Gender differences in cerebellar metabolism: test-retest reproducibility

Quantitative but Not Qualitative Performance Changes in Predictive Motor Timing as a Result of Overtraining

The possibilities of substantial long-term improvement of predictive timing might be sometimes seen as limited, with scanty information of neural substrates underlying the potential learning process. To address this issue, we have investigated the performance of 21 baseball professionals and 21 matched controls in a predictive motor timing task previously shown to engage the cerebellum. Baseball players, hypothesized as a model of overtraining of the prediction of future state of the surroundings, showed significantly higher quantitative performance than nonathletic controls, with a substantial part of the baseball players reaching levels far beyond the range observed in common population. Furthermore, the qualitative performance profile of baseball players under various conditions as target speed and acceleration modes did not differ from the profile of healthy controls. Our results suggest that regular exigent training has the potential to vastly improve predictive motor timing. Moreover, the quantitative but not qualitative difference in the performance profile allows us to hypothesize that the selective honing of the same cerebellar processes and networks as in non-trained individuals is the substrate for the quantitative performance improvement, without substantial engagement of further neural nodes.

Relative Cerebellum Size Is Not Sexually Dimorphic across Primates

BACKGROUND/AIMS

Substantive sex differences in behavior and cognition are found in humans and other primates. However, potential sex differences in primate neuroanatomy remain largely unexplored. Here, we investigate sex differences in the relative size of the cerebellum, a region that has played a major role in primate brain evolution and that has been associated with cognitive abilities that may be subject to sexual selection in primates.

METHODS

We compiled individual volumetric and sex data from published data sources and used MCMC generalized linear mixed models to test for sex effects in relative cerebellar volume while controlling for phylogenetic relationships between species. Given that the cerebellum is a functionally heterogeneous structure involved in multiple complex cognitive processes that may be under selection in males or females within certain species, and that sexual selection pressures vary so greatly across primate species, we predicted there would be no sex difference in the relative size of the cerebellum across primates.

RESULTS

Our results support our prediction, suggesting there is no consistent sex difference in relative cerebellum size.

CONCLUSION

This work suggests that the potential for sex differences in relative cerebellum size has been subject to either developmental constraint or lack of consistent selection pressures, and highlights the need for more individual-level primate neuroanatomical data to facilitate intra- and inter-specific study of brain sexual dimorphism.

A Novel Function of the Lysophosphatidic Acid Receptor 3 (LPAR3) Gene in Zebrafish on Modulating Anxiety, Circadian Rhythm Locomotor Activity, and Short-Term Memory

Lysophosphatidic acid (LPA) is a small lysophospholipid molecule that activates multiple cellular functions through pathways with G-protein-coupled receptors. So far, six LPA receptors (LPAR1 to LPAR6) have been discovered and each one of them can connect to the downstream cell message-transmitting network. A previous study demonstrated that LPA receptors found in blood-producing stem cells can enhance erythropoietic processes through the activation of LPAR3. In the current study, newly discovered functions of LPAR3 were identified through extensive behavioral tests in lpar3 knockout (KO) zebrafish. It was found that the adult lpar3 KO zebrafish display an abnormal movement orientation and altered exploratory behavior compared to that of the control group in the three-dimensional locomotor and novel tank tests, respectively. Furthermore, consistent with those results, in the circadian rhythm locomotor activity test, the lpar3 KO zebrafish showed a lower level of angular velocity and average speed during the light cycles, indicating an hyperactivity-like behavior. In addition, the mutant fish also exhibited considerably higher locomotor activity during the dark cycle. Supporting those findings, this phenomenon was also displayed in the lpar3 KO zebrafish larvae. Furthermore, several important behavior alterations were also observed in the adult lpar3 KO fish, including a lower degree of aggression, less interest in conspecific social interaction, and looser shoal formation. However, there was no significant difference regarding the predator avoidance behavior between the mutant and the control fish. In addition, lpar3 KO zebrafish displayed memory deficiency in the passive avoidance test. These in vivo results support for the first time that the lpar3 gene plays a novel role in modulating behaviors of anxiety, aggression, social interaction, circadian rhythm locomotor activity, and memory retention in zebrafish.

Test-Retest Stability of Cerebral 2-Deoxy-2-[18F]Fluoro-D-Glucose ([18F]FDG) Positron Emission Tomography (PET) in Male and Female Rats

PURPOSE

An important issue in rodent imaging is the question whether a mixed population of male and female animals can be used rather than animals of a single sex. For this reason, the present study examined the test-retest stability of positron emission tomography (PET) with 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) in male rats and female rats at different phases of the estrous cycle.

