The motivational drive to natural rewards is modulated by prenatal glucocorticoid exposure

Exposure to elevated levels of glucocorticoids (GCs) during neurodevelopment has been identified as a triggering factor for the development of reward-associated disorders in adulthood. Disturbances in the neural networks responsible for the complex processes that assign value to rewards and associated stimuli are critical for disorders such as depression, obsessive–compulsive disorders, obesity and addiction. Essential in the understanding on how cues influence behavior is the Pavlovian–instrumental transfer (PIT), a phenomenon that refers to the capacity of a Pavlovian stimulus that predicts a reward to elicit instrumental responses for that same reward. Here, we demonstrate that in utero exposure to GCs (iuGC) impairs both general and selective versions of the PIT paradigm, suggestive of deficits in motivational drive. The iuGC animals presented impaired neuronal activation pattern upon PIT performance in cortical and limbic regions, as well as morphometric changes and reduced levels of dopamine in prefrontal and orbitofrontal cortices, key regions involved in the integration of Pavlovian and instrumental stimuli. Normalization of dopamine levels rescued this behavior, a process that relied on D2/D3, but not D1, dopamine receptor activation. In summary, iuGC exposure programs the mesocorticolimbic dopaminergic circuitry, leading to a reduction in the attribution of the incentive salience to cues, in a dopamine-D2/D3-dependent manner. Ultimately, these results are important to understand how GCs bias incentive processes, a fact that is particularly relevant for disorders where differential attribution of incentive salience is critical.We thank Pedro Morgado for discussions and help in the technical aspects of PIT procedure. This project was supported by a grant of Institute for the Study of Affective Neuroscience (ISAN) and by Janssen Neuroscience Prize. CS-C, SB, MMC and AJR are recipients of Fundacao para a Ciencia e Tecnologia (FCT) fellowships (CS-C: SFRH/BD/51992/2012; SB: SFRH/BD/89936/2012; MMC: SRFH/BD/51061/2010; AJR: SFRH/BPD/33611/2009)

Assessing the influence of dopamine and mindfulness on the formation of routines in visual search

Given experience in cluttered but stable visual environments, our eye‐movements form stereotyped routines that sample task‐relevant locations, while not mixing‐up routines between similar task‐settings. Both dopamine signaling and mindfulness have been posited as factors that influence the formation of such routines, yet quantification of their impact remains to be tested in healthy humans. Over two sessions, participants searched through grids of doors to find hidden targets, using a gaze‐contingent display. Within each session, door scenes appeared in either one of two colors, with each color signaling a differing set of likely target locations. We derived measures for how well target locations were learned (target‐accuracy), how routine were sets of eye‐movements (stereotypy), and the extent of interference between the two scenes (setting‐accuracy). Participants completed two sessions, where they were administered either levodopa (dopamine precursor) or placebo (vitamin C), under double‐blind counterbalanced conditions. Dopamine and trait mindfulness (assessed by questionnaire) interacted to influence both target‐accuracy and stereotypy. Increasing dopamine improved accuracy and reduced stereotypy for high mindfulness scorers, but induced the opposite pattern for low mindfulness scorers. Dopamine also disrupted setting‐accuracy invariant to mindfulness. Our findings show that mindfulness modulates the impact of dopamine on the target‐accuracy and stereotypy of eye‐movement routines, whereas increasing dopamine promotes interference between task‐settings, regardless of mindfulness. These findings provide a link between non‐human and human models regarding the influence of dopamine on the formation of task‐relevant eye‐movement routines and provide novel insights into behavior‐trait factors that modulate the use of experience when building adaptive repertoires

Advances in non-dopaminergic treatments for Parkinson's disease

Since the 1960's treatments for Parkinson's disease (PD) have traditionally been directed to restore or replace dopamine, with L-Dopa being the gold standard. However, chronic L-Dopa use is associated with debilitating dyskinesias, limiting its effectiveness. This has resulted in extensive efforts to develop new therapies that work in ways other than restoring or replacing dopamine. Here we describe newly emerging non-dopaminergic therapeutic strategies for PD, including drugs targeting adenosine, glutamate, adrenergic, and serotonin receptors, as well as GLP-1 agonists, calcium channel blockers, iron chelators, anti-inflammatories, neurotrophic factors, and gene therapies. We provide a detailed account of their success in animal models and their translation to human clinical trials. We then consider how advances in understanding the mechanisms of PD, genetics, the possibility that PD may consist of multiple disease states, understanding of the etiology of PD in non-dopaminergic regions as well as advances in clinical trial design will be essential for ongoing advances. We conclude that despite the challenges ahead, patients have much cause for optimism that novel therapeutics that offer better disease management and/or which slow disease progression are inevitable. © 2014 Stayte and Vissel

