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Dopamine (DA) in medial prefrontal cortex is crucial in extinction of aversive or appetitive experiences. Although attention has been mostly focused on the infralimbic area of prefrontal cortex, a role of the prelimbic (PL) area has been envisaged pointing to DA transmission in the extinction of drug conditioned behavior. Evidence shows that DA exerts its action also via both D1 and D2 receptor subtypes. Here we investigated the effects of D1 and D2 receptor agonist microinfusion in the PL cortex of C57BL/6J mice on expression and extinction of amphetamine-induced conditioned place preference (CPP), in order to ascertain the effects of selective vs concomitant receptor subtypes stimulation. SKF38393 and Quinpirole were used at doses not impairing expression of amphetamine-induced CPP on the day of infusion. Acute infusion of each agonist alone did not affect extinction in subsequent days in comparison with Vehicle-treated mice, while concomitant infusion of both agonists produced a clear-cut advance of extinction of preference for the compartment previously paired with amphetamine. These results show that concomitant stimulation of D1 and D2 receptors in PL is required to foster extinction suggesting a synergic action between receptors or a heteromeric receptor involvement.

Background Recent studies support the therapeutic utility of repetitive transcranial magnetic stimulation in Parkinson's disease (PD), whose progression is correlated with loss of corticostriatal long-term potentiation and long-term depression. Glial cell activation is also a feature of PD that is gaining increasing attention in the field because astrocytes play a role in chronic neuroinflammatory responses but are also able to manage dopamine (DA) levels. Methods Intermittent theta-burst stimulation protocol was applied to study the effect of therapeutic neuromodulation on striatal DA levels measured by means of in vivo microdialysis in 6-hydroxydopamine-hemilesioned rats. Effects on corticostriatal synaptic plasticity were studied through in vitro intracellular and whole-cell patch clamp recordings while stepping test and CatWalk were used to test motor behavior. Immunohistochemical analyses were performed to analyze morphological changes in neurons and glial cells. Results Acute theta-burst stimulation induced an increase in striatal DA levels in hemiparkinsonian rats, 80 minutes post-treatment, correlated with full recovery of plasticity and amelioration of motor performances. With the same timing, immediate early gene activation was restricted to striatal spiny neurons. Intense astrocytic and microglial responses were also significantly reduced 80 minutes following theta-burst stimulation. Conclusion Taken together, these results provide a first glimpse on physiological adaptations that occur in the parkinsonian striatum following intermittent theta-burst stimulation and may help to disclose the real potential of this technique in treating PD and preventing DA replacement therapy-associated disturbances. © 2017 International Parkinson and Movement Disorder Society.

Previous findings from this laboratory demonstrate: (1) that different classes of addictive drugs require intact norepinephrine (NE) transmission in the medial pre Frontal Cortex (mpFC) to promote conditioned place preference and to increase dopamine (DA) tone in the nucleus accumbens shell (NAc Shell); (2) that only food-restricted mice require intact NE transmission in the mpFC to develop conditioned preference for a context associated with milk chocolate; and (3) that food-restricted mice show a significantly larger increase of mpFC NE outflow then free fed mice when experiencing the palatable food for the first time. In the present study we tested the hypothesis that only the high levels of frontal cortical NE elicited by the natural reward in food restricted mice stimulate mesoaccumbens DA transmission. To this aim we investigated the ability of a first experience with milk chocolate to increase DA outflow in the accumbens Shell and c-fos expression in striatal and limbic areas of food–restricted and ad-libitum fed mice. Moreover, we tested the effects of a selective depletion of frontal cortical NE on both responses in either feeding group. Only in food-restricted mice milk chocolate induced an increase of DA outflow beyond baseline in the accumbens Shell and a c-fos expression larger than that promoted by a novel inedible object in the nucleus accumbens. Moreover, depletion of frontal cortical NE selectively prevented both the increase of DA outflow and the large expression of c-fos promoted by milk chocolate in the NAc Shell of food-restricted mice. These findings support the conclusion that in food-restricted mice a novel palatable food activates the motivational circuit engaged by addictive drugs and support the development of noradrenergic pharmacology of motivational disturbances.

