Chronic unpredictable stress (CUS) impairs cognitive flexibility in rats, particularly when faced with additional mild acute stress (AS). We tested the hypothesis that this impairment is associated with alterations in dopamine activity in the dorsal striatum driven by corticotropin-releasing-factor receptor type 1 (CRFR1) in the substantia nigra pars compacta (SNpc). In experiment 1, rats received CUS or handling for 14 days, before learning two action-outcome associations (lever presses and food rewards). Learning was assessed using outcome devaluation. Cognitive flexibility was then assessed by reversing the outcome identities followed by a second outcome devaluation test, with half of the rats in each group receiving AS prior to reversal training. Dopamine and its metabolite were quantified in the dorsal striatum and CRFR1 mRNA was quantified in the SNpc. Increased dopaminergic activity in the left dorsal striatum and CRFR1 expression in the left SNpc were associated with resilience to AS in naïve rats but with impairment in CUS+AS rats, suggesting a transition in hemispheric control from left to right as a protective mechanism following CUS. This suggestion was tested in experiment 2, where SNpc CRFR1 was blocked unilaterally prior to AS and reversal training. Blocking CRFR1 in the left medial SNpc impaired cognitive flexibility following AS in naïve rats but restored it in CUS rats. Blocking CRFR1 in the left, but not right, lateral SNpc also impaired cognitive flexibility following AS in naïve rats but had no effect in CUS rats.

Compulsive actions are typically thought to reflect the dominance of habits over goal-directed action. To investigate this, we mimicked the striatal neuroinflammation that is frequently exhibited in individuals with compulsive disorders in rats, by injecting the endotoxin lipopolysaccharide into the posterior dorsomedial striatum, and assessed the consequences for behavioural control. Surprisingly, this manipulation caused rats to acquire and maintain goal-directed actions under conditions that would otherwise produce habits. Immunohistochemical analyses indicated that these behaviours were a result of astrocytic proliferation. To probe this further, we chemogenetically activated the Gi-pathway in striatal astrocytes, which altered the firing properties of nearby medium spiny neurons and modulated goal-directed action control. Together, results show that striatal neuroinflammation is sufficient to bias action selection toward excessive goal-directed control via dysregulated astrocyte function. If translatable, our findings suggest that, contrary to conventional views, individuals with striatal neuroinflammation might be more prone to maladaptive goal-directed actions than habits, and future interventions should aim to restore appropriate action control.

Hippocampal neuroinflammation is present in multiple diseases and disorders that impact motivated behaviour in a sex-specific manner, but whether neuroinflammation alone is sufficient to disrupt this behaviour is unknown. We investigated this question here using mice. First, the application of an endotoxin to primary cultures containing only hippocampal neurons did not affect their activation. However, when the same endotoxin was applied to mixed neuronal/glial cultures it did increase neuronal activation, providing initial indications of how it might be able to effect behavioural change. We next showed neuroinflammatory effects on behaviour directly, demonstrating that intra-hippocampal administration of the same endotoxin increased locomotor activity and accelerated goal-directed learning in both male and female mice. In contrast, lipopolysaccharide-induced hippocampal neuroinflammation caused sex-specific disruptions to the acquisition of instrumental actions and to Pavlovian food-approach memories. Finally, we showed that LPS-induced hippocampal neuroinflammation had a sexually dimorphic effect on neuronal activation: increasing it in females and decreasing it in males.

Compulsive actions have been confusingly described as reflecting both excessive habitual and excessive goal-directed action control. Here we sought to resolve this contradiction by inducing the neuropathology commonly observed in individuals with compulsive disorders, specifically by causing neuroinflammation in the dorsomedial striatum of rats. We found that this caused rats to be excessively goal-directed, acquiring and maintaining goal-directed actions under conditions that would otherwise produce habits. Immunohistochemical findings suggested that these behaviours were a result of astrocytic proliferation and its effects on neuronal activation. We therefore investigated the role of striatal astrocytes specifically, demonstrating that chemogenetically activating the Gi-pathway in astrocytes altered the firing properties of nearby medium spiny neurons and modulated goal-directed action control. Together, results suggest that striatal neuroinflammation is sufficient to cause excessive goal-directed action control through the dysregulation of astrocyte function suggesting that individuals with striatal neuroinflammation are excessively goal-directed rather than habitual, information that could be used to direct future interventions and/or treatments. ### Competing Interest Statement The authors have declared no competing interest.

