Posterior Cerebellar Resting-State Functional Hypoconnectivity: A Neural Marker of Schizophrenia Across Different Stages of Treatment Response

BACKGROUND

Identifying stable and consistent resting-state functional connectivity patterns across illness trajectories has the potential to be considered fundamental to the pathophysiology of schizophrenia. We aimed to identify consistent resting-state functional connectivity patterns across heterogeneous schizophrenia groups defined based on treatment response.

METHODS

In phase 1, we used a cross-sectional case-control design to characterize and compare stable independent component networks from resting-state functional magnetic resonance imaging scans of antipsychotic-naïve participants with first-episode schizophrenia (n = 54) and healthy participants (n = 43); we also examined associations with symptoms, cognition, and disability. In phase 2, we examined the stability (and replicability) of our phase 1 results in 4 groups (N = 105) representing a cross-sequential gradation of schizophrenia based on treatment response: risperidone responders, clozapine responders, clozapine nonresponders, and clozapine nonresponders following electroconvulsive therapy. Hypothesis-free whole-brain within- and between-network connectivity were examined.

RESULTS

Phase 1 identified posterior and anterior cerebellar hypoconnectivity and limbic hyperconnectivity in schizophrenia at a familywise error rate-corrected cluster significance threshold of p < .01. These network aberrations had unique associations with positive symptoms, cognition, and disability. During phase 2, we replicated the phase 1 results while comparing each of the 4 schizophrenia groups to the healthy participants. The participants in 2 longitudinal subdatasets did not demonstrate a significant change in these network aberrations following risperidone or electroconvulsive therapy. Posterior cerebellar hypoconnectivity (with thalamus and cingulate) emerged as the most consistent finding; it was replicated across different stages of treatment response (Cohen's d range -0.95 to -1.44), reproduced using different preprocessing techniques, and not confounded by educational attainment.

CONCLUSIONS

Posterior cerebellar-thalamo-cingulate hypoconnectivity is a consistent and stable state-independent neural marker of schizophrenia.

Peripherally acting anti-CGRP monoclonal antibodies alter cortical gray matter thickness in migraine patients: A prospective cohort study

Migraine is underpinned by central nervous system neuroplastic alterations thought to be caused by the repetitive peripheral afferent barrage the brain receives during the headache phase (cortical hyperexcitability). Calcitonin gene-related peptide monoclonal antibodies (anti-CGRP-mAbs) are highly effective migraine preventative treatments. Their ability to alter brain morphometry in treatment-responders vs. non-responders is not well understood. Our aim was to determine the effects of the anti-CGRP-mAb galcanezumab on cortical thickness after 3-month treatment of patients with high-frequency episodic or chronic migraine. High-resolution magnetic resonance imaging was performed pre- and post-treatment in 36 migraine patients. In this group, 19 patients were classified responders (≥50 % reduction in monthly migraine days) and 17 were considered non-responders (<50 % reduction in monthly migraine days). Following cross-sectional processing to analyze the baseline differences in cortical thickness, two-stage longitudinal processing and symmetrized percent change were conducted to investigate treatment-related brain changes. At baseline, no significant differences were found between the responders and non-responders. After 3-month treatment, decreased cortical thickness (compared to baseline) was observed in the responders in regions of the somatosensory cortex, anterior cingulate cortex, medial frontal cortex, superior frontal gyrus, and supramarginal gyrus. Non-responders demonstrated decreased cortical thickness in the left dorsomedial cortex and superior frontal gyrus. We interpret the cortical thinning seen in the responder group as suggesting that reduction in head pain could lead to changes in neural swelling and dendritic complexity and that such changes reflect the recovery process from maladaptive neural activity. This conclusion is further supported by our recent study showing that 3 months after treatment initiation, the incidence of premonitory symptoms and prodromes that are followed by headache decreases but not the incidence of the premonitory symptoms or prodromes themselves (that is, cortical thinning relates to reductions in the nociceptive signals in the responders). We speculate that a much longer recovery period is required to allow the brain to return to a more 'normal' functioning state whereby prodromes and premonitory symptoms no longer occur.

Affine image registration of arterial spin labeling MRI using deep learning networks

Convolutional neural networks (CNN) have demonstrated good accuracy and speed in spatially registering high signal-to-noise ratio (SNR) structural magnetic resonance imaging (sMRI) images. However, some functional magnetic resonance imaging (fMRI) images, e.g., those acquired from arterial spin labeling (ASL) perfusion fMRI, are of intrinsically low SNR and therefore the quality of registering ASL images using CNN is not clear. In this work, we aimed to explore the feasibility of a CNN-based affine registration network (ARN) for registration of low-SNR three-dimensional ASL perfusion image time series and compare its performance with that from the state-of-the-art statistical parametric mapping (SPM) algorithm. The six affine parameters were learned from the ARN using both simulated motion and real acquisitions from ASL perfusion fMRI data and the registered images were generated by applying the transformation derived from the affine parameters. The speed and registration accuracy were compared between ARN and SPM. Several independent datasets, including meditation study (10 subjects × 2), bipolar disorder study (26 controls, 19 bipolar disorder subjects), and aging study (27 young subjects, 33 older subjects), were used to validate the generality of the trained ARN model. The ARN method achieves superior image affine registration accuracy (total translation/total rotation errors of ARN vs. SPM: 1.17 mm/1.23° vs. 6.09 mm/12.90° for simulated images and reduced MSE/L1/DSSIM/Total errors of 18.07% / 19.02% / 0.04% / 29.59% for real ASL test images) and 4.4 times (ARN vs. SPM: 0.50 s vs. 2.21 s) faster speed compared to SPM. The trained ARN can be generalized to align ASL perfusion image time series acquired with different scanners, and from different image resolutions, and from healthy or diseased populations. The results demonstrated that our ARN markedly outperforms the iteration-based SPM both for simulated motion and real acquisitions in terms of registration accuracy, speed, and generalization.

