D1- versus D2-receptor modulation of visuospatial working memory in humans

A multi-faceted role of dual-state dopamine signaling in working memory, attentional control, and intelligence

Genetic evidence strongly suggests that individual differences in intelligence will not be reducible to a single dominant cause. However, some of those variations/changes may be traced to tractable, cohesive mechanisms. One such mechanism may be the balance of dopamine D1 (D₁R) and D2 (D₂R) receptors, which regulate intrinsic currents and synaptic transmission in frontal cortical regions. Here, we review evidence from human, animal, and computational studies that suggest that this balance (in density, activity state, and/or availability) is critical to the implementation of executive functions such as attention and working memory, both of which are principal contributors to variations in intelligence. D1 receptors dominate neural responding during stable periods of short-term memory maintenance (requiring attentional focus), while D2 receptors play a more specific role during periods of instability such as changing environmental or memory states (requiring attentional disengagement). Here we bridge these observations with known properties of human intelligence. Starting from theories of intelligence that place executive functions (e.g., working memory and attentional control) at its center, we propose that dual-state dopamine signaling might be a causal contributor to at least some of the variation in intelligence across individuals and its change by experiences/training. Although it is unlikely that such a mechanism can account for more than a modest portion of the total variance in intelligence, our proposal is consistent with an array of available evidence and has a high degree of explanatory value. We suggest future directions and specific empirical tests that can further elucidate these relationships.

Pramipexole modulates fronto-subthalamic pathway in sequential working memory

Brain dopamine may regulate the ability to maintain and manipulate sequential information online. However, the precise role of dopamine remains unclear. This pharmacological fMRI study examined whether and how the dopamine D2/3 receptor agonist pramipexole modulates fronto-subthalamic or fronto-striatal pathways during sequential working memory. This study used a double-blind, randomized crossover design. Twenty-two healthy male volunteers completed a digit ordering task during fMRI scanning after receiving a single oral dose of 0.5-mg pramipexole or placebo. The pramipexole effects on task performance, regional activity, activity pattern similarity, and functional connectivity were analyzed. Pramipexole impaired task performance, leading to less accurate and slower responses in the digit ordering task. Also, it downregulated the maintenance-related subthalamic and dorsolateral prefrontal activity, increasing reaction times for maintaining sequences. In contrast, pramipexole upregulated the manipulation-related subthalamic and dorsolateral prefrontal activity, increasing reaction time costs for manipulating sequences. In addition, it altered the dorsolateral prefrontal activity pattern similarity and fronto-subthalamic functional connectivity. Finally, pramipexole reduced maintenance-related striatal activity, which did not affect the behavior. This study confirms the role of the fronto-subthalamic pathway in sequential working memory. Furthermore, it shows that D2 transmission can regulate sequential working memory by modulating the fronto-subthalamic pathway.

Exploring the use of dopaminergic medication to treat hemispatial inattention during in-patient post-stroke neurorehabilitation

Hemispatial inattention (HSI), a lateralised impairment of spatial processing, is a common consequence of stroke. It is a poor prognostic indicator for functional recovery and interferes with the progress during in-patient neurorehabilitation. Dopaminergic medication has shown promise in improving HSI in the chronic post-stroke period but is untested in more acute settings, e.g. during in-patient neurorehabilitation. We audited the use of dopaminergic medication in ten sequential patients with post-stroke HSI, on an open-label exploratory basis. Patients' response to medication was assessed individually, using a three-week Off-On-Off protocol. We employed a mixture of bedside and functional measures, and made a multidisciplinary judgement of efficacy in individual patients. In six out of 10 patients, there was a convincing improvement of HSI while on medication, which reversed when it was paused. There was a mean 57% relative increase in target detection in the star cancellation test on the most affected side (on vs. off medication). In the six responders, medication was therefore continued throughout their admission without adverse effects. The star cancellation test was sensitive to HSI in most patients but in two cases failed to detect changes that were picked up by a functional assessment (Kessler Functional Neglect Assessment Protocol). We found this multidisciplinary approach to be feasible in an in-patient neurorehabilitation setting. We suggest further research to explore the efficacy of dopaminergic medication in improving neurorehabilitation outcomes for patients with post-stroke HSI. We suggest that more detailed N-of-1 assessments of treatment response, with internal blinding, may be a productive approach.

The Signaling and Pharmacology of the Dopamine D1 Receptor

The dopamine D1 receptor (D1R) is a Gα_s/olf-coupled GPCR that is expressed in the midbrain and forebrain, regulating motor behavior, reward, motivational states, and cognitive processes. Although the D1R was initially identified as a promising drug target almost 40 years ago, the development of clinically useful ligands has until recently been hampered by a lack of suitable candidate molecules. The emergence of new non-catechol D1R agonists, biased agonists, and allosteric modulators has renewed clinical interest in drugs targeting this receptor, specifically for the treatment of motor impairment in Parkinson's Disease, and cognitive impairment in neuropsychiatric disorders. To develop better therapeutics, advances in ligand chemistry must be matched by an expanded understanding of D1R signaling across cell populations in the brain, and in disease states. Depending on the brain region, the D1R couples primarily to either Gα_s or Gα_olf through which it activates a cAMP/PKA-dependent signaling cascade that can regulate neuronal excitability, stimulate gene expression, and facilitate synaptic plasticity. However, like many GPCRs, the D1R can signal through multiple downstream pathways, and specific signaling signatures may differ between cell types or be altered in disease. To guide development of improved D1R ligands, it is important to understand how signaling unfolds in specific target cells, and how this signaling affects circuit function and behavior. In this review, we provide a summary of D1R-directed signaling in various neuronal populations and describe how specific pathways have been linked to physiological and behavioral outcomes. In addition, we address the current state of D1R drug development, including the pharmacology of newly developed non-catecholamine ligands, and discuss the potential utility of D1R-agonists in Parkinson's Disease and cognitive impairment.

Neuromodulation of prefrontal cortex cognitive function in primates: the powerful roles of monoamines and acetylcholine

The primate prefrontal cortex (PFC) subserves our highest order cognitive operations, and yet is tremendously dependent on a precise neurochemical environment for proper functioning. Depletion of noradrenaline and dopamine, or of acetylcholine from the dorsolateral PFC (dlPFC), is as devastating as removing the cortex itself, and serotonergic influences are also critical to proper functioning of the orbital and medial PFC. Most neuromodulators have a narrow inverted U dose response, which coordinates arousal state with cognitive state, and contributes to cognitive deficits with fatigue or uncontrollable stress. Studies in monkeys have revealed the molecular signaling mechanisms that govern the generation and modulation of mental representations by the dlPFC, allowing dynamic regulation of network strength, a process that requires tight regulation to prevent toxic actions, e.g., as occurs with advanced age. Brain imaging studies in humans have observed drug and genotype influences on a range of cognitive tasks and on PFC circuit functional connectivity, e.g., showing that catecholamines stabilize representations in a baseline-dependent manner. Research in monkeys has already led to new treatments for cognitive disorders in humans, encouraging future research in this important field.

