Effect of gender on glucose utilization rates in healthy humans: a positron emission tomography study

Sex Differences in the Effect of Diabetes on Cerebral Glucose Metabolism

The neuroimaging literature indicates that brain structure and function both deteriorate with diabetes, but information on sexual dimorphism in diabetes-related brain alterations is limited. This study aimed to ascertain whether brain metabolism is influenced by sex in an animal model of diabetes. Eleven rats (male, n = 5; female, n = 6) received a single intraperitoneal injection of 70 mg/kg streptozotocin (STZ) to develop diabetes. Another 11 rats (male, n = 5; female, n = 6) received the same amount of solvent through a single intraperitoneal injection. Longitudinal positron emission tomography scans were used to assess cerebral glucose metabolism before and 4 weeks after STZ or solvent administration. Before STZ or solvent injections, there was no evidence of sexual dimorphism in cerebral metabolism (p > 0.05). Compared with healthy control animals, rats with diabetes had significantly decreased brain metabolism in all brain regions (all p < 0.05). In addition, female diabetic rats exhibited further reduction in cerebral metabolism, relative to male diabetic rats (p < 0.05). The results of this study may provide some biological evidence, supporting the existence of a sexual dimorphism in diabetes-related complications.

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.

Gender-Based Cerebral Perfusion Differences in 46,034 Functional Neuroimaging Scans

BACKGROUND

Studies have reported that females have widespread increases in regional cerebral blood flow, but the studies were relatively small and inconsistent.

OBJECTIVE

Here we analyzed a healthy and a very large clinical psychiatric population to determine the effect of gender, using single photon emission computed tomography (SPECT).

METHODS

Whole brain and region of interest (ROI) gender differences were analyzed in a total of 46,034 SPECT scans at baseline and concentration. The sample included 119 healthy subjects and 26,683 patients (60.4% male, 39.6% female); a subset of 11,587 patients had complete diagnostic information. A total of 128 regions were analyzed according to the AAL Atlas, using ROI Extract and SPSS statistical software programs, controlling for age, diagnoses, and correcting for multiple comparisons.

RESULTS

Compared to males, healthy females showed significant whole brain (p < 0.01) and ROI increases in 65 baseline and 48 concentration regions (p < 0.01 corrected). Healthy males showed non-significant increases in 9 and 22 regions, respectively. In the clinical group, there were widespread significant increases in females, especially in the prefrontal and limbic regions, and specific increases in males in the inferior occipital lobes, inferior temporal lobes, and lobule 7 and Crus 2 of the cerebellum. These findings were replicated in the subset of 11,587 patients with the effect of diagnoses removed.

CONCLUSIONS

Our results demonstrated significant gender differences in a healthy and clinical population. Understanding these differences is crucial in evaluating functional neuroimaging and may be useful in understanding the epidemiological gender differences among psychiatric disorders.

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.

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.

Estrogen: a master regulator of bioenergetic systems in the brain and body

Estrogen is a fundamental regulator of the metabolic system of the female brain and body. Within the brain, estrogen regulates glucose transport, aerobic glycolysis, and mitochondrial function to generate ATP. In the body, estrogen protects against adiposity, insulin resistance, and type II diabetes, and regulates energy intake and expenditure. During menopause, decline in circulating estrogen is coincident with decline in brain bioenergetics and shift towards a metabolically compromised phenotype. Compensatory bioenergetic adaptations, or lack thereof, to estrogen loss could determine risk of late-onset Alzheimer's disease. Estrogen coordinates brain and body metabolism, such that peripheral metabolic state can indicate bioenergetic status of the brain. By generating biomarker profiles that encompass peripheral metabolic changes occurring with menopause, individual risk profiles for decreased brain bioenergetics and cognitive decline can be created. Biomarker profiles could identify women at risk while also serving as indicators of efficacy of hormone therapy or other preventative interventions.

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.

