Striatal dopamine transporters and cognitive functioning in healthy men and women

Exploring sex differences: insights into gene expression, neuroanatomy, neurochemistry, cognition, and pathology

Increased knowledge about sex differences is important for development of individualized treatments against many diseases as well as understanding behavioral and pathological differences. This review summarizes sex chromosome effects on gene expression, epigenetics, and hormones in relation to the brain. We explore neuroanatomy, neurochemistry, cognition, and brain pathology aiming to explain the current state of the art. While some domains exhibit strong differences, others reveal subtle differences whose overall significance warrants clarification. We hope that the current review increases awareness and serves as a basis for the planning of future studies that consider both sexes equally regarding similarities and differences.

The contributions of neonatal inhalation of copper to air pollution-induced neurodevelopmental outcomes in mice

Exposures to ambient ultrafine particle (UFP) air pollution (AP) during the early postnatal period in mice (equivalent to human third trimester brain development) produce male-biased changes in brain structure, including ventriculomegaly, reduced brain myelination, alterations in neurotransmitters and glial activation, as well as impulsive-like behavioral characteristics, all of which are also features characteristic of male-biased neurodevelopmental disorders (NDDs). The purpose of this study was to ascertain the extent to which inhaled Cu, a common contaminant of AP that is also dysregulated across multiple NDDs, might contribute to these phenotypes. For this purpose, C57BL/6J mice were exposed from postnatal days 4-7 and 10-13 for 4 hr/day to inhaled copper oxide (CuxOy) nanoparticles at an environmentally relevant concentration averaging 171.9 ng/m3. Changes in brain metal homeostasis and neurotransmitter levels were determined following termination of exposure (postnatal day 14), while behavioral changes were assessed in adulthood. CuxOy inhalation modified cortical metal homeostasis and produced male-biased disruption of striatal neurotransmitters, with marked increases in dopaminergic function, as well as excitatory/inhibitory imbalance and reductions in serotonergic function. Impulsive-like behaviors in a fixed ratio (FR) waiting-for-reward schedule and a fixed interval (FI) schedule of food reward occurred in both sexes, but more prominently in males, effects which could not be attributed to altered locomotor activity or short-term memory. Inhaled Cu as from AP exposures, at environmentally relevant levels experienced during development, may contribute to impaired brain function, as shown by its ability to disrupt brain metal homeostasis and striatal neurotransmission. In addition, its ability to evoke impulsive-like behavior, particularly in male offspring, may be related to striatal dopaminergic dysfunction that is known to mediate such behaviors. As such, regulation of air Cu levels may be protective of public health.

Sex representation in neurodegenerative and psychiatric disorders' preclinical and clinical studies

Many studies show the importance of biological sex for the onset, progression, and response to treatment in brain disorders. In line with these reports, health agencies have requested that all trials, both at the clinical and preclinical level, use a similar number of male and female subjects to correctly interpret the results. Despite these guidelines, many studies still tend to be unbalanced in the use of male and female subjects. In this review we consider three neurodegenerative disorders: Alzheimer's disease, Parkinson's disease, Amyotrophic lateral sclerosis, and three psychiatric disorders: Depression, Attention Deficit Hyperactivity Disorder, and Schizophrenia. These disorders were chosen because of their prevalence and their recognized sex-specific differences in onset, progression, and response to treatment. Alzheimer's disease and Depression demonstrate higher prevalence in females, whereas Parkinson's Disease, Amyotrophic lateral sclerosis, Attention Deficit Hyperactivity Disorder, and schizophrenia show higher prevalence in males. Results from preclinical and clinical studies examining each of these disorders revealed sex-specific differences in risk factors, diagnostic biomarkers, and treatment response and efficacy, suggesting a role for sex-specific therapies in neurodegenerative and neuropsychiatric disorders. However, the qualitative analysis of the percentage of males and females enrolled in clinical trials in the last two decades shows that for most of the disorders, there is still a sex bias in the patients' enrolment.

Striatal dopamine synthesis and cognitive flexibility differ between hormonal contraceptive users and nonusers

In rodents and nonhuman primates, sex hormones are powerful modulators of dopamine (DA) neurotransmission. Yet less is known about hormonal regulation of the DA system in the human brain. Using positron emission tomography (PET), we address this gap by comparing hormonal contraceptive users and nonusers across multiple aspects of DA function: DA synthesis capacity via the PET radioligand 6-[18F]fluoro-m-tyrosine ([18F]FMT), baseline D2/3 receptor binding potential using [11C]raclopride, and DA release using methylphenidate-paired [11C]raclopride. Participants consisted of 36 healthy women (n = 15 hormonal contraceptive users; n = 21 naturally cycling/non users of hormonal contraception), and men (n = 20) as a comparison group. A behavioral index of cognitive flexibility was assessed prior to PET imaging. Hormonal contraceptive users exhibited greater DA synthesis capacity than NC participants, particularly in dorsal caudate, and greater cognitive flexibility. Furthermore, across individuals, the magnitude of striatal DA synthesis capacity was associated with cognitive flexibility. No group differences were observed in D2/3 receptor binding or DA release. Analyses by sex alone may obscure underlying differences in DA synthesis tied to women's hormone status. Hormonal contraception (in the form of pill, shot, implant, ring, or intrauterine device) is used by ~400 million women worldwide, yet few studies have examined whether chronic hormonal manipulations impact basic properties of the DA system. Findings from this study begin to address this critical gap in women's health.

Sex differences in neuroimmunoendocrine communication. Involvement on longevity

Endocrine, nervous, and immune systems work coordinately to maintain the global homeostasis of the organism. They show sex differences in their functions that, in turn, contribute to sex differences beyond reproductive function. Females display a better control of the energetic metabolism and improved neuroprotection and have more antioxidant defenses and a better inflammatory status than males, which is associated with a more robust immune response than that of males. These differences are present from the early stages of life, being more relevant in adulthood and influencing the aging trajectory in each sex and may contribute to the different life lifespan between sexes.

Does chronic use of amphetamine-type stimulants impair interference control? - A meta-analysis

In substance use and addiction, inhibitory control is key to ignoring triggers, withstanding craving and maintaining abstinence. In amphetamine-type stimulant (ATS) users, most research focused on behavioral inhibition, but largely neglected the equally important subdomain of cognitive interference control. Given its crucial role in managing consumption, we investigated the relationship between interference control and chronic ATS use in adults. A database search (Pubmed & Web of Science) and relevant reviews were used to identify eligible studies. Effect sizes were estimated with random effects models. Subgroup, meta-regression, and sensitivity analyses explored heterogeneity in effect sizes. We identified 61 studies (53 datasets) assessing interference control in 1873 ATS users and 1905 controls. Findings revealed robust small effect sizes for ATS-related deficits in interference control, which were mainly seen in methamphetamine, as compared to MDMA users. The differential effects are likely due to tolerance-induced dopaminergic deficiencies (presumably most pronounced in methamphetamine users). Similarities between different ATS could be due to noradrenergic deficiencies; but elucidating their functional role in ATS users requires further/more research.

Gender divergent effect of COMT gene rs4680 polymorphism on the association between executive dysfunction and psychotic-like experiences

AIM

Premorbid cognitive impairments are observed prior to the onset of schizophrenia. Catechol-O-methyltransferase (COMT) rs4680 is associated with psychosis and plays a crucial role in the development of the executive function. In addition, genetic COMT variations and gender affect its enzymatic activity. Therefore, the aim of this study was to evaluate the impact of COMT rs4680 on the relationship between executive dysfunction and psychotic-like experiences (PLEs) in college students, with the additional investigation of the gender difference.

METHODS

A total of 463 students provided biological samples for DNA analysis and the COMT gene rs4680 polymorphism was discriminated by the improved multiplex ligase detection reaction method. They also completed the Prodromal Questionnaire and the Dysexecutive Questionnaire.

RESULTS

Executive dysfunction significantly predicted positive PLEs in the total, male and female population (β = 0.515, 0.508 and 0.512, p < 0.001). The results of moderated analysis revealed that COMT rs4680 recessive genetic model ('AA genotype' versus 'G carrier') moderated the relationship between executive dysfunction and psychotic-like experience in the total and females (p = 0.002 and p <0.001, respectively), but not in males.

CONCLUSION

These findings revealed a female-specific effect of COMT rs4680 on the relationship between executive dysfunction and PLEs in young adults.

