Association of attentional shift and reversal learning to functional deficits in geriatric depression

OBJECTIVE

The objective of this study is to examine the association between self-reported functional disability in depressed older adults and two types of executive function processes, attentional set shifting and reversal learning.

METHODS

Participants (N = 89) were aged 60 or over and enrolled in a naturalistic treatment study of major depressive disorder. Participants provided information on self-reported function in instrumental activities of daily living (IADL) and completed the Intra-Extra Dimensional Set Shift test (IED) from the Cambridge Neuropsychological Testing Automated Battery, which assesses intra-dimensional attentional shifts, extra-dimensional attentional shifts, and reversal learning. Participants were categorized by the presence or absence of IADL difficulties and compared on IED performance using bivariable and multivariable tests.

RESULTS

Participants who reported IADL difficulties had more errors in extra-dimensional attentional shifting and reversal learning, but intra-dimensional shift errors were not associated with IADLs. Only extra-dimensional shift errors were significant in multivariable models that controlled for age, sex, and depression severity.

CONCLUSIONS

Attentional shifting across categories (i.e., extra-dimensional) was most strongly associated with increased IADL difficulties among depressed older adults, which make interventions to improve flexible problem solving a potential target for reducing instrumental disability in this population.

Stressful life events, perceived stress, and 12-month course of geriatric depression: direct effects and moderation by the 5-HTTLPR and COMT Val158Met polymorphisms

Although the relation between stressful life events (SLEs) and risk of major depressive disorder is well established, important questions remain about the effects of stress on the course of geriatric depression. Our objectives were (1) to examine how baseline stress and change in stress is associated with course of geriatric depression and (2) to test whether polymorphisms of serotonin transporter (5-HTTLPR) and catechol-O-methyltransferase (COMT Val158Met) genes moderate this relation. Two-hundred and sixteen depressed subjects aged 60 years or older were categorized by remission status (Montgomery-Asberg depression rating scale≤6) at 6 and 12 months. At 6 months, greater baseline numbers of self-reported negative and total SLEs and greater baseline perceived stress severity were associated with lower odds of remission. At 12 months, only baseline perceived stress predicted remission. When we examined change in stress, 12-month decrease in negative SLEs and level of perceived stress were associated with improved odds of 12-month remission. When genotype data were included, COMT Val158Met genotype did not influence these relations. However, when compared with 5-HTTLPR L/L homozygotes, S allele carriers with greater baseline numbers of negative SLEs and with greater decrease in negative SLEs were more likely to remit at 12 months. This study demonstrates that baseline SLEs and perceived stress severity may influence the 12-month course of geriatric depression. Moreover, changes in these stress measures over time correlate with depression outcomes. 5-HTTLPR S carriers appear to be more susceptible to both the effects of enduring stress and the benefit of interval stress reduction.

AGTR1 gene variation: association with depression and frontotemporal morphology

The renin-angiotensin system (RAS) is implicated in the response to physiological and psychosocial stressors, but its role in stress-related psychiatric disorders is poorly understood. We examined if variation in AGTR1, the gene coding for the type 1 angiotensin II receptor (AT(1)R), is associated with a diagnosis of depression and differences in white matter hyperintensities and frontotemporal brain volumes. Participants comprised 257 depressed and 116 nondepressed elderly Caucasian subjects who completed clinical assessments and provided blood samples for genotyping. We used a haplotype-tagging single nucleotide polymorphism (htSNP) analysis to test for variation in AGTR1. For measurement of hyperintense lesions, 1.5 Tesla magnetic resonance imaging (MRI) data were available on 33 subjects. For measurements of the hippocampus and dorsolateral prefrontal cortex (dlPFC), 3 Tesla MRI data were available on 70 subjects. Two htSNPs exhibited statistically significant frequency differences between diagnostic cohorts: rs10935724 and rs12721331. Although hyperintense lesion volume did not significantly differ by any htSNP, dlPFC and hippocampus volume differed significantly for several htSNPs. Intriguingly, for those htSNPs differing significantly for both dlPFC and hippocampus volume, the variant associated with smaller dlPFC volume was associated with larger hippocampal volume. This supports the idea that genetic variation in AGTR1 is associated with depression and differences in frontotemporal morphology.

