No association between striatal dopamine transporter binding and body mass index: a multi-center European study in healthy volunteers

Association between body mass index (BMI) and [123I]Ioflupane (DaTSCAN) availabilities in patients with parkinsonism using single-photon emission computed tomography-computed tomography (SPECT-CT)

AIM

[123I]Ioflupane (DaTSCAN) has a high binding affinity to the dopamine (DA) transporter (DaT) and tenfold less affinity to serotonin (5-HT) transporter (SERT). Both neurotransmitters are considered to contribute to body weight regulation. This study assesses the association between body mass index (BMI) and DaTSCAN availability in brain.

METHOD

Scans from 74 consecutive patients who had undergone DaTSCAN single-photon emission computed tomography-computed tomography (SPECT-CT) were used to obtain semi- and absolute quantitative data in several volumes of interest (VOIs). Relative semi-quantitative specific binding ratios (SBRs) from Chang attenuated SPECT were obtained from GE DaTQUANT. Absolute normalised concentration (NC) was calculated from attenuation/scatter corrected SPECT-CT images, using an adapted version of the EARL Ltd (European Association of Nuclear Medicine (EANM) Research 4 Life) template. Scans were subdivided into either degenerative parkinsonism (abnormal = 49), borderline (n = 14) or scan without evidence of dopaminergic deficit (SWEDD = 11) using visual assessment and SBR values by two nuclear medicine consultants.

RESULTS

SBRs did not correlate with BMI. However, NC values correlated negatively in the entire cohort, with the strongest correlation in the frontal (r = - 0.649. p = 0.000), occipital (r = - 0.555, p = 0.000) regions and pons (r = - 0.555, p = 0.000). In the abnormal (n = 49) and SWEDD group (n = 11), NC of the frontal region was the most correlated with BMI (r = - 0.570, p = 0.000; r = - 0.813, p = 0.002, respectively). In the borderline group (n = 14), the left posterior putamen displayed the strongest correlation (r = - 0.765, p = 0.001).

CONCLUSION

Absolute NC values demonstrate a strong inverse correlation with BMI, strongest in the extrastriatal regions. Due to the predominately non-overlapping distribution of DaT and SERT, this study suggests greater involvement of SERT in obesity with possible interplay with DA transmission.

Effects of bariatric surgery and dietary interventions for obesity on brain neurotransmitter systems and metabolism: A systematic review of positron emission tomography (PET) and single-photon emission computed tomography (SPECT) studies

This systematic review collates studies of dietary or bariatric surgery interventions for obesity using positron emission tomography and single-photon emission computed tomography. Of 604 publications identified, 22 met inclusion criteria. Twelve studies assessed bariatric surgery (seven gastric bypass, five gastric bypass/sleeve gastrectomy), and ten dietary interventions (six low-calorie diet, three very low-calorie diet, one prolonged fasting). Thirteen studies examined neurotransmitter systems (six used tracers for dopamine DRD2/3 receptors: two each for 11 C-raclopride, 18 F-fallypride, 123 I-IBZM; one for dopamine transporter, 123 I-FP-CIT; one used tracer for serotonin 5-HT2A receptor, 18 F-altanserin; two used tracers for serotonin transporter, 11 C-DASB or 123 I-FP-CIT; two used tracer for μ-opioid receptor, 11 C-carfentanil; one used tracer for noradrenaline transporter, 11 C-MRB); seven studies assessed glucose uptake using 18 F-fluorodeoxyglucose; four studies assessed regional cerebral blood flow using 15 O-H2 O (one study also used arterial spin labeling); and two studies measured fatty acid uptake using 18 F-FTHA and one using 11 C-palmitate. The review summarizes findings and correlations with clinical outcomes, eating behavior, and mechanistic mediators. The small number of studies using each tracer and intervention, lack of dietary intervention control groups in any surgical studies, heterogeneity in time since intervention and degree of weight loss, and small sample sizes hindered the drawing of robust conclusions across studies.

Striatal dopamine D2-like receptors availability in obesity and its modulation by bariatric surgery: a systematic review and meta-analysis

There is significant evidence linking a 'reward deficiency syndrome' (RDS), comprising decreased availability of striatal dopamine D2-like receptors (DD2lR) and addiction-like behaviors underlying substance use disorders and obesity. Regarding obesity, a systematic review of the literature with a meta-analysis of such data is lacking. Following a systematic review of the literature, we performed random-effects meta-analyses to determine group differences in case-control studies comparing DD2lR between individuals with obesity and non-obese controls and prospective studies of pre- to post-bariatric surgery DD2lR changes. Cohen's d was used to measure effect size. Additionally, we explored factors potentially associated with group differences in DD2lR availability, such as obesity severity, using univariate meta-regression. In a meta-analysis including positron emission tomography (PET) and single-photon emission computed tomography (SPECT) studies, striatal DD2lR availability did not significantly differ between obesity and controls. However, in studies comprising patients with class III obesity or higher, group differences were significant, favoring lower DD2lR availability in the obesity group. This effect of obesity severity was corroborated by meta-regressions showing inverse associations between the body mass index (BMI) of the obesity group and DD2lR availability. Post-bariatric changes in DD2lR availability were not found, although a limited number of studies were included in this meta-analysis. These results support lower DD2lR in higher classes of obesity which is a more targeted population to explore unanswered questions regarding the RDS.