The Effects of a Novel Non-catechol Dopamine Partial Agonist on Working Memory in the Aged Rhesus Monkey

Aged-related declines in cognition, especially working memory and executive function, begin in middle-age and these abilities are known to be mediated by the prefrontal cortex (PFC) and more specifically the dopamine (DA) system within the PFC. In both humans and monkeys, there is significant evidence that the PFC is the first cortical region to change with age and the PFC appears to be particularly vulnerable to age-related loss of dopamine (DA). Therefore, the DA system is a strong candidate for therapeutic intervention to slow or reverse age related declines in cognition. In the present study, we administered a novel selective, potent, non-catechol DA D1 R agonist PF-6294 (Pfizer, Inc.) to aged female rhesus monkeys and assessed their performance on two benchmark tasks of working memory - the Delayed Non-match to Sample Task (DNMS) and Delayed Recognition Span Task (DRST). The DNMS task was administered first with the standard 10 s delay and then with 5 min delays, with and without distractors. The DRST was administered each day with four trials with unique sequences and one trial of a repeated sequence to assess evidence learning and retention. Overall, there was no significant effect of drug on performance on any aspect of the DNMS task. In contrast, we demonstrated that a middle range dose of PF-6294 significantly increased memory span on the DRST on the first and last days of testing and by the last day of testing the increased memory span was driven by the performance on the repeated trials.

A common polymorphism in the dopamine transporter gene predicts working memory performance and in vivo dopamine integrity in aging

Dopamine (DA) integrity is suggested as a potential cause of individual differences in working memory (WM) performance among older adults. Still, the principal dopaminergic mechanisms giving rise to WM differences remain unspecified. Here, 61 single-nucleotide polymorphisms, located in or adjacent to various dopamine-related genes, were assessed for their links to WM performance in a sample of 1313 adults aged 61-80 years from the Berlin Aging Study II. Least Absolute Shrinkage and Selection Operator (LASSO) regression was conducted to estimate associations between polymorphisms and WM. Rs40184 in the DA transporter gene, SLC6A3, showed allelic group differences in WM, with T-carriers performing better than C homozygotes (p<0.01). This finding was replicated in an independent sample from the Cognition, Brain, and Aging study (COBRA; baseline: n = 181, ages: 64-68 years; 5-year follow up: n = 129). In COBRA, in vivo DA integrity was measured with ¹¹C-raclopride and positron emission tomography. Notably, WM as well as in vivo DA integrity was higher for rs40184 T-carriers at baseline (p<0.05 for WM and caudate and hippocampal D2-receptor availability) and at the 5-year follow-up (p<0.05 for WM and hippocampal D2 availability). Our findings indicate that individual differences in DA transporter function contribute to differences in WM performance in old age, presumably by regulating DA availability.

Role of Genes and Treatments for Parkinson’s Disease

Parkinson’s Disease (PD) is a complex neurodegenerative disorder that mainly results due to the loss of dopaminergic neurons in the substantia nigra of the midbrain. It is well known that dopamine is synthesized in substantia nigra and is transported to the striatumvianigrostriatal tract. Besides the sporadic forms of PD, there are also familial cases of PD and number of genes (both autosomal dominant as well as recessive) are responsible for PD. There is no permanent cure for PD and to date, L-dopa therapy is considered to be the best option besides having dopamine agonists. In the present review, we have described the genes responsible for PD, the role of dopamine, and treatment strategies adopted for controlling the progression of PD in humans.

Differential Effects of Pergolide and Bromocriptine on Working Memory Performance and Brain Activation after Mild Traumatic Brain Injury

Dopamine D1 and D2 receptors differ with respect to patterns of regional brain distribution and behavioral effects. Pre-clinical work suggests that D1 agonists enhance working memory, but the absence of selective D1 agonists has constrained using this approach in humans. This study examines working memory performance in mild traumatic brain injury (mTBI) patients when given pergolide, a mixed D1/D2 agonist, compared with bromocriptine, a selective D2 agonist. Fifteen individuals were studied 1 month after mTBI and compared with 17 healthy controls. At separate visits, participants were administered 1.25 mg bromocriptine or 0.05 mg pergolide prior to functional magnetic resonance imaging (MRI) using a working memory task (visual-verbal n-back). Results indicated a significant group-by-drug interaction for mean performance across n-back task conditions, where the mTBI group showed better performance on pergolide relative to bromocriptine, whereas controls showed the opposite pattern. There was also a significant effect of diagnosis, where mTBI patients performed worse than controls, particularly while on bromocriptine, as shown in our prior work. Functional MRI activation during the most challenging task condition (3-back > 0-back contrast) showed a significant group-by-drug interaction, with the mTBI group showing increased activation relative to controls in working memory circuitry while on pergolide, including in the left inferior frontal gyrus. Across participants there was a positive correlation between change in activation in this region and change in performance between drug conditions. Results suggest that activation of the D1 receptor may improve working memory performance after mTBI. This has implications for the development of pharmacological strategies to treat cognitive deficits after mTBI.

Effects of COMT Genotypes on Working Memory Performance in Fibromyalgia Patients

Growing research has reported the presence of a clear impairment of working memory functioning in fibromyalgia. Although different genetic factors involving dopamine availability (i.e, the COMT gene) have been associated with the more severe presentation of key symptoms in fibromyalgia, scientific evidence regarding the influence of COMT genotypes on cognitive impairment in these patients is still lacking. To this end, 167 participants took part in the present investigation. Working memory performance was assessed by the application of the SST (Spatial Span Test) and LNST (Letter and Number Sequence Test) belonging to the Weschler Memory Scale III. Significant working memory impairment was shown by the fibromyalgia patients. Remarkably, our results suggest that performance according to different working memory measures might be influenced by different genotypes of the COMT gene. Specifically, fibromyalgia patients carrying the Val/Val genotype exhibited significantly worse outcomes for the span of SST backward, SST backward score, SST total score and the Working Memory Index (WMI) than the Val/Val healthy carriers. Furthermore, the Val/Val patients performed worse on the SST backward and SST score than heterozygotes. Our findings are the first to show a link between the COMT gene and working memory dysfunction in fibromyalgia, supporting the idea that higher COMT enzyme activity would contribute to more severe working memory impairment in fibromyalgia.

A Neurofunctional Domains Approach to Evaluate D1/D5 Dopamine Receptor Partial Agonism on Cognition and Motivation in Healthy Volunteers With Low Working Memory Capacity

BACKGROUND

Dopamine D1 receptor signaling plays key roles in core domains of neural function, including cognition and reward processing; however, many questions remain about the functions of circuits modulated by dopamine D1 receptor, largely because clinically viable, selective agonists have yet to be tested in humans.

METHODS

Using a novel, exploratory neurofunctional domains study design, we assessed the safety, tolerability, pharmacodynamics, and pharmacokinetics of PF-06412562, a selective D1/D5R partial agonist, in healthy male volunteers who met prespecified criteria for low working memory capacity. Functional magnetic resonance imaging, electrophysiologic endpoints, and behavioral paradigms were used to assess working memory, executive function, and motivation/reward processing following multiple-dose administration of PF-06412562. A total of 77 patients were assigned PF-06412562 (3 mg twice daily and 15 mg twice daily) or placebo administered for 5 to 7 days. Due to the exploratory nature of the study, it was neither powered for any specific treatment effect nor corrected for multiple comparisons.

RESULTS

Nominally significant improvements from baseline in cognitive endpoints were observed in all 3 groups; however, improvements in PF-06412562-treated patients were less than in placebo-treated participants. Motivation/reward processing endpoints were variable. PF-06412562 was safe and well tolerated, with no serious adverse events, severe adverse events, or adverse events leading to dose reduction or temporary discontinuation except for 1 permanent discontinuation due to increased orthostatic heart rate.