PROCEDURES

Long-Evans rats (age 1 year) were divided into three groups: (1) males (n = 6), (2) females in metestrous (low estrogen levels, n = 9), and (3) females in proestrous (high estrogen levels, n = 7). Two standard [¹⁸F]FDG scans with rapid arterial blood sampling were made at an interval of 10 days in subjects anesthetized with isoflurane and oxygen. Body temperature, heart rate, and blood oxygenation were continuously monitored. Regional cerebral metabolic rates of glucose were calculated using a Patlak plot with plasma radioactivity as input function.

RESULTS

Regional metabolic rate of glucose (rCMR_glucose) in male and female rats, or [¹⁸F]FDG uptake in females at proestrous and metestrous, was not significantly different, but females showed significantly higher standardized uptake values (SUVs) and Patlak flux than males, particularly in the initial scan. The relative difference between the scans and the test-retest variability (TRV) were greater in females than in males. Intra-class correlation coefficients (ICCs) of rCMR_glucose, SUV, normalized SUV, and glucose flux were good to excellent in males but poor to moderate in females.

CONCLUSIONS

Based on these data for [¹⁸F]FDG, the mixing of sexes in imaging studies of the rodent brain will result in an impaired test-retest stability of PET data and a need for larger group sizes to maintain statistical power in group comparisons. The observed differences between males and females do not indicate any specific gender difference in cerebral metabolism but are related to different levels of non-radioactive glucose in blood plasma during isoflurane anesthesia.

Effects of lorazepam on saccadic eye movements: the role of sex, task characteristics and baseline traits

BACKGROUND

Saccadic eye movements are controlled by a network of parietal, frontal, striatal, cerebellar and brainstem regions. The saccadic peak velocity is an established biomarker of benzodiazepine effects, with benzodiazepines reliably reducing the peak velocity.

AIMS

In this study, we aimed to replicate the effects of benzodiazepines on peak velocity and we investigated effects on previously less studied measures of saccades. We also explored the roles of sex, task characteristics and the baseline variables age, intelligence and trait anxiety in these effects.

METHOD

Healthy adults ( N = 34) performed a horizontal step prosaccade task under 1 mg lorazepam, 2 mg lorazepam and placebo in a double-blind, within-subjects design.

RESULTS

We replicated the dose-dependent reduction in peak velocity with lorazepam and showed that this effect is stronger for saccades to targets at smaller eccentricities. We also demonstrated that this effect is independent of sex and other baseline variables. Lorazepam effects were widespread, however, occurring on mean and variability measures of most saccadic variables. Additionally, there were sex-dependent lorazepam effects on spatial consistency of saccades, indicating more adverse effects in females.

CONCLUSIONS

We conclude that saccadic peak velocity is a sensitive and robust biomarker of benzodiazepine effects. However, lorazepam has pronounced effects also on other parameters of horizontal saccades. Sex-dependent drug effects on spatial consistency may reflect cerebellar mechanisms, given the role of the cerebellum in saccadic spatial accuracy.

A sex difference in oxidative stress and behavioral suppression induced by ethanol withdrawal in rats

Ethanol withdrawal (EW) is referred to the abrupt termination of long-term heavy drinking, and provokes oxidative brain damage. Here, we investigated whether the cerebellum and hippocampus of female rats are less affected by prooxidant EW than male rats due to the antioxidant effect of 17β-estradiol (E2). Female and male rats received a four-week ethanol diet and three-week withdrawal per cycle for two cycles. Some female rats were ovariectomized with E2 or antioxidant (Vitamin E+Co-Q10) treatment. Measurements were cerebellum (Rotarod) and hippocampus (water-maze)-related behaviors, oxidative markers (O2(-), malondialdehyde, protein carbonyls), mitochondrial membrane swelling, and a key mitochondrial enzyme, cytochrome c oxidase (CcO). Separately, HT22 (hippocampal) cells were subjected to ethanol-exposure and withdrawal for two cycles to assess the effect of a CcO inhibitor on E2's protection for mitochondrial respiration and cell viability. Ethanol-withdrawn female rats showed a smaller increase in oxidative markers in cerebellum and hippocampus than male rats, and E2 treatment decreased the oxidative markers. Compared to male counterparts, ethanol-withdrawn female rats showed better Rotarod but poorer water-maze performance, accompanied by more severe mitochondrial membrane swelling and CcO suppression in hippocampus. E2 or antioxidant treatment improved Rotarod but not water-maze performance. In the presence of a CcO inhibitor, E2 treatment failed to protect mitochondrial respiration and cell viability from EW. These data suggest that antioxidant E2 contributes to smaller oxidative stress in ethanol-withdrawn female than male rats. They also suggest that EW-induced severe mitochondrial damage in hippocampus may blunt E2's antioxidant protection for hippocampus-related behavior.

