Insights into the Role of Dopamine Receptor Systems in Learning and Memory

Dopamine D1-Receptor Organization Contributes to Functional Brain Architecture

Recent work has recognized a gradient-like organization in cortical function, spanning from primary sensory to transmodal cortices. It has been suggested that this axis is aligned with regional differences in neurotransmitter expression. Given the abundance of dopamine D1-receptors (D1DR), and its importance for modulation and neural gain, we tested the hypothesis that D1DR organization is aligned with functional architecture, and that inter-regional relationships in D1DR co-expression modulate functional cross talk. Using the world's largest dopamine D1DR-PET and MRI database (N = 180%, 50% female), we demonstrate that D1DR organization follows a unimodal-transmodal hierarchy, expressing a high spatial correspondence to the principal gradient of functional connectivity. We also demonstrate that individual differences in D1DR density between unimodal and transmodal regions are associated with functional differentiation of the apices in the cortical hierarchy. Finally, we show that spatial co-expression of D1DR primarily modulates couplings within, but not between, functional networks. Together, our results show that D1DR co-expression provides a biomolecular layer to the functional organization of the brain.

Contextual memory engrams, and the neuromodulatory influence of the locus coeruleus

Here, we review the basis of contextual memory at a conceptual and cellular level. We begin with an overview of the philosophical foundations of traversing space, followed by theories covering the material bases of contextual representations in the hippocampus (engrams), exploring functional characteristics of the cells and subfields within. Next, we explore various methodological approaches for investigating contextual memory engrams, emphasizing plasticity mechanisms. This leads us to discuss the role of neuromodulatory inputs in governing these dynamic changes. We then outline a recent hypothesis involving noradrenergic and dopaminergic projections from the locus coeruleus (LC) to different subregions of the hippocampus, in sculpting contextual representations, giving a brief description of the neuroanatomical and physiological properties of the LC. Finally, we examine how activity in the LC influences contextual memory processes through synaptic plasticity mechanisms to alter hippocampal engrams. Overall, we find that phasic activation of the LC plays an important role in promoting new learning and altering mnemonic processes at the behavioral and cellular level through the neuromodulatory influence of NE/DA in the hippocampus. These findings may provide insight into mechanisms of hippocampal remapping and memory updating, memory processes that are potentially dysregulated in certain psychiatric and neurodegenerative disorders.

Fluoroalkoxylated C-3 and C-9 (S)-12-bromostepholidine analogues with D1R antagonist activity

To illuminate the tolerance of fluoroalkoxylated groups at the C-3 and C-9 positions of tetrahydroprotoberberines (THPBs) on D1R activity, C-3 and C-9 fluoroalkoxylated analogues of (S)-12-bromostepholidine were prepared and evaluated. All compounds examined were D1R antagonists as measured by a cAMP assay. Our structure-activity studies herein indicate that the C-3 position tolerates a 1,1-difluoroethoxy substituent for D1R antagonist activity. Compound 13a was the most potent cAMP-based D1R antagonist identified and was also found to antagonize β-arrestin translocation in a TANGO assay. Affinity assessments at other dopamine receptors revealed that 13a is selective for D1R and unlike other naturally-occurring THPBs such as (S)-stepholidine, lacks D2R affinity. In preliminary biopharmaceutical assays, excellent BBB permeation was observed for 13a. Further pharmacological studies are warranted on (S)-stepholidine congeners to harvest their potential as a source of novel, druggable D1R-targeted agents.

Dopaminergic D2-like receptor stimulation affects attention on contextual information and modulates BOLD activation of extinction-related brain areas

Contextual information is essential for learning and memory processes and plays a crucial role during the recall of extinction memory, and in the renewal effect, which is the context-dependent recovery of an extinguished response. The dopaminergic system is known to be involved in regulating attentional processes by shifting attention to novel and salient contextual cues. Higher dopamine levels are associated with a better recall of previously learned stimulus-outcome associations and enhanced encoding, as well as retrieval of contextual information which promotes renewal. In this fMRI study, we aimed to investigate the impact of processing contextual information and the influence of dopaminergic D2-like receptor activation on attention to contextual information during a predictive learning task as well as upon extinction learning, memory performance, and activity of extinction-related brain areas. A single oral dose of 1.25 mg bromocriptine or an identical-looking placebo was administered to the participants. We modified a predictive learning task that in previous studies reliably evoked a renewal effect, by increasing the complexity of contextual information. We analysed fixations and dwell on contextual cues by use of eye-tracking and correlated these with behavioural performance and BOLD activation of extinction-related brain areas. Our results indicate that the group with dopaminergic D2-like receptor stimulation had higher attention to task-relevant contextual information and greater/lower BOLD activation of brain regions associated with cognitive control during extinction learning and recall. Moreover, renewal responses were almost completely absent. Since this behavioural effect was observed for both treatment groups, we assume that this was due to the complexity of the altered task design.

Activation patterns of dopaminergic cell populations reflect different learning scenarios in a cichlid fish, Pseudotropheus zebra

Dopamine is present in all vertebrates and the functional roles of the subsystems are assumed to be similar. Whereas the effect of dopaminergic modulation is well investigated in different target systems, less is known about the factors that are causing the modulation of dopaminergic cells. Using the zebra mbuna, Pseudotropheus zebra, a cichlid fish from Lake Malawi as a model system, we investigated the activation of specific dopaminergic cell populations detected by double-labeling with TH and pS6 antibodies while the animals were solving different learning tasks. Specifically, we compared an intense avoidance learning situation, an instrumental learning task, and a non-learning isolated group and found strong activation of different dopaminergic cell populations. Preoptic-hypothalamic cell populations respond to the stress component in the avoidance task, and the forced movement/locomotion may be responsible for activation in the posterior tubercle. The instrumental learning task had little stress component, but the activation of the raphe superior in this group may be correlated with attention or arousal during the training sessions. At the same time, the weaker activation of the nucleus of the posterior commissure may be related to positive reward acting onto tectal circuits. Finally, we examined the co-activation patterns across all dopaminergic cell populations and recovered robust differences across experimental groups, largely driven by hypothalamic, posterior tubercle, and brain stem regions possibly encoding the valence and salience associated with stressful stimuli. Taken together, our results offer some insights into the different functions of the dopaminergic cell populations in the brain of a non-mammalian vertebrate in correlation with different behavioral conditions, extending our knowledge for a more comprehensive view of the mechanisms of dopaminergic modulation in vertebrates.

The dopamine D1 receptor antagonist SCH-23390 blocks the acquisition, but not expression of mitragynine-induced conditioned place preference in rats

Mitragynine (MG) is the primary active constituent of Mitragyna speciosa Korth (kratom), a psychoactive Southeast Asian plant with potential therapeutic use. Numerous studies support roles of dopaminergic system in drug reward. However, the involvement of the dopaminergic system in mediating MG reward and drug-seeking is poorly understood. Using conditioned place preference (CPP) paradigm, the present study aims to evaluate the roles of the dopamine (DA) D1 receptor in the acquisition and expression of MG-induced CPP in rats. The effects of SCH-23390, a selective DA D1 receptor antagonist, on the acquisition of MG-induced CPP were first investigated. Rats were pre-treated systemically with SCH-23390 (0, 0.1 and 0.3 mg/kg, i.p.) prior to MG (10 mg/kg) conditioning sessions. Next, we tested the effects of the DA D1 receptor antagonist on the expression of MG-induced CPP. Furthermore, the effects of a MG-priming dose (5 mg/kg) on the reinstatement of extinguished CPP were tested. The results showed that SCH-23390 dose-dependently suppressed the acquisition of a MG-induced CPP. In contrast, SCH-23390 had no effect on the expression of a MG-induced CPP. The findings of this study suggested a crucial role of the DA D1 receptor in the acquisition, but not the expression of the rewarding effects of MG in a CPP test. Furthermore, blockade of the D1-like receptor during conditioning did not prevent MG priming effects on CPP reinstatement test, suggesting no role for the DA D1 receptor in reinstatement sensitivity.