Predictive learning can engage a selective form of cognitive control that biases choice between actions based on information about future outcomes that the learning provides. This influence has been hypothesized to depend on a feedback circuit in the brain through which the basal ganglia modulate activity in the prefrontal cortex; however, direct evidence for this functional circuit has proven elusive. Here, using an animal model of cognitive control, we found that the influence of predictive learning on decision making is mediated by an inhibitory feedback circuit linking the medial ventral pallidum and the mediodorsal thalamus, the activation of which causes disinhibition of the orbitofrontal cortex via reduced activation of inhibitory parvalbumin interneurons during choice. Thus, we found that, for this function, the mediodorsal thalamus serves as a pallidal-cortical relay through which predictive learning controls action selection, which has important implications for understanding cognitive control and its vicissitudes in various psychiatric disorders and addiction.

Hippocampal neuroinflammation is present in multiple diseases and disorders that impact motivated behaviour in a sex-specific manner, but whether neuroinflammation alone is sufficient to disrupt such behaviour is unknown. We investigated this question here using mice. First, the application of an endotoxin to primary hippocampal neurons alone did not alter their activity but triggered neuronal excitation in mixed neuronal/glial co- or tri-cultures, providing initial indications of the potential mechanism causing neuroinflammation and the associated behavioural change. We next demonstrated neuroinflammatory effects on behaviour directly, because intra-hippocampal administration of the same endotoxin elicited a similar neuroinflammatory response in male and female mice, as well as increasing locomotor activity and accelerating goal-directed learning consistently across sexes. In contrast, hippocampal neuroinflammation caused sex-specific disruptions to the acquisition of instrumental actions and to Pavlovian food-approach memories. Finally, we showed that hippocampal neuroinflammation had a sexually dimorphic effect on neuronal activation: increasing it in females and decreasing it in males.### Competing Interest StatementThe authors have declared no competing interest.

Individuals often learn how to perform new actions for particular outcomes against a complex background of existing action-outcome associations. As such, this new knowledge can interfere or even compete with existing knowledge, such that individuals must use internal and external cues to determine which action is appropriate to the current situation. The question thus remains as to how this problem is solved at a neural level. Research over the last decade or so has begun to determine how the brain achieves situation-appropriate action selection. Several converging lines of evidence suggest that it is achieved through the complex interactions of acetylcholine and dopamine within the striatum in a manner that relies on glutamatergic inputs from the cortex and thalamus. Here we briefly review this evidence, then relate it to several very recent findings to provide new, speculative insights regarding the precise nature of striatal acetylcholine/dopamine interaction dynamics and their relation to situation- appropriate action selection.

The loss of neurons in parafascicular thalamus (Pf) and their inputs to dorsomedial striatum (DMS) in Lewy body disease (LBD) and Parkinson’s disease dementia (PDD) have been linked to the effects of neuroinflammation. We found that, in rats, these inputs were necessary for both the function of striatal cholinergic interneurons (CINs) and the flexible encoding of the action-outcome (AO) associations necessary for goal-directed action, producing a burst-pause pattern of CIN firing but only during the remapping elicited by a shift in AO contingency. Neuroinflammation in the Pf abolished these changes in CIN activity and goal-directed control after the shift in contingency. However, both effects were rescued by either the peripheral or the intra-DMS administration of selegiline, a monoamine oxidase B inhibitor that we found also enhances adenosine triphosphatase activity in CINs. These findings suggest a potential treatment for the cognitive deficits associated with neuroinflammation affecting the function of the Pf and related structures.

Cognitive-behavioral testing in preclinical models of Alzheimer's disease has failed to capture deficits in goal-directed action control. Here, we provide the first comprehensive investigation of goal-directed action in a transgenic mouse model of Alzheimer's disease. Specifically, we tested outcome devaluation performance in male and female human amyloid precursor protein (hAPP)-J20 mice. Mice were first trained to press left and right levers for pellet and sucrose outcomes, respectively (counterbalanced), over 4 d. On test, mice were prefed one of the outcomes to satiety and given a choice between levers. Devaluation performance was intact for 36-week-old wild-types of both sexes, who responded more on the valued relative to the devalued lever (Valued > Devalued). By contrast, devaluation was impaired (Valued = Devalued) for J20 mice of both sexes, and for 52-week-old male mice regardless of genotype. After additional lever press training (i.e., 8-d lever pressing in total), devaluation was intact for all mice, demonstrating that the initial deficits were not a result of a nonspecific impairment in reward processing, depression, or locomotor activity in J20 or aging mice. Follow-up analyses revealed that microglial expression in the dorsal CA1 region of the hippocampus was associated with poorer outcome devaluation performance on initial, but not later tests. Together, these data demonstrate that goal-directed action is initially impaired in J20 mice of both sexes and in aging male mice regardless of genotype, and that this impairment is related to neuroinflammation in the dorsal CA1 hippocampal region.