Hyperglycemia and hyperinsulinemia effects on anterior cingulate cortex myoinositol-relation to brain network functional connectivity in healthy adults

Brain mechanisms underlying the association of diabetes metabolic disorders-hyperglycemia and insulin resistance-with cognitive impairment are unknown. Myoinositol is a brain metabolite involved in cell osmotic balance, membrane phospholipid turnover, and second messenger neurotransmission, which affect brain function. Increased brain myoinositol and altered functional connectivity have been found in diabetes, mild cognitive impairment, and Alzheimer's disease, but the independent effects of plasma glucose and insulin on brain myoinositol and function are not characterized. We measured myoinositol concentrations in the pregenual anterior cingulate cortex (ACC), a region involved in self-reflective awareness and decision making, using proton magnetic resonance spectroscopy, and whole brain resting-state functional connectivity using fMRI, during acute hyperglycemia (with attendant hyperinsulinemia) and euglycemic-hyperinsulinemia compared with basal fasting-euglycemia (EU) in 11 healthy nondiabetic participants (5 women/6 men, means ± SD, age: 27 ± 7 yr, fasting-glucose: 5.2 ± 0.4 mmol/L, fasting-insulin: 4.9 ± 4.4 μU/mL). Brain MR data were acquired during two separate visits: 1) EU followed by a 60-min hyperglycemic-clamp (glucose: 10.7 ± 0.2 mmol/L, insulin: 33 ± 6 μU/mL); 2) EU followed by a hyperinsulinemic-euglycemic-clamp (glucose: 5.3 ± 0.1 mmol/L, insulin: 27 ± 5 μU/mL) designed to match individual insulin levels achieved during the visit 1 hyperglycemic-clamp. Myoinositol decreased by 14% during the hyperglycemic-clamp (from 7.7 ± 1.5 mmol/kg to 6.6 ± 0.8 mmol/kg, P = 0.031), and by 9% during the hyperinsulinemic-euglycemic-clamp (from 7.1 ± 0.7 mmol/kg to 6.5 ± 0.7 mmol/kg, P = 0.014), with no significant difference between the two clamps. Lower myoinositol was associated with higher functional connectivity of the thalamus and precentral cortex with insula-ACC-related networks, suggesting myoinositol is involved in insulin modulation of cognitive/emotional network function in healthy adults. Regional brain myoinositol levels may be useful biomarkers for monitoring cognitive and mood-enhancing treatment responses.NEW & NOTEWORTHY Hyperinsulinemia-related decreases of brain anterior cingulate cortex (ACC) myoinositol independent of plasma glucose levels and the association of low ACC myoinositol with increased functional connectivity between sensorimotor regions and ACC/insula-related networks suggest involvement of myoinositol in insulin-modulated brain network function in healthy adults. In diabetes, elevated brain myoinositol may be due to reduced brain insulin levels or action, rather than hyperglycemia, and may be involved in brain network dysfunctions leading to cognitive or mood disorders.

Intermittent theta burst stimulation of cerebellar vermis enhances fronto-cerebellar resting state functional connectivity in schizophrenia with predominant negative symptoms: A randomized controlled trial

OBJECTIVE

Negative symptoms of schizophrenia are substantially disabling and treatment resistant. Novel treatments like repetitive transcranial magnetic stimulation (TMS) need to be examined for the same using the experimental medicine approach that incorporates tests of mechanism of action in addition to clinical efficacy in trials.

METHODS

Study was a double-blind, parallel, randomized, sham-controlled trial recruiting schizophrenia with at least a moderate severity of negative symptoms. Participants were randomized to real or sham intermittent theta burst stimulation (iTBS) under MRI-guided neuro-navigation, targeting the cerebellar vermis area VII-B, at a stimulus intensity of 100% active motor threshold, two sessions/day for five days (total = 6000 pulses). Assessments were conducted at baseline (T0), day-6 (T1) and week-6 (T2) after initiation of intervention. Main outcomes were, a) Scale for the Assessment of Negative Symptoms (SANS) score (T0, T1, T2), b) fronto-cerebellar resting state functional connectivity (RSFC) (T0, T1).

RESULTS

Thirty participants were recruited in each arm. Negative symptoms improved in both arms (p < 0.001) but was not significantly different between the two arms (p = 0.602). RSFC significantly increased between the cerebellar vermis and the right inferior frontal gyrus (p_cluster-FWER = 0.033), right pallidum (p_cluster-FWER = 0.042) and right frontal pole (p_cluster-FWER = 0.047) in the real arm with no change in the sham arm.