Dopamine transporter blockade during adolescence increases adult dopamine function, impulsivity, and aggression

Sensitive developmental periods shape neural circuits and enable adaptation. However, they also engender vulnerability to factors that can perturb developmental trajectories. An understanding of sensitive period phenomena and mechanisms separate from sensory system development is still lacking, yet critical to understanding disease etiology and risk. The dopamine system is pivotal in controlling and shaping adolescent behaviors, and it undergoes heightened plasticity during that time, such that interference with dopamine signaling can have long-lasting behavioral consequences. Here we sought to gain mechanistic insight into this dopamine-sensitive period and its impact on behavior. In mice, dopamine transporter (DAT) blockade from postnatal (P) day 22 to 41 increases aggression and sensitivity to amphetamine (AMPH) behavioral stimulation in adulthood. Here, we refined this sensitive window to P32-41 and identified increased firing of dopaminergic neurons in vitro and in vivo as a neural correlate to altered adult behavior. Aggression can result from enhanced impulsivity and cognitive dysfunction, and dopamine regulates working memory and motivated behavior. Hence, we assessed these behavioral domains and found that P32-41 DAT blockade increases impulsivity but has no effect on cognition, working memory, or motivation in adulthood. Lastly, using optogenetics to drive dopamine neurons, we find that increased VTA but not SNc dopaminergic activity mimics the increase in impulsive behavior in the Go/NoGo task observed after adolescent DAT blockade. Together our data provide insight into the developmental origins of aggression and impulsivity that may ultimately improve diagnosis, prevention, and treatment strategies for related neuropsychiatric disorders.

Effect of l-Dopa in acute temozolomide-induced cognitive impairment in male mice: a possible antineuroinflammatory role

Temozolomide is used commonly in the treatment of some types of cancers, but it may also result in cognitive impairments such as memory deficits. l-Dopa, a well known medicine for the central nervous system, has been shown to have positive effects on some cognitive disorders. Here we sought to investigate the effect of l-Dopa on temozolomide-induced cognitive impairments. BALB/c mice were subjected to 3-days temozolomide and 6-days concomitant l-Dopa/benserazide administration in six groups (control, l-Dopa 25 mg/kg, l-Dopa 75 mg/kg, temozolomide, temozolomide + l-Dopa 25 mg/kg, and temozolomide + l-Dopa 75 mg/kg). Open field test, object location recognition, novel object recognition test, and shuttle-box test were carried out to determine the locomotor, anxiety-like behavior, and memory function of subjects. TNF-α and brain-derived neurotrophic factor (BDNF) gene expression in the hippocampus was measured by real-time PCR. Mice treated with temozolomide showed recognition memory impairment, along with hippocampal TNF-α and BDNF mRNA expression level raise, and detection of histological insults in hematoxylin and eosin hippocampal slides. Mice that received temozolomide + l-Dopa showed normal behavioral function and lower TNF-α and BDNF hippocampal mRNA expression levels, and histologically normal hippocampal CA1 region in comparison with mice in the temozolomide group. Our results provide evidence that l-Dopa prevents temozolomide-induced recognition memory deficit in mice at the acute phase probably via l-Dopa antineuroinflammatory effects.

Dopamine D1-signaling modulates maintenance of functional network segregation in aging

Past research has shown that as individuals age, there are decreases in within-network connectivity and increases in between-network connectivity, a pattern known as functional dedifferentiation. While the mechanisms behind reduced network segregation are not fully understood, evidence suggests that age-related differences in the dopamine (DA) system may play a key role. The DA D1-receptor (D1DR) is the most abundant and age-sensitive receptor subtype in the dopaminergic system, known to modulate synaptic activity and enhance the specificity of the neuronal signals. In this study from the DyNAMiC project (N = 180, 20-79y), we set out to investigate the interplay among age, functional connectivity, and dopamine D1DR availability. Using a novel application of multivariate Partial Least squares (PLS), we found that older age, and lower D1DR availability, were simultaneously associated with a pattern of decreased within-network and increased between-network connectivity. Individuals who expressed greater distinctiveness of large-scale networks exhibited more efficient working memory. In line with the maintenance hypotheses, we found that older individuals with greater D1DR in caudate exhibited less dedifferentiation of the connectome, and greater working memory, compared to their age-matched counterparts with less D1DR. These findings suggest that dopaminergic neurotransmission plays an important role in functional dedifferentiation in aging with consequences for working memory function at older age.

Chronic dietary exposure to arsenic at environmentally relevant concentrations impairs cognitive performance in adult zebrafish (Danio rerio) via oxidative stress and dopaminergic dysfunction

The current study was designed to evaluate the effects of chronic dietary arsenic exposure on the cognitive performance of adult zebrafish and uncover probable pathways by which arsenic mediates such neurotoxic effects. Adult zebrafish were treated with 3 different dietary arsenic concentrations (30, 60, and 100 μg/g dry weight (dw), as arsenite) in addition to control for 60 days. A latent learning paradigm, which employs a complex maze, was used to assess the cognitive performance of fish. Our results demonstrated that dietary treatment with arsenic, especially at medium (60 μg/g dw) and high (100 μg/g dw) exposure dose levels, significantly impaired the performance of fish in various latent learning tasks evaluated in the present study. Concomitant with cognitive dysfunction, chronic dietary exposure to arsenic was also found to increase arsenic accumulation and dopamine levels, and induce oxidative stress (reduced thiol redox, increased lipid peroxidation and expression of antioxidant enzyme genes) in the brain of zebrafish in a dose-dependent manner. Dopaminergic system in the brain is known to play a critical role in regulating cognitive behaviours in fish, and our observations suggested that chronic dietary treatment with medium and high arsenic doses leads to significant alterations in the expression of genes involved in dopamine signalling (dopamine receptors), synthesis (thyroxine hydroxylase) and metabolism (monoamine oxidase) in the zebrafish brain. Moreover, we also recorded significant downregulation of genes such as the brain-derived neurotrophic factor (BDNF) and ectonucleotidases (entpd2_mg, entpd2_mq, and 5'-nucleotidase), which are critical for learning and memory functions, in the zebrafish brain following chronic dietary exposure to arsenic. Overall, the present study suggests that chronic environmentally relevant dietary exposure to arsenic can impair the cognitive performance in zebrafish, essentially by inducing oxidative stress and disrupting the dopaminergic neurotransmission in the brain.

Memory impairments in rodent depression models: A link with depression theories

More than 80% of depressed patients struggle with learning new tasks, remembering positive events, or concentrating on a single topic. These neurocognitive deficits accompanying depression may be linked to functional and structural changes in the prefrontal cortex and hippocampus. However, their mechanisms are not yet completely understood. We conducted a narrative review of articles regarding animal studies to assess the state of knowledge. First, we argue the contribution of changes in neurotransmitters and hormone levels in the pathomechanism of cognitive dysfunction in animal depression models. Then, we used numerous neuroinflammation studies to explore its possible implication in cognitive decline. Encouragingly, we also observed a positive correlation between increased oxidative stress and a depressive-like state with concomitant memory deficits. Finally, we discuss the undeniable role of neurotrophin deficits in developing cognitive decline in animal models of depression. This review reveals the complexity of depression-related memory impairments and highlights the potential clinical importance of gathered findings for developing more reliable animal models and designing novel antidepressants with procognitive properties.