Impact of BDNF Val66Met and 5-HTTLPR polymorphism variants on neural substrates related to sadness and executive function

The brain-derived neurotrophic factor (BDNF) Val(66) Met allelic variation is linked to both the occurrence of mood disorders and antidepressant response. These findings are not universally observed, and the mechanism by which this variation results in increased risk for mood disorders is unclear. One possible explanation is an epistatic relationship with other neurotransmitter genes associated with depression risk, such as the serotonin-transporter-linked promotor region (5-HTTLPR). Further, it is unclear how the coexistence of the BDNF Met and 5-HTTLPR S variants affects the function of the affective and cognitive control systems. To address this question, we conducted a functional magnetic resonance imaging (fMRI) study in 38 older adults (20 healthy and 18 remitted from major depressive disorder). Subjects performed an emotional oddball task during the fMRI scan and provided blood samples for genotyping. Our analyses examined the relationship between genotypes and brain activation to sad distractors and attentional targets. We found that 5-HTTLPR S allele carriers exhibited stronger activation in the amygdala in response to sad distractors, whereas BDNF Met carriers exhibited increased activation to sad stimuli but decreased activation to attentional targets in the dorsolateral prefrontal and dorsomedial prefrontal cortices. In addition, subjects with both the S allele and Met allele genes exhibited increased activation to sad stimuli in the subgenual cingulate and posterior cingulate. Our results indicate that the Met allele alone or in combination with 5-HTTLPR S allele may increase reactivity to sad stimuli, which might represent a neural mechanism underlying increased depression vulnerability.

Fiber tract-specific white matter lesion severity Findings in late-life depression and by AGTR1 A1166C genotype

Past work demonstrated that late-life depression is associated with greater severity of ischemic cerebral hyperintense white matter lesions, particularly frontal lesions. However, these lesions are also associated with other neuropsychiatric deficits, so these clinical relationships may depend on which fiber tracts are damaged. We examined the ratio of lesion to nonlesioned white matter tissue within multiple fiber tracts between depressed and nondepressed elders. We also sought to determine if the AGTR1 A1166C and BDNF Val66Met polymorphisms contributed to vulnerability to lesion development in discrete tracts. The 3T structural MR images and blood samples for genetic analyses were acquired on 54 depressed and 37 nondepressed elders. Lesion maps were created through an automated tissue segmentation process and applied to a probabilistic white matter fiber tract atlas allowing for identification of the fraction of the tract occupied by lesion. The depressed cohort exhibited a significantly greater lesion ratio only in the left upper cingulum near the cingulate gyrus (F((1,86)) = 4.62, P = 0.0344), supporting past work implicating cingulate dysfunction in the pathogenesis of depression. In the 62 Caucasian subjects with genetic data, AGTR1 C1166 carriers exhibited greater lesion ratios across multiple tracts including the anterior thalamic radiation and inferior fronto-occipital fasciculus. In contrast, BDNF Met allele carriers exhibited greater lesion ratios only in the frontal corpus callosum. Although these findings did not survive correction for multiple comparisons, this study supports our hypothesis and provides preliminary evidence that genetic differences related to vascular disease may increase lesion vulnerability differentially across fiber tracts.

Reduction of dorsolateral prefrontal cortex gray matter in late-life depression

Postmortem studies have documented abnormalities in the dorsolateral prefrontal cortex (dlPFC) in depressed subjects. In this study we used magnetic resonance imaging to test for dlPFC volume differences between older depressed and non-depressed individuals. Eighty-eight subjects meeting DSM IV criteria for major depressive disorder and thirty-five control subjects completed clinical evaluations and cranial 3T magnetic resonance imaging. After tissue types were identified using an automated segmentation process, the dlPFC was measured in both hemispheres using manual delineation based on anatomical landmarks. Depressed subjects had significantly lower gray matter in the left and right dorsolateral prefrontal cortex (standardized to cerebral parenchyma) after controlling for age and sex. Our study confirmed the reduction of dorsolateral prefrontal cortex in elderly depressed subjects, especially in the gray matter. These regional abnormalities may be associated with psychopathological changes in late-life depression.

Structural integrity of the uncinate fasciculus and resting state functional connectivity of the ventral prefrontal cortex in late life depression

Background

Neuroimaging studies in late life depression have reported decreased structural integrity of white matter tracts in the prefrontal cortex. Functional studies have identified changes in functional connectivity among several key areas involved in mood regulation. Few studies have combined structural and functional imaging. In this study we sought to examine the relationship between the uncinate fasciculus, a key fronto-temporal tract and resting state functional connectivity between the ventral prefrontal cortex ((PFC) and limbic and striatal areas.

