Principal components of functional connectivity: A new approach to study dynamic brain connectivity during rest.

Functional connectivity (FC) as measured by correlation between fMRI BOLD time courses of distinct brain regions has revealed meaningful organization of spontaneous fluctuations in the resting brain. However, an increasing amount of evidence points to non-stationarity of FC; i.e., FC dynamically changes over time reflecting additional and rich information about brain organization, but representing new challenges for analysis and interpretation. Here, we propose a data-driven approach based on principal component analysis (PCA) to reveal hidden patterns of coherent FC dynamics across multiple subjects. We demonstrate the feasibility and relevance of this new approach by examining the differences in dynamic FC between 13 healthy control subjects and 15 minimally disabled relapse-remitting multiple sclerosis patients. We estimated whole-brain dynamic FC of regionally-averaged BOLD activity using sliding time windows. We then used PCA to identify FC patterns, termed "eigenconnectivities", that reflect meaningful patterns in FC fluctuations. We then assessed the contributions of these patterns to the dynamic FC at any given time point and identified a network of connections centered on the default-mode network with altered contribution in patients. Our results complement traditional stationary analyses, and reveal novel insights into brain connectivity dynamics and their modulation in a neurodegenerative disease.

Activity of the δ-Opioid Receptor Is Partially Reduced, Whereas Activity of the κ-Receptor Is Maintained in Mice Lacking the μ-Receptor

Previous pharmacological studies have indicated the possible existence of functional interactions between μ-, δ- and κ-opioid receptors in the CNS. We have investigated this issue using a genetic approach. Here we describe in vitro and in vivo functional activity of δ- and κ-opioid receptors in mice lacking the μ-opioid receptor (MOR). Measurements of agonist-induced [35S]GTPγS binding and adenylyl cyclase inhibition showed that functional coupling of δ- and κ-receptors to G-proteins is preserved in the brain of mutant mice. In the mouse vas deferens bioassay, deltorphin II and cyclic[d-penicillamine2,d-penicillamine5] enkephalin exhibited similar potency to inhibit smooth muscle contraction in both wild-type and MOR −/− mice. δ-Analgesia induced by deltorphin II was slightly diminished in mutant mice, when the tail flick test was used. Deltorphin II strongly reduced the respiratory frequency in wild-type mice but not in MOR −/− mice. Analgesic and respiratory responses produced by the selective κ-agonist U-50,488H were unchanged in MOR-deficient mice. In conclusion, the preservation of δ- and κ-receptor signaling properties in mice lacking μ-receptors provides no evidence for opioid receptor cross-talk at the cellular level. Intact antinociceptive and respiratory responses to the κ-agonist further suggest that the κ-receptor mainly acts independently from the μ-receptor in vivo. Reduced δ-analgesia and the absence of δ-respiratory depression in MOR-deficient mice together indicate that functional interactions may take place between μ-receptors and central δ-receptors in specific neuronal pathways.

Lack of CB1 receptor activity impairs serotonergic negative feedback

Serotonergic and endocannabinoid systems are important substrates for the control of emotional behavior and growing evidence show an involvement in the pathophysiology of mood disorders. In the present study, the absence of the activity of the CB1 cannabinoid receptor impaired serotonergic negative feedback in mice. Thus, in vivo microdialysis experiments revealed increased basal 5-HT extracellular levels and attenuated fluoxetine-induced increase of 5-HT extracellular levels in the prefrontal cortex of CB1 knockout compared to wild-type mice. These observations could be related to the significant reduction in the 5-HT transporter binding site density detected in frontal cortex and hippocampus of CB1 knockout mice. The lack of CB1 receptor also altered some 5-HT receptors related to the 5-HT feedback. Extracellular recordings in the dorsal raphe nucleus revealed that the genetic and pharmacological blockade of CB1 receptor induced a 5-HT1A autoreceptor functional desensitization. In situ hybridization studies showed a reduction in the expression of the 5-HT2C receptor within several brain areas related to the control of the emotional responses, such as the dorsal raphe nucleus, the nucleus accumbens and the paraventricular nucleus of the hypothalamus, whereas an overexpression was observed in the CA3 area of the ventral hippocampus. These results reveal that the lack of CB1 receptor induces a facilitation of the activity of serotonergic neurons in the dorsal raphe nucleus by altering different components of the 5-HT feedback as well as an increase in 5-HT extracellular levels in the prefrontal cortex in mice.

Epidermal growth factor and bovine growth hormone stimulate differentiation and myelination of brain cell aggregates in culture.