CONCLUSIONS

PF-06412562, in the dose range and patient population explored in this study, did not improve cognitive function or motivation/reward processing more than placebo over the 5- to 7-day treatment period.

CLINICALTRIALS.GOV IDENTIFIER

NCT02306876.

Activation of D1 receptors affects human reactivity and flexibility to valued cues

Reward-predicting cues motivate goal-directed behavior, but in unstable environments humans must also be able to flexibly update cue-reward associations. While the capacity of reward cues to trigger motivation ('reactivity') as well as flexibility in cue-reward associations have been linked to the neurotransmitter dopamine in humans, the specific contribution of the dopamine D1 receptor family to these behaviors remained elusive. To fill this gap, we conducted a randomized, placebo-controlled, double-blind pharmacological study testing the impact of three different doses of a novel D1 agonist (relative to placebo) on reactivity to reward-predicting cues (Pavlovian-to-instrumental transfer) and flexibility of cue-outcome associations (reversal learning). We observed that the impact of the D1 agonist crucially depended on baseline working memory functioning, which has been identified as a proxy for baseline dopamine synthesis capacity. Specifically, increasing D1 receptor stimulation strengthened Pavlovian-to-instrumental transfer in individuals with high baseline working memory capacity. In contrast, higher doses of the D1 agonist improved reversal learning only in individuals with low baseline working memory functioning. Our findings suggest a crucial and baseline-dependent role of D1 receptor activation in controlling both cue reactivity and the flexibility of cue-reward associations.

Effects of Dopaminergic Drugs on Cognitive Control Processes Vary by Genotype

Dopamine (DA) has been implicated in modulating multiple cognitive control processes, including the robust maintenance of task sets and memoranda in the face of distractors (cognitive stability) and, conversely, the ability to switch task sets or update the contents of working memory when it is advantageous to do so (cognitive flexibility). In humans, the limited specificity of available pharmacological probes has posed a challenge for understanding the mechanisms by which DA, acting on multiple receptor families across the PFC and striatum, differentially influences these cognitive processes. Using a within-subject, placebo-controlled design, we contrasted the impact of two mechanistically distinct DA drugs, tolcapone (an inhibitor of catechol-O-methyltransferase [COMT], a catecholamine inactivator) and bromocriptine (a DA agonist with preferential affinity for the D2 receptor), on the maintenance and switching of task rules. Given previous work demonstrating that drug effects on behavior are dependent on baseline DA tone, participants were stratified according to genetic polymorphisms associated with cortical (COMT Val158Met) and striatal (Taq1A) DA system function. Our results were partially consistent with an inverted-U-shaped relationship between tolcapone and robust rule maintenance (interaction with COMT genotype) and between bromocriptine and cued rule switching (interaction with Taq1A genotype). However, when task instructions were ambiguous, a third relationship emerged to explain drug effects on spontaneous task switching (interaction of COMT genotype and bromocriptine). Together, this pattern of results suggests that the effects of DA drugs vary not only as a function of the DA system component upon which they act but also on subtle differences in task demands and context.

Development of dopaminergic genetic associations with visuospatial, verbal and social working memory

Dopamine transmission in the prefrontal cortex (PFC) supports working memory (WM), the temporary holding, processing and manipulation of information in one's mind. The gene coding the catechol-O-methyltransferase (COMT) enzyme, which degrades dopamine, in particular in the PFC, has a common single nucleotide polymorphism leading to two versions of the COMT enzyme which vary in their enzymatic activity. The methionine (Met) allele has been associated with higher WM performance and lower activation of the PFC in executive function tasks than the valine (Val) allele. In a previous study, COMT genotype was associated with performance on verbal and visuospatial WM tasks in adults, as well as with performance on a novel social WM paradigm that requires participants to maintain and manipulate information about the traits of their friends or family over a delay. Here, data collected in children and adolescents (N = 202) were compared to data from the adult sample (N = 131) to investigate possible age differences in genetic associations. Our results replicate and extend previous work showing that the pattern of superior WM performance observed in Met/Met adults emerges during development. These findings are consistent with a decrease in prefrontal dopamine levels during adolescence. Developmentally moderated genetic effects were observed for both visuospatial and social WM, even when controlling for non-social WM performance, suggesting that the maintenance and manipulation of social information may also recruit the dopamine neurotransmitter system. These findings show that development should be considered when trying to understand the impact of genetic polymorphisms on cognitive function.

Neural Dedifferentiation in the Aging Brain

Many cognitive abilities decline with age even in the absence of detectable pathology. Recent evidence indicates that age-related neural dedifferentiation, operationalized in terms of neural selectivity, may contribute to this decline. We review here work exploring the relationship between neural dedifferentiation, cognition, and age. Compelling evidence for age effects on neural selectivity comes from both non-human animal and human research. However, current data suggest that age does not moderate the observed relationships between neural dedifferentiation and cognitive performance. We propose that functionally significant variance in measures of neural dedifferentiation reflects both age-dependent and age-independent factors. We further propose that the effects of age on neural dedifferentiation do not exclusively reflect detrimental consequences of aging.

Frontoparietal cortical thickness mediates the effect of COMT Val158Met polymorphism on age-associated executive function

Proper dopamine (DA) signaling is likely necessary for maintaining optimal cognitive performance as we age, particularly in prefrontal-parietal networks and in fronto-striatal networks. Thus, reduced DA availability is a salient risk factor for accelerated cognitive aging. A common polymorphism that affects DA D1 receptor dopamine availability, COMT Val158Met (rs4680), influences enzymatic breakdown of DA, with COMT Val carriers having a 3- to 4-fold reduction in synaptic DA compared to COMT Met carriers. Furthermore, dopamine receptors and postsynaptic availability are drastically reduced with aging, as is executive function performance that ostensibly relies on these pathways. Here, we investigated in 176 individuals aged 20-94 years whether: (1) COMT Val carriers differ from their Met counterparts in thickness of regional cortices receiving D1 receptor pathways: prefrontal, parietal, cingulate cortices; (2) this gene-brain association differs across the adult lifespan; and (3) COMT-related regional thinning evidences cognitive consequences. We found that COMT Val carriers evidenced thinner cortex in prefrontal, parietal, and posterior cingulate cortices than COMT Met carriers and this effect was not age-dependent. Further, we demonstrate that thickness of these regions significantly mediates the effect of COMT genotype on an executive function composite measure. These results suggest that poorer executive function performance is due partly to thinner association cortex in dopaminergic-rich regions, and particularly so in individuals who are genetically predisposed to lower postsynaptic dopamine availability, regardless of age.

Effects of pharmacological inhibition of dopamine receptors on memory load capacity

Memory capacity (MC) refers to the limited capacity of working memory and is defined as the number of elements that an individual can remember for a short retention interval. MC is impaired in many human pathologies, such as schizophrenia and ageing. Fronto-striatal dopamine regulates working memory, through its action on dopamine D1- and D2-like receptors. Human and rodent studies have suggested that MC is improved by D2 dopamine receptor agonists. Although D1 receptors have been crucially involved in the maintenance of working memory during delay, their role in regulating the capacity of WM remains poorly explored. In this study, we tested the effects of systemic injection of the D1-like and D2-like receptor antagonists, SCH 23390 and Haloperidol respectively, on MC in mice. For this, we used a modified version of the object recognition task, the Different/Identical Objects Task (DOT/IOT), which allows the evaluation of MC in rodents. The results showed a negative interaction between the dose of both drugs and the number of objects that could be remembered. The doses of SCH 23390 and Haloperidol that impaired novel object discrimination in the highest memory load condition were about 4 and 3 time lower, respectively, of those impairing performance in the lowest memory load condition. However, while SCH 23390 specifically impaired memory load capacity, the effects of Haloperidol were associated to impairment in exploratory behaviors. These findings may help to predict the cognitive side effects induced by Haloperidol in healthy subjects.