Sexual dimorphisms in swimming behavior, cerebral metabolic activity and adrenoceptors in adult zebrafish (Danio rerio)

Sexually dimorphic behaviors and brain sex differences, not only restricted to reproduction, are considered to be evolutionary preserved. Specifically, anxiety related behavioral repertoire is suggested to exhibit sex-specific characteristics in rodents and primates. The present study investigated whether behavioral responses to novelty, have sex-specific characteristics in the neurogenetic model organism zebrafish (Danio rerio), lacking chromosomal sex determination. For this, aspects of anxiety-like behavior (including reduced exploration, increased freezing behavior and erratic movement) of male and female adult zebrafish were tested in a novel tank paradigm and after habituation. Male and female zebrafish showed significant differences in their swimming activity in response to novelty, with females showing less anxiety spending more time in the upper tank level. When fish have habituated, regional cerebral glucose uptake, an index of neuronal activity, and brain adrenoceptors' (ARs) expression (α2-ARs and β-ARs) were determined using in vivo 2-[(14)C]-deoxyglucose methodology and in vitro neurotransmitter receptors quantitative autoradiography, respectively. Intriguingly, females exhibited higher glucose utilization than males in hypothalamic brain areas. Adrenoceptor's expression pattern was dimorphic in zebrafish telencephalic, preoptic, hypothalamic nuclei, central gray, and cerebellum, similarly to birds and mammals. Specifically, the lateral zone of dorsal telencephalon (Dl), an area related to spatial cognition, homologous to the mammalian hippocampus, showed higher α2-AR densities in females. In contrast, male cerebellum included higher densities of β-ARs in comparison to female. Taken together, our data demonstrate a well-defined sex discriminant cerebral metabolic activity and ARs' pattern in zebrafish, possibly contributing to male-female differences in the swimming behavior.

Neural Network of Predictive Motor Timing in the Context of Gender Differences

Time perception is an essential part of our everyday lives, in both the prospective and the retrospective domains. However, our knowledge of temporal processing is mainly limited to the networks responsible for comparing or maintaining specific intervals or frequencies. In the presented fMRI study, we sought to characterize the neural nodes engaged specifically in predictive temporal analysis, the estimation of the future position of an object with varying movement parameters, and the contingent neuroanatomical signature of differences in behavioral performance between genders. The established dominant cerebellar engagement offers novel evidence in favor of a pivotal role of this structure in predictive short-term timing, overshadowing the basal ganglia reported together with the frontal cortex as dominant in retrospective temporal processing in the subsecond spectrum. Furthermore, we discovered lower performance in this task and massively increased cerebellar activity in women compared to men, indicative of strategy differences between the genders. This promotes the view that predictive temporal computing utilizes comparable structures in the retrospective timing processes, but with a definite dominance of the cerebellum.

Brain: normal variations and benign findings in fluorodeoxyglucose-PET/computed tomography imaging

Brain 18F-fluorodeoxyglucose (18F-FDG) PET allows the in vivo study of cerebral glucose metabolism, reflecting neuronal and synaptic activity. 18F-FDG-PET has been extensively used to detect metabolic alterations in several neurologic diseases compared with normal aging. However, healthy subjects have variants of 18F-FDG distribution, especially as associated with aging. This article focuses on 18F-FDG-PET findings in so-called normal brain aging, and in particular on metabolic differences occurring with aging and as a function of people’s gender. The effect of different substances, medications, and therapy procedures are discussed, as well as common artifacts.

Assessment of dementia risk in aging adults using both FDG-PET and FDDNP-PET imaging

BACKGROUND

In a previous study, positron emission tomography (PET) with 2-(1-{6-[(2-[F-18]fluoroethyl)(methyl)amino]-2-naphthyl}ethylidene)malononitrile (FDDNP), a molecule that binds to plaques and tangles in vitro, identified three subgroups of non-demented subjects according to FDDNP binding patterns: low global (LG) binding; high frontal, parietal, medial temporal binding (HF/PA); and high medial and lateral temporal and posterior cingulate (HT/PC) binding. In this follow-up investigation, we compared 2-deoxy-2-[F-18]fluoro- d-glucose (FDG)-PET cerebral metabolic patterns in the three FDDNP-PET binding subgroups.

METHODS

Fifty-four subjects with normal aging (N = 28) or amnestic forms of mild cognitive impairment (N = 26) underwent FDDNP-PET and FDG-PET scanning. Subjects in the LG, HF/PA, and HT/PC FDDNP subgroups were compared according to visual ratings, statistical parametric mapping, and automated region of interest analyses of their FDG-PET data.