Alterations in cerebral metabolic rate and blood supply across the adult lifespan

With age, the brain undergoes comprehensive changes in its function and physiology. Cerebral metabolism and blood supply are among the key physiologic processes supporting the daily function of the brain and may play an important role in age-related cognitive decline. Using MRI, it is now possible to make quantitative assessment of these parameters in a noninvasive manner. In the present study, we concurrently measured cerebral metabolic rate of oxygen (CMRO(2)), cerebral blood flow (CBF), and venous blood oxygenation in a well-characterized healthy adult cohort from 20 to 89 years old (N = 232). Our data showed that CMRO(2) increased significantly with age, while CBF decreased with age. This combination of higher demand and diminished supply resulted in a reduction of venous blood oxygenation with age. Regional CBF was also determined, and it was found that the spatial pattern of CBF decline was heterogeneous across the brain with prefrontal cortex, insular cortex, and caudate being the most affected regions. Aside from the resting state parameters, the blood vessels' ability to dilate, measured by cerebrovascular reactivity to 5% CO(2) inhalation, was assessed and was reduced with age, the extent of which was more prominent than that of the resting state CBF.

Construction of a (18)F-FDG PET normative database of Japanese healthy elderly subjects and its application to demented and mild cognitive impairment patients

OBJECTIVE

To construct a (18)F-FDG PET normative database of Japanese healthy elderly subjects and to apply it to demented and mild cognitive impairment (MCI) patients.

METHODS

Seventy-seven Japanese normal volunteers from 41 to 84 years of age (36 males and 41 females) who underwent clinical, neuropsychological, and MRI examinations were selected. In these subjects, (18)F-FDG PET/CT scans were performed, (18)F-FDG PET images were analyzed using the 3D-SSP program, and a normative database for cerebral glucose metabolism was constructed. Then, (18)F-FDG PET images from 14 demented and MCI patients were evaluated based on the normative database.

RESULTS

The 77 healthy elderly subjects were divided into three groups according to their age. In these subjects, the difference in glucose metabolism between males and females was minimal in contrast, glucose metabolism showed a weak reciprocal correlation with aging in several cerebral regions. The 3D-SSP images of 14 demented and MCI patients based on the age-matched (18)F-FDG PET normative database showed decreased patterns of glucose metabolism similar to those of previous studies on dementia diseases and MCI.

CONCLUSIONS

An age-matched normative database can be applied to the evaluation of single subjects, and the application of a mixed database of males and females is viable. Normative databases are useful for detecting dementia diseases and their MCI.

PET imaging in pediatric neuroradiology: current and future applications

Molecular imaging with positron emitting tomography (PET) is widely accepted as an essential part of the diagnosis and evaluation of neoplastic and non-neoplastic disease processes. PET has expanded its role from the research domain into clinical application for oncology, cardiology and neuropsychiatry. More recently, PET is being used as a clinical molecular imaging tool in pediatric neuroimaging. PET is considered an accurate and noninvasive method to study brain activity and to understand pediatric neurological disease processes. In this review, specific examples of the clinical use of PET are given with respect to pediatric neuroimaging. The current use of co-registration of PET with MR imaging is exemplified in regard to pediatric epilepsy. The current use of PET/CT in the evaluation of head and neck lymphoma and pediatric brain tumors is also reviewed. Emerging technologies including PET/MRI and neuroreceptor imaging are discussed.

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.

Structural and Functional Imaging Correlates for Age-Related Changes in the Brain

In recent years, investigators have made significant progress in documenting brain structure and function as it relates to aging by using positron emission tomography, conventional magnetic resonance (MR) imaging, advanced MR techniques, and functional MR imaging. This review summarizes the latest advances in understanding physiologic maturation and aging as detected by these neuroimaging modalities. We also present our experience with MR volumetric and positron emission tomography analysis in separate cohorts of healthy subjects in the pediatric and adult age groups respectively. Our results are consistent with previous studies and include the following: total brain volume was found to increase with age (up to 20 years of age). Whole brain metabolism and frontal lobe metabolism both decrease significantly with age (38% and 42%, respectively), whereas cerebellar metabolism does not show a significant decline with age. Defining normal alterations in brain function and structure allows early detection of disorders such as Alzheimer's and Parkinson's diseases, which are commonly associated with normal aging.

