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In mammals, the ability to optimize and select behavioral strategies is a cardinal and conserved psychophysiological feature for maximizing the chances of survival. However, the neural circuits and underlying mechanisms regulating this flexible feature remain yet unsolved. Here, we demonstrate that such optimization relies on dopamine D2 receptors (D2R) within a subcircuit spanning across the extended amygdala (EA) and the tail of the striatum (TS). Using a mouse model carrying a temporally controlled deletion of D2R within a subcircuit defined by WFS1 neurons, we found that intact EA D2R signaling is necessary to regulate homeostasis-dependent food-seeking behaviors in both male and female mice as well as active avoidance learning and innate escape responses in males. Altogether, these findings identify EA and TS D2R signaling as a novel hub through which dopamine optimizes appetitive behaviors and regulates the switch from passive to active defensive behaviors, regardless of learned or innate threats.

International audience; Psychostimulant drugs, such as cocaine, d-amphetamine and methylphenidate, alter a wide range of behaviors including locomotor activity and somatosensory perception. These altered behaviors are accompanied by the activation of specific neuronal populations within reward-, emotion- and locomotion-related circuits. However, whether such regulation occurs at the level of the spinal cord, a key node for neural circuits integrating and coordinating sensory and motor functions has never been addressed. By evaluating the temporal and spatial expression pattern of the phosphorylated form of the immediate early gene cFos at Ser32 (pS32-cFos), used as a proxy of neuronal activation, we demonstrate that, in adult male mice, d-amphetamine increases pS32-cFos expression in both inhibitory and excitatory neurons in dorsal and ventral horns at the lumbar spinal cord level. Interestingly, a fraction of neurons activated by a first exposure to d-amphetamine can be re-activated following d-amphetamine re-exposure. Similar expression patterns were observed in response to cocaine and methylphenidate, but not following morphine and dozilcipine administration. Finally, the blockade of dopamine reuptake was sufficient to recapitulate the increase in pS32-cFos expression induced by psychostimulant drugs. Our work provides evidence that cFos expression can be activated in lumbar spinal cord in response to acute psychostimulants administration. Running title: Psychostimulant-evoked neuronal ensembles in spinal cord.

Prescription stimulants, such as d-amphetamine or methylphenidate are used to treat suffering from attention-deficit hyperactivity disorder (ADHD). They potently release dopamine (DA) and norepinephrine (NE) and cause phosphorylation of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit GluA1 in the striatum. Whether other brain regions are also affected remains elusive. Here, we demonstrate that d-amphetamine and methylphenidate increase phosphorylation at Ser845 (pS845-GluA1) in the membrane fraction of mouse cerebellum homogenate. We identify Bergmann glial cells as the source of pS845-GluA1 and demonstrate a requirement for intact NE release. Consequently, d-amphetamine-induced pS845-GluA1 was prevented by β1-adenoreceptor antagonist, whereas the blockade of DA D1 receptor had no effect. Together, these results indicate that NE regulates GluA1 phosphorylation in Bergmann glial cells in response to prescription stimulants., SCOPUS: ar.j, info:eu-repo/semantics/published

SummaryThe ability to efficiently switch from one defensive strategy to another maximizes an animal’s chance of survival. Here, we demonstrate that the selection of active defensive behaviors requires the coordinated activation of dopamine D2 receptor (D2R) signaling within the central extended amygdala (EA) comprising the nucleus accumbens, the oval bed nucleus stria terminals and the central amygdala. We find that discriminative learning between predictive and non-predictive threat auditory stimuli is unaltered in mice carrying a temporally-controlled deletion of D2R within output neurons of the EA. In contrast, intact EA D2R signaling is required for active avoidance learning and innate flight responses triggered by a visual threat stimulus (looming). Consequently, conditional D2R knockout mice biased defensive responses toward passive defensive strategies. Altogether, these findings identify EA D2R signaling as an important mechanism by which DA regulates the switch from passive to active defensive behaviors, regardless whether of learned or innate threat.

Prescription stimulants, such as d-amphetamine or methylphenidate, are potent dopamine (DA) and norepinephrine (NE) releasers used to treat children and adults diagnosed for attention-deficit/hyperactivity disorder (ADHD). Although increased phosphorylation of the AMPA receptor subunit GluA1 at Ser845 (pS845-GluA1) in the striatum has been identified as an important cellular effector for the actions of these drugs, regulation of this posttranslational modification in the cerebellum has never been recognized. Here, we demonstrate that d-amphetamine and methylphenidate increase pS845-GluA1 in the membrane fraction in both vermis and lateral hemispheres of the mouse cerebellum. This regulation occurs selectively in Bergmann Glia Cells and requires intact norepinephrine release since the effects were abolished in mice lacking the vesicular monoamine transporter-2 selectively in NE neurons. Moreover, d-amphetamine-induced pS845-GluA1 was prevented by β1-adenoreceptor antagonist, whereas the blockade of dopamine D1 receptor had no effect. Additionally, we identified transcriptional alterations of several regulators of the cAMP/PKA pathway, which might account for the absence of pS845-GluA1 desensitization in mice repeatedly exposed to d-amphetamine or methylphenidate. Together, these results point to norepinephrine transmission as a key regulator of GluA1 phosphorylation in Bergmann Glial Cells, which may represent a new target for the treatment of ADHD.