Acute administration of a dopamine D2/D3 receptor agonist alters behavioral and neural parameters in adult zebrafish

The dopaminergic neurotransmitter system is implicated in several brain functions and behavioral processes. Alterations in it are associated with the pathogenesis of several human neurological disorders. Pharmacological agents that interact with the dopaminergic system allow the investigation of dopamine-mediated cellular and molecular responses and may elucidate the biological bases of such disorders. Zebrafish, a translationally relevant biomedical research organism, has been successfully employed in prior psychopharmacology studies. Here, we evaluated the effects of quinpirole (dopamine D2/D3 receptor agonist) in adult zebrafish on behavioral parameters, brain-derived neurotrophic factor (BDNF) and neurotransmitter levels. Zebrafish received intraperitoneal injections of 0.5, 1.0, or 2.0 mg/kg quinpirole or saline (control group) twice with an inter-injection interval of 48 h. All tests were performed 24 h after the second injection. After this acute quinpirole administration, zebrafish exhibited decreased locomotor activity, increased anxiety-like behaviors and memory impairment. However, quinpirole did not affect social and aggressive behavior. Quinpirole-treated fish exhibited stereotypic swimming, characterized by repetitive behavior followed by immobile episodes. Moreover, quinpirole treatment also decreased the number of BDNF-immunoreactive cells in the zebrafish brain. Analysis of neurotransmitter levels demonstrated a significant increase in glutamate and a decrease in serotonin, while no alterations were observed in dopamine. These findings demonstrate that dopaminergic signaling altered by quinpirole administration results in significant behavioral and neuroplastic changes in the central nervous system of zebrafish. Thus, we conclude that the use of quinpirole administration in adult zebrafish may be an appropriate tool for the analysis of mechanisms underlying neurological disorders related to the dopaminergic system.

Long-term memory, synaptic plasticity and dopamine in rodent medial prefrontal cortex: Role in executive functions

Mnemonic functions, supporting rodent behavior in complex tasks, include both long-term and (short-term) working memory components. While working memory is thought to rely on persistent activity states in an active neural network, long-term memory and synaptic plasticity contribute to the formation of the underlying synaptic structure, determining the range of possible states. Whereas, the implication of working memory in executive functions, mediated by the prefrontal cortex (PFC) in primates and rodents, has been extensively studied, the contribution of long-term memory component to these tasks received little attention. This review summarizes available experimental data and theoretical work concerning cellular mechanisms of synaptic plasticity in the medial region of rodent PFC and the link between plasticity, memory and behavior in PFC-dependent tasks. A special attention is devoted to unique properties of dopaminergic modulation of prefrontal synaptic plasticity and its contribution to executive functions.

Former Training Relieves the Later Development of Behavioral Inflexibility in an Animal Model Overexpressing the Dopamine Transporter

A range of dopamine-dominating neuropsychiatric disorders present with cognitive deficits. In accordance, the dopamine transporter overexpressing rat model (DAT-tg rat) displays cognitive deficits by means of behavioral inflexibility and learning disabilities. It remains to be investigated when cognitive deficits emerge, due to the inherent DA irregularities, during the life course of the DAT-tg rat and what may relieve symptoms. The Morris water maze (MWM) was used to assess cognitive abilities in three cohorts of DAT-tg rats. In the first cohort, the development of cognitive deficits was assessed by repeatedly testing animals in the MWM at postnatal day (PND) 35, 60, and 90. In the second and third cohort, pharmacological interventions and transcranial direct current stimulation (tDCS) were tested in adult animals to understand what drives, and thus relieves, the deficits. Minor differences were observed between DAT-tg rats and control rats at PND 35 and 60, whereas cognitive deficits fully emerged at PND 90. A high dosage of methylphenidate diminished both behavioral inflexibility and improved learning abilities in adult rats. Interestingly, rats subjected early in life to the MWM also displayed improved behavioral flexibility as compared to rats naïve to the paradigm. Cognitive deficits gradually develop over time and fully emerge in adulthood. Pharmacological modulation of the ubiquitous DAT overexpression overall improves deficits in adult rats, whereas early training decreases later development of behavioral inflexibility. Thus, former training may constitute a preventive avenue that alters some aspects of cognitive deficits resulting from inherent DA abnormalities.

Novel Dopamine Transporter Inhibitor, CE-123, Ameliorates Spatial Memory Deficits Induced by Maternal Separation in Adolescent Rats: Impact of Sex

Maternal separation (MS) is a key contributor to neurodevelopmental disorders, including learning disabilities. To test the hypothesis that dopamine signaling is a major factor in this, an atypical new dopamine transporter (DAT) inhibitor, CE-123, was assessed for its potential to counteract the MS-induced spatial learning and memory deficit in male and female rats. Hence, neonatal rats (postnatal day (PND)1 to 21) were exposed to MS (180 min/day). Next, the acquisition of spatial learning and memory (Barnes maze task) and the expression of dopamine D1 receptor, dopamine transporter (DAT), and the neuronal GTPase, RIT2, which binds DAT in the vehicle-treated rats were evaluated in the prefrontal cortex and hippocampus in the adolescent animals. The results show that MS impairs the acquisition of spatial learning and memory in rats, with a more severe effect in females. Moreover, the MS induced upregulation of DAT and dopamine D1 receptors expression in the prefrontal cortex and hippocampus in adolescent rats. Regarding RIT2, the expression was decreased in the hippocampus for both the males and females, however, in the prefrontal cortex, reduction was found only in the females, suggesting that there are region-specific differences in DAT endocytic trafficking. CE-123 ameliorated the behavioral deficits associated with MS. Furthermore, it decreased the MS-induced upregulation of D1 receptor expression level in the hippocampus. These effects were more noted in females. Overall, CE-123, an atypical DAT inhibitor, is able to restore cognitive impairment and dopamine signaling in adolescent rats exposed to MS—with more evident effect in females than males.

Dopamine receptor D2 regulates GLUA1-containing AMPA receptor trafficking and central sensitization through the PI3K signaling pathway in a male rat model of chronic migraine

Background

The pathogenesis of chronic migraine remains unresolved. Recent studies have affirmed the contribution of GLUA1-containing AMPA receptors to chronic migraine. The dopamine D2 receptor, a member of G protein-coupled receptor superfamily, has been proven to have an analgesic effect on pathological headaches. The present work investigated the exact role of the dopamine D2 receptor in chronic migraine and its effect on GLUA1-containing AMPA receptor trafficking.

Methods

A chronic migraine model was established by repeated inflammatory soup stimulation. Mechanical, periorbital, and thermal pain thresholds were assessed by the application of von Frey filaments and radiant heat. The mRNA and protein expression levels of the dopamine D2 receptor were analyzed by qRT‒PCR and western blotting. Colocalization of the dopamine D2 receptor and the GLUA1-containing AMPAR was observed by immunofluorescence. A dopamine D2 receptor agonist (quinpirole) and antagonist (sulpiride), a PI3K inhibitor (LY294002), a PI3K pathway agonist (740YP), and a GLUA1-containing AMPAR antagonist (NASPM) were administered to confirm the effects of the dopamine D2 receptor, the PI3K pathway and GULA1 on central sensitization and the GLUA1-containing AMPAR trafficking. Transmission electron microscopy and Golgi-Cox staining were applied to assess the impact of the dopamine D2 receptor and PI3K pathway on synaptic morphology. Fluo-4-AM was used to clarify the role of the dopamine D2 receptor and PI3K signaling on neuronal calcium influx. The Src family kinase (SFK) inhibitor PP2 was used to explore the effect of Src kinase on GLUA1-containing AMPAR trafficking and the PI3K signaling pathway.

Results

Inflammatory soup stimulation significantly reduced pain thresholds in rats, accompanied by an increase in PI3K-P110β subunit expression, loss of dopamine receptor D2 expression, and enhanced GLUA1-containing AMPA receptor trafficking in the trigeminal nucleus caudalis (TNC). The dopamine D2 receptor colocalized with the GLUA1-containing AMPA receptor in the TNC; quinpirole, LY294002, and NASPM alleviated pain hypersensitivity and reduced GLUA1-containing AMPA receptor trafficking in chronic migraine rats. Sulpiride aggravated pain hypersensitivity and enhanced GLUA1 trafficking in CM rats. Importantly, the anti-injury and central sensitization-mitigating effects of quinpirole were reversed by 740YP. Both quinpirole and LY294002 inhibited calcium influx to neurons and modulated the synaptic morphology in the TNC. Additional results suggested that DRD2 may regulate PI3K signaling through Src family kinases.