Methods

The sample consisted of 24 older patients remitted from unipolar major depression. Each participant had a magnetic resonance imaging brain scan using standardized protocols to obtain both diffusion tensor imaging and resting state functional connectivity data. Our statistical approach compared structural integrity of the uncinate fasciculus and functional connectivity data.

Results

We found positive correlations between left uncinate fasciculus (UF) fractional anisotropy (FA) and resting state functional connectivity (rsFC) between the left ventrolateral PFC and left amygdala and between the left ventrolateral PFC and the left hippocampus. In addition, we found a significant negative correlation between left ventromedial PFC-caudate rsFC and left UF FA. The right UF FA did not correlate with any of the seed region based connectivity.

Conclusions

These results support the notion that resting state functional connectivity reflects structural integrity, since the ventral PFC is structurally connected to temporal regions by the UF. Future studies should include larger samples of patients and healthy comparison subjects in which both resting state and task-based functional connectivity are examined.

Angiotensin receptor gene polymorphisms and 2-year change in hyperintense lesion volume in men

This longitudinal study examined the relationship between 2-year change in white matter hyperintense lesion (WML) volume and polymorphisms in genes coding for the angiotensin-II type 1 and type 2 receptors, AGTR1 A1166C and AGTR2 C3123A, respectively. 137 depressed and 94 non-depressed participants aged >or=60 years were enrolled. Standard clinical evaluations were performed on all participants and blood samples obtained for genotyping. 1.5-T MRI (magnetic resonance imaging) data were obtained at baseline and approximately 2 years later. These scans were processed using a semi-automated segmentation process, which allowed for the calculation of WML volume at each time point. Statistical models were tested for the relationship between change in WML volume and genotype, while also controlling for age, sex, diagnostic strata, baseline WML volume and comorbid cerebrovascular risk factors. In men, AGTR1 1166A allele homozygotes exhibited significantly less change in WML volume than 1166C carriers. We also found that men reporting hypertension (HTN) with the AGTR2 3123C allele exhibit less change in WML volume than hypertensive men with the 3123A allele, or men without HTN. There were no significant relationships between these polymorphisms and change in WML volume in women. No significant gene-gene or gene-depression interactions were observed. Our results parallel earlier observed gender differences of the relationship between other renin-angiotensin system polymorphisms and HTN. Further work is needed to determine whether these observed relationships are secondary to polymorphisms affecting response to antihypertensive medication, and whether antihypertensive medications can slow WML progression and lower the risk of morbidity associated with WMLs.

Association analysis of the COMT/MTHFR genes and geriatric depression: an MRI study of the putamen

OBJECTIVE

Catechol-O-Methyltransferase (COMT) and Methylenetetrahydrofolate reductase (MTHFR) had been reported to relate to depression but with inconsistent results. The basal ganglia are also important in the pathophysiology of affective disorder via connections with limbic system and prefrontal cortex. The authors examined the relationship between an interaction of COMT/MTHFR polymorphisms and volumes of putamen in depressed and nondepressed elders.

METHODS

Participants included 170 depressed and 83 nondepressed subjects aged 60 years or older. Subjects completed cross-sectional assessments, including clinical evaluation, brain magnetic resonance imaging (MRI) scan, and COMT Val158Met and MTHFR C677T genotyping. Putamen volumes were measured using 1.5-Tesla whole-body MRI system. Statistical models examined the relationship between COMT/MTHFR genotype, proportional volumes of putamen and depression while controlling for age and sex.

RESULTS

After controlling for covariates, among depressed subjects with MTHFR C/C, both the right and left putamen had smaller volumes as the number of COMT 158Val increased. The left putamen volumes of depressed subjects with COMT Met/Met were smaller as the number of MTHFR 677T increased compared to nondepressed subjects.

CONCLUSIONS

Our findings do not support a major role for COMT or MTHFR alone. However, an epigenetic interaction of COMT Val158Met and MTHFR C677T polymorphisms may contribute to putamen volumes differences between depressed and nondepressed subjects. Further studies with a larger sample size are necessary to support a genetically based role for basal ganglia structures in the etiopathogenesis of depression.