The cerebellum, a primary brain structure involved in the control of sensorimotor tasks, also contributes to higher cognitive functions including reward, emotion and social interaction. Although the regulation of these behaviors has been largely ascribed to the monoaminergic system in limbic regions, the contribution of cerebellar dopamine signaling in the modulation of these functions remains largely unknown. By combining cell-type-specific transcriptomics, histological analyses, three-dimensional imaging and patch-clamp recordings, we demonstrate that cerebellar dopamine D2 receptors (D2Rs) in mice are preferentially expressed in Purkinje cells (PCs) and regulate synaptic efficacy onto PCs. Moreover, we found that changes in D2R levels in PCs of male mice during adulthood alter sociability and preference for social novelty without affecting motor functions. Altogether, these findings demonstrate novel roles for D2R in PC function and causally link cerebellar D2R levels of expression to social behaviors.

SummaryThe cerebellum, a primary center involved in the control of sensorimotor tasks, also contributes to higher cognitive functions including reward, emotion and social interaction. The regulation of these behaviors has been largely ascribed to the monoaminergic system in limbic regions. However, the contribution of cerebellar dopamine signaling in the modulation of these functions remains largely unknown due to the lack of precise characterization of cerebellar dopaminoceptive neurons. By combining cell type-specific transcriptomic and histological analyses, 3D imaging and electrophysiology we demonstrate that cerebellar dopamine D2 receptors (D2R) in mice are preferentially expressed in Purkinje cells (PCs). While activation of D2R regulate synaptic efficacy onto PCs, their deletion or overexpression in PCs bidirectionally controls preference for social novelty without affecting motor functions. Altogether, these findings demonstrate novel D2R’s roles in PC function and causally link cerebellar D2R levels of expression to social behaviors.

Stressful events can generate emotional memories linked to the traumatic incident, but they also can impair the formation of nonemotional memories. Although the impact of stress on emotional memories is well studied, much less is known about the influence of the emotional state on the formation of nonemotional memories. We used the novel object-recognition task as a model of nonemotional memory in mice to investigate the underlying mechanism of the deleterious effect of stress on memory consolidation. Systemic, hippocampal, and peripheral blockade of cannabinoid type-1 (CB1) receptors abolished the stress-induced memory impairment. Genetic deletion and rescue of CB1 receptors in specific cell types revealed that the CB1 receptor population specifically in dopamine β-hydroxylase (DBH)-expressing cells is both necessary and sufficient for stress-induced impairment of memory consolidation, but CB1 receptors present in other neuronal populations are not involved. Strikingly, pharmacological manipulations in mice expressing CB1 receptors exclusively in DBH(+) cells revealed that both hippocampal and peripheral receptors mediate the impact of stress on memory consolidation. Thus, CB1 receptors on adrenergic and noradrenergic cells provide previously unrecognized cross-talk between central and peripheral mechanisms in the stress-dependent regulation of nonemotional memory consolidation, suggesting new potential avenues for the treatment of cognitive aspects on stress-related disorders. We acknowledge a predoctoral fellowship from the Spanish Ministry of Education and a postdoctoral fellowship from the Investments for the Future Programme, Initiative of Excellence Bordeaux, ANR-10-IDEX-03-02 (to A.B.-G.); a postdoctoral fellowship from the Marie Curie action Seventh Framework Programme for Research and Technological Development, FP7-PEOPLE-2013 (to A.B.-G.); the partial support by FRAXA Research Foundation (M.G.-G.); a European Molecular Biology Organization postdoctoral fellowship (to L. Bellocchio); grants from Ministerio de Ciencia e Innovación [BFU2012-33500 and BFU2015-68568P (to A.O.), and SAF2014-59648-P (to R.M.) (MINECO/FEDER, UE)]; Instituto de Salud Carlos III Grant RD06/0001/0001 (to R.M.); Generalitat de Catalunya Grant SGR-2014-1547 (to R.M.); ICREA (Institució Catalana de Recerca i Estudis Avançats) Academia (R.M.); the German Research Council DFG Grants FOR926 (Core Unit Endocannabinoid Measurements) (to B.L.), CRC-TRR58 (to B.L.), and CRC1080 (to B.L.); EU-FP7 Grant REPROBESITY, HEALTH-F2-2008-223713 (to B.L. and G.M.); PainCage Grant HEALTH-2013-INNOVATION-1-603191 (to G.M.); INSERM (G.M.); European Research Council Grant ENDOFOOD, ERC–2010–StG–260515 (to G.M.); Fondation pour la Recherche Medicale (G.M.); Region Aquitaine (G.M.); and LABEX BRAIN Grant ANR-10-LABX-43 (to G.M.)