Dopaminergic and noradrenergic modulation of stress-induced alterations in brain activation associated with goal-directed behaviour

BACKGROUND: Acute stress is thought to reduce goal-directed behaviour, an effect purportedly associated with stress-induced release of catecholamines. In contrast, experimentally increased systemic catecholamine levels have been shown to increase goal-directed behaviour. Whether experimentally increased catecholamine function can modulate stress-induced reductions in goal-directed behaviour and its neural substrates, is currently unknown. AIM: To assess whether and how experimentally induced increases in dopamine and noradrenaline contribute to the acute stress effects on goal-directed behaviour and associated brain activation. METHODS: One hundred participants underwent a stress induction protocol (Maastricht acute stress test; MAST) or a control procedure and received methylphenidate (MPH) (40 mg, oral) or placebo according to a 2 × 2 between-subjects design. In a well-established instrumental learning paradigm, participants learnt stimulus–response–outcome associations, after which rewards were selectively devalued. Participants’ brain activation and associated goal-directed behaviour were assessed in a magnetic resonance imaging scanner at peak cortisol/MPH concentrations. RESULTS: The MAST and MPH increased physiological measures of stress (salivary cortisol and blood pressure), but only MAST increased subjective measures of stress. MPH modulated stress effects on activation of brain areas associated with goal-directed behaviour, including insula, putamen, amygdala, medial prefrontal cortex, frontal pole and orbitofrontal cortex. However, MPH did not modulate the tendency of stress to induce a reduction in goal-directed behaviour. CONCLUSION: Our neuroimaging data suggest that MPH-induced increases in dopamine and noradrenaline reverse stress-induced changes in key brain regions associated with goal-directed behaviour, while behavioural effects were absent. These effects may be relevant for preventing stress-induced maladaptive behaviour like in addiction or binge eating disorder

7-Nitroindazole down-regulates dopamine/DARPP-32 signaling in neostriatal neurons in a rat model of Parkinson's disease

Neuronal nitric oxide synthase (nNOS) is involved in the regulation of diverse intracellular messenger systems in the brain. Nitric Oxide (NO) contributes to inducing signaling cascades that involve a complex pattern of phosphorylation of DARPP-32 (in Thr-34), which controls the phosphoproteins involved in neuronal activation. However, the role of NO in the pathophysiology of Parkinson's disease (PD) and its effect in striatal neurons have been scarcely explored. In the present work, we investigate the effects of a nitric oxide synthase (NOS) inhibitor, 7-nitroindazole (7-NI) in the nigrostriatal pathway of striatal 6-hydroxydopamine (6-OHDA) lesioned rats. Our quantitative histological findings show that treatment with 7-NI significantly reduced 6-OHDA-induced dopaminergic damage in the dorsolateral striatum and Substantia Nigra pars compacta (SNpc). Moreover, 6-OHDA lesioned rats show a significant increase of nNOS+ and Phospho-Thr34-DARPP-32+ cells, accompanied by a consequent decrease of total DARPP-32+ cells, which suggests an imbalance of NO activity in the DA-depleted striatum, which is also reflected in behavioral studies. Importantly, these effects are reverted in the group treated with 7-NI. These results show a clear link between the state of phosphorylation of DARPP-32 and parkinsonism, which is regulated by nNOS. This new evidence suggests a prominent role for nitric oxide in the neurotransmitter balance within the basal ganglia in the pathophysiology of experimental parkinsonism.This work was supported by grants from the Spanish Ministry of Science (SAF 2007-62262), FIS (PI/2010/02827) and CIBERNED (Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas)