Biochemical abnormalities of the medial temporal lobe and medial prefrontal cortex in late-life depression

We utilized single-voxel (1)H magnetic resonance spectroscopy (MRS) to investigate biochemical abnormalities related to late-life depression in the medial prefrontal cortex and medial temporal lobe. Fourteen elderly subjects whose depression responded to treatment and 12 nondepressed subjects were enrolled. Subjects were scanned using a GE 3.0 Tesla whole body MR scanner. Metabolite concentrations were quantified using the LC Model software and adjusted for CSF and ratio of gray to white matter. ANCOVA models tested for group differences while controlling for age and sex. Older previously depressed individuals showed significantly reduced concentrations of total N-acetyl aspartate (NAA), choline, and creatine in the prefrontal cortex and significantly elevated left medial temporal lobe concentrations of NAA and myo-inositol. There were no significant group differences in right temporal metabolite concentrations. The prefrontal cortex observations suggest that reduced neuronal, phospolipid, and energy metabolism is present even in clinically improved depression. In contrast, elevated NAA and myo-inositol concentrations in the left medial temporal lobe could be associated with neuronal and glial cell changes in the amygdala.

Temporal lobe volume in bipolar disorder: relationship with diagnosis and antipsychotic medication use

BACKGROUND

We tested for differences in temporal lobe volume in bipolar disorder and the relationship between these volumes and psychotropic medication use.

METHODS

125 subjects with bipolar disorder and 87 comparison subjects with no psychiatric illness completed clinical interviews and 1.5T MRI brain scans. Temporal lobe volumes were manually traced and segmented into gray matter and white matter volumes using an automated process. General linear models examined the relationship between these volumes and diagnosis as the primary predictor with age, sex, education, and race as copredictors. Secondary analyses incorporated the use of psychotropic medication into the linear models, and parsimonious models developed through backwards regression.

RESULTS

In initial models, subjects with bipolar disorder exhibited larger temporal lobe white matter bilaterally (left: F(1,211)=2.86, p=0.0047; right: F(1,211)=3.25, p=0.0014). Current antipsychotic use was significantly associated with larger bilateral temporal lobe white matter volumes (left: F(2,211)=9.45, p=0.0001; right: F(2,211)=10.79, p<0.0001), wherein bipolar subjects taking antipsychotics had larger volumes than bipolar subjects not taking antipsychotics or healthy comparison subjects. Temporal lobe gray matter volume was not significantly associated with diagnosis or medication use.

LIMITATIONS

Excluding subjects with substance use disorders may limit the study's generalizability.

CONCLUSIONS

These findings indicate that differences in temporal lobe white matter are associated with bipolar disorder and use of antipsychotic medications.

APOE related hippocampal shape alteration in geriatric depression

Late-onset depression often precedes the onset of dementia associated with the hippocampal degeneration. Using large deformation diffeomorphic metric mapping (LDDMM), we evaluated apolipoprotein E epsilon-4 allele (apoE E4) effects on hippocampal volume and shape in 38 depressed patients without the apoE E4, 14 depressed patients with one apoE E4, and 31 healthy comparison subjects without the apoE E4. The hippocampal volumes were manually assessed. We applied a diffeomorphic template generation procedure for creating the hippocampal templates based on a subset of the population. The LDDMM mappings were used to generate the hippocampal shape of each subject and characterize the surface deformation of each hippocampus relative to the template. Such deformation was modeled as random field characterized by the Laplace-Beltrami basis functions in the template coordinates. Linear regression was used to examine group differences in the hippocampal volume and shape. We found that there were significant hippocampal shape alternations in both depressed groups while the groups of depressed patients and the group of healthy subjects did not differ in the hippocampal volume. The depressed patients with one apoE E4 show more pronounced shape inward-compression in the anterior CA1 than the depressed patients without the apoE E4 when compared with the healthy controls without the apoE E4. Thus, hippocampal shape abnormalities in late-onset depressed patients with one apoE E4 may indicate future conversion of this group to AD at higher risk than depressed patients without the apoE E4.