Conclusion

Modulation of GLUA1-containing AMPA receptor trafficking and central sensitization by the dopamine D2 receptor via the PI3K signaling pathway may contribute to the pathogenesis of chronic migraine in rats, and the dopamine D2 receptor could be a valuable candidate for chronic migraine treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10194-022-01469-x.

The effects of neurosteroid allopregnanolone on synaptic dysfunction in the hippocampus in experimental parkinsonism rats: An electrophysiological and molecular study

The dopaminergic system is a powerful candidate targeted for changes of synaptic plasticity in the hippocampus. Higher incidence of Parkinson's disease (PD) in men than women indicates the influence of sex hormones on the PD development. Previous studies have shown that neurodegenerative diseases such as PD are related to the decline of Allopregnanolon (Allo), a metabolite of progesterone; it is also well known that learning and memory are influenced by oscillations in steroidal hormones. Although abnormalities in hippocampal plasticity have been observed in the toxic models of PD, effects of Allo on hippocampal LTP and hippocampal synaptic protein levels, which play an important role in maintaining the integrity of neural connections, have never been analyzed thus far. Experimental groups subjected to the long-term potentiation (LTP) were studied in the CA1 area of the hippocampus. In addition, the levels of hippocampal postsynaptic density protein 95 (PSD-95), neurexin-1 (Nrxn1) and neuroligin (Nlgn) as synaptic molecular components were determined by immunoblotting. Although dopamine denervation did not alter basal synaptic transmission and pair-pulse facilitation of field excitatory postsynaptic potentials (fEPSPs), the induction and maintenance of LTP were impaired in the CA1 region. In addition, the levels of PSD-95, Nrxn1 and Nlgn were significantly decreased in the hippocampus of 6-OHDA-treated animals. Such abnormalities in synaptic electrophysiological aspects and protein levels were abolished by the treatment with Allo. These findings showed that partial dopamine depletion led to unusual synaptic plasticity in the CA1 as well as the decrease in synaptic proteins in the hippocampus. Our results demonstrated that Allo ameliorated these deficits and preserved pre- and post-synaptic proteins. Therefore, Allo may be an effective factor in maintaining synaptic integrity in the mesolimbic pathway.

DyNAMiC: A prospective longitudinal study of dopamine and brain connectomes: A new window into cognitive aging

Concomitant exploration of structural, functional, and neurochemical brain mechanisms underlying age‐related cognitive decline is crucial in promoting healthy aging. Here, we present the DopamiNe, Age, connectoMe, and Cognition (DyNAMiC) project, a multimodal, prospective 5‐year longitudinal study spanning the adult human lifespan. DyNAMiC examines age‐related changes in the brain’s structural and functional connectome in relation to changes in dopamine D1 receptor availability (D1DR), and their associations to cognitive decline. Critically, due to the complete lack of longitudinal D1DR data, the true trajectory of one of the most age‐sensitive dopamine systems remains unknown. The first DyNAMiC wave included 180 healthy participants (20–80 years). Brain imaging included magnetic resonance imaging assessing brain structure (white matter, gray matter, iron), perfusion, and function (during rest and task), and positron emission tomography (PET) with the [¹¹C]SCH23390 radioligand. A subsample (n = 20, >65 years) was additionally scanned with [¹¹C]raclopride PET measuring D2DR. Age‐related variation was evident for multiple modalities, such as D1DR; D2DR, and performance across the domains of episodic memory, working memory, and perceptual speed. Initial analyses demonstrated an inverted u‐shaped association between D1DR and resting‐state functional connectivity across cortical network nodes, such that regions with intermediate D1DR levels showed the highest levels of nodal strength. Evident within each age group, this is the first observation of such an association across the adult lifespan, suggesting that emergent functional architecture depends on underlying D1DR systems. Taken together, DyNAMiC is the largest D1DR study worldwide, and will enable a comprehensive examination of brain mechanisms underlying age‐related cognitive decline.

Current concepts in treating mild cognitive impairment in Parkinson's disease

Impairment in various aspects of cognition is recognized as an important non-motor symptom of Parkinson's disease (PD). Mild cognitive impairment in PD (PD-MCI) is common in non-demented PD patients and is often associated with severity of motor symptoms, disease duration and increasing age. Further, PD-MCI can have a significant negative effect on performance of daily life activities and may be a harbinger of development of PD dementia. Thus, there is significant interest in developing therapeutic strategies to ameliorate cognitive deficits in PD and improve cognitive functioning of PD patients. However, due to significant questions that remain regarding the pathophysiology of cognitive dysfunction in PD, remediation of cognitive dysfunction in PD has proven difficult. In this paper, we will focus on PD-MCI and will review some of the current therapeutic approaches being taken to try to improve cognitive functioning in patients with PD-MCI.

Long-lasting behavioral effects of quinpirole exposure on zebrafish

The human brain matures into a complex structure, and to reach its complete development, connections must occur along exact paths. If at any stage, the processes are altered, interrupted, or inhibited, the consequences can be permanent. Dopaminergic signaling participates in the control of physiological functions and behavioral processes, and alterations in this signaling pathway are related to the pathogenesis of several neurological disorders. For this reason, the use of pharmacological agents able to interact with the dopaminergic signaling may elucidate the biological bases of such disorders. We investigated the long-lasting behavioral effects on adult zebrafish after quinpirole (a dopamine D2/D3 receptor agonist) exposure during early life stages of development (24 h exposure at 5 days post-fertilization, dpf) to better understand the mechanisms underlying neurological disorders related to the dopaminergic system. Quinpirole exposure at the early life stages of zebrafish led to late behavioral alterations. When evaluated at 120 dpf, zebrafish presented increased anxiety-like behaviors. At the open tank test, fish remained longer at the bottom of the tank, indicating anxiety-like behavior. Furthermore, quinpirole-treated fish exhibited increased absolute turn angle, likely an indication of elevated erratic movements and a sign of increased fear or anxiety. Quinpirole-treated fish also showed altered swimming patterns, characterized by stereotypic swimming. During the open tank test, exposed zebrafish swims from corner to corner in a repetitive manner at the bottom of the tank. Moreover, quinpirole exposure led to memory impairment compared to control fish. However, quinpirole administration had no effects on social and aggressive behavior. These findings demonstrate that dopaminergic signaling altered by quinpirole administration in the early life stages of development led to late alterations in behavioral parameters of adult zebrafish.

Sex Differences in Dopamine Receptors and Relevance to Neuropsychiatric Disorders

Dopamine is an important neurotransmitter that plays a key role in neuropsychiatric illness. Sex differences in dopaminergic signaling have been acknowledged for decades and have been linked to sex-specific heterogeneity in both dopamine-related behaviours as well as in various neuropsychiatric disorders. However, the overall number of studies that have evaluated sex differences in dopamine signaling, both in health and in these disorders, is low. This review will bring together what is known regarding sex differences in innate dopamine receptor expression and function, as well as highlight the known sex-specific roles of dopamine in addiction, depression, anxiety, schizophrenia, and attention deficit hyperactivity disorder. Due to differences in prognosis, diagnosis, and symptomatology between male and female subjects in disorders that involve dopamine signaling, or in responses that utilize pharmacological interventions that target dopamine receptors, understanding the fundamental sex differences in dopamine receptors is of vital importance for the personalization of therapeutic treatment strategies.