Extinction of Pavlovian conditioning is a complex process that involves brain regions such as the medial prefrontal cortex (mPFC), the amygdala and the locus coeruleus. In particular, noradrenaline (NA) coming from the locus coeruleus has been recently shown to play a different role in two subregions of the mPFC, the prelimbic (PL) and the infralimbic (IL) regions. How these regions interact in conditioning and subsequent extinction is an open issue. We studied these processes using two approaches: computational modelling and NA manipulation in a conditioned place preference paradigm (CPP) in mice. In the computational model, NA in PL and IL causes inputs arriving to these regions to be amplified, thus allowing them to modulate learning processes in amygdala. The model reproduces results from studies involving depletion of NA from PL, IL, or both in CPP. In addition, we simulated new experiments of NA manipulations in mPFC, making predictions on the possible results. We searched the parameters of the model and tested the robustness of the predictions by performing a sensitivity analysis. We also present an empirical experiment where, in accord with the model, a double depletion of NA from both PL and IL in CPP with amphetamine impairs extinction. Overall the proposed model, supported by anatomical, physiological, and behavioural data, explains the differential role of NA in PL and IL and opens up the possibility to understand extinction mechanisms more in depth and hence to aid the development of treatments for disorders such as addiction.

Drug-associated cues exposure to induce extinction is a useful strategy to contrast cue-induced drug seeking. Treatments aimed at reducing motivational properties of cues are considered highly promising since they could decrease their ability to induce drug-conditioned behaviors. Norepinephrine (NE) in the medial prefrontal cortex (mPFC) is critical for attribution of motivational salience to highly salient stimuli, suggesting a major role in prelimbic (PL) mpFC to modulate the motivational properties of drug-related cues, invigorating them, and consequently, delaying extinction. To investigate if NE in PL fosters the maintenance of drug-seeking behavior, we assessed its role on amphetamine-induced conditioned place preference (CPP). Moreover, to affirm the specificity of NE in PL, we also assessed the role of NE in the infralimbic (IL) mPFC. The effects of selective NE depletion in the PL or in the IL of C57BL/6J mice were assessed on the expression of amphetamine-induced CPP before and after extinction procedure. NE-depleted mice in PL extinguished preference for Amph-paired chamber long before sham animals. By contrast, IL-depleted animals maintained place preference for more than 4 weeks after the procedure of extinction, having at that moment interrupted the test. Inactivation of NE in PL cortex blunts amphetamine-induced CPP, thus fostering extinction and showing to be critical for the maintenance of conditioned Amph-seeking behavior. Opposite effects of NE depletion in IL, seemingly in agreement with literature on extinction, are discussed in terms of balance of activity between PL and IL in extinction.

Although the medial prefrontal cortex (mpFC) appears to constrain stress responses, indirect evidences suggest that it might determine the stress response of the mesoaccumbens dopamine (DA) system. To test this hypothesis, we first evaluated the dynamics of norepinephrine (NE) and DA release in the mpFC and of DA release in the nucleus accumbens (NAc) of acutely stressed rats. Then, we tested the effects of selective depletion of NE or DA in the mpFC (by local 6-hydroxydopamine infusion following desipramine or 1-[2[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine(GBR 12909) on stress-induced changes in mesoaccumbens DA release. Rats experiencing restraint stress for 240 min showed an initial, short-lived increase of NE outflow in the mpFC and of DA in the NAc. These responses were followed by a sustained increase of DA in the mpFC and by a decrease to below resting levels of DA in the NAc. Moreover, selective prefrontal NE depletion eliminated the increase of NE in the mpFC and of DA in the NAc, and selective depletion of mesocortical DA eliminated the enhancement of mpFC DA as well as the inhibition of mesoaccumbens DA, without affecting basal catecholamines outflow. These results demonstrate that the opposing influences of mpFC NE and DA determine mesoaccumbens DA response to stress and suggest that alterations of this mechanism may be responsible for some major psychopathological outcomes of stress.