CONCLUSION

Cerebellar vermal iTBS engaged a target belonging to the class of cerebello-subcortical-cortical networks, implicated in negative symptoms of schizophrenia. However, this did not translate to a superior clinical efficacy. Future trials should employ enhanced midline cerebellar TMS stimulation parameters for longer durations that can potentiate and translate biological changes into clinical effects.

Altered cerebral perfusion in bipolar disorder: A pCASL MRI study

BACKGROUND

Neurovascular abnormalities are relevant to the pathophysiology of bipolar disorder (BD), which can be assessed using cerebral blood flow (CBF) imaging. CBF alterations have been identified in BD, but studies to date have been small and inconclusive. We aimed to determine cortical gray matter CBF (GM-CBF) differences between BD and healthy controls (HC) and to identify relationships between CBF and clinical or cognitive measures.

METHODS

Cortical GM-CBF maps were generated using Pseudo-Continuous Arterial Spin Labeling (pCASL) for 109 participants (BD, n = 61; HC, n = 48). We used SnPM13 to perform non-parametric voxel-wise two-sample t-tests comparing CBF between groups. We performed multiple linear regression to relate GM-CBF with clinical and cognitive measures. Analysis was adjusted for multiple comparisons with 10,000 permutations. Significance was set at a voxel level threshold of P < .001 followed by AlphaSim cluster-wise correction of P < .05.

RESULTS

Compared to HCs, BD patients had greater GM-CBF in the left lateral occipital cortex, superior division and lower CBF in the right lateral occipital, angular and middle temporal gyrus. Greater GM-CBF in the left lateral occipital cortex correlated with worse working memory, verbal memory, attention and speed of processing. We found using voxel-wise regression that decreased gray matter CBF in the bilateral thalamus and cerebellum, and increased right fronto-limbic CBF were associated with worse working memory. No clusters were associated with clinical variables after FDR correction.

CONCLUSIONS

Cortical GM-CBF alterations are seen in BD and may be related to cognitive function, which suggest neurovascular unit dysfunction as a possible pathophysiologic mechanism.

Acute Hyperglycemia Increases Brain Pregenual Anterior Cingulate Cortex Glutamate Concentrations in Type 1 Diabetes

The brain mechanisms underlying the association of hyperglycemia with depressive symptoms are unknown. We hypothesized that disrupted glutamate metabolism in pregenual anterior cingulate cortex (ACC) in type 1 diabetes (T1D) without depression affects emotional processing. Using proton MRS, we measured glutamate concentrations in ACC and occipital lobe cortex (OCC) in 13 subjects with T1D without major depression (HbA_1c 7.1 ± 0.7% [54 ± 7 mmol/mol]) and 11 healthy control subjects without diabetes (HbA_1c 5.5 ± 0.2% [37 ± 3 mmol/mol]) during fasting euglycemia followed by a 60-min +5.5 mmol/L hyperglycemic clamp (HG). Intrinsic neuronal activity was assessed using resting-state blood oxygen level-dependent functional MRI to measure the fractional amplitude of low-frequency fluctuations in slow-4 band (fALFF4). Emotional processing and depressive symptoms were assessed using emotional tasks (emotional Stroop task, self-referent encoding task [SRET]) and clinical ratings (Hamilton Depression Rating Scale [HAM-D], Symptom Checklist-90 Revised [SCL-90-R]), respectively. During HG, ACC glutamate increased (1.2 mmol/kg, 10% P = 0.014) while ACC fALFF4 was unchanged (-0.007, -2%, P = 0.449) in the T1D group; in contrast, glutamate was unchanged (-0.2 mmol/kg, -2%, P = 0.578) while fALFF4 decreased (-0.05, -13%, P = 0.002) in the control group. OCC glutamate and fALFF4 were unchanged in both groups. T1D had longer SRET negative word response times (P = 0.017) and higher depression rating scores (HAM-D P = 0.020, SCL-90-R depression P = 0.008). Higher glutamate change tended to associate with longer emotional Stroop response times in T1D only. Brain glutamate must be tightly controlled during hyperglycemia because of the risk for neurotoxicity with excessive levels. Results suggest that ACC glutamate control mechanisms are disrupted in T1D, which affects glutamatergic neurotransmission related to emotional or cognitive processing. Increased prefrontal glutamate during acute hyperglycemic episodes could explain our previous findings of associations among chronic hyperglycemia, cortical thinning, and depressive symptoms in T1D.

Abnormal perfusion fluctuation and perfusion connectivity in bipolar disorder measured by dynamic arterial spin labeling

OBJECTIVES

We sought to evaluate whether dynamic Arterial Spin Labeling (dASL), a novel quantitative technique robust to artifacts and noise that especially arise in inferior brain regions, could characterize neural substrates of BD pathology and symptoms.

METHODS

Forty-five subjects (19 BD patients, 26 controls) were imaged using a dASL sequence. Maps of average perfusion, perfusion fluctuation, and perfusion connectivity with anterior cingulate cortex (ACC) were derived. Patient symptoms were quantified along four symptom dimensions determined using factor analysis of the subjects from the Bipolar and Schizophrenia Network on Intermediate Phenotypes (BSNIP) study. Maps of the perfusion measures were compared between BD patients and controls and correlated with the symptom dimensions in the BD patients only by voxel-level and region-level analyses.