Development and Validation of a Daily Habit Scale

Habits are defined as automatic behaviours triggered by cues and performed without awareness. They are difficult to control and mentally efficient, which contrasts with goal-directed behaviour, which is characterised by active thought, high computational effort, and the ability to modify this behaviour in response to a changing environment and contextual demands. Habits are not only defined by the frequency with which a behaviour is performed but represent a complex construct that also includes the strength and automaticity of the habitual behaviour. We report here the development and validation of a Daily Habit Scale (DHS) to assess the frequency, automaticity, and strength of daily habits in healthy individuals. Item reduction based on factor analysis resulted in a scale with 38 items grouped into eight factors explaining 52.91% of the variance. The DHS showed very good internal consistency (Cronbach alpha = 0.738) and test-retest reliability (Intraclass correlation coefficient = 0.892, p<0.001) as well as convergent and divergent reliability compared to other scales measuring habits. We found a significant effect of age, gender, anxiety, and depression on the DHS. Considering certain limitations of the DHS, such as not considering the context of performance of habits, and the absence of certain items, such as transportation use, the results of this study suggest that DHS is a reliable and valid measure of daily habits that can be used by both clinicians and researchers as a measure of daily habits.

Role of Dopamine Transporter in the Relationship Between Plasma Cortisol and Cognition

OBJECTIVE

Cortisol is associated with cognition in both healthy individuals and patients with neuropsychiatric disorders. Regarding the effects of cortisol on the dopamine system and the association between dopamine transporter (DAT) and cognition, DAT might be a central target linking cortisol and cognition. This study explored the role of striatal DAT in the cortisol-cognition relationship.

METHODS

We recruited 33 patients with carbon monoxide poisoning and 33 age- and sex-matched healthy controls. All participants underwent cognitive assessments of attention, memory, and executive function. Single-photon emission computed tomography with 99mTc-TRODAT was used to determine striatal DAT availability. Plasma cortisol, tumor necrosis factor α, and interleukin-10 levels were measured using enzyme-linked immunosorbent assays.

RESULTS

Compared with healthy controls, patients with carbon monoxide poisoning had lower cognitive performance, bilateral striatal DAT availability, and plasma tumor necrosis factor-α levels and higher cortisol and interleukin-10 levels. In all participants, plasma cortisol level and bilateral striatal DAT availability were negatively and positively related to cognition, respectively, including memory and executive function with β from -0.361 (95% confidence interval [CI] = -0.633 to -0.090) to 0.588 (95% CI = 0.319 to 0.858). Moreover, bilateral striatal DAT mediated the cortisol-cognition relationship with indirect effects from -0.067 (95% CI = -0.179 to -0.001) to -0.135 (95% CI = -0.295 to -0.024). The cytokine levels did not influence the mediation effects.

CONCLUSIONS

This is the first study to demonstrate that striatal DAT mediates the cortisol-cognition relationship. Future studies are needed to comprehensively evaluate the role of the dopamine system in cortisol-cognition associations and treatment implications.

Voxel-based analysis of age and gender effects on striatal [123I] FP-CIT binding in healthy Japanese adults

OBJECTIVE

Although previous studies have investigated age and gender effects on striatal subregional dopamine transporter (DaT) binding, these studies were mostly based on a conventional regions of interest-based analysis. Here, we investigated age and gender effects on striatal DaT binding at the voxel level, using a multicenter database of [(¹²³)I] N-omega-fluoropropyl-2beta-carbomethoxy-3beta-{4-iodophenyl}nortropane ([(¹²³)I] FP-CIT)-single photon emission computed tomography (SPECT) scans in 256 healthy Japanese adults.

METHODS

We used the Southampton method to calculate the specific binding ratios (SBRs) of each subject's striatum and then converted the [¹²³I] FP-CIT SPECT images to quantitative SBRs images. To investigate the effects of age and gender effects on striatal DaT binding, we performed a voxel-based analysis using statistical parametric mapping. Gender differences were also compared between young to middle-aged subjects and elderly subjects (age threshold: 60 years).

RESULTS

When all subjects were explored as a group, DaT binding throughout the striatum decreased with advancing age. Among all subjects, the females showed higher DaT binding in the bilateral caudate compared to the males. In the young to middle-aged subjects, the females showed higher DaT binding throughout the striatum (with a slight caudate predominance) versus the males. In the elderly, there were no gender differences in striatal DaT binding.

CONCLUSION

Our findings of striatal subregional age- and gender-related differences may provide useful information to construct a more detailed DaT database in healthy Japanese subjects.

Lipid-lowering drug targets and Parkinson's disease: A sex-specific Mendelian randomization study

Parkinson's disease (PD) affects millions of individuals worldwide, and it is the second most common late-onset neurodegenerative disorder. There is no cure and current treatments only alleviate symptoms. Modifiable risk factors have been explored as possible options for decreasing risk or developing drug targets to treat PD, including low-density lipoprotein cholesterol (LDL-C). There is evidence of sex differences for cholesterol levels as well as for PD risk. Genetic datasets of increasing size are permitting association analyses with increased power, including sex-stratified analyses. These association results empower Mendelian randomization (MR) studies, which, given certain assumptions, test whether there is a causal relationship between the risk factor and the outcome using genetic instruments. Sex-specific causal inference approaches could highlight sex-specific effects that may otherwise be masked by sex-agnostic approaches. We conducted a sex-specific two-sample cis-MR analysis based on genetic variants in LDL-C target encoding genes to assess the impact of lipid-lowering drug targets on PD risk. To complement the cis-MR analysis, we also conducted a sex-specific standard MR analysis (using genome-wide independent variants). We did not find evidence of a causal relationship between LDL-C levels and PD risk in females [OR (95% CI) = 1.01 (0.60, 1.69), IVW random-effects] or males [OR (95% CI) = 0.93 (0.55, 1.56)]. The sex-specific standard MR analysis also supported this conclusion. We encourage future work assessing sex-specific effects using causal inference techniques to better understand factors that may contribute to complex disease risk differently between the sexes.

Diabetes and Cognitive Impairment: A Role for Glucotoxicity and Dopaminergic Dysfunction

Diabetes mellitus (DM) is a chronic metabolic disorder characterized by hyperglycemia, responsible for the onset of several long-term complications. Recent evidence suggests that cognitive dysfunction represents an emerging complication of DM, but the underlying molecular mechanisms are still obscure. Dopamine (DA), a neurotransmitter essentially known for its relevance in the regulation of behavior and movement, modulates cognitive function, too. Interestingly, alterations of the dopaminergic system have been observed in DM. This review aims to offer a comprehensive overview of the most relevant experimental results assessing DA’s role in cognitive function, highlighting the presence of dopaminergic dysfunction in DM and supporting a role for glucotoxicity in DM-associated dopaminergic dysfunction and cognitive impairment. Several studies confirm a role for DA in cognition both in animal models and in humans. Similarly, significant alterations of the dopaminergic system have been observed in animal models of experimental diabetes and in diabetic patients, too. Evidence is accumulating that advanced glycation end products (AGEs) and their precursor methylglyoxal (MGO) are associated with cognitive impairment and alterations of the dopaminergic system. Further research is needed to clarify the molecular mechanisms linking DM-associated dopaminergic dysfunction and cognitive impairment and to assess the deleterious impact of glucotoxicity.

Biological sex differences in afferent-mediated inhibition of motor responses evoked by TMS

Sensorimotor integration can be assessed by pairing electrical peripheral nerve stimulation with transcranial magnetic stimulation (TMS). The resulting afferent inhibition is observed when TMS precedes nerve stimulation by ∼ 20-25 ms, termed short-latency afferent inhibition (SAI), or by 200 ms, termed long-latency afferent inhibition (LAI). The purpose of this study was to determine whether biological sex influences the magnitude of SAI or LAI. SAI and LAI were assessed in fifteen males (21.5 ± 2.7 years) and fifteen females (20.2 ± 2.3 years). TMS was delivered to the primary motor cortex (M1) following stimulation of the contralateral median nerve at the wrist or digital nerve of the index finger, and motor-evoked potentials (MEPs) were obtained from the right first dorsal interosseous (FDI) muscle. SAI evoked by median and digital nerve stimulation, and LAI evoked by median nerve stimulation, were not different between males and females. LAI evoked by digital nerve stimulation was increased in females compared to males, but this difference between sexes was no longer present following the removal of datapoints where inhibition was not observed. This study is the first to investigate biological sex differences in afferent inhibition.