Dopamine D2 Receptors Enhance Population Dynamics in Primate Prefrontal Working Memory Circuits

Working memory is associated with persistent activity in the prefrontal cortex (PFC). The neuromodulator dopamine, which is released by midbrain neurons projecting into the frontal lobe, influences PFC neurons and networks via the dopamine D1 (D1R) and the D2 receptor (D2R) families. Although behavioral, clinical and computational evidence suggest an involvement of D2Rs in working memory, a neuronal explanation is missing. We report an enhancement of persistent working memory responses of PFC neurons after iontophoretically stimulating D2Rs in monkeys memorizing the number of items in a display. D2R activation improved working memory representation at the population level and increased population dynamics during the transition from visual to mnemonic representations. Computational modeling suggests that D2Rs act by modulating interneuron-to-pyramidal signaling. By increasing the population's response dynamics, D2Rs might put PFC networks in a more flexible state and enhance the neurons' working memory coding, thereby controlling dynamic cognitive control.

Age-related Decline of Visual Working Memory: Behavioral Results Simulated with a Dynamic Neural Field Model

Visual working memory (VWM) is essential for executive function and is known to be compromised in older adults. Yet, the cognitive and neural processes associated with these age-related changes remain inconclusive. The purpose of this study was to explore such factors with a dynamic neural field (DNF) model that was manipulated to replicate the behavioral performances of younger and older adults in a change detection task. Although previous work has successfully modeled children and younger adult VWM performance, this study represents the first attempt to model older adult VWM performance within the DNF architecture. In the behavioral task, older adults performed worse than younger adults and exhibited a characteristic response bias that favored "same" over "different" responses. The DNF model was modified to capture the age group differences, with three parameter manipulations producing the best fit for the behavioral performances. The best-fitting model suggests that older adults operate through altered excitatory and inhibitory coupling and decreased inhibitory signals, resulting in wider and weaker neural signals. These results support a dedifferentiation account of brain aging, with older adults operating with wider and weaker neural signals because of decreased intracortical inhibition rather than increased stochastic neural noise.

Targeting the dopamine D1 receptor or its downstream signalling by inhibiting phosphodiesterase-1 improves cognitive performance

Background and Purpose

Insufficient prefrontal dopamine 1 (D₁) receptor signalling has been linked to cognitive dysfunction in several psychiatric conditions. Because the PDE1 isoform B (PDE1B) is postulated to regulate D₁ receptor‐dependent signal transduction, in this study we aimed to elucidate the role of PDE1 in cognitive processes reliant on D₁ receptor function.

Experimental Approach

Cognitive performance of the D₁ receptor agonist, SKF38393, was studied in the T‐maze continuous alternation task and 5‐choice serial reaction time task. D₁ receptor/PDE1B double‐immunohistochemistry was performed using human and rat prefrontal brain sections. The pharmacological activity of the PDE1 inhibitor, ITI‐214, was assessed by measuring the increase in cAMP/cGMP in prefrontal brain tissue and its effect on working memory performance. Mechanistic studies on the modulation of prefrontal neuronal transmission by SKF38393 and ITI‐214 were performed using extracellular recordings in brain slices.

Key Results

SKF38393 improved working memory and attentional performance in rodents. D₁ receptor/PDE1B co‐expression was verified in both human and rat prefrontal brain sections. The pharmacological activity of ITI‐214 on its target, PDE1, was demonstrated by its ability to increase prefrontal cAMP/cGMP. In addition, ITI‐214 improved working memory performance. Both SKF38393 and ITI‐214 facilitated neuronal transmission in prefrontal brain slices.

Conclusion and Implications

We hypothesize that PDE1 inhibition improves working memory performance by increasing prefrontal synaptic transmission and/or postsynaptic D₁ receptor signalling, by modulating prefrontal downstream second messenger levels. These data, therefore, support the use of PDE1 inhibitors as a potential approach for the treatment of cognitive dysfunction.

Neuromolecular basis of faded perception associated with unreality experience

Perceptual changes in shape, size, or color are observed in patients with derealization symptoms; however, the underlying neural and molecular mechanisms are not well understood. The current study explored the relationship between neural activity associated with altered colorfulness perception assessed by fMRI and striatal dopamine D₂ receptor availability measured by [¹¹C]raclopride PET in healthy participants. Inside an fMRI scanner, participants performed the saturation adaptation task, where they rated how much vivid/faded visual objects looked like real/unreal ones using a visual analog scale. We found that participants experienced greater unreality when they perceived fadedness than vividness despite physically identical saturation. The combined fMRI and PET analyses revealed that the faded perception-related activities of the dorsolateral prefrontal and parietal cortex were positively correlated with striatal D₂ receptor availability. This finding may help to understand the neuromolecular mechanisms of faded perception associated with feeling unreal in derealization symptoms.

Transcriptomic context of DRD1 is associated with prefrontal activity and behavior during working memory

Dopamine D1 receptor (D1R) signaling shapes prefrontal cortex (PFC) activity during working memory (WM). Previous reports found higher WM performance associated with alleles linked to greater expression of the gene coding for D1Rs (DRD1). However, there is no evidence on the relationship between genetic modulation of DRD1 expression in PFC and patterns of prefrontal activity during WM. Furthermore, previous studies have not considered that D1Rs are part of a coregulated molecular environment, which may contribute to D1R-related prefrontal WM processing. Thus, we hypothesized a reciprocal link between a coregulated (i.e., coexpressed) molecular network including DRD1 and PFC activity. To explore this relationship, we used three independent postmortem prefrontal mRNA datasets (total n = 404) to characterize a coexpression network including DRD1 Then, we indexed network coexpression using a measure (polygenic coexpression index-DRD1-PCI) combining the effect of single nucleotide polymorphisms (SNPs) on coexpression. Finally, we associated the DRD1-PCI with WM performance and related brain activity in independent samples of healthy participants (total n = 371). We identified and replicated a coexpression network including DRD1, whose coexpression was correlated with DRD1-PCI. We also found that DRD1-PCI was associated with lower PFC activity and higher WM performance. Behavioral and imaging results were replicated in independent samples. These findings suggest that genetically predicted expression of DRD1 and of its coexpression partners stratifies healthy individuals in terms of WM performance and related prefrontal activity. They also highlight genes and SNPs potentially relevant to pharmacological trials aimed to test cognitive enhancers modulating DRD1 signaling.

