Jens Frahm

Stress-induced changes in cerebral metabolites, hippocampal volume, and cell proliferation are prevented by antidepressant treatment with tianeptine

Stress-induced structural remodeling in the adult hippocampus, involving debranching and shortening of dendrites and suppression of neurogenesis, provides a cellular basis for understanding the impairment of neural plasticity in the human hippocampus in depressive illness. Accordingly, reversal of structural remodeling may be a desirable goal for antidepressant therapy. The present study investigated the effect of tianeptine, a modified tricyclic antidepressant, in the chronic psychosocial stress model of adult male tree shrews (Tupaia belangeri), a model with high validity for research on the pathophysiology of major depression. Animals were subjected to a 7-day period of psychosocial stress to elicit stress-induced endocrine and central nervous alterations before the onset of daily oral administration of tianeptine (50 mg/kg). The psychosocial stress continued throughout the treatment period of 28 days. Brain metabolite concentrations were determined in vivo by proton magnetic resonance spectroscopy, cell proliferation in the dentate gyrus was quantified by using BrdUrd immunohistochemistry, and hippocampal volume was measured post mortem. Chronic psychosocial stress significantly decreased in vivo concentrations of N-acetyl-aspartate (−13%), creatine and phosphocreatine (−15%), and choline-containing compounds (−13%). The proliferation rate of the granule precursor cells in the dentate gyrus was reduced (−33%). These stress effects were prevented by the simultaneous administration of tianeptine yielding normal values. In stressed animals treated with tianeptine, hippocampal volume increased above the small decrease produced by stress alone. These findings provide a cellular and neurochemical basis for evaluating antidepressant treatments with regard to possible reversal of structural changes in brain that have been reported in depressive disorders.

Topography of the human corpus callosum revisited—Comprehensive fiber tractography using diffusion tensor magnetic resonance imaging

Several tracing studies have established a topographical distribution of fiber connections to the cortex in midsagittal cross-sections of the corpus callosum (CC). The most prominent example is Witelsons scheme, which defines five vertical partitions mainly based on primate data. Conventional MRI of the human CC does not reveal morphologically discernable structures, although microscopy techniques identified myelinated axons with a relatively small diameter in the anterior and posterior third of the CC as opposed to thick fibers in the midbody and posterior splenium. Here, we applied diffusion tensor imaging (DTI) in conjunction with a tract-tracing algorithm to gain cortical connectivity information of the CC in individual subjects. With DTI-based tractography, we distinguished five vertical segments of the CC, containing fibers projecting into prefrontal, premotor (and supplementary motor), primary motor, and primary sensory areas as well as into parietal, temporal, and occipital cortical areas. Striking differences to Witelsons classification were recognized in the midbody and anterior third of the CC. In particular, callosal motor fiber bundles were found to cross the CC in a much more posterior location than previously indicated. Differences in water mobility were found to be in qualitative agreement with differences in the microstructure of transcallosal fibers yielding the highest anisotropy in posterior regions of the CC. The lowest anisotropy was observed in compartments assigned to motor and sensory cortical areas. In conclusion, DTI-based fiber tractography of healthy human subjects suggests a modification of the widely accepted Witelson scheme and a new classification of vertical CC partitions.

Localized proton spectroscopy using stimulated echoes

This paper describes a new method for spatially resolved NMR spectroscopy that takes advantage of stimulated echo signals. STEAM (stimulated echo acquisition mode) sequences, already used for a variety of imaging purposes, almost perfectly match the requirements of image-controlled localized 1H NMR in vivo. Superior spatial discrimination as well as high flexibility with respect to location, size, and shape of the volume of interest is achieved by employing only three slice-selective 90° rf pulses in the presence of orthogonal gradients. The method is a single-step procedure minimizing rf power requirements and gradient switches. It further allows accurate determinations of localized T1 and T2 relaxation times simply by varying the length of corresponding intervals of the STEAM sequence. In fact, the inherent T2 weighting may be used for water suppression and/or reduction of residual eddy current effects. Here we present first results on phantoms and human extremities demonstrating the ease of image selection, localized spectroscopy, and localized determinations of relaxation times. Future steps will deal with water/lipid-suppressed metabolic spectroscopy.

Reduced social interaction and ultrasonic communication in a mouse model of monogenic heritable autism.