Bovine growth hormone (bGH) and epidermal growth factor (EGF) increased the activity of ornithine decarboxylase (ODC) in brain cell aggregates cultured in a serum-free chemically defined medium. ODC is considered as a marker of cell growth and differentiation. The effect of bGH and EGF on myelination was investigated by measuring two myelin markers, 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) and myelin basic protein (MBP). EGF treatment at days 2 and 5 caused a dose-dependent increase of both myelin markers at culture day 12. This increase could still be observed at culture day 19, indicating a prolonged action of EGF. The continual presence of bGH in the culture medium produced a large accumulation of MBP at day 19. This effect was dose-dependent and required the presence of triiodothyronine (T3). In contrast, the effect of bGH on CNP activity did not require the presence of T3. This is the first report showing a direct effect of bGH on CNS myelination in vitro and of EGF on both MBP accumulation and ODC activity.

Selective toxicity of the general anesthetic propofol for GABAergic neurons in rat brain cell cultures.

The intravenous, short-acting general anesthetic propofol was applied to three-dimensional (aggregating) cell cultures of fetal rat telencephalon. Both the clinically used formulation (Disoprivan, ICI Pharmaceuticals, Cheshire, England) and the pure form (2,6-diisopropylphenol) were tested at two different periods of brain development: immature brain cell cultures prior to synaptogenesis and at the time of intense synapses and myelin formation. At both time periods and for clinically relevant concentrations and time of exposure (i.e., concentrations > or = 2.0 micrograms/ml for 8 hr), propofol caused a significant decrease of glutamic acid decarboxylase activity. This effect persisted after removal of the drug, suggesting irreversible structural changes in GABAergic neurons. The gamma-aminobutyric acid type A (GABAA) blocking agents bicuculline and picrotoxin partially attenuated the neurotoxic effect of propofol in cultures treated at the more mature phase of development. This protective effect was not observed in the immature brain cells. The present data suggest that propofol may cause irreversible lesions to GABAergic neurons when given at a critical phase of brain development. In contrast, glial cells and myelin appeared resistant even to high doses of propofol.

Brain energetics (thought needs food).

PURPOSE OF REVIEW: Almost 15 years after its initial proposal, the astrocyte-neuron lactate shuttle hypothesis still occupies the center stage in research on brain energetics. Recent developments have provided further evidence for its validity and have extended its application to different areas of neuroscience. RECENT FINDINGS: Description of cell-specific metabolic characteristics have reinforced the view that a prominent conversion of glucose into lactate takes place in astrocytes, whereas neurons preferentially take up and oxidize lactate over glucose-derived pyruvate. Indeed, specific mechanisms are activated by glutamatergic activity to favor such a net lactate transfer between the two cell types. Moreover, demonstration in vivo of the existence and implication of the astrocyte-neuron lactate shuttle hypothesis for particular neurophysiological processes is beginning to appear. SUMMARY: Brain energetics has undertaken its revolution. A new concept based on metabolic compartmentalization between astrocytes and neurons is establishing itself as the leading paradigm that opens new perspectives in areas such as functional brain imaging and regulation of energy homeostasis.

Ammonia toxicity to the brain: effects on creatine metabolism and transport and protective roles of creatine.

Hyperammonemia can provoke irreversible damage to the developing brain, with the formation of cortical atrophy, ventricular enlargement, demyelination or gray and white matter hypodensities. Among the various pathogenic mechanisms involved, alterations in cerebral energy have been demonstrated. In particular, we could show that ammonia exposure generates a secondary deficiency in creatine in brain cells, by altering the brain expression and activity of the genes allowing creatine synthesis (AGAT and GAMT) and transport (SLC6A8). On the other hand, it is known that creatine administration can exert protective effects in various neurodegenerative processes. We could also show that creatine co-treatment under ammonia exposure can protect developing brain cells from some of the deleterious effects of ammonia, in particular axonal growth impairment. This article focuses on the effects of ammonia exposure on creatine metabolism and transport in developing brain cells, and on the potential neuroprotective properties of creatine in the brain exposed to ammonium.

Ammonium alters creatine transport and synthesis in a 3D culture of developing brain cells, resulting in secondary cerebral creatine deficiency.

Hyperammonemic disorders in pediatric patients lead to poorly understood irreversible effects on the developing brain that may be life-threatening. We showed previously that some of these NH4+-induced irreversible effects might be due to impairment of axonal growth that can be protected under ammonium exposure by creatine co-treatment. The aim of the present work was thus to analyse how the genes of arginine:glycine amidinotransferase (AGAT) and guanidinoacetate methyltransferase (GAMT), allowing creatine synthesis, as well as of the creatine transporter SLC6A8, allowing creatine uptake into cells, are regulated in rat brain cells under NH4+ exposure. Reaggregated brain cell three-dimensional cultures exposed to NH4Cl were used as an experimental model of hyperammonemia in the developing central nervous system (CNS). We show here that NH4+ exposure differentially alters AGAT, GAMT and SLC6A8 regulation, in terms of both gene expression and protein activity, in a cell type-specific manner. In particular, we demonstrate that NH4+ exposure decreases both creatine and its synthesis intermediate, guanidinoacetate, in brain cells, probably through the inhibition of AGAT enzymatic activity. Our work also suggests that oligodendrocytes are major actors in the brain in terms of creatine synthesis, trafficking and uptake, which might be affected by hyperammonemia. Finally, we show that NH4+ exposure induces SLC6A8 in astrocytes. This suggests that hyperammonemia increases blood-brain barrier permeability for creatine. This is normally limited due to the absence of SLC6A8 from the astrocyte feet lining microcapillary endothelial cells, and thus creatine supplementation may protect the developing CNS of hyperammonemic patients.