RESULTS

The FDDNP-PET subgroups demonstrated different glucose metabolic patterns according to visual ratings, region of interest, and statistical parametric mapping analyses of FDG-PET data. The LG FDDNP subgroup showed no areas of significant hypometabolism relative to the other subgroups and had low Alzheimer's disease risk by FDG-PET standards. The HF/PA FDDNP subgroup demonstrated hypometabolism in bilateral inferior parietal/parietotemporal, bilateral posterior cingulate, perisylvian, mid-temporal gyrus, and dorsolateral prefrontal regions, which is a pattern suggestive of high Alzheimer's disease risk. The HT/PC FDDNP subgroup demonstrated heterogeneous FDG-PET patterns with predominant anterior frontal and anterior temporal hypometabolism, suggestive of mixed etiologies, including fronto-temporal dementia risk.

CONCLUSIONS

The FDG-PET data provided independent validation that different patterns of FDDNP-PET binding in non-demented individuals may be associated with differential dementia risk.

Sex- and age-related differences in brain FDG metabolism of healthy adults: an SPM analysis

BACKGROUND AND PURPOSE

The purpose of our study was aimed to analyze the sex- and age-related differences of brain metabolism in healthy individuals.

METHODS

Consecutive 100 healthy subjects, 50 males and 50 females, undergoing routine 2-[(18)F]-fluoro-2-deoxy-d-glucose positron emission tomography (FDG PET) for health checkup in our hospital were retrospectively enrolled in this study. Statistical parametric mapping (SPM) was used for analyses of the FDG PET images to disclose the possible effects of age on brain metabolism in males and females as well as the differences of brain metabolism between male and female groups.

RESULTS

In males and females, decreased brain metabolism with aging is found in bilateral lateral orbital prefrontal and right anterior cingulate cortices. In comparisons between sexes, males are found to have more brain metabolism than females in bilateral visual cortices and cerebellum.

CONCLUSIONS

Our report discloses different sex- and age-related brain metabolism. Decreased brain metabolism with aging in males and females is similar to findings reported in previous literatures. However, whether declined brain function or volume with aging causing metabolic changes is unknown and should be further evaluated. Nevertheless, the sex-related differences are possibly compatible with the historical observation of better performance in visual-spatial tasks in males than females.

Developmental PCB exposure induces hypothyroxinemia and sex-specific effects on cerebellum glial protein levels in rats

Polychlorinated biphenyls (PCBs) are persistent lipophilic environmental contaminants which are found in fatty tissues of humans and wild-life alike. Maternal transfer of PCBs to offspring is easily achieved across the placenta and via lactation. In male rats, perinatal PCB exposure induces behavioral abnormalities, in addition to hypothyroxinemia and white matter changes. There are sex differences in white matter volume synthesis and density in adult and aged rodents. Yet whether PCB exposure effects on white matter are sex-specific is unclear, because the previous studies were conducted in male offspring. Furthermore, although hypothyroxinemia induced by PCB exposure is thought to trigger white matter changes, PCBs also affect interleukin-6 (IL-6) expression, and IL-6 regulates white matter growth. We hypothesized that perinatal PCB exposure would have sex-specific effects on white matter development associated with altered IL-6 levels. We found that female offspring had higher levels of myelin basic protein (MBP) than males did, at postnatal day (PND) 7, 18 and 21. PCB exposure induced hypothyroxinemia in males and females at PND7, 14, 21, and 42. PCB exposure also increased MBP and reduced glial fibrillary acidic protein (GFAP) levels in males at PND21, but had the opposite effect in females. In addition, at PND14 and 21, PCB exposure elevated IL-6 levels in male offspring only. The induction of sex-specific changes in white matter proteins, in the absence of sex differences in thyroxine levels after PCB exposure, suggests that serum thyroxine levels do not directly contribute to the white matter alterations. Instead, IL-6 may contribute to increased MBP levels in males, whereas in females estromimetic and thyromimetic PCB metabolites may affect white matter development. This data adds to an increasing body of literature showing that perinatal insults induce sex-specific effects in offspring.

Variation in orbitofrontal cortex volume: relation to sex, emotion regulation and affect

Sex differences in brain structure have been examined extensively but are not completely understood, especially in relation to possible functional correlates. Our two aims in this study were to investigate sex differences in brain structure, and to investigate a possible relation between orbitofrontal cortex subregions and affective individual differences. We used tensor-based morphometry to estimate local brain volume from MPRAGE images in 117 healthy right-handed adults (58 female), age 18-40 years. We entered estimates of local brain volume as the dependent variable in a GLM, controlling for age, intelligence and whole-brain volume. Men had larger left planum temporale. Women had larger ventromedial prefrontal cortex (vmPFC), right lateral orbitofrontal (rlOFC), cerebellum, and bilateral basal ganglia and nearby white matter. vmPFC but not rlOFC volume covaried with self-reported emotion regulation strategies (reappraisal, suppression), expressivity of positive emotions (but not of negative), strength of emotional impulses, and cognitive but not somatic anxiety. vmPFC volume statistically mediated sex differences in emotion suppression. The results confirm prior reports of sex differences in orbitofrontal cortex structure, and are the first to show that normal variation in vmPFC volume is systematically related to emotion regulation and affective individual differences.

