1 regulation in interneurons.

Neurodevelopmental disorder-associated ZBTB20 gene variants affect dendritic and synaptic structure.

Dendritic spine morphology and dendritic arborization are key determinants of neuronal connectivity and play critical roles in learning, memory and behavior function. Recently, defects of ZBTB20, a BTB and zinc finger domain containing transcriptional repressor, have been implicated in a wide range of neurodevelopmental disorders, including intellectual disability and autism. Here we show distinct effects of expression of two major isoforms, long and short, of ZBTB20, and its neurodevelopmental disorder-linked variants, on dendritic architecture of cultured rat cortical pyramidal neurons. The N-terminal of ZBTB20 showed a role in regulating dendritic spine morphology. Two ZBTB20 single nucleotide variants, located at the N-terminal and central regions of the protein and potentially conferring autism risk, altered dendritic spine morphology. In contrast, a single nucleotide variant identified in patients with intellectual disability and located at the C-terminus of ZBTB20 affected dendritic arborization and dendritic length but had no effect on dendritic spine morphology. Furthermore, truncation of the extreme C-terminus of ZBTB20 caused spine and dendritic morphological changes that were similar but distinct from those caused by the C-terminal variant. Taken together, our study suggests ZBTB20's role in dendritic and synaptic structure and provide possible mechanisms of its effect in neurodevelopmental disorders.

GABAAα1-mediated plasticity in the orbitofrontal cortex regulates context-dependent action selection.

An essential aspect of goal-directed action selection is differentiating between behaviors that are more, or less, likely to be reinforced. Habits, by contrast, are stimulus-elicited behaviors insensitive to action-outcome contingencies and are considered an etiological factor in several neuropsychiatric disorders. Thus, isolating the neuroanatomy and neurobiology of goal-directed action selection on the one hand, and habit formation on the other, is critical. Using in vivo viral-mediated gene silencing, we knocked down Gabra1 in the orbitofrontal prefrontal cortex (oPFC) in mice, decreasing oPFC GABAAα1 expression, as well as expression of the synaptic marker PSD-95. Mice expressing Green Fluorescent Protein or Gabra1 knockdown in the adjacent M2 motor cortex served as comparison groups. Using instrumental response training followed by action-outcome contingency degradation, we then found that oPFC GABAAα1 deficiency impaired animals' ability to differentiate between actions that were more or less likely to be reinforced, though sensitivity to outcome devaluation and extinction were intact. Meanwhile, M2 GABAAα1 deficiency enhanced sensitivity to action-outcome relationships. Behavioral abnormalities following oPFC GABAAα1 knockdown were rescued by testing mice in a distinct context relative to that in which they had been initially trained. Together, our findings corroborate evidence that chronic GABAAα1 deficiency remodels cortical synapses and suggest that neuroplasticity within the healthy oPFC gates the influence of reward-related contextual stimuli. These stimuli might otherwise promote maladaptive habit-based behavioral response strategies that contribute to-or exacerbate-neuropsychiatric illness.

Developmental exposure to the organochlorine insecticide endosulfan damages the nigrostriatal dopamine system in male offspring.

The contribution of environmental toxicants to the etiology and risk of Parkinson's disease (PD) has been clearly established, with organochlorine insecticides routinely shown to damage the nigrostriatal dopamine pathway. Although PD is generally considered an adult onset disease, it has been postulated that exposure to environmental contaminants or other factors early in life during critical periods of neurodevelopment could alter the dopaminergic circuit and predispose individuals to developing PD. Recent epidemiological evidence has found exposure to the organochlorine insecticide endosulfan to be a risk factor for PD. However, the specific dopaminergic targets or vulnerable developmental time points related to endosulfan exposure have not been investigated. Thus, we sought to investigate dopaminergic neurotoxicity following developmental exposure to endosulfan as well as following an additional challenge with MPTP. Our in vitro findings demonstrate a reduction in SK-N-SH cells and ventral mesencephalic primary cultures after endosulfan treatment. Using an in vivo developmental model, exposure to endosulfan during gestation and lactation caused a reduction in DAT and TH in the striatum of male offspring. These alterations were exacerbated following subsequent treatment with MPTP. In contrast, exposure of adult mice to endosulfan did not elicit dopaminergic damage and did not appear to increase the vulnerability of the dopamine neurons to MPTP. These findings suggest that development during gestation and lactation represents a critical window of susceptibility to endosulfan exposure and development of the nigrostriatal dopamine system. Furthermore, these exposures appear to sensitize the dopamine neurons to additional insults that may occur later in life.

Glucocorticoid receptor regulation of action selection and prefrontal cortical dendritic spines.

We recently reported that prolonged exposure to the glucocorticoid receptor (GR) ligand corticosterone impairs decision-making that is dependent on the predictive relationship between an action and its outcome (Gourley et al.; Proceedings of the National Academy of Sciences, 2012). Additionally, acute GR blockade, when paired with action-outcome conditioning, also blocks new learning. We then showed that dendritic spines in the prelimbic prefrontal cortex remodeled under both conditions. Nonetheless, the relationship between deep-layer dendritic spines and outcome-based decision-making remains opaque. We report here that a history of prolonged corticosterone exposure increases dendritic spine density in deep-layer prelimbic cortex. When spines are imaged simultaneously with corticosteroid exposure (i.e., without a washout period), dendritic spine densities are, however, reduced. Thus, the morphological response of deep-layer prelimbic cortical neurons to prolonged corticosteroid exposure may be quite dynamic, with spine elimination during a period of chronic exposure and spine proliferation during a subsequent washout period. We provide evidence, using a Rho-kinase inhibitor, that GR-mediated dendritic spine remodeling is causally related to complex decision-making. Finally, we conclude this report with evidence that a history of early-life (adolescent) GR blockade, unlike acute blockade in adulthood, enhances subsequent outcome-based decision-making. Together, our findings suggest that physiological levels of GR binding enable an organism to learn about the predictive relationship between an action and its outcome, but a history of GR blockade may, under some circumstances, also have beneficial consequences.