Sex-specific Disruption of the Prairie Vole Hypothalamus by Developmental Exposure to a Flame Retardant Mixture

Prevalence of neurodevelopmental disorders (NDDs) with social deficits is conspicuously rising, particularly in boys. Flame retardants (FRs) have long been associated with increased risk, and prior work by us and others in multiple species has shown that developmental exposure to the common FR mixture Firemaster 550 (FM 550) sex-specifically alters socioemotional behaviors including anxiety and pair bond formation. In rats, FRs have also been shown to impair aspects of osmoregulation. Because vasopressin (AVP) plays a role in both socioemotional behavior and osmotic balance we hypothesized that AVP and its related nonapeptide oxytocin (OT) would be vulnerable to developmental FM 550 exposure. We used the prairie vole (Microtus ochrogaste) to test this because it is spontaneously prosocial. Using siblings of prairie voles used in a prior study that assessed behavioral deficits resulting from developmental FM 550 exposure across 3 doses, here we tested the hypothesis that FM 550 sex-specifically alters AVP and OT neuronal populations in critical nuclei, such as the paraventricular nucleus (PVN), that coordinate those behaviors, as well as related dopaminergic (determined by tyrosine hydroxylase (TH) immunolabeling) populations. Exposed females had fewer AVP neurons in the anterior PVN and more A13 TH neurons in the zona incerta than controls. By contrast, in FM 550 males, A13 TH neuron numbers in the zona incerta were decreased but only in 1 dose group. These results expand on previous work showing evidence of endocrine disruption of OT/AVP pathways, including to subpopulations of PVN AVP neurons that coordinate osmoregulatory functions in the periphery.

The Free-movement pattern Y-maze: A cross-species measure of working memory and executive function

Numerous neurodegenerative and psychiatric disorders are associated with deficits in executive functions such as working memory and cognitive flexibility. Progress in developing effective treatments for disorders may benefit from targeting these cognitive impairments, the success of which is predicated on the development of animal models with validated behavioural assays. Zebrafish offer a promising model for studying complex brain disorders, but tasks assessing executive function are lacking. The Free-movement pattern (FMP) Y-maze combines aspects of the common Y-maze assay, which exploits the inherent motivation of an organism to explore an unknown environment, with analysis based on a series of sequential two-choice discriminations. We validate the task as a measure of working memory and executive function by comparing task performance parameters in adult zebrafish treated with a range of glutamatergic, cholinergic and dopaminergic drugs known to impair working memory and cognitive flexibility. We demonstrate the cross-species validity of the task by assessing performance parameters in adapted versions of the task for mice and Drosophila, and finally a virtual version in humans, and identify remarkable commonalities between vertebrate species' navigation of the maze. Together, our results demonstrate that the FMP Y-maze is a sensitive assay for assessing working memory and cognitive flexibility across species from invertebrates to humans, providing a simple and widely applicable behavioural assay with exceptional translational relevance.

Dopaminergic modulation of working memory and cognitive flexibility in a zebrafish model of aging-related cognitive decline

Healthy aging is associated with a decline in memory and executive function, which have both been linked with aberrant dopaminergic signaling. We examined the relationship between cognitive performance and dopamine function of young and aging zebrafish (Danio rerio). We revealed age-related decreases in working memory and cognitive flexibility in the Free-Movement Pattern (FMP) Y-maze. An increase in drd5 gene expression in aging adults coincided with a decrease in cognitive performance. Treatment with a D1/D5 receptor agonist (SKF-38393, 35 µM) 30 minutes prior to behavioral assessment resulted in improved working memory in aging zebrafish, but no effect in younger adults. However, an "overdosing" effect caused by agonist treatment resulted in downregulation of dat expression in 6-month old, treated zebrafish. The translational relevance of these findings was tested in humans by analyzing exploratory behavior in young-adult, 18-35-year olds, and aged adults, 70+ year olds, in a virtual FMP Y-maze. Our findings revealed similar age-related decline in working memory. Thus, strongly supporting zebrafish as a translational model of aging and cognitive decline.

The critical role of hippocampal dopamine in the pathogenesis of hepatic encephalopathy

The pathogenesis of hepatic encephalopathy (HE) has been generally linked to blood ammonia, gamma-aminobutyric acid and serotonin. However, the exact mechanism remains unclear. In the present study, we aimed to explore the role of hippocampal dopamine (DA) and its receptors in the pathogenesis of HE through the use of behavioral testing, western blotting, and immunofluorescence staining in normal rats, HE model rats and rats treated with the DA precursor-levodopa (L-DOPA). HE model rats manifested fibrotic livers and showed serious behavioral disorders. They also had significantly lower hippocampal DA content and increased expression of both D1 and D2 receptors relative to normal rats. After treatment with L-DOPA, the HE model rats showed normal behavior and expression of D1 returned to normal levels. Furthermore, pretreatment with the D1 antagonist SCH23390 blocked the therapeutic effect of L-DOPA on behavior in HE model rats. Taken together, these results clarify that the decrease in hippocampal DA plays a role in the pathogenesis of HE and that this effect is mediated by D1. These findings provide new evidence for the pathogenesis of HE.

Effects of dopamine D1- and D2-like receptors in the CA1 region of the hippocampus on expression and extinction of morphine-induced conditioned place preference in rats

Considering the extent of drug use and its relapse rate worldwide, in the present study, we explored the role of intra-CA1 administration of D1-like and D2-like receptor antagonists on the expression and extinction of morphine-induced CPP. To induce morphine CPP, adult male Wistar rats received a daily subcutaneous injection of morphine (5 mg/kg) during a 3-day conditioning phase. Different doses of SCH23390 (0.25, 1 or 4 μg/0.5 μl saline), as a selective D1-like receptor antagonist, and sulpiride (0.25, 1, or 4 μg/0.5 μl DMSO), as a selective D2-like receptor antagonist, were bilaterally microinjected into the CA1 region in the expression and extinction phases 1 h before CPP evaluation. Conditioning scores and locomotor activities were recorded during the tests. Results indicated that the injection of the antagonists into the CA1 region dose-dependently attenuated the expression of the morphine-induced CPP and sulpiride revealed prominent behavioral results compared to SCH23390 in the expression phases. Furthermore, microinjections of SCH23390 and sulpiride shortened the extinction phase of the morphine-induced CPP without changing the locomotor activity. The results indicated the involvement of D1- and D2-like receptors within the CA1 region in the expression and extinction of rewarding properties of morphine.

Accelerated habitual learning resulting from L-dopa exposure in rats is prevented by N-acetylcysteine

Instrumental actions are initially goal-directed and driven by their associated outcome. However, with repeated experience habitual actions develop which are automated and efficient, as they are instead driven by antecedent stimuli. Dopamine is thought to facilitate the transition from goal-directed to habitual actions. This idea has been largely derived from evidence that psychostimulants accelerate the development of habitual actions. In the current study, we examined the impact of L-dopa (levodopa or L-dihydroxyphenylalanine), which also potentiates dopamine activity, on habitual learning. L-dopa was systemically administered prior to training rats to press a lever for a food outcome. When tested, L-dopa exposed animals were insensitive to changes in the value of the food outcome, and hence demonstrated accelerated habitual behavioral control compared to control animals that remained goal directed. We also showed that when N-acetylcysteine (NAC), an antioxidant and regulator of glutamate activity, was co-administered with L-dopa, it prevented the transition to habitual behavior; an effect demonstrated previously for cocaine. Therefore, this study establishes similarities between L-dopa and psychostimulants in both the development and prevention of habitual actions, and supports the notion that excess dopamine potentiates habitual learning. This finding extends the limited existing knowledge of the impact of L-dopa on learning and behavior, and has implications for neurological disorders where L-dopa is the primary treatment.