Steroids, sex and the cerebellar cortex: implications for human disease

Neurosteroids play an important role in the development of the cerebellum. In particular, estradiol and progesterone appear capable of inducing increases in dendritic spine density during development, and there is evidence that both are synthesized de novo in the cerebellum during critical developmental periods. In normal neonates and adults, there are few differences in the cerebellum between the sexes and most studies indicate that hormone and receptor levels also do not differ significantly during development. However, the sexes do differ significantly in risk of neuropsychological diseases associated with cerebellar pathology, and in animal models there are noticeable sex differences in the response to insult and genetic mutation. In both humans and animals, males tend to fare worse. Boys are more at risk for autism and Attention Deficit Hyperactivity Disorder than girls, and schizophrenia manifests at an earlier age in men. In rats males fare worse than females after perinatal exposure to polychlorinated biphenyls, and male mice heterozygous for the staggerer and reeler mutation show a more severe phenotype. Although very recent evidence suggests that differences in neurosteroid levels between the sexes in diseased animals may play a role in generating different disease phenotypes, the reason this hormonal difference occurs in diseased but not normal animals is currently unknown.

Brain development, environment and sex: what can we learn from studying graviperception, gravitransduction and the gravireaction of the developing CNS to altered gravity?

As man embarks on space exploration and contemplates space habitation, there is a critical need for basic understanding of the impact of the environmental factors of space, and in particular gravity, on human survival, health, reproduction and development. This review summarizes our present knowledge on the effect of altered gravity on the developing CNS with respect to the response of the developing CNS to altered gravity (gravireaction), the physiological changes associated with altered gravity that could contribute to this effect (gravitransduction), and the possible mechanisms involved in the detection of altered gravity (graviperception). Some of these findings transcend gravitational research and are relevant to our understanding of the impact of environmental factors on CNS development on Earth.

Changes in glucose metabolism due to aging and gender-related differences in the healthy human brain

Using [(18)F]fluoro-deoxy-glucose-PET, we studied relative metabolic changes due to age- and gender-related differences in the brain of 126 healthy subjects from their twenties to seventies. We used a data-extraction technique, the three-dimensional stereotactic surface projections (3D-SSP) method, to measure metabolic changes with fewer effects of regional anatomic variances. Simple regression analysis revealed significant age-related increases in relative metabolic values in the parahippocampal and amygdala regions in both sexes in their twenties to forties, and significant age-related decreases in both sexes in their fifties to seventies. Relative values in the frontal lobe showed significant age-related decreases in both sexes in their twenties to forties, but these effects were not seen in subjects in their fifties to seventies. Significant gender differences in correlation coefficients of relative values with age were shown in the parahippocampal, primary sensorimotor, temporal, thalamus and vermis regions in subjects in their 20s to 40s, but disappeared in subjects in their twenties to forties, but were not apparent in subjects in their fifties to seventies except in the vermis. Males in their twenties to sixties and females in their fifties showed significant laterality in relative values in the temporal lobes. Our study demonstrated age- and gender-related differences in glucose metabolism in healthy subjects.

Lifelong consumption of sodium selenite: gender differences on blood-brain barrier permeability in convulsive, hypoglycemic rats

The aim of this study was to compare the effects of hypoglycemia and induced convulsions on the blood-brain barrier permeability in rats with or without lifelong administration of sodium selenite. There is a significant decrease of the blood-brain barrier permeability in three brain regions of convulsive, hypoglycemic male rats treated with sodium selenite when compared to sex-matched untreated rats (p<0.05), but the decrease was not significant in female rats (p>0.05). The blood-brain barrier permeability of the left and right hemispheres of untreated, moderately hypoglycemic convulsive rats of both genders was better than their untreated counterparts (p<0.05). Our results suggest that moderate hypoglycemia and lifelong treatment with sodium selenite have a protective effect against blood-brain barrier permeability during convulsions and that the effects of sodium selenite are gender-dependent.