ROLE OF LIMONENE IN AN EXPERIMENTAL MODEL OF ROTENONE INDUCED PARKINSON’S DISEASE

Parkinson\u27s disease (PD) is one of the prevalent neurodegenerative diseases in elderly population. The symptoms of PD often begin with motor and cognitive impairment that are attributed to the dopaminergic neurons degeneration. Rotenone (ROT) is a naturally derived pesticide that is used in agriculture to control pests. It is a neurotoxin well-established for use in resembling PD symptoms in research. Limonene (LMN) is a plant derived monoterpene extracted from citrus peel with a wide range of therapeutic effects. Due to the shortage in available therapeutic agents that can cure or halt the progressive degeneration of PD, the main aim of this thesis is to scrutinize and to reach a consensus regarding the potential neuroprotective effects of LMN in a rat model of ROT-induced PD against underlying mechanisms including oxidative stress, neuro-inflammation and apoptosis. An animal model of PD was established on Wistar rats by intraperitoneal injection of (2.5 mg/kg) ROT for 28 days. Modulatory functions of LMN (50 mg/kg, p.o) were investigated by performing immunofluorescence for Ionized calcium-binding adaptor protein-1 (Iba-I), Glial fibrillary acidic protein (GFAP) and Tyrosine Hydroxylase (TH) in both striatum and substantia nigra. Superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), malondialdehyde (MDA) were also evaluated. Neuro-inflammation biomarkers; interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α) were assessed by ELISA. Immunoblotting was performed for measuring other biomarkers including cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), Bax, Bcl-2, cleaved caspase-3 and caspase-9, Cytochrome C, Brain Derived Neurotrophic Factor (BDNF), mitochondrial complex-I (MC-I), α-Synuclein and NF-κB. Rotarod test was also performed to assess motor coordination. Results showed a significant loss in dopaminergic neurons following ROT administration. However, LMN treatment rescued the dopaminergic neurons from the progressive loss in both substantia nigra and striatum. LMN attenuated the activation of astrocytes and microglia observed in ROT-injected rats and decreased the raised levels of inflammatory mediators, such as COX-2 and iNOS, IL-1β, IL-6 and TNF-α in addition to suppressing NF-κB signaling pathway. LMN treatment restored the activity of antioxidant enzymes, prevented glutathione depletion and inhibited lipid peroxidation. The phosphorylated JNK and P38 kinases were downregulated in LMN pretreated rats, while p-mTOR was upregulated. Apoptosis was remarkably alleviated by LMN administration evident by the increase in anti-apoptotic and the reduction in pro-apoptotic proteins. Motor functions were also improved significantly in LMN treated rats. Findings reported a regressive α-Synuclein expression, improved BDNF level and a restoration of complex-1 activity following LMN administration. Given these findings, LMN mitigated ROT-induced dopaminergic neurodegeneration, which is suggestive of the protective properties of LMN in PD treatment through various biological mechanisms

Neuropathological role of alpha-synuclein: major contribution of inflammation in the evolution of both motor and non-motor symptoms of Parkinson’s disease

Neuroinflammation is nowadays considered a cardinal pathological feature of Parkinson’s disease (PD), in which glial cells lose their homeostatic function in favour of a pro-inflammatory profile. Such sustained glial response within the brain parenchyma is characterized by a chronic release of a number of pro-inflammatory mediators, likely driven by pathological interactions with toxic forms of α-Synuclein (αSyn). Moreover, the contribution of the peripheral immune system to PD neuropathology has been demonstrated, promoting the view of PD as a systemic pathology. While the contribution of inflammation to the neuropathology of motor symptoms has been ascertained, its role in non-motor symptoms is still under-investigated, particularly in relation to cognitive disturbances. Here, we targeted inflammation in PD by testing the immunomodulatory imide drug (IMiD) Pomalidomide (Pom) for its disease-modifying properties against motor deficits in a translational rat model of PD based on the intranigral infusion of toxic oligomers of human α-synuclein (H-αSynOs) (study I). Moreover, we investigated the contribution of neuroinflammation in PD cognitive symptoms, in the same PD preclinical model (study II). Study I: The neuroprotective effect of Pom (20 mg/kg; i.p. three times/week for two months) was tested in the early stage of the disease. We found that the infusion of H-αSynOs induced an impairment in motor performance that was fully rescued by Pom, as assessed via a battery of motor tests. Moreover, H-αSynOs-infused rats displayed a 40–45% cell loss within the substantia nigra (SN), that was largely abolished by Pom. The inflammatory response to H-αSynOs infusion and the Pom treatment was evaluated both in CNS and peripherally. After H-αSynOs infusion, microglia displayed a proinflammatory profile, producing a large amount of the cytokine Tumour Necrosis Factor (TNF)-α. In contrast, Pom inhibited the TNF-α overproduction and elevated the anti-inflammatory cytokine Interleukin (IL)-10. Moreover, the H-αSynOs infusion induced a systemic inflammation with a dysregulated production of serum cytokines and chemokines, that was largely restored by Pom. Study II: We asked whether the H-αSynOs-based model of PD is an effective tool to study PD-related cognitive disturbances, thus investigating the contribution of neuroinflammation. We show that H-αSynOs-infused rats displayed memory deficits three months after the infusion. These were underpinned by an altered electrophysiological neuronal activity and altered expression of the neuron-specific immediate early gene (IEG) Npas4 (Neuronal PAS domain protein 4) in cognitive regions, such as the anterior cingulate cortex (ACC). Moreover, the brain of cognitively impaired rats showed a neuroinflammatory response in the ACC and discrete subareas of the hippocampus, in the absence of any evident neuronal loss, supporting a role of neuroinflammation in cognitive decline. Such neuroinflammatory response was epitomized by the acquisition of a pro-inflammatory phenotype by microglia cells, as indicated by the increased levels of TNF-α. Taken together, results of the present study indicate that neuroinflammation is a common feature of both motor and non-motor aspects of PD, and suggest that targeting inflammation might represent a novel therapeutic strategy to treat the disease as a whole