Rationale Attempts to lose weight often fail despite knowledge of the health risks associated with obesity and determined efforts. We previously showed that rodents fed an obesogenic diet displayed premature habitual behavioural control and weakened flexible decision-making based on the current value of outcomes produced by their behaviour. Thus, habitual control may contribute to failed attempts to modify eating behaviours. Objectives To examine the effects of an obesogenic diet on behavioural control and glutamate transmission in dorsal striatum regions and to assess the ability of N-acetylcysteine (NAC) to reverse deficits. Methods Here, we examined diet-induced changes to decision-making and used in vitro electrophysiology to investigate the effects of diet on glutamate transmission within the dorsomedial (DMS) and dorsolateral (DLS) striatum, areas that control goal-directed and habitual behaviours, respectively. We administered NAC in order to normalize glutamate release and tested whether this would restore goal-directed performance following an obesogenic diet. Results We found that an obesogenic diet reduced sensitivity to outcome devaluation and increased glutamate release in the DMS, but not DLS. Administration of NAC restored goal-directed control and normalized mEPSCs in the DMS. Finally, NAC administered directly to the DMS was sufficient to reinstate sensitivity to outcome devaluation following an obesogenic diet. Conclusions These data indicate that obesogenic diets alter neural activity in the basal ganglia circuit responsible for goal-directed learning and control which leads to premature habitual control. While the effects of diet are numerous and widespread, normalization of glutamatergic activity in this circuit is sufficient for restoring goal-directed behaviour.

Cognitive-behavioural testing in preclinical models of Alzheimer’s disease has typically been limited to visuo-spatial memory tests and has failed to capture the broad scope of deficits patients also display in goal-directed action control. The current study addresses this gap by providing the first comprehensive investigation of how goal-directed actions are affected in a transgenic mouse model of Alzheimer’s disease. Specifically, we tested outcome devaluation performance – a popular test of goal-directed action – in male and female human amyloid precursor protein (hAPP)-J20 mice. Mice were first trained to press a left and right lever for unique pellet and sucrose outcomes respectively (counterbalanced) over four days. On test, mice were fed one of the two outcomes to reduce its value via sensory specific satiety and subsequently given a choice between levers. Goal-directed action was intact for 36-week-old wildtype mice of both sexes, because they responded more on the lever associated with the still-valued outcome than that associated with the devalued outcome (i.e. Valued > Devalued). Goal-directed action was impaired (Valued = Devalued) for J20 mice of both sexes, and for 52-week-old male mice regardless of genotype. Following an additional 4 days of lever press training (i.e., 8 days lever pressing in total), outcome devaluation was intact for all mice regardless of age or genotype. Immunohistochemical analysis revealed that increased microglial expression in the dorsal CA1 region of the hippocampus was associated with poorer outcome devaluation performance on initial tests, but not with tests performed after 8 days of lever pressing. Together, these data demonstrate that goal-directed action is transiently impaired in J20 mice of both sexes and in aging male mice regardless of genotype, and that this impairment is related to neuroinflammation in the dorsal CA1 region of the hippocampus.

Stress reduces cognitive flexibility and dopamine D1 receptor-related activity in the prelimbic cortex (PL), effects hypothesized to depend on reduced corticotropic releasing factor receptor type 1 (CRFr1) regulation of dopamine neurons in the ventral tegmental area (VTA). We assessed this hypothesis in rats by examining the effect of chronic unpredictable restraint stress (CUS), mild acute stress, or their combination on cognitive flexibility, CRFr1 expression in the VTA and D1-related activity in PL. In Experiment 1, rats received either CUS or equivalent handling for 14 days before being trained to press two levers to earn distinct food outcomes. Initial learning was assessed using an outcome devaluation test after which cognitive flexibility was assessed by reversing the outcomes earned by the actions. Prior to each reversal training session, half the CUS and controls receiving acute stress with action-outcome updating assessed using a second devaluation test and CRFr1 expression in the VTA assessed using in-situ hybridisation. Although CUS did not itself affect action-outcome learning, its combination with acute stress blocked reversal learning and decreased VTA CRFr1 expression after acute shock. The relationship between these latter two effects was assessed in Experiment 2 by pharmacologically disconnecting the VTA and PL, unilaterally blocking neurons expressing CRFr1 in the VTA and D1 receptors in the contralateral PL during reversal learning after acute stress. Acute stress again blocked reversal learning but only in the group with VTA-PL disconnection, demonstrating that VTA CRFr1-induced facilitation of dopaminergic activity in the PL is necessary for maintaining cognitive flexibility after acute stress. [250].