Evaluation of Age and Sex-Related Metabolic Changes in Healthy Subjects: An Italian Brain 18F-FDG PET Study

Background: 18F-fluorodeoxyglucose (18F-FDG) positron-emission-tomography (PET) allows detection of cerebral metabolic alterations in neurological diseases vs. normal aging. We assess age- and sex-related brain metabolic changes in healthy subjects, exploring impact of activity normalization methods. Methods: brain scans of Italian Association of Nuclear Medicine normative database (151 subjects, 67 Males, 84 Females, aged 20–84) were selected. Global mean, white matter, and pons activity were explored as normalization reference. We performed voxel-based and ROI analyses using SPM12 and IBM-SPSS software. Results: SPM proved a negative correlation between age and brain glucose metabolism involving frontal lobes, anterior-cingulate and insular cortices bilaterally. Narrower clusters were detected in lateral parietal lobes, precuneus, temporal pole and medial areas bilaterally. Normalizing on pons activity, we found a more significant negative correlation and no positive one. ROIs analysis confirmed SPM results. Moreover, a significant age × sex interaction effect was revealed, with worse metabolic reduction in posterior-cingulate cortices in females than males, especially in post-menopausal age. Conclusions: this study demonstrated an age-related metabolic reduction in frontal lobes and in some parieto-temporal areas more evident in females. Results suggested pons as the most appropriate normalization reference. Knowledge of age- and sex-related cerebral metabolic changes is critical to correctly interpreting brain 18F-FDG PET imaging.

Dopamine Transporter Imaging, Current Status of a Potential Biomarker: A Comprehensive Review

A major goal of current clinical research in Parkinson's disease (PD) is the validation and standardization of biomarkers enabling early diagnosis, predicting outcomes, understanding PD pathophysiology, and demonstrating target engagement in clinical trials. Molecular imaging with specific dopamine-related tracers offers a practical indirect imaging biomarker of PD, serving as a powerful tool to assess the status of presynaptic nigrostriatal terminals. In this review we provide an update on the dopamine transporter (DAT) imaging in PD and translate recent findings to potentially valuable clinical practice applications. The role of DAT imaging as diagnostic, preclinical and predictive biomarker is discussed, especially in view of recent evidence questioning the incontrovertible correlation between striatal DAT binding and nigral cell or axon counts.

Evaluation of dopamine transporter density in healthy Brazilians using Tc-99m TRODAT-1 SPECT

The presynaptic dopamine transporter (DAT) modulates the uptake of dopamine by regulating its concentration in the central nervous system. We aimed to evaluate the DAT binding potential (DAT-BP) in a sample of healthy Brazilians through technetium-99 metastable TRODAT-1 single-photon emission computed tomography imaging.We selected 126 healthy individuals comprising 72 men and 54 women, aged 18 to 80 years. We conducted semi-quantitative evaluation in transaxial slices, following which we identified the regions of interest in the striatal region using the occipital lobe as a region of non-specific DAT-BP.We found a decrease in DAT-BP in healthy individuals aged over 30 years, culminating in a 42% mean reduction after 80 years. There was no difference in the decrease by age group between the right (linear regression test [R2] linear = 0.466) and left striatum (R2 linear = 0.510). Women presented a higher DAT-BP than men (women: R2 linear = 0.431; men: R2 linear = 0.457); nonetheless, their decrease by age group was equal to that in men.Our study sheds light on important DAT-BP findings in healthy Brazilian subjects. Our results will facilitate understanding of brain illnesses that involve the dopamine system, such as neuropsychiatric disorders.

A causal role of estradiol in human reinforcement learning

The sex hormone estradiol is hypothesized to play a key role in human cognition, and reward processing specifically, via increased dopamine D1-receptor signalling. However, the effect of estradiol on reward processing in men has never been established. To fill this gap, we performed a double-blind placebo-controlled study in which men (N = 100) received either a single dose of estradiol (2 mg) or a placebo. Subjects performed a probabilistic reinforcement learning task where they had to choose between two options with varying reward probabilities to maximize monetary reward. Results showed that estradiol administration increased reward sensitivity compared to placebo. This effect was observed in subjects' choices, how much weight they assigned to their previous choices, and subjective reports about the reward probabilities. Furthermore, effects of estradiol were moderated by reward sensitivity, as measured through the BIS/BAS questionnaire. Using reinforcement learning models, we found that behavioral effects of estradiol were reflected in increased learning rates. These results demonstrate a causal role of estradiol within the framework of reinforcement learning, by enhancing reward sensitivity and learning. Furthermore, they provide preliminary evidence for dopamine-related genetic variants moderating the effect of estradiol on reward processing.

Sex and the dopaminergic system: Insights from addiction studies

Sex differences are present in psychiatric disorders associated with disrupted dopamine function, and thus, sex differences in dopamine neurobiology may underlie these clinical disparities. In this chapter, we review sex differences in the dopaminergic system with a focus on substance use disorders, especially tobacco smoking, as our exemplar disorder. This chapter is organized into five sections describing sex differences in the dopaminergic system: (1) neurobiology, (2) role of sex hormones, (3) genetic underpinnings, (4) cognitive function, and (5) influence on addiction. In each section, we provide an overview of the topic area, summarize sex differences identified to date, highlight addiction research, especially clinical neuroimaging studies, and suggest avenues for future research.

Clinical implications for dopaminergic and functional neuroimage research in cognitive symptoms of Parkinson's disease

Evidence from dopaminergic image and cerebral blood flow/metabolism images have shed light on symptomatology of cognitive aspects in brain physiology of healthy human as well as patients with Parkinson's disease. Cognitive impairment in Parkinson's disease is characterized by executive, visuospatial, attentional disturbances. Dopaminergic system includes triadic parallel pathways. The mesostriatal pathway consist of posterolateral putamen and motor areas, the mesocortical pathway of dorsal caudate nucleus and dorsolateral prefrontal cortex, and the mesolimbic pathway of ventral striatum, anterior cingulate cortex. The mesocortical pathway is responsible for the executive function which may change by administration of dopaminergic medication. The mesolimbic pathway is associated with motivation and reward prediction which may result in depression or apathy when dopamine level was suboptimal, impulse control disorder and punding when dopamine was over the optimal level. Abnormal brain metabolism/perfusion related to cognitive impairment in Parkinson's disease are relatively reduced activity located in frontal and parietal association areas and relatively increased activity in the cerebellum. In the anterior brain, the mesocortical pathway, is responsible for verbal memory and executive function, which originates with caudate dopaminergic system and account for mild cognitive impairment of Parkinson's disease. The posterior brain system which includes the parietal, temporal, and occipital cortices, is responsible for the memory and visuospatial function, and related to cholinergic dysfunction and possibly glucocerebrosidase gene variants, relating to dementia in Parkinson's disease. The role of cerebellum in Parkinson's disease remains unclear but emerging evidence suggests that it may relate to the sequencing detection and affective symptoms. The dual syndrome hypothesis is helpful for understanding the mechanism of cognitive impairment in Parkinson's disease and optimal symptom management.

Is there a Neurobiological Rationale for the Utility of the Iowa Gambling Task in Parkinson's Disease?

Up to 23% of newly diagnosed, non-demented, Parkinson’s disease (PD) patients experience deficits in executive functioning (EF). In fact, EF deficits may occur up to 39-months prior to the onset of motor decline. Optimal EF requires working memory, attention, cognitive flexibility, and response inhibition underlying appropriate decision-making. The capacity for making strategic decisions requires inhibiting imprudent decisions and are associated with noradrenergic and dopaminergic signaling in prefrontal and orbitofrontal cortex. Catecholaminergic dysfunction and the loss of noradrenergic and dopaminergic cell bodies early in PD progression in the aforementioned cortical areas likely contribute to EF deficits resulting in non-strategic decision-making. Thus, detecting these deficits early in the disease process could help identify a significant portion of individuals with PD pathology (14–60%) before frank motor impairment. A task to evaluate EF in the domain of non-strategic decision-making might be useful to indicate the moderate loss of catecholamines that occurs early in PD pathology prior to motor decline and cognitive impairment. In this review, we focus on the potential utility of the Iowa Gambling Task (IGT) for this purpose, given significant overlap between in loss of dopaminergic and noradrenergic cells bodies in early PD and the deficits in catecholamine function associated with decreased EF. As such, given the loss of catecholamines already well-underway after PD diagnosis, we evaluate the potential utility of the IGT to identify the risk of therapeutic non-compliance and a potential companion approach to detect PD in premotor stages.