Social support in older individuals: the role of the BDNF Val66Met polymorphism

Although often viewed as a purely environmental construct, perception of social support may be influenced by genetic factors. This study examined the relationship between the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism and social support measures in older subjects. The sample consisted of 243 depressed and 115 nondepressed older subjects, age 60 years or older; 233 were Val66 allele homozygotes, while 125 were Met66 allele carriers. All subjects completed clinical assessments, including a self-report questionnaire assessing four social support domains, and provided blood for genotyping. Statistical models examined the relationship between scale scores of social support and BDNF Val66Met genotype, while controlling for presence or absence of major depressive disorder and other demographic factors significantly associated with social support. As social support measures were not normally distributed, log-transformed scores were examined. After controlling for diagnosis and education level, the Met66 allele was associated with lower levels of subjective social support (F(1,357) = 5.33, P = 0.0216) and a trend for fewer social interactions (F(1,357) = 3.66, P = 0.0567). To our knowledge, this is the first report associating a measure of social support with a genetic polymorphism. This supports previous work that genetic factors may influence social support perception. Further work is needed to determine the generalizability of this finding to the broader population, as well as its significance for clinical outcomes.

The brain-derived neurotrophic factor VAL66MET polymorphism and cerebral white matter hyperintensities in late-life depression

OBJECTIVE

In animal models, brain-derived neurotrophic factor (BDNF) appears to protect against cerebral ischemia. The authors examined whether the BDNF Val66Met polymorphism, which affects BDNF distribution, was associated with greater volumes of hyperintense lesions as detected on magnetic resonance imaging in a cohort of depressed and nondepressed elders.

DESIGN

Subjects completed cross-sectional assessments, including clinical evaluation and a brain magnetic resonance imaging scan, and provided blood samples for Val66Met genotyping.

SETTING

The study was conducted at a university-based academic hospital.

PARTICIPANTS

Participants included 199 depressed and 113 nondepressed subjects aged 60 years or older.

MEASUREMENT

Hyperintensity lesion volumes were measured using a semiautomated segmentation procedure. Statistical models examined the relationship between genotype and lesion volume while controlling for depression, presence of hypertension, age, and sex.

RESULTS

After controlling for covariates, Met66 allele carriers exhibited significantly greater white matter hyperintensity volumes (F(1,311) = 4.09, p = 0.0442). This effect was independent of a diagnosis of depression or report of hypertension. Genotype was not significantly related to gray matter hyperintensity volume (F(1,311) = 1.14, p = 0.2871).

CONCLUSIONS

The BDNF Met66 allele is associated with greater white matter hyperintensity volumes in older individuals. Further work is needed to determine how this may be associated with other clinically relevant findings in late-life depression.

Hippocampus shape analysis and late-life depression

Major depression in the elderly is associated with brain structural changes and vascular lesions. Changes in the subcortical regions of the limbic system have also been noted. Studies examining hippocampus volumetric differences in depression have shown variable results, possibly due to any volume differences being secondary to local shape changes rather than differences in the overall volume. Shape analysis offers the potential to detect such changes. The present study applied spherical harmonic (SPHARM) shape analysis to the left and right hippocampi of 61 elderly subjects with major depression and 43 non-depressed elderly subjects. Statistical models controlling for age, sex, and total cerebral volume showed a significant reduction in depressed compared with control subjects in the left hippocampus (F_1,103 = 5.26; p = 0.0240) but not right hippocampus volume (F_1,103 = 0.41; p = 0.5213). Shape analysis showed significant differences in the mid-body of the left (but not the right) hippocampus between depressed and controls. When the depressed group was dichotomized into those whose depression was remitted at time of imaging and those who were unremitted, the shape comparison showed remitted subjects to be indistinguishable from controls (both sides) while the unremitted subjects differed in the midbody and the lateral side near the head. Hippocampal volume showed no difference between controls and remitted subjects but nonremitted subjects had significantly smaller left hippocampal volumes with no significant group differences in the right hippocampus. These findings may provide support to other reports of neurogenic effects of antidepressants and their relation to successful treatment for depressive symptoms.

Short/long heterozygotes at 5HTTLPR and white matter lesions in geriatric depression

OBJECTIVE

We examined the relationship between 5HTTLPR genotype and volume of magnetic resonance imaging (MRI) brain lesions.

METHOD

We studied 217 older depressed patients and 141 individuals in the comparison group using a standard brain MRI protocol to calculate lesion volumes. Genotype at 5HTTLPR was determined for each subject.

RESULTS

In age-adjusted models, the l/s genotype was associated with increased volume of total and white-matter lesions among depressed patients. This relationship lost significance in models controlling for reported hypertension.

CONCLUSIONS

The finding that 5HTTLPR heterozygotes have higher vascular lesion volumes may be related to development of hypertension.

