Factors associated with morphometric brain changes in cognitively normal aging

The influence of age and sex on the absolute cell numbers of the human brain cerebral cortex

The human cerebral cortex is one of the most evolved regions of the brain, responsible for most higher-order neural functions. Since nerve cells (together with synapses) are the processing units underlying cortical physiology and morphology, we studied how the human neocortex is composed regarding the number of cells as a function of sex and age. We used the isotropic fractionator for cell quantification of immunocytochemically labeled nuclei from the cerebral cortex donated by 43 cognitively healthy subjects aged 25-87 years old. In addition to previously reported sexual dimorphism in the medial temporal lobe, we found more neurons in the occipital lobe of men, higher neuronal density in women's frontal lobe, but no sex differences in the number and density of cells in the other lobes and the whole neocortex. On average, the neocortex has ~10.2 billion neurons, 34% in the frontal lobe and the remaining 66% uniformly distributed among the other 3 lobes. Along typical aging, there is a loss of non-neuronal cells in the frontal lobe and the preservation of the number of neurons in the cortex. Our study made possible to determine the different degrees of modulation that sex and age evoke on cortical cellularity.

Resilience of Neural Cellularity to the Influence of Low Educational Level

BACKGROUND

Education is believed to contribute positively to brain structure and function, as well as to cognitive reserve. One of the brain regions most impacted by education is the medial temporal lobe (MTL), a region that houses the hippocampus, which has an important role in learning processes and in consolidation of memories, and is also known to undergo neurogenesis in adulthood. We aimed to investigate the influence of education on the absolute cell numbers of the MTL (comprised by the hippocampal formation, amygdala, and parahippocampal gyrus) of men without cognitive impairment.

METHODS

The Isotropic Fractionator technique was used to allow the anisotropic brain tissue to be transformed into an isotropic suspension of nuclei, and therefore assess the absolute cell composition of the MTL. We dissected twenty-six brains from men aged 47 to 64 years, with either low or high education.

RESULTS

A significant difference between groups was observed in brain mass, but not in MTL mass. No significant difference was found between groups in the number of total cells, number of neurons, and number of non-neuronal cells. Regression analysis showed that the total number of cells, number of neurons, and number of non-neuronal cells in MTL were not affected by education.

CONCLUSIONS

The results indicate a resilience of the absolute cellular composition of the MTL of typical men to low schooling, suggesting that the cellularity of brain regions is not affected by formal education.

Microcephaly measurement in adults and its association with clinical variables

OBJECTIVE

To establish a microcephaly cut-off size in adults using head circumference as an indirect measure of brain size, as well as to explore factors associated with microcephaly via data mining.

METHODS

In autopsy studies, head circumference was measured with an inelastic tape placed around the skull. Total brain volume was also directly measured. A linear regression was used to determine the association of head circumference with brain volume and clinical variables. Microcephaly was defined as head circumference that were two standard deviations below the mean of significant clinical variables. We further applied an association rule mining to find rules associating microcephaly with several sociodemographic and clinical variables.

RESULTS

In our sample of 2,508 adults, the mean head circumference was 55.3 ± 2.7cm. Head circumference was related to height, cerebral volume, and sex (p < 0.001 for all). Microcephaly was present in 4.7% of the sample (n = 119). Out of 34,355 association rules, we found significant relationships between microcephaly and a clinical dementia rating (CDR) > 0.5 with an informant questionnaire on cognitive decline in the elderly (IQCODE) ≥ 3.4 (confidence: 100% and lift: 5.6), between microcephaly and a CDR > 0.5 with age over 70 years (confidence: 42% and lift: 2.4), and microcephaly and males (confidence: 68.1% and lift: 1.3).

CONCLUSION

Head circumference was related to cerebral volume. Due to its low cost and easy use, head circumference can be used as a screening test for microcephaly, adjusting it for gender and height. Microcephaly was associated with dementia at old age.

β-amyloid pathology is not associated with depression in a large community sample autopsy study

BACKGROUND

Depression has been associated with dementia. This study aimed to verify if β-amyloid Alzheimer's disease-type burden was associated with lifetime major depressive disorder (MDD) and with current depressive symptoms in a large population-based autopsy study.

METHODS

We included 1013 deceased subjects submitted to autopsy (mean age=74.3±11.6 years, 49% men) in a community sample. β-amyloid burden was measured in all cases based on the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) criteria for presence and density of neuritic plaques. Lifetime MDD was defined when at least one previous episode according to the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders - DSM (SCID). Depressive symptoms and cognitive impairment were determined using the depression item of the Neuropsychiatric Inventory (D-NPI>0) and the Clinical Dementia Rating scale (CDR>0.5) respectively.

RESULTS

Lifetime MDD, late life depression (LLD) and current depressive symptoms were associated with cognitive impairment (p<0.001). Additionally, neuritic plaques were associated with cognitive impairment (p<0.001). Moderate or frequent neurite plaque density was not associated with MDD, LLD or current depressive symptoms in multiple logistic models adjusted for age, gender, and cognitive impairment.

LIMITATIONS

In this cross-sectional study, all neuropsychiatric and cognitive assessment were based on informant-report of deceased participants.

CONCLUSIONS

Different clinical depictions of depression were associated with dementia in this large community sample of elderly individuals with multiethnic backgrounds. Notwithstanding, they were unrelated to β-amyloid pathology in the brain areas studied. The link between depression and dementia might be complex and determined by multiple factors.

Neuropsychiatric Inventory in Community-Dwelling Older Adults with Mild Cognitive Impairment and Dementia

BACKGROUND

Behavioral and psychological symptoms (BPSD) can be a prodrome of dementia, and the Neuropsychiatric Inventory (NPI) is widely used for BPSD evaluation.

