Sex-dependent alterations in hippocampal connectivity are linked to cerebrovascular and amyloid pathologies in normal aging

INTRODUCTION

Compared to males, females have an accelerated trajectory of cognitive decline in Alzheimer's disease (AD). The neurobiological factors underlying the more rapid cognitive decline in AD in females remain unclear. This study explored how sex-dependent alterations in hippocampal connectivity over 2 years are associated with cerebrovascular and amyloid pathologies in normal aging.

METHODS

Thirty-three females and 21 males 65 to 93 years of age with no cognitive impairment performed a face-name associative memory functional magnetic resonance imaging (fMRI) task with a 2-year follow-up. We acquired baseline carbon 11-labeled Pittsburgh compound B ([11 C]PiB) positron emission tomography (PET) and T2-weighted fluid-attenuated inversion recovery (T2-FLAIR) MRI to quantify amyloid β (Aβ) burden and white matter hyperintensity (WMH) volume, respectively.

RESULTS

Males had increased hippocampal-prefrontal connectivity over 2 years, associated with greater Aβ burden. Females had increased bilateral hippocampal functional connectivity, associated with greater WMH volume.

DISCUSSION

These findings suggest sex-dependent compensatory mechanisms in the memory network in the presence of cerebrovascular and AD pathologies and may explain the accelerated trajectory of cognitive decline in females.

Identifying sex-specific risk architectures for predicting amyloid deposition using neural networks

In older adults without dementia, White Matter Hyperintensities (WMH) in MRI have been shown to be highly associated with cerebral amyloid deposition, measured by the Pittsburgh compound B (PiB) PET. However, the relation to age, sex, and education in explaining this association is not well understood. We use the voxel counts of regional WMH, age, one-hot encoded sex, and education to predict the regional PiB using a multilayer perceptron with only rectilinear activations using mean squared error. We then develop a novel, robust metric to understand the relevance of each input variable for prediction. Our observations indicate that sex is the most relevant predictor of PiB and that WMH is not relevant for prediction. These results indicate that there is a sex-specific risk architecture for Aβ deposition.

CenTauR: Toward a universal scale and masks for standardizing tau imaging studies

INTRODUCTION

Recently, an increasing number of tau tracers have become available. There is a need to standardize quantitative tau measures across tracers, supporting a universal scale. We developed several cortical tau masks and applied them to generate a tau imaging universal scale.

METHOD

One thousand forty-five participants underwent tau scans with either ¹⁸F-flortaucipir, ¹⁸F-MK6240, ¹⁸F-PI2620, ¹⁸F-PM-PBB3, ¹⁸F-GTP1, or ¹⁸F-RO948. The universal mask was generated from cognitively unimpaired amyloid beta (Aβ)- subjects and Alzheimer's disease (AD) patients with Aβ+. Four additional regional cortical masks were defined within the constraints of the universal mask. A universal scale, the CenTauR_z, was constructed.

RESULTS

None of the regions known to display off-target signal were included in the masks. The CenTauR_z allows robust discrimination between low and high levels of tau deposits.

DISCUSSION

We constructed several tau-specific cortical masks for the AD continuum and a universal standard scale designed to capture the location and degree of abnormality that can be applied across tracers and across centers. The masks are freely available at https://www.gaain.org/centaur-project.

The Association of Age-Related and Off-Target Retention with Longitudinal Quantification of [18F]MK6240 Tau PET in Target Regions