Mild Motor Signs Matter in Typical Brain Aging: The Value of the UPDRS Score Within a Functionally Intact Cohort of Older Adults

Objectives: To characterize the clinical correlates of subclinical Parkinsonian signs, including longitudinal cognitive and neural (via functional connectivity) outcomes, among functionally normal older adults.

Methods: Participants included 737 functionally intact community-dwelling older adults who performed prospective comprehensive evaluations at ~15-months intervals for an average of 4.8 years (standard deviation 3.2 years). As part of these evaluations, participants completed the Unified Parkinson's Disease Rating Scale (UPDRS) longitudinally and measures of processing speed, executive functioning and verbal episodic memory. T1-weighted structural scans and task-free functional MRI scans were acquired on 330 participants. We conducted linear mixed-effects models to determine the relationship between changes in UPDRS with cognitive and neural changes, using age, sex, and education as covariates.

Results: Cognitive outcomes were processing speed, executive functioning, and episodic memory. Greater within-person increases in UPDRS were associated with more cognitive slowing over time. Although higher average UPDRS scores were significantly associated with overall poorer executive functions, there was no association between UPDRS and executive functioning longitudinally. UPDRS scores did not significantly relate to longitudinal memory performances. Regarding neural correlates, greater increases in UPDRS scores were associated with reduced intra-subcortical network connectivity over time. There were no relationships with intra-frontoparietal or inter-subcortical-frontoparietal connectivity.

Conclusions: Our findings add to the aging literature by indicating that mild motor changes are negatively associated with cognition and network connectivity in functionally intact adults.

Classification of PPMI MRI scans with voxel-based morphometry and machine learning to assist in the diagnosis of Parkinson's disease

BACKGROUND AND OBJECTIVES

Qualitative and quantitative analyses of Magnetic Resonance Imaging (MRI) scans are carried out to study and understand Parkinson's Disease, the second most common neurodegenerative disorder in people at their 60's. Some quantitative analyses are based on the application of voxel-based morphometry (VBM) on magnetic resonance images to determine the regions of interest, within gray matter, where there is a loss of the nerve cells that generate dopamine. This loss of dopamine is indicative of Parkinson's disease. The purpose of this research is the introduction of a new method to classify the 3-D magnetic resonance scans of an individual, as an assisting tool for diagnosis of Parkinson's disease by using the largest MRI dataset (Parkinson's Progression Markers Initiative) from a population of patients with Parkinson's disease and control individuals. A contribution is that separate studies are conducted for men and women since gender plays a significant role within Neurobiology, which is demonstrated by the fact that men are more prone to Parkinson's disease than women are.

METHODS

Previous to classification, VBM is conducted on magnetic resonance images to detect the regions where features are extracted by using first- and second-order statistics methods. Furthermore, the number of features is considerably reduced by using feature selection techniques. Seven classifiers are used and we are conducting separate experiments for men and women.

RESULTS

The best detection performance achieved in men is 99.01% of accuracy, 99.35% of sensitivity, 100% of specificity, and 100% of precision. The best detection performance achieved in women is 96.97% of accuracy, 100% of sensitivity, 96.15% of specificity, and 97.22% of precision. During classification of magnetic resonance images, the corresponding computational complexity is reduced since few features are selected.

CONCLUSIONS

The proposed method provides high performance as an assisting tool in the diagnosis of Parkinson's disease, by conducting separate experiments in men and women. While previous works have focused their analysis to the striatum region of the brain (the largest nuclear complex of the basal ganglia), the proposed approach is based on analysis over the whole brain by looking for decreases of tissue thickness, with the consequence of finding other regions of interest such as the cortex.

Strong age but weak sex effects in eye movement performance in the general adult population: Evidence from the Rhineland Study

Assessing physiological changes that occur with healthy ageing is prerequisite for understanding pathophysiological age-related changes. Eye movements are studied as biomarkers for pathological changes because they are altered in patients with neurodegenerative disorders. However, there is a lack of data from large samples assessing age-related physiological changes and sex differences in oculomotor performance. Thus, we assessed and quantified cross-sectional relations of age and sex with oculomotor performance in the general population. We report results from the first 4,000 participants (aged 30-95 years) of the Rhineland Study, a community-based prospective cohort study in Bonn, Germany. Participants completed fixation, smooth pursuit, prosaccade and antisaccade tasks. We quantified associations of age and sex with oculomotor outcomes using multivariable linear regression models. Performance in 12 out of 18 oculomotor measures declined with increasing age. No differences between age groups were observed in five antisaccade outcomes (amplitude-adjusted and unadjusted peak velocity, amplitude gain, spatial error and percentage of corrected errors) and for blink rate during fixation. Small sex differences occurred in smooth pursuit velocity gain (men have higher gain) and blink rate during fixation (men blink less). We conclude that performance declines with age in two thirds of oculomotor outcomes but that there was no evidence of sex differences in eye movement performance except for two outcomes. Since the percentage of corrected antisaccade errors was not associated with age but is known to be affected by pathological cognitive decline, it represents a promising candidate preclinical biomarker of neurodegeneration.

Gender Differences and Quality of Life in Parkinson's Disease

Parkinson's disease has been found to significantly affect health-related quality of life. The gender differences of the health-related quality of life of subjects with Parkinson's disease have been observed in a number of studies. These differences have been reported in terms of the age at onset, clinical manifestations, and response to therapy. In general, women with Parkinson's disease showed more positive disease outcomes with regard to emotion processing, non-motor symptoms, and cognitive functions, although women report more Parkinson's disease-related clinical manifestations. Female gender predicted poor physical functioning and socioemotional health-related quality of life, while male gender predicted the cognitive domain of health-related quality of life. Some studies reported gender differences in the association between health-related quality of life and non-motor symptoms. Depression and fatigue were the main causes of poorer health-related quality of life in women, even in the early stages of Parkinson's disease. The aim of this review was to collect the best available evidence on gender differences in the development of Parkinson's disease symptoms and health-related quality of life.

Preliminary evidence for an association between intake of high-fat high-sugar diet, variations in peripheral dopamine precursor availability and dopamine-dependent cognition in humans

Obesity is associated with alterations in dopaminergic transmission and cognitive function. Rodent studies suggest that diets rich in saturated fat and refined sugars (HFS), as opposed to diets diets low in saturated fat and refined sugars (LFS), change the dopamine system independent of excessive body weight. However, the impact of HFS on the human brain has not been investigated. Here, we compared the effect of dietary dopamine depletion on dopamine-dependent cognitive task performance between two groups differing in habitual intake of dietary fat and sugar. Specifically, we used a double-blind within-subject cross-over design to compare the effect of acute phenylalanine/tyrosine depletion on a reinforcement learning and a working memory task, in two groups that are on opposite ends of the spectrum of self-reported HFS intake (low vs high intake: LFS vs HFS group). We tested 31 healthy young women matched for body mass index (mostly normal weight to overweight) and IQ. Depletion of peripheral precursors of dopamine reduced the working memory specific performance on the operation span task in the LFS, but not in the HFS group (P = 0.016). Learning from positive- and negative-reinforcement (probabilistic selection task) was increased in both diet groups after dopamine depletion (P = 0.049). As a secondary exploratory research question, we measured peripheral dopamine precursor availability (pDAP) at baseline as an estimate for central dopamine levels. The HFS group had a significantly higher pDAP at baseline compared to the LFS group (P = 0.025). Our data provide the first evidence indicating that the intake of HFS is associated with changes in dopamine precursor availability, which is suggestive of changes in central dopamine levels in humans. The observed associations are present in a sample of normal to overweight participants (ie, in the absence of obesity), suggesting that the consumption of a HFS might already be associated with altered behaviours. Alternatively, the effects of HFS diet and obesity might be independent.