Dopamine receptor and dopamine transporter in obesity: A meta-analysis

The brain plays a major role in controlling the desire to eat. This meta-analysis aimed to assess the association between dopamine receptor (DR) availability and dopamine transporter (DAT) availability, measured using positron emission tomography, and obesity. We performed a systematic search of MEDLINE (from inception to November 2020) and EMBASE (from inception to November 2020) for articles published in English using the keywords "dopamine receptor," "dopamine transporter," "obesity," and "neuroimaging." Body mass index (BMI) and the corresponding binding potential (BP_ND ) were extracted from figures in each study using Engauge Digitizer, version 12.1, and plotted for radiopharmaceuticals and regions of interest (ROIs). Five studies involving 119 subjects with DR and five studies including 421 subjects with DAT were eligible for inclusion in this study. In overweight or obese subjects with BMI of 25 kg/m² or higher, DR availability from ¹¹ C-Racloprie was negatively associated with BMI. However, DR availability from ¹¹ C-PHNO was positively associated with BMI. DAT ratio was calculated after dividing DAT availabilities of overweight/obese BMI with mean DAT availabilities of normal BMI. The association between DAT ratio and BMI was not significant regardless of radiopharmaceuticals. In conclusion, dopamine plays a main role in the reward system with regard to obesity. Overweight and obese subjects had negative association between DR availability from ¹¹ C-Raclopride and BMI. However, the association of DR availability with BMI was dependent on radiopharmaceuticals. DAT availability did not show the significant relationship with BMI regardless of radiopharmaceuticals.

Molecular Imaging of Central Dopamine in Obesity: A Qualitative Review across Substrates and Radiotracers

Dopamine is a neurotransmitter that plays a crucial role in adaptive behavior. A wealth of studies suggests obesity-related alterations in the central dopamine system. The most direct evidence for such differences in humans comes from molecular neuroimaging studies using positron emission tomography (PET) and single-photon emission computed tomography (SPECT). The aim of the current review is to give a comprehensive overview of molecular neuroimaging studies that investigated the relation between BMI or weight status and any dopamine target in the striatal and midbrain regions of the human brain. A structured literature search was performed and a summary of the extracted findings are presented for each of the four available domains: (1) D2/D3 receptors, (2) dopamine release, (3) dopamine synthesis, and (4) dopamine transporters. Recent proposals of a nonlinear relationship between severity of obesity and dopamine imbalances are described while integrating findings within and across domains, after which limitations of the review are discussed. We conclude that despite many observed associations between obesity and substrates of the dopamine system in humans, it is unlikely that obesity can be traced back to a single dopaminergic cause or consequence. For effective personalized prevention and treatment of obesity, it will be crucial to identify possible dopamine (and non-dopamine) profiles and their functional characteristics.

Striatal Dopamine Transporter Availability Is Not Associated with Food Craving in Lean and Obese Humans; a Molecular Imaging Study

Brain dopamine signaling is essential for the motivation to eat, and obesity is associated with altered dopaminergic signaling and increased food craving. We used molecular neuroimaging to explore whether striatal dopamine transporter (DAT) availability is associated with craving as measured with the General Food Craving Questionnaire-Trait (G-FCQ-T). We here show that humans with obesity (n = 34) experienced significantly more craving for food compared with lean subjects (n = 32), but food craving did not correlate significantly with striatal DAT availability as assessed with ¹²³I-FP-CIT single-photon emission computed tomography. We conclude that food craving is increased in obesity, but the scores for food craving are not related to changes in striatal DAT availability.

Striatal DAT availability does not change after supraphysiological glucose loading dose in humans

Brain dopamine neurotransmission is regulated by the dopamine transporter (DAT), which drives reuptake of extracellular dopamine into the presynaptic neurons. We hypothesized that the glucose loading dose would affect the striatal DAT availability. An i.v. bolus injection of 18F-FP-CIT was administered after infusion of low-dose glucose (300 mg/kg), high-dose glucose (600 mg/kg) or placebo (normal saline). The emission data were acquired over 90 min in 23 healthy male subjects. Substantial increases of binding potential (BPNDs) from ventral striatum (VST), caudate nucleus, and putamen were observed after low-dose glucose loading (+26.0, +87.0, and +37.8%) and after high-dose glucose loading (+10.4, +51.9, and +22.0%). BPNDs of the caudate nucleus and putamen showed significant differences (P = 0.0472 and 0.0221) after placebo, low-dose glucose, and high-dose glucose loading. BPNDs in the caudate nucleus and putamen after placebo, low-dose glucose, and high-dose glucose loading were positively intercorrelated with each other. In conclusion, striatal DAT changes after physiological glucose loading, but not after supraphysiological glucose loading in humans. DAT availabilities after placebo, low-dose glucose, high-dose glucose loading were correlated to each other in the caudate nucleus and putamen, but not in the VST. Therefore, sub-regional variability in DAT regulatory mechanisms mediated by insulin may exist in humans.

Impact of age and sex correction on the diagnostic performance of dopamine transporter SPECT

Purpose

The specific binding ratio (SBR) of ¹²³I-FP-CIT (FP-CIT) in the putamen decreases with age by about 5% per decade and most likely is about 10% higher in females. However, the clinical utility of age and sex correction of the SBR is still a matter of debate. This study tested the impact of age and sex correction on the diagnostic performance of the putamen SBR in three independent patient samples.