Autism spectrum conditions (ASCs) are heritable conditions characterized by impaired reciprocal social interactions, deficits in language acquisition, and repetitive and restricted behaviors and interests. In addition to more complex genetic susceptibilities, even mutation of a single gene can lead to ASC. Several such monogenic heritable ASC forms are caused by loss-of-function mutations in genes encoding regulators of synapse function in neurons, including NLGN4. We report that mice with a loss-of-function mutation in the murine NLGN4 ortholog Nlgn4, which encodes the synaptic cell adhesion protein Neuroligin-4, exhibit highly selective deficits in reciprocal social interactions and communication that are reminiscent of ASCs in humans. Our findings indicate that a protein network that regulates the maturation and function of synapses in the brain is at the core of a major ASC susceptibility pathway, and establish Neuroligin-4-deficient mice as genetic models for the exploration of the complex neurobiological disorders in ASCs.

Simultaneous recording of cerebral blood oxygenation changes during human brain activation by magnetic resonance imaging and near-infrared spectroscopy

Changes in cerebral blood oxygenation due to functional activation of the primary sensorimotor cortex during a unilateral finger opposition task were simultaneously mapped by deoxyhemoglobin-sensitive magnetic resonance imaging (MRI) and monitored by near-infrared spectroscopy (NIRS). Activation foci along the contralateral central sulcus displayed task-associated increases in MRI signal intensity, indicating a concomitant decrease of the focal concentration of deoxyhemoglobin. This interpretation was confirmed by simultaneous reductions in deoxyhemoglobin measured optically. Since observation of the latter effect required exact spatial matching of the MRI-detected activation foci and position of the fiber optic bundles (“optodes”) used for transmitting and receiving light, it may be concluded that optical recordings of changes in deoxyhemoglobin during functional challenge probe only a restricted brain tissue region. While deoxyhemoglobin responses seen by NIRS were smaller for ipsi- than for contralateral finger movements, task-related increases in oxyhemoglobin were rather similar between both conditions and, thus, seem to be less specific. Furthermore, no consistent changes were obtained for total hemoglobin during task performance, possibly due to the short timing of the repetitive protocol. In general, results underline, in humans, the hitherto assumed signal physiology for functional brain mapping by oxygenation-sensitive MRI and allow assessment of both constraints and practicability of functional studies by NIRS.

Essential role of protein kinase B gamma (PKB gamma/Akt3) in postnatal brain development but not in glucose homeostasis.

Protein kinase B is implicated in many crucial cellular processes, such as metabolism, apoptosis and cell proliferation. In contrast to Pkbα and Pkbβ-deficient mice, Pkbγ-/- mice are viable, show no growth retardation and display normal glucose metabolism. However, in adult Pkbγ mutant mice, brain size and weight are dramatically reduced by about 25%. In vivo magnetic resonance imaging confirmed the reduction of Pkbγ-/- brain volumes with a proportionally smaller ventricular system. Examination of the major brain structures revealed no anatomical malformations except for a pronounced thinning of white matter fibre connections in the corpus callosum. The reduction in brain weight of Pkbγ-/- mice is caused, at least partially, by a significant reduction in both cell size and cell number. Our results provide novel insights into the physiological role of PKBγ and suggest a crucial role in postnatal brain development.

Functional MRI of the immediate impact of transcranial magnetic stimulation on cortical and subcortical motor circuits

Recent studies indicate that the cortical effects of transcranial magnetic stimulation (TMS) may not be localized to the site of stimulation, but spread to other distant areas. Using echo‐planar imaging with blood‐oxygenation‐level‐dependent (BOLD) contrast at 3 Tesla, we measured MRI signal changes in cortical and subcortical motor regions during high‐frequency (3.125 Hz) repetitive TMS (rTMS) of the left sensorimotor cortex (M1/S1) at intensities above and below the active motor threshold in healthy humans. The supra‐ and subthreshold nature of the TMS pulses was confirmed by simultaneous electromyographic monitoring of a hand muscle. Suprathreshold rTMS activated a network of primary and secondary cortical motor regions including M1/S1, supplementary motor area, dorsal premotor cortex, cingulate motor area, the putamen and thalamus. Subthreshold rTMS elicited no MRI‐detectable activity in the stimulated M1/S1, but otherwise led to a similar activation pattern as obtained for suprathreshold stimulation though at reduced intensity. In addition, we observed activations within the auditory system, including the transverse and superior temporal gyrus, inferior colliculus and medial geniculate nucleus. The present findings support the notion that re‐afferent feedback from evoked movements represents the dominant input to the motor system via M1 during suprathreshold stimulation. The BOLD MRI changes in motor areas distant from the site of subthreshold stimulation are likely to originate from altered synaptic transmissions due to induced excitability changes in M1/S1. They reflect the capability of rTMS to target both local and remote brain regions as tightly connected constituents of a cortical and subcortical network.