6-(fluoro-18F)-3-(1H-pyrrolo[2,3-c]pyridin-1-yl)isoquinolin-5-amine ([18F]MK6240) tau PET tracer quantifies the brain tau neurofibrillary tangle load in Alzheimer disease. The aims of our study were to test the stability of common reference region estimates in the cerebellum over time and across diagnoses and evaluate the effects of age-related and off-target retention on the longitudinal quantification of [18F]MK6240 in target regions. Methods: We assessed reference, target, age-related, and off-target regions in 125 individuals across the aging and Alzheimer disease spectrum with longitudinal [18F]MK6240 SUVs and SUV ratios (SUVRs) (mean ± SD, 2.25 ± 0.40 y of follow-up). We obtained SUVR from meninges, exhibiting frequent off-target retention with [18F]MK6240. Additionally, we compared tracer uptake between 37 cognitively unimpaired young (CUY) (mean age, 23.41 ± 3.33 y) and 27 cognitively unimpaired older (CU) adults (amyloid-β-negative and tau-negative, 58.50 ± 9.01 y) to identify possible nonvisually apparent, age-related signal. Two-tailed t testing and Pearson correlation testing were used to determine the difference between groups and associations between changes in region uptake, respectively. Results: Inferior cerebellar gray matter SUV did not differ on the basis of diagnosis and amyloid-β status, cross-sectionally and over time. [18F]MK6240 uptake significantly differed between CUY and CU adults in the putamen or pallidum (affecting ∼75% of the region) and in the Braak II region (affecting ∼35%). Changes in meningeal and putamen or pallidum SUVRs did not significantly differ from zero, nor did they vary across diagnostic groups. We did not observe significant correlations between longitudinal changes in age-related or meningeal off-target retention and changes in target regions, whereas changes in all target regions were strongly correlated. Conclusion: Inferior cerebellar gray matter was similar across diagnostic groups cross-sectionally and stable over time and thus was deemed a suitable reference region for quantification. Despite not being visually perceptible, [18F]MK6240 has age-related retention in subcortical regions, at a much lower magnitude but topographically colocalized with significant off-target signal of the first-generation tau tracers. The lack of correlation between changes in age-related or meningeal and target retention suggests little influence of possible off-target signals on longitudinal tracer quantification. Nevertheless, the age-related retention in the Braak II region needs to be further investigated. Future postmortem studies should elucidate the source of the newly reported age-related [18F]MK6240 signal, and in vivo studies should further explore its impact on tracer quantification.

Imaging beta-amyloid (Aβ) burden in the brains of middle-aged individuals with alcohol-use disorders: a [11C]PIB PET study

No in vivo human studies have examined the prevalence of Alzheimer's disease (AD) neuropathology in individuals with alcohol-use disorder (AUD), although recent research suggests that a relationship between the two exists. Therefore, this study used Pittsburgh Compound-B ([¹¹C]PiB) PET imaging to test the hypothesis that AUD is associated with greater brain amyloid (Aβ) burden in middle-aged adults compared to healthy controls. Twenty healthy participants (14M and 6F) and 19 individuals with AUD (15M and 4F), all aged 40-65 years, underwent clinical assessment, MRI, neurocognitive testing, and positron emission tomography (PET) imaging. Global [¹¹C]PiB standard uptake value ratios (SUVRs), cortical thickness, gray matter volumes (GMVs), and neurocognitive function in subjects with AUD were compared to healthy controls. These measures were selected because they are considered markers of risk for future AD and other types of neurocognitive dysfunction. The results of this study showed no significant differences in % global Aβ positivity or subthreshold Aβ loads between AUD and controls. However, relative to controls, we observed a significant 6.1% lower cortical thickness in both AD-signature regions and in regions not typically associated with AD, lower GMV in the hippocampus, and lower performance on tests of attention as well as immediate and delayed memory in individuals with AUD. This suggest that Aβ accumulation is not greater in middle-aged individuals with AUD. However, other markers of neurodegeneration, such as impaired memory, cortical thinning, and reduced hippocampal GMV, are present. Further studies are needed to elucidate the patterns and temporal staging of AUD-related pathophysiology and cognitive impairment. Imaging β-amyloid in middle age alcoholics as a mechanism that increases their risk for Alzheimer's disease; Registration Number: NCT03746366 .

Acute Elevations in Cortisol Increase the In Vivo Binding of [11C]NOP-1A to Nociceptin Receptors: A Novel Imaging Paradigm to Study the Interaction Between Stress- and Antistress-Regulating Neuropeptides

BACKGROUND

An imbalance between neuropeptides that promote stress and resilience, such as corticotropin-releasing factor and nociceptin, has been postulated to underlie relapse in addiction. The objective of this study was to develop a paradigm to image the in vivo interaction between stress-promoting neuropeptides and nociceptin (NOP) receptors in humans.