A sex-specific metabolite identified in a marine invertebrate utilizing phosphorus-31 nuclear magnetic resonance

Hormone level differences are generally accepted as the primary cause for sexual dimorphism in animal and human development. Levels of low molecular weight metabolites also differ between men and women in circulating amino acids, lipids and carbohydrates and within brain tissue. While investigating the metabolism of blue crab tissues using Phosphorus-31 Nuclear Magnetic Resonance, we discovered that only the male blue crab (Callinectes sapidus) contained a phosphorus compound with a chemical shift well separated from the expected phosphate compounds. Spectra obtained from male gills were readily differentiated from female gill spectra. Analysis from six years of data from male and female crabs documented that the sex-specificity of this metabolite was normal for this species. Microscopic analysis of male and female gills found no differences in their gill anatomy or the presence of parasites or bacteria that might produce this phosphorus compound. Analysis of a rare gynandromorph blue crab (laterally, half male and half female) proved that this sex-specificity was an intrinsic biochemical process and was not caused by any variations in the diet or habitat of male versus female crabs. The existence of a sex-specific metabolite is a previously unrecognized, but potentially significant biochemical phenomenon. An entire enzyme system has been synthesized and activated only in one sex. Unless blue crabs are a unique species, sex-specific metabolites are likely to be present in other animals. Would the presence or absence of a sex-specific metabolite affect an animal's development, anatomy and biochemistry?

Advances in the neurobiology of ADHD

Attention-deficit/hyperactivity disorder (ADHD) is a lifelong condition that begins in childhood and continues with adult manifestations related to the core symptoms. Approximately 50% to 75% of children with ADHD continue to meet criteria for the disorder as adolescents and adults. Adults with the disorder increasingly present to primary care physicians, psychiatrists, and other practitioners for diagnosis and treatment. Understanding the diagnosis of ADHD in adults requires knowledge of age-dependent decline of symptoms over time. Retrospective recall of symptoms and impairment are valid methods of diagnosing the disorder. ADHD is also a brain disorder with a strong neurobiologic basis, complex etiology, and genetic component. Genetic and environmental vulnerabilities give rise to abnormalities in the brain and subsequent behavioral and cognitive deficits, which may produce the symptoms associated with ADHD. Magnetic resonance imaging studies of ADHD have provided evidence that abnormalities in the brain are caused by the disorder itself rather than treatment of the disorder. Psychiatric comorbidity is common among patients with ADHD and tends to complicate treatment. Acute and long-term use of long-acting stimulant formulations (methylphenidate and amphetamine compounds) have shown robust efficacy and tolerability consistent with the treatment response established in children with ADHD. Non-stimulant medications have demonstrated efficacy as well, and may be preferred in patients with tic and substance use disorders.

In this expert roundtable supplement, Timothy E. Wilens, MD, reviews the epidemiology and clinical presentation of adult ADHD. Next, Joseph Biederman, MD, provides an overview of recent advances in the neurobiology of ADHD. Thomas J. Spencer, MD, reviews stimulant treatment of adult ADHD, and Lenard A. Adler concludes with a discussion of non-stimulant trials in adult ADHD.

Brain FDG PET study of normal aging in Japanese: effect of atrophy correction

PURPOSE

The aim of this study was to investigate the effects of atrophy correction on the results of 18F-fluorodeoxyglucose positron emission tomography (FDG PET) in the context of normal aging.

METHODS

Before the human study was performed, a Hoffman 3D brain phantom experiment was carried out in order to validate a newly developed correction method for partial volume effects (PVEs). Brain FDG PET was then performed in 139 healthy Japanese volunteers (71 men, 68 women; age 24-81 years). PET images were corrected for PVEs using grey matter volume, which was segmented from co-registered magnetic resonance images and convoluted with the spatial resolution of the PET scanner. We investigated the correlation between advancing age and relative regional FDG activity, which was normalised to the global activity before and after PVE correction using Statistical Parametric Mapping 99.

RESULTS

The PET image, when corrected for PVEs, provided more homogeneous tracer distribution in the whole phantom than in the original PET image. The human PET study of both sexes revealed significant negative correlations between age and relative FDG activity in the bilateral perisylvian and medial frontal areas before PVE correction. However, these negative correlations were largely resolved after PVE correction.

CONCLUSION

Correction for PVEs was effective in our FDG PET study. The reduction in FDG uptake with advancing age that was detected by FDG PET without PVE correction could be accounted for largely by an age-related cerebral volume loss in the bilateral perisylvian and medial frontal areas.

Gender difference in brain perfusion 99mTc-ECD SPECT in aged healthy volunteers after correction for partial volume effects

BACKGROUND

Previous reports have yielded controversial results concerning gender differences in regional cerebral blood flow (rCBF). To elucidate this issue, we compared 99mTc ethyl cysteinate dimer single photon emission computed tomography (SPECT) images for brain perfusion between aged-matched healthy men and women after correction for partial volume effects (PVEs).

METHODS

Brain perfusion SPECT in the resting state was performed on 40 healthy, right-handed subjects, 20 men and 20 women, with an age range of 58-86 years, who did not differ sociodemographically. PVE correction was performed using grey matter volume measured by magnetic resonance imaging. Statistical parametric mapping was used for the analysis of the adjusted rCBF images of relative flow distribution.