Interaction of dopamine transporter and metabolite ratios underpinning the cognitive dysfunction in patients with carbon monoxide poisoning: A combined SPECT and MRS study

Cognitive dysfunction has been reported in patients with carbon monoxide (CO) poisoning. However, the underpinning mechanism remained unclear. This study examined dopamine transporter (DAT) and metabolite ratios concurrently and their relationships with cognitive dysfunction in CO poisoning. Eighteen suicide attempters with charcoal burning which results in CO poisoning and 18 age- and gender- matched normal controls were recruited. A battery of cognitive assessments including attention, memory, and executive function was administered. Each participant received one single photon emission computed tomography with ^99mTc-TRODAT for measuring striatal DAT availability and proton magnetic resonance spectroscopy to determine N-acetyl aspartate/creatine (NAA/Cr), choline-containing compounds/creatine (Cho/Cr) and myo-inositol/creatine (mI/Cr) in the left parietal white matter and mid-occipital gray matter (OGM). CO poisoning patients had significant impairments in memory and executive function. Compared to normal, CO poisoning patients had lower striatal DAT availability, lower NAA/Cr levels in both regions and higher Cho/Cr levels in both regions. In CO poisoning patients, the altered left striatal DAT availability and Cho/Cr level in OGM were significantly associated with executive dysfunction in the expected directions. Moreover, there was a significant interaction between these two imaging indices on their relationships with executive dysfunction and combination of them could adequately predict executive dysfunction in more CO poisoning cases than either alone. The current results suggested that both alterations in DAT availability and metabolite ratios might play crucial roles in executive dysfunction in CO poisoning. This research also highlights the importance of multimodal imaging approaches for studying neurotoxicity effects.

Sex and strain differences in dynamic and static properties of the mesolimbic dopamine system

Sex is a biological variable that contributes to the incidence, clinical course, and treatment outcome of brain disorders. Chief among these are disorders associated with the dopamine system. These include Parkinson's disease, ADHD, schizophrenia, and mood disorders, which show stark differences in prevalence and outcome between men and women. In order to reveal the influence of biological sex as a risk factor in these disorders, there is a critical need to collect fundamental information about basic properties of the dopamine system in males and females. In Long Evans rats, we measured dynamic and static properties related to the mesolimbic dopamine system. Static measures included assessing ventral tegmental area (VTA) dopamine cell number and volume and expression of tyrosine hydroxylase and dopamine transporter. Dynamic measures in behaving animals included assessing (1) VTA neuronal encoding during learning of a cue-action-reward instrumental task and (2) dopamine release in the nucleus accumbens in response to electrical stimulation of the VTA, vesicular depletion of dopamine, and amphetamine. We found little or no sex difference in these measures, suggesting sexual congruency in fundamental static and dynamic properties of dopamine neurons. Thus, dopamine related sex-differences are likely mediated by secondary mechanisms that flexibly influence the function of the dopamine cells and circuits. Finally, we noted that most behavioral sex differences had been reported in Sprague-Dawley rats and repeated some of the above measures in that strain. We found some sex differences in those animals highlighting the importance of considering strain differences in experimental design and result interpretation.

Sex differences in the human reward system: convergent behavioral, autonomic and neural evidence

Several studies have suggested that females and males differ in reward behaviors and their underlying neural circuitry. Whether human sex differences extend across neural and behavioral levels for both rewards and punishments remains unclear. We studied a community sample of 221 young women and men who performed a monetary incentive task known to engage the mesoaccumbal pathway and salience network. Both stimulus salience (behavioral relevance) and valence (win vs loss) varied during the task. In response to high- vs low-salience stimuli presented during the monetary incentive task, men showed greater subjective arousal ratings, behavioral accuracy and skin conductance responses (P < 0.006, Hedges' effect size g = 0.38 to 0.46). In a subsample studied with functional magnetic resonance imaging (n = 44), men exhibited greater responsiveness to stimulus salience in the nucleus accumbens, midbrain, anterior insula and dorsal anterior cingulate cortex (P < 0.02, g = 0.86 to 1.7). Behavioral, autonomic and neural sensitivity to the valence of stimuli did not differ by sex, indicating that responses to rewards vs punishments were similar in women and men. These results reveal novel and robust sex differences in reward- and punishment-related traits, behavior, autonomic activity and neural responses. These convergent results suggest a neurobehavioral basis for sexual dimorphism observed in the reward system, including reward-related disorders.

Volume reduction of caudate nucleus is associated with movement coordination deficits in patients with hippocampal atrophy due to perinatal hypoxia-ischaemia

Acute sentinel hypoxia-ischaemia in neonates can target the hippocampus, mammillary bodies, thalamus, and the basal ganglia. Our previous work with paediatric patients with a history of hypoxia-ischaemia has revealed hippocampal and diencephalic damage that impacts cognitive memory. However, the structural and functional status of other brain regions vulnerable to hypoxia-ischaemia, such as the basal ganglia, has not been investigated in these patients. Furthermore, it is not known whether there are any behavioural sequelae of such damage, especially in patients with no diagnosis of neurological disorder. Based on the established role of the basal ganglia and the thalamus in movement coordination, we studied manual motor function in 20 participants exposed to neonatal hypoxia-ischaemia, and a group of 17 healthy controls of comparable age. The patients' handwriting speed and accuracy was within the normal range (Detailed Assessment of Speed of Handwriting), and their movement adaptation learning (Rotary Pursuit task) was comparable to the control group's performance. However, as a group, patients showed an impairment in the Grooved Pegboard task and a trend for impairment in speed of movement while performing the Rotary Pursuit task, suggesting that some patients have subtle deficits in fine, complex hand movements. Voxel-based morphometry and volumetry showed bilateral reduction in grey matter volume of the thalamus and caudate nucleus. Reduced volumes in the caudate nucleus correlated across patients with performance on the Grooved Pegboard task. In summary, the fine movement coordination deficit affecting the hand and the wrist in patients exposed to early hypoxic-ischaemic brain injury may be related to reduced volumes of the caudate nucleus, and consistent with anecdotal parental reports of clumsiness and coordination difficulties in this cohort.

Faster Acquisition for Dopamine Transporter Imaging Using Swiftscan Step and Shoot Continuous SPECT Without Impairing Visual and Semiquantitative Analysis

Aim: Dopamine transporter (DAT) imaging with [123I] FP-CIT (DaTSCAN) is an established diagnostic tool in parkinsonism and dementia. Using a low energy high resolution and sensitivity (LEHRS) collimator and step and shoot continuous scanning mode, Swiftscan single photon emission computed tomography (SPECT) (GE Healthcare) enhances sensitivity and enables time or dose reduction. In this phantom and clinical study, we aim to validate a 25% reduction of the acquisition time using Swiftscan and its lack of effect on visual or quantitative analysis.

Methods: Anthropomorphic striatal phantom with fillable striata was used. SPECT data from 30 normals (12 men, 18 women; age range, 39–91 years; mean, 71 years ± 11) and 30 patients with Parkinson disease or other neurodegenerative disease with extra-pyramidal syndrome (16 men, 14 women; age range, 43–84 years; mean, 69 years ± 10) were also included. Both phantom and clinical data were acquired using Swiftscan and reconstructed with full-time and 25%-time reduction. Striatal binding ratios (SBRs) were calculated using DaTQUANT software.

Results: Both in phantom experiments and in clinical cases, visual analysis remained stable and SBRs were not significantly different whether using Swiftscan or Swiftscan with 25%-time reduction (p < 0.001). There was an excellent inter-rater agreement and no effect of time reduction on diagnosis or on image quality.

Conclusion: Using Swiftscan step and shoot continuous SPECT mode, 25%-time reduction can be applied to DaTSCAN acquisition protocols, without impairing visual or quantitative analysis.

An improved sex-specific and age-dependent classification model for Parkinson's diagnosis using handwriting measurement

BACKGROUND AND OBJECTIVES

Diagnosis of Parkinson's with higher accuracy is always desirable to slow down the progression of the disease and improved quality of life. There are evidences of inherent neurological differences between male and females as well as between elderly and adults. However, the potential of such gender and age infomration have not been exploited yet for Parkinson's identification.

METHODS

In this paper, we develop a sex-specific and age-dependent classification method to diagnose the Parkinson's disease using the online handwriting recorded from individuals with Parkinson's (n = 37; m/f-19/18;age-69.3 ± 10.9yrs) and healthy controls (n = 38; m/f-20/18;age-62.4 ± 11.3yrs). A support vector machine ranking method is used to present the features specific to their dominance in sex and age group for Parkinson's diagnosis.