METHODS

[11C]NOP-1A positron emission tomography was used to measure the binding to NOP receptors at baseline (BASE) and following an intravenous hydrocortisone challenge (CORT) in 19 healthy control subjects. Hydrocortisone was used as a challenge because in microdialysis studies it has been shown to increase corticotropin-releasing factor release in extrahypothalamic brain regions such as the amygdala. [11C]NOP-1A total distribution volume (VT) in 11 regions of interest were measured using a 2-tissue compartment kinetic analysis. The primary outcome measure was hydrocortisone-induced ΔVT calculated as (VT CORT - VT BASE)/VT BASE.

RESULTS

Hydrocortisone led to an acute increase in plasma cortisol levels. Regional [11C]NOP-1A VT was on average 11% to 16% higher in the post-hydrocortisone condition compared with the baseline condition (linear mixed model, condition, p = .005; region, p < .001; condition × region, p < .001). Independent Student's t tests in all regions of interest were statistically significant and survived multiple comparison correction. Hydrocortisone-induced ΔVT was significantly negatively correlated with baseline VT in several regions of interest.

CONCLUSIONS

Hydrocortisone administration increases NOP receptor availability. Increased NOP in response to elevated cortisol might suggest a compensatory mechanism in the brain to counteract corticotropin-releasing factor and/or stress. The [11C]NOP-1A and hydrocortisone imaging paradigm should allow for the examination of interactions between stress-promoting neuropeptides and NOP in addictive disorders.

Relationships Between Executive Control Circuit Activity, Amyloid Burden, and Education in Cognitively Healthy Older Adults

INTRODUCTION

In cognitively healthy older adults, amyloid-beta (Aβ) burden is associated with greater activity on task-based functional magnetic resonance imaging. Higher levels of functional activation are associated with other factors along with amyloid and the authors investigated these relationships as well as how they relate to Aβ in cognitively healthy older adults.

METHODS

The authors recruited cognitive healthy older adults (N = 50) from the Pittsburgh community that underwent extensive cognitive batteries, activation during a working memory (digit symbol substitution task, DSST), positron emission tomography scan for Pittsburgh Compound B (PiB, measuring amyloid), and other demographic measures. The authors tested the association between DSST activation and global PiB, neurocognitive batteries, and education.

RESULTS

The authors found that the DSST robustly activated expected structures involved in working memory. The authors found that greater global Aβ deposition was associated with greater DSST activation in the right calcarine, precuneus, middle temporal as well as the left insula and inferior frontal gyrus. The authors also found that greater education was associated with lower DSST activation - however this was not significant after adjusting for Aβ.

DISCUSSION

Greater amyloid was associated with greater activation, which may represent compensatory activation. Greater education was associated with lower activation, which may represent more efficient activation (i.e., less activation for the same task). After adjusting for amyloid, education was not significantly associated with activation suggesting that during the preclinical stage amyloid is the primary determinant of activation. Further, activation was not associated with cognitive function. Compensatory activation in the preclinical stage may help maintain cognitive function.

Decreased Nociceptin Receptors Are Related to Resilience and Recovery in College Women Who Have Experienced Sexual Violence: Therapeutic Implications for Posttraumatic Stress Disorder

BACKGROUND

Posttraumatic stress disorder (PTSD) is a stress disorder that develops in only some individuals following a traumatic event. Data suggest that a substantial fraction of women recover after sexual violence. Thus, the investigation of stress and antistress neuropeptides in this sample has the potential to inform the neurochemistry of resilience following trauma. Nociceptin is an antistress neuropeptide in the brain that promotes resilience in animal models of PTSD.