Background Advanced Parkinson's disease (PD) is characterized by massive degeneration of nigral dopaminergic neurons, dramatic motor and cognitive alterations, and presence of nigral Lewy bodies, whose main constituent is α-synuclein (α-syn). However, the synaptic mechanisms underlying behavioral and motor effects induced by early selective overexpression of nigral α-syn are still a matter of debate. Methods We performed behavioral, molecular, and immunohistochemical analyses in two transgenic models of PD, mice transgenic for truncated human α-synuclein 1-120 and rats injected with the adeno-associated viral vector carrying wild-type human α-synuclein. We also investigated striatal synaptic plasticity by electrophysiological recordings from spiny projection neurons and cholinergic interneurons. Results We found that overexpression of truncated or wild-type human α-syn causes partial reduction of striatal dopamine levels and selectively blocks the induction of long-term potentiation in striatal cholinergic interneurons, producing early memory and motor alterations. These effects were dependent on α-syn modulation of the GluN2D-expressing N -methyl-D-aspartate receptors in cholinergic interneurons. Acute in vitro application of human α-syn oligomers mimicked the synaptic effects observed ex vivo in PD models. Conclusions We suggest that striatal cholinergic dysfunction, induced by a direct interaction between α-syn and GluN2D-expressing N -methyl-D-aspartate receptors, represents a precocious biological marker of the disease.

BackgroundEating disorders appear to be caused by a complex interaction between environmental and genetic factors, and compulsive eating in response to adverse circumstances characterizes many eating disorders.Materials and methodsWe compared compulsion-like eating in the form of conditioned suppression of palatable food-seeking in adverse situations in stressed C57BL/6J and DBA/2J mice, two well-characterized inbred strains, to determine the influence of gene-environment interplay on this behavioral phenotype. Moreover, we tested the hypothesis that low accumbal D2 receptor (R) availability is a genetic risk factor of food compulsion-like behavior and that environmental conditions that induce compulsive eating alter D2R expression in the striatum. To this end, we measured D1R and D2R expression in the striatum and D1R, D2R and α1R levels in the medial prefrontal cortex, respectively, by western blot.ResultsExposure to environmental conditions induces compulsion-like eating behavior, depending on genetic background. This behavioral pattern is linked to decreased availability of accumbal D2R. Moreover, exposure to certain environmental conditions upregulates D2R and downregulates α1R in the striatum and medial prefrontal cortex, respectively, of compulsive animals. These findings confirm the function of gene-environment interplay in the manifestation of compulsive eating and support the hypothesis that low accumbal D2R availability is a "constitutive" genetic risk factor for compulsion-like eating behavior. Finally, D2R upregulation and α1R downregulation in the striatum and medial prefrontal cortex, respectively, are potential neuroadaptive responses that parallel the shift from motivated to compulsive eating.

Neuregulin 1 (NRG1) is a trophic factor that has an essential role in the nervous system by modulating neurodevelopment, neurotransmission and synaptic plasticity. Despite the evidence that NRG1 and its receptors, ErbB tyrosine kinases, are expressed in mesencephalic dopaminergic nuclei and their functional alterations are reported in schizophrenia and Parkinson's disease, the role of NRG1/ErbB signalling in dopaminergic neurons remains unclear. Here we found that NRG1 selectively increases the metabotropic glutamate receptor 1 (mGluR1)-activated currents by inducing synthesis and trafficking to membrane of functional receptors and stimulates phosphatidylinositol 3-kinase-Akt-mammalian target of rapamycin (PI3K-Akt-mTOR) pathway, which is required for mGluR1 function. Notably, an endogenous NRG1/ErbB tone is necessary to maintain mGluR1 function, by preserving its surface membrane expression in dopaminergic neurons. Consequently, it enables striatal mGluR1-induced dopamine outflow in in vivo conditions. Our results identify a novel role of NRG1 in the dopaminergic neurons, whose functional alteration might contribute to devastating diseases, such as schizophrenia and Parkinson's disease.