RESULTS

BD patients exhibited (i) significantly increased perfusion fluctuations in the left fusiform and inferior temporal regions (P = .020, voxel-level corrected) and marginally increased perfusion fluctuations in the right temporal pole and inferior temporal regions (P = .063, cluster-level corrected), (ii) significantly increased perfusion connectivity between ACC and the occipitoparietal cortex (P = .050, cluster-level corrected). In BD patients, positive symptoms were negatively associated with ACC perfusion connectivity to the right orbitofrontal and superior frontal regions (P = .002, cluster-level corrected) and right orbitofrontal and inferior frontal regions (P = .023, cluster-level corrected).

CONCLUSION

The abnormal perfusion fluctuations and connectivity alterations may underlie the mood fluctuations and cognitive and emotional dysregulation that characterize BD.

NRXN1 is associated with enlargement of the temporal horns of the lateral ventricles in psychosis

Schizophrenia, Schizoaffective, and Bipolar disorders share behavioral and phenomenological traits, intermediate phenotypes, and some associated genetic loci with pleiotropic effects. Volumetric abnormalities in brain structures are among the intermediate phenotypes consistently reported associated with these disorders. In order to examine the genetic underpinnings of these structural brain modifications, we performed genome-wide association analyses (GWAS) on 60 quantitative structural brain MRI phenotypes in a sample of 777 subjects (483 cases and 294 controls pooled together). Genotyping was performed with the Illumina PsychChip microarray, followed by imputation to the 1000 genomes multiethnic reference panel. Enlargement of the Temporal Horns of Lateral Ventricles (THLV) is associated with an intronic SNP of the gene NRXN1 (rs12467877, P = 6.76E-10), which accounts for 4.5% of the variance in size. Enlarged THLV is associated with psychosis in this sample, and with reduction of the hippocampus and enlargement of the choroid plexus and caudate. Eight other suggestively significant associations (P < 5.5E-8) were identified with THLV and 5 other brain structures. Although rare deletions of NRXN1 have been previously associated with psychosis, this is the first report of a common SNP variant of NRXN1 associated with enlargement of the THLV in psychosis.

Diabetes and the link between neuroplasticity and glutamate in the aging human motor cortex

OBJECTIVES

In older adults, type-2 diabetes mellitus (T2DM) impacts cognition and increases dementia risk. Prior studies suggest that impaired neuroplasticity may contribute to the cognitive decline in T2DM, but the underlying mechanisms of altered neuroplasticity are unclear. We investigated the relationship of the concentration of glutamatergic metabolites with measures of cortical plasticity in older adults across the spectrum of glucose intolerance/insulin resistance.

METHODS

Forty adults (50-87 years: 17-T2DM, 14-pre-diabetes, 9-controls) underwent magnetic resonance spectroscopy to quantify glutamate and other key metabolites within a 2 cm3 region around the hand knob of the left primary motor cortex. Thirty-six also underwent a separate transcranial magnetic stimulation (TMS) assessment of cortical excitability and plasticity using single-pulse TMS and intermittent theta-burst stimulation targeting the same brain region.

RESULTS

Group differences were observed in relative concentrations of glutamine (p = .028), glucose (p = .008), total cholines (p = .048), and the glutamine/glutamate ratio (p = .024). Cortical plasticity was reduced in both T2DM and pre-diabetes groups relative to controls (p-values < .05). Only the T2DM group showed a significant positive association between glutamate concentration and plasticity (r = .56, p = .030).

CONCLUSIONS

Neuroplastic mechanisms are already impaired in pre-diabetes. In T2DM, reduced cortico-motor plasticity is associated with lower cortical glutamate concentration.

SIGNIFICANCE

Impaired plasticity in T2DM is associated with low glutamatergic metabolite levels. The glutamatergic neurotransmission system constitutes a potential therapeutic target for cognitive problems linked to plasticity-related deficiencies in T2DM.

Prefronto-temporal white matter microstructural alterations 20 years after the diagnosis of type 1 diabetes mellitus

OBJECTIVE

Microvascular pathophysiology that uniquely manifests as white matter (WM) abnormalities is often implicated in type 1 diabetes mellitus (T1DM)-related central nervous system (CNS) complications. This study sought to identify regional WM abnormalities in young adults diagnosed with T1DM and further examine their association with cognitive and emotional dysfunction.

RESEARCH DESIGN AND METHODS

Diffusion tensor images (DTI) obtained from 34 young adults with T1DM for ≥15 years (mean duration, 20.9 years), and 16 age- and sex-matched healthy control subjects were analyzed using tract-based spatial statistics. Fractional anisotropy (FA) values of the whole brain were analyzed, and their associations with memory function and depressive symptoms were assessed.

RESULTS

Whole brain voxel-wise analyses showed that T1DM-related FA reductions were most prominent within the fronto-temporo-parietal regions of the brain. Reduced FA values in the bilateral superior longitudinal fasciculi, at which group differences were most prominent, correlated with lower working memory performance in young adults with T1DM (left, P < .001; right, P = .009). Subsyndromal depressive symptoms were also associated with lower FA values in the right inferior fronto-occipital fasciculus (P = .004).