METHODS

[¹¹C]NOP-1A positron emission tomography was used to measure the in vivo binding to nociceptin receptors in 18 college women who had experienced sexual violence irrespective of whether they met DSM-5 diagnostic criteria for PTSD. [¹¹C]NOP-1A data from 18 healthy control subjects were also included to provide a contrast with the sexual violence group. [¹¹C]NOP-1A total distribution volume (V_T) in the regions of interest were measured with kinetic analysis using the arterial input function. The relationships between regional V_T and Clinician-Administered PTSD Scale for DSM-5 total symptom and subscale severity were examined using correlational analyses.

RESULTS

No differences in [¹¹C]NOP-1A V_T were noted between the sexual violence and control groups. V_T in the midbrain and cerebellum were positively correlated with PTSD total symptom severity in the past month before positron emission tomography. Intrusion/re-experiencing and avoidance subscale symptoms drove this relationship. Stratification of subjects by a DSM-5 PTSD diagnosis and contrasting their V_T with that in control subjects showed no group differences.

CONCLUSIONS

Decreased midbrain and cerebellum nociceptin receptors are associated with less severe PTSD symptoms. Medications that target nociceptin should be explored to prevent and treat PTSD.

Nociceptin Receptors Upregulated in Cocaine Use Disorder: A Positron Emission Tomography Imaging Study Using [11C]NOP-1A

OBJECTIVE

Nociceptin/orphanin FQ (N/OFQ) is an antistress neuropeptide transmitter in the brain that counteracts corticotropin-releasing factor (CRF)-mediated stress and anxiety symptoms during drug and alcohol withdrawal. It also inhibits the release of a wide array of neurotransmitters, including dopamine and glutamate, which allows for it to block the rewarding properties of cocaine. Chronic cocaine administration in rodents has been shown to decrease N/OFQ and increase nociceptive opioid peptide (NOP) receptors in the nucleus accumbens. No previous studies have reported on the in vivo status of NOP in chronic cocaine-abusing humans.

METHODS

[11C]NOP-1A and positron emission tomography (PET) were used to measure in vivo NOP binding in 24 individuals with cocaine use disorder and 26 healthy control subjects matched for age, sex, and smoking status. Participants with cocaine use disorder with no comorbid psychiatric or medical disorders were scanned after 2 weeks of outpatient-monitored abstinence. [11C]NOP-1A distribution volume (VT) was measured with kinetic analysis using the arterial input function in brain regions that mediate reward and stress behaviors. Participants with cocaine use disorder were followed up for 12 weeks after PET scanning to document relapse and relate it to VT.

RESULTS

A significant increase in [11C]NOP-1A VT was observed in the cocaine use disorder group compared with the healthy control group. This increase, which was generalized across all regions of interest (approximately 10%), was most prominent in the midbrain, ventral striatum, and cerebellum. However, increased VT in these regions did not predict relapse.

CONCLUSIONS

Increased NOP in cocaine use disorder suggests an adaptive response to decreased N/OFQ, or increased CRF transmission, or both. Future studies should examine the interactions between CRF and NOP to elucidate their role in negative reinforcement and relapse. NOP agonist medications to enhance N/OFQ should be explored as a therapeutic to treat cocaine use disorder.

Effect of S-equol and Soy Isoflavones on Heart and Brain

BACKGROUND

Observational studies in Asia show that dietary intake of soy isoflavones had a significant inverse association with coronary heart disease (CHD). A recent randomized controlled trial (RCT) of soy isoflavones on atherosclerosis in the US, however, failed to show their benefit. The discrepancy may be due to the much lower prevalence of S-equol producers in Westerners: Only 20-30% of Westerners produce S-equol in contrast to 50-70% in Asians. S-equol is a metabolite of dietary soy isoflavone daidzein by gut microbiome and possesses the most antiatherogenic properties among all isoflavones. Several short-duration RCTs documented that soy isoflavones improves arterial stiffness. Accumulating evidence shows that both atherosclerosis and arterial stiffness are positively associated with cognitive decline/dementia. Therefore, potentially, soy isoflavones, especially S-equol, are protective against cognitive decline/dementia.