Orbitofrontal cortex volume in late life depression: influence of hyperintense lesions and genetic polymorphisms

BACKGROUND

Orbitofrontal cortex (OFC) volumetric differences have been reported in depression, but in relatively small samples. Factors associated with these differences are not well described. We examined OFC volumes in a large sample of elderly depressed and non-depressed subjects, exploring the relationship between OFC volume, 5HTTLPR genotype, apolipoprotein E (APOE) genotype and hyperintense lesion volume. We hypothesized that smaller OFC volume would be associated with depression, greater hyperintense lesion volume and severity, and APOE epsilon4 or 5HTTLPR short allele carriers.

METHOD

A total of 226 depressed and 144 non-depressed older subjects completed 1.5 T magnetic resonance imaging (MRI) and genotyping. OFC volumes and lesion volumes were measured using standardized methods. Lesion severity was additionally rated using the Coffey rating scale. Differences between groups were compared while controlling for age, sex and total cerebral volume; separate models added lesion measures and genetic polymorphisms.

RESULTS

Depressed subjects exhibited smaller OFC volumes. There was a trend for a negative association between white-matter lesion volume and OFC volume; however, rated white-matter lesion severity was significantly negatively associated with OFC volume. There was no association between gray-matter lesion measures or 5HTTLPR genotype and OFC volume. Contrary to our hypothesis, subjects who were APOE epsilon4 allele positive exhibited larger OFC volumes; in secondary analyses, this finding was limited to the non-depressed group.

CONCLUSIONS

Reduced OFC volumes are seen in depression and associated with greater severity of white-matter lesions. Healthy subjects who are APOE epsilon4 allele positive exhibited larger OFC volumes. This finding should be examined in other populations.

Allelic differences in the brain-derived neurotrophic factor Val66Met polymorphism in late-life depression

OBJECTIVE

The Val66Met polymorphism of the brain-derived neurotrophic factor gene is associated with cognitive and neuroimaging changes. The authors examined the relationship between this polymorphism and depression in an elderly sample, hypothesizing that the Met66 allele would be associated with late-life depression.

METHODS

A total of 245 elderly depressed white subjects and 94 elderly comparison white subjects completed clinical assessments and provided a blood sample for genotyping. Subjects were dichotomized as either homozygous for the Val66 allele or Met66 allele carriers. Gene frequencies were compared between groups, with separate analyses examining for differences in gene frequencies based on age of depression onset, family history, and depression history. Logistic regression models examined the relationship between genotype and depression after controlling for age, sex, and race.

RESULTS

Depressed subjects were more likely to be Met66 allele carriers than were comparison subjects (38.8% versus 24.4%; chi(2) = 6.13, 1 df, p = 0.0133). This relationship remained significant after controlling for covariates (Wald chi(2) = 5.10, 1 df, p = 0.024; odds ratio: 1.92, 95% confidence interval: 1.09-3.38). There were no significant relationships between genotype and age of onset, number of episodes, or family history of depression.

CONCLUSION

Met66 allele carriers have almost double the odds of having geriatric depression than do Val66 allele homozygotes. This polymorphism was unrelated to other clinical characteristics of depression in later life.

Translational research in late-life mood disorders: implications for future intervention and prevention research

Clinical and epidemiological studies have consistently observed the heterogeneous symptomatology and course of geriatric depression. Given the importance of genetic and environmental risk factors, aging processes, neurodegenerative and cerebrovascular disease processes, and medical comorbidity, the integration of basic and clinical neuroscience research approaches is critical for the understanding of the variability in illness course, as well as the development of prevention and intervention strategies that are more effective. These considerations were the impetus for a workshop, sponsored by the Geriatrics Research Branch in the Division of Adult Translational Research and Treatment Development of the National Institute of Mental Health that was held on September 7-8, 2005. The primary goal of the workshop was to bring together investigators in geriatric psychiatry research with researchers in specific topic areas outside of geriatric mental health to identify priority areas to advance translational research in geriatric depression. As described in this report, the workshop focused on a discussion of the development and application of integrative approaches combining genetics and neuroimaging methods to understand such complex issues as treatment response variability, the role of medical comorbidity in depression, and the potential overlap between depression and dementia. Future directions for integrative research were identified. Understanding the nature of geriatric depression requires the application of translational research and interdisciplinary research approaches. Geriatric depression could serve as a model for translational research integrating basic and clinical neuroscience approaches that would have implications for the study of other neuropsychiatric disorders.