Methods

Research sample: 207 healthy controls (HC) and 438 Parkinson’s disease (PD) patients. Clinical sample A: 183 patients with neurodegenerative parkinsonian syndrome (PS) and 183 patients with non-neurodegenerative PS from one site. Clinical sample B: 84 patients with neurodegenerative PS and 38 patients with non-neurodegenerative PS from another site. Correction for age and sex of the putamen SBR was based on linear regression in the HC or non-neurodegenerative PS, separately in each sample. The area under the ROC curve (AUC) was used as performance measure.

Results

The putamen SBR was higher in females compared to males (PPMI: 14%, p < 0.0005; clinical sample A: 7%, p < 0.0005; clinical sample B: 6%, p = 0.361). Age-related decline of the putamen SBR ranged between 3.3 and 10.4% (p ≤ 0.019). In subjects ≥ 50 years, age and sex explained < 10% of SBR between-subjects variance. Correction of the putamen SBR for age and sex resulted in slightly decreased AUC in the PPMI sample (0.9955 versus 0.9969, p = 0.025) and in clinical sample A (0.9448 versus 0.9519, p = 0.057). There was a small, non-significant AUC increase in clinical sample B (0.9828 versus 0.9743, p = 0.232).

Conclusion

These findings do not support age and sex correction of the putaminal FP-CIT SBR in the diagnostic workup of parkinsonian syndromes. This most likely is explained by the fact that the proportion of between-subjects variance caused by age and sex is considerably below the symptom threshold of about 50% reduction in neurodegenerative PS.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-020-05085-2.

Low dopamine transporter binding in the nucleus accumbens in geriatric patients with severe depression

AIM

Dysfunction of dopaminergic neurons in the central nervous system is considered to be related to major depressive disorder (MDD). Especially, MDD in geriatric patients is characterized by anhedonia, which is assumed to be associated with reduced dopamine neurotransmission in the reward system. Dopamine transporter (DAT) is considered to reflect the function of the dopamine nerve system. However, previous DAT imaging studies using single photon emission computed tomography or positron emission tomography (PET) have shown inconsistent results. The radioligand [¹⁸ F]FE-PE2I for PET enables more precise evaluation of DAT availability. Hence, we aimed to evaluate the DAT availability in geriatric patients with MDD using [¹⁸ F]FE-PE2I.

METHODS

Eleven geriatric patients with severe MDD and 27 healthy controls underwent PET with [¹⁸ F]FE-PE2I, which has high affinity and selectivity for DAT. Binding potentials (BP_ND ) in the striatum (caudate and putamen), nucleus accumbens (NAc), and substantia nigra were calculated. BP_ND values were compared between MDD patients and healthy controls.

RESULTS

MDD patients showed significantly lower DAT BP_ND in the NAc (P = 0.009), and there was a trend of lower BP_ND in the putamen (P = 0.032) compared to controls.

CONCLUSION

We found low DAT in the NAc and putamen in geriatric patients with severe MDD, which could be related to dysregulation of the reward system.

Striatal dopamine transporter changes after glucose loading in humans

AIMS

The dopamine transporter (DAT) actively translocates dopamine that is released from the presynaptic neurons across the membranes of nerve terminals into the extracellular space. We hypothesized that glucose loading-induced changes in striatal DAT levels could be associated with food intake in humans.

MATERIALS AND METHODS

An intravenous bolus injection of ¹⁸ F-FP-CIT was administered after infusion of glucose or placebo (normal saline), and emission data were acquired over 90 minutes in 33 healthy males. For a volume-of-interest-based analysis, an atlas involving sub-striatal regions of ventral striatum (VST), caudate nucleus and putamen was applied. DAT availability and binding potential (BP_ND ) were measured using a simplified reference tissue method with cerebellum as the reference.

RESULTS

The glucose-loaded BP_ND from the VST negatively correlated with body mass index (BMI), whereas the placebo-loaded BP_ND from the VST did not. After loading with glucose, there were substantial increases in BP_ND s: 18.3%, 71.7% and 34.0% on average in the VST, caudate nucleus and putamen, respectively.

CONCLUSION

Striatal DAT changes after glucose loading, and BMI is associated with glucose-loaded DAT availability, not with placebo-loaded DAT availability. DAT might have a role in the reward system of eating behavior.

The Neuroendocrine and Metabolic Outcomes of Bariatric Surgery Depend on Presurgical Control over Eating

BACKGROUND

The outcomes of bariatric surgery are very irregular and mostly unpredictable. The search for variables of predictive value is encouraged to help preventing therapeutic failures.

OBJECTIVE

We aimed to confirm the hypothesis that preexisting eating behaviors could predict neuroendocrine and metabolic outcomes of gastric bypass surgery in morbidly obese subjects.

METHODS

Twenty-one morbidly obese patients from the Bariatric Surgery Program of our hospital were selected according to the specific inclusion and exclusion criteria for this study. The subjects filled out a validated questionnaire to quantify the "loss-of-control" (LC) dimension of food craving and provided serum samples at the onset of the study and 1 year after gastric bypass surgery. Hematological, metabolic, and hormonal variables were studied by conventional clinical tests and enzyme immunoassays and checked for correlations with LC both before and after surgery.

RESULTS

Those patients that had exhibited worse eating control at the beginning of the study experienced a better metabolic response 1 year after surgery in terms of reduction of serum insulin, HOMA1-IR, HOMA2-IR, and vitamin D1; all these variables were inversely correlated with presurgical LC. Serum brain-derived neurotrophic factor (BDNF) levels showed the same tendency; in fact, BDNF significantly decreased only in those patients with worse eating control.