Cytochrome P-450 activities in human and rat brain microsomes.

The role of cytochrome P450 in the metabolism of dextromethorphan, amitriptyline, midazolam, S-mephenytoin, citalopram, fluoxetine and sertraline was investigated in rat and human brain microsomes. Depending on the parameters, the limit of quantification using gas chromatography-mass spectrometry methods was between 1.6 and 20 pmol per incubation, which generally contained 1500 microg protein. Amitriptyline was shown to be demethylated to nortriptyline by both rat and human microsomes. Inhibition studies using ketoconazole, furafylline, sulfaphenazole, omeprazole and quinidine suggested that CYP3A4 is the isoform responsible for this reaction whereas CYP1A2, CYP2C9, CYP2C19 and CYP2D6 do not seem to be involved. This result was confirmed by using a monoclonal antibody against CYP3A4. Dextromethorphan was metabolized to dextrorphan in rat brain microsomes and was inhibited by quinidine and by a polyclonal antibody against CYP2D6. Only the addition of exogenous reductase allowed the measurement of this activity in human brain microsomes. Metabolites of the other substrates could not be detected, possibly due to an insufficiently sensitive method. It is concluded that cytochrome P450 activity in the brain is very low, but that psychotropic drugs could undergo a local cerebral metabolism which could have pharmacological and/or toxicological consequences.

Insulin-like growth factor I (IGF I) stimulates DNA synthesis in fetal rat brain cell cultures.

Addition of insulin, IGF I or IGF II to serum-free cultures of fetal rat brain cells (gestation day 15/16) significantly stimulates DNA synthesis. The dose-response curves show that IGF I is more potent than insulin; half maximal stimulation of [3H]thymidine incorporation is obtained at about 0.4 nM IGF I and 14 nM insulin, respectively. Cultures initiated 2 days later (gestation day 17/18) showed a decreased responsiveness to both peptides. No additive effect was observed after combined addition of both peptides at near-maximal doses. Both peptides show a latency of action of about 12-18 h. In the presence of either IGF or insulin, neuronal as well as glial enzymes are increased, suggesting that neuronal and glial precursor cell division is influenced. IGF I and IGF II interact with a specific binding site for which insulin competes very weakly; however IGF I and IGF II bind with relatively high affinity to the insulin specific binding site. The present results support the hypothesis that both insulin and IGF stimulate mitotic activity by interacting with specific somatomedin receptors and suggest a physiological role of IGF in the developing brain.

The place preference task: a new tool for studying the relation between behavior and place cell activity in rats

This study describes a task that combines random searching with goal directed navigation. The testing was conducted on a circular elevated open field (80 cm in diameter), with an unmarked target area (20 cm in diameter) in the center of 1 of the 4 quadrants. Whenever the rat entered the target area, the computerized tracking system released a pellet to a random point on the open field. Rats were able to learn the task under light and in total darkness, and on a stable or a rotating arena. Visual information was important in light, but idiothetic information became crucial in darkness. Learning of a new position was quicker under light than in total darkness on a rotating arena. The place preference task should make it possible to study place cells (PCs) when the rats use an allothetic (room frame) or idiothetic (arena frame) representation of space and to compare the behavioral response with the PCs' activity.

Phase II study of imatinib in patients with recurrent gliomas of various histologies: a European Organisation for Research and Treatment of Cancer Brain Tumor Group Study.

PURPOSE: To evaluate the safety and the efficacy of imatinib in recurrent malignant gliomas. PATIENTS: AND METHODS: This was a single-arm, phase II study. Eligible patients had recurrent glioma after prior radiotherapy with an enhancing lesion on magnetic resonance imaging. Three different histologic groups were studied: glioblastomas (GBM), pure/mixed (anaplastic) oligodendrogliomas (OD), and low-grade or anaplastic astrocytomas (A). Imatinib was started at a dose of 600 mg/d with dose escalation to 800 mg in case of no toxicity; during the trial this dose was increased to 800 mg/d with escalation to 1,000 mg/d. Trial design was one-stage Fleming; both an objective response and 6 months of progression-free survival (PFS) were considered a successful outcome to treatment. RESULTS: A total of 112 patients (51 patients with GBM, 25 patients with A, and 36 patients with OD) were enrolled. Imatinib was in general well tolerated. The median number of cycles was 2.0 (range, 1 to 43 cycles). Five patients had an objective partial response, including three patients with GBM; all had 6 months of PFS. The 6-month PFS rate was 16% (95% CI, 8.0% to 34.0%) in GBM, 4.0% (95% CI, 0.3% to 15.0%) in OD, and 9% (95% CI, 2.0% to 25.0%) in A. The exposure to imatinib was significantly lower in patients using enzyme-inducing antiepileptic drugs. The presence of ABCG2 point mutations were not correlated with pharmacokinetic findings. No somatic activating mutations of KIT or platelet-derived growth factor receptor-A or -B were found. CONCLUSION: In the dose range of 600 to 1,000 mg/d, single-agent imatinib is well tolerated but has limited antitumor activity in patients with recurrent gliomas.