Why Is Working Memory Performance Unstable? A Review of 21 Factors

In this paper, we systematically reviewed twenty-one factors that have been shown to either vary with or influence performance on working memory (WM) tasks. Specifically, we review previous work on the influence of intelligence, gender, age, personality, mental illnesses/medical conditions, dieting, craving, stress/anxiety, emotion/motivation, stereotype threat, temperature, mindfulness training, practice, bilingualism, musical training, altitude/hypoxia, sleep, exercise, diet, psychoactive substances, and brain stimulation on WM performance. In addition to a review of the literature, we suggest several frameworks for classifying these factors, identify shared mechanisms between several variables, and suggest areas requiring further investigation. This review critically examines the breadth of research investigating WM while synthesizing the results across related subfields in psychology.

Functional differentiation between convergence and non-convergence zones of the striatum in children

Most cortical areas send projections to the striatum. In some parts of the striatum, the connections converge from several cortical areas. It is unknown whether the convergence and non-convergence zones of the striatum differ functionally. Here, we used diffusion-weighted magnetic resonance imaging and probabilistic fiber tracking to parcellate the striatum based on its connections to dorsolateral prefrontal, parietal and orbitofrontal cortices in two different datasets (children aged 6-7 years and adults). In both samples, quantitative susceptibility mapping (QSM) values were significantly correlated with working memory (WM) in convergence zones, but not in non-convergence zones. In children, this was also true for mean diffusivity, MD. The association of MD to WM specifically in the convergent zone was replicated in the Pediatric Imaging, Neurocognition, and Genetics (PING) dataset for 135 children aged 6-9 years. QSM data was not available in the PING dataset, and the association to QSM still needs to be replicated. These results suggest that connectivity-based segments of the striatum exhibit functionally different characteristics. The association between convergence zones and WM performance might relate to a role in integrating and coordinating activity in different cortical areas.

Variability in the Precision of Children's Spatial Working Memory

Cognitive modeling studies in adults have established that visual working memory (WM) capacity depends on the representational precision, as well as its variability from moment to moment. By contrast, visuospatial WM performance in children has been typically indexed by response accuracy—a binary measure that provides less information about precision with which items are stored. Here, we aimed at identifying whether and how children’s WM performance depends on the spatial precision and its variability over time in real-world contexts. Using smartphones, 110 Grade 3 and Grade 4 students performed a spatial WM updating task three times a day in school and at home for four weeks. Measures of spatial precision (i.e., Euclidean distance between presented and reported location) were used for hierarchical modeling to estimate variability of spatial precision across different time scales. Results demonstrated considerable within-person variability in spatial precision across items within trials, from trial to trial and from occasion to occasion within days and from day to day. In particular, item-to-item variability was systematically increased with memory load and lowered with higher grade. Further, children with higher precision variability across items scored lower in measures of fluid intelligence. These findings emphasize the important role of transient changes in spatial precision for the development of WM.

Prenatal cocaine exposure and its impact on cognitive functions of offspring: a pathophysiological insight

It is estimated that approximately 0.5%-3% of fetuses are prenatally exposed to cocaine (COC). The neurodevelopmental implications of this exposure are numerous and include motor skill impairments, alterations of social function, predisposition to anxiety, and memory function and attention deficits; these implications are commonly observed in experimental studies and ultimately affect both learning and IQ. According to previous studies, the clinical manifestations of prenatal COC exposure seem to persist at least until adolescence. The pathophysiological cellular processes that underlie these impairments include dysfunctional myelination, disrupted dendritic architecture, and synaptic alterations. On a molecular level, various neurotransmitters such as serotonin, dopamine, catecholamines, and γ-aminobutyric acid seem to participate in this process. Finally, prenatal COC abuse has been also associated with functional changes in the hormones of the hypothalamic-pituitary-adrenal axis that mediate neuroendocrine responses. The purpose of this review is to summarize the neurodevelopmental consequences of prenatal COC abuse, to describe the pathophysiological pathways that underlie these consequences, and to provide implications for future research in the field.

Neither Cholinergic Nor Dopaminergic Enhancement Improve Spatial Working Memory Precision in Humans

Acetylcholine and dopamine are neurotransmitters that play multiple important roles in perception and cognition. Pharmacological cholinergic enhancement reduces excitatory receptive field size of neurons in marmoset primary visual cortex and sharpens the spatial tuning of visual perception and visual cortical fMRI responses in humans. Moreover, previous studies show that manipulation of cholinergic or dopaminergic signaling alters the spatial tuning of macaque prefrontal cortical neurons during the delay period of a spatial working memory (SWM) task and can improve SWM performance in macaque monkeys and human subjects. Here, we investigated the effects of systemic cholinergic and dopaminergic enhancement on the precision of SWM, as measured behaviorally in human subjects. Cholinergic transmission was increased by oral administration of 5 mg of the cholinesterase inhibitor donepezil, and dopaminergic signaling was enhanced with 100 mg levodopa/10 mg carbidopa. Each neurotransmitter system was separately investigated in double-blind placebo-controlled studies. On each trial of the SWM task, a square was presented for 150 ms at a random location along an invisible circle with a radius of 12 degrees of visual angle, followed by a 900 ms delay period with no stimulus shown on the screen. Then, the square was presented at new location, displaced in either a clockwise (CW) or counterclockwise (CCW) direction along the circle. Subjects used their memory of the location of the original square to report the direction of displacement. SWM precision was defined as the amount of displacement corresponding to 75% correct performance. We observed no significant effect on SWM precision for either donepezil or levodopa/carbidopa. There was also no significant effect on performance on the SWM task (percent correct across all trials) for either donepezil or levodopa/carbidopa. Thus, despite evidence that acetylcholine and dopamine regulate spatial tuning of individual neurons and can improve performance of SWM tasks, pharmacological enhancement of signaling of these neurotransmitters does not substantially affect a behavioral measure of the precision of SWM in humans.

Role of dopamine on functional recovery in the contralateral hemisphere after focal stroke in the somatosensory cortex

Functional recovery after a stroke is important for patients' quality of life. Not only medical care during the acute phase, but also rehabilitation during the chronic phase after a stroke is important. However, the mechanisms underlying functional recovery, particularly the chronic phase after stroke, are still not fully understood. Thus, further basic study on brain after focal stroke is necessary. In this study, we found that the concentration of dopamine (DA) increased during first week after a stroke in the hemisphere contralateral in the site of stroke by in vivo microdialysis. When we applied haloperidol (HPD), a potent DA receptor blocker, functional recovery was inhibited. Interestingly, administration of aripiprazole (ARP), a novel partial agonist of the DA receptor, during the chronic phase improved the remodeling of neuronal circuits in somatosensory cortex (SSC). These findings indicate that the DAergic system play a critical role in functional compensation by the non-infarcted hemisphere after a focal stroke in SSC. It is also revealed that administration of HPD/ARP to stroke patients affects functional recovery after a stroke, and stimulation of the DAergic system during the chronic phase of stroke potentially benefits stroke patients.