CONCLUSIONS

Problematic eating behaviors may predict a better response of insulin resistance and a specific reduction of serum BDNF in morbidly obese patients after gastric bypass surgery.

Chronic abdominal vagus stimulation increased brain metabolic connectivity, reduced striatal dopamine transporter and increased mid-brain serotonin transporter in obese miniature pigs

Background/objective

Changes in brain metabolism has been investigated thoroughly during unilateral cervical chronic vagal stimulation in epileptic or depressive patients. Bilateral stimulation of the abdominal vagus (_aVNS) has received less attention despite the reduction in body weight and an altered feeding behavior in obese animals that could be clinically relevant in obese individuals. Our study aims to examine the changes in brain glucose metabolism (CMR_glu) induced by _aVNS in obese adult miniature pigs. Dopamine (DAT) and serotonin transporters (SERT) were also quantified to further understand the molecular origins of the alterations in brain metabolism.

Subjects/methods

Pairs of stimulating electrodes were implanted during laparoscopy on both abdominal vagal trunks in 20 obese adult’s miniature pigs. Half of the animals were permanently stimulated while the remaining were sham stimulated. Two months after the onset of stimulation, dynamic ₁₈FDG PET and ¹²³I-ioflupane SPECT were performed. Food intake, resting energy expenditure and fat deposition were also assessed longitudinally.

Results

Food intake was halved and resting energy expenditure was increased by 60% in _aVNS group compared to sham. The gain in body weight was also 38% less in _aVNS group compared to sham. Brain metabolic connectivity increased between numerous structures including striatum, mid-brain, amygdala and hippocampus. On the contrary, increased CMR_glu were restricted to the thalamus, the periaqueducal grey and the amygdala. DAT binding potential was decreased by about one third in the striatum while SERT was about doubled in the midbrain.

Conclusions

Our findings demonstrated that _aVNS reduced weight gain as a consequence of diminished daily food intake and increased resting energy expenditure. These changes were associated with enhanced connectivity between several brain areas. A lower striatal DAT together with a doubled mid-brain SERT were likely causative for these changes.

Electronic supplementary material

The online version of this article (10.1186/s12967-019-1831-5) contains supplementary material, which is available to authorized users.

The role of central dopamine and serotonin in human obesity: lessons learned from molecular neuroimaging studies

Obesity results from an imbalance between energy intake and expenditure, and many studies have aimed to determine why obese individuals continue to (over)consume food under conditions of caloric excess. The two major "neurotransmitter hypotheses" of obesity state that increased food intake is partially driven by decreased dopamine-mediated reward and decreased serotonin-mediated homeostatic feedback in response to food intake. Using molecular neuroimaging studies to visualize and quantify aspects of the central dopamine and serotonin systems in vivo, recent PET and SPECT studies have also implicated alterations in these systems in human obesity. The interpretation of these data, however, is more complex than it may appear. Here, we discuss important characteristics and limitations of current radiotracer methods and use this framework to comprehensively review the available human data on central dopamine and serotonin in obesity. On the basis of the available evidence, we conclude that obesity is associated with decreased central dopaminergic and serotonergic signaling and that future research, especially in long-term follow-up and interventional settings, is needed to advance our understanding of the neuronal pathophysiology of obesity in humans.

Persistent effects of obesity: a neuroplasticity hypothesis

The obesity epidemic is a leading cause of health problems in the United States, increasing the risk of cardiovascular, endocrine, and psychiatric diseases. Although many people lose weight through changes in diet and lifestyle, keeping the weight off remains a challenge. Here, we discuss a hypothesis that seeks to explain why obesity is so persistent. There is a great degree of overlap in the circuits implicated in substance use disorder and obesity, and neural plasticity of these circuits in response to drugs of abuse is well documented. We hypothesize that obesity is also associated with neural plasticity in these circuits, and this may underlie persistent changes in behavior, energy balance, and body weight. Here, we discuss how obesity-associated reductions in motivation and physical activity may be rooted in neurophysiological alterations in these circuits. Such plasticity may alter how humans and animals use, expend, and store energy, even after weight loss.

The Effect of Obesity on the Availabilities of Dopamine and Serotonin Transporters

The authors investigated relations between obesity, age, and sex and the availabilities of striatal dopamine transporter (DAT) and extrastriatal serotonin transporter (SERT) by ¹²³I-FP-CIT single-photon emission computed tomography. The study population consisted of 192 healthy controls with screening ¹²³I-FP-CIT scans. Specific bindings of ¹²³I-FP-CIT to DAT and SERT were calculated using regions of interest. Specific binding ratios (SBRs) of DAT and SERT except pons (r = 0.2217, p = 0.0026), were not correlated with body mass index (BMI). SBRs of midbrains correlated negatively with the BMIs of obese subjects (r = −0.3126, p = 0.0496), and positively with the those of non-obese subjects (r = 0.2327, p = 0.0053). SBRs of caudate nucleus (r = −0.3175, p < 0.0001), striatum (r = −0.226, p = 0.0022), and thalamus (r = −0.1978, p = 0.0074) reduced with age, and SERT availability was higher in males. However, DAT availability was similar in males and females. In conclusion, obesity has an effect on midbrain SERT availability. In addition, BMI was correlated with pontine SERT availability but not with striatal DAT availability. SERT availability was higher in males, but DAT availability showed no gender predilection.

Central noradrenaline transporter availability in highly obese, non-depressed individuals

PURPOSE

The brain noradrenaline (NA) system plays an important role in the central nervous control of energy balance and is thus implicated in the pathogenesis of obesity. The specific processes modulated by this neurotransmitter which lead to obesity and overeating are still a matter of debate.