Reproducibility of intraperitoneal 2-deoxy-2-[18F]-fluoro-D-glucose cerebral uptake in rodents through time

INTRODUCTION

One strength of small animal imaging is the ability to obtain longitudinal measurements within the same animal, effectively reducing the number of animals needed and increasing statistical power. However, the variability of within-rodent brain glucose uptake after an intraperitoneal injection across an extended time has not been measured.

METHODS

Small animal imaging with 2-deoxy-2-[(18)F]-fluoro-D-glucose ((18)FDG) was used to determine the variability of a 50-min brain (18)FDG uptake following an intraperitoneal injection over time in awake male and female Sprague-Dawley rodents.

RESULTS

After determining the variability of an intraperitoneal injection in the awake rat, we found that normalization of brain (18)FDG uptake for (1) injected dose and body weight or (2) body weight, plasma glucose concentration and injected dose resulted in a coefficient of variation (CV) of 15%. However, if we normalized regional uptake to whole brain to compare relative regional changes, the CV was less than 5%. Normalized cerebral (18)FDG uptake values were reproducible for a 2-week period in young adult animals. After 1 year, both male and female animals had reduced whole-brain uptake, as well as reduced regional hippocampal and striatal (18)FDG uptake.

CONCLUSION

Overall, our results were similar to findings in previous rodent and human clinical populations; thus, using a high throughput study with intraperitoneal (18)FDG is a promising preclinical model for clinical populations. This is particularly relevant for measuring changes in brain function after experimental manipulation, such as long-term pharmacological administration.

Sex-related differences in amygdala functional connectivity during resting conditions

Recent neuroimaging studies have established a sex-related hemispheric lateralization of amygdala involvement in memory for emotionally arousing material. Here, we examine the possibility that sex-related differences in amygdala involvement in memory for emotional material develop from differential patterns of amygdala functional connectivity evident in the resting brain. Seed voxel partial least square analyses of regional cerebral blood flow data revealed significant sex-related differences in amygdala functional connectivity during resting conditions. The right amygdala was associated with greater functional connectivity in men than in women. In contrast, the left amygdala was associated with greater functional connectivity in women than in men. Furthermore, the regions displaying stronger functional connectivity with the right amygdala in males (sensorimotor cortex, striatum, pulvinar) differed from those displaying stronger functional connectivity with the left amygdala in females (subgenual cortex, hypothalamus). These differences in functional connectivity at rest may link to sex-related differences in medical and psychiatric disorders.

Effect of age on visuomotor functional MR imaging

RATIONALE AND OBJECTIVES

We sought to determine the effect of age on functional MR imaging experiments performed with visual and motor stimulation. We hypothesized that there would be a diminution in the amplitude of fMRI activation with increasing subjects' age.

MATERIALS AND METHODS

We used fixed effects models to study the amplitude of activation during a block design visuomotor task in three different age groups: old (mean: 75 years; standard deviation: 6 years), middle-aged (mean: 52 years; standard deviation: 9 years) and young (mean: 29 years; standard deviation: 5 years). Each group included 7 subjects. Regions of interest (ROI) were left primary motor area (LM1), supplementary motor area (SMA), and right and left occipital (RO, LO) visual areas. Individual subjects and group statistical parametric maps (SPMs) were generated for each ROI, and then the mean amplitude of activation was compared using the group analysis and t test.

RESULTS

The young age group showed higher amplitude of activation than middle and old age groups in all ROI (P < 0.01 uncorrected). Unpaired two tailed t test results between the groups showed significant differences between middle and young, and old and young age groups in all ROIs (P < or = 0.05), with the exception of old and young age groups in RO region (P = 0.11).