CONCLUSION

Widespread WM microstructural abnormalities in the fronto-temporo-parietal brain regions, which are associated with emotional and cognitive dysfunction, may be a contributing factor to the neural mechanisms underlying T1DM-related CNS complications, thus affecting the quality of life in young adults with T1DM.

Task-induced brain activity patterns in type 2 diabetes: a potential biomarker for cognitive decline

Patients with type 2 diabetes demonstrate reduced functional connectivity within the resting state default mode network (DMN), which may signal heightened risk for cognitive decline. In other populations at risk for cognitive decline, additional magnetic resonance imaging abnormalities are evident during task performance, including impaired deactivation of the DMN and reduced activation of task-relevant regions. We investigated whether middle-aged type 2 diabetic patients show these brain activity patterns during encoding and recognition tasks. Compared with control participants, we observed both reduced 1) activation of the dorsolateral prefrontal cortex during encoding and 2) deactivation of the DMN during recognition in type 2 diabetic patients, despite normal cognition. During recognition, activation in several task-relevant regions, including the dorsolateral prefrontal cortex and DMN regions, was positively correlated with HbA1c and insulin resistance, suggesting that these important markers of glucose metabolism impact the brain's response to a cognitive challenge. Plasma glucose ≥11 mmol/L was associated with impaired deactivation of the DMN, suggesting that acute hyperglycemia contributes to brain abnormalities. Since elderly type 2 diabetic patients often demonstrate cognitive impairments, it is possible that these task-induced brain activity patterns observed in middle age may signal impending cognitive decline.

Cerebral white matter integrity and resting-state functional connectivity in middle-aged patients with type 2 diabetes

Early detection of brain abnormalities at the preclinical stage can be useful for developing preventive interventions to abate cognitive decline. We examined whether middle-aged type 2 diabetic patients show reduced white matter integrity in fiber tracts important for cognition and whether this abnormality is related to preestablished altered resting-state functional connectivity in the default mode network (DMN). Diabetic and nondiabetic participants underwent diffusion tensor imaging, functional magnetic resonance imaging, and cognitive assessment. Multiple diffusion measures were calculated using streamline tractography, and correlations with DMN functional connectivity were determined. Diabetic patients showed lower fractional anisotropy (FA) (a measure of white matter integrity) in the cingulum bundle and uncinate fasciculus. Control subjects showed stronger functional connectivity than patients between the posterior cingulate and both left fusiform and medial frontal gyri. FA of the cingulum bundle was correlated with functional connectivity between the posterior cingulate and medial frontal gyrus for combined groups. Thus, middle-aged patients with type 2 diabetes show white matter abnormalities that correlate with disrupted functional connectivity in the DMN, suggesting that common mechanisms may underlie structural and functional connectivity. Detecting brain abnormalities in middle age enables implementation of therapies to slow progression of neuropathology.

Time-dependent effects of haloperidol on glutamine and GABA homeostasis and astrocyte activity in the rat brain

RATIONALE

Schizophrenia is a severe, persistent, and fairly common mental illness. Haloperidol is widely used and is effective against the symptoms of psychosis seen in schizophrenia. Chronic oral haloperidol administration decreased the number of astrocytes in the parietal cortex of macaque monkeys (Konopaske et al., Biol Psych 63:759-765, 2008). Since astrocytes play a key role in glutamate metabolism, chronic haloperidol administration was hypothesized to modulate astrocyte metabolic function and glutamate homeostasis.

OBJECTIVES

This study investigated the effects of chronic haloperidol administration on astrocyte metabolic activity and glutamate, glutamine, and GABA homeostasis.

METHODS

We used ex vivo ¹³C magnetic resonance spectroscopy along with high-performance liquid chromatography after [1-¹³C]glucose and [1,2-¹³C]acetate administration to analyze forebrain tissue from rats administered oral haloperidol for 1 or 6 months.

RESULTS

Administration of haloperidol for 1 month produced no changes in ¹³C labeling of glutamate, glutamine, or GABA, or in their total levels. However, a 6-month haloperidol administration increased ¹³C labeling of glutamine by [1,2-¹³C]acetate. Moreover, total GABA levels were also increased. Haloperidol administration also increased the acetate/glucose utilization ratio for glutamine in the 6-month cohort.

CONCLUSIONS

Chronic haloperidol administration in rats appears to increase forebrain GABA production along with astrocyte metabolic activity. Studies exploring these processes in subjects with schizophrenia should take into account the potential confounding effects of antipsychotic medication treatment.