METHODS/RESULTS

This narrative review of clinical and epidemiological studies provides an overview of the health benefits of soy isoflavones and introduces S-equol. Second, we review recent evidence on the association of soy isoflavones and S-equol with CHD, atherosclerosis, and arterial stiffness as well as the association of atherosclerosis and arterial stiffness with cognitive decline/ dementia. Third, we highlight recent studies that report the association of soy isoflavones and S-equol with cognitive decline/dementia. Lastly, we discuss the future directions of clinical and epidemiological research on the relationship of S-equol and CHD and dementia.

CONCLUSIONS

Evidence from observational studies and short-term RCTs suggests that S-equol is anti-atherogenic and improves arterial stiffness and may prevent CHD and cognitive impairment/ dementia. Well-designed long-term (≥ 2years) RCTs should be pursued.

Nociceptin Receptors in Alcohol Use Disorders: A Positron Emission Tomography Study Using [11C]NOP-1A

BACKGROUND

The neuropeptide transmitter nociceptin, which binds to the nociceptin/orphanin FQ peptide (NOP) receptor, is a core component of the brain's antistress system. Nociceptin exerts its antistress effect by counteracting the functions of corticotropin-releasing factor, the primary stress-mediating neuropeptide in the brain. Basic investigations support a role for medications that target nociceptin receptors in the treatment of alcohol use disorders. Thus, it is of high interest to measure the in vivo status of NOP receptors in individuals with alcohol use disorders.

METHODS

Here, we used [11C]NOP-1A and positron emission tomography to measure the in vivo binding to NOP receptors in 15 alcohol-dependent humans as identified by DSM-IV and 15 healthy control subjects matched for age, sex, and smoking status. Alcohol-dependent individuals with no comorbid psychiatric, medical, or drug abuse disorders were scanned following 2 weeks of outpatient monitored abstinence (confirmed with three times per week urine alcohol metabolite testing). [11C]NOP-1A distribution volume in regions of interest (including the amygdala, hippocampus, and midbrain, striatal, and prefrontal cortical subdivisions) was measured with kinetic analysis using the arterial input function.

RESULTS

Regional [11C]NOP-1A distribution volume in alcohol dependence was not significantly different compared with healthy control subjects. No relationship between [11C]NOP-1A distribution volume and other clinical measures (including duration and severity of alcohol abuse, craving, and anxiety or depressive symptoms) were significant after correction for the multiple hypotheses tested.

CONCLUSIONS

The results of this study do not support alterations in the binding to NOP receptors in alcohol dependence. However, this finding does not necessarily rule out alterations in nociceptin transmission in alcohol dependence.

Imaging phosphodiesterase-10a availability in cocaine use disorder with [11 C]IMA107 and PET

Phosphodiesterase-10a (PDE10a) is located exclusively in medium spiny neurons (MSN). Rodent studies show an increase in striatal MSN spine density following exposure to cocaine. These increases in MSN spine density are suggested to underlie neurobiological changes which contribute to cocaine self-administration. No postmortem or imaging studies have confirmed this finding in humans. Here, we hypothesized an increase in the MSN marker PDE10a in subjects with cocaine use disorder ("cocaine users") compared to controls. PDE10a availability was measured with [¹¹ C]IMA107 and positron emission tomography in 15 cocaine users and 15 controls matched for age, gender, and nicotine status. Cocaine users with no comorbid psychiatric, medical, or drug abuse disorders were scanned following two weeks of outpatient-monitored abstinence. [¹¹ C]IMA107 binding potential relative to nondisplaceable uptake (BP_ND ) in the regions of interest was derived with the simplified reference tissue method. No significant effect of diagnosis on BP_ND was demonstrated using linear mixed modeling with [¹¹ C]IMA107 BP_ND as the dependent variable and regions of interest as a repeated measure. There were no significant relationships between BP_ND and clinical rating scales. To the extent that PDE10a is a valid proxy for MSN spine density, these results do not support its increase in recently abstinent cocaine users.

Preventive immunization of aged and juvenile non-human primates to β-amyloid

Background

Immunization against beta-amyloid (Aβ) is a promising approach for the treatment of Alzheimer’s disease, but the optimal timing for the vaccination remains to be determined. Preventive immunization approaches may be more efficacious and associated with fewer side-effects; however, there is only limited information available from primate models about the effects of preclinical vaccination on brain amyloid composition and the neuroinflammatory milieu.