CONCLUSION

The group analysis, and unpaired t test results reveal higher amplitude of fMRI activation in the young versus the old and middle-aged groups.

Positron emission tomography of regional brain metabolic responses to a serotonergic challenge in major depressive disorder with and without borderline personality disorder

Previous neuroimaging studies of major depression have not controlled for the presence of personality disorders characterized by impulsive aggressive behavior, such as borderline personality disorder (BPD). Using positron emission tomography (PET), we studied regional glucose uptake in response to fenfluramine (FEN) in depressed subjects with BPD (n=11) and depressed patients without Cluster B Axis II disorders (n=8). Subjects were scanned while medication-free after a single blind placebo administration and after FEN on a second day. Brain responses were measured by PET imaging of [18F]fluorodeoxyglucose (FDG) and serial prolactin levels. Scans were compared at a voxel level using statistical parametric mapping. Correlations of changes in relative regional cerebral uptake (rCMRglu) with clinical measures were assessed. Depressed borderline patients had greater relative activity in parietotemporal cortical regions (BA 40, BA 22, and BA 42) before and after FEN activation compared to those without BPD. They also had less relative uptake in the anterior cingulate cortex (BA 32) at baseline compared to depressed patients without BPD and FEN abolished this difference. Impulsivity was positively correlated with rCMRglu in superior and middle frontal cortex (BA 6 and 44). Hostility was positively correlated with rCMRglu in temporal cortical regions (BA 21 and 22). In conclusions, borderline pathology in the context of a Major Depressive Disorder is associated with altered activity in parietotemporal and anterior cingulate cortical regions. Controlling for the presence of BPD in future imaging studies of mood disorders may elucidate similarities and differences in regional serotonergic function in these two often comorbid disorders.

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.

Resting state brain glucose metabolism is not reduced in normotensive healthy men during aging, after correction for brain atrophy

Studies using positron emission tomography (PET) have reported that global and regional values for cerebral blood flow and metabolic rates for glucose (CMRglc and rCMRglc) decline with age in humans. We wished to determine if such decreases could have reflected a partial volume effect (PVE) of cerebral atrophy in the elderly, rather than "intrinsic" reductions per gram brain. We used PET to compare rCMRglc, before and after correcting for the PVE, between 13 healthy older men (aged: 55-82 years) and 11 healthy young men (aged: 22-34 years). PET was performed with 18F-fluoro-2-deoxy-d-glucose while the subjects were in the "resting" state (eyes covered and ears plugged with cotton). The PET scans were normalized to a common brain volume after superimposing them on the subjects' tissue segmented magnetic resonance scans. Analysis showed that rCMRglc in the absence of a PVE correction was significantly less in the older group in insular, frontal, superior temporal cortical, and thalamic regions. Statistical significant differences in rCMRglc, however, were absent after the PVE correction. Thus, statistically significant age reductions in regional brain glucose metabolism, corrected for brain atrophy, are not detectable in healthy normotensive men scanned while in the resting state.

Normal patterns and variants in single-photon emission computed tomography and positron emission tomography brain imaging

One of the most important issues in evaluating functional brain scans for research or clinical purposes is to be able to identify normal variants. Determining the baseline "normal" state of the brain is not easy to characterize since many normal brain functions and mental processes affect brain activity. This article reviews issues pertaining to the technical and neurophysiological aspects of functional brain imaging that might alter "normal" activity and will also consider how normal brain activity changes throughout the lifespan.