RESULTS

The sex-specific and age-dependent classifier was observed significantly outperforming the generalized classifier. An improved accuracy of 83.75% (SD = 1.63) with the female-specific classifier, and 79.55% (SD = 1.58) with the old-age dependent classifier was observed in comparison to 75.76% (SD = 1.17) accuracy with the generalized classifier.

CONCLUSIONS

Combining the age and sex information proved to be encouraging in classification. A distinct set of features were observed to be dominating for higher classification accuracy in a different category of classification.

Stratifying drug treatment of cognitive impairments after traumatic brain injury using neuroimaging

Cognitive impairment is common following traumatic brain injury. Dopaminergic drugs can enhance cognition after traumatic brain injury, but individual responses are highly variable. This may be due to variability in dopaminergic damage between patients. We investigate whether measuring dopamine transporter levels using 123I-ioflupane single-photon emission computed tomography (SPECT) predicts response to methylphenidate, a stimulant with dopaminergic effects. Forty patients with moderate-severe traumatic brain injury and cognitive impairments completed a randomized, double-blind, placebo-controlled, crossover study. 123I-ioflupane SPECT, MRI and neuropsychological testing were performed. Patients received 0.3 mg/kg of methylphenidate or placebo twice a day in 2-week blocks. Subjects received neuropsychological assessment after each block and completed daily home cognitive testing during the trial. The primary outcome measure was change in choice reaction time produced by methylphenidate and its relationship to stratification of patients into groups with normal and low dopamine transporter binding in the caudate. Overall, traumatic brain injury patients showed slow information processing speed. Patients with low caudate dopamine transporter binding showed improvement in response times with methylphenidate compared to placebo [median change = -16 ms; 95% confidence interval (CI): -28 to -3 ms; P = 0.02]. This represents a 27% improvement in the slowing produced by traumatic brain injury. Patients with normal dopamine transporter binding did not improve. Daily home-based choice reaction time results supported this: the low dopamine transporter group improved (median change -19 ms; 95% CI: -23 to -7 ms; P = 0.002) with no change in the normal dopamine transporter group (P = 0.50). The low dopamine transporter group also improved on self-reported and caregiver apathy assessments (P = 0.03 and P = 0.02, respectively). Both groups reported improvements in fatigue (P = 0.03 and P = 0.007). The cognitive effects of methylphenidate after traumatic brain injury were only seen in patients with low caudate dopamine transporter levels. This shows that identifying patients with a hypodopaminergic state after traumatic brain injury can help stratify the choice of cognitive enhancing therapy.

The role of catecholamines in modulating responses to stress: Sex-specific patterns, implications, and therapeutic potential for post-traumatic stress disorder and opiate withdrawal

Emotional arousal is one of several factors that determine the strength of a memory and how efficiently it may be retrieved. The systems at play are multifaceted; on one hand, the dopaminergic mesocorticolimbic system evaluates the rewarding or reinforcing potential of a stimulus, while on the other, the noradrenergic stress response system evaluates the risk of threat, commanding attention, and engaging emotional and physical behavioral responses. Sex-specific patterns in the anatomy and function of the arousal system suggest that sexually divergent therapeutic approaches may be advantageous for neurological disorders involving arousal, learning, and memory. From the lens of the triple network model of psychopathology, we argue that post-traumatic stress disorder and opiate substance use disorder arise from maladaptive learning responses that are perpetuated by hyperarousal of the salience network. We present evidence that catecholamine-modulated learning and stress-responsive circuitry exerts substantial influence over the salience network and its dysfunction in stress-related psychiatric disorders, and between the sexes. We discuss the therapeutic potential of targeting the endogenous cannabinoid system; a ubiquitous neuromodulator that influences learning, memory, and responsivity to stress by influencing catecholamine, excitatory, and inhibitory synaptic transmission. Relevant preclinical data in male and female rodents are integrated with clinical data in men and women in an effort to understand how ideal treatment modalities between the sexes may be different.

The Correlation Between Mid-Brain Serotonin Transporter Availability and Intelligence Quotient in Healthy Volunteers

Purpose:

This study was performed to investigate the association between the mid-brain serotonin transporter (SERT) availability and intelligence quotient (IQ).

Methods:

One hundred and thirteen healthy participants, including 52 male and 61 female subjects, were recruited. We used SPECT with [123I]ADAM images to determine the SERT availability in the mid-brain, and measured the subjects’ IQ using the WAIS-R.

Results:

We found a significant positive correlation between the mid-brain SERT availability and the IQ of the participants. Even when controlling for age and sex, the significant association still existed.

Conclusion:

This result implied that the higher the SERT binding in the mid-brain, the better the IQ in healthy participants.

Association of striatal dopaminergic neuronal integrity with cognitive dysfunction and cerebral cortical metabolism in Parkinson's disease with mild cognitive impairment

OBJECTIVES

Cognitive impairment is a common non-motor feature of Parkinson's disease (PD). However, the underlying pathophysiology of cognitive decline is unclear. We investigated the association of striatal dopamine transporter (DAT) loss with cognitive function and cerebral cortical metabolism in PD.

METHODS

Twenty-eight patients (63.1 ± 7.1 yrs, M:F = 15:13) with advanced stage of PD were enrolled, including 15 (53.6%) diagnosed with mild cognitive impairment (MCI). All patients underwent FP-CIT PET/CT, neuropsychological tests, and FDG PET/CT within a 2-week interval. We calculated the specific to non-specific binding ratio on FP-CIT PET images in 12 striatal subregional VOIs, using one occipital VOI template as a reference. Age-adjusted normalized specific to non-specific binding ratios (%BRs) of striatal subregions were compared in two groups: PD with MCI versus PD (without cognitive impairment).

RESULTS

There were no statistical differences in age, age at onset, disease duration, motor symptoms, or level of education between the two groups. The PD with MCI had lower %BRs in all striatal subregions (P < 0.05) except the posterior putamen, compared with the PD. Striatal DAT availability correlated with frontal/executive function (r = 0.567, P = 0.003) and visuospatial function (r = 0.614, P = 0.001) but not with memory function. Dopamine transporter binding of striatal subregions also correlated with posterior cortical metabolism.

CONCLUSION

This study suggest that DAT loss in the striatum, except in the posterior putamen, is associated with cognitive dysfunction, specifically frontal/executive function and visuospatial function in PD subjects.

Single-site 123I-FP-CIT reference values from individuals with non-degenerative parkinsonism-comparison with values from healthy volunteers

Purpose

Iodine 123-radiolabeled 2β-carbomethoxy-3β-(4-iodophenyl)-N-(3-fluoropropyl) nortropane (¹²³I-FP-CIT) SPECT can be performed to distinguish degenerative forms of movement disorders/parkinsonism/tremor from other entities such as idiopathic tremor or drug-induced parkinsonism. For equivocal cases, semi-quantification and comparison to reference values are a necessary addition to visual interpretation of ¹²³I-FP-CIT scans. To overcome the challenges of multi-center recruitment and scanning of healthy volunteers, we generated ¹²³I-FP-CIT reference values from individuals with various neurological conditions but without dopaminergic degeneration, scanned at a single center on the same SPECT-CT system following the same protocol, and compared them to references from a multi-center database built using healthy volunteers’ data.

Methods

From a cohort of 1884 patients, we identified 237 subjects (120 men, 117 women, age range 16–88 years) through a two-stage selection process. Every patient had a final clinical diagnosis after a mean follow-up of 4.8 ± 1.3 years. Images were reconstructed using (1) Flash3D with scatter and CT-based attenuation corrections (AC) and (2) filtered back projection with Chang AC. Volume-of-interest analysis was performed using a commercial software to calculate specific binding ratios (SBRs), caudate-to-putamen ratios, and asymmetry values on different striatal regions. Generated reference values were assessed according to age and gender and compared with those from the ENC-DAT study, and their robustness was tested against a cohort of patients with different diagnoses.