Chronic cannabis exposure can lead to cerebellar dysfunction in humans, but the neurobiological mechanisms involved remain incompletely understood. Here, we found that in mice, subchronic administration of the psychoactive component of cannabis, delta9-tetrahydrocannabinol (THC), activated cerebellar microglia and increased the expression of neuroinflammatory markers, including IL-1β. This neuroinflammatory phenotype correlated with deficits in cerebellar conditioned learning and fine motor coordination. The neuroinflammatory phenotype was readily detectable in the cerebellum of mice with global loss of the CB1 cannabinoid receptor (CB1R, Cb1(-/-) mice) and in mice lacking CB1R in the cerebellar parallel fibers, suggesting that CB1R downregulation in the cerebellar molecular layer plays a key role in THC-induced cerebellar deficits. Expression of CB2 cannabinoid receptor (CB2R) and Il1b mRNA was increased under neuroinflammatory conditions in activated CD11b-positive microglial cells. Furthermore, administration of the immunosuppressant minocycline or an inhibitor of IL-1β receptor signaling prevented the deficits in cerebellar function in Cb1(-/-) and THC-withdrawn mice. Our results suggest that cerebellar microglial activation plays a crucial role in the cerebellar deficits induced by repeated cannabis exposure. This study was supported by grants from the Ministerio de Ciencia e Innovación (BFU2008-03390, to A. Gruart; BFU2008-00899, to J.M. Delgado-García; SAF2007-64062 and SAF2011-29864, to R. Maldonado; and SAF2009-07309 and BFU2012-33500, to A. Ozaita); the European Commission (PHECOMP, LSHM-CT-2007-037669, to R. Maldonado); the Instituto de Salud Carlos III (RTA-RETICS, RD06/001/001, to R. Maldonado); the Generalitat de Catalunya (SGR2009-SGR00731, to R. Maldonado); the Fundació La Marató de TV3 (090910, to A. Ozaita); and the ICREA Academia (to R. Maldonado). Partial support from the EU FEDER funds is also acknowledged.

Repeated psychostimulant exposure induces persistent gene expression modifications that contribute to enduring changes in striatal GABAergic spiny projecting neurons (SPNs). However, it remains unclear whether changes in the control of mRNA translation are required for the establishment of these durable modifications. Here we report that repeated exposure to D-amphetamine decreases global striatal mRNA translation. This effect is paralleled by an enhanced phosphorylation of the translation factors, eIF2α and eEF2, and by the concomitant increased translation of a subset of mRNAs, among which the mRNA encoding for the activity regulated cytoskeleton-associated protein, also known as activity regulated gene 3.1 (Arc/Arg3.1). The enrichment of Arc/Arg3.1 mRNA in the polysomal fraction is accompanied by a robust increase of Arc/Arg3.1 protein levels within the striatum. Immunofluorescence analysis revealed that this increase occurred preferentially in D1R-expressing SPNs localized in striosome compartments. Our results suggest that the decreased global protein synthesis following repeated exposure to D-amphetamine favors the translation of a specific subset of mRNAs in the striatum.

Microglial cells, a subpopulation of brain cells of immune origin, survey the brain parenchyma and the synaptic contacts between neurons under healthy/naive conditions. This cell population is sensitive to a number of chemical signals that modify its phenotype from resting/surveillance to an activated state. This later phenotype is associated with the production and secretion of cell mediators, including nitric oxide or cytokines, which may affect glial and neuronal functionality in the surrounding area, causing neuroinflammation, and finally brain dysfunction. The components of the endocannabinoid system have been found to modulate microglial states. The activated state of microglia during neuroinflammation responds, among others, to CB2 cannabinoid receptor agonists, reducing microglial reactivity. On the other hand, brain exposure to cannabis deregulates the endocannabinoid system in ways that produce microglial reactivity, as it has been described in the molecular layer of the cerebellum. In this case, microglial reactivity secondary to CB1 cannabinoid receptor downregulation has an assessable impact on cerebellar function, which can be remediated by drugs reducing neuroinflammation.