The intent to exercise influences the cerebral O(2)/carbohydrate uptake ratio in humans

During and after maximal exercise there is a 15-30 % decrease in the metabolic uptake ratio (O(2)/[glucose + 1/2 lactate]) and a net lactate uptake by the human brain. This study evaluated if this cerebral metabolic uptake ratio is influenced by the intent to exercise, and whether a change could be explained by substrates other than glucose and lactate. The arterial-internal jugular venous differences (a-v difference) for O(2), glucose and lactate as well as for glutamate, glutamine, alanine, glycerol and free fatty acids were evaluated in 10 healthy human subjects in response to cycling. However, the a-v difference for the amino acids and glycerol did not change significantly, and there was only a minimal increase in the a-v difference for free fatty acids after maximal exercise. After maximal exercise the metabolic uptake ratio of the brain decreased from 6.1 +/- 0.5 (mean +/- S.E.M.) at rest to 3.7 +/- 0.2 in the first minutes of the recovery (P < 0.01). Submaximal exercise did not change the uptake ratio significantly. Yet, in a second experiment, when submaximal exercise required a maximal effort due to partial neuromuscular blockade, the ratio decreased and remained low (4.9 +/- 0.2) in the early recovery (n = 10; P < 0.05). The results indicate that glucose and lactate uptake by the brain are increased out of proportion to O(2) when the brain is activated by exhaustive exercise, and that such metabolic changes are influenced by the will to exercise. We speculate that the uptake ratio for the brain may serve as a metabolic indicator of 'central fatigue'.

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.

Comparison of regional cerebral blood flow and glucose metabolism in the normal brain: effect of aging

The regional cerebral blood flow (rCBF) and metabolic rate for glucose (rCMRGlc) are associated with functional activity of the neural cells. The present work reports a comparison study between rCBF and rCMRGlc in a normal population as a function of age. 10 young (25.9+/-5.6 years) and 10 old (65.4+/-6.1 years) volunteers were similarly studied at rest. In each subject, rCBF and rCMRGlc were measured in sequence, during the same session. Both rCBF and rCMRGlc values were found to decrease from young (mean rCBF=43.7 ml/100 g per min; mean rCMRGlc=40.6 micromol/100 g per min) to old age (mean rCBF=37.3 ml/100 g per min; mean rCMRGlc=35.2 micromol/100 g per min), resulting in a drop over 40 years of 14.8% (0.37%/year) and 13.3% (0.34%/year), respectively. On a regional basis, the frontal and the visual cortices were observed to have, respectively, the highest and the lowest reduction in rCBF, while, for rCMRGlc, these extremes were observed in striatum and cerebellum. Despite these differences, the ratio of rCBF to rCMRGlc was found to have a similar behavior in all brain regions for young and old subjects as shown by a correlation coefficient of 88%. This comparative study indicates a decline in rCBF and rCMRGlc values and a coupling between CBF and CMRGlc as a function of age.

Chemical heterogeneity of the living human brain: a proton MR spectroscopy study on the effects of sex, age, and brain region

Brain chemistry was compared between 19 male and female normal volunteers in the age group 19-31 years, across six brain regions and nine metabolites using in vivo proton magnetic resonance spectroscopy. The relative concentrations of N-acetyl aspartate, choline, glutamate, glutamine, GABA, inositol, glucose, and lactate were measured relative to creatine within 8-cm(3) brain voxels. These measurements were performed in six brain regions: thalamus and cingulate, insula, sensorimotor, dorsolateral prefrontal, and orbital frontal cortices in the left hemisphere. Total metabolite concentration was highest in prefrontal regions (28% higher in orbital frontal cortex and 18.7% higher in dorsolateral prefrontal cortex compared with insula and thalamus, P < 10(-7)). Subjects 25-31 years of age demonstrated a significant increase in total metabolite concentration in the orbital frontal cortex (35%, P < 10(-7)) and sensorimotor cortex (16.7%, P < 10(-5)) compared to those 19-20 years of age. These two brain regions also showed gender dependence, with women demonstrating increased metabolite concentrations compared to men (9% increase in sensorimotor cortex, P < 0.002, and 2.1% in orbital frontal cortex). Most other brain regions showed no gender- or age-dependent differences. The results indicate that the living human brain is chemically heterogeneous. The chemical heterogeneity is sex and age dependent and specific for brain region.

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.