The COMT Val158Met polymorphism and temporal lobe morphometry in healthy adults

We examined the relationship between COMT Val158Met genotype and temporal lobe volumes, including the caudate as a control region. Thirty-one healthy subjects completed 1.5T brain MRI and genotyping. After controlling for demographics, Val158 allele homozygotes exhibited significantly smaller temporal lobe and hippocampal volumes, with a trend for smaller amygdala volumes.

Widespread effects of hyperintense lesions on cerebral white matter structure

OBJECTIVE

Hyperintense lesions are a common finding on neuroimaging and are associated not only with aging, medical illness, and some invasive medical procedures, but also with neurologic and psychiatric morbidity. We hypothesized that hyperintense lesions are associated with alterations in white matter structure beyond the visible lesion boundaries as assessed with diffusion tensor imaging (DTI).

SUBJECTS AND METHODS

Eighty-two neurologically intact older individuals completed brain MRI with DTI. DTI scans were analyzed using regions of interest placed in normal-appearing white matter to measure fractional anisotropy and diffusivity in the white matter of the frontal lobe, the genu of the corpus callosum, and the internal capsule. Hyperintense lesions volumes were measured separately in subcortical gray matter and anterior white matter through a semiautomated segmentation program. The relationship between lesion volumes and DTI measures was examined while controlling for patient age, patient sex, and total cerebral volume.

RESULTS

Greater anterior white matter lesion volumes were associated with higher diffusivity and lower anisotropy in the white matter of the dorsolateral prefrontal cortex and with higher diffusivity of the internal capsule and white matter lateral to the anterior cingulate cortex. Gray matter lesion volumes were associated with higher diffusivity in the genu of the corpus callosum and the internal capsule.

CONCLUSION

Ischemic hyperintense lesions are associated with widespread effects on the structure of the frontal lobe white matter and central white matter structures. This may reflect effects of lesions on neural circuits or identification of white matter changes that have not yet become visible on conventional MRI.

Structural integrity of the uncinate fasciculus in geriatric depression: Relationship with age of onset

BACKGROUND

The uncinate fasciculus connects limbic structures, such as the hippocampus and amygdala, with frontal regions. This study utilized diffusion tensor imaging to examine the structural integrity of the uncinate fasciculus in late-life depression.

METHOD

18 elderly depressed and 19 elderly nondepressed subjects were matched for age and sex; 8 subjects had mid- to late-onset of depression while 10 subjects had early-onset depression. 3T diffusion tensor imaging-based fiber tract mapping delineated the uncinate fasciculus in each hemisphere, which guided measurement of the fractional anisotropy of the uncinate fasciculus in the temporal stem. After controlling for age and sex, differences between diagnostic groups were assessed.

RESULTS

After controlling for age and sex, individuals with early onset depression exhibited lower anisotropy of the left uncinate fasciculus than did mid- and late-onset or nondepressed subjects (F(2,36) = 4.50, p = 0.02). Analyses of the right uncinate fasciculus were not statistically significant.

CONCLUSIONS

This provides preliminary evidence that there is a structural connectivity deficit between left frontal and limbic structures in early-onset depression. Further work is needed to determine if this is seen in younger depressed subjects, and if it influences treatment outcomes.

Geosmin and MIB events in a new reservoir in southern California

Diamond Valley Lake is a large drinking water reservoir in western Riverside County, California near the city of Hemet. In almost 6 years since filling began in 1999, this reservoir has experienced five episodes involving either geosmin or 2-methylisoborneol (MIB). The first one was a short-lived but intense geosmin event in May 2000, associated with a planktonic cyanobacterium, Anabaena circinalis. Geosmin levels reached 750 ng/L at the surface. All the other episodes involved benthic proliferations in the littoral zone. In September 2002, an MIB-producing growth developed in a shallow area near the outlet tower, dominated by Oscillatoria cf. curviceps and O. limosa. A similar event occurred in October 2003. In March 2004, an extensive growth of cyanobacteria that included two geosmin producers developed at the east dam, but had minimal effect on geosmin levels in the water. Finally, there was a major MIB episode in October 2004, in which the primary causative organism was again Oscillatoria cf. curviceps. A band of benthic cyanobacteria developed all around the shoreline from 3-9 m deep, and surface MIB levels reached 63 ng/L. These events showed that a new reservoir in a mild climate can be colonised by benthic cyanobacteria that produce MIB and geosmin, within a relatively short time.