METHODS

We tested the hypothesis that in vivo NA transporter (NAT) availability is changed in obesity by using positron emission tomography (PET) and S,S-[¹¹C]O-methylreboxetine (MRB) in twenty subjects comprising ten highly obese (body mass index BMI > 35 kg/m²), metabolically healthy, non-depressed individuals and ten non-obese (BMI < 30 kg/m²) healthy controls.

RESULTS

Overall, we found no significant differences in binding potential (BP_ND) values between obese and non-obese individuals in the investigated brain regions, including the NAT-rich thalamus (0.40 ± 0.14 vs. 0.41 ± 0.18; p = 0.84) though additional discriminant analysis correctly identified individual group affiliation based on regional BP_ND in all but one (control) case. Furthermore, inter-regional correlation analyses indicated different BP_ND patterns between both groups but this did not survive testing for multiple comparions.

CONCLUSIONS

Our data do not find an overall involvement of NAT changes in human obesity. However, preliminary secondary findings of distinct regional and associative patterns warrant further investigation.

Functional Neuroimaging in Obesity Research

Functional neuroimaging is beginning to yield valuable insights into the neurobiological underpinnings of the effects of obesity on neural circuits. Functional magnetic resonance imaging (fMRI), positron emission tomography (PET), and single-photon emission computed tomography (SPECT) studies have been used to identify aberrant activation patterns in regions implicated in reward (e.g., striatum, orbitofrontal cortex, insula), emotion and memory (e.g., amygdala, hippocampus), sensory and motor processing (e.g., insula, precentral gyrus), and cognitive control and attention (e.g., prefrontal cortex, cingulate) in obese individuals. Although a great amount of research using these techniques has already unveiled the influence of different neural response patterns on obesogenic behaviors, in this chapter we will, otherwise, try to highlight the effects of obesity on specific neuronal circuits and discuss recent developments in fMRI-based neurofeedback approaches as an alternative in obesity treatment.

Serotonin Transporter Binding in the Diencephalon Is Reduced in Insulin-Resistant Obese Humans

BACKGROUND

Altered brain dopaminergic and serotonergic pathways have been shown in obese rodents and humans, but it is unknown whether this is related to obesity per se or to the metabolic derangements associated with obesity.

METHODS

We performed a case-control study in insulin-sensitive obese (ISO) and insulin-resistant obese (IRO) subjects (n = 12) and age-matched lean controls (n = 8) and measured serotonin transporter (SERT) binding in the whole diencephalon and specifically in the hypothalamus, as well as dopamine transporter (DAT) binding in the striatum using 123I- FP-CIT single-photon emission computed tomography. We assessed insulin sensitivity using the homeostatic model assessment of insulin resistance.

RESULTS

BMI did not differ between the IRO and ISO subjects. SERT binding in the diencephalon was significantly lower in IRO than in ISO subjects, but was not different between lean and obese subjects. SERT binding in the hypothalamus tended to be reduced in obese versus lean subjects, but was not different between IRO and ISO subjects. Striatal DAT binding was similar between lean and obese subjects as well as between ISO and IRO subjects.

CONCLUSIONS

We conclude that SERT binding in the diencephalon is reduced in insulin-resistant subjects independently of body weight, while hypothalamic SERT binding tends to be lower in obesity, with no difference between insulin-resistant and insulin-sensitive subjects. This suggests that the metabolic perturbations associated with obesity independently affect SERT binding within the diencephalon.

Building a FP-CIT SPECT Brain Template Using a Posterization Approach

Spatial affine registration of brain images to a common template is usually performed as a preprocessing step in intersubject and intrasubject comparison studies, computer-aided diagnosis, region of interest selection and brain segmentation in tomography. Nevertheless, it is not straightforward to build a template of [123I]FP-CIT SPECT brain images because they exhibit very low intensity values outside the striatum. In this work, we present a procedure to automatically build a [123I]FP-CIT SPECT template in the standard Montreal Neurological Institute (MNI) space. The proposed methodology consists of a head voxel selection using the Otsu's method, followed by a posterization of the source images to three different levels: background, head, and striatum. Analogously, we also design a posterized version of a brain image in the MNI space; subsequently, we perform a spatial affine registration of the posterized source images to this image. The intensity of the transformed images is normalized linearly, assuming that the histogram of the intensity values follows an alpha-stable distribution. Lastly, we build the [123I]FP-CIT SPECT template by means of the transformed and normalized images. The proposed methodology is a fully automatic procedure that has been shown to work accurately even when a high-resolution magnetic resonance image for each subject is not available.

Brain dopamine and serotonin transporter binding are associated with visual attention bias for food in lean men

BACKGROUND

In rodents, the striatal dopamine (DA) system and the (hypo)thalamic serotonin (5-HT) system are involved in the regulation of feeding behavior. In lean humans, little is known about the relationship between these brain neurotransmitter systems and feeding. We studied the relationship between striatal DA transporters (DAT) and diencephalic 5-HT transporters (SERT), behavioral tasks and questionnaires, and food intake.

METHOD

We measured striatal DAT and diencephalic SERT binding with [123I]FP-CIT SPECT in 36 lean male subjects. Visual attention bias for food (detection speed and distraction time) and degree of impulsivity were measured using response-latency-based computer tasks. Craving and emotional eating were assessed with questionnaires and ratings of hunger by means of VAS scores. Food intake was assessed through a self-reported online diet journal.