A fenfluramine-activated FDG-PET study of borderline personality disorder

BACKGROUND

Impulsive aggression in patients with personality disorders is associated with diminished levels of cerebrospinal fluid (CSF) 5-HIAA, blunted neuroendocrine responses to serotonergic agonists, and decreased glucose utilization in the prefrontal cortex. We tested the hypothesis that impulsive aggression in borderline personality disorder (BPD) may be associated with diminished serotonergic regulation in the prefrontal cortex, using positron-emission tomography (PET) neuroimaging during pharmacologic challenge with d,l fenfluramine (FEN).

METHODS

A 2-day, single-blind, placebo-controlled FEN challenge study was conducted in five patients with BPD (and no Axis I MDD) and eight healthy control participants. On Day 1, 4 mCi [(18)F]-fluorodeoxyglucose (FDG) was injected 3 hours after ingestion of placebo; on Day 2, FDG was injected 3 hours after ingestion of.8 mg/kg to 60 mg of d,l fenfluramine. After 30 min, a 45-min emission scan was acquired on the Siemans/CTI 951r/31 scanner. PET data were aligned to MR images and analyzed by Statistical Parametric Mapping (SPM96).

RESULTS

In response to placebo, uptake of FDG was greater in control participants than patients in large areas of the prefrontal cortex including medial and orbital regions bilaterally (BA 10-11), left superior temporal gyrus, and right insular cortex. There were no areas in which patients had greater relative regional uptake than control participants. In response to FEN, relative regional uptake of FDG (relative to placebo) was greater in control participants compared to patients in medial and orbital regions of right prefrontal cortex (BA 10), left middle and superior temporal gyri (BA 22-23), left parietal lobe (BA 40), and left caudate body.

CONCLUSIONS

Patients with BPD have diminished response to serotonergic stimulation in areas of prefrontal cortex associated with regulation of impulsive behavior.

In vitro evaluation of aromatase enzyme in granulosa cells using a [11C]vorozole binding assay

An in vitro method for measuring aromatase cytochrome P450 enzyme (P450AROM) in human granulosa cells (GC) has been developed, based on binding of the 11C-labeled aromatase inhibitor vorozole. GC were obtained following superstimulation during in vitro fertilisation. The method revealed a binding affinity (Kd) of 0.4 nM and a maximum binding (Bmax) at 11 fmol/4000 cells which is equal to 1.6 million binding sites per cell. Linear Scatchard plots indicated a single type of binding site. P450AROM concentrations measured by [11C]vorozole binding correlated positively with aromatisation of [1beta-3H]androst-4-ene-3,17-dione measured as [3H]water release, and a positive association was also found with the ovarian in vivo response to follicle-stimulating hormone (FSH) stimulation expressed as 1000 times the ratio of the number of oocytes recovered from a patient and the total dose of recombinant FSH administered. Frozen cells could be used for P450AROM quantitation, provided the correct freezing procedure was used. Quantitation of P450AROM, based on binding of [11C]vorozole is an accurate and sensitive in vitro method, which might be extended to the measurement of aromatase expression by a noninvasive technique in the intact ovary in vivo using positron emission tomography.

Gender effects on odor-stimulated functional magnetic resonance imaging

On standardized tests of odor identification and odor detection, women tend to score better than men at nearly all age groups. We sought to determine if these findings would translate to differences between the sexes in the volume of activated brain when odors are presented to subjects as the stimulants for functional magnetic resonance imaging (FMRI) experiments. The activation maps of eight right-handed women (mean age 25.3 years old, range 20-44, S.D. 8.3 years) were compared with those of 8 right-handed men (mean age 30.5, range 18-37, S.D. 6.5 years) given the same olfactory nerve stimuli in an FMRI experiment at 1.5 T. Olfactory stimuli were delivered to the patients in a passive fashion using a Burghart OM4-B olfactometer with a nose piece inserted into the patients' nostrils. We used agents (eugenol, phenyl ethyl alcohol, or phenyl ethyl alcohol alternating with hydrogen sulfide) that were selective for olfactory nerve stimulation in the nose. The odorants were delivered to both nostrils for 1 s every 4 s during a 30 s 'on-period'. During the 30 s 'off-period', the patient received room air at the same flow rate. The women's group-averaged activation maps showed up to eight times more activated voxels than men for specific regions of the brain (frontal and perisylvian regions). The left and right inferior frontal regions showed a statistically significant increase in activation in women at p<0.01. In general, more women showed activation than men. The results suggest that (1) FMRI activation maps in subject groups can demonstrate correlates to psychophysical tests of olfaction, and (2) one must control for gender when performing odor-stimulated FMRI experiments.