Methods

Ten non-human primates (NHP) of advanced age (18–26 years) and eight 2-year-old juvenile NHPs were immunized at 0, 2, 6, 10 and 14 weeks with aggregated Aβ₄₂ admixed with monophosphoryl lipid A as adjuvant, and monitored for up to 6 months. Anti-Aβ antibody levels and immune activation markers were assessed in plasma and cerebrospinal fluid samples before and at several time-points after immunization. Microglial activity was determined by [¹¹C]PK11195 PET scans acquired before and after immunization, and by post-mortem immunohistochemical and real-time PCR evaluation. Aβ oligomer composition was assessed by immunoblot analysis in the frontal cortex of aged immunized and non-immunized control animals.

Results

All juvenile animals developed a strong and sustained serum anti-Aβ IgG antibody response, whereas only 80 % of aged animals developed detectable antibodies. The immune response in aged monkeys was more delayed and significantly weaker, and was also more variable between animals. Pre- and post-immunization [¹¹C]PK11195 PET scans showed no evidence of vaccine-related microglial activation. Post-mortem brain tissue analysis indicated a low overall amyloid burden, but revealed a significant shift in oligomer size with an increase in the dimer:pentamer ratio in aged immunized animals compared with non-immunized controls (P < 0.01). No differences were seen in microglial density or expression of classical and alternative microglial activation markers between immunized and control animals.

Conclusions

Our results indicate that preventive Aβ immunization is a safe therapeutic approach lacking adverse CNS immune system activation or other serious side-effects in both aged and juvenile NHP cohorts. A significant shift in the composition of soluble oligomers towards smaller species might facilitate removal of toxic Aβ species from the brain.

Consideration of optimal time window for Pittsburgh compound B PET summed uptake measurements

The standardized uptake value ratio (SUVR, or summed tissue ratio) has been used effectively in Pittsburgh compound B (PiB) PET studies to distinguish subjects who have significant amyloid-beta deposition in their brain from those who do not. Relative to quantitative measurements, advantages of the SUVR are improved study feasibility and low test-retest variation; disadvantages include inherent bias (PiB retention overestimation) and potential for time-varying outcomes. The PiB SUVR has proven to be highly correlated with quantitative outcomes and to allow reliable detection of significant group differences (or effective contrasts). In this work, regional PiB SUVRs were examined across 9 time windows to select the window that provided the best trade-offs between bias, correlation, and effective contrast.

METHODS

A total of 40 dynamic PiB PET studies were performed on controls (n = 16), patients with Alzheimer disease (AD; n = 11), and patients with mild cognitive impairment (MCI; n = 13) (555 MBq [15 mCi], 90-min scan, and arterial blood sampling). The SUVR was computed for five 20-min and four 30-min windows that spanned the 30- to 90-min postinjection period. The SUVRs were compared with Logan graphical distribution volume ratio (DVR) measurements (35-90 min), determined with arterial blood as input and without arterial blood as input (cerebellum as reference).

RESULTS

Greater correlation and more bias were generally observed for the SUVR measurement at later times than at earlier times (relative to DVR). The effective contrast between the control and AD PiB SUVRs was slightly better for earlier data than for later data. The temporal dynamics of the SUVR measurement indicated greater stability in the measurement at 40 min after injection.

CONCLUSION

The 50- to 70-min time window provided a good compromise between physiologic validity, stability, sensitivity, and clinical feasibility across the control, MCI, and AD subject data examined in this study. The 40- to 60-min period demonstrated many advantages and should be used in studies limited by low injected dose. Although more biased than the 40- to 60-min SUVR, the 50- to 70-min SUVR was thought to be optimal because of greater measurement stability, which may prove to be important for longitudinal multisite studies performed in control, MCI, and AD subjects that are not dose-limited.