The Dopamine D5 Receptor Is Involved in Working Memory

Pharmacological studies indicate that dopamine D₁-like receptors (D₁ and D₅) are critically involved in cognitive function. However, the lack of pharmacological ligands selective for either the D₁ or D₅ receptors has made it difficult to determine the unique contributions of the D₁-like family members. To circumvent these pharmacological limitations, we used D₅ receptor homozygous (-/-) and heterozygous (+/-) knockout mice, to identify the specific role of this receptor in higher order cognitive functions. We identified a novel role for D₅ receptors in the regulation of spatial working memory and temporal order memory function. The D₅ mutant mice acquired a discrete paired-trial variable-delay T-maze task at normal rates. However, both [Formula: see text] and [Formula: see text] mice exhibited impaired performance compared to [Formula: see text] littermates when a higher burden on working memory faculties was imposed. In a temporal order object recognition task, [Formula: see text] exhibited significant memory deficits. No D₅-dependent differences in locomotor functions and interest in exploring objects were evident. Molecular biomarkers of dopaminergic functions within the prefrontal cortex (PFC) revealed a selective gene-dose effect on Akt phosphorylation at Ser473 with increased levels in [Formula: see text] knockout mice. A trend toward reduced levels in CaMKKbeta brain-specific band (64 kDa) in [Formula: see text] compared to [Formula: see text] was also evident. These findings highlight a previously unidentified role for D₅ receptors in working memory function and associated molecular signatures within the PFC.

Dynamic Brains and the Changing Rules of Neuroplasticity: Implications for Learning and Recovery

A growing number of research publications have illustrated the remarkable ability of the brain to reorganize itself in response to various sensory experiences. A traditional view of this plastic nature of the brain is that it is predominantly limited to short epochs during early development. Although examples showing that neuroplasticity exists outside of these finite time-windows have existed for some time, it is only recently that we have started to develop a fuller understanding of the different regulators that modulate and underlie plasticity. In this article, we will provide several lines of evidence indicating that mechanisms of neuroplasticity are extremely variable across individuals and throughout the lifetime. This variability is attributable to several factors including inhibitory network function, neuromodulator systems, age, sex, brain disease, and psychological traits. We will also provide evidence of how neuroplasticity can be manipulated in both the healthy and diseased brain, including recent data in both young and aged rats demonstrating how plasticity within auditory cortex can be manipulated pharmacologically and by varying the quality of sensory inputs. We propose that a better understanding of the individual differences that exist within the various mechanisms that govern experience-dependent neuroplasticity will improve our ability to harness brain plasticity for the development of personalized translational strategies for learning and recovery following brain injury or disease.

Mechanisms of Cognitive Aging in the HIV-Positive Adult

PURPOSE OF REVIEW

As of the year 2016, an estimated 50% of the United States' HIV-Positive population is aged 50 years or older. Due to a combination of increased rates of infection in older adults, and successful anti-retroviral (ART) regimens allowing HIV-positive adults to survive for decades with the disease, we are now faced with a steadily graying HIV-positive population, with only limited knowledge of how the cognitive and physiological effects of aging intersect with those of chronic HIV-infection.

RECENT FINDINGS

Age-related changes to mood, cognition, and neurological health may be experienced differently in those living with HIV, and research concerning quality of life, mental health, and cognitive aging needs to account for and explore these factors more carefully in the coming years.

SUMMARY

This review will explore the topic of cognitive aging with HIV: 1. Central nervous system (CNS) infection of HIV and how the virus affects brain integrity and function; 2. Cognitive and behavioral symptoms of HIV-Associated Neurocognitive Disorders (HAND); 3. Neurobiological theories of Cognitive Aging and how these processes may be exacerbated by HIV-infection; 4: Clinical implications and complications of aging with HIV and factors that may result in poorer cognitive outcomes.

Plasticity in the Working Memory System: Life Span Changes and Response to Injury

Working memory acts as a key bridge between perception, long-term memory, and action. The brain regions, connections, and neurotransmitters that underlie working memory undergo dramatic plastic changes during the life span, and in response to injury. Early life reliance on deep gray matter structures fades during adolescence as increasing reliance on prefrontal and parietal cortex accompanies the development of executive aspects of working memory. The rise and fall of working memory capacity and executive functions parallels the development and loss of neurotransmitter function in frontal cortical areas. Of the affected neurotransmitters, dopamine and acetylcholine modulate excitatory-inhibitory circuits that underlie working memory, are important for plasticity in the system, and are affected following preterm birth and adult brain injury. Pharmacological interventions to promote recovery of working memory abilities have had limited success, but hold promise if used in combination with behavioral training and brain stimulation. The intense study of working memory in a range of species, ages and following injuries has led to better understanding of the intrinsic plasticity mechanisms in the working memory system. The challenge now is to guide these mechanisms to better improve or restore working memory function.

Dopamine and memory dedifferentiation in aging

The dedifferentiation theory of aging proposes that a reduction in the specificity of neural representations causes declines in complex cognition as people get older, and may reflect a reduction in dopaminergic signaling. The present pharmacological fMRI study investigated episodic memory-related dedifferentiation in young and older adults, and its relation to dopaminergic function, using a randomized placebo-controlled double-blind crossover design with the agonist Bromocriptine (1.25mg) and the antagonist Sulpiride (400mg). We used multi-voxel pattern analysis to measure memory specificity: the degree to which distributed patterns of activity distinguishing two different task contexts during an encoding phase are reinstated during memory retrieval. As predicted, memory specificity was reduced in older adults in prefrontal cortex and in hippocampus, consistent with an impact of neural dedifferentiation on episodic memory representations. There was also a linear age-dependent dopaminergic modulation of memory specificity in hippocampus reflecting a relative boost to memory specificity on Bromocriptine in older adults whose memory was poorer at baseline, and a relative boost on Sulpiride in older better performers, compared to the young. This differed from generalized effects of both agents on task specificity in the encoding phase. The results demonstrate a link between aging, dopaminergic function and dedifferentiation in the hippocampus.

The many facets of motor learning and their relevance for Parkinson's disease

The final goal of motor learning, a complex process that includes both implicit and explicit (or declarative) components, is the optimization and automatization of motor skills. Motor learning involves different neural networks and neurotransmitters systems depending on the type of task and on the stage of learning. After the first phase of acquisition, a motor skill goes through consolidation (i.e., becoming resistant to interference) and retention, processes in which sleep and long-term potentiation seem to play important roles. The studies of motor learning in Parkinson's disease have yielded controversial results that likely stem from the use of different experimental paradigms. When a task's characteristics, instructions, context, learning phase and type of measures are taken into consideration, it is apparent that, in general, only learning that relies on attentional resources and cognitive strategies is affected by PD, in agreement with the finding of a fronto-striatal deficit in this disease. Levodopa administration does not seem to reverse the learning deficits in PD, while deep brain stimulation of either globus pallidus or subthalamic nucleus appears to be beneficial. Finally and most importantly, patients with PD often show a decrease in retention of newly learned skill, a problem that is present even in the early stages of the disease. A thorough dissection and understanding of the processes involved in motor learning is warranted to provide solid bases for effective medical, surgical and rehabilitative approaches in PD.

Dopamine-dependent visual attention preference to social stimuli in nonhuman primates

RATIONALE

Dopamine (DA) plays a central role in reward processing. Accumulating evidence suggests that social interaction and social stimuli have rewarding properties that activate the DA reward circuits. However, few studies have attempted to investigate how DA is involved in the processing of social stimuli.

OBJECTIVES

In this study, we investigated the effects of pharmacological manipulations of DA D1 and D2 receptors on social vs. nonsocial visual attention preference in macaques.

METHODS

Japanese macaques were subjected to behavioral tests in which visual attention toward social (monkey faces with and without affective expressions) and nonsocial stimuli was examined, with D1 and D2 antagonist administration.

RESULTS

The macaques exhibited significantly longer durations of gazing toward the images with social cues than did those with nonsocial cues. Both D1 and D2 antagonist administration decreased duration of gazing toward the social images with and without affective valences. In addition, although D1 antagonist administration increased the duration of gazing toward the nonsocial images, D2 antagonism had no effect.