Resting-state brain functional connectivity is altered in type 2 diabetes

Type 2 diabetes mellitus (T2DM) is a risk factor for Alzheimer disease (AD). Populations at risk for AD show altered brain activity in the default mode network (DMN) before cognitive dysfunction. We evaluated this brain pattern in T2DM patients. We compared T2DM patients (n = 10, age = 56 ± 2.2 years, fasting plasma glucose [FPG] = 8.4 ± 1.3 mmol/L, HbA(1c) = 7.5 ± 0.54%) with nondiabetic age-matched control subjects (n = 11, age = 54 ± 1.8 years, FPG = 4.8 ± 0.2 mmol/L) using resting-state functional magnetic resonance imaging to evaluate functional connectivity strength among DMN regions. We also evaluated hippocampal volume, cognition, and insulin sensitivity by homeostasis model assessment of insulin resistance (HOMA-IR). Control subjects showed stronger correlations versus T2DM patients in the DMN between the seed (posterior cingulate) and bilateral middle temporal gyrus (β = 0.67 vs. 0.43), the right inferior and left medial frontal gyri (β = 0.75 vs. 0.54), and the left thalamus (β = 0.59 vs. 0.37), respectively, with no group differences in cognition or hippocampal size. In T2DM patients, HOMA-IR was inversely correlated with functional connectivity in the right inferior frontal gyrus and precuneus. T2DM patients showed reduced functional connectivity in the DMN compared with control subjects, which was associated with insulin resistance in selected brain regions, but there were no group effects of brain structure or cognition.

Brain activation during working memory is altered in patients with type 1 diabetes during hypoglycemia

OBJECTIVE

To investigate the effects of acute hypoglycemia on working memory and brain function in patients with type 1 diabetes.

RESEARCH DESIGN AND METHODS

Using blood oxygen level-dependent (BOLD) functional magnetic resonance imaging during euglycemic (5.0 mmol/L) and hypoglycemic (2.8 mmol/L) hyperinsulinemic clamps, we compared brain activation response to a working-memory task (WMT) in type 1 diabetic subjects (n = 16) with that in age-matched nondiabetic control subjects (n = 16). Behavioral performance was assessed by percent correct responses.

RESULTS

During euglycemia, the WMT activated the bilateral frontal and parietal cortices, insula, thalamus, and cerebellum in both groups. During hypoglycemia, activation decreased in both groups but remained 80% larger in type 1 diabetic versus control subjects (P < 0.05). In type 1 diabetic subjects, higher HbA(1c) was associated with lower activation in the right parahippocampal gyrus and amygdala (R(2) = 0.45, P < 0.002). Deactivation of the default-mode network (DMN) also was seen in both groups during euglycemia. However, during hypoglycemia, type 1 diabetic patients deactivated the DMN 70% less than control subjects (P < 0.05). Behavioral performance did not differ between glycemic conditions or groups.

CONCLUSIONS

BOLD activation was increased and deactivation was decreased in type 1 diabetic versus control subjects during hypoglycemia. This higher level of brain activation required by type 1 diabetic subjects to attain the same level of cognitive performance as control subjects suggests reduced cerebral efficiency in type 1 diabetes.

Brain bioenergetics and response to triiodothyronine augmentation in major depressive disorder

BACKGROUND

Low cerebral bioenergetic metabolism has been reported in subjects with major depressive disorder (MDD). Thyroid hormones have been shown to increase brain bioenergetic metabolism. We assessed whether changes in brain bioenergetics measured with phosphorus magnetic resonance spectroscopy ((31)P MRS) correlate with treatment outcome during augmentation treatment with triiodothyronine (T3) in MDD.

METHODS

Nineteen subjects meeting DSM-IV criteria for MDD who had previously failed to respond to selective serotonin reuptake inhibitor (SSRI) antidepressant drugs received open label and prospective augmentation treatment with T3 for 4 weeks. We obtained (31)P MRS spectra before and after treatment from all MDD subjects and baseline (31)P MRS from nine normal control subjects matched for age and gender.

RESULTS

At baseline, depressed subjects had lower intracellular Mg(2+) compared with control subjects. Seven MDD subjects (38.9%) were treatment responders (>or= 50% improvement). Total nucleoside triphosphate (NTP), which primarily represents adenosine triphosphate (ATP), increased significantly in MDD subjects responding to T3 augmentation compared with treatment nonresponders. Phosphocreatine, which has a buffer role for ATP, decreased in treatment responders compared with nonresponders.

CONCLUSIONS

The antidepressant effect of thyroid hormone (T3) augmentation of SSRIs is correlated with significant changes in the brain bioenergetic metabolism. This seems to be a re-normalization of brain bioenergetics in treatment responders. Further studies will determine whether these findings can be generalized to other antidepressant treatments.

Triacetyluridine (TAU) decreases depressive symptoms and increases brain pH in bipolar patients

Eleven patients with bipolar depression were given doses of up to 18 g per day of triacetyluridine (TAU) over 6 weeks to test the effect of uridine on symptoms of depression via Montgomery-Asberg Depression Rating Scale (MADRS; Asberg, Montgomery, Perris, Schalling, & Sedvall, 1978) scores and on cellular bioenergetics using phosphorus magnetic resonance spectroscopic imaging (31P-MRSI). All patients and comparison participants (n = 9) completed baseline 31P-MRSI scans, and 9 patients completed posttherapy scans. The percentage changes for MADRS scores (Week 2, -23.8; Week 3, -34.9; Week 4, -42.5) and the time effects of TAU on MADRS scores (Week 2, z = -2.07, p = .039; Week 3, z = -4.28, p < .001; Week 4, z = -4.54, p < .001) may reflect TAU effects on early symptom improvement. TAU responders (patients who had a 50% or greater reduction in MADRS scores from baseline at any time) demonstrated a significant difference from nonresponders in pH changes from baseline (effect size = 150). These results suggest that TAU treatment may decrease symptoms of depression and improve mitochondrial functioning.