We combined in vitro amperometric, optical analysis of fluorescent false neurotransmitters and microdialysis techniques to unveil that cocaine and methylphenidate induced a marked depression of the synaptic release of dopamine (DA) in mouse striatum. In contrast to the classical dopamine transporter (DAT)-dependent enhancement of the dopaminergic signal observed at concentrations of cocaine lower than 3 μM, the inhibitory effect of cocaine was found at concentrations higher than 3 μM. The paradoxical inhibitory effect of cocaine and methylphenidate was associated with a decrease in synapsin phosphorylation. Interestingly, a cocaine-induced depression of DA release was only present in cocaine-insensitive animals (DAT-CI). Similar effects of cocaine were produced by methylphenidate in both wild-type and DAT-CI mice. On the other hand, nomifensine only enhanced the dopaminergic signal either in wild-type or in DAT-CI mice. Overall, these results indicate that cocaine and methylphenidate can increase or decrease DA neurotransmission by blocking reuptake and reducing the exocytotic release, respectively. The biphasic reshaping of DA neurotransmission could contribute to different behavioral effects of psychostimulants, including the calming ones, in attention deficit hyperactivity disorder.

Endogenous opioids could play a major role in the mesocorticolimbic dopamine (DA) responses to stress challenge. However, there is still no direct evidence of an influence of endogenous opioids on any of these responses. We assessed whether and how endogenous opioids modulate fluctuations of mesocortical and mesoaccumbens DA tone in rats during a first experience with restraint stress. We first evaluated the effects of systemic naltrexone (NTRX) on DA outflow in the medial prefrontal cortex (mpFC) and in the nucleus accumbens (NAc) through dual-probe microdialysis. Second, we assessed the effect of perfusion, through reverse microdialysis, of direct DA receptor agonists in mpFC on NAc DA outflow in NTRX-pretreated stressed rats. Finally, we tested the effects of ventral tegmental area (VTA) perfusion of NTRX, the selective mu1 antagonist naloxonazine and the selective delta antagonist naltrindole on mpFC and NAc DA outflow in stressed rats, with multiple probe experiments. Systemic NTRX, at behaviorally effective doses, selectively prevented the increase of mpFC DA levels and the reduction of NAc DA levels observable during prolonged restraint. Local co-perfusion of D1 and D2 agonists in mpFC recovered inhibition of NAc DA in NTRX-pretreated restrained rats. Finally, intra-VTA perfusion of either NTRX or the mu1 antagonist, but not the delta antagonist, mimicked the effects of systemic NTRX. During prolonged experience with a novel unavoidable/uncontrollable stressor, endogenous opioids, through stimulation of mu1 receptors in the VTA, elevate mesocortical DA tone thus reducing DA tone in the NAc DA.

Evidence shows that maternal care and postnatal traumatic events can exert powerful effects on brain circuitry development but little is known about the impact of early postnatal experiences on processing of rewarding and aversive stimuli related to the medial prefrontal cortex (mpFC) function in adult life. In this study, the unstable maternal environment induced by repeated cross-fostering (RCF) impaired palatable food conditioned place preference and disrupted the natural preference for sweetened fluids in the saccharin preference test. By contrast, RCF increased sensitivity to conditioned place aversion (CPA) and enhanced immobility in the forced swimming test. Intracerebral microdialysis data showed that the RCF prevents mpFC dopamine (DA) outflow regardless of exposure to rewarding or aversive stimuli, whereas it induces a strong and sustained prefrontal norepinephrine (NE) release in response to different aversive experiences. Moreover, the selective mpFC NE depletion abolished CPA, thus indicating that prefrontal NE is required for motivational salience attribution to aversion-related stimuli. These findings demonstrate that an unstable maternal environment impairs the natural propensity to seek pleasurable sources of reward, enhances sensitivity to negative events in adult life, blunts prefrontal DA outflow, and modulates NE release in the reverse manner depending on the exposure to rewarding or aversive stimuli.