RESULTS

The PVE correction revealed that women had higher rCBF in left inferior frontal gyrus, bilateral middle temporal gyri, and left superior temporal gyrus. Men had higher rCBF in left superior frontal gyrus, right medial frontal gyrus, right superior parietal lobule, right postcentral gyrus, right cerebellum, right middle frontal gyrus, right fusiform gyrus, and right precuneus.

CONCLUSION

Significant gender differences in rCBF existed in these healthy volunteers. The PVE correction of SPECT images revealed gender differences that were consistent with the universal findings of better performance on verbal tasks in women and on visuospatial tasks in men.

Sexual dimorphism in cerebellar structure, function, and response to environmental perturbations

Sexual dimorphism of CNS structure and function has been observed in humans and animals, but remains relatively unrecognized in the context of the cerebellum. Recent research in our laboratory has examined whether these gender differences extend to cerebellar structure and function, as well as the impact of environmental factors on the developing cerebellum. Perinatal exposure to both chemical and physical perturbations in the environment (in our experiments, PCBs or hypergravity) affects growth, neurodevelopment, and motor coordination differently in males and females. These neurodevelopmental and behavioral effects are accompanied by sex-related changes in cerebellar mass and cerebellar protein expression. Exposure to chemical toxins (PCBs) resulted in more dramatic neurodevelopmental and behavioral changes in male neonates. It is possible that gender-related differences in male and female cerebellar structure and function are related to sex-specific development of the cerebellum and sex-specific distribution of specific receptors, local synthesis of trophic factors, and maturation of the pituitary hypophesial axis. These sex-related differences may underlie the sex-specific preponderance of certain neuropsychiatric disorders, and must be incorporated in the design of future basic and clinical investigations.

Gender differences in cerebral glucose metabolism: a PET study

OBJECTIVE

Some studies have examined gender differences in brain function based on cerebral blood flow and cerebral metabolism by using positron emission tomography (PET). However, the findings of these studies are controversial and most of them were analyzed by the regions of interest (ROIs) method. Here, we evaluated gender differences of cerebral glucose metabolism under the resting state in a voxel-based analysis.

METHODS

We studied 44 healthy volunteers (22 females, 63.0+/-6.3 years, and 22 males, 63.1+/-8.4 years). Cerebral glucose metabolic images were obtained with (18)F-fluorodeoxyglucose (FDG) and PET. All individual data were transformed to standard brain space and the male and female groups were compared using statistical parametric mapping (SPM).

RESULTS

The males had significantly higher glucose metabolism in the right insula, middle temporal gyrus, and medial frontal lobe than the females. Glucose metabolism in the hypothalamus was significantly higher in females than in males. There was a significant correlation between aging and glucose metabolism in the left thalamus in males and in the left caudate nucleus and hypothalamus in females. In males, but not females, there was a significant asymmetry between the bilateral hemispheres.

CONCLUSION

We found that there were obvious gender differences in regional cerebral glucose metabolism and this is the first report of higher glucose metabolism in the hypothalamus in females than in males.

Age, sex and laterality effects on cerebral glucose metabolism in healthy adults

Normal cerebral glucose metabolism (CMRglc) was assessed with positron emission tomography in 66 healthy adults (28 women, 38 men; mean age 39, range 20--69 years) to determine effects of age, sex and laterality on CMRglc using statistical parametric mapping. Significant age-related decreases in global metabolism (gCMRglc) were noted in the entire sample and in both sexes, as well as widespread and bilateral decreases in cortical absolute regional metabolism (rCMRglc) and more focal anterior paralimbic normalized rCMRglc. However, significant positive correlations of age with normalized rCMRglc were observed in cerebellum, thalamus and occipital areas. Although the declines in gCMRglc and rCMRglc with age did not significantly differ between sexes, men compared with women had significantly lower gCMRglc and widespread decreased cortical and subcortical absolute rCMRglc. In the entire sample, and similarly in both sexes, left greater than right asymmetry was observed in medial frontal gyrus, posterior thalamus, lingual gyrus, cuneus and superior cingulate. The opposite laterality appeared in mesio-anterior cerebellum, and lateral frontal and temporal regions. Few regions showed significant interactions of metabolic laterality with either age or sex. These findings contribute toward a convergence in the literature, and the regression models of CMRglc vs. age serve as a normative database to which patients may be compared.