CONCLUSIONS

These results suggest that both D1 and D2 receptors may have roles in the processing of social signals but through separate mechanisms.

Acetyl-L-Carnitine via Upegulating Dopamine D1 Receptor and Attenuating Microglial Activation Prevents Neuronal Loss and Improves Memory Functions in Parkinsonian Rats

Parkinson's disease is accompanied by nonmotor symptoms including cognitive impairment, which precede the onset of motor symptoms in patients and are regulated by dopamine (DA) receptors and the mesocorticolimbic pathway. The relative contribution of DA receptors and astrocytic glutamate transporter (GLT-1) in cognitive functions is largely unexplored. Similarly, whether microglia-derived increased immune response affects cognitive functions and neuronal survival is not yet understood. We have investigated the effect of acetyl-L-carnitine (ALCAR) on cognitive functions and its possible underlying mechanism of action in 6-hydroxydopamine (6-OHDA)-induced hemiparkinsonian rats. ALCAR treatment in 6-OHDA-lesioned rats improved memory functions as confirmed by decreased latency time and path length in the Morris water maze test. ALCAR further enhanced D1 receptor levels without altering D2 receptor levels in the hippocampus and prefrontal cortex (PFC) regions, suggesting that the D1 receptor is preferentially involved in the regulation of cognitive functions. ALCAR attenuated microglial activation and release of inflammatory mediators through balancing proinflammatory and anti-inflammatory cytokines, which subsequently enhanced the survival of mature neurons in the CA1, CA3, and PFC regions and improved cognitive functions in hemiparkinsonian rats. ALCAR treatment also improved glutathione (GSH) content, while decreasing oxidative stress indices, inducible nitrogen oxide synthase (iNOS) levels, and astrogliosis resulting in the upregulation of GLT-1 levels. Additionally, ALCAR prevented the loss of dopaminergic (DAergic) neurons in ventral tagmental area (VTA)/substantia nigra pars compacta (SNpc) regions of 6-OHDA-lesioned rats, thus maintaining the integrity of the nigrostriatal pathway. Together, these results demonstrate that ALCAR treatment in hemiparkinsonian rats ameliorates neurodegeneration and cognitive deficits, hence suggesting its therapeutic potential in neurodegenerative diseases.

Cell-type-specific modulation of targets and distractors by dopamine D1 receptors in primate prefrontal cortex

The prefrontal cortex (PFC) is crucial for maintaining relevant information in working memory and resisting interference. PFC neurons are strongly regulated by dopamine, but it is unknown whether dopamine receptors are involved in protecting target memories from distracting stimuli. We investigated the prefrontal circuit dynamics and dopaminergic modulation of targets and distractors in monkeys trained to ignore interfering stimuli in a delayed-match-to-numerosity task. We found that dopamine D1 receptors (D1Rs) modulate the recovery of task-relevant information following a distracting stimulus. The direction of modulation is cell-type-specific: in putative pyramidal neurons, D1R inhibition enhances and D1R stimulation attenuates coding of the target stimulus after the interference, while the opposite pattern is observed in putative interneurons. Our results suggest that dopaminergic neuromodulation of PFC circuits regulates mental representations of behaviourally relevant stimuli that compete with task-irrelevant input and could play a central role for cognitive functioning in health and disease.

Dopamine D1 and D2 Receptors Make Dissociable Contributions to Dorsolateral Prefrontal Cortical Regulation of Rule-Guided Oculomotor Behavior

Studies of neuromodulation of spatial short-term memory have shown that dopamine D1 receptor (D1R) stimulation in dorsolateral prefrontal cortex (DLPFC) dose-dependently modulates memory activity, whereas D2 receptors (D2Rs) selectively modulate activity related to eye movements hypothesized to encode movement feedback. We examined localized stimulation of D1Rs and D2Rs on DLPFC neurons engaged in a task involving rule representation in memory to guide appropriate eye movements toward or away from a visual stimulus. We found dissociable effects of D1R and D2R on DLPFC physiology. D1R stimulation degrades memory activity for the task rule and increases stimulus-related selectivity. In contrast, D2R stimulation affects motor activity tuning only when eye movements are made to the stimulus. Only D1R stimulation degrades task performance and increases impulsive responding. Our results suggest that D1Rs regulate rule representation and impulse control, whereas D2Rs selectively modulate eye-movement-related dynamics and not rule representation in the DLPFC.

Dopamine D2 receptor availability is linked to hippocampal-caudate functional connectivity and episodic memory

D1 and D2 dopamine receptors (D1DRs and D2DRs) may contribute differently to various aspects of memory and cognition. The D1DR system has been linked to functions supported by the prefrontal cortex. By contrast, the role of the D2DR system is less clear, although it has been hypothesized that D2DRs make a specific contribution to hippocampus-based cognitive functions. Here we present results from 181 healthy adults between 64 and 68 y of age who underwent comprehensive assessment of episodic memory, working memory, and processing speed, along with MRI and D2DR assessment with [(11)C]raclopride and PET. Caudate D2DR availability was positively associated with episodic memory but not with working memory or speed. Whole-brain analyses further revealed a relation between hippocampal D2DR availability and episodic memory. Hippocampal and caudate D2DR availability were interrelated, and functional MRI-based resting-state functional connectivity between the ventral caudate and medial temporal cortex increased as a function of caudate D2DR availability. Collectively, these findings indicate that D2DRs make a specific contribution to hippocampus-based cognition by influencing striatal and hippocampal regions, and their interactions.

COMT val158met moderation of dopaminergic drug effects on cognitive function: a critical review

The relationship between dopamine (DA) tone in the prefrontal cortex (PFC) and PFC-dependent cognitive functions (for example, working memory, selective attention, executive function) may be described by an inverted-U-shaped function, in which both excessively high and low DA is associated with impairment. In the PFC, the COMT val158met single nucleotide polymorphism (rs4680) confers differences in catechol-O-methyltransferase (COMT) efficacy and DA tone, and individuals homozygous for the val allele display significantly reduced cortical DA. Many studies have investigated whether val158met genotype moderates the effects of dopaminergic drugs on PFC-dependent cognitive functions. A review of 25 such studies suggests evidence for this pharmacogenetic effect is mixed for stimulants and COMT inhibitors, which have greater effects on D1 receptors, and strong for antipsychotics, which have greater effects on D2 receptors. Overall, COMT val158met genotype represents an enticing target for identifying individuals who are more likely to respond positively to dopaminergic drugs.

Biological mechanisms underlying evolutionary origins of psychotic and mood disorders

Psychotic and mood disorders are brain dysfunctions that are caused by gene environment interactions. Although these disorders are disadvantageous and involve behavioral phenotypes that decrease the reproductive success of afflicted individuals in the modern human society, the prevalence of these disorders have remained constant in the population. Here, we propose several biological mechanisms by which the genes associated with psychotic and mood disorders could be selected for in specific environmental conditions that provide evolutionary bases for explanations of when, why, and where these disorders emerged and have been maintained in humans. We discuss the evolutionary origins of psychotic and mood disorders with specific focuses on the roles of dopamine and serotonin in the conditions of social competitiveness/hierarchy and maternal care and other potential mechanisms, such as social network homophily and symbiosis.