Although the wake-promoting drug modafinil has been shown to bind quite exclusively to the dopamine transporter (DAT), its action in the brain has been thought to be partially independent from the facilitation of the dopaminergic signals. Here we used electrophysiological and amperometric techniques to investigate the effects of modafinil on the dopaminergic neurons of the substantia nigra pars compacta (SNpc) and on the synaptic overflow of dopamine in the dorsal striatum from the sliced tissue of wild-type and cocaine-insensitive genetically modified mice (DAT-CI). Moreover, we examined the consequences of modafinil administration on the locomotor behavior of wild-type and DAT-CI mice. In in vitro experiments, modafinil inhibited the spontaneous firing discharge of the dopaminergic neurons. More consistently, it potentiated firing inhibition and the membrane responses caused by exogenously applied dopamine on these cells. Furthermore, it augmented the stimulus-evoked outflow of DA in the striatum. Noteworthy, modafinil caused locomotor activation in wild-type mice. On the other hand, neither the electrophysiological nor the behavioral effects of modafinil were detected in DAT-CI animals. These results demonstrate that modafinil potentiates brain dopaminergic signals via DAT inhibition by acting at the same binding site of cocaine. Therefore, this mechanism of action explains most of the pharmacological properties of this compound in the clinical setting.

Although patients with Parkinson's disease show impairments in cognitive performance even at the early stage of the disease, the synaptic mechanisms underlying cognitive impairment in this pathology are unknown. Hippocampal long-term potentiation represents the major experimental model for the synaptic changes underlying learning and memory and is controlled by endogenous dopamine. We found that hippocampal long-term potentiation is altered in both a neurotoxic and transgenic model of Parkinson's disease and this plastic alteration is associated with an impaired dopaminergic transmission and a decrease of NR2A/NR2B subunit ratio in synaptic N-methyl-d-aspartic acid receptors. Deficits in hippocampal-dependent learning were also found in hemiparkinsonian and mutant animals. Interestingly, the dopamine precursor l-DOPA was able to restore hippocampal synaptic potentiation via D1/D5 receptors and to ameliorate the cognitive deficit in parkinsonian animals suggesting that dopamine-dependent impairment of hippocampal long-term potentiation may contribute to cognitive deficits in patients with Parkinson's disease.

Background Eating disorders are multifactorial psychiatric disorders. Chronic stressful experiences and caloric restriction are the most powerful triggers of eating disorders in human and animals. Although compulsive behavior is considered to characterize pathological excessive food intake, to our knowledge, no evidence has been reported of continued food seeking/intake despite its possible harmful consequences, an index of compulsive behavior. Brain monoamine transmission is considered to have a key role in vulnerability to eating disorders, and norepinephrine in medial prefrontal cortex has been shown to be critical for food-related motivated behavior. Here, using a new paradigm of conditioned suppression, we investigated whether the ability of a foot-shock-paired conditioned stimulus to suppress chocolate-seeking behavior was reversed by previous exposure to a food restriction experience, thus modeling food seeking in spite of harmful consequences in mice. Moreover, we assessed the effects of selective norepinephrine inactivation in medial prefrontal cortex on conditioned suppression test in stressed and caloric restricted mice. Results While Control (non food deprived) animals showed a profound conditioned suppression of chocolate seeking during presentation of conditioned stimulus, previously food restricted animals showed food seeking/intake despite its possible harmful consequences. Moreover, food seeking in spite of harmful consequences was prevented by selective norepinephrine inactivation, thus showing that prefrontal cortical norepinephrine is critical also for maladaptive food-related behavior. Conclusions These findings indicate that adaptive food seeking/intake can be transformed into maladaptive behaviors and point to "top-down" influence on eating disturbances and to new targets for therapy of aberrant eating behaviors.