Neurophysiological origin of human brain asymmetry for speech and language.

The physiological basis of human cerebral asymmetry for language remains mysterious. We have used simultaneous physiological and anatomical measurements to investigate the issue. Concentrating on neural oscillatory activity in speech-specific frequency bands and exploring interactions between gestural (motor) and auditory-evoked activity, we find, in the absence of language-related processing, that left auditory, somatosensory, articulatory motor, and inferior parietal cortices show specific, lateralized, speech-related physiological properties. With the addition of ecologically valid audiovisual stimulation, activity in auditory cortex synchronizes with left-dominant input from the motor cortex at frequencies corresponding to syllabic, but not phonemic, speech rhythms. Our results support theories of language lateralization that posit a major role for intrinsic, hardwired perceptuomotor processing in syllabic parsing and are compatible both with the evolutionary view that speech arose from a combination of syllable-sized vocalizations and meaningful hand gestures and with developmental observations suggesting phonemic analysis is a developmentally acquired process.

Sagopilone (ZK-EPO, ZK 219477) for recurrent glioblastoma. A phase II multicenter trial by the European Organisation for Research and Treatment of Cancer (EORTC) Brain Tumor Group.

Background: Sagopilone (ZK 219477), a lipophylic and synthetic analog of epothilone B, that crosses the blood-brain barrier has demonstrated preclinical activity in glioma models.Patients and methods: Patients with first recurrence/progression of glioblastoma were eligible for this early phase II and pharmacokinetic study exploring single-agent sagopilone (16 mg/m(2) over 3 h every 21 days). Primary end point was a composite of either tumor response or being alive and progression free at 6 months. Overall survival, toxicity and safety and pharmacokinetics were secondary end points.Results: Thirty-eight (evaluable 37) patients were included. Treatment was well tolerated, and neuropathy occurred in 46% patients [mild (grade 1) : 32%]. No objective responses were seen. The progression-free survival (PFS) rate at 6 months was 6.7% [95% confidence interval (CI) 1.3-18.7], the median PFS was just over 6 weeks, and the median overall survival was 7.6 months (95% CI 5.3-12.3), with a 1-year survival rate of 31.6% (95% CI 17.7-46.4). Maximum plasma concentrations were reached at the end of the 3-h infusion, with rapid declines within 30 min after termination.Conclusions: No evidence of relevant clinical antitumor activity against recurrent glioblastoma could be detected. Sagopilone was well tolerated, and moderate-to-severe peripheral neuropathy was observed in despite prolonged administration.

Correlation of O6-methylguanine methyltransferase (MGMT) promoter methylation with clinical outcomes in glioblastoma and clinical strategies to modulate MGMT activity.

Resistance to alkylating agents via direct DNA repair by O(6)-methylguanine methyltransferase (MGMT) remains a significant barrier to the successful treatment of patients with malignant glioma. The relative expression of MGMT in the tumor may determine response to alkylating agents, and epigenetic silencing of the MGMT gene by promoter methylation plays an important role in regulating MGMT expression in gliomas. MGMT promoter methylation is correlated with improved progression-free and overall survival in patients treated with alkylating agents. Strategies to overcome MGMT-mediated chemoresistance are being actively investigated. These include treatment with nontoxic pseudosubstrate inhibitors of MGMT, such as O(6)-benzylguanine, or RNA interference-mediated gene silencing of MGMT. However, systemic application of MGMT inhibitors is limited by an increase in hematologic toxicity. Another strategy is to deplete MGMT activity in tumor tissue using a dose-dense temozolomide schedule. These alternative schedules are well tolerated; however, it remains unclear whether they are more effective than the standard dosing regimen or whether they effectively deplete MGMT activity in tumor tissue. Of note, not all patients with glioblastoma having MGMT promoter methylation respond to alkylating agents, and even those who respond will inevitably experience relapse. Herein we review the data supporting MGMT as a major mechanism of chemotherapy resistance in malignant gliomas and describe ongoing studies that are testing resistance-modulating strategies.