Regional brain activation during hypoglycemia in type 1 diabetes

CONTEXT

Mechanisms underlying the brain response to hypoglycemia are not well understood.

OBJECTIVE

Our objective was to determine the blood glucose level at which the hypothalamus and other brain regions are activated in response to hypoglycemia in type 1 diabetic patients and control subjects.

DESIGN

This was a cross-sectional study evaluating brain activity using functional magnetic resonance imaging in conjunction with a hyperinsulinemic hypoglycemic clamp to lower glucose from euglycemia (90 mg/dl) to hypoglycemia (50 mg/dl).

SETTING

The study was performed at the Brain Imaging Center in the McLean Hospital.

STUDY PARTICIPANTS

Seven type 1 diabetic patients between 18 and 50 yr old and six matched control subjects were included in the study.

INTERVENTION

Hyperinsulinemic hypoglycemic clamp was performed.

MAIN OUTCOME MEASURES

Blood glucose level at peak hypothalamic activation, amount of regional brain activity during hypoglycemia in both groups, and difference in regional brain activation between groups were calculated.

RESULTS

The hypothalamic region activates at 68 +/- 9 mg/dl in control subjects and 76 +/- 8 mg/dl in diabetic patients during hypoglycemia induction. Brainstem, anterior cingulate cortex, uncus, and putamen were activated in both groups (P < 0.001). Each group also activated unique brain areas not active in the other group.

CONCLUSIONS

This application of functional magnetic resonance imaging can be used to identify the glucose level at which the hypothalamus is triggered in response to hypoglycemia and whether this threshold differs across patient populations. This study suggests that a core network of brain regions is recruited during hypoglycemia in both diabetic patients and control subjects.

Occipital cortical proton MRS at 4 Tesla in human moderate MDMA polydrug users

The recreational drug MDMA (3,4, methylenedioxymethamphetamine; sold under the street name of Ecstasy) is toxic to serotonergic axons in some animal models of MDMA administration. In humans, MDMA use is associated with alterations in markers of brain function that are pronounced in occipital cortex. Among neuroimaging methods, magnetic resonance spectroscopy (MRS) studies of brain metabolites N-acetylaspartate (NAA) and myoinositol (MI) at a field strength of 1.5 Tesla (T) reveal inconsistent results in MDMA users. Because higher field strength proton MRS has theoretical advantages over lower field strengths, we used proton MRS at 4.0 T to study absolute concentrations of occipital cortical NAA and MI in a cohort of moderate MDMA users (n=9) versus non-MDMA using (n=7) controls. Mean NAA in non-MDMA users was 10.47 mM (+/-2.51), versus 9.83 mM (+/-1.94) in MDMA users. Mean MI in non-MDMA users was 7.43 mM (+/-.68), versus 6.57 mM (+/-1.59) in MDMA users. There were no statistical differences in absolute metabolite levels for NAA and MI in occipital cortex of MDMA users and controls. These findings are not supportive of MDMA-induced alterations in NAA or MI levels in this small sample of moderate MDMA users. Limitations to this study suggest caution in the interpretation of these results.

Magnetic resonance spectroscopy for measuring the biodistribution and in situ in vivo pharmacokinetics of fluorinated compounds: validation using an investigation of liver and heart disposition of tecastemizole

BACKGROUND AND OBJECTIVE

The study of biodistribution and in situ pharmacokinetics is a challenging, but sometimes very important, aspect of premarketing characterization of drugs. We aimed to develop a non-invasive fluorine magnetic resonance (MR) spectroscopic method for the absolute quantitation of a mono-fluorinated compound and of its metabolites in the heart and liver of healthy subjects for this purpose.

METHOD

We used fluorine MR spectroscopy (MRS) at 4 T (Tesla) and external standardization in an open label multiple-dose study. Twenty-three healthy adult subjects were enrolled in the study. The surface coil localized fluorine MR spectrum was monitored in the heart and liver at baseline and after oral administration of multiple doses of tecastemizole. Steady-state measurements were made at set time points that depended upon dose, and washout measurements were made only on subjects in which in vivo fluorine signal was observed.

RESULTS AND DISCUSSION

At 4 T, under the given experimental conditions, the method had a lower limit of quantitation (LLOQ) of about 2.6 microm and a limit of detection (LOD) of about 0.3 microm for solution state samples (linewidth approximately 15 Hz). The measurement reproducibility was 6.4% using a 50 microm phantom. The effect of MR operator and spectral analyst on the calculated calibration curve slope was small, with inter-rater correlation coefficients of 0.999 and 0.998 respectively. MR signal from fluorine-containing tecastemizole-related moieties was observed in situ only at day 8 in the liver of three of five subjects dosed at 270 mg/day. The average in situ concentration was estimated to be 58+/-22 microm, with an average test-retest reproducibility of 216%. Extrapolating the in vitro results to human measurements, with an approximate linewidth of 250 Hz, predicts in situ LOD and LLOQ values of approximately 6 and 44 microm respectively. However, the human study had a fluorine MRS LOD of approximately 20 microm. The decrease in sensitivity and the increase in variability of the in vivo, in situ measurements compared with the validation study most likely arose from coil placement and incomplete rephasing of the MR signal by the respiratory phase compensation method.