In the hippocampus, a functional role of dopamine D1 receptors (D1R) in synaptic plasticity and memory processes has been suggested by electrophysiological and pharmacological studies. However, comprehension of their function remains elusive due to the lack of knowledge on the precise localization of D1R expression among the diversity of interneuron populations. Using BAC transgenic mice expressing enhanced green fluorescent protein under the control of D1R promoter, we examined the molecular identity of D1R-containing neurons within the CA1 subfield of the dorsal hippocampus. In agreement with previous findings, our analysis revealed that these neurons are essentially GABAergic interneurons, which express several neurochemical markers, including calcium-binding proteins, neuropeptides, and receptors among others. Finally, by using different tools comprising cell type-specific isolation of mRNAs bound to tagged-ribosomes, we provide solid data indicating that D1R is present in a large proportion of interneurons expressing dopamine D2 receptors. Altogether, our study indicates that D1Rs are expressed by different classes of interneurons in all layers examined and not by pyramidal cells, suggesting that CA1 D1R mostly acts via modulation of GABAergic interneurons. Electronic supplementary material The online version of this article (doi:10.1007/s00429-016-1314-x) contains supplementary material, which is available to authorized users.

Food palatability produces behavioral modifications that resemble those induced by drugs of abuse. Palatability-induced behavioral changes require both, the activation of the endogenous cannabinoid system, and changes in structural plasticity in neurons of the brain reward pathway. The ERK intracellular pathway is activated by CB1 receptors (CB1-R) and plays a crucial role in neuroplasticity. We investigated the activation of the ERK signaling cascade in the mesocorticolimbic system induced by operant training to obtain highly palatable isocaloric food and the involvement of the CB1-R in these responses. Using immunofluorescence techniques, we analyzed changes in ERK intracellular pathway activation in the mesocorticolimbic system of wild-type and CB1 knockout mice (CB1-/-) trained on an operant paradigm to obtain standard, highly caloric or highly palatable isocaloric food. Operant training for highly palatable isocaloric food, but not for standard or highly caloric food, produced a robust activation of the ERK signaling cascade in the same brain areas where this training modified structural plasticity. These changes induced by the operant training were absent in CB1-/-. We can conclude that the activation of the ERK pathway is associated to the neuroplasticity induced by operant training for highly palatable isocaloric food and might be involved in CB1-R mediated alterations in behavior and structural plasticity. This work was supported by the Spanish “Ministerio de Ciencia e Innovación” (#SAF2007-64062 and #SAF2008-00962), “Instituto de Salud Carlos III” (#RD06/001/001), “Plan Nacional sobre Drogas, the Catalan Government” (SGR2009-00131 and SGR 2009-224), the “ICREA Foundation” (ICREA Academia-2008), the “DG Research of the European Commission” (GENADDICT, #LSHM-CT-2004-05166; and PHECOMP, #LSHM-CT-2007-037669) the “FIS” (PI07/0715), “ATIP-Avenir” and “Sanofi-Aventis” grants. This work was also supported by the “Plan Nacional Sobre Drogas” (#2009/026) to R.M

Palatability enhances food intake by hedonic mechanisms that prevail over caloric necessities. Different studies have demonstrated the role of endogenous cannabinoids in the mesocorticolimbic system in controlling food hedonic value and consumption. We hypothesize that the endogenous cannabinoid system could also be involved in the development of food-induced behavioral alterations, such as food-seeking and binge-eating, by a mechanism that requires neuroplastic changes in the brain reward pathway. For this purpose, we evaluated the role of the CB1 cannabinoid receptor (CB1-R) in the behavioral and neuroplastic changes induced by operant training for standard, highly caloric or highly palatable isocaloric food using different genetics, viral and pharmacological approaches. Neuroplasticity was evaluated by measuring changes in dendritic spine density in neurons previously labeled with the dye DiI. Only operant training to obtain highly palatable isocaloric food induced neuroplastic changes in neurons of the nucleus accumbens shell and prefrontal cortex that were associated to changes in food-seeking behavior. These behavioral and neuroplastic modifications induced by highly palatable isocaloric food were dependent on the activity of the CB1-R. Neuroplastic changes induced by highly palatable isocaloric food are similar to those produced by some drugs of abuse and may be crucial in the alteration of food-seeking behavior leading to overweight and obesity. This work was supported by the Spanish Ministerio de Ciencia e Innovació (#SAF2007-64062 and #SAF2008-00962), the Instituto de Salud CarlosIII (#RD06/001/001), the Plan Nacional sobre Drogas, the Catalan Government (SGR2009-00131 and SGR2009-224), the ICREA Foundation (ICREA Academia-2008), the DG Research of the European Commission (GENADDICT,/n#LSHM-CT-2004-05166; and PHECOMP, #LSHM-CT-2007-037669) the FIS’’ (PI07/0715),ATIP-Avenir and Sanofi-Aventis grants.This work was also supported by the Plan Nacional Sobre Drogas (#2009/026) to R.M.