RESULTS

Striatal DAT and diencephalic SERT binding negatively correlated with food detection speed (p = 0.008, r = -0.50 and p = 0.002, r = -0.57, respectively), but not with food distraction time, ratings of hunger, craving or impulsivity. Striatal DAT and diencephalic SERT binding did not correlate with free choice food intake, whereas food detection speed positively correlated with total caloric intake (p = 0.001, r = 0.60), protein intake (p = 0.01, r = 0.44), carbohydrate intake (p = 0.03, r = 0.39) and fat intake (p = 0.06, r = 0.35).

CONCLUSIONS

These results indicate a role for the central 5-HT and DA system in the regulation of visual attention bias for food, which contributes to the motivation to eat, in non-obese, healthy humans. In addition, this study confirms that food detection speed, measured with the latency-based computer task, positively correlates with total food and macronutrient intake.

Mesolimbic dopamine and its neuromodulators in obesity and binge eating

Obesity has reached epidemic prevalence, and much research has focused on homeostatic and nonhomeostatic mechanisms underlying overconsumption of food. Mesocorticolimbic circuitry, including dopamine neurons of the ventral tegmental area (VTA), is a key substrate for nonhomeostatic feeding. The goal of the present review is to compare changes in mesolimbic dopamine function in human obesity with diet-induced obesity in rodents. Additionally, we will review the literature to determine if dopamine signaling is altered with binge eating disorder in humans or binge eating modeled in rodents. Finally, we assess modulation of dopamine neurons by neuropeptides and peripheral peptidergic signals that occur with obesity or binge eating. We find that while decreased dopamine concentration is observed with obesity, there is inconsistency outside the human literature on the relationship between striatal D2 receptor expression and obesity. Finally, few studies have explored how orexigenic or anorexigenic peptides modulate dopamine neuronal activity or striatal dopamine in obese models. However, ghrelin modulation of dopamine neurons may be an important factor for driving binge feeding in rodents.

Argument for a non-linear relationship between severity of human obesity and dopaminergic tone

Alterations in the dopaminergic system have been implicated in both animal and human obesity. However, to date, a comprehensive model on the nature and functional relevance of this relationship is missing. In particular, human data remain equivocal in that seemingly inconsistent reports exist of positive, negative or even no relationships between dopamine D2/D3 receptor availability in the striatum and measures of obesity. Further, data on receptor availability have been commonly interpreted as reflecting receptor density, despite the possibility of an alternative interpretation, namely alterations in the basal levels of endogenous dopaminergic tone. Here, we provide a unifying framework that is able to explain the seemingly contradictory findings and offer an alternative and novel perspective on existing data. In particular, we suggest (i) a quadratic relationship between alterations in the dopaminergic system and degree of obesity, and (ii) that the observed alterations are driven by shifts in the balance between general dopaminergic tone and phasic dopaminergic signalling. The proposed model consistently integrates human data on molecular and behavioural characteristics of overweight and obesity. Further, the model provides a mechanistic framework accounting not only for the consistent observation of altered (food) reward-responsivity but also for the differences in reinforcement learning, decision-making behaviour and cognitive performance associated with measures of obesity.

Reduced insulin sensitivity is related to less endogenous dopamine at D2/3 receptors in the ventral striatum of healthy nonobese humans

BACKGROUND

Food addiction is a debated topic in neuroscience. Evidence suggests diabetes is related to reduced basal dopamine levels in the nucleus accumbens, similar to persons with drug addiction. It is unknown whether insulin sensitivity is related to endogenous dopamine levels in the ventral striatum of humans. We examined this using the agonist dopamine D2/3 receptor radiotracer [(11)C]-(+)-PHNO and an acute dopamine depletion challenge. In a separate sample of healthy persons, we examined whether dopamine depletion could alter insulin sensitivity.

METHODS

Insulin sensitivity was estimated for each subject from fasting plasma glucose and insulin using the Homeostasis Model Assessment II. Eleven healthy nonobese and nondiabetic persons (3 female) provided a baseline [(11)C]-(+)-PHNO scan, 9 of which provided a scan under dopamine depletion, allowing estimates of endogenous dopamine at dopamine D2/3 receptor. Dopamine depletion was achieved via alpha-methyl-para-tyrosine (64mg/kg, P.O.). In 25 healthy persons (9 female), fasting plasma and glucose was acquired before and after dopamine depletion.

RESULTS

Endogenous dopamine at ventral striatum dopamine D2/3 receptor was positively correlated with insulin sensitivity (r(7)=.84, P=.005) and negatively correlated with insulin levels (r(7)=-.85, P=.004). Glucose levels were not correlated with endogenous dopamine at ventral striatum dopamine D2/3 receptor (r(7)=-.49, P=.18). Consistently, acute dopamine depletion in healthy persons significantly decreased insulin sensitivity (t(24)=2.82, P=.01), increased insulin levels (t(24)=-2.62, P=.01), and did not change glucose levels (t(24)=-0.93, P=.36).

CONCLUSION

In healthy individuals, diminished insulin sensitivity is related to less endogenous dopamine at dopamine D2/3 receptor in the ventral striatum. Moreover, acute dopamine depletion reduces insulin sensitivity. These findings may have important implications for neuropsychiatric populations with metabolic abnormalities.