Results

Age had a significant negative linear effect on all SBRs. Overall, the reduction rate per decade in SBR was between 3.80 and 5.70%. Women had greater SBRs than men, but this gender difference was only statistically significant for the Flash3D database. Linear regression was used to correct for age-dependency of SBRs and to allow comparisons to age-matched reference values and “normality” limits. Generated regression parameters and their 95% confidence intervals (CIs) were comparable to corresponding European Normal Control Database of DaTscan (ENC-DAT) results. For example, 95% CI mean slope for the striatum in women is − 0.015 ([− 0.019, − 0.011]) for the Flash3D database versus − 0.015 ([− 0.021, − 0.009]) for ENC-DAT. Caudate-to-putamen ratios and asymmetries were not influenced by age or gender.

Conclusion

The generated ¹²³I-FP-CIT references values have similar age-related distribution, with no increase in variance due to comorbidities when compared to values from a multi-center study with healthy volunteers. This makes it possible for sites to build their ¹²³I-FP-CIT references from scans acquired during routine clinical practice.

The Relationship Between the Striatal Dopaminergic Neuronal and Cognitive Function With Aging

Both cognitive function and striatal dopamine function decline by normal aging. However, the relationship among these three factors remains unclear. The aim of this study was to elucidate the association among age-related changes in the striatal dopamine transporter (DAT) and cognitive function in healthy subjects. The 30 healthy volunteers were enrolled in this research, the age ranged from 41 to 82 (64.5 ± 11.5, mean ± SD). All subjects were scanned with both T1-weighted magnetic resonance imaging (MRI) and ¹²³I-FP-CIT single-photon emission computed tomography (SPECT) images. The Wechsler Adult Intelligence Scale-Third Edition (WAIS-III) was used to evaluate cognitive function. Six spherical regions of interest (ROI) using 10 mm in diameter on the caudate nucleus, anterior putamen and posterior putamen were manually drawn on MRI image which was applied onto SPECT image. The relationship between striatal occipital ratio (SOR) values and WAIS-III subscore were analyzed by multiple regression analysis. Subscores which was significant were further analyzed by path analyses. Full intelligence quotient (IQ), verbal IQ, verbal comprehension were all positively correlated with age-adjusted striatal DAT binding (P < 0.01). Multiple regression analyses revealed that the coding digit symbol correlated with all striatal regions except for the left caudate (P < 0.04). Picture completion and right caudate, similarities and left caudate also showed a positive correlation (P < 0.04). Path analysis found that the right caudate and picture completion; the left caudate and similarities were correlated independently from age, whereas the models of coding digit symbol were not significant. These results suggest that age-based individual diversity of striatal DAT binding was associated with verbal function, and the caudate nucleus plays an important role in this association.

Reproducibility of the correlative triad among aging, dopamine receptor availability, and cognition

The evidence that dopamine function mediates the association between aging and cognition is one of the most cited findings in the cognitive neuroscience of aging. However, few and relatively small studies have directly examined these associations. Here we examined correlations among adult age, dopamine D2-like receptor (D2R) availability, and cognition in two cross-sectional studies of healthy human adults. Participants completed a short cognitive test battery and, on a separate day, a PET scan with either the high-affinity D2R tracer [18F]Fallypride (Study 1) or [11C]FLB457 (Study 2). Digit span, a measure of short-term memory maintenance and working memory, was the only cognitive test for which dopamine D2R availability partially mediated the age effect on cognition. In Study 1, age was negatively correlated with digit span. Striatal D2R availability was positively correlated with digit span controlling for age. The age effect on digit span was smaller when controlling for striatal D2R availability. Although other cognitive measures used here have individually been associated with age and D2R availability in prior studies, we found no consistent evidence for significant associations between low D2R availability and low cognitive performance on these measures. These results at best only partially supported the correlative triad of age, dopamine D2R availability, and cognition. While a wealth of other research in human and nonhuman animals demonstrates that dopamine makes critical contributions to cognition, the present studies suggest caution in interpreting PET findings as evidence that dopamine D2R loss is a primary cause of broad age-related declines in fluid cognition. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

The dopamine transporter VNTR polymorphism moderates the relationship between acute response to alcohol and future alcohol use disorder symptoms

Alcohol use disorder (AUD) is a genetically influenced disease with peak onset in young adulthood. Identification of factors that predict whether AUD symptoms will diminish or persist after young adulthood is a critical public health need. King and colleagues previously reported that acute response to alcohol predicted future AUD symptom trajectory. Genes associated with brain dopamine signaling, which underlies alcohol's rewarding effects, might influence this finding. This study analyzed whether variation at a variable number tandem repeat polymorphism in DAT1/SLC6A3, the gene encoding the dopamine transporter, moderated the predictive relationships between acute response to alcohol and future AUD symptoms among participants enrolled in the Chicago Social Drinking Project (first two cohorts). Heavy-drinking young adults (N = 197) completed an alcohol challenge, in which acute response (liking, wanting, stimulation, and sedation) was measured. Alcohol use disorder symptoms were assessed over the following 6 years. DAT1 genotype significantly moderated the interactions between follow-up time and alcohol liking (P = 0.006) and wanting (P = 0.006) in predicting future AUD symptoms. These predictive effects were strongest among participants who carried the DAT1 9-repeat allele, previously associated with enhanced striatal dopamine tone relative to the 10-repeat allele. Exploratory analyses indicated that DAT1 effects on the relationship between alcohol liking and AUD symptoms appeared stronger for females (n = 79) than males (n = 118) (P = 0.0496). These data suggest that heavy-drinking DAT1 9-repeat allele carriers who display high alcohol-induced reward in young adulthood may be predisposed to persistent AUD symptoms and support combining genotypic and phenotypic information to predict future AUD risk.

Lost in translational biology: Understanding sex differences to inform studies of diseases of the nervous system

Female and male humans are different. As simple and obvious as that statement is, in biomedical research there has been an historical tendency to either not consider sex at all or to only use males in clinical and in preclinical model system studies. The result is a large volume of research that reflects the average biology and pathology of males even though we know that disease risk, presentation, and response to therapies can be different between females and males. This is true, albeit to differing degrees, for virtually all neurological and psychiatric diseases. However, the days of ignoring sex as a biological variable are over - both because of the realization that genetic sex impacts brain function, and because of the 2014 mandate by the U.S. National Institutes of Health that requires that "sex as a biological variable" be addressed in each grant application. This review is written for neuroscientists who may not have considered sex as a biological variable previously but who now are navigating the best way to adapt their research programs to consider this important biology. We first provide a brief overview of the evidence that male versus female differences in the brain are biologically and clinically meaningful. We then present some fundamental principles that have been forged by a dedicated but small group of ground-breaking researchers along with a description of tools and model systems for incorporating a sex differences component into a research project. Finally, we will highlight some key technologies that, in the coming years, are likely to provide critical information about sex differences in the human brain.

Dopaminergic abnormalities following traumatic brain injury

Traumatic brain injury can reduce striatal dopamine levels. The cause of this is uncertain, but is likely to be related to damage to the nigrostriatal system. We investigated the pattern of striatal dopamine abnormalities using 123I-Ioflupane single-photon emission computed tomography (SPECT) scans and their relationship to nigrostriatal damage and clinical features. We studied 42 moderate-severe traumatic brain injury patients with cognitive impairments but no motor parkinsonism signs and 20 healthy controls. 123I-Ioflupane scanning was used to assess dopamine transporter levels. Clinical scan reports were compared to quantitative dopamine transporter results. Advanced MRI methods were used to assess the nigrostriatal system, including the area through which the nigrostriatal projections pass as defined from high-resolution Human Connectome data. Detailed clinical and neuropsychological assessments were performed. Around 20% of our moderate-severe patients had clear evidence of reduced specific binding ratios for the dopamine transporter in the striatum measured using 123I-Ioflupane SPECT. The caudate was affected more consistently than other striatal regions. Dopamine transporter abnormalities were associated with reduced substantia nigra volume. In addition, diffusion MRI provided evidence of damage to the regions through which the nigrostriatal tract passes, particularly the area traversed by dopaminergic projections to the caudate. Only a small percentage of patients had evidence of macroscopic lesions in the striatum and there was no relationship between presence of lesions and dopamine transporter specific binding ratio abnormalities. There was also no relationship between reduced volume in the striatal subregions and reduced dopamine transporter specific binding ratios. Patients with low caudate dopamine transporter specific binding ratios show impaired processing speed and executive dysfunction compared to patients with normal levels. Taken together, our results suggest that the dopaminergic system is affected by a moderate-severe traumatic brain injury in a significant proportion of patients, even in the absence of clinical motor parkinsonism. Reduced dopamine transporter levels are most commonly seen in the caudate and this is likely to reflect the pattern of nigrostriatal tract damage produced by axonal injury and associated midbrain damage.