Regional age dependence of human brain metabolites from infancy to adulthood as detected by quantitative localized proton MRS.

Regional changes of metabolite concentrations during human brain development were assessed by quantitative localized proton magnetic resonance spectroscopy in vivo. Apart from measurements in young healthy adults, the study was based on regional spectra from 97 children who were either healthy or suffered from mental retardation, movement disorders, epilepsies, neoplasm, or vascular malformation. Metabolite quantitation focused on cortical gray and white matter, cerebellum, thalamus, and basal ganglia in six age groups from infancy to adulthood. During infancy and childhood, the concentration of the neuroaxonally located N-acetylaspartate increased in gray matter, cerebellum, and thalamus, whereas a constant level was detected in white matter. These findings are in line with regional differences in the formation of synaptic connections during early development and suggest a role of N-acetylaspartate as a marker of functioning neuroaxonal tissue rather than of the mere presence of nerve cells. This view is further supported by high concentrations of taurine in gray matter and cerebellum during infancy, because taurine is also believed to be involved in the process of synapse formation. Remarkably, in basal ganglia both N-acetylaspartate and taurine remain constant at relatively high concentrations. Other metabolite changes during maturation include increases of N-acetylaspartylglutamate, especially in thalamus and white matter, and a decrease of glutamine in white matter. Despite regional differences and some small changes during the first year of life, the concentrations of creatine, phosphocreatine, choline-containing compounds, myo-inositol, and glutamate remain constant afterward. The creatine to phosphocreatine concentration ratio yields 2:1 throughout the human brain irrespective of region or age. The observed increase of the proton resonance line-width with age is most pronounced in basal ganglia and corresponds to the age-related and tissue-dependent increase of brain iron.

Axonal loss and neuroinflammation caused by peroxisome-deficient oligodendrocytes.

Oligodendrocytes myelinate axons for rapid impulse conduction and contribute to normal axonal functions in the central nervous system. In multiple sclerosis, demyelination is caused by autoimmune attacks, but the role of oligodendroglial cells in disease progression and axon degeneration is unclear. Here we show that oligodendrocytes harbor peroxisomes whose function is essential for maintaining white matter tracts throughout adult life. By selectively inactivating the import factor PEX5 in myelinating glia, we generated mutant mice that developed normally, but within several months showed ataxia, tremor and premature death. Absence of functional peroxisomes from oligodendrocytes caused widespread axonal degeneration and progressive subcortical demyelination, but did not interfere with glial survival. Moreover, it caused a strong proinflammatory milieu and, unexpectedly, the infiltration of B and activated CD8+ T cells into brain lesions. We conclude that peroxisomes provide oligodendrocytes with an essential neuroprotective function against axon degeneration and neuroinflammation, which is relevant for human demyelinating diseases.

Self-diffusion NMR imaging using stimulated echoes

Abstract NMR imaging of molecular self-diffusion is demonstrated for the first time using stimulated-echo (STE) NMR signals. Stimulated-echo acquisition-mode (STEAM) imaging has been described in a preceding paper. It is based on a 90°-t1-90°-t2-90°-t3 rf excitation sequence and relies on the detection of the STE signal appearing at t3 = t1. By incorporating a pair of pulsed magnetic field gradients into the first and third intervals of the STEAM sequence, the effect of molecular self-diffusion on NMR images may be qualitatively demonstrated. A variation of the strength of the gradient pulses and/or the diffusion time, i.e., the length of the second interval, yields a series of diffusion weighted images which allows the calculation of a synthetical image solely displaying the self-diffusion coefficient. Experimental results on 1H NMR images of phantoms are presented which clearly demonstrate the potential of diffusion imaging as a new tool in medical diagnosis as well as for nonmedical applications.