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.

Gender differences in regional cerebral blood flow during transient self-induced sadness or happiness

Men, compared to women, are less likely to experience mood disorders. We wondered if gender differences exist in the ability to self-induce transient sadness and happiness, and in regional cerebral blood flow (rCBF) either at rest or during transient emotions. Ten adult men and 10 age-matched women, all healthy and never mentally ill, were scanned using H2(15)O positron emission tomography at rest and during happy, sad, and neutral states self-induced by recalling affect-appropriate life events and looking at happy, sad, or neutral human faces. At rest, women had decreased temporal and prefrontal cortex rCBF, and increased brainstem rCBF. There were no significant between-group differences in difficulty, effort required, or the degree of happiness or sadness induced. Women activated a significantly wider portion of their limbic system than did men during transient sadness, despite similar self-reported changes in mood. These findings may aid in understanding gender differences with respect to emotion and mood.

Sex differences in patterns of hemispheric cerebral metabolism: a multiple regression/discriminant analysis of positron emission tomographic data

Sex differences in brain hemispheric structure and function have been reported, and sex-related differences in hemispheric interregional correlations were reported in a prior analysis of resting PET glucose metabolic (rCMRglc) data. To explore further the effect of sex on patterns of hemispheric brain functional interactions, we applied a multiple regression/discriminant analysis to resting rCMRglc PET data from young normal men and women to test two hypotheses: (1) women have stronger between-hemisphere functional interactions; (2) men have stronger within-hemisphere functional interactions. Two separate discriminant functions based on these hypotheses distinguished men and women: the first reflected rCMRglc interdependencies between hemispheres and correctly classified all women and 94% of the men; the second reflected rCMRglc interdependencies within the left hemisphere and correctly classified 82% of the women and 88% of the men. Because the discriminant functions successfully distinguished men and women, these results provide support for both hypotheses.

Sex differences in regional cerebral glucose metabolism during a resting state

Positron emission tomography was used to evaluate the regional distribution of cerebral glucose metabolism in 61 healthy adults at rest. Although the profile of metabolic activity was similar for men and women, some sex differences and hemispheric asymmetries were detectable. Men had relatively higher metabolism than women in temporal-limbic regions and cerebellum and relatively lower metabolism in cingulate regions. In both sexes, metabolism was relatively higher in left association cortices and the cingulate region and in right ventro-temporal limbic regions and their projections. These results are consistent with the hypothesis that differences in cognitive and emotional processing have biological substrates.

Reduced brain metabolism in hyperactive girls

OBJECTIVE

This study assesses the effect of attention-deficit hyperactivity disorder (ADHD) and gender on cerebral glucose metabolism (CMRglu), using positron emission tomography and 18F-fluorodeoxyglucose.

METHOD

Nineteen normal (6 females; 14.3 +/- 1.3 years old) and 20 ADHD adolescents (5 females; 14.7 +/- 1.6 years old) participated in the study. An auditory continuous performance task was used during the 30-minute uptake of 18F-fluorodeoxyglucose.