Aberrant Dopamine Receptor Signaling Plays Critical Role in the Impairment of Striatal Neurons in Experimental Cerebral Malaria

One-fourth survivors of cerebral malaria (CM) retain long-term cognitive and behavioral deficits. Structural abnormalities in striatum are reported in 80% of children with CM. Dopamine receptors (D1 and D2) are widely expressed in striatal medium spiny neurons (MSNs) that regulate critical physiological functions related to behavior and cognition. Dysregulation of dopamine receptors alters the expression of downstream proteins such as dopamine- and cAMP-regulated phosphoprotein (DARPP), Ca²⁺/calmodulin-dependent protein kinase II alpha (CaMKIIα), and p25/cyclin-dependent kinase 5 (cdk5). However, the role of dopamine receptor signaling dysfunction on the outcome of striatal neuron degeneration is unknown underlying the pathophysiology of CM. Using experimental CM (ECM), the present study attempted to understand the role of aberrant dopamine receptor signaling and its possible relation in causing MSNs morphological impairment. The effect of antimalarial drug artemether (ARM) rescue therapy was also assessed after ECM on the outcome of dopamine receptors downstream signaling. ECM was induced in C57BL/6 mice (male and female) infecting with Plasmodium berghei ANKA (PbA) parasite that reiterates the clinical setting of CM. We demonstrated that ECM caused a significant increase in the expression of D1, D2 receptors, phosphorylated DARPP, p25, cdk5, CaMKIIα, and D1-D2 heteromers. A substantial increase in neuronal damage observed in the dorsolateral striatum region of ECM brains (particularly in MSNs) as revealed by increased Fluoro-Jade C staining, reduced dendritic spine density, and impaired dendritic arborization with varicosities. While the ARM rescue therapy significantly altered the effects of ECM induced dopamine receptor signaling dysfunction and neurodegeneration. Overall, our data suggest that dysregulation of dopamine receptor signaling plays an important role in the degeneration of MSNs, and the ARM rescue therapy might provide better insights to develop effective therapeutic strategies for CM.

Melatonin and dopamine serum level associations with motor, cognitive, and sleep dysfunctions in patients with Parkinson's disease: A cross-sectional research study

BACKGROUND

Parkinson's disease (PD) is a multisystem-progressive neurodegenerative disease characterized by dopaminergic neurons, however, the role of the non-dopaminergic system (such as melatonin hormone) in the pathogenesis of PD is now emerging.

OBJECTIVE

To identify any potential correlation between the dopamine and melatonin serum levels, and motor, cognitive, and sleep dysfunctions in patients with PD.

METHOD

Cross-sectional piloting study conducted with a sample of 34 patients with PD (aged 50-72 yrs old). Correlation tests performed to identify any potential correlations between the biomarkers' serum levels and motor, cognitive, and sleep dysfunctional levels in "on-medication" status.

RESULTS

Spearman's test showed significant correlations between the melatonin serum level and sleep dysfunctions including overall sleep quality (P = 0.010) and subjective sleep quality sub-score (P = 0.001). On the other hand, spearman's test showed significant correlations between the dopamine serum level and motor dysfunctions including Berg Balance Scale (P = 0.026), 10-Meter Walk Test (P = 0.016), and Fear of Falling Index (P = 0.007), as well as comparisons between the dopamine serum level and cognitive dysfunction (P = 0.048).

CONCLUSIONS

Melatonin serum level would serve as a potential biomarker in understanding the PD pathogenesis, and the melatonin serum level should be considered in future studies related to PD besides the dopamine serum level.

Alteration of the Dopamine Receptors' Expression in the Cerebellum of the Lysosomal Acid Phosphatase 2 Mutant (Naked-Ataxia (NAX)) Mouse

A spontaneous mutation in the lysosomal acid phosphatase (Acp2) enzyme (nax: naked-ataxia) in experimental mice results in delayed hair appearance and severe cytoarchitectural impairments of the cerebellum, such as a Purkinje cell (PC) migration defect. In our previous investigation, our team showed that Acp2 expression plans a significant role in cerebellar development. On the other hand, the dopaminergic system is also a player in central nervous system (CNS) development, including cerebellar structure and function. In the current investigation, we have explored how Acp2 can be involved in the regulation of the dopaminergic pathway in the cerebellum via the regulation of dopamine receptor expression and patterning. We provided evidence about the distribution of different dopamine receptors in the developing cerebellum by comparing the expression of dopamine receptors on postnatal days (P) 5 and 17 between nax mice and wild-type (wt) littermates. To this aim, immunohistochemistry and Western blot analysis were conducted using five antibodies against dopamine receptors (DRD1, -2, -3, -4, and -5) accompanied by RNAseq data. Our results revealed that DRD1, -3, and -4 gene expressions significantly increased in nax cerebella but not in wt, while gene expressions of all 5 receptors were evident in PCs of both wt and nax cerebella. DRD3 was strongly expressed in the PCs' somata and cerebellar nuclei neurons at P17 in nax mice, which was comparable to the expression levels in the cerebella of wt littermates. In addition, DRD3 was expressed in scattered cells in a granular layer reminiscent of Golgi cells and was observed in the wt cerebella but not in nax mice. DRD4 was expressed in a subset of PCs and appeared to align with the unique parasagittal stripes pattern. This study contributes to our understanding of alterations in the expression pattern of DRDs in the cerebellum of nax mice in comparison to their wt littermates, and it highlights the role of Acp2 in regulating the dopaminergic system.

Cognitive dysfunction in mice lacking proper glucocorticoid receptor dimerization

Stress is a major risk factor for depression and anxiety. One of the effects of stress is the (over-) activation of the hypothalamic-pituitary-adrenal (HPA) axis and the release of stress hormones such as glucocorticoids (GCs). Chronically increased stress hormone levels have been shown to have detrimental effects on neuronal networks by inhibiting neurotrophic processes particularly in the hippocampus proper. Centrally, GCs modulate metabolic as well as behavioural processes by activating two classes of corticoid receptors, high-affinity mineralocorticoid receptors (MR) and low-affinity glucocorticoid receptors (GR). Upon activation, GR can modulate gene transcription either as a monomeric protein, or as a dimer interacting directly with DNA. GR can also modulate cellular processes via non-genomic mechanisms, for example via a GPCR-protein interaction. We evaluated the behavioral phenotype in mice with a targeted mutation in the GR in a FVB/NJ background. In GRdim/dim mice, GR proteins form poor homodimers, while the GR monomer remains intact. We evaluated the effect of poor GR dimerization on hippocampus-dependent cognition as well as on exploration and emotional behavior under baseline and chronically increased stress hormone levels. We found that GRdim/dim mice did not behave differently from GRwt/wt littermates under baseline conditions. However, after chronic elevation of stress hormone levels, GRdim/dim mice displayed a significant impairment in hippocampus-dependent memory compared to GRwt/wt mice, which correlated with differential expression of hippocampal Bdnf/TrkB and Fkbp5.