Gender Effects in the Efficacy of Racemic Amphetamine Sulfate in Children with Attention-Deficit/Hyperactivity Disorder

Introduction

A laboratory classroom study in children aged 6–12 years with attention-deficit/hyperactivity disorder (ADHD) found that racemic amphetamine sulfate (RA-AMPH) significantly improved performance versus placebo from 45 min through 10 h post-dose (NCT01986062). A secondary analysis assessed gender as a potential moderator of response to treatment comparing the ADHD Rating Scale-IV (ADHD-RS-IV) and Swanson, Kotkin, Agler, M-Flynn and Pelham (SKAMP) rating scales.

Methods

After 8 weeks of open-label RA-AMPH dose optimization using improvement in ADHD-RS-IV symptoms as a guide, 97 subjects (38 females and 59 males) were randomized to the sequence of 2 weeks of double-blind treatment with the optimized dose of RA-AMPH followed by placebo or vice versa during a laboratory classroom day. Efficacy measures included the SKAMP and the Permanent Product Measure of Performance (PERMP). The average difference for RA-AMPH versus placebo was estimated using least-square (LS) means. Treatment interaction by gender was analyzed using a cross-sectional fixed-effects model.

Results

ADHD-RS-IV scores were comparable for males and females at study entry and at the end of open-label treatment. During double-blind treatment, LS mean scores significantly improved for both genders versus placebo on the SKAMP scale and the PERMP (average p < 0.0001 for all post-dose time points). Beginning at baseline, males had significantly higher (worse) SKAMP scores than females but not worse ADHD-RS-IV or PERMP scores.

Conclusion

Both genders responded well to treatment with RA-AMPH, with comparable onset and duration of effect. The ADHD-RS-IV and SKAMP scales both measure changes in attention and hyperactive-impulsive behavior, but the SKAMP scale also measures associated disruptive behaviors, such as frustration, lying, and interpersonal conflict, that are more characteristic of oppositional and conduct disorders and more prevalent in boys with ADHD. Therefore, the SKAMP may be more sensitive for measuring the range of symptoms of boys with ADHD than the ADHD-RS-IV.

Funding

Arbor Pharmaceuticals, LLC.

Behavioral and neural correlates of normal aging effects on motor preparatory mechanisms of speech production and limb movement

Normal aging is associated with decline of the sensorimotor mechanisms that support movement function in the human brain. In this study, we used behavioral and event-related potential (ERP) recordings to investigate the effects of normal aging on the motor preparatory mechanisms of speech production and limb movement. The experiment involved two groups of older and younger adults who performed randomized speech vowel vocalization and button press motor reaction time tasks in response to temporally predictable and unpredictable visual stimuli. Behavioral results revealed age-related slowness of motor reaction time only during speech production in response to temporally unpredictable stimuli, and this effect was accompanied by increased pre-motor ERP activities in older vs. younger adults during the speech task. These results indicate that motor preparatory mechanisms of limb movement during button press are not affected by normal aging, whereas the functional capacity of these mechanisms is reduced in older adults during speech production in response to unpredictable sensory stimuli. These findings suggest that the aging brain selectively compromises the motor timing of speech and recruits additional neural resources for motor planning and execution of speech, as indexed by the increased pre-motor ERP activations in response to temporally unpredictable vs. predictable sensory stimuli.

Investigating the perceived timing of sensory events triggering actions in patients with Parkinson's disease and the effects of dopaminergic therapy

Few studies have investigated if Parkinson's disease (PD), advancing age, or exogenous dopamine therapy affect the perceived timing of past events. Here we show a phenomenon of 'temporal repulsion' of a sensory event relative to an action decision in patients with PD. In these patients, the timing of a sensory event triggering an action was perceived to have occurred earlier in time than it really did. In other words, the event appeared to be pushed away in time from the performance of the action. This finding stands in sharp contrast to the 'temporal binding' we have observed here and elsewhere (Yabe et al., 2017; Yabe & Goodale, 2015) in young healthy participants for whom the perceived onset of a sensory event triggering an action is typically delayed, as if it were pulled towards the action in time. In elderly patients, sensory events were neither repulsed nor pulled toward the action decision event. Exogenous dopamine alleviated the temporal repulsion in PD patients and normalized the temporal binding in healthy elderly controls. In contrast, dopaminergic therapy worsened temporal binding in healthy young participants. We discuss this pattern of findings, relating temporal binding processes to dopaminergic and striatal mechanisms.

Sex-dependent regulation of social reward by oxytocin receptors in the ventral tegmental area

Social reward is critical for social relationships, and yet we know little about the characteristics of social interactions that are rewarding or the neural mechanisms underlying that reward. Here, we investigate the sex-dependent role of oxytocin receptors within the ventral tegmental area (VTA) in mediating the magnitude and valence of social reward. Operant and classical conditioning tests were used to measure social reward associated with same-sex social interactions. The effects of oxytocin, selective oxytocin receptor agonists, antagonists, and vehicle injected into the VTA on social reward was determined in male and female Syrian hamsters. The colocalization of FOS and oxytocin in sites that project to the VTA following social interaction was also determined. Females find same-sex social interactions more rewarding than males and activation of oxytocin receptors in the VTA is critical for social reward in females, as well as males. These studies provide support for the hypothesis that there is an inverted U relationship between the duration of social interaction and social reward, mediated by oxytocin; and that in females the dose-response relationship is initiated at lower doses compared with males. Same-sex social interaction is more rewarding in females than in males, and an inverted U relationship mediated by oxytocin may have a critical role in assigning positive and negative valence to social stimuli. Understanding these sex differences in social reward processing may be essential for understanding the sex differences in the prevalence of many psychiatric disorders and the development of gender-specific treatments of neuropsychiatric disorders.

Lack of consistent sex differences in D-amphetamine-induced dopamine release measured with [18F]fallypride PET

RATIONALE

Sex differences in the dopaminergic response to psychostimulants could have implications for drug abuse risk and other psychopathology involving the dopamine system, but human data are limited and mixed.

OBJECTIVES

Here, we sought to investigate sex differences in dopamine release after oral D-amphetamine administration.

METHODS

We used [¹⁸F]fallypride positron emission tomography (PET) to measure the change in dopamine D2/3 receptor availability (%ΔBP_ND, an index of dopamine release) between placebo and D-amphetamine sessions in two independent datasets containing a total of 39 females (on either hormonal birth control n = 18, postmenopausal n = 10, or studied in the first 10 days of their menstrual cycle n = 11) and 37 males.

RESULTS

Using both a priori anatomical regions of interest based on previous findings and voxelwise analyses, we failed to consistently detect broad sex differences in D-amphetamine-induced dopamine release. Nevertheless, there was limited evidence for greater right ventral striatal dopamine release in young adult males relative to similarly aged females, but this was not consistently observed across samples. Plasma estradiol did not correlate with dopamine release and this measure did not differ in females on and off hormonal birth control.

CONCLUSIONS

While our finding in young adults from one dataset of greater %ΔBP_ND in males is partially consistent with a previously published study on sex differences in D-amphetamine-induced dopamine release, our data do not support the presence of consistent widespread sex differences in this measure of dopamine release.

Sex-dependent regulation of social reward by oxytocin: an inverted U hypothesis

The rewarding properties of social interactions are essential for the expression of social behavior and the development of adaptive social relationships. Here, we review sex differences in social reward, and more specifically, how oxytocin (OT) acts in the mesolimbic dopamine system (MDS) to mediate the rewarding properties of social interactions in a sex-dependent manner. Evidence from rodents and humans suggests that same-sex social interactions may be more rewarding in females than in males. We propose that there is an inverted U relationship between OT dose, social reward, and neural activity within structures of the MDS in both males and females, and that this dose-response relationship is initiated at lower doses in females than males. As a result, depending on the dose of OT administered, OT could reduce social reward in females, while enhancing it in males. Sex differences in the neural mechanisms regulating social reward may contribute to sex differences in the incidence of a large number of psychiatric and neurodevelopmental disorders. This review addresses the potential significance of a sex-dependent inverted U dose-response function for OT's effects on social reward and in the development of gender-specific therapies for these disorders.