Neuroimaging and neuromodulation approaches to study eating behavior and prevent and treat eating disorders and obesity

Functional, molecular and genetic neuroimaging has highlighted the existence of brain anomalies and neural vulnerability factors related to obesity and eating disorders such as binge eating or anorexia nervosa. In particular, decreased basal metabolism in the prefrontal cortex and striatum as well as dopaminergic alterations have been described in obese subjects, in parallel with increased activation of reward brain areas in response to palatable food cues. Elevated reward region responsivity may trigger food craving and predict future weight gain. This opens the way to prevention studies using functional and molecular neuroimaging to perform early diagnostics and to phenotype subjects at risk by exploring different neurobehavioral dimensions of the food choices and motivation processes. In the first part of this review, advantages and limitations of neuroimaging techniques, such as functional magnetic resonance imaging (fMRI), positron emission tomography (PET), single photon emission computed tomography (SPECT), pharmacogenetic fMRI and functional near-infrared spectroscopy (fNIRS) will be discussed in the context of recent work dealing with eating behavior, with a particular focus on obesity. In the second part of the review, non-invasive strategies to modulate food-related brain processes and functions will be presented. At the leading edge of non-invasive brain-based technologies is real-time fMRI (rtfMRI) neurofeedback, which is a powerful tool to better understand the complexity of human brain-behavior relationships. rtfMRI, alone or when combined with other techniques and tools such as EEG and cognitive therapy, could be used to alter neural plasticity and learned behavior to optimize and/or restore healthy cognition and eating behavior. Other promising non-invasive neuromodulation approaches being explored are repetitive transcranial magnetic stimulation (rTMS) and transcranial direct-current stimulation (tDCS). Converging evidence points at the value of these non-invasive neuromodulation strategies to study basic mechanisms underlying eating behavior and to treat its disorders. Both of these approaches will be compared in light of recent work in this field, while addressing technical and practical questions. The third part of this review will be dedicated to invasive neuromodulation strategies, such as vagus nerve stimulation (VNS) and deep brain stimulation (DBS). In combination with neuroimaging approaches, these techniques are promising experimental tools to unravel the intricate relationships between homeostatic and hedonic brain circuits. Their potential as additional therapeutic tools to combat pharmacorefractory morbid obesity or acute eating disorders will be discussed, in terms of technical challenges, applicability and ethics. In a general discussion, we will put the brain at the core of fundamental research, prevention and therapy in the context of obesity and eating disorders. First, we will discuss the possibility to identify new biological markers of brain functions. Second, we will highlight the potential of neuroimaging and neuromodulation in individualized medicine. Third, we will introduce the ethical questions that are concomitant to the emergence of new neuromodulation therapies.

A post-mortem stereological study of striatal cell number in human obesity

OBJECTIVE

Neuroimaging studies have revealed abnormalities in brain structure, including the striatum, in obese people. In this study, the cellular and parenchymal basis for these findings in post-mortem brain tissue was investigated.

METHODS

Design-based (unbiased) stereology combined with histochemical and immunocytochemical staining was used to quantify total number of neurons and astrocytes in post-mortem striatal brain samples from nine obese (BMI 40.2 ± 6.1 kg/m(2) ) and eight lean (BMI 24.4 ± 1.0 kg/m(2) ) donors. Total numbers of Nissl-stained neurons and glial fibrillary acidic protein-immunopositive astrocytes were counted in 10 systematic-random sections starting from the frontal pole of the striatum.

RESULTS

There were no differences in mean total numbers of neurons (obese: 7.60 E+06; SD 2.50 E+06; lean: 7.85 E+06; SD 8.26 E+05; P < 0.78) or astrocytes (obese: 7.42 E+06; SD 2.27 E+06; lean: 7.43 E+06; SD 2.50 E+06; P < 0.99). A higher variance was found for number of neurons (P < 0.007) but not astrocytes (P < 0.72) in the obese group. Neuron/glia ratios were similar in both groups (obese: 1.07, SD 0.39; lean: 1.15, SD 0.37; P < 0.70) with an overall striatal neuron/glia ratio of 1.11 (SD 0.37) across the entire study population (n = 17).

CONCLUSIONS

No difference was found in the average numbers of neurons and astrocytes in the anterior striatum between lean and obese people. The morphological basis for structural brain changes in obesity requires further investigation.

CT-based attenuation correction in I-123-ioflupane SPECT

PURPOSE

Attenuation correction (AC) based on low-dose computed tomography (CT) could be more accurate in brain single-photon emission computed tomography (SPECT) than the widely used Chang method, and, therefore, has the potential to improve both semi-quantitative analysis and visual image interpretation. The present study evaluated CT-based AC for dopamine transporter SPECT with I-123-ioflupane.

MATERIALS AND METHODS

Sixty-two consecutive patients in whom I-123-ioflupane SPECT including low-dose CT had been performed were recruited retrospectively at 3 centres. For each patient, 3 different SPECT images were reconstructed: without AC, with Chang AC and with CT-based AC. Distribution volume ratio (DVR) images were obtained by scaling voxel intensities using the whole brain without striata as reference. For assessing the impact of AC on semi-quantitative analysis, specific-to-background ratios (SBR) in caudate and putamen were obtained by fully automated SPM8-based region of interest (ROI) analysis and tested for their diagnostic power using receiver-operator-characteristic (ROC) analysis. For assessing the impact of AC on visual image reading, screenshots of stereotactically normalized DVR images presented in randomized order were interpreted independently by two raters at each centre.