Sex-related differences in the muscarinic acetylcholinergic receptor in the healthy human brain--a positron emission tomography study

We evaluated the sex-related differences in the decline of the cerebral muscarinic acetylcholinergic receptor (mACh-R) due to aging by using 11C-N-methyl-4-piperidyl benzilate (11C-NMPB) and positron emission tomography (PET). The subjects consisted of 37 (20 males and 17 females) healthy volunteers. The 11C-NMPB uptake was evaluated by the ratio method (regional 11C-NMPB uptake/Cerebellar 11C-NMPB uptake; rNMPB ratio). The correlation between sex, aging, and the rNMPB ratio in normal aging was evaluated by a multiple regression analysis. The rNMPB ratio was higher in females than in males throughout the entire cerebral region (p < 0.01-p < 0.0001) and the rNMPB ratio might thus possibly decline with age more rapidly in females. Our study therefore revealed the existence of sex-related differences in the cerebral mACh-R.

Gender differences in regional cerebral activity during sadness

Functional magnetic resonance imaging and echo-planar-imaging were used to investigate affect related gender differences in regional cerebral activity. The experiment was conducted using a standardized mood induction procedure. Blood-oxygen-level-dependent effect was measured in 13 male and 13 female healthy subjects, during both moods of happiness and sadness, respectively. Parallel to earlier neuroimaging findings, our results show brain activity in the amygdala of males during negative affect. Females failed to demonstrate a similar activation pattern despite matched subjective ratings of negative affect to males. Results point to differential regional cerebral correlates of emotional experience in males and females, which is suggestive of a more focal and subcortical processing of sadness in men.

Brain opioid receptor measurements by positron emission tomography in normal cycling women: relationship to luteinizing hormone pulsatility and gonadal steroid hormones

The regulation of central mu-opioid receptors in women during the menstrual cycle was explored with positron emission tomography and the selective radiotracer [11C]carfentanil. Ten healthy women were studied twice, during their follicular and luteal phases. Plasma concentrations of estradiol, progesterone, testosterone, and beta-endorphin were determined immediately before scanning. LH pulsatility was measured over the 9 h preceding each of the two positron emission tomography scans. No significant differences in the binding potential of mu-opioid receptors (binding capacity/Kd) were observed between phases of the menstrual cycle. However, significant negative correlations were observed between circulating levels of estradiol during the follicular phase and mu-receptor binding measures in the amygdala and hypothalamus, two regions thought to be involved in the regulation of GnRH pulsatility. LH pulse amplitude was positively correlated with mu binding in the amygdala, whereas LH pulse number was negatively correlated with binding in this same region. No significant associations were noted between LH pulse measures and the hypothalamus for this sample. These results suggest that amygdalar mu-opioid receptors exert a modulatory effect on GnRH pulsatility, and that circulating levels of estradiol also regulate central mu-opioid function.

Effects of healthy aging on the regional cerebral metabolic rate of glucose assessed with statistical parametric mapping

The aging process is thought to result in changes in synaptic activity reflecting both functional and structural cell derangement. However, previous PET reports on age-related changes in resting brain glucose utilization (CMRglc) have been discrepant, presumably because of methodological as well as subject screening differences. In contrast to other studies, which used a region of interest approach, the objective of the present work was to determine, by means of the SPM software, the changes in regional CMRglc as a function of age in 24 optimally healthy, unmedicated volunteers of ages from 20 to 67 years. Global CMRglc showed a significant decline with age (approximately 6% per decade, P < 0.05), which concerned all the voxels studied save for most of the occipital cortex and part of the cerebellum. The most significant effects (P < 0.001) concerned the association neocortex in perisylvian temporoparietal and anterior temporal areas, the insula, the inferior and posterior-lateral frontal regions, the anterior cingulate cortex, the head of caudate nucleus, and the anterior thalamus, in a bilateral and essentially symmetrical fashion. The high posterior parietal cortex was not sampled in this study. This distribution of changes in CMRglc with age may differ from that seen in Alzheimer' disease, where the earliest metabolic reduction has been shown to affect the posterior cingulate cortex.

A review of functional neuroimaging in mood disorders: positron emission tomography and depression

OBJECTIVE

To examine the progress of positron emission tomography (PET) as a tool for understanding the psychobiology of mood disorders, particularly major depression and bipolar disorder.

METHOD

Review of the literature on functional imaging of mood disorders.

RESULTS

Functional imaging techniques have been used in psychiatric research as a noninvasive method to study the behaviour and function of the brain. Techniques used so far have involved the manipulation of emotion in healthy volunteers, the evaluation of depressed (unipolar and bipolar as well as secondary depression), manic, and normal subjects under resting and various activation conditions, such as cognitive activation, acute pharmacological challenge, and chronic thymoleptic treatments. As a result, functional imaging studies tend to support abnormalities in specific frontal and limbic regions.

CONCLUSION

Different PET methods demonstrate consistent abnormalities in the prefrontal, cingulate, and amygdala regions. These findings are in agreement with past animal and clinical anatomical correlates of mood and emotions.