Effects of Sulpiride on True and False Memories of Thematically Related Pictures and Associated Words in Healthy Volunteers

Episodic memory, working memory, emotional memory, and attention are subject to dopaminergic modulation. However, the potential role of dopamine on the generation of false memories is unknown. This study defined the role of the dopamine D2 receptor on true and false recognition memories. Twenty-four young, healthy volunteers ingested a single dose of placebo or 400 mg oral sulpiride, a dopamine D2-receptor antagonist, just before starting the recognition memory task in a randomized, double-blind, and placebo-controlled trial. The sulpiride group presented more false recognitions during visual and verbal processing than the placebo group, although both groups had the same indices of true memory. These findings demonstrate that dopamine D2 receptors blockade in healthy volunteers can specifically increase the rate of false recognitions. The findings fit well the two-process view of causes of false memories, the activation/monitoring failures model.

Identification of dopamine- and serotonin-related genes modulated by bisphenol A in the prefrontal cortex of male rats

There is concern that exposure of embryos and/or infants to bisphenol A (BPA) may lead to neurological and behavioral disorders with unknown prefrontal cortex (PFC) involvement. Critical PFC functions are modulated by dopamine (DA) and serotonin (5-HT) systems, whose alterations have been associated with psychopathologies that may appear in youth and/or adulthood. This study aims to determine in the PFC of male rats exposed to a low dose of BPA (10μgkg(-1)d(-1)) from gestational day 12 (GD12) to postnatal day 21 (PND21): (i) DA- and 5-HT-related genes modulated by BPA at the juvenile stage (PND21); (ii) reversible and irreversible transcriptional effects; (iii) long-term consequences (effects in adult rats, PND90). In juvenile rats, BPA altered significantly the transcription of 12 out of the 84 genes analyzed using PCR-array techniques. Interestingly, transcript levels of the neurotrophic factor Gdnf were decrease by BPA in both juvenile and adult rats. At adulthood, disruptions in genes encoding rate-limiting enzymes for DA and 5-HT synthesis emerged. Overall, the results indicate that early-life exposure to BPA has consequences on DA and 5-HT systems in both juvenile- and adult-life stages. Additionally, we reveal molecular targets that could provide the foundation for future BPA neurotoxicity studies.

The effect of modafinil on the rat dopamine transporter and dopamine receptors D1-D3 paralleling cognitive enhancement in the radial arm maze

A series of drugs have been reported to increase memory performance modulating the dopaminergic system and herein modafinil was tested for its working memory (WM) enhancing properties. Reuptake inhibition of dopamine, serotonin (SERT) and norepinephrine (NET) by modafinil was tested. Sixty male Sprague–Dawley rats were divided into six groups (modafinil-treated 1–5–10 mg/kg body weight, trained and untrained and vehicle treated trained and untrained rats; daily injected intraperitoneally for a period of 10 days) and tested in a radial arm maze (RAM), a paradigm for testing spatial WM. Hippocampi were taken 6 h following the last day of training and complexes containing the unphosphorylated or phosphorylated dopamine transporter (DAT-CC and pDAT-CC) and complexes containing the D1–3 dopamine receptor subunits (D1–D3-CC) were determined. Modafinil was binding to the DAT but insignificantly to SERT or NET and dopamine reuptake was blocked specifically (IC₅₀ = 11.11 μM; SERT 1547 μM; NET 182 μM). From day 8 (day 9 for 1 mg/kg body weight) modafinil was decreasing WM errors (WMEs) in the RAM significantly and remarkably at all doses tested as compared to the vehicle controls. WMEs were linked to the D2R-CC and the pDAT-CC. pDAT and D1–D3-CC levels were modulated significantly and modafinil was shown to enhance spatial WM in the rat in a well-documented paradigm at all the three doses and dopamine reuptake inhibition with subsequent modulation of D1–3-CC is proposed as a possible mechanism of action.

The relationship between dopamine receptor D1 and cognitive performance

BACKGROUND

Cognitive impairment cuts across traditional diagnostic boundaries and is one of the most typical symptoms in various psychiatric and neurobiological disorders.

AIMS

The objective of this study was to examine the genetic association between 94 candidate genes, including receptors and enzymes that participate in neurotransmission, with measures of cognition.

METHODS

The Clinical Dementia Rating (CDR), a global measure of cognition, and genotypes derived from a custom array of 1,536 single-nucleotide polymorphisms (SNPs) in 94 genes were available for a large postmortem cohort of Caucasian cases with Alzheimer's disease (AD), schizophrenia and controls (n=727). A cohort of healthy young males (n=1,493) originating from the LOGOS project (Learning On Genetics Of Schizophrenia Spectrum) profiled across multiple cognitive domains was available for targeted SNP genotyping. Gene expression was quantified in the superior temporal gyrus of control samples (n=109). The regulatory effect on transcriptional activity was assessed using the luciferase reporter system.

RESULTS

The rs5326-A allele at the promoter region of dopamine receptor D1 (DRD1) locus was associated with: (i) poorer cognition (higher CDR) in the postmortem cohort (P=9.325×10(-4)); (ii) worse cognitive performance relevant to strategic planning in the LOGOS cohort (P=0.008); (iii) lower DRD1 gene expression in the superior temporal gyrus of controls (P=0.038); and (iv) decreased transcriptional activity in human neuroblastoma (SH-SY5Y) cells (P=0.026).

CONCLUSIONS

An interdisciplinary approach combining genetics with cognitive and molecular neuroscience provided a possible mechanistic link among DRD1 and alterations in cognitive performance.

Association study of dopamine receptor genes polymorphism with cognitive functions in bipolar I disorder patients

OBJECTIVE

To determine the correlation among the polymorphisms of dopamine receptor genes, cognitive function of Bipolar disorder (BD) patients, and BD.

METHODS

Twenty-three Single Nucleotide Polymorphisms (SNPs) of dopamine receptor genes were genotyped using Illumina GoldenGate genotyping assay in 375 patients with bipolar I disorder (BD-I) (patients group) and 475 healthy controls (control group). Cognitive function tests were performed in 158 patients who were clinically stable and 307 healthy controls who were matched with the patients in age, sex, and education.

RESULTS

The allele frequencies of rs3758653 in the promoter region of the DRD4 gene were significantly different between patients group and control group (χ(2)=9.386, Corrected P=0.046). This significant difference was also observed between BD-I patients with psychotic symptoms and healthy controls (χ(2)=9.27, Corrected P=0.049). Patients with BD-I performed significantly worse than healthy controls in all cognitive domains (p<0.01) except TMTA errors and illegal time. Significant interactions between polymorphisms of rs5326 in DRD1 gene and phenotype (affected or unaffected with BD-I) were found in non-perseverative errors (β=3.20 and Corrected P=0.0034) on the Wisconsin Card Sorting Test (WCST). The allele of this SNP denoted the positive effect on the WCST non-perseverative errors in BD-I patients group (β=2.80 and Corrected P=0.017). The genotypic association analyses also supported the findings (F=4.24 and P=0.007), but this effect was not found in controls.

LIMITATIONS

The sample size was relatively small and the SNP coverage was limited, making it very important to be cautious when drawing a conclusion.

CONCLUSIONS

DRD4 gene may play an important role in psychotic symptomatology rather than in unique diagnosis, BD, for example. A genetic association exists between DRD1 gene and impaired cognition in BD.