Ecotoxicity Assessment of Fe3O4 Magnetic Nanoparticle Exposure in Adult Zebrafish at an Environmental Pertinent Concentration by Behavioral and Biochemical Testing

Magnetic Nanoparticles (MNPs) are widely being investigated as novel promising multifunctional agents, specifically in the fields of development for theranostics, electronics, waste water treatment, cosmetics, and energy storage devices. Unique, superior, and indispensable properties of magnetization, heat transfer, and melting temperature make MNPs emerge in the field of therapeutics in future healthcare industries. However, MNPs ecotoxicity as well as behavioral toxicity is still unexplored. Ecotoxicity analysis may assist investigate MNPs uptake mechanism and its influence on bioavailability under a given set of environmental factors, which can be followed to investigate the biomagnification of MNPs in the environment and health risk possessed by them in an ecological food chain. In this study, we attempted to determine the behavioral changes in zebrafishes at low (1 ppm) or high (10 ppm) concentration levels of Fe₃O₄ MNPs. The synthesized Fe₃O₄ MNPs sized at 15 nm were characterized by the transmission electron microscope (TEM), the superconducting quantum interference device (SQUID) magnetometer, and the multiple behavior tests for novel tank, mirror biting, conspecific social interaction, shoaling, circadian rhythm, and short-term memory of zebrafish under MNPs chronic exposure were demonstrated. Low concentration MNP exposure did not trigger alteration for majority behavioral and biochemical tests in adult zebrafish. However, tight shoal groups were observed at a high concentration of MNPs exposure along with a modest reduction in fish exploratory behavior and a significant reduction in conspecific social interaction behavior. By using enzyme-linked immunosorbent assays (ELISA), we found a high dose of MNPs exposure significantly elevated cortisol, acetylcholine, and catalase levels while reducing serotonin, acetylcholine esterase, and dopamine levels in the brain. Our data demonstrates chronic MNPs exposure at an environmentally-relevant dose is relatively safe by supporting evidence from an array of behavioral and biochemical tests. This combinational approach using behavioral and biochemical tests would be helpful for understanding the MNPs association with anticipated colloids and particles effecting bioavailability and uptake into cells and organisms.

Effects of milk fat globule membrane and its various components on neurologic development in a postnatal growth restriction rat model

BACKGROUND

Milk fat globule membrane (MFGM) is a component of breast milk that consists of glycosylated membrane-bound proteins, polar lipids and carbohydrates originating from the mammary gland plasma membrane. A commercially available bovine MFGM added to infant formula has been shown to improve cognitive development in infants at 12 months of age.

OBJECTIVE

Considering that MFGM is a complex mixture, our aim was to determine which component(s) may be leading to these cognitive outcomes.

METHODS

Growth-restricted rat pups were supplemented with one of five treatments: (a) bovine MFGM, (b) bovine phospholipid concentrate (PL), (c) sialic acid (SIA) at 200 mg/kg body weight (bw) SIA100, (d) SIA at 2 mg/kg bw and (e) nonfat milk as control. Pups were randomized, cross-fostered into litters of 17 pups per dam and supplemented from postnatal day (PD) 2 to PD 21. The following behavioral tests were performed at adulthood: T-Maze Spontaneous Alternation, Novel Object Recognition and Morris Water Maze. Hippocampus was isolated at PD14 and PD21. Expression of four genes were measured including brain-derived neurotrophic factor (BDNF), dopamine receptor 1, (Drd1), glutamate receptor (GluR-1) and ST8 alpha-N-acetyl-neuraminide alpha-2,8-sialytransferase 4 (St8Sia4). Following behavioral testing, brains were collected for nonbiased stereology.

RESULTS

Increased expression of genes due to supplementation was most pronounced at the PD14 time point. The MFGM group exhibited higher T-Maze scores compared to the SIA group (P=.01), whereas the SIA100 group visited the novel object more frequently than the MFGM group in the Novel Object test (P=.02). No differences due to supplementation were found in the Morris Water Maze or nonbiased stereology, CONCLUSIONS: In this trial, MFGM, compared to its individual components, had the largest impact on neurodevelopment in rat pups through up-regulation of genes and improved T-Maze scores compared to the SIA group.

Microstructure changes in whiter matter relate to cognitive impairment in Wilson's disease

Purpose: Wilson’s disease (WD) is a genetic disorder of copper metabolism with pathological copper accumulation in the brain. The purpose of the present study was to evaluate the relationship between the damaged white matter and the impaired cognitive function in WD patients. Materials and methods: Thirty WD adolescents and thirty age- and sex-matched healthy controls (HC) were enrolled. All subjects had received brain MRI, including conventional and diffusion-tensor imaging (DTI) scans. The DTI parameter of fractional anisotropy (FA) was calculated by diffusion kurtosis estimator software. The t test was used to compare the differences between two groups. The correlation between cognitive function and whiter matter disorders were analyzed by linear regression. The results of FA parameter and MD parameter intergroup analysis were both corrected with False Discovery Rate (FDR) simulations by SPSS. Results: WD adolescents showed significantly lower scores of time-based prospective memory (TBPM) and verbal fluency test (VFT) compared with HC. We found significantly higher FA in the right thalamus, right lentiform nucleus, left thalamus, left lentiform nucleus, and brain stem in WD adolescents. Besides, WD adolescents exhibited significantly lower FA in right cerebellum and cingulum and left middle frontal lobe compared with controls (P<0.05). There were significantly negative correlations between FA in bilateral lentiform and thalamus and cognitive impairment in WD adolescents (P<0.05). Conclusion: The whiter matter of WD adolescents was impaired and mainly distributed in subcortical brain regions. The impaired cognitive function was affected by the damaged whiter matter. The present study may be helpful for recognition and understanding of WD.

Gas chromatography-mass spectrometry based metabolomics profile of hippocampus and cerebellum in mice after chronic arsenic exposure

Intake of arsenic (As) via drinking water has been a serious threat to global public health. Though there are numerous reports of As neurotoxicity, its pathogenesis mechanisms remain vague especially its chronic effects on metabolic network. Hippocampus is a renowned area in relation to learning and memory, whilst recently, cerebellum is argued to be involved with process of cognition. Therefore, the study aimed to explore metabolomics alternations in these two areas after chronic As exposure, with the purpose of further illustrating details of As neurotoxicity. Twelve 3-week-old male C57BL/6J mice were divided into two groups, receiving deionized drinking water (control group) or 50 mg/L of sodium arsenite (via drinking water) for 24 weeks. Learning and memory abilities were tested by Morris water maze (MWM) test. Pathological and morphological changes of hippocampus and cerebellum were captured via transmission electron microscopy (TEM). Metabolic alterations were analyzed by gas chromatography-mass spectrometry (GC-MS). MWM test confirmed impairments of learning and memory abilities of mice after chronic As exposure. Metabolomics identifications indicated that tyrosine increased and aspartic acid (Asp) decreased simultaneously in both hippocampus and cerebellum. Intermediates (succinic acid) and indirect involved components of tricarboxylic acid cycle (proline, cysteine, and alanine) were found declined in cerebellum, indicating disordered energy metabolism. Our findings suggest that these metabolite alterations are related to As-induced disorders of amino acids and energy metabolism, which might therefore, play an important part in mechanisms of As neurotoxicity.

Alcohol Activates Scabrous-Notch to Influence Associated Memories

Drugs of abuse, like alcohol, modulate gene expression in reward circuits and consequently alter behavior. However, the in vivo cellular mechanisms through which alcohol induces lasting transcriptional changes are unclear. We show that Drosophila Notch/Su(H) signaling and the secreted fibrinogen-related protein Scabrous in mushroom body (MB) memory circuitry are important for the enduring preference of cues associated with alcohol's rewarding properties. Alcohol exposure affects Notch responsivity in the adult MB and alters Su(H) targeting at the dopamine-2-like receptor (Dop2R). Alcohol cue training also caused lasting changes to the MB nuclear transcriptome, including changes in the alternative splicing of Dop2R and newly implicated transcripts like Stat92E. Together, our data suggest that alcohol-induced activation of the highly conserved Notch pathway and accompanying transcriptional responses in memory circuitry contribute to addiction. Ultimately, this provides mechanistic insight into the etiology and pathophysiology of alcohol use disorder.

Dopamine D1 Receptor-Positive Neurons in the Lateral Nucleus of the Cerebellum Contribute to Cognitive Behavior

BACKGROUND

Studies in humans and nonhuman primates have identified a region of the dentate nucleus of the cerebellum, or the lateral cerebellar nucleus (LCN) in rodents, activated during performance of cognitive tasks involving complex spatial and sequential planning. Whether such a subdivision exists in rodents is not known. Dopamine and its receptors, which are implicated in cognitive function, are present in the cerebellar nuclei, but their function is unknown.