OBJECTIVE

To compare the prevalence of BPSD according to cognitive status, and to determine NPI cutoffs that best discern individuals with mild cognitive impairment (MCI) and dementia from those without dementia.

METHODS

We included 1,565 participants (mean age = 72.7±12.2 years, 48% male). BPSD and cognitive status were assessed with the NPI and the Clinical Dementia Rating (CDR). We used multivariable logistic regression models to investigate the association of BPSD with cognitive status. The area under the curve (AUC) was used to assess model discrimination, and to determine the best NPI cutoff for MCI and dementia.

RESULTS

Participants were cognitively normal (CDR = 0; n = 1,062), MCI (CDR = 0.5; n = 145), or dementia (CDR≥1.0, n = 358). NPI symptoms were more frequent in dementia and MCI when compared to cognitively normal. Higher odds for delusions, hallucinations, disinhibition, and psychomotor alterations were found among participants with dementia and MCI than in those who were cognitively normal. The best NPI cutoff to discern participants with dementia from those cognitively normal was 11 (AUC = 0.755). Poor discrimination (AUC = 0.563) was found for the comparison of MCI and those cognitively normal.

CONCLUSIONS

We found an increase in BPSD frequencies across the continuum of cognitive impairment. BPSD severity and frequency in MCI was more similar to individuals cognitively normal than with dementia. NPI scores≥to 11 in individuals with no diagnosis of dementia can support the decision for further investigation of dementia.

Hypertension is the underlying cause of death assessed at the autopsy of individuals

OBJECTIVE

To analyze hypertension and its relationship with the causes of death identified by the autopsy.

METHOD

Cross-sectional study analyzed 356 participants belonging to the Brazilian Aging Brain Study Group, over 50 years of age, autopsied at the Sao Paulo Autopsy Service between 2004 to 2014. A clinical interview was conducted with the informant of the deceased. Hypertension was defined by reporting the disease and/or use of antihypertensive medication, by the informant of the deceased. Descriptive analyzes and bivariate and multivariable associations were performed.

RESULTS

The prevalence of hypertension was 66.2% and it was the second leading cause of death (25.6%) identified by autopsy, preceded by atherosclerosis (37.8%). The variables associated with hypertension were: female gender (OR=2.30 (1.34-3.90)); living with partner [OR=0.55 (0.32-0.92)]; Body Mass Index [OR=1.14 (1.08-1.22)] and history of diabetes [OR=2.39 (1.34-4.27)].

CONCLUSION

The prevalence of hypertension was high, and it was the second most common underlying cause of death. The gold standard for the definition of cause of death, the autopsy, shows important results, which confirmed the relevance of hypertension as a public health problem.

Low brain-derived neurotrophic factor levels in post-mortem brains of older adults with depression and dementia in a large clinicopathological sample

BACKGROUND

Disturbances in peripheral brain-derived neurotrophic factor (BDNF) have been reported in major depressive disorder (MDD). However, there are no studies measuring BDNF levels directly in post-mortem brains of older subjects with MDD and dementia. We aimed to verify if brain BDNF levels were lower in older adults with lifetime history of MDD with and without dementia.

METHODS

BDNF levels of post-mortem brains from 80 community-dwelling older individuals with lifetime MDD with and without dementia were compared with levels from 80 controls without lifetime MDD. Participants with no reliable close informant, or with prolonged agonal state were excluded. Lifetime MDD was defined as at least one previous episode according to the Structured Clinical Interview for DSM (SCID).

RESULTS

BDNF levels were lower in the MDD group with dementia than in participants with dementia and without MDD as confirmed by multivariate analysis adjusted for clinical and cardiovascular risk factors (ß = -0.106, 95%CI = -0.204; -0.009, p = 0.034). No difference was found in the group with MDD without dementia compared with their controls.

LIMITATIONS

The retrospective assessment of a lifetime history of depression may be subject to information bias and this study only establishes a cross-sectional association between lifetime history of MDD and lower levels of BDNF in patients with dementia.

CONCLUSIONS

In this community sample of older individuals, lower brain BDNF levels were found in cases with both lifetime MDD and dementia. Low BDNF levels could be a moderator to accelerated brain aging observed in MDD with dementia.

Factors associated with brain volume in major depression in older adults without dementia: results from a large autopsy study

OBJECTIVE

We examined brain volume and atrophy in individuals with major depressive disorder (MDD) without dementia that were referred to a large autopsy service. We also examined potential risk factors for brain atrophy, including demographics and clinical variables.

METHODS

In this study, 1373 participants (787 male) aged 50 years or older who died from natural causes were included. Participants with no reliable informant, with cognitive impairment or dementia, with a medical history of severe chronic disease, or with prolonged agonal state were excluded. Presence of MDD at least once in their lifetime was defined according to the Structured Clinical Interview for DSM. Brain volume was measured immediately after removal from the skull.

RESULTS

Mean age at death was 68.6 ± 11.6, and MDD was present in 185 (14%) individuals. Smaller brain volume was associated with older age (p < 0.001), lower education (years; p < 0.001), hypertension (p = 0.001), diabetes (p = 0.006), and female gender (p < 0.001). In the multivariate analysis adjusted for sociodemographics and cardiovascular risk factors, smaller brain volume was not associated with major depression (β = -0.86, 95% CI = -26.50 to 24.77, p = 0.95).

CONCLUSIONS

In this large autopsy study of older adults, MDD was not associated with smaller brain volumes. Regardless of the presence of MDD, in this sample of older adults without dementia, we found that smaller brain volumes were associated with risk factors for brain neurodegeneration such as older age, diabetes, hypertension, and lower education. Copyright © 2017 John Wiley & Sons, Ltd.