RESULTS

CT-based AC resulted in intermediate SBRs about half way between no AC and Chang. Maximum area under the ROC curve was achieved by the putamen SBR, with negligible impact of AC (0.924, 0.935 and 0.938 for no, CT-based and Chang AC). Diagnostic accuracy of visual interpretation also did not depend on AC.

CONCLUSIONS

The impact of CT-based versus Chang AC on the interpretation of I-123-ioflupane SPECT is negligible. Therefore, CT-based AC cannot be recommended for routine use in clinical patient care, not least because of the additional radiation exposure.

Dopamine and glucose, obesity, and reward deficiency syndrome

Obesity as a result of overeating as well as a number of well described eating disorders has been accurately considered to be a world-wide epidemic. Recently a number of theories backed by a plethora of scientifically sound neurochemical and genetic studies provide strong evidence that food addiction is similar to psychoactive drug addiction. Our laboratory has published on the concept known as Reward Deficiency Syndrome (RDS) which is a genetic and epigenetic phenomena leading to impairment of the brain reward circuitry resulting in a hypo-dopaminergic function. RDS involves the interactions of powerful neurotransmitters and results in abnormal craving behavior. A number of important facts which could help translate to potential therapeutic targets espoused in this focused review include: (1) consumption of alcohol in large quantities or carbohydrates binging stimulates the brain’s production of and utilization of dopamine; (2) in the meso-limbic system the enkephalinergic neurons are in close proximity, to glucose receptors; (3) highly concentrated glucose activates the calcium channel to stimulate dopamine release from P12 cells; (4) a significant correlation between blood glucose and cerebrospinal fluid concentrations of homovanillic acid the dopamine metabolite; (5) 2-deoxyglucose (2DG), the glucose analog, in pharmacological doses is associated with enhanced dopamine turnover and causes acute glucoprivation. Evidence from animal studies and fMRI in humans support the hypothesis that multiple, but similar brain circuits are disrupted in obesity and drug dependence and for the most part, implicate the involvement of DA-modulated reward circuits in pathologic eating behaviors. Based on a consensus of neuroscience research treatment of both glucose and drug like cocaine, opiates should incorporate dopamine agonist therapy in contrast to current theories and practices that utilizes dopamine antagonistic therapy. Considering that up until now clinical utilization of powerful dopamine D2 agonists have failed due to chronic down regulation of D2 receptors newer targets based on novel less powerful D2 agonists that up-regulate D2 receptors seems prudent. We encourage new strategies targeted at improving DA function in the treatment and prevention of obesity a subtype of reward deficiency.

Differences of various region-of-interest methods for measuring dopamine transporter availability using 99mTc-TRODAT-1 SPECT

This study was to investigate whether various region-of-interest (ROI) methods for measuring dopamine transporter (DAT) availabilities by single photon emission computed tomography (SPECT) are statistically different, whether results of medical research are thereby influenced, and causes of these differences. Eighty-four healthy adults with ^99mTc-TRODAT-1 SPECT and magnetic resonance imaging (MRI) scans were included. Six major analysis approaches were compared: (1) ROI drawn on the coregistered MRI; (2) ROIs drawn on the SPECT images; (3) standard ROI templates; (4) threshold-ROIs; (5) atlas-based mappings with coregistered MRI; and (6) atlas-based mappings with SPECT images. Using the atlas-based approaches we assessed the influence of striatum ROIs by slice-wise and voxel-wise comparisons. In (5) and (6), three partial-volume correction (PVC) methods were also explored. The results showed that DAT availabilities obtained from different methods were closely related but quite different and leaded to significant differences in determining the declines of DAT availability per decade (range: 5.95–11.99%). Use of 3D whole-striatum or more transverse slices could avoid biases in measuring the striatal DAT declines per decade. Atlas-based methods with PVC may be the preferable methods for medical research.

Decreased norepinephrine transporter availability in obesity: Positron Emission Tomography imaging with (S,S)-[(11)C]O-methylreboxetine

OBJECTIVES

Noradrenergic dysfunction is implicated in obesity. The norepinephrine transporter (NET) regulates the synaptic availability of norepinephrine. However, NET availability has not been previously characterized in vivo in obese people using Positron Emission Tomography (PET) imaging. Here we report findings evaluating NET availability in individuals with obesity and matched lean (i.e., normal weight) comparison subjects.

METHODS

Seventeen obese but otherwise healthy individuals with a mean±SD body mass index (BMI) of 34.7±2.6 and 17 lean individuals with a mean±SD BMI of 23.1±1.4 were studied using a high-resolution research tomograph (HRRT) and (S,S)-[(11)C]O-methylreboxetine ([(11)C]-MRB), a radioligand selective for the NET. The regional brain NET binding potential (BPND) was estimated by the multilinear reference tissue model 2 (MRTM2) with the occipital cortex as a reference region. BPND for regions of interest were obtained with the Automated Anatomic Labeling (AAL) template registered to individual's structural MR scans.

RESULTS

Obese individuals had lower NET BPND values in the thalamus (p<0.038, 27% reduction) including within the pulvinar (p<0.083, 30% reduction), but not in the hypothalamus, locus coeruleus or the raphe nuclei, compared to lean individuals. When age was included as a covariate, the difference in NET BPND values remained significant in the thalamus (p<0.025) and pulvinar (p<0.042).

CONCLUSIONS

These results indicate that NET availability is decreased in the thalamus, including the pulvinar, in obese individuals. These findings further support data indicating noradrenergic dysfunction in obesity and suggest impaired NE clearance in obesity.