L-dopa-Dependent Effects of GLP-1R Agonists on the Survival of Dopaminergic Cells Transplanted into a Rat Model of Parkinson Disease

Cell therapy is a promising treatment for Parkinson’s disease (PD), however clinical trials to date have shown relatively low survival and significant patient-to-patient variability. Glucagon Like Peptide-1 receptor (GLP-1R) agonists have potential neuroprotective effects on endogenous dopaminergic neurons. This study explores whether these agents could similarly support the growth and survival of newly transplanted neurons. 6-OHDA lesioned Sprague Dawley rats received intra-striatal grafts of dopaminergic ventral mesencephalic cells from embryonic day 14 Wistar rat embryos. Transplanted rats then received either saline or L-dopa (12 mg/kg) administered every 48 h prior to, and following cell transplantation. Peripheral GLP-1R agonist administration (exendin-4, 0.5 μg/kg twice daily or liraglutide, 100 μg/kg once daily) commenced immediately after cell transplantation and was maintained throughout the study. Graft survival increased under administration of exendin-4, with motor function improving significantly following treatment with both exendin-4 and liraglutide. However, this effect was not observed in rats administered with L-dopa. In contrast, L-dopa treatment with liraglutide increased graft volume, with parallel increases in motor function. However, this improvement was accompanied by an increase in leukocyte infiltration around the graft. The co-administration of L-dopa and exendin-4 also led to indicators of insulin resistance not seen with liraglutide, which may underpin the differential effects observed between the two GLP1-R agonists. Overall, there may be some benefit to the supplementation of grafted patients with GLP-1R agonists but the potential interaction with other pharmacological treatments needs to be considered in more depth

The neurochemical substrates of habitual and goal-directed control

Abstract: Our daily decisions are governed by the arbitration between goal-directed and habitual strategies. However, the neurochemical basis of this arbitration is unclear. We assessed the contribution of dopaminergic, serotonergic, and opioidergic systems to this balance across reward and loss domains. Thirty-nine participants (17 healthy controls, 15 patients with pathological gambling, and 7 with binge eating disorder) underwent positron emission tomography (PET) imaging with [18F]FDOPA, [11C]MADAM and [11C]carfentanil to assess presynaptic dopamine, and serotonin transporter and mu-opioid receptor binding potential. Separately, participants completed a modified two-step task, which quantifies the degree to which decision-making is influenced by goal-directed or habitual strategies. All participants completed a version with reward outcomes; healthy controls additionally completed a version with loss outcomes. In the context of rewarding outcomes, we found that greater serotonin transporter binding potential in prefrontal regions was associated with habitual control, while greater serotonin transporter binding potential in the putamen was marginally associated with goal-directed control; however, the findings were no longer significant when controlling for the opposing valence (loss). In blocks with loss outcomes, we found that the opioidergic system, specifically greater [11C]carfentanil binding potential, was positively associated with goal-directed control and negatively associated with habit-directed control. Our findings illuminate the complex neurochemical basis of goal-directed and habitual behavior, implicating differential roles for prefrontal and subcortical serotonin in decision-making across healthy and pathological populations

The neurochemical substrates of habitual and goal-directed control

Abstract: Our daily decisions are governed by the arbitration between goal-directed and habitual strategies. However, the neurochemical basis of this arbitration is unclear. We assessed the contribution of dopaminergic, serotonergic, and opioidergic systems to this balance across reward and loss domains. Thirty-nine participants (17 healthy controls, 15 patients with pathological gambling, and 7 with binge eating disorder) underwent positron emission tomography (PET) imaging with [18F]FDOPA, [11C]MADAM and [11C]carfentanil to assess presynaptic dopamine, and serotonin transporter and mu-opioid receptor binding potential. Separately, participants completed a modified two-step task, which quantifies the degree to which decision-making is influenced by goal-directed or habitual strategies. All participants completed a version with reward outcomes; healthy controls additionally completed a version with loss outcomes. In the context of rewarding outcomes, we found that greater serotonin transporter binding potential in prefrontal regions was associated with habitual control, while greater serotonin transporter binding potential in the putamen was marginally associated with goal-directed control; however, the findings were no longer significant when controlling for the opposing valence (loss). In blocks with loss outcomes, we found that the opioidergic system, specifically greater [11C]carfentanil binding potential, was positively associated with goal-directed control and negatively associated with habit-directed control. Our findings illuminate the complex neurochemical basis of goal-directed and habitual behavior, implicating differential roles for prefrontal and subcortical serotonin in decision-making across healthy and pathological populations