RESULTS

There were no statistically significant differences in global or regional CMRglu between ADHD (N = 20) and normal (N = 19) adolescents. However, the global CMRglu in ADHD girls (N = 5) was 15.0% lower than in normal girls (N = 6) (p = .04), while global CMRglu in ADHD boys was not different than in normal boys. Furthermore, global CMRglu in ADHD girls was 19.6% lower than in ADHD boys (p = .02) and was not different between normal girls and normal boys. Clinical rating scales did not differentiate ADHD girls from ADHD boys, nor normal girls from normal boys.

CONCLUSIONS

The greater brain metabolism abnormalities in females than males strongly stress that more attention be given to the study of girls with ADHD.

Gender-related differences in regional cerebral glucose metabolism in normal volunteers

Positron emission tomography studies have correlated changes in the cerebral metabolic rate of glucose utilization (CMRglu) with symptoms of depression, aggression, impulsivity, and hyperactivity. Psychiatric disorders in which these symptoms are manifested are disproportionately represented among the sexes. We evaluated gender differences in regional CMRglu in control subjects (21 men and 18 women) with particular interest in the global, orbital frontal, and left anterolateral prefrontal cortical (LAPFC) CMRglu. A trend was present for global CMRglu to be greater in women than in men. Regional CMRglu was lower in men than in women in the orbital frontal area. No differences were observed in the LAPFC region.

Interregional correlations of resting cerebral glucose metabolism in old and young women

A correlational analysis of normalized (regional to whole-brain) regional cerebral metabolic rates for glucose obtained in the 'resting' state (eyes covered, ears plugged) using [18F]fluorodeoxyglucose, demonstrated differences between old and young women in patterns of functional associations. Fifteen healthy young (age less than 40 years) and 17 healthy old women (age greater than 64 years) were scanned with a Scanditronix PC1024-7B tomograph. The brain was divided into 65 regions of interest. The old women had fewer and less positive correlations between pairs of metabolic ratios in the frontal and parietal cortices. The results suggest an age-related reduction in frontal and parietal functional interactions in the 'resting' state that is consistent with a prior correlation analysis using a low resolution ECAT II scanner on young and old men. Reduced functional interactions may reflect age-related cognitive changes.

Gender differences in correlations of cerebral glucose metabolic rates in young normal adults

Correlational analysis of normalized regional cerebral metabolic data obtained by positron emission tomography, in healthy subjects in the 'resting' state (eyes covered, ears plugged) using [18F]2-fluoro-2-deoxy-D-glucose, demonstrated gender differences in patterns of functional associations. Fifteen women and 18 men (less than 40 yr) were scanned with a Scanditronix PC1024-7B tomograph. The brain was divided into 65 regions of interest (ROIs). There were no differences between men and women in global or regional metabolic rates, or in metabolic right-left asymmetries. Although the total number of significant correlations did not differ between men and women, patterns differed: female correlations rF were most positive than male correlations rM more often than rM greater than rF; and most rF greater than rM cases involved left frontal and sensorimotor ROIs, whereas most rM greater than rF cases involved right sensorimotor and occipital ROIs. The findings demonstrate gender differences in the pattern of functional neocortical interactions at the 'resting' state.

Glucose metabolism in psychiatric disorders: how can we facilitate comparisons among studies?

Positron emission tomography (PET) offers a possibility to study brain function and its relationship to psychiatric disorders. Clinical studies have demonstrated that several psychiatric diseases are coupled with changes in brain glucose metabolism. Schizophrenia seems to involve a lower metabolism in wide areas of the brain--both cortical and subcortical structures. Depression probably involves dysfunction of the metabolism in dorsolateral prefrontal cortex. Obsessive compulsive disorder, panic disorder, anorexia nervosa and the experience of anxiety may involve increased metabolic rates. The results from the different studies do not allow quantitative comparisons or detailed analyses because of large differences in experimental and clinical methodology. The term Good Clinical PET Practice (GCPP) is suggested to encourage standardization in clinical investigations. GCPP includes standardization of both experimental factors (lumped constant, arterialization, purity of tracer, regions of interest, relative rates) and clinical factors (state of the subject, wakefulness, anxiety, gender, course of the disease) in PET performance.