Cognitive correlates of alterations in acetylcholinesterase in Alzheimer's disease

We recently reported findings of modest loss of cortical acetylcholinesterase (AChE) activity in patients with overall mild Alzheimer's disease (AD) using N-[11C]methyl-pi-peridin-4-yl propionate ([11C]PMP) AChE positron emission tomography (PET). To determine cognitive correlates of in vivo cortical AChE activity in patients with mild to moderate AD (n=15), and in normal controls (NC, n=12) using [11C]PMP AChE PET imaging. Mean cortical AChE activity in the AD subjects was mildly reduced (-11.1%) compared to the control subjects (P<0.05). Analysis of the cognitive data showed that mean cortical AChE activity was significantly associated with performance on a test of attention and working memory (WAIS-III Digit Span, R=0.46, P=0.01) but not with tests of delayed short or long-term memory functions. Similar findings were present when the analysis was limited to the temporal cortex. Cortical AChE activity is more robustly associated with functions of attention and working memory compared to performance on primary memory tests in AD.

Cortical cholinergic function is more severely affected in parkinsonian dementia than in Alzheimer disease: an in vivo positron emission tomographic study

BACKGROUND

Pathology reports have shown that cholinergic forebrain neuronal losses in parkinsonian dementia (PDem) are equal to or greater than those in Alzheimer disease (AD). We hypothesized that patients with PDem would have cholinergic deficits that were similar to or greater than those of patients with AD.

OBJECTIVE

To determine in vivo cortical acetylcholinesterase (AChE) activity in healthy control subjects and in patients with mild AD, PDem, and Parkinson disease without dementia using AChE positron emission tomography.

SETTING

University and Veterans' Administration medical center. Design and Patients Group comparison design of patients with AD (n = 12), PDem (n = 14), and Parkinson disease without dementia (n = 11), and controls (n = 10) who underwent AChE imaging between July 1, 2000, and January 31, 2003. Patients with AD and PDem had approximately equal dementia severity.

MAIN OUTCOME MEASURES

Cerebral AChE activity.

RESULTS

Compared with controls, mean cortical AChE activity was lowest in patients with PDem (-20.0%), followed by patients with Parkinson disease without dementia (-12.9%; P<.001). Mean cortical AChE activity was relatively preserved in patients with AD (-9.1%), except for regionally selective involvement of the lateral temporal cortex (-15%; P<.001).

CONCLUSION

Reduced cortical AChE activity is more characteristic of patients with PDem than of patients with mild AD.

Gender-specific aging effects on the serotonin 1A receptor

The effects of age on serotonergic function have been hypothesized to underlie age-related changes in mood and behaviors such as sleep and eating. Of particular interest is the serotonin type-1A (5-HT1A) receptor, due to its putative role in mediating the therapeutic efficacy of antidepressant treatment. Using positron emission tomography (PET) and [11C--carbonyl] WAY100635, we assessed 5-HT1A receptor binding in 21 healthy subjects (10 men, 11 women) ranging in age from 21 to 80 years. Regional binding potential values were generated using a reference tissue model and corrected for partial volume effects. We observed an inverse relationship between age and binding of [11C--carbonyl] WAY100635 to the 5-HT1A receptor in men, but not women. This finding is in accord with observations reported in the postmortem literature. Gender-specific effects of age on central serotonergic function may relate to differences between men and women in behavior, mood, and susceptibility to neuropsychiatric disease across the adult lifespan.

Effects of estradiol and progesterone administration on human serotonin 2A receptor binding: a PET study

BACKGROUND

Preclinical studies demonstrate that 17beta-estradiol (E(2)) increases serotonin-2A receptor (5-HT(2A)R) density in rat frontal cortex.

METHODS

We investigated the impact of hormone replacement therapy on 5-HT(2A)R binding potential (BP) using positron emission tomography and [(18)F]altanserin in five postmenopausal women. Subjects were imaged at baseline, following 8 to 14 weeks of transdermal E(2), 0.1 mg/d, and following 2 to 6 weeks of E(2) plus micronized progesterone (P) 100 mg per os twice daily. Regional BPs in the anterior cingulate cortex, dorsolateral prefrontal cortex, and lateral orbitofrontal cortex were calculated by Logan analysis.