CONCLUSION

The measured concentrations were the lowest ever recorded for a multi-dose exogenous mono-fluorinated compound in the human liver using a validated fluorine MR quantitation method. The proposed non-invasive MR method for studying the biodistribution and in situ pharmacokinetics of mono-fluorinated compounds in the liver and heart should have broader application to the development of non-invasive biomarkers.

Long-term sequestration of fluorinated compounds in tissues after fluvoxamine or fluoxetine treatment: a fluorine magnetic resonance spectroscopy study in vivo

Fluorine magnetic resonance spectroscopy (19F MRS), spectroscopic imaging (MRSI) and proton anatomical magnetic resonance imaging (1H MRI) were performed on brains and lower extremities of six subjects in vivo concurrently with HPLC of serum to investigate tissue and plasma drug localization and withdrawal kinetics in humans treated with fluvoxamine or fluoxetine. 19F MRS signal was unexpectedly detected in the lower extremities months after complete disappearance of signal from plasma and brain. MRSI suggested that the lower extremity fluvoxamine signal originated mainly from bone marrow. Results suggest long-term sequestration of these drugs or their metabolites mainly in bone marrow and possibly in surrounding tissue and demonstrate the usefulness of MRS to reveal drug-trapping compartments in the body.

Brain pharmacokinetics and tissue distribution in vivo of fluvoxamine and fluoxetine by fluorine magnetic resonance spectroscopy

This investigation of fluvoxamine and fluoxetine-norfluoxetine distributions in vivo at steady-state and of quantitative kinetics in brain and plasma after drug therapy interruption was performed by fluorine nuclear magnetic resonance spectroscopy (19F MRS), spectroscopic imaging (MRSI), and plasma HPLC on 12 subjects treated for depression. MRSI suggests a homogeneous distribution of 19F MRS visible fluvoxamine mainly in brain. Fluvoxamine steady-state brain concentrations (12 +/- 5 microM; n = 13) and brain-to-plasma concentration ratios (10 +/- 2; n = 12) were similar to those of combined fluoxetine-norfluoxetine (CF-norfluoxetine) (13 +/- 6 microM; n = 4 and 10 +/- 6; n = 4). Fluvoxamine brain elimination half-life (79 +/- 24 hours; n = 4) was significantly shorter than that of CF-norfluoxetine (382 +/- 48 hours; n = 2). Fluvoxamine brain-to-plasma-half-life-ratio was 2.2 +/- 0.3 (n = 4), contrarily to CF-norfluoxetine (1.0 +/- 0.3; n = 2). This study shows that quantitative pharmacokinetics in target organs by 19F MRS in vivo should prove useful for understanding and investigating outcome of treatment modifications and side effects.

Combined measurements of hippocampal N-acetyl-aspartate and T2 relaxation time in the evaluation of mesial temporal lobe epilepsy: correlation with clinical severity and memory performances

PURPOSE

In this study we tried to find a correlation between the clinical severity and memory performances, by comparing proton magnetic resonance (MR) spectroscopy and T2 relaxation time measurements in the hippocampi, in a homogeneous group of 27 patients with unilateral mesial temporal lobe epilepsy with ipsilateral hippocampal sclerosis on MR imaging, with a view to answer the following questions: (a) how sensitive is this approach for the assessment of the apparently normal contralateral hippocampus, (b) do the results relate to the clinical severity, and (c) does it allow evaluation of the degree of hippocampal dysfunction.

METHODS

Volume-selective proton MR spectroscopy of the head of both hippocampi was performed at 3 T, by using the PRESS sequence, with an echo time of 135 ms, to estimate NAA/(Cho + Cr) ratios. The relaxation times were measured at 0.28 T, by using a conventional Carr-Purcell-Meiboom-Gill sequence, with a repetition time of 2,000 ms, an echo time of 15 ms, and 48 echoes.

RESULTS

The combination of NAA/(Cho + Cr) ratio and T2 relaxation time values was allowed to classify contralateral hippocampus abnormalities in two groups: first, decreased NAA/(Cho + Cr) ratio with strongly increased T2 relaxation time values corresponding to abnormalities observed in sclerotic ipsilateral hippocampi; and second, decreased NAA/(Cho + Cr) ratio with normal or slightly increased T2 relaxation time values. Whereas the NAA/(Cho + Cr) ratio or T2 relaxation time value alone was not correlated with memory performances, their association shows that left hippocampal injury evaluated both by NAA and T2 relaxation time measurements was clearly correlated with verbal memory scores, and right hippocampal injury, with visual memory scores. On the other hand, the maximal seizure frequency reported by the patients was correlated with ipsilateral NAA/(Cho + Cr) ratio and T2 relaxation time values but not with contralateral results.

CONCLUSIONS

We showed that the combination of NAA and T2 relaxation time measurements can be used to examine the degree of ipsi- and contralateral hippocampal dysfunction or injuries and their relations with memory performances in the presurgical evaluation of patients.