Background Changes in dopaminergic neural function can be induced by an acute inflammatory state that, by altering the integrity of the neurovasculature, induces neuronal stress, cell death and causes functional deficits. Effectively blocking these effects of inflammation could, therefore, reduce both neuronal and functional decline. To test this hypothesis, we inhibited vascular adhesion protein 1 (VAP-1), a membrane-bound protein expressed on the endothelial cell surface, that mediates leukocyte extravasation and induces oxidative stress. Method We induced dopaminergic neuronal loss by infusing lipopolysaccharide (LPS) directly into the substantia nigra (SN) in rats and administered the VAP-1 inhibitor, PXS-4681A, daily. Results LPS produced: an acute inflammatory response, the loss of dopaminergic neurons in the SN, reduced the dopaminergic projection to SN target regions, particularly the dorsolateral striatum (DLS), and a deficit in habit learning, a key function of the DLS. In an attempt to protect SN neurons from this inflammatory response we found that VAP-1 inhibition not only reduced neutrophil infiltration in the SN and striatum, but also reduced the associated striatal microglia and astrocyte response. We found VAP-1 inhibition protected dopamine neurons in the SN, their projections to the striatum and promoted the functional recovery of habit learning. Thus, we reversed the loss of habitual actions, a function usually dependent on dopamine release in DLS and sensitive to striatal dysfunction. Conclusions We establish, therefore, that VAP-1 inhibition has an anti-inflammatory profile that may be beneficial in the treatment of dopamine neuron dysfunction caused by an acute inflammatory state in the brain.

BACKGROUND AND PURPOSE:Neuroinflammation is initiated by a variety of stimuli including infections, sepsis, neurodegenerative diseases or traumatic brain injury and, if not adequately controlled, can lead to various degrees of neuronal damage and behavioural impairment. A critical event in the initial steps of inflammation is neutrophil extravasation. Semicarbazide-sensitive amine oxidase (SSAO, also known as vascular adhesion protein 1 or VAP-1) regulates neutrophil adhesion and extravasation. Here, we elucidate the role of SSAO/VAP-1 in the early stage inflammatory response after LPS insult in the brain. EXPERIMENTAL APPROACH:PXS-4681A, a selective and irreversible SSAO/VAP-1 inhibitor, was tested in two rat models of neuroinflammation, following systemic or i.c.v. LPS. Immunohistochemical and immunofluorescence techniques were used to measure neutrophils and microglia. VAP-1 was quantitated by Western blotting. KEY RESULTS:Both systemic and i.c.v. administration of LPS induced an increase in neutrophil recruitment and microglial response in various brain areas including the substantia nigra and striatum. PXS-4681A produced a significant inhibition of neutrophil recruitment and extravasation after i.c.v. LPS injection and also reversed microglial cell recruitment and morphological changes to the level of the sham controls in both LPS models. CONCLUSIONS AND IMPLICATIONS:PXS-4681A acted as an effective anti-inflammatory agent after both systemic and i.c.v. LPS injections suggesting that SSAO/VAP-1 inhibition could be beneficial in the treatment of brain inflammation.

Studies of Quantum Dots biodistribution have shown that these nanoparticles accumulate in various organs, including brain parenchyma, possibly causing functional alterations. To investigate its potential neurotoxicity, we administered QDs to young mice and studied their behaviour during the following weeks. Spontaneous locomotor behaviour in the home cage was not significantly altered in treated mice, the Rotarod and Grip Strength Meter tests were normal, whereas memory deficits were found with the Novel Object Recognition test up to three weeks after the injection. We also found a significant increase in the neuronal excitability of QDstreated mice, following the administration of a Pentylenetetrazol challenge.

The development of major depression requires both genetic and environmental factors. A brain proteomic investigation on the genetic model of Flinders sensitive and resistant line (FSL-FRL) rats was performed. Maternal separation (MS) was also applied to identify protein networks affected by stress exposure, since early-life trauma is considered an important antecedent of depression. Hippocampus (HIP) and prefrontal/frontal cortex proteins were extracted and separated by 2-Dimensional (2-D) gel electrophoresis. After image analysis, significantly modulated proteins in the different conditions analysed were identified by mass spectrometry. The expression of proteins involved in energy metabolism, cellular localization and transport, cytoskeleton organization and apoptosis differed in the two lines. Maternal separation differently affected the genetic backgrounds, by modulating cytoskeleton and neuron morphogenesis proteins in FSL; energy metabolism, cellular localization, neuron differentiation and intracellular transport in FRL. The present work shows that different mechanisms could be involved in the pathophysiology of depression and the vulnerability to stress, suggesting possible new cellular pathways and key markers for the study of affective disorders.

Biocompatible highly bright silica nanoparticles were designed, prepared and tested in small living organisms for both in vivo and ex vivo imaging. The results that we report here demonstrate that they are suitable for optical imaging applications as a possible alternative to commercially available fluorescent materials including quantum dots. Moreover, the tunability of their photophysical properties, which was enhanced by the use of different dyes as doping agents, constitutes a very important added value in the field of medical diagnostics.