RESULTS

There was a main effect of time (p = .017) for 5-HT(2A)R BP, which increased 21.2%+/-2.6% following combined E(2) and P administration relative to baseline. This effect was evident in all cerebral cortex regions examined.

CONCLUSIONS

5-HT(2A)R BP increased in widespread areas of the cerebral cortex following combined E(2) + P administration.

PET measures of amphetamine-induced dopamine release in ventral versus dorsal striatum

Regional differences in dextroamphetamine (AMPH)-induced dopamine (DA) release in the baboon striatum were assessed using positron emission tomographic (PET) measures of [11C]raclopride specific binding to DA D2/D3 receptors acquired before and after AMPH administration. The magnitude of the reduction in [11C]raclopride binding, following AMPH administration, was two-fold greater in the anteroventral striatum (comprised of ventral caudate, anteroventral putamen, and nucleus accumbens) than the dorsal striatum (dorsal caudate). A simulation study demonstrated that any potential biases due to resolution (partial volume) and alignment effects were significantly smaller than the magnitude of the observed results. These regional differences in the sensitivity of AMPH are compatible with microdialysis evidence in rats indicating that the magnitude of DA release in response to AMPH concentrations in the range tested is greater in ventral than dorsal striatal regions. Post hoc tests involving measures in other striatal regions showed that the baseline DA D2/D3 binding was highest and the correlation between AMPH dose and change in [11C]raclopride binding most significant in the putamen.

PET imaging of serotonin type 2A receptors in late-life neuropsychiatric disorders

OBJECTIVE

To determine whether there are abnormalities in the in vivo status of the serotonin type 2A (5-HT2A) receptor in late-life depression and Alzheimer's disease, the authors used positron emission tomography (PET) to assess patients with these two conditions and healthy subjects.

METHOD

PET was performed by using [18F]altanserin to evaluate 5-HT2A receptor binding in 11 elderly patients with depression (four men, seven women; mean age = 65.0 years, SD = 5.5); nine Alzheimer's disease patients, including three with concurrent depression (two men, seven women; mean age = 69.7 years, SD = 5.0); and 10 age-matched healthy subjects (four men, six women; mean age = 69.8 years, SD = 5.0). Partial-volume correction of regional specific binding estimates was performed by using a method based on magnetic resonance imaging.

RESULTS

No significant abnormalities in [18F]altanserin binding (binding potential) were observed in the patients with late-life depression, and no effect of depression on binding potential was present within the Alzheimer's disease group. However, the patients with Alzheimer's disease had significantly lower binding than the normal subjects in several brain regions, including the anterior cingulate, prefrontal cortex, and sensorimotor cortex.

CONCLUSIONS

These results suggest that the 5-HT2A receptor is differentially affected in late-life depression and Alzheimer's disease, a finding that has implications for the etiological basis of mood and cognitive features of neuropsychiatric disorders of late life.

Reduced binding of [18F]altanserin to serotonin type 2A receptors in aging: persistence of effect after partial volume correction

The serotonin (5-HT) neurotransmitter system, which has a widespread distribution in the central nervous system, has been implicated in regulating mood and many human behaviors. There is evidence from postmortem human studies and limited information from prior in vivo studies to support a decline in 5-HT2A receptor density with aging. We examined nine elderly (ages 61-76) and nine young (ages 18-29) healthy individuals with positron emission tomography (PET) and [18F]altanserin, a ligand with high affinity for the 5-HT2A binding site. The PET data were corrected for differences in brain tissue volume between the young and elderly subjects using a magnetic resonance (MR) imaging-based partial volume correction method. Highly significant and widespread cortical reductions in 5-HT2A specific binding were demonstrated in the elderly group relative to young controls. Regional losses averaged 61% before and 57% following correction for effects of cerebral atrophy. This finding, which is consistent with prior postmortem and in vivo studies, has both etiological and potential therapeutic implications for behavioral changes commonly observed in the elderly, including geriatric depression.