METHODS

Using viral and genetic strategies in mice, we examined cellular phenotypes of dopamine D₁ receptor-positive (D1R+) cells in the LCN with whole-cell patch clamp recordings, messenger RNA profiling, and immunohistochemistry to examine D1R expression in mouse LCN and human dentate nucleus of the cerebellum. We used chemogenetics to inhibit D1R+ neurons and examined behaviors including spatial navigation, social recognition memory, prepulse inhibition of the acoustic startle reflex, response inhibition, and working memory to test the necessity of these neurons in these behaviors.

RESULTS

We identified a population of D1R+ neurons that are localized to an anatomically distinct region of the LCN. We also observed D1R+ neurons in human dentate nucleus of the cerebellum, which suggests an evolutionarily conserved population of dopamine-receptive neurons in this region. The genetic, electrophysiological, and anatomical profile of mouse D1R neurons is consistent with a heterogeneous population of gamma-aminobutyric acidergic, and to a lesser extent glutamatergic, cell types. Selective inhibition of D1R+ LCN neurons impairs spatial navigation memory, response inhibition, working memory, and prepulse inhibition of the acoustic startle reflex.

CONCLUSIONS

Collectively, these data demonstrate a functional link between genetically distinct neurons in the LCN and cognitive behaviors.

Extinction of Contextual Cocaine Memories Requires Cav1.2 within D1R-Expressing Cells and Recruits Hippocampal Cav1.2-Dependent Signaling Mechanisms

Exposure to cocaine-associated contextual cues contributes significantly to relapse. Extinction of these contextual associations, which involves a new form of learning, reduces cocaine-seeking behavior; however, the molecular mechanisms underlying this process remain largely unknown. We report that extinction, but not acquisition, of cocaine conditioned place preference (CPP) in male mice increased Ca_v1.2 L-type Ca²⁺ channel mRNA and protein in postsynaptic density (PSD) fractions of the hippocampus, a brain region involved in drug-context associations. Moreover, viral-mediated deletion of Ca_v1.2 in the dorsal hippocampus attenuated extinction of cocaine CPP. Molecular studies examining downstream Ca_v1.2 targets revealed that extinction recruited calcium/calmodulin (Ca²⁺/CaMK)-dependent protein kinase II (CaMKII) to the hippocampal PSD. This occurred in parallel with an increase in phosphorylation of the AMPA GluA1 receptor subunit at serine 831 (S831), a CaMKII site, along with an increase in total PSD GluA1. The necessity of S831 GluA1 was further demonstrated by the lack of extinction in S831A GluA1 phosphomutant mice. Of note hippocampal GluA1 levels remained unaltered at the PSD, but were reduced near the PSD and at perisynaptic sites of dendritic spines in extinction-resistant S831A mutant mice. Finally, conditional knock-out of Ca_v1.2 in dopamine D1 receptor (D1R)-expressing cells resulted in attenuation of cocaine CPP extinction and lack of extinction-dependent changes in hippocampal PSD CaMKII expression and S831 GluA1 phosphorylation. In summary, we demonstrate an essential role for the hippocampal Ca_v1.2/CaMKII/S831 GluA1 pathway in cocaine CPP extinction, with data supporting contribution of hippocampal D1R-expressing cells in this process. These findings demonstrate a novel role for Ca_v1.2 channels in extinction of contextual cocaine-associated memories.SIGNIFICANCE STATEMENT Continued drug-seeking behavior, a defining characteristic of cocaine addiction, can be precipitated by contextual cues, yet the molecular mechanisms required for extinction of these context-specific memories remain poorly understood. Here, we have uncovered a novel and selective role of the Ca_v1.2 L-type Ca²⁺ channel and its downstream signaling pathway in the hippocampus that mediate extinction of cocaine conditioned place preference (CPP). We additionally provide evidence that supports a role of Ca_v1.2 within dopamine D1 receptor-expressing cells of the hippocampus for extinction of cocaine CPP. Therefore, these findings reveal a previously unknown role of Ca_v1.2 channels within the hippocampus and in D1 receptor-expressing cells in extinction of cocaine-associated memories, providing a framework for further exploration of mechanisms underlying extinction of cocaine-seeking behavior.

Translating advances in the molecular basis of schizophrenia into novel cognitive treatment strategies

The presence and severity of cognitive symptoms, including working memory, executive dysfunction and attentional impairment, contributes materially to functional impairment in schizophrenia. Cognitive symptoms have proved to be resistant to both first- and second-generation antipsychotic drugs. Efforts to develop a consensus set of cognitive domains that are both disrupted in schizophrenia and are amenable to cross-species validation (e.g. the National Institute of Mental Health Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia and Research Domain Criteria initiatives) are an important step towards standardization of outcome measures that can be used in preclinical testing of new drugs. While causative genetic mutations have not been identified, new technologies have identified novel genes as well as hitherto candidate genes previously implicated in the pathophysiology of schizophrenia and/or mechanisms of antipsychotic efficacy. This review comprises a selective summary of these developments, particularly phenotypic data arising from preclinical genetic models for cognitive dysfunction in schizophrenia, with the aim of indicating potential new directions for pro-cognitive therapeutics. Linked Articles This article is part of a themed section on Pharmacology of Cognition: a Panacea for Neuropsychiatric Disease? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.19/issuetoc.

Ramelteon Improves Post-traumatic Stress Disorder-Like Behaviors Exhibited by Fatty Acid-Binding Protein 3 Null Mice

We previously reported that fatty acid-binding protein 3 (FABP3) knockout (Fabp3 ^-/-) mice exhibit abnormal dopamine-related behaviors such as enhanced dopamine D2 receptor antagonist-induced catalepsy behaviors. Here, we report that Fabp3 null mice exhibit cognitive deficits, hyperlocomotion and impaired fear extinction, and thus show post-traumatic stress disorder (PTSD)-like behaviors. Notably, chronic administration of ramelteon (1.0 mg/kg, p.o.), a melatonin receptor agonist, improved all PTSD-like behaviors tested in Fabp3 ^-/- mice. Relevant to mechanisms underlying impaired fear extinction, we observed significantly reduced levels of Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation without changes in ERK phosphorylation in the anterior cingulate cortex (ACC). Inversely, CaMKII autophosphorylation increased in the basolateral amygdala (BLA) but remained relatively unchanged in hippocampus of Fabp3 ^-/- mice. Likewise, the number of c-Fos-positive neurons in BLA significantly increased after exposure to contextual fear conditions but remained unchanged in the central nucleus of the amygdala (CeA). Importantly, chronic ramelteon administration (1.0 mg/kg, p.o.) restored abnormal c-Fos expression and CaMKII autophosphorylation in the ACC and BLA of Fabp3 ^-/- mice. Finally, the melatonin receptor antagonist luzindole (2.5 mg/kg, i.p.) blocked ramelteon-dependent improvements. Taken together, Fabp3 ^-/- mice show PTSD-like behaviors, and ramelteon is a likely attractive candidate for PTSD therapy.

Effect of undifferentiated versus hepatogenic partially differentiated mesenchymal stem cells on hepatic and cognitive functions in liver cirrhosis

Liver cirrhosis is the outcome of chronic liver injury. The current study aimed to investigate the therapeutic effect of undifferentiated mesenchymal stem cells versus in vitro partially differentiated mesenchymal stem cells on liver cirrhosis and hepatic encephalopathy. 50 adult male albino rats constituted the animal model and were divided into the following groups: control, thioacetamide, undifferentiated mesenchymal stem cells and hepatocyte growth factor-differentiated mesenchymal stem cells groups. Cognitive assessment was achieved by open field test and Y-maze task. We measured serum alanine aminotransferase, albumin and transforming growth factor-beta1, gene expression of α-smooth muscle actin, matrix metalloprotein-2, its tissue inhibitor and apoptotic markers: Bax and Bcl2, brain glial fibrillary acidic protein, synaptophysin, and dopaminergic receptors.